Design of broadband reflector at the visible wavelengths using particle swarm optimization

We design and theoretically investigate freestanding gallium nitride (GaN) high contrast grating (HCG) membranes as broadband reflectors operating at the visible wavelengths. Optimization of the grating structural parameters is accomplished by using particle swarm optimization (PSO), and rigorous coupled-wave analysis (RCWA) method is adopted to evaluate the optical spectrum and internal electric field intensity distribution of all structures. The proposed reflector exhibits a 99% reflectance bandwidth of 84 nm, and good angular insensitivity of about 10.2° at the wavelength of 470 nm. The tolerance of fabrication deviation is also examined by numerical analysis of the reflector performance through varying the grating structural parameters. The GaN HCG broadband reflector can be potentially assembled in GaN-based vertical cavity surface-emitting lasers (VCSELs) or other novel integrated photonic devices.