Abstract: An air bubble (23) in the core (3) of an optical fiber (1, 1') constitutes a broad band reflector to light waves propagated in the fiber. A fiber end (3) is first stripped and cut in the conventional way, after which in the end surface, a pit (13) in the core region is produced by etching. The fiber end is therefor treated with e.g. diluted hydrofluoric acid, that etches the higher doped core (3) more rapidly than the cladding (5). The etched fiber end (1) is then welded to a standard fiber so that a splice (21) is obtained where the desired air bubble (23) is enclosed in the fiber core. The magnitude of the reflectance of the produced reflector can then be changed by repeated heating steps, in the same way as in welding, of the splice (21) and/or by filling the bubble (23) with another medium than air or by coating one of its walls with a suitable material, e.g. a metal.

Abstract: A fiber-optic system for measuring a desired environmental parameter, such as temperature, is disclosed. The system includes a fiber-optic sensing head that alters light of a prescribed frequency as a function of the environmental parameter to be measured. Light not of the prescribed frequency is not so altered. In a preferred embodiment of the fiber-optic sensing head, a semiconductor material is positioned between two substantially parallel optical fibers at a distal end of the fibers. One fiber serves as in input channel and the other fiber serves as an output channel. Both fibers approach the semiconductor material from the same direction. Light channeled to the semiconductor material is reflected at the distal end of the input fiber so as to pass through the semiconductor material, and then is reflected again at the distal end of the output fiber so as to pass back out the output fiber. The semiconductor material absorbs the light of the prescribed frequency as a function of temperature.