Improving the performance of Fourier transform spectrometers for new applications

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This research program will focus on adapting Fourier transform spectrometers (FTSs) for unconventional applications. Three areas of applications are targeted for the five years time span of this proposal. These are: optical communications, hyperspectral microscopy and differential spectrometry using infrared fibers for in situ measurements. Models of FTS using the theory of partial coherence for optical fields will be further improved to predict and explain the behavior of the instruments developed. The first application is in continuity with the program carried in recent years. The ultimate performances of FTSs used as optical spectrum analyzers for optical communications were theoretically established and demonstrated experimentally. Methods to minimize the effects of SONET modulation on the measured spectra were also devised.  In this proposal, we describe a revolutionary all-fiber FTS designed to measure spectra of signals traveling in an optical fiber. Such a small robust and low-cost high-resolution spectrometer would be very appealing for the optical communication markets. For the second application, we recently started to assemble an instrument that will spectrally image microscopy samples with a spatial resolution as small as 1 µm. The image size is 320x256 pixels. The spectral range extends from 1.5 to 5 µm and the spectral resolution is 1 cm-1.  To reach such a large number of pixels, a CCD-type camera must be used. One of the problems of high-performance interferometric hyper spectral imagers lies in the adaptation of the interferometer with the camera.  An important aspect of our work in this area will be to devise acquisition schemes that maximize the measurement duty cycle while staying away from conditions where the instrument is more sensitive to various noise sources. Finally, we intend to use infrared fibers coupled to the two input ports of a differential FTS. Such an instrument could be used as a "point and shoot" spectrometer to detect small quantities of chemicals, possibly inside a package. While fiber-optics "add-on" exist for commercial FTS, none extend in the thermal infrared. The differential approach will also allow a far better sensitivity given the balancing of the self-emission in the two input paths.