Abstract

A Vertical-Cavity-Surface-Emitting Lasers (VCSEL) submitted to an optical external feedback through a quarter-wave plate could have its intensity self-modulated [1] in the microwave range. One effect of the plate is to impose the eigen axes of the coupled cavity [2], When the axes of the inserted plate are at 45° with respect to the laser ones, the beating between two spatially-separated combs of modes, frequency-separated by c/4L, can be observed along the axes of the bare laser. Introducing a vectorial Airy function, we show here that the effect of a rotation of the quarter-wave plate is to shift one comb of modes with respect to the other one and enables to control the longitudinal modes of the external cavity The beating can thus generate a frequency lower or higher than c/4L depending on the mode selection. This shift is related to the inner birefringence e inside the laser cavity. This small birefringence is boosted by the high reflectivity of the laser output mirror.

© 1998 IEEE