Instability of coherence in semiconductor laser due to external feedback in hybrid-integrated optical waveguide components

The coherence instability of oscillation-frequency shift and spectrum-linewidth fluctuation of a distributed feedback (DFB) semiconductor laser due to reflected feedback from input or output facets in a butt-coupled waveguide device is theoretically analyzed. A low-loss butt-coupling method between a semiconductor laser and a waveguide device for hybrid-integrated optical components used in coherent optical-fiber systems is presented. The calculated results indicate that (1) the coherence instability of the DFB lasers is sensitive to external optical feedback, (2) feedback from the waveguide input facet affects the laser frequency and gain shifts, and (3) feedback from the output facet intensifies the linewidth fluctuations.<
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