PURPOSE:To decrease the number of parts by simplifying constitution by arranging a half-mirror and total reflective mirror in parallel and at a prescribed interval, and by providing beam transmitters at equal intervals. CONSTITUTION:Half-mirror and reflective mirror 16 and 17 are arranged in parallel and at prescribed interval (t), and optical fibers 1-4 radiating digital light beams a1-a4 are held at prescribed angle theta deg. to the mirror surface and arranged at equal intervals (d). Digital light beams a1-a4 are incident to half-mirror 16 and totally reflected by total reflective mirror 17; light beam a1 is passed through and reflected by half-mirror 16 repeated four times to obtain output (b), which has 1/16 light intensity. Similarly, light beams a2, a3 and a4 are reduced to 1/8, 1/4 and 1/2, respectively. Then, the intensity of light beams a1-a4 are added together to obtain analog light signal (b) which corresponds to digital beams a1-a4. This constitution is simplified and decreases the number of parts even if the number of bits is large.
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