Tunable Three-Dimensional Photonic Crystal Microwave Resonator with Ultra-Small Mode Volume

Abstract

Microwave resonator is an important electromagnetic tool with applications in many areas, including communication, nonlinear optics, cavity quantum electrodynamics, and precision metrology. In this work, we did simulations and experiments on a design of three-dimensional (3D) dielectric photonic crystal (PhC) cavity (PhCC) based on ABCD woodpile structure. Low material loss of the dielectric and radiation loss suppression of the 3D PhC’s complete bandgap give PhCC high quality factor (𝑄). The design also includes field focusing structure into the PhCC to achieve ultrasmall effective mode volume (𝑉ₑ subscript 𝑓𝑓). Moreover, the topology of the woodpile structure allows us to tune the PhCC’s resonance frequency as well.

Our simulation results agree with the experiments’ on the band structure of the PhC, 𝑄, and the tunability of the PhCC. Furthermore, the simulation shows that we can achieve indefinitely small 𝑉ₑ subscript 𝑓𝑓 by the field focusing structure limited only by the fabrication resolution. Our experiments on the design’s 6 × 6 × 5 unit-cell PhCC demos give a complete bandgap between 3.6 GHz and 4.1 GHz. We measured their 𝑄 to be in the order of 10² for the resonance inside the complete bandgap regardless of the existence of the field focusing structure which normally cause high radiation loss. We also can tune the resonance of the PhCC up to 64% of the width of the complete bandgap.