An optical switch for routing optical signals between optical fibers is shown. Signals are guided internally in an optically transparent substrate by buried waveguides that are directly coupled to the optical fibers. These waveguides form a 3-dimensional optical routing structure internal to the substrate. Signals are coupled between adjacent waveguides by total internal reflection at the surfaces of the substrate. A moveable diffraction grating is coupled to these optical signals at points of total internal reflection via evanescent coupling. This coupling causes a change in direction of the optical signal and routes the signal to the desired waveguide. Known techniques can be used to form the waveguides by writing them with a pulsed laser. Local heating causes a permanent increase in refractive index that forms a single mode waveguide structure. The resulting device has low losses and can be formed by low cost MEMs processes.