A cost-effective photosensor system for rotor position detection includes securing an aperture assembly to an off-the-shelf infrared radiation-emitting component and/or an off-the-shelf infrared radiation-detecting component. The application discloses an aperture assembly that may be stamped from a thin, opaque, elongated piece of plastic having an aperture window through which a radiation beam may pass and be focused. The aperture assembly also has a locking system for securing the assembly to the off-the-shelf photosensor system component, and an alignment system to direct the infrared radiation beam. A replaceable stamped aperture assembly for use in a rotor-sensing system and a method of providing a replaceable aperture assembly and securing it to an infrared component of a photosensor system are also disclosed.