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Abstract

An electrically tunable interference filter comprises a semiconductor body which has a plurality of semiconductor layers. Each semiconductor layer comprises first and second sublayers which together define a heterojunction and first and second portions which together define a pn junction located at or closely adjacent to the heterojunction. Electrical contacts are provided for biasing the pn junctions. Application of a forward bias to some of the pn junctions causes injection of carriers from the second sublayers across the heterojunctions into the first sublayers to modify the refractive index of the first sublayers. Application of a reverse bias to other of the pn junctions enhances an inherent electric field at the pn junctions to modify the refractive indices of regions adjacent to the pn junctions. The applied reverse bias also depletes carriers from regions of the first and second sublayers to modify the refractive indices of those regions. Such refractive index modifications alter the optical filter characteristics of the plurality of layers, so the filter may be electrically tuned.

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