Broad-band mirror (1.12-1.62 μm) using a subwavelength grating

We report the first experimental demonstration of a novel single-layer subwavelength grating (SWG) that has >500-nm-wide reflection spectrum from 1.12-1.62 μm and very high reflectivity (>98.5%). This SWG is scalable for different wavelengths by simply changing the grating dimensions, which, thus, facilitates monolithic integration of devices over a wide range of wavelengths.

I. Introduction

Broad-Band mirrors with very high reflectivity are essential for numerous applications, including telecommunications, surveillance, sensors and imaging, ranging from 0.7- to 12-m wavelength regimes. Fig. 1. Scheme of the SWG reflector. The low index material under the grating is essential for the broad-band mirror effect. Metal mirrors have larger reflection bandwidths but are limited by absorptive loss. Hence, they are not suitable for transmission-type devices such as etalon filters. Dielectric mirrors have low loss. However, to achieve high reflectivity, high precision in layer thicknesses, and refractive indexes are required. In addition, different materials are required for near versus far infared wavelengths. Semiconductor-based distributed Bragg reflectors have been used for tunable etalon type devices, such as microelectromechanical vertical-cavity surface-emitting lasers (VCSELs) [1], [2], detectors [3], and filters [4], [5] because of their higher thermal and electrical conductivities. However, limited by the small index difference, the mirror bandwidth and the resulting tuning range are limited to .