Highly Reflective and Ultra Broadband Mirror Using Sub-Wavelength Grating (SWG)
Broadband mirrors (Δλ/λ>15%) with very high reflectivity (R>99%) are essential for numerous applications, including telecommunications, surveillance, sensors and imaging, ranging from 0.7μm to 12μm wavelength regimes. Semiconductor-based distributed Bragg reflectors (DBRs) have been used for tunable etalon type devices, such as micro-electro-mechanical (MEM) vertical cavity surface emitting lasers (VCSEL), detectors and filters because of their higher thermal and electrical conductivities. However, limited by the small refractive index difference, the mirror bandwidth and the resulting wavelength tuning range are limited toΔλ/λ~3-9% (~100nm @1.55μm).
Recently we have reported the theoretical calculations and experimental demonstration of a novel design of a silicon-based sub-wavelength grating (SWG) that yields a very broad (Δλ/λ>35%) reflection spectrum with very high reflectivity (R>99%). The design requires a single layer of high index material (e.g. silicon) sandwiched in-between low index materials. It can be easily fabricated and scaled for different wavelengths, thus facilitating the monolithic integration of optoelectronic devices over a wide range of wavelengths, and has the potential to create low-voltage and widely tunable MEMS optoelectronic devices.
