Abstract

Four wave mixing in optical fibers has long been recognised as important method of generating new optical frequencies. While most investigations have been concerned with the small signal regime, recently attention has been focussed on the nonlinear dynamics in the strong conversion regime (1,2). The process holds promise as a means of wavelength switching for optical communications, but the presence of a nonlinear term in the phase-matching condition normally prevents strong energy exchange between the waves (1). We present here a scheme for optimising the power switching efficiency. The four wave mixingprocess considered here is called polarisation modulation instability (PMI) where a strong pump wave on one axis of a birefringent fiber results in the growth of two equally detuned sidebands on the other axis. In the absence of any external seed the sidebands grow at the phase-matched frequency shift where the wavevector mismatch, is zero. The wavevector mismatch is a function of the power of the pump and the fiber's dispersion, birefringence, and nonlinearity. The analysis of the evolution of the power in the sidebands utilises three coupled mode equations which describe the interaction of the pump, with a pair of sidebands polarised along the orthogonal fibre axis. In the absence of Raman gain, it is possible to solve for the birefringence as a function of position in the fibre which is required to maintain the phase matching condition.

© 1998 Optical Society of America