FM characteristics and compact modules for coherent semiconductor lasers coupled to an external cavity

Measured FM responses of a semiconductor laser optically coupled off-axis to a confocal Fabry-Perot cavity are discussed. It was found that this cavity acted as a frequency discriminator and as a phase comparator for slow and fast frequency fluctuations, respectively. The crossover between them was determined by a half linewidth of the cavity. On the basis of these investigations, two kinds of coherent semiconductor laser modules were constructed. External Fabry-Perot cavities were made by using an optical fiber and a hemispherical microlens. The linewidths of these lasers were less than 25 kHz.<
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