Unpolarized resonance grating reflectors with 44% fractional bandwidth

Abstract

There is immense scientific interest in the properties of resonant thin films embroidered with periodic nanoscale features. This device class possesses considerable innovation potential. Accordingly, we report unpolarized broadband reflectors enabled by a serial arrangement of a pair of polarized subwavelength gratings. Optimized with numerical methods, our elemental gratings consist of a partially etched crystalline-silicon film on a quartz substrate. The resulting reflectors exhibit extremely wide spectral reflection bands in one polarization. By arranging two such reflectors sequentially with orthogonal periodicities, there results an unpolarized spectral band that exceeds those of the individual polarized bands. In the experiments reported herein, we achieve zero-order reflectance exceeding 97% under unpolarized light incidence over a 500 nm wide wavelength band. This wideband represents a ∼44% fractional band in the near infrared. Moreover, the resonant unpolarized broadband accommodates an ultra-high reflection band spanning ∼85 nm and exceeding 99.9% in efficiency. The elemental polarization-sensitive reflectors based on one-dimensional (1D) resonant gratings have a simple design and robust performance, and are straightforward to fabricate. Hence, this technology is a promising alternative to traditional multilayer thin-film reflectors, especially at longer wavelengths of light where multilayer deposition may be infeasible or impractical.

Tunable Frequency Filter Based on Twisted Bilayer Photonic Crystal Slabs

“…The guided resonances typically manifest as narrow spectral features with Fano lineshapes in the transmission spectrum of the slab. These features have been widely explored for filter applications. − …”

Sc2O3 on sapphire all-crystalline grating–waveguide resonant reflectors

“…In this work, we report on the first resonant reflectors based on GWS made entirely of all-dielectric crystalline materials, specifically, scandium oxide (Sc 2 O 3 ) epitaxially grown on a structured sapphire (α-Al 2 O 3 ) substrate. These devices are similar to those of Si-on-quartz (SOQ) systems that capitalise on the all-crystalline nature of the component materials [6]. However, the intrinsic absorption in semiconductor materials at the wavelengths of interest for high-power lasers would limit their utility.…”

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

“…Comparatively, it is easier to be realized by using multilayer gratings. For example, two orthogonal gratings were demonstrated experimentally, and achieved a broad independent polarized bandwidth with a high reflectance (Niraula et al 2016; Broadband reflector based on double-layer subwavelength gratings Qi Wang*, Rui Li, Xufeng Gao, Shuhua Cao, Chunxian Tao, Ruijin Hong, and Dawei Zhang Ko et al 2017). Nevertheless, it is difficult to combine separate SWGs compactly.…”