Optical communication system

1. An optical communication system comprising an optical line terminal (OLT) connected to a trunk optical fiber, and a plurality of optical network terminals (ONTs) connected to branched optical fibers diverged from said trunk optical fiber,

wherein each of said ONTs comprises:

a plurality of code-division spreaders, each having a different spreading code as allocated by the OLT;

a reception processing unit that selectively distributes transmission data to the plurality of code-division spreaders;

at least one optical transmitter that transmits a signal spread with a code to said branched optical fiber as an optical signal of a carrier wavelength different from that of the other optical transmitters; and

a signal multiplexing unit that selectively supplies output of the plurality of code-division spreaders to the optical transmitter,

wherein each ONT converts the transmission data into a CDMA signal by the plurality of code-division spreaders having different spreading codes, and converts the CDMA signal into an optical signal by the optical transmitter having a carrier wavelength allocated by the OLT,

wherein said OLT comprises:

an optical receiver that receives a wavelength-division-multiplexed CDMA signal from said trunk optical fiber and outputs an output signal; and

a plurality of despreaders connected to the optical receiver and different in their spreading code, each of the despreaders reproducing a CDMA signal corresponding to its spreading code from the output signal of said optical receiver, and

wherein each of said ONTs has a flow identifier table indicating the correspondence between flow identifiers of transmission data and spreading codes, and said reception processing unit correlates said transmission data and said code-division spreader according to the flow identifier table.

2. The optical communication system according to claim 1 ,

wherein, each of said ONTs includes a plurality of optical transmitters different in their carrier wavelength, and said signal multiplexing unit selectively supplies outputs of the plurality of code-division spreaders to the plurality of optical transmitters; and

wherein each of said ONTs converts said transmission data into a CDMA signal by said code-division spreader having a spreading code allocated by the OLT, and converts the CDMA signal into an optical signal by said optical transmitter having a carrier wavelength allocated from said OLT.

3. The optical communication system according to claim 1 ,

wherein said OLT is provided with a management table for storing a carrier wavelength and a spreading code allocated to each of said ONTs, in association with an identifier of the ONT.

4. The optical communication system according to claim 1 ,

wherein each of said optical transmitters is composed of a laser element adjustable its oscillation wavelength, and

wherein each of said ONTs controls each of said laser elements so that the optical transmitter has a carrier wavelength allocated in advance.

5. The optical communication system according to claim 3 ,

wherein each of said ONTs changes said oscillation wavelength by controlling temperature of each of said laser elements.

6. The optical communication system according to claim 2 ,

wherein each of said ONTs has a wavelength allocation table indicating the correspondence between spreading codes and carrier wavelengths, and said signal multiplexing unit correlates said code-division spreaders and said optical transmitters according to the wavelength allocation table.

7. The optical communication system according to claim 2 ,

wherein said OLT is provided with a management table for storing a carrier wavelength and a spreading code allocated to each of said ONTs, in association with an identifier of the ONT.

8. The optical communication system according to claim 2 ,

wherein each of said optical transmitters is composed of a laser element adjustable its oscillation wavelength, and

wherein each of said ONTs controls each of said laser elements so that the optical transmitter has a carrier wavelength allocated in advance.

9. The optical communication system according to claim 7 ,

wherein each of said ONTs changes said oscillation wavelength by controlling temperature of each of said laser elements.

10. An optical line terminal (OLT) connected to a trunk optical fiber in an optical communication system having a plurality of optical network terminals (ONTs) connected to branched optical fibers diverged from said trunk optical fiber, each of said ONTs having a plurality of code-division spreaders, each having a different spreading code; a reception processing unit that selectively distributes transmission data to the plurality of code-division spreaders; at least one optical transmitter that transmits a signal spread with a code to said branched optical fiber as an optical signal of a carrier wavelength different from that of the other optical transmitters; and a signal multiplexing unit that selectively supplies output of the plurality of code-division spreaders to the optical transmitter, wherein each ONT converts the transmission data into a CDMA signal by the plurality of code-division spreaders having different spreading codes, and converts the CDMA signal into an optical signal by the optical transmitter having a carrier wavelength allocated by the OLT,

said OLT comprising:

an optical receiver that receives a wavelength-division-multiplexed CDMA signal from said trunk optical fiber and outputs an output signal; and

a plurality of despreaders connected to the optical receiver and different in their spreading code, each of the despreaders reproducing a CDMA signal corresponding to its spreading code from the output signal of said optical receiver,

wherein the OLT allocates the different spreading codes to the plurality of code-division spreaders of each ONT, and

wherein each of said ONTs has a flow identifier table indicating the correspondence between flow identifiers of transmission data and spreading codes, and said reception processing unit correlates said transmission data and said code-division spreader according to the flow identifier table.

11. An optical network terminal (ONT) in an optical communication system comprising an optical line terminal (OLT) connected to a trunk optical fiber, and having a plurality of optical network terminals (ONTs) connected to branched optical fibers diverged from said trunk optical fiber, the OLT having an optical receiver that receives a wavelength-division-multiplexed CDMA signal from said trunk optical fiber and outputs an output signal; and a plurality of despreaders connected to the optical receiver and different in their spreading code, each of the despreaders reproducing a CDMA signal corresponding to its spreading code from the output signal of said optical receiver,

said ONT comprising:

a plurality of code-division spreaders, each having a different spreading code as allocated by the OLT;

a reception processing unit that selectively distributes transmission data to the plurality of code-division spreaders;

at least one optical transmitter that transmits a signal spread with a code to said branched optical fiber as an optical signal of a carrier wavelength different from that of the other optical transmitters; and

a signal multiplexing unit that selectively supplies output of the plurality of code-division spreaders to the optical transmitter,

wherein the ONT converts the transmission data into a CDMA signal by the plurality of code-division spreaders having different spreading codes, and converts the CDMA signal into an optical signal by the optical transmitter having a carrier wavelength allocated by the OLT, and

wherein each of said ONTs has a flow identifier table indicating the correspondence between flow identifiers of transmission data and spreading codes, and said reception processing unit correlates said transmission data and said code-division spreader according to the flow identifier table.