film 804 fig8 b shows an embodiment in which the edge emitter 800 is coupled to an optical structure in the form of a hemispherical lens 806 via at least one coupling film 808 the optical structures 804 and 806 serve to take light 810 which is incident normally and increase the angle of incidence with which it strikes the active area to which it is coupled light which is incident on a surface at higher angles of incidence has enhanced ability to induce surface plasmons consequently the efficiency of this effect can be increased by proper design of the optical structure these structures may take on arbitrary shapes depending on the expected average angle of incidence on the structure as a whole during operation the structure is generally made from a material which is transparent at the wavelengths of interest in addition to optical structure designs based on refraction designs exploiting the phenomena of diffraction and interference are also useful and may present design advantages the coupling films 804 and 808 are made of materials that are also optically transparent to allow radiation to pass thorough to the edge emitter on which it resides the thickness and refractive properties of these films are chosen to enhance coupling of the light into the surface in general this requires that at least one of the films be of a material with a refractive index less than that of the optical structure one of the films may also be air referring now to fig9 a a rectenna 900 is shown in accordance with one embodiment of the invention the rectenna 900 is designed to ensure greater conversion of energy from incident light the rectenna 900 comprises a transparent collector emitter structure indicated generally by reference.