Abstract:
A solid state electro-optic switch employing first order electro-optic effect in bulk material. Selectively energized contact patterns define divergent optical waveguide paths in the bulk material.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to electro-optic switch devices for switching optical signals from an input between a pair of outputs, analogues to a single pole changeover switch for electrical signals. 
     According to the invention, there is provided an electro-optic material, said body having at least two plane opposing faces and two plane end faces normal to said opposing faces, at least one of said opposing faces being provided with a number of electrical contact patterns which in selected combinations combine to define at least two tangentially divergent paths having a common origin, said paths at their ends being substantially normal to the end faces, the other of said opposing faces having electrical contact means thereon whereby an electric field may be applied to the body between a selected combination of electrical contact patterns on the one opposing face and the electrical contact means on the other opposing face. 
     Embodiment of the invention will now be described with reference to the accompanying drawings, in which: 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates a simple electro-optic switch according to the invention, and 
     FIG. 2 illustrates a more complex switch employing multiple internal reflections. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In the arrangement shown in FIG. 1 a rectangular body of electro-optic material 1, e.g. lithium niobate, has a set of metal contact patterns 2,3 and 4 deposited on one longitudinal face (the &#34;top&#34; face). The opposing (&#34;bottom&#34;) face either has a corresponding set of metal patterns or a metal ground plane thereon. Optical fibers 5, 6 and 7 have their ends aligned with the ends of optical paths defined in the body when an electric field is applied thereto by connecting the metal contacts on the top and bottom faces to a voltage source. If the electric field is applied via contacts 2 and 3 only on the top face and corresponding contacts on the bottom face (or the ground plane, whichever is the case) the resulting electro-optic effect forms the equivalent of an optical waveguide within the body, the shape of the waveguide following the shape of the contacts 2 and 3. Thus light entering the body 1 from the fibre 5 is guided through the body to emerge opposite the end of fibre 6. If now the electrical connections are changed from contacts 2 and 3 to contacts 2 and 4 a new waveguide path is defined, the light emerging opposite the end of fibre 7. 
     In practice contact 2, being common to both light paths, is left permanently connected to the voltage source while the electrical switching is confined to contacts 3 and 4 only. The allowable curvature of the contacts 3 and 4 is dependent on the effective change in refracted index in the bulk material. Although mention has been made only of metal contacts on lithium niobate other structures are envisaged, e.g. Schottky barrier depletion strips on a body of semiconductor materials. 
     The principal difficulty with the configuration of FIG. 1 is that for a reasonable field the change in refractive index Δ n is small, the permissible radius of curvature is therefore large and the device must be physically fairly long to achieve separation of paths. To overcome this, the configuration of FIG. 2 utilizes multiple reflections within the body to double cumulatively the incremental electro-optic deflections. The contacts 22 are common to both paths and are permanently connected to the voltage source while the contacts 23 and 24 are alternatively connected to the voltage source to effect the optical switching. It should be noted that in fact the sides of the contacts would normally be arcs of circles of large radius, not straight lines as drawn in the figure for the sake of simplicity. The end faces of the body 21 are of necessity angled with respect to the side faces of the body to introduce the required internal reflections, though these end faces are, of course, normal to the top and bottom faces. 
     Electro-optic switches according to the invention combine the features of electro-optical activation and waveguide configuration. The switch illustrated in FIG. 2 also includes the feature of passive amplification.