Fiber-optic thermometer

In a fiber-optic thermometer comprising a fiber-optic input for applying input light, a fiber-optic output for extracting output light, and a temperature-sensitive medium optically coupling said fiber-optic input to said fiber-optic output for transferring a proportion of the applied input light from said fiber-optic output, the size of said transferred proportion being a single-valued function of the temperature of said medium;

• the improvement therein;
• wherein said medium comprises a gas-sealing movable reflecting element disposed within a capillary that has one end thereof sealed, and a column of trapped gas situated between said one end of said capillary and said element, said element being supported by the pressure and moved by changes in the pressure of said trapped gas, whereby the length of said gas column and, hence, the position of said element along the length of said capillary is determined by the temperature of said gas, and
• wherein each of said fiber-optic input and fiber-optic output extends into the other end of said capillary and terminates at a fixed point along the length of said capillary situated between said element and said other end of said capillary, whereby the proportion of applied input light transferred from said fiber-optic output by reflection from said element is a single-valued function of the position of said element along the length of said capillary.