Switchable holograms offer the possibility of real-time electro-optical control of diffractive optic components. We have recently demonstrated recording of diffractive optic components. We have recently demonstrated recording of transmission holographic Bragg gratings in a material system consisting of a photoinitiator dye, co-initiator, a chain extender, a multifunctional acrylate and a low molecular weight nematic liquid crystal. Low voltage scanning electron microscopy studies have shown that the gratings consist of periodic polymer-dispersed liquid crystal (PDLC) planes. Electrical switching of a first order Bragg diffracted beam into the zero-order with an applied field of 10 V/micrometers was observed. Addition of a surfactant to the pre-polymer syrup reduces the switching field to approximately 5 V/micrometers . Fast response times of the order of microseconds were observed for switching and relaxation. In this paper, we have demonstrated the concept of a switchable guided substrate-mode coupler by writing a slanted transmission grating. The diffracted light form this grating is trapped in a glass slab by total internal reflection. The added electrical switchability of PDLC grating allows for the effective control of the intensity and position for light into or out of the substrate.