Amplitude modulation using a nonlinear optical loop mirror

Abstract

The nonlinear optical loop mirror (NOLM) configuration has been studied extensively within the context of pulsed and/or quasi-CW laser sources. As such, the NOLM holds great promise in the areas of soliton switching, pulse compression and high data rate communications. However, comparatively little research has been done with CW sources. In this investigation, the theoretical properties of the NOLM are explored experimentally with the aid of a CW Nd:YAG laser operating in the infrared region. Specifically, the nonlinear effects of self-phase modulation are characterized. For a beam of sufficient intensity, its optical path through the fiber may be altered due to the dependence of the phase on intensity. Thus, two coherent beams of light of differing intensity can be made to interfere constructively or destructively even though the physical paths are identical. In the NOLM configuration, the potential result is an amplitude modulated output beam exhibiting a repetition rate several orders of magnitude greater than that of the input. Two dissimilar single-mode fibers as well as two custom-built fixed-ratio asymmetric fiberoptic couplers are utilized in the experiment. Correlation with theory is emphasized and follow-on projects are discussed