Abstract: Unpolarized broadband reflectors enabled by a serial arrangement of a pair of polarized subwavelength gratings are disclosed. Device illustrations include partially-etched crystalline-silicon films on quartz substrates and amorphous silicon films on glass. The individual 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 prototypes disclosed, there results 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 spectral band. The elemental polarization-sensitive reflectors based on one-dimensional resonant gratings have simple design, robust performance, and are straightforward to fabricate.

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, the elemental gratings can be fabricated in various materials systems. Illustrative examples provided consist of a partially-etched crystalline-silicon films on a quartz substrate and amorphous silicon films on glass. The resulting reflectors exhibit extremely wide spectral reflection bands in one polarization. By arranging two such reflectors sequentially with orthogonal there results an unpolarized spectral band that exceeds those of the individual polarized bands. In the prototypes disclosed herein, there results zero-order reflectance exceeding 97% under unpolarized light incidence over a 500-nm-wide wavelength band.