Modular photo interrupters manufactured on mounting strips

A photo interrupter which features at least one transmission element and at least one receiver element separated by an optical transmission path. To ensure a flexible structure with variable characteristics, the photo interrupter features a modular structure comprised of two joinable housing parts. In order to reduce production costs and simplify the production process, the housing parts of the photo interrupter respectively feature one carrier unit each which is designed as a panel of a mounting strip, as well as at least one semiconductor device located on the carrier unit, and a housing body forming the two side surfaces of the photo interrupter, which housing body-in a first partial area of the carrier unit containing the semiconductor device(s)-encloses the carrier unit; at least one semiconductor device of the one housing part will be a transmission element, and at least one semiconductor device of the other housing part will be a receiver element. To enable easy assembly of the two housing parts, at least one of the two housing parts features a connecting part which is mounted on the housing body and forms the base area of the photo interrupter; this connecting part provides a flush joint for the two housing parts.