REFLECTION INTENSITY OPTICAL-FIBER SENSORS FOR THE MIDINFRARED

Two kinds of reflection intensity sensor made of chalcogenide glass fi ber for the mid-IR region are demonstrated. One is a double-fiber refl ection Sensor based on two tied fibers with a gold-coated hollow metal waveguide connected to the far end of the fibers. The other is a sing le-fiber reflection sensor based on contact couplers. These reflectanc e sensors were coupled to a Fourier-transform IR spectrometer by a uni que accessory based on nonimaging concentrators. This setup was built to measure absorption spectra of a polymer coating of an aluminum can and a sheet of drafting paper. A theoretical model treating the ratio between the signal from the target and the background is introduced. T his model was helpful in deriving the sensitivity characteristics of t he sensors from experimental absorption peak heights. Hence, the absor ption peaks heights that we obtained using a single-fiber reflection s ensor with a symmetric coupler were nearly 50% relative to those obtai ned with a double-fiber reflection sensor. (C) 1997 Optical Society of America.