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Photonics

Optical Communications

Tunable Lasers

We work on various semiconductor optical devices including single mode lasers, widely tunable lasers, Mach-Zehnder modulators, arrayed waveguide gratings and high speed balanced photodiodes. Our strongest interest lies in monolithically integrating several the above devices onto a single semiconductor chip to realize novel transmitters and receivers for next generation optical communication systems.

  1. Single mode lasers based on slots. We are developing novel single mode lasers by etching slots into the ridge of conventional ridge waveguide Fabry-Perot lasers. These single mode optical sources can be made simply and cheaply. We are integrating these lasers with mode converters and electro-absorption modulators to further increase their advantages
  2. Widely tunable lasers based on slots and other novel mechanisms. Monolithically integrated widely tunable lasers are being deployed by system providers at the moment and have shown to possess a huge potential market. We have developed novel and simple discretely and widely tunable lasers based on slots, which is an extension of the above single mode laser work. We are also working on other mechanisms to realize widely and quasi-continuously tunable lasers which can potentially be made with low costs.
  3. Mach-Zehnder modulators and arrayed waveguide gratings. Next generation optical communication networks need high spectral efficiency, reconfigure ability, and adaptability. These requirements can only be satisfied by using more sophisticated transmitters and receivers. For transmitters we are trying to integrate single mode lasers/arrays and widely tunable lasers/arrays with several Mach-Zehnder modulators and arrayed waveguide gratings onto a single InP chip.
  4. High speed balanced photodiodes. Just as introduced above next generation optical communication systems will use more complex modulation formats which will need more sophisticated receivers. A key part will be balanced photodiodes. We are working on high speed balanced photodiodes and are trying to integrate balanced photodiodes with other optical circuits such as optical hybrids and optical delay interferometers.

With the complexity of future optical networks increasing further and further, higher and higher requirement on performance monitoring at the optical level will be needed. Optical-signal-to-noise-ratio (OSNR), chromatic dispersion and polarization mode dispersion are generally thought need to be monitored in order to implement the optical performance monitoring task. We are trying to develop techniques potentially capable of monitoring these parameters.

  1. Microcavity enhanced two-photon absorption (TPA) photodetectors. TPA, which has a quadratic dependence on the input optical signal intensity, has shown to be sensitive to OSNR, chromatic dispersion and polarization mode dispersion. TPA photodetectors potentially can monitor these parameters simultaneously, but unfortunately suffer a low sensitivity because of the third-order nonlinearity intrinsic of TPA. We are trying to develop compact and low cost and highly sensitive TPA detectors by using a microcavity structure which has been shown to be able to improve the TPA efficiency by more than four orders of magnitude.
  2. Simple OSNR monitoring technique based on optical delay interferometers. OSNR is thought to be of the first priority for the optical performance monitoring task. Various schemes have been developed, of which the method based on optical delay interferometers has been shown to be robust and of really low cost. We are trying to optimize this technique to make it really work practically.
  3. Novel optical pulse characterization techniques. To improve the spectral efficiency future optical networks will use more advanced modulation formats, modulating not only the amplitude but also the phase. This imposes challenges on characterizing these pulses. We are trying to develop non-iterative and linear characterization techniques which are potentially fast and sensitive.

References:

1. "Non-Resonant Wavelength Modulation Saturation Spectroscopy in Acetylene-Filled Hollow-Core Photonic Bandgap Fibres Applied to Modulation-Free Laser Stabilization", submitted to Optics Express, 2009
2. David McInerney, , Michael Lynch, John Donegan, Vincent Weldon, "Mode referencing of an external cavity diode laser for continuous frequency stabilization", Optical Engineering, February 2008, Volume 47(2).
3. Vincent Weldon, David McInerney, Richard Phelan, Michael Lynch, John Donegan, "Characteristics of several NIR tuneable diode lasers for spectroscopic based gas sensing: A comparison." Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy Volume 63, Issue 5 , April 2006, Pages 1013-1020
4. David McInerney, John Donegan, Michael Lynch, and Vincent Weldon, "Spectral Linewidth and Tuning Requirements of Sources for Gas Sensing in Space based Applications" , IEE Proc.-Optoelectron., Vol. SIOE 2005.
5. Vincent Weldon, "Spectroscopic based Gas Sensing using Tuneable Diode Lasers", Encyclopedia of Sensors 2005, edited by Craig A. Grimes, Elizabeth C. Dickey and Michael V. Pishko, published by American Scientific Publishers, 25650 North Lewis Way, Stevenson Ranch, California 91381-1439, USA.
6. R. Phelan, M. Lynch, J. F. Donegan, V. Weldon, "Multi-species gas sensing using monolithic widely tuneable laser diodes" Proc. SPIE Vol. 5826, pp 449-459, Opto-Ireland June 2005: Optical Sensing and Spectroscopy; Hugh J. Byrne, Elfed Lewis, Brian D. MacCraith, Enda McGlynn, James A. McLaughlin, Gerard D. O'Sullivan, Alan G. Ryder, James E. Walsh; Eds.
7. R. Phelan, M. Lynch, J.F. Donegan and V. Weldon, "Simultaneous multi-species gas sensing using a sampled grating-DBR and modulated-grating Y laser diode", Appl. Optics, 20 September, 2005, Vol.44, No. 27, pp5824-5831.
8. R. Phelan, M. Lynch, J.F. Donegan and V. Weldon, "Absorption Line Shift with Temperature and Pressure: Impact on Laser Diode based H2O Sensing at 1.393m" Applied Optics. -LP 2003, Volume 42, Issue 24, pp4968-4974.
9. Richard Phelan, Michael Lynch, John Donegan and Vincent Weldon, "Investigation of a Strongly Gain Coupled DFB Laser Cascade for Simultaneous Multigas Sensing", IEE Proc.-Optoelectron., Vol. 150, No.2, 2003, pp182-186.