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Liam P. Barry

Bio: Liam P. Barry is an academic researcher from Dublin City University. The author has contributed to research in topics: Laser & Phase noise. The author has an hindex of 34, co-authored 565 publications receiving 5556 citations. Previous affiliations of Liam P. Barry include University College Dublin & Trinity College, Dublin.


Papers
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Journal ArticleDOI
TL;DR: In this paper, the authors demonstrate the generation of a highly coherent multicarrier signal that consists of eight clearly resolved 10.7 GHz coherent sidebands generated within 3 dB of the spectral envelope peak and with an extinction ratio in excess of 45 dB by gain switching a discrete mode (DM) laser.
Abstract: The authors demonstrate the generation of a highly coherent multicarrier signal that consists of eight clearly resolved 10.7-GHz coherent sidebands generated within 3 dB of the spectral envelope peak and with an extinction ratio in excess of 45 dB by gain switching a discrete mode (DM) laser. The generated spectral comb displays a corresponding picosecond pulse train at a repetition rate of 10.7 GHz with a pulse duration of 24 ps and a temporal jitter of ~450 fs. The optical spectra and associated pulses of the gain-switched DM laser are subsequently compared with a gain-switched distributed feedback (DFB) laser that generates a spectrum with no discernible sidebands and corresponding pulses with ~3 ps of temporal jitter. By means of external injection, the temporal jitter of the gain-switched DFB laser is then reduced to <; 1 ps, resulting in visible tones on the output spectrum. Finally, a nonlinear scheme is employed and initially tailored to compress the optical pulses, after which, the setup is slightly altered to expand the original frequency comb from the gain-switched DM laser.

147 citations

Journal ArticleDOI
TL;DR: In this paper, the nonlinear process of two-photon absorption in a commercial laser diode may be used for all-optical demultiplexing in terabit per second optical time division multiplexing networks.
Abstract: The authors describe how the nonlinear process of two-photon absorption in a commercial laser diode may be used for all-optical demultiplexing in terabit per second optical time division multiplexing networks. Switching windows of 650 fs in duration have been observed, with corresponding switching energies of a few picojoules.

140 citations

Journal ArticleDOI
TL;DR: The phase profile dependence on cavity length and injection current is experimentally evaluated, demonstrating the possibility of efficiently using the wide spectral bandwidth exhibited by these quantum dash structures for the generation of high peak power sub-picosecond pulses with low radio frequency linewidths.
Abstract: Mode locking features of single section quantum dash based lasers are investigated. Particular interest is given to the static spectral phase profile determining the shape of the mode locked pulses. The phase profile dependence on cavity length and injection current is experimentally evaluated, demonstrating the possibility of efficiently using the wide spectral bandwidth exhibited by these quantum dash structures for the generation of high peak power sub-picosecond pulses with low radio frequency linewidths.

137 citations

Journal ArticleDOI
TL;DR: In this paper, a summary of readily available commercial devices suitable for TPA autocorrelation of femtosecond pulses in the near-IR from 0.7-3 μm is presented.
Abstract: Optical autocorrelation of ultrashort pulses using two photon absorption (TPA) in commercial semiconductor devices provides a convenient, sensitive, and inexpensive alternative to standard techniques using nonlinear crystals. A summary of readily available commercial devices suitable for TPA autocorrelation of picosecond and femtosecond pulses in the near-IR from 0.7–3 μm is presented.

102 citations

Journal ArticleDOI
TL;DR: A 10GHz FSR optical comb, tunable over C-band with <200KHz optical linewidth, based on an externally seeded gain-switched FP laser diode is presented, achieving doubling of comb lines with a phase modulator.
Abstract: A wavelength tunable optical comb is generated based on the gain-switching of an externally seeded Fabry-Perot laser diode. The comb consists of about eight clearly resolved 10GHz coherent sidebands within 3dB spectral envelope peak and is tunable over the entire C-band (1530 to 1570nm). The optical linewidth of the individual comb tones is measured to be lower than 100kHz, and the RIN of the individually filtered comb tones (<-120dB/Hz) is shown to be comparable to the entire unfiltered comb (<-135dB/Hz). Besides, expansion of the tunable gain switched comb is achieved with the aid of an optical phase modulator, resulting in near doubling of the number of comb tones.

98 citations


Cited by
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Journal ArticleDOI
04 Oct 2006
TL;DR: In this paper, a review of numerical and experimental studies of supercontinuum generation in photonic crystal fiber is presented over the full range of experimentally reported parameters, from the femtosecond to the continuous-wave regime.
Abstract: A topical review of numerical and experimental studies of supercontinuum generation in photonic crystal fiber is presented over the full range of experimentally reported parameters, from the femtosecond to the continuous-wave regime. Results from numerical simulations are used to discuss the temporal and spectral characteristics of the supercontinuum, and to interpret the physics of the underlying spectral broadening processes. Particular attention is given to the case of supercontinuum generation seeded by femtosecond pulses in the anomalous group velocity dispersion regime of photonic crystal fiber, where the processes of soliton fission, stimulated Raman scattering, and dispersive wave generation are reviewed in detail. The corresponding intensity and phase stability properties of the supercontinuum spectra generated under different conditions are also discussed.

3,361 citations

Journal ArticleDOI
TL;DR: In this article, temporal dissipative solitons are observed in a nonlinear, high-finesse, optical microresonator driven by a continuous-wave laser, enabling ultrashort pulses to be generated in spectral regimes lacking broadband laser gain media and saturable absorbers.
Abstract: Temporal dissipative solitons are observed in a nonlinear, high-finesse, optical microresonator driven by a continuous-wave laser. This approach enables ultrashort pulses to be generated in spectral regimes lacking broadband laser gain media and saturable absorbers, making it potentially useful for applications in broadband spectroscopy, telecommunications, astronomy and low-phase-noise microwave generation.

1,602 citations

Journal ArticleDOI
TL;DR: In this article, the authors summarize the problem of measuring an ultrashort laser pulse and describe in detail a technique that completely characterizes a pulse in time: frequency-resolved optical gating.
Abstract: We summarize the problem of measuring an ultrashort laser pulse and describe in detail a technique that completely characterizes a pulse in time: frequency-resolved optical gating. Emphasis is placed on the choice of experimental beam geometry and the implementation of the iterative phase-retrieval algorithm that together yield an accurate measurement of the pulse time-dependent intensity and phase over a wide range of circumstances. We compare several commonly used beam geometries, displaying sample traces for each and showing where each is appropriate, and we give a detailed description of the pulse-retrieval algorithm for each of these cases.

1,447 citations

Journal Article
TL;DR: In this paper, techniques developed in the last few years in microwave photonics are reviewed with an emphasis on the systems architectures for photonic generation and processing of microwave signals, photonic true-time delay beamforming, radio-over-fiber systems, and photonic analog-to-digital conversion.
Abstract: Broadband and low loss capability of photonics has led to an ever-increasing interest in its use for the generation, processing, control and distribution of microwave and millimeter-wave signals for applications such as broadband wireless access networks, sensor networks, radar, satellite communitarians, instrumentation and warfare systems. In this tutorial, techniques developed in the last few years in microwave photonics are reviewed with an emphasis on the systems architectures for photonic generation and processing of microwave signals, photonic true-time delay beamforming, radio-over-fiber systems, and photonic analog-to-digital conversion. Challenges in system implementation for practical applications and new areas of research in microwave photonics are also discussed.

1,332 citations

Journal ArticleDOI
TL;DR: The 2017 roadmap of terahertz frequency electromagnetic radiation (100 GHz-30 THz) as discussed by the authors provides a snapshot of the present state of THz science and technology in 2017, and provides an opinion on the challenges and opportunities that the future holds.
Abstract: Science and technologies based on terahertz frequency electromagnetic radiation (100 GHz–30 THz) have developed rapidly over the last 30 years. For most of the 20th Century, terahertz radiation, then referred to as sub-millimeter wave or far-infrared radiation, was mainly utilized by astronomers and some spectroscopists. Following the development of laser based terahertz time-domain spectroscopy in the 1980s and 1990s the field of THz science and technology expanded rapidly, to the extent that it now touches many areas from fundamental science to 'real world' applications. For example THz radiation is being used to optimize materials for new solar cells, and may also be a key technology for the next generation of airport security scanners. While the field was emerging it was possible to keep track of all new developments, however now the field has grown so much that it is increasingly difficult to follow the diverse range of new discoveries and applications that are appearing. At this point in time, when the field of THz science and technology is moving from an emerging to a more established and interdisciplinary field, it is apt to present a roadmap to help identify the breadth and future directions of the field. The aim of this roadmap is to present a snapshot of the present state of THz science and technology in 2017, and provide an opinion on the challenges and opportunities that the future holds. To be able to achieve this aim, we have invited a group of international experts to write 18 sections that cover most of the key areas of THz science and technology. We hope that The 2017 Roadmap on THz science and technology will prove to be a useful resource by providing a wide ranging introduction to the capabilities of THz radiation for those outside or just entering the field as well as providing perspective and breadth for those who are well established. We also feel that this review should serve as a useful guide for government and funding agencies.

1,068 citations