A NOVEL TYPE OF OPTICAL OSCILLATOR BASED ON A LIQUID CRYSTAL GAIN MEDIUM

Abstract

A nonlinear optical medium results by the collective orientation of liquid crystal molecules tightly coupled to a transparent photoconductive layer made of a thin photorefractive BSO crystal. For this new kind of liquid crystal light-valve, we have recently demonstrated signal beam amplification and self-pumped phase conjugation. After giving a description of the device and its properties, we show here that the liquid crystal light-valve, when inserted in a ring optical cavity, has a gain large enough to overcome the losses, thus resulting in unidirectional field oscillation. The wide transverse size and the high nonlinearity of the liquid crystal medium allow us to explore dynamical regimes where a huge number of longitudinal and transverse modes are simultaneously amplified in the cavity. Up to date, such regimes have remained inaccessible for all the known types of optical cavities. In particular, we report the observation of high amplitude spatiotemporal pulses appearing in random space points and confined along the three space directions. Then, we present a theoretical model that takes into account the longitudinal dependence of the field in the liquid crystal optical oscillator, and show that spatiotemporal pulses confined in 3D space directions arise from the random superposition of many longitudinal and transverse modes oscillating at different frequencies.