optoelectonics

Research activities:

The primary research activity of my group is the design, characterisation and applications of lasers and semiconductor optical amplifiers (SOA) for telecommunications and Terahertz signal generation. A specific example is the DC-biased passively mode-locked lasers (PMLL). Our lasers do not integrate a saturable absorber and they work at room temperature. Originally our research was concerned with radio-frequency signal generation for all-optical data processing. We were able to demonstrate a linewidth of 30 MHz at a frequency of 40 GHz with no modulation applied. More recently, one of our papers in Optics Express 2009 has been selected to be included in Virtual Journal of Ultrafast Science, January 2010. We were the first to demonstrate a 700-fs width pulses with normal dispersion generated by a dc-biased MLLs. Based on the understanding of the origin of the RF signal generated in the MLLs, we have carried out some study on the generation of THz signal. We were the first to demonstrate the generation of THz signal, (APL 2008) Virtual Journal of Ultrafast Science, March 2008. Mostly recently we have joined our SOA activity and PMML activity to design a novel technique to detect the high speed modulation in our PMML (APL 2010).

We are currently developing two novel types of SOA with a control of their carrier distribution along the active section of the device. The carrier density controls the gain material and therefore the gain of the SOA, the noise figure and the saturation power. It is well known that in order to reduce the noise figure of a transmission scheme the noisiest elements have to be placed at the end of the scheme and the quietest elements at the beginning of it. Based on this fact, we have developed a simulation tool of SOAs. The SOAs are divided into subsections, each subsection is considered as an element of a transmission scheme, which is the overall SOA. According to the above rule, the noisiest subsections have to be placed closer to the output facet of the SOA. The noise and the gain levels are dictated by the carrier distribution. Therefore by controlling the carrier distribution it is possible to reduce the noise figure of SOAs or to boost the saturation power. In the methods proposed, the controlled carrier distribution leads to a minimum value of the noise figure and keeps a gain. This result has been achieved by a simulation tool developed in our laboratory and have been demonstrated experimentally.

In parallel to this research activities we carry out some theoretical study based on finite element method of THz waveguides, based on photonics crystals (PhC) produced in metals. The motivations are to guide and to manipulate the powerfull THz radiation in an efficient way in order to increase the performances of the actual THz devices. In free space THz signal transmission is limited by the water absorption band and by the signal quality degraded by the black-body radiation of environment at room temperature. A sealed THz waveguide will prevent from moisture along the THz link and noise coupled into the detector.

Patents

P. McEvoy, P. Landais, S.A. Lynch, J. O'Gorman,“A Self-pulsating laser diode and a method for causing a laser to output light pulses”, Patent number: WO0178205, Publication date: 18/10/2001.

P. McEvoy, P. Landais, D. McDonald, F. Logue, J. O'Gorman, “ An optical waveguide and a method for providing an optical waveguide”, Patent number: WO0122543, Publication date: 29/03/2001.

P. Landais, "A self-pulsating laser," S2005/0251.

P. Landais and F. Surre “A semiconductor optical amplifier for amplifying an optical signal” US 2010/0134877A1, publication date: 03/06/10 and GB0821602.0, publication date: 26/11/08 and renewed 25/11/10.