Patent ID: 7231149

Claim:
A bidirectional optical add-drop multiplexer for WDM (wavelength division multiplexing) optical signals being transmitted in directions opposite to each other through different WDM channels of one optical transmission line in an optical WDM bidirectional ring network, said multiplexer comprising: first and second optical circulators each having four ports, and among the ports, respective first ports for input of an optical signal having a wavelength to be added; a first WDD (wavelength division demultiplexer) which drops an optical signal having a specific wavelength by demultiplexing optical WDM signals transmitted through a first portion of said one optical transmission line, outputs to a third port of the first optical circulator optical signals not being dropped, and transmits to said first portion optical signals from a second portion of said optical transmission line inputted from the third port of the first optical circulator; a first optical wavelength selector which is connected between a fourth port of the first optical circulator and a second port of the second optical circulator, reflects an optical signal that is to be added among optical signals inputted from the third port of the first optical circulator, and passes optical signals not being added; a second WDD which drops an optical signal having a specific wavelength by demultiplexing optical WDM signals transmitted through said second portion, outputs to a third port of the second optical circulator optical signals not being dropped, and transmits to said second portion optical signals inputted from the third port of the second optical circulator; and a second optical wavelength selector which is connected between a second port of the first optical circulator and a fourth port of the second optical circulator, reflects an optical signal having a wavelength that is to be added among the optical signals inputted from the third port of the second optical circulator, and passes optical signals not being added.