LIGHT TRANSMITTING DEVICE

PURPOSE:To adjust accurately the optical coupling by spreading the light from a light source with an optical member to make this light incident to an optical fiber group for light transmission and that for monitor and monitoring the optical coupling state of the optical fiber group for light transmission on a basis of the optical signal. CONSTITUTION:A lens 31 is held in a lens holding cylinder 32, which is attached to the laser emission exit of a laser device 1, vertically to the emission direction of the laser light. An optical fiber bundle 33 consists of an optical fiber group 34 for light transmission and an optical fiber group 35 for monitor, and this optical fiber bundle 33 is attached to a jig 37, which is fixed to the end part of the lens holding cylinder 32 by a screw 36 so that the center of the optical fiber bundle 33 coincides with the optical axis of the lens 31, and the optical fiber bundle 33 is fixed by a screw 38. The optical fiber group 34 for light transmission consisting of optical fibers 34a-34g is formed in the center part on the incidence end face of the optical fiber bundle 33, and the optical fiber group 35 for monitor consisting of optical fibers 35a-35h is formed on the outside of this optical fiber group 34 to surround this optical fiber group 34.