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.
Highlights
Introduction under External Optical FeedbackThe effect of external optical feedback (EOF) on diode laser dynamics has been extensively studied for the past half century [1,2]
EOF has been proven to affect laser performance, showing regimes that can aid in linewidth reduction [3,4,5,6], as well as others responsible for highly unstable behavior, from mode hopping to the case of coherence collapse [7,8,9,10,11,12]
This work explores an extension of the theoretical background of EOF
Summary
The effect of external optical feedback (EOF) on diode laser dynamics has been extensively studied for the past half century [1,2]. Methods to improve laser stability need to take EOF into account, as even weak feedback can be detrimental. A traditional approach to mitigate its effects is to include an off-chip isolator at the laser output. This component negatively impacts the dimensions of packaged devices as well as fabrication times and costs. Research is ongoing to develop an integrated solution that can minimize the negative effects of EOF
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