Coherence collapse in single-mode semiconductor lasers due to optical feedback

TLDR

The study connects the observed coherence collapse to recently suggested chaotic behavior. The authors measured coherence with a Michelson interferometer, showing a 1000‑fold reduction in coherence length, and developed a self‑consistent theory attributing collapse to optical‑feedback‑delay effects rather than quantum fluctuations. The study reports up to 25 GHz line broadening and a 1000‑fold reduction in coherence length, with theoretical predictions matching measurements qualitatively and reasonably quantitatively.

Abstract

Line broadening up to 25 GHz in a single-mode semiconductor laser with relatively strong optical feedback is reported and theoretically analyzed. Measurements of the coherence function were performed using a Michelson interferometer and demonstrate that the coherence length decreases by a factor 1000 (to approximately 10 mm) due to optical feedback. A self-consistent theoretical description is given, which is based on the view that coherence collapse is maintained due to optical-feedback-delay effects, in which quantum fluctuations play no role of importance. A connection with recently suggested chaotic behavior is made. The theoretical results obtained are in good qualitative and reasonable quantitative agreement with measurements.