Spectral imaging characterization of MOEM tunable Fabry-Perot filter

Abstract

A miniature MOEM tunable Fabry-Perot (FP) filter development program to fabricate filters operating over spectral regions from the visible to the longwave infrared has recently succeeded in fabricating filters operating over visible/near infrared wavelength region from 400 to 800 nm. The main objective of this program is to design miniature hyperspectral imagers by placing such a miniature tunable FP filter in front of a commercial focal plane array with a suitable optical train. This novel MOEM filter design is based on using two semitransparent 30-nm thick silver-film mirrors-one fixed and one moving with application of an electrostatic force. The silver films were grown on low-cost thin commercial quartz wafers with low total thickness variation. The moving mirror is held in place by three leaf spring arm structures which were fabricated by wet etching of the quartz substrate. The size of the MOEM device is 18×24 mm². The tunable FP filter has a 6-mm optical aperture. The fixed part has three electrodes to apply voltages and the moving mirror is used as a ground electrode. Au bumps were deposited in both parts in order to control the initial air gap distance and an Au-Au bonding was used to bond the two parts together. The electrostatic actuation changes the spacing between the two mirrors which changes the transmitted wavelength. The spectral imaging performance of MOEM filter was characterized using a tunable source and a CCD camera with suitable optics. This paper describes the MOEM filter, its characteristics and present spectral imaging characterization experiment and results.