Magnet-Free Circulator Based on Spatiotemporal Modulation of Photonic Crystal Defect Cavities

Implementing optical circulators in a microphotonic platform is challenging because magneto-optical effects are weak and the required materials are difficult to integrate in subwavelength geometries. Herein we propose a realistic geometry, verified by finite-difference time-domain simulations, showing how spatiotemporal modulation of an array of photonic crystal cavities via the electro-optic effect can be used to induce efficient nonreciprocal wave propagation in a realistic platform. The modulation is applied to three coupled cavities in a two-dimensional photonic crystal lattice, resulting in a compact spatial footprint. The resulting system requires modest modulation amplitudes and frequencies and cavities with realistic cavity quality factors, all of which are within the range of experimental implementation. We also explore the effects of unavoidable geometrical imperfections, and we show how the spatiotemporal modulation scheme can be optimized to compensate for the performance degradation resulting from these issues. The resulting device is dynamically tunable, which makes it a versatile component for various microphotonic applications.