Polarization coupler for polarization-rotating Mach-Zehnder interferometer

Abstract

We propose a 3dB polarization coupler in which the input light of the TE mode is converted into two out-of-phase TM modes, and the input light of the TM mode is split into two in-phase TM modes. This was designed with a 3-steps taper structure. When a Mach-Zehnder interferometer (MZI) is composed of the proposed 3dB coupler, the polarization of the output light is rotated depending on the phase difference between the two arms. By incorporating optical phase shifters, polarization rotation can be controlled in MZ devices. In this study, we optimized the design of the proposed 3dB coupler, and numerically demonstrated polarization rotation in an MZI with the proposed couplers, depending on the phase difference between the two arms.