Large quality factor enhancement based on cascaded uniform lithium niobate bichromatic photonic crystal cavities

In this Letter, by cascading several bichromatic photonic crystals we demonstrate that the quality factor can be much larger compared with that in an isolated cavity without increasing the total size of a device. We take a lithium niobate photonic crystal as an example to illustrate that the simulated quality factor of the cascaded cavity can reach 10⁵ with a 70° slant angle, which is an order of magnitude larger than that in an isolated cavity. The device can be fabricated easily by current etching techniques for lithium niobate. We have fabricated the proposed device experimentally including holes with ∼70° slant angle. This work is expected to provide guidance to the design of photonic crystal cavities with high quality factor.