Compact reconfigurable polarization converter based on phase-change subwavelength tilted grating.

Subwavelength gratings serve as a pivotal tool in optical devices, enabling the flexible modulation of the effective refractive index of waveguide modes and modulating the guided mode through intense optical scattering at subwavelength intervals. Nevertheless, the modulation space remains limited. Incorporating phase change materials (PCMs) can achieve significantly higher modulation efficiency. This paper proposes a compact reconfigurable polarization converter based on PCMs, which is shaped into a subwavelength tilted grating. Effects of the tilted angle on effective refractive indices of TE mode and TM mode are systematically investigated for the subwavelength tilted grating. Through precise control of the transition between the crystalline and amorphous states of the phase-change material, the reconfiguration of the polarization converter is achieved with high efficiency and low insertion loss. In the crystalline state of the PCM, the slight difference in effective refractive index, along with the perturbation caused by the tilted grating, promotes mode coupling, allowing the conversion of the input TE mode into the TM mode. After the crystalline-to-amorphous transition, the periodic perturbation has almost no effect on the guided mode in the waveguide, and the device is in the normal on-state. The device realizes the free conversion of TE mode and TM mode with a small coupling length (17.89μm) and low extra loss (<1.5 dB). It has high conversion efficiency and mode purity in the broad range of 1500nm-1600 nm. Through dynamically controlling electrical pulses, we achieve 21-level programming operations, demonstrating multiple levels of tunability. Our work provides a feasible method to solve the polarization sensitivity of silicon-based photonic devices and shows a prospect of application in neuromorphic computing networks due to its multistage tunability.