We report a new design of differential phase-shift keying (DPSK) receivers which utilize a single demodulator to receive
polarization division multiplexed signals. More than 20 dB extinction-ratio can be achieved by optimizing the phase
detuning with a polarization controller in the receiver. Experimental demonstrations using 20 Gb/s polarization
multiplexed DPSK signals and 2<sup>15</sup>-1 pseudorandom binary sequence are conducted to show the performance of the
proposed receiver. After 60 km of optical fiber transmission, the receiver has less than 3 dB power penalty at bit-error
rate (BER) of 10<sup>-9</sup>.