An optical element having a variable index of refraction. The optical element utilizes a layer of a transparent dielectric material having an index of refraction determined by the concentration of hydrogen in the dielectric material. A layer of a hydrogen reservoir medium that includes a material that acts as a source or a sink for hydrogen is placed adjacent to the transparent dielectric layer. The reservoir medium accepts hydrogen from the transparent layer in response to a first electric field being applied across the transparent layer and reservoir layer and donates hydrogen to the transparent layer in response to a second electric field being applied across the transparent layer and the reservoir layer. The electric fields are generated by applying appropriate potentials across first and second electrodes that sandwich the dielectric and reservoir layers. The preferred reservoir material is KOH. The transparent dielectric material preferably includes a material chosen from the group consisting of hydrides of an alkali, alkaline-earth, rare-earth metals, and alloys thereof.