Accurate determination of the thermal variation of the aperture of step-index optical fibers.
Thermal variations of the aperture of step-index optical fibers have been studied by measuring the transmitted power when a laser beam is launched with a variable incidence. For not too-long fibers only the rays launched with the higher incidence are affected. The variations of their transmittance have been accurately related to the refractive-index ones. Silicone clad silica fibers are sensitive to temperature because the silicone index varies much more the the silica index. On the contrary, due to a compensation phenomenon between index variations of core and cladding materials, PMMA core fibers have apertures that are nearly insensitive to temperature.
Thermal variations of refractive index of PMMA, polystyrene, and poly (4-methyl-1 -pentene)
Abstract The refractive indexes of PMMA, polystyrene, and poly-(methyl pentene), three transparent polymers having various morphologies, have been measured between about -100°C and +150°C. The prism method was used in order to make the sample quite free of any contact and mechanical interaction. Thermally stimulated current experiments were concurrently performed to observe and to confirm the existence of the transitions occurring in the various samples. It is verified that the refractive index variations, on the one hand, perfectly follow the Lorentz-Lorenz law and, on the other hand, systematically exhibit anomalies every time a morphological change temperature is overstepped by the material. So, it is shown that measurement of the thermal variations of the refractive index of polymers is another means to follow the behavior of their specific volume while avoiding the application of any stress from the experimental device.
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 –5°C due to the refractive indices of the core and of the cladding becoming equal.