Compact FTIR engine made through MOEMS technology

More and more small spectrometers have been brought to market in recent years. Compactness is certainly a necessary feature for spectrometers used in the field, but keeping the detection capability sufficiently high is also key to fulfilling application requirements. Using MOEMS technologies, we developed an FTIR engine for field use that is both compact and has good detection capability. The FTIR engine measures 59mm x 28mm x 35mm and weighs about 130g. Although compact, it has a signal-to-noise ratio (SNR) higher than 40 dB, a light efficiency higher than 15%, and sensitivity from 4000 to 8500 cm^-1. This new FTIR engine has a φ3mm MEMS movable mirror formed on a Si wafer surface to enhance light utilization. The MEMS actuator is driven with an amplitude of 125 micrometers orthogonal to the surface. A fixed mirror was formed on the 4.4mm thick compensating plate through metal deposition. A miniature MEMS mirror device measuring 21mm x 14mm x 4.8mm was fabricated, which integrates the movable mirror and fixed mirror by direct bonding. A 4.4mm thick trapezoidal prism beam splitter was placed on the MEMS device, and it combines two light arms reflected in the same direction to obtain interferograms with an InGaAs PIN photodiode. In addition, a VCSEL was integrated in the housing of the FTIR engine to monitor the driving mirror position.