There is a need to develop miniature optical tunable filters for small hyperspectral imagers. We plan to develop a number of miniature Fabry-Perot tunable filters (FPTFs) using microelectromechanical systems (MEMS) technology, each operating over a different wavelength region, to cover spectral regions from the visible to the longwave infrared (IR). Use of a MEMS-based FPTF as a dispersive element will reduce the size, weight, and power requirements of hyperspectral imagers and make them less expensive. A key requirement for such a filter is a large optical aperture. Recently, we succeeded in fabricating FPTFs with a 6 mm optical aperture operating in the visible to near IR spectral region (400 to 800 nm) using commercially available thin quartz wafers as the substrate. The FPTF design contains one fixed silver (Ag) mirror and one electrostatically movable Ag mirror, each grown on a quartz substrate with a low total thickness variation. Gold (Au) bumps are used to control the initial air gap distance between the two mirrors, and Au-Au bonding is used to bond the device. We describe material selection, device design, modeling, fabrication, interferometric, and spectral characterizations.
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 mm2 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.
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