Variable symbol-rate DPSK receiver based on silicon photonics coupled-resonator delay line

We present a compact (< 0.65 mm2) silicon photonics variable-delay receiver for DPSK optical transmission systems consisting of a Mach-Zehnder interferometer (MZI) loaded with an integrated tunable delay line. The delay line is realized by using a thermally actuated coupled-resonator optical waveguide (CROW) in reflective configuration, providing a continuous control of the MZI delay from 66 to 102 ps, thus allowing the optimization of the receiver performance for the detection of DPSK signals at any symbol rates between 9.8 and 15 Gsym/s. The tuning scheme is simple, requiring the control of only two ring resonators, and enables the active compensation of thermal effects induced by silicon nonlinearity at high input power. The scalability of the proposed scheme to 100 Gsym/s systems and the maximum achievable tunability range are also discussed.