Improving the performance of Fourier transform spectrometers for new applications

这项研究计划将重点放在将傅里叶变换光谱仪(FTSS)用于非常规应用上。在这项提案的五年时间跨度内，有三个应用领域是目标。它们是：光学通信、高光谱显微镜和使用红外光纤进行现场测量的差示光谱分析。使用光场部分相干理论的FTS模型将得到进一步改进，以预测和解释所开发仪器的行为。第一次申请是与近年来开展的计划保持连续性的。从理论上确定了FTSS作为光通信光谱分析仪的极限性能，并进行了实验验证。还设计了将SONET调制对测量光谱的影响降至最低的方法。在该方案中，我们描述了一种革命性的全光纤FTS，旨在测量在光纤中传输的信号的光谱。这种小巧、坚固、低成本的高分辨率光谱仪对于光通信市场来说是非常有吸引力的。对于第二个应用，我们最近开始组装一台仪器，可以对空间分辨率低至1微米的显微镜样品进行光谱成像。图像大小为320x256像素。光谱范围从1.5到5微米，光谱分辨率为1厘米-1。要达到如此大的像素数量，必须使用CCD型相机。高性能干涉高光谱成像仪的问题之一在于干涉仪与相机的适配。我们在这方面工作的一个重要方面将是设计采集方案，使测量占空比最大化，同时避免仪器对各种噪声源更敏感的条件。最后，我们打算将红外光纤耦合到差动FTS的两个输入端口。这样的仪器可以用来作为一个“点和射”光谱仪来检测少量的化学物质，可能是在包装内。虽然商用FTS存在光纤“附加组件”，但没有扩展到热红外。考虑到两个输入路径中的自发射的平衡，差分方法还将允许更好的灵敏度。

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.