13.1 INTRODUCTION

Infrared (IR) optical fibers are fibers that transmit radiation from 2 to approximately 20 m. The first IR fibers were fabricated in the mid-1960s from a rather special class of IR transparent glasses called chalcogenide glasses. It was well known that mixing chalcogen elements, for example, arsenic and sulfur, can form a dark red glass that is transparent well beyond 2 m. In 1965, this arsenic trisulfide (As ₂S ₃) glass was first drawn into crude optical fiber by Kapany et al. [1], but the losses were more than 10 dB/m from 2 to 8 m. A loss of 10 dB/m means that a 1-m length of As ₂S ₃ fiber would transmit only 10% of the incident light. Energy would also be lost because of reflection from the fiber end-faces, which for this high refractive index glass ( n=2.3) amounts to an additional 31%. Furthermore, their As ₂S ₃ fiber was quite brittle. During the mid-1970s, there was interest in developing an efficient and reliable IR fiber to link broadband long wavelength radiation to remote photodetectors in military sensor applications. For example, researchers at Hughes Research Laboratories in Malibu, California, studied various IR fibers that could be used in a surveillance satellite application to transmit IR radiation in the 3- to 5- m, 8- to 12- m, and longer wavelength bands...