Investigation of the temperature dependence of the optical losses in low-loss fiber-optic waveguides

The results are given of an investigation into the temperature dependence of the optical losses in low-loss fiber-optic waveguides. In waveguides with a core and cladding of quartz glass and having a protective polyamide coating, additional losses appear on cooling. These losses are caused by microscopic kinks which appear due to the compression of the coating material as it is cooled. The magnitude of the additional losses depends on the numerical aperture and on the quality of the waveguide coating. In waveguides with a quartz glass core and a reflecting cladding of silicone rubber, a sharp drop in the transmission is observed at a temperature of about $-50^\circ C$ due to the refractive indices of the core and of the cladding becoming equal.