Interleaving bi-directional optical add/drop multiplexer

A bi-directional optical transmission system which comprises a first and a second transmitting/receiving unit for transmitting and receiving an optical signal having a plurality of channels, and a bi-directional optical add/drop multiplexer connected through an optical fiber between the first and second transmitting/receiving unit for adding or dropping a selected one of said plurality of channels, wherein the bi-directional optical add/drop multiplexer comprises:

• a first interleaver for outputting a forward optical signal inputted through a first end connected to the optical fiber to a second end, and outputting a backward optical signal inputted through a third end to the first end;
• a second interleaver for interleaving the forward optical signal inputted through a first end and the backward optical signal inputted through a second end by wavelengths, and outputting the interleaved signals through the third end;
• an optical add/drop multiplexing unit for adding a selected channel to the interleaved optical signal or dropping the selected channel from the interleaved optical signal;
• a third interleaver for outputting the backward optical signal to the first interleaver through a first end, and the forward optical signal through a third end among the channel-modified optical signals received through a second end;
• and
• a fourth interleaver for outputting the backward optical signal inputted through a second end connected to an optical fiber to the second interleaver through a first end, and the forward optical signal inputted from the third interleaver to a third end.