Passive optical network using loop back of multi-wavelength light generated at central office

A passive optical network including a central office and at least one subscriber-side apparatus connected with the central office through an optical fiber link for communication upstream from the subscriber-side apparatus to the central office and downstream from the central office to the subscriber-side apparatus, in which the subscriber-side apparatus performs communication with the central office based on wavelength-division-multiplexed optical signals, the central office comprising:

• a routing section, provided with first to fourth multiplexing ports, for demultiplexing multi-wavelength light inputted through the fourth multiplexing port into a plurality of channels, for amplifying and multiplexing each of the demultiplexed channels, for outputting the results through the first multiplexing port, for demultiplexing and outputting upstream optical signals inputted through the third multiplexing port, for multiplexing channels of downstream optical signals and for outputting the multiplexed channels through the second multiplexing port;
• a splitting section, provided with first to third splitting ports and arranged on a loop optical waveguide connecting the first and fourth multiplexing port with each other, for causing some of multi-wavelength light inputted into the first splitting port to be outputted through the second splitting port and for causing the remaining portion of multi-wavelength light to be outputted through the third splitting port connected with the fourth multiplexing port;
• a circulator for causing the multi-wavelength light inputted from the second splitting port to be transmitted to the subscriber-side apparatus and for causing upstream optical signals received from the subscriber-side apparatus to be outputted to the third multiplexing port.