SEMICONDUCTOR LASER MODULE

PURPOSE:To prevent the generation of noises by unnecessary waves and to assure stable oscillation by providing a band-pass optical filter which allows the passage of only the exit light at the intermediate point of an optical path from a semiconductor laser element to an optical fiber. CONSTITUTION:The band-pass optical filter 3 which allows the passage of only the exit light is provided at the intermediate point of the optical path from the semiconductor laser element to the optical fiber 6. The exit light emitted with a spreading angle of about 10 to 40 deg. from an LD chip 1 is made by a lens 2 into collimated beams of light which are made incident to the band- pass optical filter 3. The arrival of the unnecessary waves spreading in a broad wavelength band at the semiconductor laser element is prevented in this way even if such waves enter from the outside.