This paper reports the design, fabrication, and characterization of a millimeter diameter, surface micromachined
Micro-Electro-Mechanical-Systems (MEMS) mirror, which is assembled perpendicular to the substrate and can be
linearly and repeatedly traversed through 600 μm. The moving mirror, when combined with a fixed mirror and
beamsplitter, make up a monolithic MEMS Michelson interferometer; all are made on the same substrate and in the
same surface micromachined fabrication process. The beamsplitter has been specifically designed such that the
motion of the mirror enables modulation of light over the 2-14 μm spectral region. The rapid scan MEMS
Michelson interferometer is the engine behind a miniaturized, Fourier transform infrared (FTIR) absorption
spectrometer. The FTIR measures the absorption of infrared (IR) radiation by a target material, which can be used
for the detection and identification of gases, liquids, or solids. The fabrication of the mirror with the ability to
displace 600 μm along the optical axis enables the miniaturized system to have species identification resolution,
while leveraging wafer scale batch fabrication to enable extremely low system cost. The successful fabrication of
the millimeter diameter mirrors and beamsplitter with interferometric alignment over the range of travel of the
moving mirror promises unprecedented sensitivity relative to the size of the FTIR spectrometer system.
This paper describes design, fabrication, and characterization of a miniaturized, Fourier transform
infrared (FTIR) spectrometer for the detection and identification of toxic or flammable gases. By
measuring the absorption by the target material of IR radiation, unambiguous detection and
identification can be achieved. The key component of the device is a micromachined Michelson
interferometer capable of modulating light in the 2 - 14 μm spectral region. Two major technical
achievements associated with developing a MEMS interferometer module are discussed:
development of a micromirror assembly having an order of magnitude larger modulation stroke to
approach laboratory instrument-grade spectral resolutions; and assembly of monolithic,
millimeter-scale optical components using multi-layer surface micromachining techniques to
produce an extremely low cost MEMS interferometer, which has an unprecedented optical
throughput. We have manufactured and tested the device. Reported optical characterization
results include a precisely aligned, static interferogram acquired from an assembled Michelson
interferometer using visible light wavelengths, which promises a high sensitivity FTIR
spectrometer for its size.
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