MEMS-based tunable Fabry-Perot filters

Abstract

We present a miniature tunable Fabry-Perot (FP) filter development effort based on using MEMS technology to fabricate and package it. The tunable filter development is intended to cover spectral regions from the visible to the longwave infrared by developing a number of different filters each operating over a different wavelength region. The main objective of developing such miniature tunable filters is to use each in a miniature hyperspectral imager by placing it in front of a commercial focal plane array with a suitable optical train. Such a miniature tunable device has many more applications, i.e., in developing tunable sources. Recently, we succeeded in fabricating some operational FP filters operating in the visible/near infrared (VIS/NIR) wavelength region from 400 to 800 nm. The filter design uses one fixed mirror and the second mirror moves using an electrostatic force. The device with a dimension of 18x24 mm 2 is composed of two parts: one fixed Ag mirror and one electrostatically moveable Ag mirror. Commercially available thin quartz wafer with low total thickness variation (TTV) was used as the substrate for each of these two parts. Au bumps were deposited in both parts in order to control the initial air gap distance and Au-Au bonding was used to bond two parts together. This paper will describe the device design considerations, the fabrication process, the effect of electrostatic force, the optical spectral measurements, and present test results.