Tunable stabilized single-frequency GRINROD external coupled cavity semiconductor lasers

A computer simulation based on the modified mode-selection theory of the semiconductor laser with graded index-rod external coupled cavity (GRECC) is presented. It is found that the graded-index-rod (GRINROD) external coupled cavity improves the side-mode suppression greatly, and any displacement of the GRINROD with respect to the laser chip degrades optical coupling, thus reducing side-mode suppression. The tunable GRECC laser diode is presented. A tuning range of over 11 nm and side-mode suppression better than 35 dB have been obtained. Long-term center frequency fluctuations and drift of less than 2 MHz are achieved by frequency locking the GRECC laser diode to NH₃ absorption lines. A demonstration of its use in a frequency shift keying heterodyne experimental transmission system indicates that the tunable GRECC laser diode is a promising light source for coherent optical-fiber communication