Dynamics and stability conditions of semiconductor lasers under external optical feedback from both sides of the laser cavity

TL;DR

This paper investigates the effects of external optical feedback from both sides of a semiconductor laser cavity, demonstrating improved stability and linewidth reduction through phase-controlled double feedback, advancing integrated laser technology.

Contribution

It generalizes the analysis of external optical feedback to both sides of the laser cavity and shows how phase control can enhance stability and performance.

Findings

Double feedback improves laser stability over single feedback.

Proper phase adjustment broadens the stable operational regime.

Numerical results indicate potential for integrated narrow-linewidth lasers.

Abstract

To increase the spectral efficiency of coherent communication systems, lasers with ever-narrower linewidths are required as they enable higher-order modulation formats with lower bit-error rates. In particular, semiconductor lasers are a key component due to their compactness, low power consumption, and potential for mass production. In field-testing scenarios their output is coupled to a fiber, making them susceptible to external optical feedback (EOF). This has a detrimental effect on its stability, thus it is traditionally countered by employing, for example, optical isolators and angled output waveguides. In this work, EOF is explored in a novel way with the aim to reduce and stabilize the laser linewidth. EOF has been traditionally studied in the case where it is applied to only one side of the laser cavity. In contrast, this work gives a generalization to the case of feedback on both sides. It is implemented using photonic components available via generic foundry platforms, thus creating a path towards devices with high technology-readiness level. Numerical results shows an improvement in performance of the double-feedback case with respect to the single-feedback case. In particularly, by appropriately selecting the phase of the feedback from both sides, a broad stability regime is discovered. This work paves the way towards low-cost, integrated and stable narrow-linewidth integrated lasers.