An optical process sensor for measuring at least one measured variable of a medium in a container includes: a housing; a light source in the housing for emitting transmission light; a light detector in the housing for receiving reception light; and an interface including a first mechanical section, which is an integrated part of the housing, and a first optical section having a first path and a first light guide, wherein the first light guide is configured such that transmission light is guided from the light source into the first path via the first light guide and decouples transmission light from the housing, and having a second path and a second light guide, wherein the second light guide is configured such that reception light is coupled into the interior of the housing and guided from the second path to the light detector via the second light guide.