Square wave excitability in quantum dot lasers under optical injection

TL;DR

This paper reports the experimental observation of square wave excitability in quantum dot lasers under optical injection, revealing a thermally induced transition from predicted bistability to oscillatory phenomena.

Contribution

It demonstrates experimentally that square wave phenomena occur instead of phase-locked bistability in quantum dot lasers under optical injection, supported by a rate equation model.

Findings

Square waves observed instead of bistability in quantum dot lasers.

Thermal effects induce the transition to square wave excitability.

Model shows excellent agreement with experimental results.

Abstract

Quantum dot lasers display many unique dynamic phenomena when optically injected. Bistability has been predicted in a region of high injection strength. We show experimentally, rather than a phase-locked bistability, a square wave phenomenon is observed in this region. The squares can manifest as a periodic train but also as noise driven Type II excitable events. We interpret the appearance of the square waves as a thermally induced breaking of the bistability. Indeed we find experimentally that over the duration of a square the relative detuning between the master and the slave evolves deterministically. A relatively simple, physically motivated, rate equation model is presented and displays excellent agreement with the experiment.