Abstract: The present invention provides a method of controlling light and an apparatus of controlling light capable of extracting sufficiently large and speedy optical responses from the photoresponsive photoelement with a high reproducibility, wherein the control light is emitted from the light source 1, and the signal light from the light source 2. The control light and signal light are converged by the converging lens 7, and illuminated to the film photoelement 8 filled in with the photoresponsive composition. Via the collimate lens 9 and the band-pass filter 20, only the signal light is detected with the photodetector 22. By turning the control light on and off, the transmittance and/or refractive index of the signal light are reversibly increased or decreased, realizing the modulation of photointencity.

Abstract: A reflective optical rotary encoder device detects an angular speed or position of a rotatable member with a light beam applied to and reflected from a reflective optical encoder disc. The reflective optical rotary encoder disc has an annular encoder track for reflecting the light beam, the encoder track being composed of an annular pattern of angularly spaced pit units each including a plurality of radially spaced arcuate pits, and a pit-free annular focus servo track for focusing the light beam onto the encoder track, the focus servo track extending along and being disposed radially substantially centrally in the annular encoder track.

Abstract: An optical detection system for detecting a displacement amount of a movement device with an optical encoder movable in accordance with a movement of the movable device has on a light-reflecting layer a plurality of pits successively strung in a predetermined direction. An optical pickup optically picks up the pit information by irradiating the optical encoder with light beams and receiving reflected light beams from the optical encoder. The optical pickup comprises a light-division device for dividing the light beam from a light-emitting device into three light beams so that the divided three light beams are directed to the pit string to apply three light spots to the pit string. The light-division device is adapted to be rotatable with respect to the optical encoder so that a light passing through the three light spots intersects the pit string at a predetermined angle.