Frost-resistant fiber waveguides with a quartz glass core and a silicone rubber cladding

An investigation was made of the numerical aperture and excess losses in fiber waveguides with a silicone reflecting cladding at temperatures from $-100\dots+20^\circ$ C. A rapid rise of the optical losses was due to an increase in the refractive index of the silicone cladding because of its crystallization. The use of silicone rubber with a lower crystallization temperature made it possible to extend the working temperature range. Even better results were achieved at low temperatures by the use of waveguides with a core doped with $GeO_2$.