Polarization and frequency control of a semiconductor laser with a new external cavity structure

Abstract

A technique using a new external cavity structure to cause degeneration at the frequencies of two orthogonally polarized modes and to control the polarization and the frequency in a semiconductor laser has been devised. The phase difference between the polarizations in the gain medium can be canceled in a round trip through quarter-wave plates set in the cavity. By rotating one of the quarter-wave plates, orthogonally polarized laser beams can theoretically be made to oscillate at slightly different frequencies. Experimentally, two orthogonally polarized oscillations with rather large frequency differences occurred. The difference between the two frequencies alternated according to the quarter-wave plate rotation. This phenomenon could be explained theoretically.