Broadband guided-mode resonant reflectors with quasi-equilateral triangle grating profiles

Abstract

We present the design of broadband guided-mode resonant reflectors consisting of a grating layer with quasi-equilateral grating profiles and a homogeneous layer made of silicon on glass. Using the coordinate-transformation-based differential method of Chandezon (the C method) to determine the optimized base angles of the grating and thickness of the homogeneous layer, we arrive at example reflector designs for TM polarization. We quantify the effects of deviation of the parameters, simulate the inner magnetic field distribution at resonance wavelengths, and compute the tolerance in the incident angle of the optimized broadband reflector. For broadband structures with different thicknesses of the homogeneous layer, the base angles of the triangles are all close to 60°. The optimized reflector has reflectance of R0 > 99% across a 567 nm bandwidth in the 1432-1999 nm wavelength range with fractional bandwidth of Δλ/λcenter ≈33.3%. Base angles play a critical role in determining the reflection bandwidth and the quasi-equilateral triangle profile is found to be the optimal configuration. This model can be used to design broadband guided-mode resonant reflectors operating in different spectral bands and guide the fabrication of these devices with diamond-tip based grating ruling engines.