A Static Multiplex Fabry-Perot Spectrometer Nan Zheng, Nathan Hagen, Renu John * and David J. Brady Fitzpatrick Institute for Photonics, Box 90291, Duke University, Durham, NC 27707 USA ABSTRACT We demonstrate a static multiplex spectrometer based on a Fabry-Perot interferometric filter for measuring the mean spectral content of diffuse sources. By replacing the slit of a low-dispersion grating spectrometer with a Fabry-Perot interferometric filter, we improve the resolving power of the instrument while simultaneously overcoming the free spectral range limitation of the Fabry Perot. The resulting instrument is smaller than con- ventional spectrometers having the same resolving power. We present experimental results from the spectrometer using neon lamp, He-Ne laser, and diode laser sources over a wavelength range from 620 nm to 660 nm. 1. INTRODUCTION Traditional slit-based dispersive spectrographs are restricted by the physical rule that the efficiency increases with the volume of the spectrograph, preventing one from building a spectrograph with both high efficiency and small volume. Recently, our research group has used coded aperture techniques to overcome this design limitation to create spectrometers with a greatly improved efficiency when measuring diffuse sources. 2, 4 In this work, we use resonant spectrographs as a means of further exploring spectrometer design space. In the discussion below, we first review the design limitations of conventional spectrometers and show how the static multiplex Fabry-Perot spectrometer can be used to improve on them. After presenting the measurement principle and reconstruction algorithm used, we discuss our initial experimental results and indicate directions for future research. The performance and utility of a spectrometer is characterized by its • Spectral resolution,Δλ, which is the smallest difference in wavelengths that can be distinguished by the spectrometer; • Spectral range, the wavelength range over which the spectrometer works; • Resolving power, R = λ/Δλ, indicating the number of resolvable wavelengths, where λ is the center operating wavelength of the spectrometer; • Etendue, L, which is a measure of the light energy throughput and is the product of the area of the entrance pupil and the solid angle subtended by the instrument aperture; • Instrument volume, V ; • SNR, the signal to noise ratio, usually defined as the mean value in the spectrum divided by the standard deviation of the background noise. Figure 1 illustrates a traditional slit-based spectrometer. This is a 4F imaging system with a spatial filter (a slit) in the input plane and a dispersive element placed in the collimated region between the two lenses. The distance between all neighboring components is F , the focal length of the lenses, so that the first lens forms the Fourier transform of the slit at the input plane of the grating, and the second lens forms Fourier transform of the grating output at the detector plane. The dispersive element, which is often a diffraction grating, produces a * R. John is currently at the Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana- Champaign, 405 North Mathews Avenue, Urbana, Illinois 61801, U.S.A Send correspondence to David J. Brady, at dbrady@duke.edu, telephone: 1 919 660 5394 1 Sensors, Cameras, and Systems for Industrial/Scientific Applications X, edited by Erik Bodegom, Valérie Nguyen, Proc. of SPIE-IS&T Electronic Imaging, SPIE Vol. 7249, 72490Z © 2009 SPIE-IS&T · CCC code: 0277-786X/09/$18 · doi: 10.1117/12.805663 SPIE-IS&T Vol. 7249 72490Z-1