Channel gain control for an optical communications system utilizing frequency division multiplexing

• US 7,228,077 B2
• Filed: 05/11/2001
• Issued: 06/05/2007
• Est. Priority Date: 05/12/2000
• Status: Expired due to Term

• Current Assignee: Far North Patents, LLC
• Original Assignee: Forster Energy LLC (Intellectual Ventures LLC)
• Inventors: Newell, Laurence J., Coward, James F.
• Primary Examiner(s): Bello; Agustin
• Application Number:
  US09/854,153
• Publication Number:
  US 20020012493A1
• Time in Patent Office: 2,216 Days
• Field of Search: 398/13, 398/14, 398/15, 398/16, 398/28, 398/29, 398/30, 398/32, 398/34, 398/38, 398158-162, 398192-198, 398/81
• US Class Current: 398/159
• 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. In an optical fiber communications system including an optical fiber, a method for compensating for dispersion effects in the optical fiber, the method comprising:

receiving at least two low-speed channels, each low-speed channel allocated a different frequency band of an optical fiber communications system for transmission across the communications system;

for each low-speed channel, estimating attenuation caused by dispersion resulting from transmission of the low-speed channel across the optical fiber in the frequency band allocated to the low-speed channel;

adjusting a power of each low-speed channel to compensate for the estimated attenuation caused by dispersion; and

frequency division multiplexing the power-adjusted low-speed channels to produce an electrical high-speed channel for transmission across the communications system.

2. The method of claim 1 wherein the step of adjusting a power of each low-speed channel comprises applying a gain to each low-speed channel which is equal in magnitude to the estimated attenuation for that low-speed channel.

3. The method of claim 2 wherein the step of adjusting a power of each low-speed channel comprises applying a constant gain to each low-speed channel which is equal in magnitude to the estimated attenuation at a center frequency of the frequency band allocated to the low-speed channel.

4. The method of claim 1 wherein the step of adjusting a power of each low-speed channel comprises applying a gain ramp to the low-speed channels.

5. The method of claim 1 wherein the step of estimating an attenuation caused by dispersion comprises estimating an attenuation caused by chromatic dispersion.

6. The method of claim 1 wherein the step of estimating an attenuation caused by dispersion comprises estimating an attenuation caused by polarization mode dispersion.

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

a variable gain block for adjusting a power of each low-speed channel to compensate for an estimated attenuation caused by dispersion resulting from transmission of the low-speed channel across an optical fiber in a frequency band allocated to the low-speed channel; and

a FDM multiplexer coupled to the variable gain block for combining the power-adjusted low-speed channels into an electrical high-speed channel suitable for transmission across the communications system.

8. The communications system of claim 7 wherein the variable gain block applies a gain to each low-speed channel which is equal in magnitude to the estimated attenuation for that low-speed channel.

9. The communications system of claim 8 wherein the variable gain block applies a constant gain to each low-speed channel which is equal in magnitude to the estimated attenuation at a center frequency of the frequency band allocated to the low-speed channel.

10. The communications system of claim 7 wherein the variable gain block applies a gain ramp to the low-speed channels.

11. The communications system of claim 7 wherein the variable gain block is for adjusting a power of each low-speed channel to compensate for an estimated attenuation caused by chromatic dispersion.

12. The communications system of claim 7 wherein the variable gain block is for adjusting a power of each low-speed channel to compensate for an estimated attenuation caused by polarization mode dispersion.