CMOS-compatible compact optical isolator based on space-time modulated coupled resonators

This work shows how phase-shifted time-modulations applied to two or more near-field coupled resonators can be engineered to achieve magnet-free optical isolation in a compact footprint. Because of the strong light-matter interaction afforded by high quality factor resonant cavities, only modest modulation amplitudes are required. A coupled mode theory model is developed which is subject to simulated annealing to optimize device performance. Then it is shown via finite-difference time-domain simulation how the device may be implemented in a one dimensional photonic crystal geometry etched in a silicon ridge waveguide. These devices can be implemented in native silicon with standard electrical contacts thereby maintaining CMOS-compatible fabrication without the need for additional specialized materials. Isolation ratios of over 40 dB with insertion loss less than 1 dB using modulation frequencies under 25 GHz are achievable in this device platform.