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Abstract

An optical system (10) includes an optical switching module (210,300,350) that is adjustable between first and second conditions to selectively direct an incident light signal (240,301,351) between either of at least two optical paths (236,238,304,303). At least one optical switch (218) is integrated into a substantially planar waveguide substrate in order selectively switch light (240,301,351) entering the switch from one waveguide (232,234) to exit the switch along either of at least two other waveguides (236,238). The optical switch (218) includes an electro-optic material (222) that is deposited into a cavity (220) formed within the substrate (214) such that the respectively optically coupled waveguides (232,234,236,238) interface with the switch (218) along the cavity walls. The switch (218) includes first and second regions (226,228) that interface at a boundary (230), and the electro-optic material (222) is located in one of the regions (226,228) such that an electrical field source (212,213,224) coupled to the material (222) in the one region (226) adjusts the boundary (230) between transmission and reflection modes with respect to at least one polarization of a light signal (232) incident upon the boundary (230) from a waveguide (232). The cavity and integrated switch are arranged such that the incident light signal (232) enters the switch from a waveguide (232) as a light beam that is not guided as it projects onto the boundary (230). Switching of light polarizations aligned with the applied electric field is accomplished in one regard by filling the second region (opposite the region receiving the incident light) with PLZT that has a reducing index of refraction in the presence of an applied field. PLZT is provided in the switch (11) in a formulation that provides substantially little hysteresis with respect to the applied field, and in particular is a non-ferroelectric, cubic, relaxor, polycrystalline, ceramic type having a lanthanum concentration of between about 8.5% and about 9.0%. The electro-optic material (222) may be in both regions (98,100,226,228) with the applied field region being thicker in the plane of the applied field than the other region. Or, the electro-optic material (222) may be in one region (100,226) with a second different material in the other region (98,228,411) that is less electro-optically active than the first region (100, 226, 417). The second material may be the electro-optic material (222) with another material that inhibits electro-optic activity, such as PLZT in combination with silica. The PLZT is deposited within the cavity (220) by a sol-gel process preferably after the cavity is coated with an optically transparent coating that forms a barrier to silica migration during heat treatment of the PLZT and that also provides for good adhesion for the PLZT. Polarization independent switching is achieved by optically coupling the light signal to generally two polarization dependent TIR boundaries (415,425,665,675) in series that separate and switch two polarization components of the light signal which are then combined by a combiner (330,390). An add-drop multiplexing system (900) is described that incorporates an array of the optical switching modules (S1,S2,S3) with a WDM de-multiplexor assembly (920) onto a single planar silicon wafer substrate (900).

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