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.
Effect of temperature on optical fiber transmission.
Results are presented concerning the effects of temperature on the transmission properties of various optical fibers including a silicone plastic clad, an acrylic plastic clad, and CVD step-index fibers both with and without polyurethane jackets. Results are presented for the normalized transmitted power vs temperature, the index of refraction vs temperature, and induced attenuation coefficients vs temperature. The data show that the intrinsic transmission of a CVD fiber is independent of temperature over the -110 to +150 C range. Plastic clad fused silica fibers are subject to transmission losses at lower temperatures due to changes in the optical index of the cladding polymer. Acrylic-clad and plastic-clad silica fibers also show transmission losses at lower temperatures, but to lesser extents.
Dilatometric measurements on poly(4‐methyl‐1‐pentene) glass and melt transition temperatures, crystallization rates, and unusual density behavior
Dilatometers were used to measure the volume-temperature curves of seven poly(4-methyl-1-pentene) (PMP) samples between −30 and +270°C., and to measure crystallization rates on one sample between 220 and 236°C. A glass transition temperature of 18–29°C. was found, and the crystalline melting point was found to be 250°C. The value of dV/dT above and below the glass temperature was used to measure the degree of crystallinity. The results indicate that the crystalline PMP is less dense at room temperature than the amorphous polymer. However, because of different rates of expansion, the normal positive volume change on melting is observed. A density value of 0.828 ± 0.002 g./ml. at 20°C. is calculated for the PMP crystal.