An optical sensor that includes multiple filter cavities for the
simultaneous, co-located measurement of pressure and a temperature in a
single structure. The sensor may include a single launch fiber bonded to
a tube a pre-determined distance from a reflective fiber. The end of the
reflective fiber not encased within the tube is enclosed within a cap
formed of a material that has a refractive index that changes with
changing temperature. Alternatively, a material having a refractive index
that changes with changing temperature can be inserted into the tube to
take the place of the reflective fiber. Multiple launch fibers may be
incorporated within a tube.