Abstract: A compressor is driven by a brushless electric motor which includes a stator and rotor mounted in a closed housing. An optical fiber device detects the rotational position of the rotor by transmitting light into the housing from an outside light source and directing that light toward a surface of the rotor which has light reflecting and non-reflecting sections. The optical fiber device transmits reflected light out of the housing and to a photoelectric converting element. The optical fiber device comprises an internal optical fiber segment disposed within the housing, and an external optical fiber segment disposed outside of the housing. Light is transmitted between the internal and external segments by positioning respective ends of those segments in mutually facing relationship on opposite sides of a transparent window member disposed in the housing.