An actuator was built that positions three fiber optic bundles in front of an optical sensor at different times. The design is such that while the sensor views one bundle, it does not see the light from the other two bundles. The device may be described as a linear-displacement, tandem-mounted, solenoid-actuated optical switch. It is the optical equivalent of a single-pole triple-throw electrical switch. Its operation is based upon a three-position linear displacement. The displacement is the result of allowing the termination block of the fiber optic bundles and one pull-type solenoid to be mounted on near-frictionless slider tables. Another solenoid mounted behind the first one displaces these two items so that three positions are possible. Springs return the system to its initial position, predetermined by stop blocks. The solenoids are energized by 120 V ac and controlled by a simple relay circuit that is prompted by a computer.