INFLUENCE OF RANDOMLY VARYING DOMAIN LENGTHS AND NONUNIFORM EFFECTIVE INDEX ON 2ND-HARMONIC GENERATION IN QUASI-PHASE-MATCHING WAVE-GUIDES

The degradation of second-harmonic generation in quasi-phase-matching waveguides, when random errors occur in the domain boundary position and when the effective index varies along the waveguide, is studied theoretically. Two models for random errors are used, one assuming independent shifts of the domain boundaries and one assuming independent domain lengths. Only the influence of random errors following the statistics in the second model might be of any significance in practical implementations. It is shown that in this case the normalized output power is a decreasing function of the product of the number of domains and a relative variance of the stochastic disturbances. If the differences in effective indices between the interacting modes varies along the waveguide, the same kind of ripple that has been observed in birefringence phase matching occurs.