Optical fiber having a lens formed at an end thereof

Abstract

An optical fiber having a lens formed at an end thereof comprises a fiber body including a core and a cladding, and an incident light guide portion having a uniform refractive index and integrally formed at an end portion of the fiber body, wherein the incident light guide portion has a convex surface, and the core has a distal end located within the incident light guide portion at a position close to a focal point of the incident light guide portion. When the incident light guide portion is arranged in alignment with a light source such that an extremity of the convex surface of the incident light guide portion faces a light-emitting surface of the light source, assuming that an X-Y coordinate system is established wherein the X axis coincides with the optical axis of the fiber body and the Y axis coincides with a radius direction of the fiber body, the relationship expressed by the following equation is fulfilled: ##EQU1## where coordinates of the extremity of the convex surface of the incident light guide portion are (0, 0), coordinates of the light-emitting surface of the light source are (-k, 0), coordinates of the distal end of the core are (L, 0), coordinates of an incident point at which light from the light-emitting surface of the light source falls upon the convex surface of the incident light guide portion are (z, r), and the refractive index of the incident light guide portion is n. Accordingly, no phase difference of laser beams occurs when the optical fiber is connected to a semiconductor laser, making it possible to provide a high coupling efficiency optical fiber.