Silicon based polarization insensitive filter for WDM-PDM signal processing

We propose and fabricate a novel circuit that combines two two-dimensional (2D) grating couplers and a microring resonator (MRR). According to the polarization states, one 2D grating coupler first splits the input signals into two orthogonal paths, which co-propagate in the loop and share a common MRR, and then the two paths are combined together by the other 2D grating coupler. The proposed circuit is polarization insensitive and can be used as a polarization insensitive filter. For demonstration, the wavelength division and polarization division multiplexing (WDM-PDM) non return-to-zero differential-phase-shift-keying (NRZ-DPSK) signals can be demodulated successfully. The bit error ratio measurements show an error free operation, reflecting the good performance and the practicability.