Variable ratio fiber optic coupler optical signal processing element

Abstract

The coupler includes a waist region formed by merging and fusing a plurality of optical fibers with the waist region encapsulated in photorefractive encapsulating material. The index of refraction of the encapsulating material is modulated by applying illumination thereto, so as to vary the coupler output ratio. The applied illumination can direct the coupler output from one output fiber to another output fiber thereby providing an optically actuated switch. The illumination applied to the encapsulating material can direct a large optical power signal applied to an input fiber from one output fiber to another output fiber thereby providing an optical amplifier analogous to a transistor. One of the output fibers of the element can be utilized to provide the encapsulating material illumination thereby providing an optical feedback oscillator. Bias illumination applied to the encapsulating material results in a narrow band of a broadband input optical signal to be directed to an output fiber thereby providing an externally tuned spectrometer or optically tuned wavelength division demultiplexer. An input optical signal can correlate with the illumination applied to the encapsulating material to provide an optical correlator. In an element with encapsulating material that is both photoelastic and photorefractive, or both bend sensitive and photorefractive, the photorefractive effect can be utilized to bias the device to a predetermined point on the operating curve irrespective of applied stress. Networks of the optical signal processing elements can be interconnected to provide computing systems.