Short (~10-11 seconds) and ultrashort (~10-12 seconds and shorter) optical pulses will be required for the next generation of optical communications systems. They may also find their use in laser radars, microwave communications (microwave-over-fibre techniques), diagnostics and measurements in biology and medicine.
Semiconductor lasers constructions are particularly attractive for generating such pulses, due to their compactness, ease of control, and manufacturability. Several constructions exist to date that are capable of generating short pulses (such as gain-switched and self-pulsating lasers) and trains of ultrashort pulses (mode-locked and dual-mode lasers). However, these sources, particularly the latter construction, suffer from various instabilities that limit their performance as regards pulse power and duration. Additional instabilities may arise when a fraction of the laser light is reflected back into the laser (optical feedback) which looks unavoidable in future densely integrated systems.
In this project, we analyse the physics behind these various instabilities and aim at arriving at laser constructions that minimise them, allowing for powerful, stable short and ultrashort pulse generation. The project thus brings together approaches from quantum electronics, nonlinear dynamics, and semiconductor physics and technology.
We developed advanced theoretical model for both self-pulsating, gain-switched, and mode-locked semiconductor lasers, with particular emphasis on saturable absorbers – the part of the laser that allows short-pulse generation. In collaboration with our coworkers at Ioffe Institute, we have proposed new, fast and efficient absorber structures, and recently proposed a novel design of semiconductor saturable absorber mirror (SESAM) based on a robust principle and promising significant performance improvement.
An important direction of work involves the use of the so called quantum-dot lasers, using the fast, strong nonlinearities that exist in semiconductor nanostructures to add short pulse generation. This is ongoing work in collaboration with the Ioffe Institute, the Universities of Dundee and St.Andrews and Weierstrass Institute in Germany.
Other collaborators include the University of Glasgow (and potentially others) in the UK, the Vrije Universiteit Brussels, Belgium, and the University of Oulu, Finland.