High-Q THz Photonic Crystal Cavity on a Low-Loss Suspended Silicon Platform

In this article, we present an ultrahigh-Q cavity at terahertz (THz) frequencies. The designed cavity is built on a low-loss suspended silicon (Si) waveguide. The substrate removal under the waveguide and the use of optimized deep reactive ion etching processing are the main reasons for observing very low losses of this design α <; 0.09 dB/mm. This very low-loss behavior of this designed platform is also demonstrated by the measurement of a one-dimensional photonic wire crystal cavity with Q > 18000. Different cavity layouts are adjusted in order to maximize the transmittance while maintaining high Q. A design with reduced number of etched crystal holes achieve Q > 1500 and high transmittance T > 70%. These structures are presented at sub-mm waves (around 600 GHz) for the design of a gas sensor in this frequency region, but the principles can be scaled and redesigned for other frequencies in the THz band.