LIGHT TRANSMISSION DEVICE

PURPOSE:To allow the transmission of the light signal of an adequate level to an optical link for signal reception by using optical fibers for repeating, the core diameter of at least one of which is smaller than the core diameter of an optical fiber for transmission and using an optical fiber which is smaller in numerical aperture than the optical fiber for transmission as the optical fiber for repeating of an optical receiver. CONSTITUTION:This transmission device has the optical link 2 for signal transmission and the optical fiber 4 for repeating to connect an optical output part 3 of the optical signal receiver. The fiber 5 which has the core diameter or numerical aperture varying according to the transmission distance is made selectively usable for at least one of the optical fibers 8 for repeating connecting the light input part 7 of the optical receiver and the optical link 9 for signal reception. Namely, the fiber having the core diameter further smaller than the core diameter of the optical fiber 5 for transmission is used for at least one of the optical fibers 4, 8 for repeating. And the optical fiber having the numerical aperture smaller than the numerical aperture of the optical fiber 5 for transmission is used for the optical fiber 8 for repeating connecting the optical input part 7 of the optical signal receiver and the optical link 9 for signal reception. The loss with the optical fiber 5 for transmission is generated in this way and the light signal of the adequate level is transmitted to the optical link 9 for signal reception.