Thermooptic fiber switch

A study was made of the return of radiation (back to the core of a fiber waveguide) by a sharp bend in a short transition region between a rectilinear section and a section bent to a selected radius. When the bend was placed in an immersion medium, the radiation escaped in the form of narrow beams. When the refractive index of the ambient medium varied with temperature, the intensities and directions of such beams changed. This was used to construct a thermooptic fiber switch. At room temperature the light emerging from the bend into the ambient medium was directed to a second fiber waveguide. When the medium was heated to 150 °C, the light remained in the waveguide with the bend. The decoupling of the channels amounted to 28 dB, the internal losses were 3–5 dB, and the switching time was 10 sec. The switch withstood 2500 operations without a change in its parameters.