Improving the performance of Fourier transform spectrometers for new applications

该研究计划将专注于使傅里叶变换光谱仪（FTSs）适应非常规应用。在本提案的五年时间跨度内，有三个应用领域的目标。它们是：光学通信、超光谱显微镜和使用红外光纤进行现场测量的差分光谱法。利用光场部分相干理论的FTS模型将进一步改进，以预测和解释所开发的仪器的行为。第一个应用程序是与近年来进行的程序的连续性。从理论上建立并实验验证了光纤传输系统作为光通信光谱分析仪的性能指标。还设计了使SONET调制对测量光谱的影响最小化的方法。 在这个建议中，我们描述了一个革命性的全光纤FTS设计用于测量在光纤中传播的信号的光谱。这种小型、坚固、低成本的高分辨率光谱仪对于光通信市场将非常有吸引力。对于第二个应用，我们最近开始组装一台仪器，它将以小至1 μ m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。光谱范围从1.5到5 µ m，光谱分辨率为1 cm-1。 为了达到如此大的像素数，必须使用CCD类型的相机。高性能干涉超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FTS的两个输入端口。这种仪器可用作"瞄准和射击"分光计，探测可能在包件内的少量化学品。虽然光纤“附加”存在于商业FTS中，但没有延伸到热红外。考虑到两个输入路径中自发射的平衡，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.