Bidirectional optical add-drop multiplexer

A bidirectional optical add-drop multiplexer for wave division multiplexing (WDM) 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;
• first WDDs (wavelength division multiplexers), connected in tandem on a first portion of said one optical transmission line, which drop optical signals having specific respective wavelengths, output to a third port of the first optical circulator optical signals not being dropped. and transmit to said first portion optical signals inputted from the third port of the first optical circulator;
• first optical wavelength selectors which are connected between a fourth port of the first optical circulator and a second port of the second optical circulator, reflect one by one in order optical signals that are to be added among optical signals inputted from the third port of the first optical circulator, and pass optical signals not being added;
• second WDDs, connected in tandem on a second portion of said optical transmission line, which drop optical signals having specific respective wavelengths, output to a third port of the second optical circulator optical signals not being dropped, and transmit to a second portion of said optical transmission line optical signals inputted from the third port of the second optical circulator;
• and
• second optical wavelength selectors which are connected between a second port of the first optical circulator and a fourth port of the second optical circulator, reflect optical signals having respective wavelengths that are to be added among the optical signals inputted from the third port of the second optical circulator, and pass optical signals not being added.

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 multiplexer) which drops optical signals having specific respective wavelengths by demultiplexing the 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 inputted from the third port of the first optical circulator;
• first optical wavelength selectors which are connected between a fourth port of the first optical circulator and a second port of the second optical circulator, reflect one by one in order optical signals that are 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 optical signals having specific respective wavelengths by demultiplexing optical signals transmitted through a second portion of said optical transmission line, 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
• second optical wavelength selectors which are connected between a second port of the first optical circulator and a fourth port of the second optical circulator, reflect one by one in order optical signals having specific respective wavelengths that are to be added among the optical signals inputted from the third port of the second optical circulator, and pass optical signals not being added.