Spectral linewidth of external cavity semiconductor lasers with strong, frequency-selective feedback

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Abstract
The spectral linewidth of 1.5 μm external cavity semiconductor lasers is investigated. For nonzero intermediate facet reflectivity, detuning from exact resonance is found to reduce linewidths substantially for strong, frequency-selective feedback. A 10 cm cavity gives linewidths below 1 kHz, while coherent systems requirements will be met by cavities under 2.5 cm.