Fast and accurate calculation of Q factor of 2D photonic crystal cavity

Abstract

We developed a method for calculating the Q-factor of a 2D photonic crystal nanocavity directly from the in-plane wavevector distribution of the cavity mode. A high-Q of >10 7 was obtained with high accuracy and speed. OCIS codes: (230.5298) Photonic crystals; (230.5750) Resonators IntroductionThe theoretical quality factor (Q) of a two-dimensional (2D) photonic crystal (PhC) nanocavity is usually dominated by the out-of-slab radiation loss. Since a higher experimental Q is obtained with a cavity with a better design (i.e. a higher theoretical Q), it is important to for us to undertake fast and accurate numerical studies. Q is usually determined with a three-dimensional finite-difference time-domain (3D-FDTD) calculation. Since the theoretical Q value is now higher than 10 7 , a long calculation time is required to obtain the cavity Q accurately. The theoretical Q is usually obtained by calculating the total energy in the calculation area at every calculation step and observing the field decay.In this work, we developed a new method that allows us to calculate Q by using a 2D mode profile at the center of the slab, without the need to conduct a time-consuming 3D energy calculation. Although we still use 3D-FDTD, we greatly shorten the calculation time by more than 4 times, because we can use a much smaller calculation area. More importantly, as we show later in this work, we obtain a highly accurate Q with our method, even when we finish the calculation immediately after the light excitation.