Optimisation of a collinear acoustooptic TEm-TEn mode convertor LiNbO3

An analysis is given of the optimisation of the mode conversion of guided optical waves resulting from interaction with collinearly travelling surface acoustic waves of Rayleigh type. The effects of electrooptic and acoustooptic index fluctuations together with the phase matching condition and interaction lenghts are considered. Design criteria and numerical results are given. A number of acoustooptic mode converters are then demonstrated experimentally. A 50% conversion efficiency is obtained for TE1¿¿TM1 conversion in LiNbO3 with acoustic input power of 10 mW. Angular dispersion of laser light has been found to reduce the effective interaction length and this is demonstrated and discussed.