SPECTRAL ATTENUATION OF OPTICAL FIBERS MEASURED BY FT-IR SPECTROSCOPY

For this study a commercial detector (InAs) was used which had a receiving area of 2 multiplied by 2 mm**2. Fitting the detector to the small light field diameter of the optical fiber should result in a significant noise reduction. The results are given. They show well-known spectral features. The GRIN fiber shows a strong band at 1. 39 mu m containing a weaker one at 1. 41 mu m. These are caused by the first harmonics of the minus OH fundamentals of Si-OH and Ge-OH, which are commonly given in wavenumbers at 3663 cm** minus **1, and 3540 cm** minus **1, respectively. The unresolved weak bands at 0. 94 mu m in the GRIN fiber are the second harmonics of the minus OH fundamentals. Beyond the application in fiber testing, the authors' experiments show the possibility for the use of optical fibers for remote sensing in analytical chemistry.