Masked ion beam lithography (MIBL) was employed to fabricate optical filters as a critical component of an energy conversion system which utilizes semiconductor photovoltaics. This article will describe the operation and novel application of these devices and the MIBL pilot production line being facilitized. The conversion concept, thermophotovoltaics (TPV), when coupled with these MIBL produced bandpass filters, is capable of converting heat to electrical power with >20% conversion efficiency. The EDTEK TPV filter is based on a high density array of slotted antenna elements patterned into a single layer of thin gold film.