Improving the performance of Fourier transform spectrometers for new applications

该研究项目将重点研究傅立叶变换光谱仪（FTSs）的非常规应用。在这项提案的五年时间跨度内，有三个领域的申请是有针对性的。它们是：光通信、高光谱显微镜和使用红外光纤进行原位测量的微分光谱法。利用光场部分相干理论的傅立叶变换模型将进一步改进，以预测和解释所开发仪器的行为。第一次申请与近年来的计划保持一致。本文从理论上建立了光纤陀螺用作光通信光谱分析仪的极限性能，并进行了实验验证。设计了减小SONET调制对测量光谱影响的方法。在这个提议中，我们描述了一种革命性的全光纤FTS，用于测量在光纤中传播的信号的光谱。这样一种体积小、性能好、成本低的高分辨率光谱仪对光通信市场非常有吸引力。对于第二个应用，我们最近开始组装一种仪器，该仪器将以小至1微米的空间分辨率对显微镜样品进行光谱成像。图像大小为320x256像素。光谱范围为1.5 ~ 5µm，光谱分辨率为1 cm-1。为了获得如此大量的像素，必须使用ccd型摄像机。高性能干涉型高光谱成像仪存在的问题之一是干涉仪与相机的适配问题。我们在这一领域工作的一个重要方面是设计采集方案，使测量占空比最大化，同时远离仪器对各种噪声源更敏感的条件。最后，我们打算使用红外光纤耦合到差分傅里叶变换的两个输入端口。这种仪器可以作为“定点发射”光谱仪，用于检测可能在包装内的少量化学物质。虽然光纤“附加组件”存在于商用FTS中，但没有一个扩展到热红外。差分方法也将允许一个更好的灵敏度给予平衡的自发射在两个输入路径。

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.