Spectral range of operation of coupled‐mode optical filters

摘要

The spectral range of operation of optical coupled‐mode filters (CMF) is investigated. The CMF principle is based upon the stress‐induced energy transfer between orthogonal polarized optical modes, which occurs in birefringent materials at the isotropic wavelength where phase‐matching is ensured. A nonexhaustive list of birefringent materials which exhibit an isotropic wavelength is drawn up. The whole visible spectral range is covered continuously by using mixed graded‐band‐gap hexagonal crystals such as CdS‐CdSe and ZnS‐CdS. This range is extended up to 2.1 μm by using piezobirefringent cubic compounds. Materials with other crystalline structures enable the extension of this spectral range down to 1200 Å. The optical activity of chalcopyrite‐structure semiconductors can advantageously replace stress‐induced mode coupling.