Robust Optical Design of Angled Multilayer Dielectric Mirrors Optimized for Rubidium Vapor Cell Return Reflection

Abstract

This paper reports on the design and implementation of thin film multilayer dielectric to form Bragg reflectors on the sidewalls of micromachined atomic cells. Due to deposition shadowing, significant variations in the thicknesses of the thin films are encountered when the layers are deposited using PECVD. These gradients in thickness may limit optical performance of the reflector in atomic cells. An optimized design procedure is described to maximize the performance of the reflector at a wavelength of 795 nm under the variations in material thickness. In addition, an optical design based on two shifted quarter wave Bragg reflectors in series is used to form a reflector with extended optical bandwidth for added robustness. The extended reflectance range maintains high reflection at the D1 absorption wavelength of 87 Rb despite variations in uniformity greater than 70 %. The developed reflector technology is ideally suited for use in miniature rubidium vapor cells. We demonstrate less than 1.5 dB of return loss with circular polarization ellipticity maintained to ±2 • is demonstrated, as required for many atomic MEMS applications.

Review of atomic MEMS: driving technologies and challenges

“…Honeywell company applies a patent of an atomic MEMS gyroscope with a double-beam scheme, in which the \111[ surface of the silicon etched by KOH is used to reflect the light from out-of-plane to in-plane direction . And the reflectivity of the 54.74°surface can be improved through multi-layer coating (Perez et al 2008a(Perez et al , b, 2009. NIST also applies a patent based on a diverging beam of light that passes through an alkali atom vapor cell.…”

Microfabricated Vapor Cells with Reflective Sidewalls for Chip Scale Atomic Sensors

“…In 2009, Bragg reflectors, composed of layers of amorphous silicon, silicon dioxide (SiO 2 ), and silicon nitride (Si 3 N 4 ) were integrated, which improved the reflectance of angled sidewalls by nearly three times (as compared to that of uncoated silicon), resulting in an eight-times increase of the return reflection efficiency [ 18 ]. The variation in the dielectric thin film thickness due to the arrival angles of plasma enhanced chemical vapor deposition (PECVD) was optimized by the deposition rate [ 19 , 20 , 21 ]. Sandia National Lab reported a tunable miniature SERF atomic magnetometer with gratings and movable mirrors in the probe light path [ 22 ].…”