Hybride fiber-optic temperature sensors on the base of LiNbO3 and LiNbO3:Ti waveguides

摘要

Abstract: Two modifications of fiber-optic temperature sensors which utilize the temperature-dependent birefringence of optical crystals have been investigated. In a first approach, an additional compensator crystal has been introduced into the customary birefringent filter. The thickness of this crystal was chosen to compensate almost completely the birefringence of the sensor crystal, but the temperature dependence of its birefringence must be negligible. For this purpose the authors used $alpha@-quartz. With this sensor they obtained a high modulation depth of the output signal even for LED light sources. In a second approach the bulk birefringent filter has been completely replaced by a titanium-indiffused waveguide in LiNbO$-3$/. Polarization maintaining fibers have been coupled directly to the waveguide ends with appropriate orientation, so that collimating and focusing lenses as well as the two polarizers can be omitted from the sensor head, and thus the compactness is considerably increased.!