Polarization insensitive 25-Gbaud direct D(Q)PSK receiver based on polymer planar lightwave hybrid integration platform.

We report a direct DPSK receiver based on polymer planar lightwave circuit technology, which incorporates a 2x25 GHz photodiode (PD) array hybridly integrated via 45° mirrors. In this direct DPSK receiver, a half-wave plate and heating electrodes are implemented to eliminate the polarization-dependent frequency-shift (PDFS) of the delay-line interferometer (DLI). By applying a proper heating current, a residual PDFS of practically zero at 1550 nm and within ±125 MHz was achieved over the full C-band.