Integrated quasi-collinear acousto-optic mode converter with weighted coupling

In the paper, a weighted-coupling scheme of a SiO₂ film-loaded Ti:LiNbO₃ quasi-collinear integrated acousto-optic mode converter is reported, in which an angular offset between the acoustic and optical waveguides is introduced to implement an optimized Hamming weighted function for realization of ultralow sidelobe level. Acoustic wave guiding properties have been investigated for films such as SiO₂, ZnO on LiNbO₃ firstly. SiO₂ film on LiNbO₃ was selected as acoustic waveguide. With the mode analysis of the acoustic wave guide and the theory of coupling mode the limit of the width, weighted coupling coefficient and the characteristics of the conversion of acousto-optic modes are obtained. As the angle between acoustical and optical waveguides is 0.45°, the worst sidelobe level is -16.8dB and the theoretical values of bandwidths of -3dB and -10dB is 1.37nm and 2.31nm respectively, which have excelled the domestic reported level.