Polarization splitter with variable TE-TM mode converter using Zn and Ni codiffused LiNbO3 waveguides

We propose and demonstrate a polarization splitter, in which the power ratio between transverse electric (TE) and transverse magnetic (TM) modes at two output arms can be electrically controlled. The mode-sorting effect and off-diagonal electrooptic coefficient of LiNbO₃ are utilized for polarization splitting and conversion, respectively. To simplify design and fabrication processes, we apply a newly developed zinc and nickel codiffusion technique in LiNbO₃, by which TE-, TM-, and randomly polarized waveguides can all be made by simply using different fabrication parameters. To lower the applied voltage, ridge structure is used to increase the overlap integral between electric and optical fields. Measured extinction ratios of polarization splitting are higher than 21 dB for TE mode and 18 dB for TM mode, and the applied voltage can be reduced by a factor of one-third with a ridge of height 3 μm. Finally an application example is proposed for future study.