Patent ID: 6327060
Filing Date: 2001-12-04
Classification: H04B

Abstract:
An optical transmission system comprising:an optical transmission line having up and down systems, means for looping back a supervisory light between the up and down systems, and an optical branching, unit for adding and dropping a specific wavelength, said optical branching unit having a bypass line for bypassing the supervisory light;a trunk station at each end of the optical transmission line; anda branch station connected to the optical branching unit, wherein the optical branching, unit further comprises in each of the up and down systems:a reflecting means for selectively reflecting the specific wavelength;means for dropping light of said specific wavelength;means for adding light of said specific wavelength; andfirst and second optical circulators each having first, second, third and fourth in/out ports, each said circulator adapted for outputting to said second port light inputted into the first port, for outputting to said third port light inputted into the second port, and for outputting to said first port light inputted into the fourth port, the first optical circulator having the first port connected to an up flow side of the optical transmission line, the second port connected to one end of the reflecting means, the third port connected to the means for dropping light, and the fourth port connected to one end of the bypass line, and the second optical circulator having the first port connected to the other end of the reflecting means, the second port connected to a down flow side of the optical transmission line, the third port connected to the other end of the bypass line, and the fourth port connected to the means for adding light, andwherein the means for adding light and the means for dropping light each comprise an optical amplifier, and further comprise a first loop back circuit between an output stage of the optical amplifier of the means for dropping light of the up system and an output stage of the optical amplifier of the means for adding light of the down system, and a second loop back circuit between an output stage of the optical amplifier of the means for dropping light of the down system and an output stage of the optical amplifier of the means for adding light of the up system.