We present a miniaturized Fourier transform spectrometer (FTS) based on optical microelectromechanical system technology. The FTS is a Michelson interferometer with one scanning mirror. A new type of electrostatic comb drive actuator moves the mirror. We have measured a nonlinearity of the driving system of 60.5 mm for a displacement of 38.5 mm. A method is presented to correct the spectrum to get rid of the nonlinearity. The driving reproducibility is 625 nm. The measured resolution of the spectrometer after the phase correction is 6 nm at a wavelength of 633 nm.Fourier transform (FT) spectroscopy is a well-known technique to measure the spectra of weak extended sources. It offers distinct throughput and multiplex advantages, which provide higher signal-to-noise ratio performance than other methods. However, commonly used FT spectrometers require a mirrorscanning mechanism with very high precision, resulting in large size and high cost. Low-cost, miniature spectrometers are key components that permit the realization of small-size, portable sensor solutions for applications such as color measurement and industrial process control. Therefore, recent investigations have dealt with low-cost, miniature spectrometers.
2,3A spatially modulated FT spectrometer (e.g., a Michelson interferometer with a tilted mirror and a photodiode array) is compact and has no moving parts. 4 However, stationary FT spectrometers have poor resolution and do not benefit entirely from the throughput advantage. We report here on a FT spectrometer with a moving mirror that is extremely compact ͑5 mm 3 4 mm͒ and has a scanning system that allows precise motion of the mirror. Low-cost fabrication is possible thanks to the use of silicon technology.
5A schematic of the actuator and the basic concept of FT spectroscopy are shown in Fig. 1. In FT spectroscopy we measure the intensity variation I R ͑d͒ as a function of the optical path difference d when a partially coherent plane wave is introduced into a Michelson interferometer. The relation between I R and d is known as an interferogram. The power spectrum B͑s͒ and the recorded intensity modulation I R ͑d͒ are related by a Fourier transform:where s is the wave number ͑s 1͞l͒. The theoretical resolution of a FT spectrometer is given bywhere d max 2Dx max and Dx max is the maximum displacement of the mirror. Electrostatic comb drive actuators are widely used in microelectromechanical systems because of their simple construction and reliable operation. These actuators permit a considerable displacement of as much as 100 mm, 6 but they cannot drive large loads. Therefore applications are mainly found in the area of optics in which no output force is needed. 6 Nevertheless, in many optical applications, such as Michelson interferometers and linear shutters, one would like to have a displacement that is linear to the applied voltage. Since a conventional comb drive actuator has a voltagedisplacement response that is quadratic, other actuator principles, such as piezoelectric or electrodynamic princip...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.