Parallel-to-orthogonal optical polarization conversion for the generation of phase-modulated millimeter-wave signals

A novel technique, to our knowledge, for manipulating the polarization states of two longitudinal oscillation modes emitted from a <i>N</i><i>d</i>:<i>Y</i><i>V</i><i>O</i>₄ microchip laser was developed. The laser was designed to oscillate in two longitudinal modes with a frequency difference of over 100 GHz, thereby making it suitable as a light source for generating high-purity millimeter waves above 100 GHz. A birefringent crystal was used to orthogonalize the polarization states of the two modes, such that their difference in retardations differed by <i>π</i> radian. The resultant polarization states were successfully stabilized using an active feedback control through the electro-optic effect of the birefringent crystal.