Bandpass AR coating design for bismuth silicon oxide

Abstract

Bismuth silicon oxide is a high-index (2.54 at 514 nm) electrooptic and photorefractive material used for optical information processing devices such as the Pockels readout optical modulator (PROM), the photorefractive incoherent-to-coherent optical converter (PICOC), and volume holographic optical elements (VHOEs). In the latter two applications, the bismuth silicon oxide crystals have typically been used uncoated, even though the resultant high single-surface reflectivity (~19%) gives rise to problematic multiple reflections. For example, in the use of two-beam coupling experiments in Bi12SiO20 for signal amplification1 or materials parameter analysis, the modulation depth of the volume holographic gratings is reduced by multiple reflections, and the effective gain is decreased.2 For such experiments, a two-layer quarterwave stack of electron-beam deposited zirconium dioxide and magnesium fluoride was employed to fabricate a broadband (500–800-nm) AR coating, which encompassed both the write (514-nm) and read (633-nm) beams. At both wavelengths, the reflectivity was reduced to ~1 %, and the coating was found to be relatively insensitive to large angles of incidence (of the order of 45°). In two-beam coupling experiments, the effective gain was increased by 10%, and the resolution of the technique was significantly improved for low-intensity measurements.