Patent ID: 7277639

Claim:
A bi-directional optical add/drop multiplexer which is connected to an optical fiber for transmitting optical signals multiplexed in a wavelength division multiplexing optical network and which performs adding/dropping of the optical signals, the bi-directional optical add/drop multiplexer comprising: a first wavelength division multiplexer provided with a multiplexing port providing a path for a forward or backward optical signal and with a plurality of demultiplexing ports, each providing a path for demultiplexed channels; a plurality of add/drop parts, each performing adding or dropping of predetermined channels, and connected with the demultiplexing ports of the first wavelength division multiplexer, each said plurality of add/drop parts including: a first coupler connected with a corresponding demultiplexing port of the first wavelength division multiplexer; a second coupler, connected with a corresponding demultiplexing port of the second wavelength division multiplexer, providing a path of a corresponding forward channel and a path of a corresponding backward channel, together with the first coupler; a first optical switch, disposed on the path of the corresponding forward channel, for adding or dropping the corresponding forward channel; and a second optical switch, disposed on the path of the corresponding backward channel, for adding or dropping the corresponding backward channel; and a second wavelength division multiplexer provided with a plurality of demultiplexing ports, each providing a path for demultiplexed channels and with a multiplexing port providing a path for the forward or backward optical signal, the plurality of demultiplexing ports of the second wavelength division multiplexer connected to the plurality of add/drop parts, wherein the first wavelength division multiplexer has a free spectral range equal to that of the second wavelength division multiplexer, in which a wavelength band of the forward optical signals is included in the free spectral range having one period, while a wavelength band of the backward optical signals is included in the free spectral range having another period.