DQPSK demodulation using integrated silicon microring resonators

In this paper, we fabricate an ultra-small 20 Gb/s differential quadrature phase-shift keying (DQPSK) demodulator using silicon based microring resonators and show that the separation between the microring resonance and optical carrier can be tuned for DQPSK demodulation at different bit rates. The double-waveguide microring resonators enable detection of I (in phase) and Q (quadrature phase) signals as well as inverted I and Q signals simultaneously. Experimental verification is performed for DQPSK demodulation using a single waveguide microring. We generate DQPSK signal in a serial configuration and demodulate the I or Q channel by offsetting the resonance peak. The offset between the resonance and center carrier is adjusted to be 4.87 GHz and the phase shift (phase offset) is calculated to be exactly π/4.