Fiber optic thermal imaging system based on hollow glass waveguides or silver halide fibers as scanning elements

A simple fiber optic thermal imaging system based on a thin and flexible IR waveguide is constructed. Two types of waveguides are used: silver halide fiber and hollow glass waveguide. The thermal image of a warm object is formed at the focal plane of an IR transmitting lens. The proximal end of the waveguide is fixed and attached to a pyroelectric IR detector. The distal end of the waveguide scans the thermal image in two directions. The IR radiation is transmitted through the waveguide to the detector. The signals from the detector are coupled into a suitable monitor, which produces a representation of the thermal image. In preliminary experiments, we attach a small magnet to the distal tip of the waveguide and move the tip using an electromagnetic field. For a target of spatial frequency 1.25 cycles/mm the modulation transfer function (MTF) of the system is 0.2 and for a target of spatial frequency of 0.1 cycles/mm the minimum resolvable temperature difference (MRTD) is 0.5 °C. The system could be applied in industry or in medicine where imaging in the mid-IR and in a restricted space is required.