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Silicon-based optical waveguides function quite well to wavelengths of approximately 2 µm, demonstrating peak transparency in the near-IR region of 1.3 to 1.6 µm and approaching 0.15 dB/km at the latter wavelength. The need for optical fibers with IR transmission extended beyond that of silicon is driven by a variety of applications that will be briefly summarized in this overview. Since each material's class of IR fibers tends to focus on or be associated with specific applications, the general introduction is followed by a detailed treatment that highlights applications for fluoride glass, chalcogenide glass, and crystalline and hollow waveguide configurations. Regardless of the specific type of fiber under consideration, the questions that must always be addressed relate to whether the application demands an IR-transmitting fiber and, if so, what specifications the waveguide must meet optically, mechanically, and environmentally. These specification$ will determine which IR fiber described in Sections 1 and 2 could be used. Many applications of IR fiber optics are being realized today; others, beyond current technology, spur the IR fiber optics for future applications.
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