Broadband near-infrared reflector based on double-layer subwavelength gratings

A broadband reflector with a reflectance up to 97.8% over a 144 nm spectral range from 1476 to 1620 nm is proposed by comprising double-layer subwavelength gratings with one grating layer embedded in SiO2 layer. An analysis of the resonance leaky modes with overlapping gratings shows the physical mechanism of the wide broad high-reflectivity band. The tolerance of structural parameter is analyzed and the variation of bandwidth is explained by combining the behaviors of the two guided mode resonances. The guided mode resonance and high refractive index contrast properties lead to a good angular tolerance that exhibited an angular insensitivity (similar to 11 degrees) at 1550 nm. Overall, the broadband reflector may benefit the monolithic integration of optoelectronic devices.