title: Square-wave oscillations in semiconductor ring lasers with delayed optical feedback.
abstract: We analyze experimentally and theoretically the effects of delayed optical cross-feedback in semiconductor ring lasers. We show that under appropriate conditions, feeding of only one directional mode back into the counter-propagating mode leads to square-wave oscillations. In this regime, the laser switches regularly between the two counter-propagating modes with a period close to twice the roundtrip time in the external feedback loop. We find that these oscillations are robust and appear for a wide range of parameters as long as a small asymmetry in the linear coupling between both modes is present. We show that by increasing the feedback strength or the injection current, the square-wave oscillations gradually disappear. Due to noise, mode-hopping between stable lasing in one directional mode and square wave oscillations is observed in this transition region.
authors.affiliation: Applied Physics Research Group (APHY), Vrije Universiteit Brussel, Pleinlaan 2, B-1050 Brussel, Belgium. lmashal@vub.ac.be
authors.forename: Lilia
authors.initials: L
authors.lastname: Mashal
authors.forename: Guy
authors.initials: G
authors.lastname: Van der Sande
authors.forename: Lendert
authors.initials: L
authors.lastname: Gelens
authors.forename: Jan
authors.initials: J
authors.lastname: Danckaert
authors.forename: Guy
authors.initials: G
authors.lastname: Verschaffelt
mesh_terms: D003198:Computer Simulation; D017076:Computer-Aided Design; D004867:Equipment Design; D019544:Equipment Failure Analysis; D005246:Feedback; D054023:Lasers, Semiconductor; D008962:Models, Theoretical; D009991:Oscillometry / Q000295:instrumentation* / Q000379:methods*; D020349:Surface Plasmon Resonance / Q000295:instrumentation* / Q000379:methods*