SYNCHRONIZING NODES IN AN OPTICAL COMMUNICATIONS SYSTEM UTILIZING FREQUENCY DIVISION MULTIPLEXING

• US 20070154223A1
• Filed: 03/07/2007
• Published: 07/05/2007
• Est. Priority Date: 05/12/2000
• Status: Active Grant

• Current Assignee: Far North Patents, LLC
• Original Assignee: Forster Energy LLC (Intellectual Ventures LLC)
• Inventors: Coward, James, Newell, Laurence
• Granted Patent: US 7,664,403 B2
• Time in Patent Office: Days
• US Class Current: 398/147
• CPC Class Codes: B82Y 15/00 Nanotechnology for interacting, sensing or actuating, e.g. quantum dots as markers in protein assays or molecular motors
• CPC Class Codes: H04B 10/2507 for the reduction or elimination of distortion or dispersion
• CPC Class Codes: H04B 10/2513 due to chromatic dispersion
• CPC Class Codes: H04B 10/2569 due to polarisation mode dispersion [PMD]
• CPC Class Codes: H04J 1/065 Synchronisation of carrier sources at the receiving station with the carrier source at the transmitting station
• CPC Class Codes: H04J 1/14 Arrangements providing for calling or supervisory signals
• CPC Class Codes: H04J 14/02 Wavelength-division multiplex systems
• CPC Class Codes: H04J 14/0221 Power control, e.g. to keep the total optical power constant
• CPC Class Codes: H04J 14/0298 with sub-carrier multiplexing [SCM]
• CPC Class Codes: H04J 3/0685 Clock or time synchronisation in a node; Intranode synchronisation
• CPC Class Codes: H04L 5/06 the signals being represented by different frequencies combined with time-division multiplexing H04L5/26
• CPC Class Codes: H04L 61/50 Address allocation

Abstract

Attenuation caused by dispersion in an optical fiber communications system is compensated. A number of low-speed channels is to be transmitted across an optical fiber. Each low-speed channel is allocated a different frequency band for transmission. The attenuation caused by dispersion is estimated for each of the frequency bands. The power of each low-speed channel is adjusted to compensate for the estimated attenuation. The power-adjusted low-speed channels are frequency division multiplexed together to produce an electrical high-speed channel suitable for transmission across the communications system.

Claims

1-12. -12. (canceled)

13. In an optical fiber communications system including a transmitter node coupled to a receiver node by an optical fiber, a method for synchronizing the receiver node with the transmitter node, the method comprising:

at the transmitter node;

generating a reference signal;

synchronizing the transmitter node with the reference signal;

wherein said synchronizing the transmitter node comprises adjusting the data rate of a data signal to match the rate of the reference signal;

modulating the reference signal and the data signal onto an optical signal; and

transmitting the optical signal across the optical fiber to the receiver node; and

at the receiver node;

receiving the optical signal;

recovering the reference signal and the data signal from the optical signal; and

synchronizing the receiver node with the recovered reference signal;

wherein said synchronizing the receiver node comprises adjusting the data rate of the recovered data signal to match the rate of the recovered reference signal.

14. The method of claim 13 wherein:

each of the transmitter node and the receiver node includes a local oscillator;

synchronizing the transmitter node with the reference signal comprises synchronizing a local oscillator at the transmitter node with the reference signal; and

synchronizing the receiver node with the recovered reference signal comprises synchronizing a local oscillator at the receiver node with the recovered reference signal.

15. The method of claim 13 wherein:

modulating the reference signal and the data signal onto an optical signal comprises;

generating a harmonic of the reference signal; and

modulating the harmonic onto the optical signal; and

recovering the reference signal and the data signal from the optical signal comprises;

recovering the harmonic from the optical signal; and

frequency dividing the harmonic to recover the reference signal.

16. The method of claim 13 wherein:

modulating the reference signal and the data signal onto an optical signal comprises;

frequency division multiplexing the reference signal with a plurality of electrical low-speed channels to form an electrical high-speed channel; and

converting the electrical high-speed channel from electrical to optical form to form the optical signal; and

recovering the reference signal and the data signal from the optical signal comprises;

converting the optical signal from optical to electrical form to recover the electrical high-speed channel; and

frequency division demultiplexing the reference signal from the electrical high-speed channel.

17. The method of claim 16 wherein, in the electrical high-speed channel, the reference signal is located at a frequency lower than that of the electrical low-speed channels.

18. The method of claim 13 wherein:

each of the transmitter node and the receiver node includes a local oscillator;

synchronizing the transmitter node with the reference signal comprises locking a local oscillator used in the transmitter node to the reference signal; and

synchronizing the receiver node with the recovered reference signal comprises locking a local oscillator used in the receiver node to the recovered reference signal.

19. The method of claim 18 wherein:

modulating the reference signal onto an optical signal comprises;

generating a harmonic of the reference signal; and

modulating the harmonic onto the optical signal; and

recovering the reference signal from the optical signal comprises;

recovering the harmonic from the optical signal; and

frequency dividing the harmonic to recover the reference signal.

20. The method of claim 19 wherein:

the substep of modulating the harmonic onto an optical signal comprises;

frequency division multiplexing the harmonic with a plurality of electrical low-speed channels to form an electrical high-speed channel; and

converting the electrical high-speed channel from electrical to optical form to form the optical signal; and

the substep of recovering the harmonic from the optical signal comprises;

converting the optical signal from optical to electrical form to recover the electrical high-speed channel; and

frequency division demultiplexing the harmonic from the electrical high-speed channel.

21. The method of claim 20 wherein, in the electrical high-speed channel, the harmonic is located at a frequency lower than that of the electrical low-speed channels.

22. The method of claim 20 wherein each of the electrical low-speed channels and the harmonic is allocated a different frequency band within the electrical high-speed channel and within the optical signal.

23. An optical fiber communications system for transmitting at least two low-speed channels across the communications system, the communications system comprising:

a transmitter node including;

a local oscillator for generating a reference signal; and

an FDM multiplexer coupled to the local oscillator for combining the low-speed channels with the reference signal into an electrical high-speed channel; and

a receiver node coupled to the transmitter node by an optical fiber, the receiver node including;

an FDM demultiplexer for recovering the reference signal from the electrical high-speed channel;

a local oscillator; and

electronics coupled to the local oscillator and the FDM demultiplexer for synchronizing the local oscillator with the recovered reference signal.

24. The optical fiber communications system of claim 23 wherein:

the transmitter node further includes;

electronics coupled between the local oscillator and the FDM multiplexer for generating a pilot tone from a harmonic of the reference signal, wherein the FDM multiplexer combines the low-speed channels with the pilot tone into an electrical high-speed channel; and

an E/O converter coupled to the FDM multiplexer for converting the electrical high-speed channel into an optical high-speed channel; and

the receiver node further includes;

an O/E converter coupled to the FDM demultiplexer for receiving the optical high-speed channel and converting it to the electrical high-speed channel;

wherein the FDM demultiplexer recovers the pilot tone from the electrical high-speed channel and the electronics in the receiver node recover the reference signal from the pilot tone.

25. The optical fiber communications system of claim 24 wherein, in the electrical high-speed channel, the pilot tone is located at a frequency lower than that of the electrical low-speed channels.

26. The optical fiber communications system of claim 24 wherein each of the electrical low-speed channels and the pilot tone is allocated a different frequency band within the electrical high-speed channel and within the optical high-speed channel.