# 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.

## Key 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.

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Source: https://tomesphere.com/paper/1812.05036