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.
Behavior of the refractive index and of the coefficient of thermal expansion of silicone with temperature.
Variation avec la temperature de l'indice de refraction du polydimethylsiloxane utilise pour le revetement des fibres optiques
Influence de la Stereorégularite des Chaînes sur les Transitions du Polyméthacrylate de Méthyle
Dilatometric studies on five PMM samples of different tacticities show generally three transition ranges between −35 and 150°C. The main glass transition temperature depends on the relative proportion of the iso- or syndiotactic segments. The secondary transition, located around 60°C., seems to be related to the presence of heterotactic segments. The third transition range, common to all the five samples, located around 0°C., may be attributed tentatively to the freezing in of the ester side groups.