Method and apparatus for controlling the temperature of or indicating the presence of a material by means of a waveguide, heat activatable articles incorporating waveguides; and novel waveguides and a method of making such waveguides.

摘要

Method and apparatus for controlling temperature of a material by means of an optical waveguide having a core and cladding, the refractive index of the core becoming lower than that of the cladding to induce blackout of light transmission at pre-selected temperatures. The material is heated or cooled as indicated by the change in light transmission at or near the blackout temperature, which phenomenon can also be used to detect the presence or level of a material. New waveguides comprising several sections having different blackout temperatures are provided.