Simulation and implementation of photonic integrated circuits for the filtering and optical heterodyning of mode-locked comb-lines

We present the simulation and implementation of a photonic integrated circuit (PIC) designed for the filtering and optical heterodyning of comb-lines generated by a 20.97 GHz mode-locked fiber ring laser emitting at the optical C-band. We compare simulations obtained for the coupling junction of the microrings in the PIC with the use of an analytic approach and the finite difference time-domain (FDTD) method. A PIC designed for fabrication with the Triplex asymmetric double-stripe (ADS) waveguides was demonstrated. Using the PIC, we demonstrated the optical heterodyning of pairs of comb-lines filtered by tunable microrings. The phase noise of beat signals located at 20.97 and 41.94 GHz was characterized. We provide a discussion on enhancing the RF power of the beat signals with the use of optical injection locking.