@article{loSimplifiedIntensityPhasemodulated2023,
title = {Simplified intensity- and phase-modulated transmitter for modulator-free decoy-state quantum key distribution},
author = {Y. S. Lo and R. I. Woodward and N. Walk and M. Lucamarini and I. De Marco and T. K. Paraïso and M. Pittaluga and T. Roger and M. Sanzaro and Z. L. Yuan and A. J. Shields},
url = {https://www.riwoodward.com/publication_files/lo_2023_simp.pdf},
doi = {10.1063/5.0128445},
year  = {2023},
date = {2023-01-01},
urldate = {2023-01-01},
journal = {APL Photonics},
volume = {8},
number = {3},
pages = {036111},
abstract = {Quantum key distribution (QKD) allows secret key exchange between two users with unconditional security. For QKD to be widely deployed, low cost and compactness are crucial requirements alongside high performance. Currently, the majority of QKD systems demonstrated rely on bulk intensity and phase modulators to generate optical pulses with precisely defined amplitude and relative phase difference—i.e., to encode information as signal states and decoy states. However, these modulators are expensive and bulky, thereby limiting the compactness of QKD systems. Here, we present and experimentally demonstrate a novel optical transmitter design to overcome this disadvantage by generating intensity- and phase-tunable pulses at GHz clock speeds. Our design removes the need for bulk modulators by employing directly modulated lasers in combination with optical injection locking and coherent interference. This scheme is, therefore, well suited to miniaturization and photonic integration, and we implement a proof-of-principle QKD demonstration to highlight potential applications.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
@article{pistoiaPavingWay8002023,
title = {Paving the way toward 800 Gbps quantum-secured optical channel deployment in mission-critical environments},
author = {M. Pistoia and O. Amer and M. R. Behera and J. A. Dolphin and J. F. Dynes and B. John and P. A. Haigh and Y. Kawakura and D. H. Kramer and J. Lyon and N. Moazzami and T. D. Movva and A. Polychroniadou and S. Shetty and G. Sysak and F. Toudeh-Fallah and S. Upadhyay and R. I. Woodward and A. J. Shields},
url = {https://www.riwoodward.com/publication_files/pistoia_2023_qkd.pdf},
doi = {10.1088/2058-9565/acd1a8},
year  = {2023},
date = {2023-01-01},
urldate = {2023-01-01},
journal = {Quantum Science and Technology},
volume = {8},
number = {3},
pages = {035015},
abstract = {This article describes experimental research studies conducted toward understanding the implementation aspects of high-capacity quantum-secured optical channels in mission-critical metro-scale operational environments using quantum key distribution (QKD) technology. To the best of our knowledge, this is the first time that an 800 Gbps quantum-secured optical channel—along with several other dense wavelength division multiplexed channels on the C-band and multiplexed with the QKD channel on the O-band-was established at distances up to 100 km, with secret key-rates relevant for practical industry use cases. In addition, during the course of these trials, transporting a blockchain application over this established channel was utilized as a demonstration of securing a financial transaction in transit over a quantum-secured optical channel. The findings of this research pave the way toward the deployment of QKD-secured optical channels in high-capacity, metro-scale, mission-critical operational environments, such as Inter-Data Center Interconnects.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
@inbook{Woodward2022,
title = {Modeling mid-infrared fiber laser systems},
author = {R. I. Woodward and M. Gorjan},
editor = {S. D. Jackson and M. Bernier and R. Vallee},
url = {https://riwoodward.com/publication_files/woodward_2022_mirmodel.pdf},
doi = {10.1016/B978-0-12-818017-4.00003-3},
isbn = {978-0-12-818017-4},
year  = {2022},
date = {2022-01-14},
urldate = {2022-01-14},
publisher = {Woodhead Publishing},
chapter = {13},
abstract = {Mid-IR fibre lasers are complex nonlinear dynamical systems, involving interplay between many physical phenomena and offering vast design freedom. The development of numerical models to simulate laser behaviour is therefore an invaluable tool, both to optimize output performance and to advance understanding of novel laser transitions. Such insight would be significantly slower and more costly to obtain (or indeed, impossible) through laboratory experimentation alone. In this Chapter, we offer a general introduction to various topics in mid-IR fibre laser modelling, with a particular emphasis on rate equation simulations. Complete formalisms are developed from first principles, notably using a matrix approach which is well suited for complex mid-IR transitions, and we discuss practical solution strategies. Case studies are presented for CW, Q-switched and gain-switched lasers, considering both the dysprosium and erbium ion. The second part of the Chapter then considers thermal modelling to identify cooling strategies for high-power systems and ultrashort pulse simulations for modelling mode-locked lasers.},
keywords = {},
pubstate = {published},
tppubtype = {inbook}
}
@inbook{Woodward2022b,
title = {Mode-locked mid-infrared fiber systems},
author = {R. I. Woodward and D. D. Hudson},
editor = {S. D. Jackson and M. Bernier and R. Vallee},
url = {https://riwoodward.com/publication_files/woodward_2022_mirml.pdf},
doi = {https://doi.org/10.1016/B978-0-12-818017-4.00002-1},
isbn = {978-0-12-818017-4},
year  = {2022},
date = {2022-01-14},
urldate = {2022-01-14},
publisher = {Woodhead Publishing},
chapter = {11},
abstract = {The generation of ultrashort optical pulses from laser technologies significantly broadens their range of applications. While near-IR ultrafast fiber lasers are now essential tools in science, industry, and medicine, devices operating in the mid-IR are currently much less mature. Alongside the general challenges of extending fiber lasers to longer wavelengths, there are also numerous complications to the application of current mode-locking techniques to generate picosecond and femtosecond pulsed outputs in this spectral region. Fortunately, there has been significant progress in this field in recent years, leading to record performance and opening up new transformative applications. In this chapter, we review the technical challenges and state of the art in long-wavelength mode-locked fiber lasers, including consideration of pulse metrology, mid-IR modulation techniques and cavity designs, and soliton physics in soft glasses. By capitalizing on these advances, recent works have demonstrated impressive mid-IR laser sources with few-cycle pulse durations, 10s kW peak powers, and tunability over 100s nm. The future appears bright for mid-IR mode-locked fiber lasers and we conclude with a perspective on the future work and routes to practical deployment.},
keywords = {},
pubstate = {published},
tppubtype = {inbook}
}
@article{loSelftuningTransmitterQuantum2022,
title = {Self-tuning transmitter for quantum key distribution using machine intelligence},
author = {Y. S. Lo and R. I. Woodward and T. Roger and V. Lovic and T. K. Paraïso and I. De Marco and Z. L. Yuan and A. J. Shields},
url = {https://www.riwoodward.com/publication_files/lo_2022_tune.pdf},
doi = {10.1103/PhysRevApplied.18.034087},
year  = {2022},
date = {2022-01-01},
urldate = {2022-01-01},
journal = {Physical Review Applied},
volume = {18},
number = {3},
pages = {034087},
abstract = {The development and performance of quantum technologies heavily relies on the properties of the quantum states, which often require careful optimization of the driving conditions of all underlying components. In quantum key distribution (QKD), optical injection locking (OIL) of pulsed lasers has recently been shown as a promising technique to realize high-speed quantum transmitters with efficient system design. However, due to the complex underlying laser dynamics, tuning such laser system is both a challenging and time-consuming task. Here, we experimentally demonstrate an OIL-based QKD transmitter that can be automatically tuned to its optimum operating state by employing a genetic algorithm. Starting with minimal knowledge of the laser operating parameters, the phase coherence and the quantum bit error rate of the system are optimized autonomously to a level matching the state of the art. },
keywords = {},
pubstate = {published},
tppubtype = {article}
}
@article{demarcoRealtimeOperationMultirate2021a,
title = {Real-time operation of a multi-rate, multi-protocol quantum key distribution transmitter},
author = {I. De Marco and R. I. Woodward and G. L. Roberts and T. K. Paraiso and T. Roger and M. Sanzaro and M. Lucamarini and Z. Yuan and A. J. Shields},
doi = {10.1364/OPTICA.423517},
year  = {2021},
date = {2021-01-01},
urldate = {2021-01-01},
journal = {Optica},
volume = {8},
number = {6},
pages = {911},
abstract = {Quantum key distribution (QKD) is the best candidate for securing communications against attackers, who may in the future exploit quantum-enhanced computational powers to break classical encryption. As such, new challenges are arising from our need for large-scale deployment of QKD systems. In a realistic scenario, transmitting and receiving devices from different vendors should be able to communicate with each other without the need for matching hardware. Therefore, practical deployment of QKD would require hardware capable of adapting to different protocols and clock rates. Here, we address this challenge by presenting a multi-rate, multi-protocol QKD transmitter linked to a correspondingly adaptable QKD receiver. The flexibility of the transmitter, achieved by optical injection locking, allows us to connect it with two receivers with inherently different clock rates. Furthermore, we demonstrate the multi-protocol operation of our transmitter, communicating with receiving parties employing different decoding circuits.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
@article{paraisoAdvancedLaserTechnology2021a,
title = {Advanced laser technology for quantum communications (tutorial review)},
author = {T. K. Paraïso and R. I. Woodward and D. G. Marangon and V. Lovic and Z. Yuan and A. J. Shields},
url = {https://www.riwoodward.com/publication_files/paraiso_2021_laser.pdf},
doi = {10.1002/qute.202100062},
year  = {2021},
date = {2021-01-01},
urldate = {2021-01-01},
journal = {Advanced Quantum Technologies},
volume = {4},
number = {10},
pages = {2100062},
abstract = {Quantum communications is the art of exchanging and manipulating information beyond the capabilities of the conventional technologies using the laws of quantum mechanics. With applications ranging from quantum computing to cryptographic systems with information-theoretic security, there is strong incentive to introduce quantum communications into many areas of the society. However, an important challenge is to develop viable technologies meeting the stringent requirements of low noise and high coherence for quantum state encoding, of high bit rate and low power for the integration with classical communication networks, and of scalable and low-cost production for a practical wide-deployment. This tutorial presents recent advances in laser modulation technologies that have enabled the development of efficient and versatile light sources for quantum communications, with a particular focus on quantum key distribution (QKD). Such approaches have been successfully used to demonstrate several QKD protocols with state-of-the-art performance. The applications and experimental results are reviewed and interpreted in the light of a complete theoretical background, allowing the reader to model and simulate such sources.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
@article{paraisoPhotonicIntegratedQuantum2021a,
title = {A photonic integrated quantum secure communication system},
author = {T. K. Paraïso and T. Roger and D. G. Marangon and I. De Marco and M. Sanzaro and R. I. Woodward and J. F. Dynes and Z. Yuan and A. J. Shields},
doi = {10.1038/s41566-021-00873-0},
issn = {1749-4885, 1749-4893},
year  = {2021},
date = {2021-01-01},
urldate = {2021-01-01},
journal = {Nature Photonics},
volume = {15},
number = {11},
pages = {850},
abstract = {Photonic integrated circuits hold great promise in enabling the practical wide-scale deployment of quantum communications; however, despite impressive experiments of component functionality, a fully operational quantum communication system using photonic chips is yet to be demonstrated. Here we demonstrate an entirely standalone secure communication system based on photonic integrated circuits—assembled into compact modules—for quantum random number generation and quantum key distribution at gigahertz clock rates. The bit values, basis selection and decoy pulse intensities used for quantum key distribution are chosen at random, and are based on the output of a chip-based quantum random number generator operating at 4 Gb s–1. Error correction and privacy amplification are performed in real time to produce information-theoretic secure keys for a 100 Gb s–1 line speed data encryption system. We demonstrate long-term continuous operation of the quantum secured communication system using feedback controls to stabilize the qubit phase and propagation delay over metropolitan fibre lengths. These results mark an important milestone for the realistic deployment of quantum communications based on quantum photonic chips.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
@article{pittaluga600kmRepeaterlikeQuantum2021a,
title = {600-km repeater-like quantum communications with dual-band stabilization},
author = {M. Pittaluga and M. Minder and M. Lucamarini and M. Sanzaro and R. I. Woodward and M.-J. Li and Z. Yuan and A. J. Shields},
url = {https://www.riwoodward.com/publication_files/pittaluga_2022_tf.pdf},
doi = {10.1038/s41566-021-00811-0},
year  = {2021},
date = {2021-01-01},
urldate = {2021-01-01},
journal = {Nature Photonics},
volume = {15},
number = {7},
pages = {530},
abstract = {Twin-field (TF) quantum key distribution (QKD) fundamentally alters the rate-distance relationship of QKD, offering the scaling of a single-node quantum repeater. Although recent experiments have demonstrated the new opportunities for secure long-distance communications allowed by TF-QKD, formidable challenges remain to unlock its true potential. Previous demonstrations have required intense stabilisation signals at the same wavelength as the quantum signals, thereby unavoidably generating Rayleigh scattering noise that limits the distance and bit rate. Here, we introduce a novel dual-band stabilisation scheme that overcomes past limitations and can be adapted to other phase-sensitive single-photon applications. Using two different optical wavelengths multiplexed together for channel stabilisation and protocol encoding, we develop a setup that provides repeater-like key rates over record communication distances of 555 km and 605 km in the finite-size and asymptotic regimes respectively, and increases the secure key rate at long distance by two orders of magnitude to values of practical significance. },
keywords = {},
pubstate = {published},
tppubtype = {article}
}
@article{woodwardGigahertzMeasurementdeviceindependentQuantum2021a,
title = {Gigahertz measurement-device-independent quantum key distribution using directly modulated lasers},
author = {R. I. Woodward and Y. S. Lo and M. Pittaluga and M. Minder and T. K. Paraïso and M. Lucamarini and Z. L. Yuan and A. J. Shields},
url = {https://www.riwoodward.com/publication_files/woodward_2021_mdi.pdf},
doi = {10.1038/s41534-021-00394-2},
year  = {2021},
date = {2021-01-01},
urldate = {2021-01-01},
journal = {npj Quantum Information},
volume = {7},
number = {1},
pages = {58},
abstract = {Measurement-device-independent quantum key distribution (MDI-QKD) is a technique for quantum-secured communication that eliminates all detector side-channels, although is currently limited by implementation complexity and low secure key rates. Here, we introduce a simple and compact MDI-QKD system design at gigahertz clock rates with enhanced resilience to laser fluctuations—thus enabling free-running semiconductor laser sources to be employed without spectral or phase feedback. This is achieved using direct laser modulation, carefully exploiting gain-switching and injection-locking laser dynamics to encode phase-modulated time-bin bits. Our design enables secure key rates that improve upon the state of the art by an order of magnitude, up to 8 bps at 54 dB channel loss and 2 kbps in the finite-size regime for 30 dB channel loss. This greatly simplified MDI-QKD system design and proof-of-principle demonstration shows that MDI-QKD is a practical, high-performance solution for future quantum communication networks.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
@conference{Bawden2020,
title = {Q-switched and mode-­locked 3.5 μm fiber laser},
author = {N. Bawden and O. Henderson-Sapir and M. R. Majewski and R. I. Woodward and S. D. Jackson and D. J. Ottaway},
url = {https://riwoodward.com/publication_files/bawden_2020_er.pdf},
doi = {10.1364/CLEOPR.2020.C3A_3},
year  = {2020},
date = {2020-11-01},
booktitle = {CLEO Pacific Rim: 2020, OSA Technical Digest},
abstract = {We report on a tunable mid-infrared erbium fiber laser mode-locked via frequency shifted-feedback provided by an acousto-optic tunable filter. Q-switched pulses were produced when the driving frequency of the acousto-optic tunable filter was square-wave modulated.},
note = {Paper C3A-3},
keywords = {fibre laser},
pubstate = {published},
tppubtype = {conference}
}
@article{Hu2020,
title = {A general ink formulation of 2D crystals for wafer-scale inkjet printing},
author = {G. Hu and L. Yang and Z. Yang and Y. Wang and X. Jin and J. Dai and Q. Wu and S. Liu and X. Zhu and X. Wang and T. -C. Wu and R. C. T. Howe and T. Albrow-Owen and L. W. T. Ng and Q. Yang and L. G. Occhipinti and R. I. Woodward and E. J. R Kelleher and Z. Sun and X. Huang and M. Zhang and C. D. Bain and T. Hasan},
url = {https://www.riwoodward.com/publication_files/hu_2020_ink.pdf},
doi = {10.1126/sciadv.aba5029},
year  = {2020},
date = {2020-08-01},
journal = {Science Advances},
volume = {6},
number = {33},
pages = {eaba5029},
abstract = {Recent advances in inkjet printing of two-dimensional (2D) crystals show great promise for next-generation printed electronics development. Printing nonuniformity, however, results in poor reproducibility in device performance, and remains a major impediment to their large-scale manufacturing. At the heart of this challenge lies the coffee-ring effect (CRE), ring-shaped nonuniform deposits formed during post-deposition drying. We present an experimental study of the drying mechanism of a binary solvent ink formulation. We show that Marangoni-enhanced spreading in this formulation inhibits contact line pinning and deforms the droplet shape to naturally suppress the capillary flows that give rise to the CRE. This general formulation supports uniform deposition of 2D crystals and their derivatives, enabling scalable and even wafer-scale device fabrication, moving them closer to industrial-level additive manufacturing.},
keywords = {nanomaterials},
pubstate = {published},
tppubtype = {article}
}
@article{Amin2020b,
title = {Novel near-infrared pump wavelengths for dysprosium fiber lasers},
author = {M. Z. Amin and M. R. Majewski and R. I. Woodward and A. Fuerbach and S. D. Jackson},
url = {https://www.riwoodward.com/publication_files/amin_2020_wls.pdf},
doi = {10.1109/jlt.2020.3004428},
year  = {2020},
date = {2020-08-01},
journal = {Journal of Lightwave Technology},
volume = {38},
number = {20},
pages = {5801},
abstract = {We report two new near-infrared pump wavelengths at 0.8 µm and 0.9 µm for dysprosium (Dy3+)-doped mid-infrared fiber lasers, which are free from detrimental pump excited state absorption that has limited all previous Dy3+ fiber lasers using longer near-infrared pump wavelengths (i.e., 1.1 µm, 1.3 µm, and 1.7 µm). The maximum measured laser slope efficiencies were 18.5% and 23.7% with respect to launched pump power for 0.8 µm and 0.9 µm pump wavelengths, respectively. These new pump wavelengths provide higher fractional Stokes limits (which are 70% and 79% for 0.8 µm and 0.9 µm pumping wavelengths, respectively) than previous demonstrations. While our measured efficiencies are still below the Stokes limit, we have identified the causes to be background loss and multi-mode behaviour at the pump wavelengths; both easily solvable for future systems. A numerical model was used to confirm performance, paving the way to efficient future near-infrared-pumped, potentially diode-pumped Dy3+ fiber lasers emitting in the mid-infrared.},
keywords = {dysprosium, mid-infrared},
pubstate = {published},
tppubtype = {article}
}
@article{Majewski2020,
title = {Dysprosium mid‐infrared lasers: Current status and future prospects},
author = {M. R. Majewski and R. I. Woodward and S. D. Jackson},
url = {https://www.riwoodward.com/publication_files/majewski_2020_dy.pdf},
doi = {10.1002/lpor.201900195},
year  = {2020},
date = {2020-02-10},
journal = {Laser & Photonics Reviews},
volume = {14},
number = {3},
pages = {1900195},
abstract = {With growing interest in the mid‐infrared spectral region, dysprosium has recently been revisited for efficient high‐performance infrared source development. Despite historically receiving less attention than other rare earth ions, in recent years lasers utilizing the dysprosium ion as the laser material have set record mid‐infrared performance, including tunability from 2.8 to 3.4 µm (in addition to 4.3 µm lasing), continuous wave powers exceeding 10 W, greater than 73% slope efficiencies, and even ultrafast pulsed operation. Herein, the unique energy level structure and spectroscopy of the dysprosium ion are examined and the major developments that have led to this resurgence of interest and subsequent record mid‐infrared laser performance are surveyed. Also mid‐infrared applications of emerging dysprosium lasers are highlighted, in addition to surveying the many opportunities that lie ahead.1},
keywords = {dysprosium},
pubstate = {published},
tppubtype = {article}
}
@conference{Amin2020,
title = {New excitation wavelengths for dysprosium-doped mid-infrared fiber lasers},
author = {M. Z. Amin and M. R. Majewski and R. I. Woodward and A. Fuerbach and S. D. Jackson},
url = {https://www.riwoodward.com/publication_files/amin_2020_pw.pdf},
doi = {10.1117/12.2547152},
year  = {2020},
date = {2020-02-01},
booktitle = {Proc. SPIE 11260, Fiber Lasers XVII: Technology and Systems, San Francisco, USA, 2020, (Paper 112601R).},
abstract = {Mid-infrared (mid-IR) fiber lasers that are based on dysprosium (Dy) as the active laser ion provide emission in the wavelength range between 2.6–3.4 μm and can thus bridge the spectral gap between holmium (Ho) and erbium (Er) based mid-IR lasers. Another distinct feature is the wide choice of pump wavelengths (1.1 μm, 1.3 μm, 1.7 μm, and 2.8 μm) that can be used. To date, pump wavelengths shorter than 1.1 μm have not been reported and all demonstrated pump wavelengths apart from in-band pumping suffer from pump excited state absorption (ESA). In this paper, we report new excitation wavelengths, 0.8 μm and 0.9 μm, for Dy-doped mid-IR fiber lasers. We have measured 18.5% and 23.7% slope efficiency (relative to launched pump power) for 0.8 μm and 0.9 μm pumping wavelengths, respectively. By comparing the residual pump power of experimental and numerical simulation data of a 0.5 m Dy-doped fiber, we have found that these new excitation wavelengths are free from pump ESA. Moreover, the high power laser diodes are commercially available at these new excitation wavelengths; therefore, the realization of a diode-pumped Dy-doped mid-infrared fiber laser might become feasible in the near future.},
keywords = {dysprosium},
pubstate = {published},
tppubtype = {conference}
}
@article{Henderson-Sapir2020,
title = {Mode-locked and tunable fiber laser at the 3.5 µm band using frequency-shifted feedback},
author = {O. Henderson-Sapir and N. Bawden and M. R. Majewski and R. I. Woodward and D. J. Ottaway and S. D. Jackson},
url = {https://riwoodward.com/publication_files/hendersonsapir_2019_fsf.pdf},
doi = {10.1364/OL.45.000224},
year  = {2020},
date = {2020-01-01},
journal = {Optics Letters},
volume = {45},
number = {1},
pages = {224},
abstract = {We report on a mid-infrared mode-locked fiber laser that uses an acousto-optic tunable filter to achieve frequency- shifted feedback pulse generation with frequency tuning over a 215 nm range. The laser operates on the 3.5 µm transition in erbium-doped zirconium fluoride-based fiber and utilizes the dual-wavelength pumping scheme. Stable, self-starting mode locking with a minimum pulse duration of 53 ps was measured using a two-photon absorption autocorrelator. The longest wavelength demonstrated was 3612 nm, and the maximum average powers achieved were 50 and 167 mW in fundamental and multi-pulse mode-locking regimes, respectively. To the best of our knowledge, this is the longest wavelength rare-earth-doped mode-locked fiber laser demonstrated. The broad tunability promises potential uses for environmental sensing applications.},
keywords = {fibre laser},
pubstate = {published},
tppubtype = {article}
}
@conference{Bharathan2019b,
title = {Direct femtosecond laser inscription of highly reflective and low loss mid-infrared fiber Bragg gratings},
author = {G. Bharathan and T. T. Fernandez and M. Ams and R. I. Woodward and D. D. Hudson and A. Fuerbach},
url = {https://www.riwoodward.com/publication_files/bharathan_2019_cleo.pdf https://www.osapublishing.org/abstract.cfm?uri=cleo_europe-2019-ce_8_2},
year  = {2019},
date = {2019-07-01},
booktitle = {CLEO Europe:2019, OSA Technical Digest},
publisher = {The Optical Society},
address = {Munich, Germany},
abstract = {Mid-infrared (mid-IR) fiber lasers in the 2.5-5 µm wavelength range have great potential to play a pivotal role in spectroscopy and medicine [1]. However, at present the non-existence of fiber-coupled optical components for these wavelengths severely limits the ability to build highly efficient alignment-free, low loss all-fiber lasers. This relates to the fact that fabricating various in-fiber components in fluoride fiber is a challenging problem, due to the difference in glass properties and handling requirements compared to standard silica fibers. Here, we address this problem by reporting the direct femtosecond (fs) laser inscription of high reflectivity (99.98%), low loss (<0.5 dB), Type-I fiber Bragg gratings (FBGs) into the core of soft-glass ZBLAN fibers for mid-IR applications.},
note = {Paper CE-8.2},
keywords = {fbg},
pubstate = {published},
tppubtype = {conference}
}
@conference{Majewski2019b,
title = {High energy pulses from a wavelength tunable Dy:ZBLAN mid-infrared fiber laser},
author = {M. R. Majewski and R. I. Woodward and S. D. Jackson},
url = {https://www.riwoodward.com/publication_files/majewski_2019_cleo_qs.pdf https://www.osapublishing.org/abstract.cfm?uri=cleo_europe-2019-cj_5_3},
year  = {2019},
date = {2019-07-01},
booktitle = {CLEO Europe:2019, OSA Technical Digest},
publisher = {The Optical Society},
address = {Munich, Germany},
abstract = {Laser sources in the mid-infrared (MIR 3 - 5 μm) are increasingly in demand to meet the needs of a variety of applications which exploit the strong ro-vibrational molecular absorption lines in this spectral region. Requirement of high energy pulsed light is found in time-resolved sensing applications such as LIDAR. Fiber lasers in the midinfrared are promising candidates for generating such pulses, with Q-switched erbium-doped systems demonstrated covering both the 2.8 μm and 3.5 μm bands. However, there remains a sizable ‘gap’ in spectral coverage of such lasers, motivating interest in pursuing alternative rare earth dopants. Dysprosium in particular is a compelling solution, as it possesses a wide gain bandwidth covering 2.8 to 3.4 μm with recent electronically tunable systems closing much of this ‘gap’.},
note = {Paper CJ-5.3},
keywords = {fibre laser},
pubstate = {published},
tppubtype = {conference}
}
@conference{Majewski2019c,
title = {Generating picosecond pulses from mid-infrared fiber lasers using frequency-shifted feedback},
author = {M. R. Majewski and R. I. Woodward and S. D. Jackson},
url = {https://www.riwoodward.com/publication_files/majewski_2019_cleo_fsf.pdf https://www.osapublishing.org/abstract.cfm?uri=cleo_europe-2019-cf_3_4},
year  = {2019},
date = {2019-07-01},
booktitle = {CLEO Europe:2019, OSA Technical Digest},
publisher = {The Optical Society},
address = {Munich, Germany},
abstract = {Ultrafast mode-locked fiber lasers in the near infrared have enabled a host of key applications in a variety of fields such as medicine and defense. In recent years there has been significant interest in pushing the emission wavelength of these fiber laser systems to the mid infrared (MIR 3–5 μm) due to the presence of strong molecular absorption features in this spectral range. Various techniques to achieve this have been demonstrated, with a majority of the work focused on implementation of loss modulation via real saturable absorbers. While this has been successful in generating picosecond pulses in the mid-infrared [1], commercial availability of absorbers is currently limited, and alternatives such as nanomaterials (graphene, black phosphorous) raise questions regarding long-term stability. Virtual absorbers based on nonlinear polarization evolution have shown comparatively superior performance in terms of pulse duration [2] but this method is highly sensitive to small environmental perturbations.},
note = {Paper CF-3.4},
keywords = {fibre laser},
pubstate = {published},
tppubtype = {conference}
}
@article{Woodward2019b,
title = {Q-switched Dy:ZBLAN fiber lasers beyond 3 μm: comparison of pulse generation using acousto-optic modulation and inkjet-printed black phosphorus},
author = {R. I. Woodward and M. R. Majewski and N. Macadam and G. Hu and T. Albrow-Owen and T. Hasan and S. D. Jackson},
url = {https://riwoodward.com/publication_files/woodward_2019_dyqs.pdf},
doi = {10.1364/OE.27.015032},
year  = {2019},
date = {2019-05-10},
journal = {Optics Express},
volume = {27},
number = {11},
pages = {15032},
abstract = {We report high-energy mid-infrared pulse generation by Q-switching of dysprosium-doped fiber lasers for the first time. Two different modulation techniques are demonstrated. Firstly, using active acousto-optic modulation, pulses are produced with up to 12 μJ energy and durations as short as 270 ns, with variable repetition rates from 100 Hz to 20 kHz and central wavelengths tunable from 2.97 to 3.23 μm. Experiments are supported by numerical modeling, identifying routes for improved pulse energies and to avoid multi-pulsing by careful choice of modulator parameters. Secondly, we demonstrate passive Q-switching by fabricating an inkjet-printed black phosphorus saturable absorber, simplifying the cavity and generating 1.0 μJ pulses with 740 ns duration. The performance and relative merits of each modulation approach are then critically discussed. These demonstrations highlight the potential of dysprosium as a versatile gain medium for high-performance pulsed sources beyond 3 μm.},
keywords = {fibre laser},
pubstate = {published},
tppubtype = {article}
}
@article{Majewski2019,
title = {Ultrafast mid-infrared fiber laser mode-locked using frequency-shifted feedback},
author = {M. R. Majewski and R. I. Woodward and S. D. Jackson},
url = {https://riwoodward.com/publication_files/majewski_2019_fsf.pdf},
doi = {10.1364/OL.44.001698},
year  = {2019},
date = {2019-04-01},
journal = {Optics Letters},
volume = {44},
number = {7},
pages = {1698},
abstract = {We demonstrate ultrashort pulse generation from a fluoride fiber laser co-doped with holmium and praseodymium. To date the majority of work focused on short pulse generation from this class of fiber laser has employed loss modulators in the cavity, both real and artificial. In this work we alternatively employ a frequency shifting element: an acousto-optic modulator (AOM) in the cavity. This results in mode-locked output of sub-5 ps pulses with 10 nJ of energy at a center wavelength of 2.86 μm, and a pulse repetition frequency of 30.1 MHz, equating to a peak power of 1.9 kW. Additional experimental investigation of the relationship between frequency shift and cavity round trip offer insight into the complex underlying dynamics. As a complementary mode-locking technique to conventional loss modulation, this method of pulse formation may greatly expand the design flexibility of pulsed mid-infrared fiber lasers.},
keywords = {fibre laser},
pubstate = {published},
tppubtype = {article}
}
@conference{Woodward2019d,
title = {Electronically tunable mid-infrared mode-locked dysprosium fiber laser with over 330 nm tunability [Invited]},
author = {R. I. Woodward and M. R. Majewski and S. D. Jackson},
url = {https://riwoodward.com/publication_files/woodward_2019_pw_fsf.pdf},
doi = {10.1117/12.2507093},
year  = {2019},
date = {2019-03-30},
booktitle = {Proc. SPIE 10897, Fiber Lasers XVI: Technology and Systems},
address = {San Francisco, USA},
abstract = {Mode-locked fiber lasers are currently limited to sub-3-µm wavelengths, despite application-driven demand for longer wavelength mid-IR pulse sources. Erbium- and holmium-doped fluoride fiber lasers are emerging for 2.7–2.9 µm emission, yet further extending this coverage is challenging. Here, we propose a new approach using dysprosium-doped fiber with frequency shifted feedback (FSF), achieving 33 ps pulses with up to 2.7 nJ energy, tunable from 2.97 to 3.30 µm. Notably, this is the longest wavelength mode-locked fiber laser and the most broadly tunable pulsed fiber source to date. Simulations are also performed, offering insights into the dynamics of FSF pulse generation.},
note = {Paper 108970R},
keywords = {fibre laser},
pubstate = {published},
tppubtype = {conference}
}
@conference{Woodward2019c,
title = {Mid-infrared fiber sources for real-time biomedical sensing [Invited]},
author = {R. I. Woodward and M. R. Majewski and G. Bharathan and D. D. Hudson and A. Fuerbach and S. D. Jackson},
url = {https://www.riwoodward.com/publication_files/woodward_2019_pw_bio.pdf},
doi = {10.1117/12.2507322},
year  = {2019},
date = {2019-03-09},
booktitle = {Proc. SPIE 10873, Optical Biopsy XVII: Toward Real-Time Spectroscopic Imaging and Diagnosis},
address = {San Francisco, USA},
abstract = {The development of new, compact mid-infrared light sources is critical to enable biomedical sensing applications in resource-limited environments. Here, we review progress in fiber-based mid-IR sources, which are ideally suited for clinical environments due to their compact size and waveguide format. We first discuss recent developments in mid-IR supercontinuum sources, which exploit nonlinear optic phenomena in highly nonlinear materials (pumped by ultrashort pulse lasers) to generate broadband spectra. An emerging alternative approach is then presented, based on broadly tunable mid-IR fiber lasers, using the promising dysprosium ion to achieve orders of magnitude higher spectral power density than typical supercontinua. By employing an acousto-optic tunable filter for wavelength tuning, an electronically controlled swept-wavelength mid-IR fiber laser is developed, which is applied for absorption spectroscopy of ammonia (NH3)—an important biomarker—with 0.3 nm resolution and 40 ms acquisition time.},
note = {Paper 1087311},
keywords = {fibre laser},
pubstate = {published},
tppubtype = {conference}
}
@article{Woodward2019,
title = {Swept-wavelength mid-infrared fiber laser for real-time ammonia gas sensing [Invited]},
author = {R. I. Woodward and M. R. Majewski and D. D. Hudson and S. D. Jackson},
url = {https://www.riwoodward.com/publication_files/woodward_2019_nh3.pdf},
doi = {10.1063/1.5065415},
year  = {2019},
date = {2019-02-01},
journal = {APL Photonics},
volume = {4},
pages = {020801},
abstract = {The mid-infrared (mid-IR) spectral region holds great promise for new laser-based sensing technologies, based on measuring strong mid-IR molecular absorption features. Practical applications have been limited to date, however, by current low-brightness broadband mid-IR light sources and slow acquisition-time detection systems. Here, we report a new approach by developing a swept-wavelength mid-infrared fiber laser, exploiting the broad emission of dysprosium and using an acousto-optic tunable filter to achieve electronically controlled swept-wavelength operation from 2.89 to 3.25 μm (3070-3460 cm^-1). Ammonia (NH3) absorption spectroscopy is demonstrated using this swept source with a simple room-temperature single-pixel detector, with 0.3 nm resolution and 40 ms acquisition time. This creates new opportunities for real-time high-sensitivity remote sensing using simple, compact mid-IR fiber-based technologies.},
note = {Editor's Pick},
keywords = {dysprosium, fibre laser, mid-infrared},
pubstate = {published},
tppubtype = {article}
}
@article{Bharathan2019,
title = {Optimized laser written ZBLAN fiber Bragg gratings with high reflectivity and low loss},
author = {G. Bharathan and T. T. Fernandez and M. Ams and R. I. Woodward and D. D. Hudson and A. Fuerbach},
url = {https://riwoodward.com/publication_files/bharathan_2019_fbg.pdf},
doi = {10.1364/OL.44.000423},
year  = {2019},
date = {2019-02-01},
journal = {Optics Letters},
volume = {44},
number = {2},
pages = {423},
abstract = {We report the direct femtosecond (fs) laser inscription of Type-I fiber Bragg gratings (FBGs) into the core of soft-glass ZBLAN fibers. We investigate and compare various fabrication methods such as single pass (line-by-line), double pass and stacking (plane-by-plane) to create the highest reflectivity FBGs (99.98%) for mid-infrared (mid-IR) applications. In addition, we experimentally demonstrate how the parameters that influence the coupling coefficient, i.e. refractive index modulation and overlap factor, can be controlled in these gratings to specifically tailor the FBG properties. The performance of the direct-written Type-I gratings after 6 hours of annealing is further analyzed and the reflectivity increased by approximately 10 dB. To the best of our knowledge, this is the first demonstration of temperature-stable mid-IR FBGs with the highest coupling coefficient (464 m^−1) and lowest loss (< 0.5 dB/cm) without the use of an expensive phase mask.},
keywords = {fbg},
pubstate = {published},
tppubtype = {article}
}
@article{Woodward_2018_aplp,
title = {Mode-locked dysprosium fiber laser: picosecond pulse generation from 2.97 to 3.30 µm},
author = {R. I. Woodward and M. R. Majewski and S. D. Jackson},
url = {https://www.riwoodward.com/publication_files/woodward_2018_fsf.pdf 
http://bit.ly/dy_lfw},
doi = {10.1063/1.5045799},
year  = {2018},
date = {2018-11-06},
journal = {APL Photonics},
volume = {3},
pages = {116106},
abstract = {Mode-locked fiber laser technology to date has been limited to sub-3 µm wavelengths, despite significant application-driven demand for compact pulse sources at longer wavelengths. Erbium- and holmium-doped fluoride fiber lasers incorporating a saturable absorber are emerging as promising pulse sources for 2.7–2.9 µm, yet it remains a major challenge to extend this coverage. Here, we propose a new approach using dysprosium-doped fiber with frequency shifted feedback (FSF). Using a simple linear cavity with an acousto-optic tunable filter, we generate ∼33 ps pulses with up to 2.7 nJ energy and 330 nm tunability from 2.97 to 3.30 µm (∼3000–3400 cm −1 )—the longest wavelength mode-locked fiber laser and the most broadly tunable pulsed fiber laser to date. Numerical simulations show excellent agreement with experiments and also offer new insights into the underlying dynamics of FSF pulse generation. This highlights the remarkable potential of both dysprosium as a gain material and FSF for versatile pulse generation, opening new opportunities for mid-IR laser development and practical applications outside the laboratory.},
note = {Editor Featured Article. 
Highlighted by Laser Focus World: www.bit.ly/dy_lfw},
keywords = {fibre laser, mid-infrared, mode-locked},
pubstate = {published},
tppubtype = {article}
}
@conference{Woodward2018g,
title = {Mid-infrared technologies and opportunities using dysprosium-doped fluoride fiber [Invited]},
author = {R. I. Woodward and M. R. Majewski and G. Bharathan and D. D. Hudson and A. Fuerbach and S. D. Jackson},
url = {https://riwoodward.com/publication_files/woodward_2018_ogc.pdf},
year  = {2018},
date = {2018-11-01},
booktitle = {IEEE Optoelectronics Global Conference (OGC) 2018},
publisher = {IEEE},
address = {Shenzhen, China},
abstract = {The mid-infrared (mid-IR) spectral region holds many opportunities for new optical technologies and potentially transformative applications in medicine, manufacturing and defence. To date, however, such applications have been held back by a lack of high-brightness coherent light sources at mid-IR wavelengths with sufficient flexibility and robustness for practical deployment. Rare-earth-doped fluoride fibers are currently emerging as a promising and highly versatile platform for mid-IR laser technology and in the past few years, there has been particularly strong progress using the dysprosium ion, which offers broadband emission from ∼2.7–3.5 µm and even has potential to enable a new class of 4-µm fiber lasers. In this presentation, we review the spectroscopy of dysprosium-doped fluoride fibers and present recent developments of compact, high-power, broadly tunable mid-IR sources, in addition to offering an outlook towards further developments and practical applications.},
keywords = {dysprosium, fibre laser, mid-infrared},
pubstate = {published},
tppubtype = {conference}
}
@article{Bharathan2018a,
title = {In-fiber polarizer based on a 45-degree tilted fluoride fiber Bragg grating for mid-infrared fiber laser technology},
author = {G. Bharathan and D. D. Hudson and R. I. Woodward and S. D. Jackson and A. Fuerbach},
url = {https://www.riwoodward.com/publication_files/bharathan_2018_fbg.pdf},
doi = {10.1364/OSAC.1.000056},
year  = {2018},
date = {2018-09-14},
journal = {OSA Continuum},
volume = {1},
pages = {56},
abstract = {We report the direct femtosecond laser inscription of a 45-deg tilted fiber Bragg grating (TFBG) into fluoride fiber, creating an in-fiber mid-infrared polarizer. Utilizing a 16 mm long intracavity TFBG, we demonstrate a 2.862 µm Ho3+Pr3+:ZBLAN fiber laser with 21.6 dB output polarization extinction ratio (PER), up to 0.37 W output power and 31.3% slope efficiency. In addition, we experimentally demonstrate that the laser PER is a linear function of grating length. Our results show that fluoride TFBGs are a promising route to replace bulk polarizers in mid-IR laser cavities, paving the way to all-fiber mid-infrared laser systems.},
keywords = {fibre laser, mid-infrared},
pubstate = {published},
tppubtype = {article}
}
@conference{Woodward2018b,
title = {Versatile mid-infrared mode-locked fiber laser, electronically tunable from 2.97 to 3.30 μm [Postdeadline]},
author = {R. I. Woodward and M. R. Majewski and S. D. Jackson},
url = {https://www.riwoodward.com/publication_files/woodward_2018_cleo_ml.pdf},
doi = {10.1364/CLEOPR.2018.Th5A.8},
year  = {2018},
date = {2018-08-10},
booktitle = {CLEO Pacific Rim: 2018, OSA Technical Digest},
publisher = {The Optical Society},
address = {Hong Kong},
abstract = {We demonstrate the first dysprosium mode-locked laser: the longest wavelength and most widely tunable mode-locked fiber laser to date. Picosecond pulses are generated by a novel frequency-shifted feedback mechanism using an intracavity acousto-optic tunable filter.},
note = {Paper PDP.8},
keywords = {dysprosium, fibre laser},
pubstate = {published},
tppubtype = {conference}
}
@conference{Woodward2018,
title = {High-efficiency watt-level mid-infrared fiber lasers beyond 3 µm using Dy:ZBLAN},
author = {R. I. Woodward and M. R. Majewski and G. Bharathan and D. D. Hudson and A. Fuerbach and S. D. Jackson},
url = {https://www.riwoodward.com/publication_files/woodward_2018_cleo_watt.pdf},
doi = {10.1364/CLEOPR.2018.F1A.1},
year  = {2018},
date = {2018-08-09},
booktitle = {CLEO Pacific Rim: 2018, OSA Technical Digest},
publisher = {The Optical Society},
address = {Hong Kong},
abstract = {We demonstrate an optimized in-band-pumped dysprosium fiber laser with 73% slope efficiency and 1.1 W output at 3.15 µm: the first watt-level fiber source in the 3.0–3.4 µm region and highest ever efficiency mid-IR fiber laser.},
note = {Paper F1A.1},
keywords = {dysprosium, fibre laser},
pubstate = {published},
tppubtype = {conference}
}
@conference{Fuerbach2018,
title = {Line-by-line femtosecond FBG inscription for innovative fiber lasers [Invited]},
author = {A. Fuerbach and G. Bharathan and S. Antipov and M. Ams and R. J. Williams and D. D. Hudson and R. I. Woodward and S. D. Jackson},
url = {https://www.riwoodward.com/publication_files/fuerbach_2018_1.pdf},
doi = {10.1364/BGPPM.2018.BW3A.6},
year  = {2018},
date = {2018-07-01},
booktitle = {OSA Advanced Photonics Congress},
abstract = {We report the fabrication of Bragg gratings in passive and doped fibers using femtosecond laser line-by-line inscription. Narrow-linewidth and broadband chirped gratings with engineered dispersion are written into silica- and fluoride-glass fibers},
note = {Paper BW3A.6},
keywords = {fibre laser},
pubstate = {published},
tppubtype = {conference}
}
@conference{Fuerbach2018b,
title = {Mid-IR supercontinuum generation [Invited]},
author = {A. Fuerbach and D. D. Hudson and S. D. Jackson and S. Antipov and R. I. Woodward and L. Li and I. Alamgir and M. E. Amraoui and Y. Messaddeq and M. Rochette},
url = {https://www.riwoodward.com/publication_files/fuerbach_2018_2.pdf},
doi = {10.1364/SOF.2018.SoTh3H.1},
year  = {2018},
date = {2018-07-01},
booktitle = {OSA Advanced Photonics Congress},
abstract = {Output pulses from an ultrafast holmium-praseodymium co-doped fiber ring laser are spectrally broadened in highly nonlinear chalcogenide fibers. Under optimized conditions, an ultra-broadband supercontinuum spanning from 2–12 μm is demonstrated.},
note = {Paper SoTh3H.1},
keywords = {fibre laser},
pubstate = {published},
tppubtype = {conference}
}
@conference{Bharathan2018,
title = {In-fibre polarizer for mid-infrared fibre lasers based on 45 tilted fluoride fibre Bragg grating},
author = {G. Bharathan and R. I. Woodward and D. D. Hudson and S. D. Jackson and A. Fuerbach},
url = {https://www.riwoodward.com/publication_files/bharathan_2018_adv.pdf},
doi = {10.1364/BGPPM.2018.BW3A.2},
year  = {2018},
date = {2018-07-01},
booktitle = {OSA Advanced Photonics Congress},
abstract = {We report the femtosecond laser inscription of a 45◦ tilted fibre Bragg grating (TFBG) into ZBLAN fibre. Integrating this TFBG into a mid-IR fibre laser cavity resulted in 20.5 dB output polarization extinction ratio.},
note = {Paper BW3A.2},
keywords = {fbg, fibre laser},
pubstate = {published},
tppubtype = {conference}
}
@conference{Woodward2018_cleo_fs,
title = {Few-cycle pulse generation from a 3 µm fiber laser [Invited]},
author = {R. I. Woodward and D. D. Hudson and A. Fuerbach and S. D. Jackson},
url = {https://www.riwoodward.com/publication_files/woodward_2018_cleo_fs.pdf},
doi = {10.1364/CLEO_SI.2018.STh4K.1},
year  = {2018},
date = {2018-05-19},
booktitle = {CLEO:2018, OSA Technical Digest},
publisher = {The Optical Society},
address = {San Jose, USA},
abstract = {We demonstrate the generation of 70-fs pulses (~7 optical-cycles) from a mid-infrared mode-locked Ho:ZBLAN fiber laser using nonlinear compression with step- index chalcogenide fiber. Experiments are supported by numerical modelling, confirming the scalability of this approach.},
note = {Paper STh4K.1},
keywords = {fibre laser, mid-infrared, mode-locked, ultrafast},
pubstate = {published},
tppubtype = {conference}
}
@conference{Majewski2018_cleo,
title = {Emission beyond 4 µm and mid-infrared lasing from a Dy3+:InF3 fiber},
author = {M. R. Majewski and R. I. Woodward and J. -Y. Carreé and S. Poulain and M. Poulain and S. D. Jackson},
url = {https://www.riwoodward.com/publication_files/majewski_2018_cleo_inf.pdf},
doi = {10.1364/CLEO_SI.2018.STh4K.3},
year  = {2018},
date = {2018-05-18},
booktitle = {CLEO:2018, OSA Technical Digest},
publisher = {The Optical Society},
address = {San Jose, USA},
abstract = {We present a dysprosium-doped InF3 fiber exhibiting emission beyond 4 microns; the longest wavelength to date from a fluoride-based fiber. Laser emission around 3 µm is also demonstrated.},
note = {Paper STh4K.3},
keywords = {dysprosium, fibre laser, mid-infrared},
pubstate = {published},
tppubtype = {conference}
}
@article{Majewski2018b,
title = {Emission beyond 4 μm and mid-infrared lasing in a dysprosium-doped indium fluoride (InF3) fiber},
author = {M. R. Majewski and R. I. Woodward and J. -Y. Carreé and S. Poulain and M. Poulain and S. D. Jackson},
url = {https://www.riwoodward.com/publication_files/majewski_2018_inf3.pdf},
doi = {10.1364/OL.43.001926},
year  = {2018},
date = {2018-04-13},
journal = {Optics Letters},
volume = {43},
number = {8},
pages = {1926},
abstract = {Optical emission from rare-earth-doped fluoride fibers has thus far been limited to less than 4 μm. We extend emission beyond this limit by employing an indium fluoride (InF3) glass fiber as the host, which exhibits an increased infrared transparency over commonly used zirconium fluoride (ZBLAN). Near-infrared pumping of a dysprosium-doped InF3 fiber results in broad emission centered around 4.3 μm, representing the longest emission yet achieved from a fluoride fiber. The first laser emission in an InF3 fiber is also demonstrated from the 3 μm dysprosium transition. Finally, a frequency domain excited state lifetime measurement comparison between fluoride hosts suggests that multiphonon effects are significantly reduced in indium fluoride fiber, paving the way to more efficient, longer wavelength lasers compared to ZBLAN fibers.},
keywords = {dysprosium, fibre laser, mid-infrared},
pubstate = {published},
tppubtype = {article}
}
@article{Woodward2018_watt,
title = {Watt-level dysprosium fiber laser at 3.15 µm with 73% slope efficiency},
author = {R. I. Woodward and M. R. Majewski and G. Bharathan and D. D. Hudson and A. Fuerbach and S. D. Jackson},
url = {https://riwoodward.com/publication_files/woodward_2018_watt.pdf},
doi = {10.1364/OL.43.001471},
year  = {2018},
date = {2018-03-20},
journal = {Optics Letters},
volume = {43},
number = {7},
pages = {1471},
abstract = {Rare-earth-doped fiber lasers are emerging as promising high-power mid-infrared sources for the 2.6–3.0 μm and 3.3–3.8 μm regions based on erbium and holmium ions. The intermediate wavelength range, however, remains vastly underserved, despite prospects for important manufacturing and defense applications. Here, we demonstrate the potential of dysprosium-doped fiber to solve this problem, with a simple in-band pumped grating-stabilized linear cavity generating up to 1.06 W at 3.15 μm. A slope efficiency of 73% with respect to launched power (77% relative to absorbed power) is achieved—the highest value for any mid-infrared fiber laser to date, to the best of our knowledge. Opportunities for further power and efficiency scaling are also discussed.},
keywords = {dysprosium, fibre laser, mid-infrared},
pubstate = {published},
tppubtype = {article}
}
@conference{Majewski2018a,
title = {Near infrared pumped full gain bandwidth tunable 3 micron dysprosium fiber laser},
author = {M. R. Majewski and R. I. Woodward and S. D. Jackson},
url = {https://www.riwoodward.com/publication_files/majewski_2018_pw.pdf},
doi = {10.1117/12.2289382},
year  = {2018},
date = {2018-03-01},
booktitle = {Proc. SPIE 10512, Fiber Lasers XV: Technology and Systems},
abstract = {Previously reported progress in 3 micron dysprosium doped ZBLAN fiber lasers achieved record conversion efficiency but was limited in tuneability due to the inband nature of the pumping scheme. Near infrared pumping has also been demonstrated but was limited in conversion efficiency due both to pump excited state absorption and large quantum defect. We address these limitations by employing a Raman fiber laser operating at 1700 nm as a pump source. Reduced quantum defect shows promise for efficiency gains while maintaining near infrared pumping and the increased gain bandwidth shows promise for pulsed operation.},
note = {Paper 105120U},
keywords = {fibre laser, mid-infrared},
pubstate = {published},
tppubtype = {conference}
}
@article{Majewski2018,
title = {Dysprosium-doped ZBLAN fiber laser tunable from 2.8 μm to 3.4 μm, pumped at 1.7 μm},
author = {M. R. Majewski and R. I. Woodward and S. D. Jackson},
url = {https://www.riwoodward.com/publication_files/majewski_2018_ol_dytune.pdf},
doi = {10.1364/OL.43.000971},
year  = {2018},
date = {2018-02-16},
journal = {Optics Letters},
volume = {43},
number = {5},
pages = {971},
abstract = {We demonstrate a mid-infrared dysprosium-doped fluoride fiber laser with a continuously tunable output range of 573 nm, pumped by a 1.7 μm Raman fiber laser. To the best of our knowledge, this represents the largest tuning range achieved to date from any rare-earth-doped fiber laser and, critically, spans the 2.8–3.4 μm spectral region, which contains absorption resonances of many important functional groups and is uncovered by other rare-earth ions. Output powers up to 170 mW are achieved, with 21% slope efficiency. We also discuss the relative merits of the 1.7 μm pump scheme, including possible pump excited-state absorption.},
note = {Editors' Pick},
keywords = {dysprosium, fibre laser, mid-infrared},
pubstate = {published},
tppubtype = {article}
}
@article{Woodward2018_jo,
title = {Dispersion engineering of mode-locked fibre lasers [Invited]},
author = {R. I. Woodward},
url = {https://www.riwoodward.com/publication_files/woodward_2018_jopt_disp_eng.pdf},
doi = {10.1088/2040-8986/aaa9f5},
year  = {2018},
date = {2018-02-14},
journal = {Journal of Optics},
volume = {20},
pages = {033002},
abstract = {Mode-locked fibre lasers are important sources of ultrashort pulses, where stable pulse generation is achieved through a balance of periodic amplitude and phase evolutions. A range of distinct cavity pulse dynamics have been revealed, arising from the interplay between dispersion and nonlinearity in addition to dissipative processes such as filtering. This has led to the discovery of numerous novel operating regimes, offering significantly improved laser performance. In this Topical Review, we summarise the main steady-state pulse dynamics reported to date through cavity dispersion engineering, including average solitons, dispersion-managed solitons, dissipative solitons, giant-chirped pulses and similaritons. Characteristic features and the stabilisation mechanism of each regime are described, supported by numerical modelling, in addition to the typical performance and limitations. Opportunities for further pulse energy scaling are discussed, in addition to considering other recent advances including automated self-tuning cavities and fluoride-fibre-based mid-infrared mode-locked lasers.},
keywords = {fibre laser, mode-locked, ultrafast},
pubstate = {published},
tppubtype = {article}
}
@conference{Woodward2018a,
title = {Towards diode-pumped mid-infrared praseodymium-ytterbium-doped fluoride fiber lasers},
author = {R. I. Woodward and D. D. Hudson and S. D. Jackson},
url = {https://www.riwoodward.com/publication_files/woodward_2018_pw.pdf},
doi = {10.1117/12.2294508},
year  = {2018},
date = {2018-02-01},
booktitle = {Proc. SPIE 10512, Fiber Lasers XV: Technology and Systems},
abstract = {We explore the potential of a new mid-infrared laser transition in praseodymium-doped fluoride fiber for emission around 3.4 μm, which can be conveniently pumped by 0.975 μm diodes via ytterbium sensitizer co-doping. Optimal cavity designs are determined through spectroscopic measurements and numerical modeling, suggesting that practical diode-pumped watt-level mid-infrared fiber sources beyond 3 μm could be achieved.},
note = {Paper 105120S},
keywords = {fibre laser, mid-infrared},
pubstate = {published},
tppubtype = {conference}
}
@conference{Bharathan2017a,
title = {Widely tunable mid-infrared all-fibre lasers based on mechanically robust fibre Bragg gratings},
author = {G. Bharathan and R. I. Woodward and M. Ams and D. D. Hudson and S. D. Jackson and A. Fuerbach},
url = {https://www.riwoodward.com/publication_files/bharathan_2017_anzcop_fbg.pdf},
year  = {2017},
date = {2017-12-06},
booktitle = {Australian and New Zealand Conference on Optics and Photonics (ANZCOP 2017)},
abstract = {We report on the inscription of a mechanically robust fibre Bragg grating and its integration into a tunable all-fibre mid-infrared laser. Experimental results show a 37 nm wavelength tuning range of a fluoride fibre laser.},
note = {Paper 8},
keywords = {mid-infrared},
pubstate = {published},
tppubtype = {conference}
}
@conference{Woodward2017a,
title = {Self-tuning short-pulse fibre lasers with automated algorithmic optimisation},
author = {R. I. Woodward and Kelleher E. J. R},
url = {https://www.riwoodward.com/publication_files/woodward_2017_anzcop_algo.pdf},
year  = {2017},
date = {2017-12-06},
booktitle = {Australian and New Zealand Conference on Optics and Photonics (ANZCOP 2017)},
abstract = {We report self-optimising fibre lasers that achieve on-demand autonomous spectral tuning and variable short-pulse generation by passive birefringent filtering, governed by genetic algorithms and electronic control of the cavity transfer function.},
note = {Paper 15},
keywords = {fibre laser},
pubstate = {published},
tppubtype = {conference}
}
@conference{Woodward2017c,
title = {Mid-infrared few-cycle pulse generation with a Ho:ZBLAN fibre laser},
author = {R. I. Woodward and D. D. Hudson and A. Fuerbach and S. D. Jackson},
url = {https://www.riwoodward.com/publication_files/woodward_2017_anzcop_fewcycle.pdf},
year  = {2017},
date = {2017-12-06},
booktitle = {Australian and New Zealand Conference on Optics and Photonics (ANZCOP 2017)},
abstract = {We demonstrate a simple and compact route to few-cycle pulse generation from mid-infrared fibre lasers through nonlinear compression with step-index As2S3 fibre and a grating pair, achieving 73 fs pulses (7.6 optical cycles) at 2.86 µm.},
note = {Paper 115},
keywords = {fibre laser, mid-infrared},
pubstate = {published},
tppubtype = {conference}
}
@conference{Woodward2017b,
title = {Fibre lasers beyond 3 µm using PrYb:ZBLAN},
author = {R. I. Woodward and D. D. Hudson and S. D. Jackson},
url = {https://www.riwoodward.com/publication_files/woodward_2017_anzcop_pryb.pdf},
year  = {2017},
date = {2017-12-04},
booktitle = {Australian and New Zealand Conference on Optics and Photonics (ANZCOP 2017)},
abstract = {We propose a new mid-infrared laser transition in praseodymium-doped ZBLAN fibre, diode pumped at 0.975 µm via ytterbium sensitiser, and identify optimal cavity designs through detailed spectroscopic measurements and numerical modelling.},
note = {Paper 16},
keywords = {fibre laser, mid-infrared},
pubstate = {published},
tppubtype = {conference}
}
@article{woodward_2017_70fs,
title = {Generation of 70-fs pulses at 2.86 μm from a mid-infrared fiber laser},
author = {R. I. Woodward and D. D. Hudson and A. Fuerbach and S. D. Jackson},
url = {https://riwoodward.com/publication_files/woodward_2017_70fs.pdf},
doi = {10.1364/OL.42.004893},
year  = {2017},
date = {2017-11-22},
urldate = {2017-11-22},
journal = {Optics Letters},
volume = {42},
pages = {4893},
abstract = {We propose and demonstrate a simple route to few-optical-cycle pulse generation from a mid-infrared fiber laser through nonlinear compression of pulses from a holmium-doped fiber oscillator using a short length of chalcogenide fiber and a grating pair. Pulses from the oscillator with 265-fs duration at 2.86 μm are spectrally broadened through self-phase modulation in step-index As2S3 fiber to 141-nm bandwidth and then re-compressed to 70 fs (7.3 optical cycles). These are the shortest pulses from a mid-infrared fiber system to date, and we note that our system is compact, robust, and uses only commercially available components. The scalability of this approach is also discussed, supported by numerical modeling.},
note = {Editors' Pick},
keywords = {fibre laser, mid-infrared},
pubstate = {published},
tppubtype = {article}
}
@article{Bharathan2017,
title = {Direct inscription of Bragg gratings into coated fluoride fibers for widely tunable and robust mid-infrared lasers},
author = {G. Bharathan and R. I. Woodward and M. Ams and D. D. Hudson and S. D. Jackson and A. Fuerbach},
url = {https://riwoodward.com/publication_files/bharathan_2017_fbg.pdf},
doi = {10.1364/OE.25.030013},
year  = {2017},
date = {2017-11-20},
urldate = {2017-11-20},
journal = {Optics Express},
volume = {25},
pages = {30013},
abstract = {We report the development of a widely tunable all-fiber mid-infrared laser system based on a mechanically robust fiber Bragg grating (FBG) which was inscribed through the polymer coating of a Ho3+-Pr3+ co-doped double clad ZBLAN fluoride fiber by focusing femtosecond laser pulses into the core of the fiber without the use of a phase mask. By applying mechanical tension and compression to the FBG while pumping the fiber with an 1150 nm laser diode, a continuous wave (CW) all-fiber laser with a tuning range of 37 nm, centered at 2870 nm, was demonstrated with up to 0.29 W output power. These results pave the way for the realization of compact and robust mid-infrared fiber laser systems for real-world applications in spectroscopy and medicine.},
keywords = {fbg, fibre laser},
pubstate = {published},
tppubtype = {article}
}
@article{Hu_2017_natcomm,
title = {Black phosphorus ink formulation for inkjet printing of optoelectronics and photonics},
author = {G. Hu and T. Albrow-Owen and X. Jin and A. Ali and Y. Hu and R. C. T. Howe and K. Shehzad and Z. Yang and X. Zhu and R. I. Woodward and T. -C. Wu and H. Jussila and J. -B. Wu and P. Peng and P. -H. Tan and Z. Sun and E. J. R. Kelleher and M. Zhang and Y. Xu and T. Hasan},
url = {https://www.riwoodward.com/publication_files/hu_2017_natcomm.pdf},
doi = {10.1038/s41467-017-00358-1},
year  = {2017},
date = {2017-08-17},
urldate = {2017-08-17},
journal = {Nature Communications},
volume = {8},
pages = {278},
abstract = {Black phosphorus is a two-dimensional material of great interest, in part because of its high carrier mobility and thickness dependent direct bandgap. However, its instability under ambient conditions limits material deposition options for device fabrication. Here we show a black phosphorus ink that can be reliably inkjet printed, enabling scalable development of optoelectronic and photonic devices. Our binder-free ink suppresses coffee ring formation through induced recirculating Marangoni flow, and supports excellent consistency (< 2% variation) and spatial uniformity (< 3.4% variation), without substrate pre-treatment. Due to rapid ink drying (< 10 s at < 60 °C), printing causes minimal oxidation. Following encapsulation, the printed black phosphorus is stable against long-term (> 30 days) oxidation. We demonstrate printed black phosphorus as a passive switch for ultrafast lasers, stable against intense irradiation, and as a visible to near-infrared photodetector with high responsivities. Our work highlights the promise of this material as a functional ink platform for printed devices.},
keywords = {black phosphorus},
pubstate = {published},
tppubtype = {article}
}
@inbook{Erkintalo2017,
title = {Instabilities and extreme events in all-normal dispersion mode-locked fibre lasers},
author = {M. Erkintalo and A. Runge and R. I. Woodward and E. J. R. Kelleher and N. G. R. Broderick},
editor = {S. Wabnitz},
doi = {10.1088/978-0-7503-1460-2ch5},
year  = {2017},
date = {2017-07-01},
urldate = {2017-07-01},
booktitle = {Nonlinear Guided Wave Optics: A testbed for extreme waves},
publisher = {IOP Publishing},
chapter = {5},
abstract = {We present an overview of extreme events and complex dissipative phenomena in all-normal dispersion mode-locked fibre lasers. In particular, we describe how stimulated Raman scattering can destabilize the laser operation, giving rise to noise-like pulses displaying long-tailed statistics. We also discuss the appearance and dynamics of transient 'soliton explosion' events, as well as rogue dark solitons that can manifest themselves during the build-up phase of laser radiation. Our focus is on surveying experimental findings, but we also describe results from numerical simulations where pertinent.},
keywords = {dark soliton, fibre laser},
pubstate = {published},
tppubtype = {inbook}
}
@conference{Phelan_graphene17,
title = {Characterization of the nonlinear optical susceptibilities of monolayer MoS2 and comparison with graphene},
author = {C. F. Phelan and R. I. Woodward and R. T. Murray and R. E. P. Oliveira and T. H. Runcorn and E. J. R. Kelleher and S. Li and E. C. Oliveira and G. J. M. Fechine and G. Eda and C. J. S. Matos},
url = {https://www.riwoodward.com/publication_files/phelan_2017_grap.pdf},
year  = {2017},
date = {2017-03-28},
booktitle = {Graphene2017},
abstract = {We report the determination of the second and, for the first time, third order optical nonlinear susceptibilities of monolayer MoS2 by measurements of second and third harmonic generation.},
keywords = {MoS2},
pubstate = {published},
tppubtype = {conference}
}
@article{Woodward_2017_ga,
title = {Genetic algorithm-based control of birefringent filtering for self-tuning, self-pulsing fiber lasers},
author = {R. I. Woodward and E. J. R. Kelleher},
url = {https://www.riwoodward.com/publication_files/woodward_2017_ga.pdf},
doi = {10.1364/OL.42.002952},
year  = {2017},
date = {2017-02-21},
journal = {Optics Letters},
volume = {42},
number = {15},
pages = {2952},
abstract = {Polarization-based filtering in fiber lasers is well-known to enable spectral tunability and a wide range of dynamical operating states. This effect is rarely exploited in practical systems, however, because optimization of cavity parameters is non-trivial and evolves due to environmental sensitivity. Here, we report a genetic algorithm-based approach, utilizing electronic control of the cavity transfer function, to autonomously achieve broad wavelength tuning and the generation of Q-switched pulses with variable repetition rate and duration. The practicalities and limitations of simultaneous spectral and temporal self-tuning from a simple fiber laser are discussed, paving the way to on-demand laser properties through algorithmic control and machine learning schemes.},
note = {Editors' Pick},
keywords = {fibre laser},
pubstate = {published},
tppubtype = {article}
}
@article{Woodward_2016_mos2,
title = {Characterization of the second- and third-order nonlinear optical susceptibilities of monolayer MoS2 using multiphoton microscopy},
author = {R. I. Woodward and R. T. Murray and C. F. Phelan and R. E. P. Oliveira and T. H. Runcorn and E. J. R. Kelleher and S. Li and E. C. Oliveira and G. J. M. Fechine and G. Eda and C. J. S. Matos},
url = {https://www.riwoodward.com/publication_files/woodward_2017_mos2.pdf},
doi = {10.1088/2053-1583/4/1/011006},
year  = {2017},
date = {2017-01-01},
journal = {2D Materials},
volume = {4},
number = {1},
pages = {011006},
abstract = {We report second- and third-harmonic generation in monolayer MoS2 as a tool for imaging and accurately characterizing the material’s nonlinear optical properties under 1560 nm excitation. Using a surface nonlinear optics treatment, we derive expressions relating experimental measurements to second- and third-order nonlinear sheet susceptibility magnitudes, obtaining values of |χ(2)s|=2.0×10^−20 m^2 V^−1 and, for the first time for monolayer MoS2, χ(3)s|=1.7×10^−28 m^3 V^−2. These sheet susceptibilities correspond to effective bulk nonlinear susceptibility values of 2.9×10^-11 m V^−1 and 2.4×10^-19 m^2 V^−2, accounting for the sheet thickness. Experimental comparisons between MoS2 and graphene are also performed, demonstrating∼3.4 times stronger third-order sheet nonlinearity in monolayer MoS2, highlighting the material’s potential for nonlinear photonics in the telecommunications C band.},
keywords = {fibre laser, MoS2},
pubstate = {published},
tppubtype = {article}
}
@article{Woodward_2016_ga,
title = {Towards 'smart lasers': self-optimisation of an ultrafast pulse source using a genetic algorithm},
author = {R. I. Woodward and E. J. R. Kelleher},
url = {https://www.riwoodward.com/publication_files/woodward_2016_ga.pdf},
doi = {10.1038/srep37616},
year  = {2016},
date = {2016-07-19},
journal = {Scientific Reports},
volume = {6},
pages = {37616},
abstract = {Short-pulse fibre lasers are a complex dynamical system possessing a broad space of operating states that can be accessed through control of cavity parameters. Determination of target regimes is a multi-parameter global optimisation problem. Here, we report the implementation of a genetic algorithm to intelligently locate optimum parameters for stable single-pulse mode-locking in a Figure-8 fibre laser, and fully automate the system turn-on procedure. Stable ultrashort pulses are repeatably achieved by employing a compound fitness function that monitors both temporal and spectral output properties of the laser. Our method of encoding photonics expertise into an algorithm and applying machine-learning principles paves the way to self-optimising `smart' optical technologies.},
keywords = {fibre laser},
pubstate = {published},
tppubtype = {article}
}
@conference{woodward_2016_photon16,
title = {Dispersion engineering of mode-locked fibre lasers [Invited]},
author = {R. I. Woodward},
url = {https://www.riwoodward.com/publication_files/woodward_2016_photon16.pdf},
year  = {2016},
date = {2016-07-06},
booktitle = {Photon16},
publisher = {Institute of Physics},
abstract = {In this talk, I will review recent progress in all-normal dispersion lasers with a focus on our long-cavity laser architecture. Experimental results will be presented showing nanosecond-pulse generation at kilohertz repetition rates, suitable for direct amplification and compressible by two orders of magnitude. This design thus offers a route to simplifying chirped pulse amplification (CPA) schemes. Additionally, the high-duty-factor compressed pulse are shown to be ideal for low-threshold supercontinuum generation in photonic crystal fibre. 
 
I will also discuss the numerical modelling of these lasers using a generalised nonlinear Schrodinger equation, which is able to accurately predict the output pulse properties and offers additional insight into the intracavity nonlinear dynamics and pulse shaping mechanisms.},
keywords = {fibre laser},
pubstate = {published},
tppubtype = {conference}
}
@conference{Woodward_cleo16_ga,
title = {Self-optimizing mode-locked laser using a genetic algorithm},
author = {R. I. Woodward and E. J. R. Kelleher},
url = {https://www.riwoodward.com/publication_files/woodward_cleo_2016_fig8.pdf},
doi = {10.1364/CLEO_SI.2016.STu3P.6},
year  = {2016},
date = {2016-06-09},
booktitle = {CLEO:2016, OSA Technical Digest},
publisher = {The Optical Society},
abstract = {We apply the concept of natural selection to intelligently find optimum operating regimes in a fiber laser – a multi-parameter space. Using a compound fitness function we reliably achieve self-optimizing mode-locked operation.},
note = {Paper STu3P.6},
keywords = {fibre laser},
pubstate = {published},
tppubtype = {conference}
}
@conference{Sugavanam_cleo16_fbs,
title = {Pulse bunching in the soliton rain regime of an ultralong fiber laser mediated by forward Brillouin scattering},
author = {S. Sugavanam and A. El-Taher and R. I. Woodward and E. J. R. Kelleher and D. V. Churkin},
url = {https://www.riwoodward.com/publication_files/woodward_cleo_2016_fbs.pdf},
doi = {10.1364/CLEO_QELS.2016.FTu4A.4},
year  = {2016},
date = {2016-06-08},
booktitle = {CLEO:2016, OSA Technical Digest},
publisher = {Optical Society of America},
abstract = {We present experimental evidence for soliton bunching mediated by forward Brillouin scattering in the soliton rain regime of an ultralong fiber laser. Spatio-temporal dynamics show an initial acceleration followed by self-organization of the rain solitons.},
note = {Paper FTu4A.4},
keywords = {fibre laser},
pubstate = {published},
tppubtype = {conference}
}
@conference{Woodward_cleo16_mos2,
title = {Characterization of the nonlinear susceptibility of monolayer MoS2 using second- and third-harmonic generation microscopy},
author = {R. I. Woodward and R. T. Murray and C. F. Phelan and R. E. P. Oliveira and S. Li and G. Eda and C. J. S. Matos},
url = {https://www.riwoodward.com/publication_files/woodward_cleo_2016_mos2.pdf},
doi = {10.1364/CLEO_SI.2016.STu1R.3},
year  = {2016},
date = {2016-06-07},
booktitle = {CLEO:2016, OSA Technical Digest},
publisher = {Optical Society of America},
abstract = {Second- and third-harmonic generation microscopy of monolayer MoS2 is reported for imaging and characterization of the material's nonlinearity. A telecommunication wavelength pump is used, revealing the material's promise for use in nonlinear optical devices.},
note = {Paper STu1R.3},
keywords = {MoS2},
pubstate = {published},
tppubtype = {conference}
}
@article{@Woodward_2016_dark,
title = {Dark solitons in laser radiation build-up dynamics},
author = {R. I. Woodward and E. J. R. Kelleher},
url = {https://www.riwoodward.com/publication_files/woodward_2016_dark.pdf},
doi = {10.1103/PhysRevE.93.032221},
year  = {2016},
date = {2016-03-29},
journal = {Physical Review E},
volume = {93},
number = {3},
pages = {032221},
organization = {arXiv:1601.03330},
abstract = {We reveal the existence of slowly-decaying dark solitons in the radiation build-up dynamics of bright pulses in all-normal dispersion mode-locked fiber lasers, numerically modeled in the framework of a generalized nonlinear Schrodinger equation. The evolution of noise perturbations to quasi-stationary dark solitons is examined, and the significance of background shape and soliton-soliton collisions on the eventual soliton decay is established. We demonstrate the role of a restoring force in extending soliton interactions in conservative systems to include the effects of dissipation, as encountered in laser cavities, and generalize our observations to other nonlinear systems.},
keywords = {dark soliton, fibre laser},
pubstate = {published},
tppubtype = {article}
}
@phdthesis{Woodward2016,
title = {Exploiting nonlinearity in optical fibres and nanomaterials for short-pulse laser technology},
author = {R. I. Woodward},
url = {https://www.riwoodward.com/publication_files/riwoodward_thesis.pdf},
year  = {2016},
date = {2016-03-11},
school = {Imperial College London},
abstract = {The importance of short-pulse laser technology in all branches of science and engineering continues to grow, increasing demands on their performance. In this thesis, we explore approaches for advancing such technologies using optical nonlinearity in emerging nanomaterials and fibres to manipulate the spectral and temporal properties of light. 
 
Firstly, we introduce a long-cavity mode-locked fibre laser architecture for generating high-energy pulses with a giant chirp at low repetition rates. Chirped fibre Bragg gratings are developed for pulse compression (and peak-power enhancement) by a factor of a hundred and the system is shown to be an ideal pump source for low-threshold supercontinuum generation in photonic crystal fibre (PCF). Experimental work is supported by numerical simulations to reveal insight into the pulse dynamics. 
 
Two-dimensional nanomaterials, specifically few-layer transition metal dichalcogenides such as MoS2 are then considered. We report a harmonic generation microscopy technique for rapidly characterising the structure and optical properties of nanomaterial samples. These materials are then integrated into fibre lasers to act as saturable absorbers for pulse generation by Q-switching and mode-locking. We present a range of sources with pulse durations from femtoseconds to microseconds and kilohertz to megahertz repetition rates, operating throughout the near-infrared, highlighting the wide parameter space that can be accessed. We also propose a theory based on edge states to explain the wideband saturable absorption. 
 
Finally, we study stimulated Brillouin scattering in PCF with a focus on the role of acoustic dynamics. With careful choice of wavelength relative to the microstructured fibre length scales, PCFs are shown to exhibit a stronger Brillouin response than conventional fibre, which we use to develop a compact self-mode-locked Brillouin laser. 
 
We conclude that emerging nanomaterials and optical fibre designs could be leveraged to yield tangible benefits for short-pulse laser technology and we place our results in context of ongoing research.},
keywords = {thesis},
pubstate = {published},
tppubtype = {phdthesis}
}
@article{@Howe_2016_pssb,
title = {Surfactant-aided exfoliation of molybdenum disulfide for ultrafast pulse generation through edge-state saturable absorption},
author = {R. C. T. Howe and R. I. Woodward and G. Hu and Z. Yang and E. J. R. Kelleher and T. Hasan},
url = {https://www.riwoodward.com/publication_files/howe_2016_pssb.pdf},
doi = {10.1002/pssb.201552304},
year  = {2016},
date = {2016-01-11},
journal = {Physica Status Solidi (B)},
volume = {253},
number = {5},
pages = {911},
abstract = {We use liquid phase exfoliation to produce dispersions of molybdenum disulfide (MoS2) nanoflakes in aqueous surfactant solutions. The chemical structures of the bile salt surfactants play a crucial role in the exfoliation and stabilization of MoS2. The resultant MoS2 dispersions are heavily enriched in single and few-layer flakes with large edge to surface area ratio. We use the dispersions to fabricate free-standing polymer composite wide-band saturable absorbers to develop mode-locked and Q-switched fiber lasers, tunable from 1535 to 1565 and 1030 to 1070 nm, respectively. We attribute this sub-bandgap optical absorption and its nonlinear saturation behavior to edge-mediated states introduced within the material band-gap of the exfoliated MoS2 nanoflakes.},
keywords = {MoS2},
pubstate = {published},
tppubtype = {article}
}
@article{Woodward2015_as_2d,
title = {2D Saturable Absorbers for Fibre Lasers [Invited]},
author = {R. I. Woodward and E. J. R. Kelleher},
url = {https://www.riwoodward.com/publication_files/woodward_2015_appsci.pdf},
doi = {10.3390/app5041440},
year  = {2015},
date = {2015-11-30},
journal = {Applied Sciences},
volume = {5},
number = {4},
pages = {1440-1456},
abstract = {Two-dimensional (2D) nanomaterials are an emergent and promising platform for future photonic and optoelectronic applications. Here, we review recent progress demonstrating the application of 2D nanomaterials as versatile, wideband saturable absorbers for Q-switching and mode-locking fibre lasers. We focus specifically on the family of few-layer transition metal dichalcogenides, including MoS2, MoSe2 and WS2.},
keywords = {fibre laser, MoS2, MoSe2, saturable absorber, WS2},
pubstate = {published},
tppubtype = {article}
}
@conference{Woodward2016a,
title = {Brillouin solitons and enhanced mirror in the presence of acoustic dispersion in a small-core photonic crystal fiber},
author = {R. I. Woodward and E. Picholle and C. Montes},
url = {https://www.riwoodward.com/publication_files/woodward_2015_jnog.pdf 
https://hal.archives-ouvertes.fr/hal-01323737/},
year  = {2015},
date = {2015-07-01},
booktitle = {35e Journées Nationales d’Optique 
Guidée (JNOG’35)},
keywords = {fibre laser},
pubstate = {published},
tppubtype = {conference}
}
@conference{@Woodward_oecc2015,
title = {Optical nonlinearity of few-layer MoS2 devices and applications in short-pulse laser technology [Invited]},
author = {R. I. Woodward and T. Hasan and E. J. R. Kelleher},
url = {https://www.riwoodward.com/publication_files/woodward_oecc_2015_revi.pdf},
doi = {10.1109/OECC.2015.7340109},
year  = {2015},
date = {2015-06-28},
booktitle = {Optoelectronics and Communications Conference (OECC 2015)},
publisher = {IEEE},
abstract = {Few-layer transition metal dichalcogenides such as molybdenum disulfide (MoS2) present new opportunities for photonic devices. Here, we review recent progress in few-layer MoS2-based nonlinear optics and state-of-the-art pulsed lasers using this new nanomaterial.},
note = {Paper JSuB.08},
keywords = {MoS2},
pubstate = {published},
tppubtype = {conference}
}
@conference{@Woodward_cleo15_nano,
title = {Nanosecond to picosecond fiber Bragg grating compression of giant-chirped pulses from an ultra-long mode-locked fiber laser},
author = {R. I. Woodward and E. J. R. Kelleher and T. H. Runcorn and S. Loranger and D. Popa and V. J. Wittwer and A. C. Ferrari and S. V. Popov and R. Kashyap and J. R. Taylor},
url = {https://www.riwoodward.com/publication_files/woodward_cleo_2015_comp.pdf https://www.osapublishing.org/abstract.cfm?uri=CLEO_Europe-2015-CJ_9_6},
year  = {2015},
date = {2015-06-24},
booktitle = {The European Conference on Lasers and Electro-Optics 2015},
publisher = {Optical Society of America},
abstract = {We demonstrate compression of nanosecond giant-chirped pulses from an ultra-long all-normal dispersion mode-locked fiber laser by a factor of 100, offering a simple route to short-pulse high-peak-power sources at low repetition rates by cavity elongation.},
note = {Paper CJ-9.6},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}
@conference{@Woodward_cleo2015_dark,
title = {Dark soliton statistics during radiation build-up of bright dissipative solitons in long-cavity mode-locked fiber lasers},
author = {R. I. Woodward and E. J. R. Kelleher},
url = {https://www.riwoodward.com/publication_files/woodward_cleo_2015_dark.pdf https://www.osapublishing.org/abstract.cfm?uri=EQEC-2015-EF_5_4},
year  = {2015},
date = {2015-06-22},
booktitle = {European Quantum Electronics Conference 2015},
publisher = {Optical Society of America},
abstract = {We numerically study the start-up dynamics of long-cavity, normal dispersion mode-locked fiber lasers, and reveal the birth and persistence of dark soliton-like structures within the evolution of a stationary bright dissipative soliton.},
note = {Paper EF-5.4},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}
@article{Woodward_oe_2015_mose2,
title = {Wideband saturable absorption in few-layer molybdenum diselenide (MoSe2) for Q-switching Yb-, Er- and Tm-doped fiber lasers},
author = {R. I. Woodward and R. C. T. Howe and T. H. Runcorn and G. Hu and F. Torrisi and E. J. R. Kelleher and T. Hasan},
url = {https://www.riwoodward.com/publication_files/woodward_2015_mose2.pdf},
doi = {10.1364/OE.23.020051},
year  = {2015},
date = {2015-03-27},
journal = {Optics Express},
volume = {23},
number = {15},
pages = {20051},
abstract = {We fabricate a free-standing molybdenum diselenide (MoSe2) saturable absorber by embedding liquid-phase exfoliated few-layer MoSe2 flakes into a polymer film. The MoSe2-polymer composite is used to Q-switch fiber lasers based on ytterbium (Yb), erbium (Er) and thulium (Tm) gain fiber, producing trains of microsecond-duration pulses with kilohertz repetition rates at 1060 nm, 1566 nm and 1924 nm, respectively. Such operating wavelengths correspond to sub-bandgap saturable absorption in MoSe2, which is explained in the context of edge-states, building upon studies of other semiconducting transition metal dichalcogenide (TMD)-based saturable absorbers. Our work adds few-layer MoSe2 to the growing catalog of TMDs with remarkable optical properties, which offer new opportunities for photonic devices.},
keywords = {MoSe2},
pubstate = {published},
tppubtype = {article}
}
@conference{Woodward_setforbritain,
title = {Exploiting nanomaterials for ultrafast photonics},
author = {R. I. Woodward and E. J. R. Kelleher and S. V. Popov and J. R. Taylor},
url = {https://www.riwoodward.com/publication_files/woodward_setforbritain_2015_expl.pdf 
http://www.setforbritain.org.uk/2015winners.asp},
year  = {2015},
date = {2015-03-09},
booktitle = {SET for Britain 2015},
publisher = {UK Parliamentary and Scientific Committee},
keywords = {.},
pubstate = {published},
tppubtype = {conference}
}
@article{Woodward_prj_2015,
title = {Few-layer MoS2 saturable absorbers for short-pulse laser technology: current status and future perspectives [Invited]},
author = {R. I. Woodward and R. C. T. Howe and G. Hu and F. Torrisi and M. Zhang and T. Hasan and E. J. R. Kelleher},
url = {https://www.riwoodward.com/publication_files/woodward_prj_2015_fewl.pdf},
doi = {10.1364/PRJ.3.000A30},
year  = {2015},
date = {2015-01-01},
journal = {Photonics Research},
volume = {3},
number = {2},
pages = {A30--A42},
abstract = {Few-layer molybdenum disulfide (MoS2) is emerging as a promising quasi-two-dimensional material for photonics and optoelectronics, further extending the library of suitable layered nanomaterials with exceptional optical properties for use in saturable absorber devices that enable short- pulse generation in laser systems. In this work, we catalog and review the nonlinear optical properties of few-layer MoS2, summarize recent progress in processing and integration into saturable absorber devices, and comment on the current status and future perspectives of MoS2-based pulsed lasers.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
@article{Woodward_ol_2015_gco,
title = {Fiber grating compression of giant-chirped nanosecond pulses from an ultra-long nanotube mode-locked fiber laser},
author = {R. I. Woodward and E. J. R. Kelleher and T. H. Runcorn and S. Loranger and D. Popa and V. J. Wittwer and A. C. Ferrari and S. V. Popov and R. Kashyap and J. R. Taylor},
url = {https://www.riwoodward.com/publication_files/woodward_ol_2015_fibe.pdf},
doi = {10.1364/OL.40.000387},
year  = {2015},
date = {2015-01-01},
journal = {Optics Letters},
volume = {40},
number = {3},
pages = {387--390},
abstract = {We demonstrate that the giant chirp of coherent, nanosecond pulses generated in an 846 m long, all-normal dispersion, nanotube mode-locked fiber laser can be compensated using a chirped fiber Bragg grating compressor. Linear compression to 11 ps is reported, corresponding to an extreme compression factor of ~100. Experimental results are supported by numerical modeling, which is also used to probe the limits of this technique. Our results unequivocally conclude that ultra-long cavity fiber lasers can support stable dissipative soliton attractors and highlight the design simplicity for pulse-energy scaling through cavity elongation.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
@article{Zhang2015b,
title = {Solution processed MoS2-PVA composite for sub-bandgap mode-locking of a wideband tunable ultrafast Er:fiber laser},
author = {M. Zhang and R. C. T. Howe and R. I. Woodward and E. J. R. Kelleher and F. Torrisi and G. Hu and S. V. Popov and J. R. Taylor and T. Hasan},
url = {https://www.riwoodward.com/publication_files/zhang_nr_2015_solu.pdf},
doi = {10.1007/s12274-014-0637-2},
year  = {2015},
date = {2015-01-01},
journal = {Nano Research},
volume = {8},
number = {5},
pages = {1522--1534},
abstract = {We fabricate a free-standing few-layer molybdenum disulfide (MoS2)-polymer composite by liquid phase exfoliation of chemically pristine MoS2 crystals and use this to demonstrate a wideband tunable, ultrafast mode-locked fiber laser. Stable, picosecond pulses, tunable from 1,535 nm to 1,565 nm, are generated, corresponding to photon energies below the MoS2 material bandgap. These results contribute to the growing body of work studying the nonlinear optical properties of transition metal dichalcogenides that present new opportunities for ultrafast photonic applications.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
@conference{MZhang2014,
title = {Fiber laser mode-locked with MoS2 saturable absorber},
author = {M. Zhang and Kelleher E. J. R and R. I. Woodward and S. V. Popov and F. Torrisi and R. C. T. Howe and J. R. Taylor and T. Hasan},
url = {https://www.riwoodward.com/publication_files/zhang_2014_poem.pdf},
year  = {2014},
date = {2014-06-01},
booktitle = {POEM:2014},
note = {Paper FTh2D.2},
keywords = {fibre laser, MoS2},
pubstate = {published},
tppubtype = {conference}
}
@article{Hu2014c,
title = {Fiber-integrated 780 nm source for visible parametric generation},
author = {D. J. J. Hu and R. T. Murray and T. Legg and T. H. Runcorn and M. Zhang and R. I. Woodward and J. L. Lim and Y. Wang and F. Luan and B. Gu and P. P. Shum and E. J. R. Kelleher and S. V. Popov and J. R. Taylor},
url = {https://www.riwoodward.com/publication_files/hu_oe_2014_fibe.pdf},
doi = {10.1364/OE.22.029726},
year  = {2014},
date = {2014-01-01},
journal = {Optics Express},
volume = {22},
number = {24},
pages = {29726},
abstract = {We report the development of a fully fiber-integrated pulsed master oscillator power fibre amplifier (MOPFA) source at 780 nm, producing 3.5 W of average power with 410 ps pulses at a repetition rate of 50 MHz. The source consists of an intensity modulated 1560 nm laser diode amplified in an erbium fiber amplifier chain, followed by a fiber coupled periodically poled lithium niobate crystal module for frequency doubling. The source is then used for generating visible light through four-wave mixing in a length of highly nonlinear photonic crystal fiber: 105 mW at 668 nm and 95 mW at 662 nm are obtained, with pump to anti-Stokes conversion slope efficiencies exceeding 6% in both cases.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
@article{Mamidala2014,
title = {Graphene-based passively mode-locked bidirectional fiber ring laser},
author = {V. Mamidala and R. I. Woodward and Y. Yang and H. H. Liu and K. K. Chow},
url = {https://www.riwoodward.com/publication_files/mamidala_oe_2014_grap.pdf},
doi = {10.1364/OE.22.004539},
year  = {2014},
date = {2014-01-01},
journal = {Optics Express},
volume = {22},
number = {4},
pages = {4539},
abstract = {We present an all-fiber bidirectional passively mode-locked soliton laser with a graphene-based saturable absorber for the first time to the best of our knowledge. Our design includes a four-port circulator to introduce different sections of cavity for the two counter-propagating pulses, so they have distinct output characteristics. Simultaneous bidirectional operation is achieved by appropriately adjusting the net cavity birefringence and loss. In the clockwise direction, the laser emits ~750 fs pulses at 1561.6 nm, with a repetition rate of 7.68 MHz. In the counter clockwise direction, the central wavelength, pulse width, and repetition rate are 1561.0 nm, ~850 fs, and 6.90 MHz, respectively.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
@article{Woodward_oe_2014_mos2,
title = {Tunable Q-switched fiber laser based on saturable edge-state absorption in few-layer molybdenum disulfide (MoS2)},
author = {R. I. Woodward and E. J. R. Kelleher and R. C. T. Howe and G. Hu and F. Torrisi and T. Hasan and S. V. Popov and J. R. Taylor},
url = {https://www.riwoodward.com/publication_files/woodward_oe_2014_tuna.pdf},
doi = {10.1364/OE.22.031113},
year  = {2014},
date = {2014-01-01},
journal = {Optics Express},
volume = {22},
number = {25},
pages = {31113},
abstract = {We fabricate a few-layer molybdenum disulfide (MoS2) polymer composite saturable absorber by liquid-phase exfoliation, and use this to passively Q-switch an ytterbium-doped fiber laser, tunable from 1030 to 1070 nm. Self-starting Q-switching generates 2.88 $mu$s pulses at 74 kHz repetition rate, with over 100 nJ pulse energy. We propose a mechanism, based on edge states within the bandgap, responsible for the wideband nonlinear optical absorption exhibited by our few-layer MoS2 sample, despite operating at photon energies lower than the material bandgap.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
@article{Woodward_ol_2014_sbs,
title = {Stimulated Brillouin scattering of visible light in small-core photonic crystal fibers},
author = {R. I. Woodward and E. J. R. Kelleher and S. V. Popov and J. R. Taylor},
url = {https://www.riwoodward.com/publication_files/woodward_ol_2014_stim.pdf},
doi = {10.1364/OL.39.002330},
year  = {2014},
date = {2014-01-01},
journal = {Optics Letters},
volume = {39},
number = {8},
pages = {2330--2333},
abstract = {We characterize stimulated Brillouin scattering (SBS) of visible light in small-core photonic crystal fiber (PCF). Threshold powers under 532 nm excitation agree with established theory, in contrast to measured values up to five times greater than expected for Brillouin scattering of 1550 nm light. An isolated, single-peaked signal at a Stokes shift of 33.5 GHz is observed, distinct from the multi-peaked Stokes spectra expected when small-core PCF is pumped in the infrared. This wavelength-dependence of the Brillouin threshold, and the corresponding spectrum, are explained by the acousto-optic interactions in the fiber, governed by dimensionless length scales that relate the modal area to the core size, and the pump wavelength to PCF hole pitch. Our results suggest new opportunities for exploiting SBS of visible light in small-core PCFs.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
@conference{Woodward_cleo14_sbs,
title = {Visible light stimulated Brillouin scattering in small-core photonic crystal fibers},
author = {R. I. Woodward and E. J. R. Kelleher and S. V. Popov and J. R. Taylor},
url = {https://www.riwoodward.com/publication_files/woodward_cleo_2014_visi.pdf},
doi = {10.1364/CLEO_SI.2014.SM4N.1},
year  = {2014},
date = {2014-01-01},
booktitle = {CLEO:2014, OSA Technical Digest},
publisher = {Optical Society of America},
abstract = {A reduced stimulated Brillouin scattering threshold power in small-core PCFs is achieved using visible wavelength excitation. We explain this in the context of acousto-optic interactions at length-scales relative to the fiber geometry.},
note = {Paper SM4N.1},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}
@conference{Woodward_cleo14_scg,
title = {Nanotube mode-locked, low repetition rate pulse source for fiber-based supercontinuum generation at low average pump power},
author = {R. I. Woodward and E. J. R. Kelleher and T. H. Runcorn and D. Popa and T. Hasan and A. C. Ferrari and S. V. Popov and J. R. Taylor},
url = {https://www.riwoodward.com/publication_files/woodward_cleo_2014_nano.pdf},
doi = {10.1364/CLEO_SI.2014.STh3N.8},
year  = {2014},
date = {2014-01-01},
booktitle = {CLEO:2014, OSA Technical Digest},
publisher = {Optical Society of America},
abstract = {We demonstrate a nanotube mode-locked fiber laser with low repetition rate (244 kHz), enabling supercontinuum generation in photonic crystal fiber spanning 600 to 2000 nm, at a low average pump power of 87 mW.},
note = {Paper STh3N.8},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}
@conference{Woodward_cleo14_mos2,
title = {Q-switched fiber laser with MoS2 saturable absorber},
author = {R. I. Woodward and E. J. R. Kelleher and T. H. Runcorn and S. V. Popov and F. Torrisi and R. C. T. Howe and T. Hasan},
url = {https://www.riwoodward.com/publication_files/woodward_cleo_2014_qswi.pdf},
doi = {10.1364/CLEO_SI.2014.SM3H.6},
year  = {2014},
date = {2014-01-01},
booktitle = {CLEO:2014, OSA Technical Digest},
publisher = {Optical Society of America},
abstract = {A MoS2-based saturable absorber is fabricated using wet chemistry techniques. We use it to passively Q-switch a fiber laser at 1068 nm.},
note = {Paper SM3H.6},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}
@article{Woodward_ptl_2014,
title = {Scalar nanosecond pulse generation in a nanotube mode-locked environmentally stable fiber laser},
author = {R. I. Woodward and E. J. R. Kelleher and D. Popa and T. Hasan and F. Bonaccorso and A. C. Ferrari and S. V. Popov and J. R. Taylor},
url = {https://www.riwoodward.com/publication_files/woodward_ptl_2014_scal.pdf},
doi = {10.1109/LPT.2014.2330739},
year  = {2014},
date = {2014-01-01},
journal = {IEEE Photonics Technology Letters},
volume = {26},
number = {16},
pages = {1672--1675},
abstract = {We report an environmentally stable nanotube mode-locked fiber laser producing linearly-polarized, nanosecond pulses. A simple all-polarization-maintaining fiber ring cavity is used, including 300 m of highly nonlinear fiber to elongate the cavity and increase intracavity dispersion and nonlinearity. The laser generates scalar pulses with a duration of 1.23 ns at a center wavelength of 1042 nm, with 1.3-nm bandwidth and at 641-kHz repetition rate. Despite the long cavity, the output characteristics show no significant variation when the cavity is perturbed, and the degree of polarization remains at 97%.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}