Diamond thin-film Fabry-Perot optical resonators

R. A. Booth and D. K. Reinhard

Department of Electrical and Computer Engineering

Michigan State University

East Lansing, MI 48824-1226

Abstract

Diamond thin-film based Fabry-Perot optical resonators are fabricated on a silicon substrate, based upon established integrated-circuit fabrication technology. Processing procedures include thermal oxidation, photolithography, wet etching, plasma enhanced chemical vapor deposition, and sputtering. The resonant structure consists of a diamond membrane with partially-reflecting gold films on both sides. The through-transmission of the resulting structures is investigated both experimentally and theoretically.

Simulations of device performance are based upon standard optics theory, using the matrix approach for multi-layer optical structures. The simulations account for absorption and phase shifts in the front and back gold films and use published empirical data for constants such as the gold absorption coefficient and index of refraction for gold and diamond. A limitation of the theoretical calculations is that the matrix approach used to determine percent transmission assumes smooth, scatter-free interfaces.

The experimental performance of the diamond-film resonators has been investigated from the ultraviolet, through the visible, and into the infrared region of the optical spectrum (185 nm – 2500 nm). Experimental results will primarily be presented for the range of 700nm to 1600nm. Simulations accurately predict the wavelengths at which peak transmission is observed and the general shape of the transmission peaks. However, the simulations predict higher percent transmission and higher Q values than are actually observed. Simulation results suggest that the difference in theory and experiment is not due to absorption in the diamond. Therefore the role of scattering at the cavity surfaces is currently being studied. The rms surface roughness of the diamond film is found to be on the order of 15nm, as measured by AFM.

Roger Booth

Department of Electrical and Computer Engineering

Michigan State University

2120 Engineering Building

East Lansing, MI 48823-1226

Email: boothrog@msu.edu

fax: 517/353-1980

phone: 517/355-5214

An interesting optical application of diamond thin-film technology is presented which utilizes established IC fabrication methods to form operational on-silicon Fabry-Perot resonators. The operation of the resonators is investigated experimentally and theoretically.

Keywords: Fabry-Perot, thin-film, diamond, optical, filter.