Transmission power optimization apparatus and method

• US 7,522,846 B1
• Filed: 12/23/2003
• Issued: 04/21/2009
• Est. Priority Date: 12/23/2003
• Status: Active Grant

• Current Assignee: Ciena Corporation
• Original Assignee: Nortel Networks Limited (Nortel Networks Corporation)
• Inventors: Lewis, Stephen, Bragg, Nigel
• Primary Examiner(s): Tran; Dzung D
• Application Number:
  US10/744,359
• Time in Patent Office: 1,946 Days
• Field of Search: 398/26, 398/27, 398193-195, 398/197, 398/201
• US Class Current: 398/197
• CPC Class Codes: H04B 10/07955 Monitoring or measuring power
• CPC Class Codes: H04J 14/0221 Power control, e.g. to keep the total optical power constant
• CPC Class Codes: H04J 14/02216 by gain equalization

Abstract

A method and system is provided that is capable of controlling transmit power to achieve a desired OSNR at a receive endpoint. The system utilizes the fact that the aggregate power for a plurality of channels is controllable between a transmission point and a receive point in the network, and uses this characteristic to coarsely adjust transmission powers in the network to achieve desired OSNR results.

Claims

1. A method of designing an optical communication path for carrying a plurality of channels, where each channel is used for forwarding a signal, includes the steps of:

transmitting signals on each of the channels from a transmit point to an end point using a Directly Modulated Laser (DML) having a selectable power range comprising a plurality of coarse incremental steps associated with a plurality of output power levels, the transmitted signals having an aggregate power level; and

decreasing deviation of output signal characteristics between a first channel transmitted at a first initial power level and a second channel transmitted at a second initial power level by coarsely modifying the first and second initial transmit power levels by equal but opposite coarse while maintaining the aggregate power level of the transmitted signals.

2. The method of claim 1, wherein the characteristic of the transmitted signal is a measured change in power level of the transmitted signal at the end point.

3. The method according to claim 2, further including the steps of:

following the step of modifying, transmitting each of the signals to the endpoint; and

repeating the steps of transmitting, measuring and modifying until it is determined that the signals in the channels have desirable characteristics.

4. The method of claim 1, wherein the characteristic of the transmitted signal is a measured Bit Error Ratio (BER) of the transmitted signal at the end point.

5. The method of claim 1, wherein the characteristic of the transmitted signal is an estimated change in power level of the transmitted signal based on specifications of the components in a path between the transmit point and the end point.

6. The method of claim 1, wherein the characteristic of the transmitted signal is a measured Signal to Noise Ratio (SNR) of the transmitted signal at the end point.

7. The method of claim 1, further comprising the step of performing any fine tuning of a transmit signal using a Variable Optical Attenuator (VOA) prior to the step of coarsely adjusting.

8. The method of claim 1, wherein the step of coarsely modifying the initial transmit power of the at least one channel to compensate for characteristics of the transmitted signal at the end point includes the step of measuring the characteristic of the channel at the end point.

9. The method according to claim 8, wherein the step of measuring includes the steps of:

measuring each of the plurality of channels at the endpoint;

selecting a pair of channels, with a first channel of the pair having a decreased power at the end point and a second channel of the pair having an increased power at the endpoint;

modifying a first transmit power of the first channel by increasing the first transmit power by a determined amount; and

modifying a second transmit power of the second channel by decreasing the second transmit power by the determined amount.

10. The method of claim 1, wherein the step of coarsely modifying the initial transmit power of the at least one channel to compensate for characteristics of the transmitted signal at the end point includes the steps of estimating the characteristic of the channel at the end point in response to design specifications of the system.

11. The method according to claim 1, wherein the step of coarsely modifying the initial transmit power selects a first transmit power from a predefined set of coarsely distributed alternative transmit powers for transmit the at least one channel.

12. The method according to claim 1, wherein the step of modifying the initial channel power selects a transmit power from a predefined set of coarsely distributed alternative transmit powers for transmit of another one of the plurality channels.

13. An optical network comprising:

a transmitter comprising a plurality of Directly Modulated Lasers (DML which provide transmitted signals having transmit powers selectable by coarse increments, the transmitter for generating a corresponding plurality of signals, each of the signals operating at a different channel frequency, wherein each laser provides a signal having a wavelength and a transmit power in response to a selected increment of the DML to an end point;

a controller, coupled to each of the lasers, the controller for modifying the transmission power used by first and second DMLs by equal but opposite coarse increments to decrease deviation of an output signal characteristic between a first channel transmitted by the first DML and a second channel transmitted the second DML in response to feedback, wherein aggregate power at the end point is unchanged by modifying the transmission power of the first and second DMLs by equal but opposite coarse increments.

14. The optical network of claim 13, wherein the characteristic of the transmitted signal is a measured change in power level of the transmitted signal at the end point.

15. The optical network of claim 13, wherein the characteristic of the transmitted signal is a measured Bit Error Ratio (BER) of the transmitted signal at the end point.

16. The optical network of claim 13, wherein the characteristic of the transmitted signal is an estimated change in power level of the transmitted signal based on specifications of the components in a path between the transmit point and the end point.

17. The optical network of claim 13, wherein the characteristic of the transmitted signal is a measured Signal to Noise Ratio (SNR) of the signal at the end point.

18. The optical network of claim 13, further comprising at least one Variable Optical Attenuator (VOA) coupled prior to the controller.

19. The optical network of claim 13, including means for measuring the characteristic of the channel at the end point.

20. The optical network of claim 13, wherein including means for estimating the characteristic of the channel at the end point in response to design specifications of the system.

21. An apparatus for designing an optical network wherein a plurality of signals are transmitted over a corresponding plurality of channels including:

means for determining, at an endpoint in the optical network, a change in a characteristic of each of the plurality of signals,

means for determining an aggregate power of the plurality of signals, and

means for coarsely modifying the transmission power of at least two of the plurality of signals by equal but opposite coarse increments to reduce deviation in the characteristic between ones of the plurality of signals at the endpoint without changing the aggregate power of the plurality of signals.

22. The apparatus of claim 21, wherein the means for determining and the means for modifying comprise a graphical user interface.

23. The apparatus of claim 21 wherein the plurality of signals are transmitted with a total initial aggregate transmission power, and transmission powers of at least two of the plurality of signals are modified such that the total modified aggregate transmission power of the plurality of signals is equal to the total initial aggregate transmission power.

24. The apparatus of claim 21, wherein the characteristic of the transmitted signal is a measured change in power level of the transmitted signal at the end point.

25. The apparatus of claim 21, wherein the characteristic of the transmitted signal is a measured Bit Error Ratio (BER) of the transmitted signal at the end point.

26. The apparatus of claim 21, wherein the characteristic of the transmitted signal is a measured Signal to Noise Ratio (SNR) at the end point.

27. The apparatus of claim 21, wherein the characteristic of the transmitted signal is an estimated change in power level of the transmitted signal based on specifications of the components in a path between the transmit point and the end point.

28. The apparatus of claim 21, further comprising at least one Variable Optical Attenuator (VOA) coupled prior to the controller.

29. The apparatus of claim 21, including means for measuring the characteristic of the channel at the end point.

30. The apparatus of claim 21, wherein including means for estimating the characteristic of the channel at the end point in response to design specifications of the system.