COUPLING LENS AND SEMICONDUCTOR LASER MODULE

摘要

A coupling lens (104) used for coupling the emerging light beam emerging from a semiconductor laser (101) to an optical fiber (108). The coupling lens (104) comprises a single lens integral with a diffraction lens composed of concentric ring bands on the plane of incidence or plane of emergence of the single lens. The diffraction lens has a positive refractive power. The relief function of the diffraction lens is generally an isosceles triangle. The depth W of the relief function satisfies the inequalities (1) 0.6 ≤ W(n-1)/ lambda ≤ 1.0 where n is the index of refraction of the lens material, and lambda is the wavelength of the semiconductor laser. When the coupling lens is used for a semiconductor laser module, the output power of the module can be so controlled as to conform with the safety standards even if the attenuation film, polarizer, or optical fiber comes off without using any control circuit for automatically stopping the lasing of the laser.