Study of the coherence of a semiconductor laser with feedback

Dec 05, 2024

Maria Duque defended her thesis co-directed by Cristina Masoller and Jordi Tiana on December 5 at the Terrassa Campus. Entitled "Experimental study of the coherence of the light emitted by a semiconductor laser with optical feedback", the thesis studies the appearance and evolution of coherence during laser start-up in different optical feedback scenarios. In addition, the impact of sinusoidal modulation in the injection current on the coherence of lasers is investigated and includes a chapter on the impact of optical injection

Study of the coherence of a semiconductor laser with feedback — Experimental setup (top left), speckle image recorded with CCD camera (bottom left) and spectral and speckle characterization of the transition to coherent emission without (top right) and with optical feedback (bottom right). While during the turn-on transition the coherence increases gradually in the absence of feedback, it increases abruptly when the laser is subject to optical feedback from an external grating.

Semiconductor lasers are present in many areas of our daily life due to their compact size, efficiency and versatility. We find applications in telecommunications, sensors, metrology and biomedicine. This thesis investigates the impact of optical feedback on the temporal and spatial coherence of semiconductor lasers using a technique based on random intensity patterns, i. e., speckle.

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