Photonic-crystal surface emitting lasers (PCSELs) exhibit several unique features compared to conventional vertical cavity surface-emitting lasers (VCSEL) including scalability, high power, and high beam quality. They are promising candidates in power-demanding applications such as free-space sensing. Motivated by the experimental advances, there have been significant efforts in developing the simulation tools for PCSELs. In particular, a coupled mode theory (CWT) model for PCSEL was developed, which provides important insights into the operating mechanisms. However, CWT makes several uncontrolled approximations such as a small number of waveguide modes as the basis, which is difficult to justify since the index contrast in PCSELs can be quite large.
Here we show that PCSELs, especially its lasing threshold, can be simulated from first-principles by using rigorous coupled-wave analysis (RCWA). Traditionally, RCWA has been widely used to simulate the transmission or reflection of such structures, where the frequency is real. Here, we use RCWA to calculate the scattering matrix (S-matrix) of PCSELs on the complex frequency plane. This approach builds upon the concepts from steady-state ab initio laser theory (SALT). On the complex frequency plane, the poles of the S-matrix correspond to various resonances of the structure, including Fabry-Pérot resonances and the guided resonances. We gradually increase the material gain in the PCSEL, and the threshold is retrieved as the gain value for which the first pole crosses the real axis. Other important characteristics such as the quality factor of each mode and the power efficiency of the laser can be computed as well.
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