B.S.T.J. Briefs: Effect of Ambient Temperature on Infrared Transmission Through a Glass Fiber

Recent progress in reducing the losses in optical fibers1 has increased the possibility that such fibers might be used as dielectric waveguides in future optical communication systems.2 The loss properties of such fibers are therefore of interest. This note concerns the measured change in transmission loss of a glass fiber for an ambient temperature variation of -- 196°C to 4-200°C. The results indicate that the loss in glass fibers varies only slightly with temperature. The attenuation measurements were made on single fibers taken from a Corning type 5900 optical fiber bundle. These fibers were approximately 60 ^m in diameter and had a very thin cladding with a refractive index about 10 percent below that of the core. The elevated temperature measurement was performed on a 39-meter length which was made up of three 10- to 20-meter lengths joined into a single piece by a low-loss fusing process.3 The reduced-temperature tests were made with a 12-meter segment of this same fiber. The light source consisted of a 50-/xm-diameter gallium arsenide light emitter diode (GaAs LED) 4 which was used to supply about 0.05 mW of power into the fiber at a wavelength of 0.9 nm. Detection was accomplished with a silicon PIN photodetector. The high-temperature test was carried out with the major portion of the fiber on a reel in an oven; for the low-temperature test, the fiber was coiled in a Dewar flask filled with liquid nitrogen. In both cases, the source and the detector were outside the test chamber in a room-temperature ambient.