Method and apparatus for balancing the power of optical channels traversing an optical add drop multiplexer

• US 20050069248A1
• Filed: 08/11/2003
• Published: 03/31/2005
• Est. Priority Date: 08/11/2003
• Status: Active Grant

• Current Assignee: ARRIS Enterprises LLC (CommScope Holding Company, Inc.)
• Original Assignee: General Instrument Corporation (CommScope Holding Company, Inc.)
• Inventors: Gysel, Hermann, Ramachandran, Mani, Jasti, Chandra Sekhar
• Granted Patent: US 7,151,875 B2
• Time in Patent Office: Days
• US Class Current: 385/24
• CPC Class Codes: H04J 14/0201 Add-and-drop multiplexing
• CPC Class Codes: H04J 14/0221 Power control, e.g. to keep the total optical power constant

Abstract

A method and apparatus is provided for power balancing an optical signal wavelength to be added to an OADM having at least one drop port and at least one add port. The method begins by monitoring a power level of a first signal wavelength being dropped on the drop port and a power level of a second signal wavelength being added on the add port. The power level of the first signal wavelength is compared to the power level of the second signal wavelength. Based on the step of comparing, the optical attenuation is adjusted along the add port so that the power level of the second signal wavelength becomes substantially equal to the power level of the first signal wavelength.

Claims

1. A method of power balancing an optical signal wavelength to be added to an OADM having at least one drop port and at least one add port, said method comprising the steps of:

monitoring a power level of a first signal wavelength being dropped on the drop port;

monitoring a power level of a second signal wavelength being added on the add port;

comparing the power level of the first signal wavelength to the power level of the second signal wavelength;

based on the step of comparing, adjusting optical attenuation along the add port so that the power level of the second signal wavelength becomes substantially equal to the power level of the first signal wavelength.

2. The method of claim 1 wherein the step of monitoring the power level of the first signal wavelength comprises the steps of tapping a portion of the power from the first signal wavelength as it traverses the drop port and generating a first electrical reference signal that corresponds to the tapped portion of power of the first signal wavelength.

3. The method of claim 2 wherein the step of monitoring the power level of the second signal wavelength comprises the steps of tapping a portion of the power from the second signal wavelength as it traverses the add port and generating a second electrical reference signal that corresponds to the tapped portion of power of the second signal wavelength.

4. The method of claim 1 wherein the comparing step is performed in the electrical domain.

5. The method of claim 1 wherein the step of adjusting the optical attenuation is performed by a variable optical attenuator coupled to the add port.

6. A method of power balancing an optical signal wavelength to be added to OADM having a plurality of drop ports and at least one add port, said method comprising the steps of:

monitoring a power level on each of the plurality of drop ports;

monitoring a power level of a second signal wavelength being added on the add port;

comparing the power level of at least one first signal wavelength traversing one of the plurality of drop ports to the power level of the second signal wavelength;

based on the step of comparing, adjusting optical attenuation along the add port so that the power level of the second signal wavelength becomes substantially equal to the power level of the first signal wavelength.

7. The method of claim 6 wherein the step of monitoring the power level on each of the plurality of drop orts comprises the steps of tapping a portion of the power traversing each drop port and generating a first electrical reference signal that corresponds to the tapped portion of power.

8. The method of claim 7 wherein the step of monitoring the power level of the second signal wavelength comprises the steps of tapping a portion of the power from the second signal wavelength as it traverses the add port and generating a second electrical reference signal that corresponds to the tapped portion of power of the second signal wavelength.

9. The method of claim 6 wherein the comparing step is performed in the electrical domain.

10. The method of claim 6 wherein the step of adjusting the optical attenuation is performed by a variable optical attenuator coupled to the add port.

11. An optical add drop multiplexer (OADM) comprising:

an input port for receiving a WDM optical signal that includes a plurality of signal wavelengths;

at least one drop port for extracting one of the plurality of signal wavelengths from the WDM optical signal;

at least one add port for inserting an add wavelength into the WDM optical signal;

an output port for transmitting to an external element the WDM optical signal with the add wavelength present and the extracted one of the plurality of wavelengths absent;

a first monitoring arrangement for monitoring a power level of said extracted one of the plurality of signal wavelengths;

a second monitoring arrangement for monitoring a power level of the add wavelength;

a comparator for comparing the power level of said extracted one of the plurality of signal wavelengths to the power level of the add wavelength; and

a variable optical attenuator coupled to the add port for adjusting optical attenuation of the add wavelength in response to a control signal received from the comparator.

12. The OADM of claim 11 wherein said first monitoring arrangement includes a first optical tap located at the drop port and a first photodetector coupled to the optical tap for receiving a portion of said extracted one of the plurality of signal wavelengths.

13. The OADM of claim 11 wherein said second monitoring arrangement includes a second optical tap located at the add port and a second photodetector coupled to the second optical tap for receiving a portion of the add wavelength.

14. The OADM of claim 12 wherein said second monitoring arrangement includes a second optical tap located at the add port and a second photodetector coupled to the second optical tap for receiving a portion of the add wavelength.

15. The OADM of claim 14 wherein said comparator is an electrical comparator electrically coupled to the first and second photodetectors.

16. The OADM of claim 15 wherein said first and second photodetectors are photodiodes.

17. The OADM of claim 11 wherein said control signal adjusts the optical attenuation of the add wavelength so that the power level of the add wavelength is substantially equal to the power level of said extracted one of the plurality of signal wavelengths.

18. An optical add drop multiplexer (OADM) comprising:

an input port for receiving a WDM optical signal that includes a plurality of signal wavelengths;

a plurality of drop ports each extracting one of the plurality of signal wavelengths from the WDM optical signal;

a plurality of add ports each inserting an add signal wavelength into the WDM optical signal;

an output port for transmitting to an external element the WDM optical signal with one or more add wavelengths present and one or more extracted wavelengths absent;

a plurality of first monitoring arrangements each associated with one of the drop ports, each of said first monitoring arrangements monitoring a power level of one of the extracted wavelengths and generating a first reference signal in response thereto;

a plurality of second monitoring arrangements each associated with one of the add ports, each of said second monitoring arrangements monitoring a power level of one of the add wavelengths and generating a second reference signal in response thereto;

a processor receiving the plurality of first reference signals and selecting one of the plurality of first reference signals that represents a non-zero optical power level;

a comparator arrangement for comparing the selected one of the first reference signals to each of the second reference signals; and

a plurality of variable optical attenuators respectively coupled to the plurality of add ports for adjusting optical attenuation of the add wavelengths in response to control signals received from the comparator arrangement.

19. The OADM of claim 18 wherein each of said first monitoring arrangements includes a first optical tap located at one of the drop ports and a first photodetector coupled to the first optical tap for receiving a portion of one of the extracted wavelengths.

20. The OADM of claim 18 wherein each of said second monitoring arrangements includes a second optical tap located at one of the add ports and a second photodetector coupled to the second optical tap for receiving a portion of one of the add wavelengths.

21. The OADM of claim 19 wherein each of said second monitoring arrangements includes a second optical tap located at one of the add ports and a second photodetector coupled to the second optical tap for receiving a portion of one of the add wavelengths.

22. The OADM of claim 21 wherein said comparator arrangement is an electrical comparator electrically coupled to the second photodetectors and an output of the processor.

23. The OADM of claim 21 wherein said first and second photodetectors are photodiodes.

24. The OADM of claim 18 wherein said control signals adjust the optical attenuation of the add wavelengths so that the power level of each of the add wavelengths is substantially equal to the power level of the extracted wavelength associated with said selected first reference signal.

25. An optical add drop multiplexer (OADM) comprising:

an input port for receiving a WDM optical signal that includes a plurality of signal wavelengths;

at least one drop port for extracting one of the plurality of signal wavelengths from the WDM optical signal;

at least one add port for inserting an add wavelength into the WDM optical signal;

an output port for transmitting to an external element the WDM optical signal with the add wavelength present and the extracted one of the plurality of wavelengths absent;

a first monitoring arrangement for monitoring an average power level of the signal wavelengths in said WDM optical signal;

a second monitoring arrangement for monitoring a power level of the add wavelength;

a comparator for comparing the average power level of the signal wavelengths in said WDM signal to the power level of the add wavelength; and

a variable optical attenuator coupled to the add port for adjusting optical attenuation of the add wavelength in response to a control signal received from the comparator.

26. The OADM of claim 25 wherein said first monitoring arrangement includes:

a first optical tap located at the input port;

an optical tunable filter coupled to the first optical tap for receiving a portion of WDM optical signal therefrom;

a first photodetector coupled to the optical tunable filter;

an electric circuit receiving a first reference signal from the first photodetector and generating a second reference signal that is provided to a first input of the comparator.

27. The OADM of claim 25 wherein said first monitoring arrangement includes:

a first optical tap located at the input port;

an optical splitter having an input coupled to the first optical tap for receiving a portion of WDM optical signal therefrom;

an optical tunable filter coupled to a first output of the optical splitter;

a first photodetector coupled to the optical tunable filter;

a second photodetector coupled to a second output of the optical splitter;

an electric circuit receiving first and second reference signals from the first and second photodetectors, respectively, and generating a third reference signal that is provided to a first input of the comparator.

28. The OADM of claim 25 wherein said first monitoring arrangement includes:

a first optical tap located at the output port;

an optical tunable filter coupled to the first optical tap for receiving a portion of WDM optical signal therefrom;

a first photodetector coupled to the optical tunable filter;

an electric circuit receiving a first reference signal from the first photodetector and generating a second reference signal that is provided to a first input of the comparator.

29. The OADM of claim 25 wherein said first monitoring arrangement includes:

a first optical tap located at the output port;

an optical splitter having an input coupled to the first optical tap for receiving a portion of WDM optical signal therefrom;

an optical tunable filter coupled to a first output of the optical splitter;

a first photodetector coupled to the optical tunable filter;

a second photodetector coupled to a second output of the optical splitter;

an electric circuit receiving first and second reference signals from the first and second photodetectors, respectively, and generating a third reference signal that is provided to a first input of the comparator.

30. The OADM of claim 26 wherein said second monitoring arrangement includes a second optical tap located at the add port and a second photodetector coupled to the second optical tap for receiving a portion of the add wavelength.

31. The OADM of claim 27 wherein said second monitoring arrangement includes a second optical tap located at the add port and a third photodetector coupled to the second optical tap for receiving a portion of the add wavelength.

32. The OADM of claim 27 wherein said first and second photodetectors are photodiodes.

33. The OADM of claim 25 wherein said control signal adjusts the optical attenuation of the add wavelength so that the power level of the add wavelength is substantially equal to the average power level of the signal wavelengths in said WDM signal.

34. A method of power balancing an optical signal wavelength to be added to OADM having an input port for receiving a WDM optical signal that includes a plurality of signal wavelengths, at least one drop port, at least one add port, and an output port, said method comprising the steps of:

monitoring an average power level of the signal wavelengths in the WDM signal;

monitoring a power level of a second signal wavelength being added on the add port;

comparing the average power level of the signal wavelengths in the WDM signal to the power level of the second signal wavelength;

based on the step of comparing, adjusting optical attenuation along the add port so that the power level of the second signal wavelength becomes substantially equal to the average power level of the signal wavelengths in the WDM optical signal.

35. The method of claim 34 wherein the step of monitoring the average power level comprises the steps of tapping a portion of the power from the WDM optical signal, splitting said portion into first and second subportions of the WDM optical signal, monitoring the first subportion to determine a power level of each of the signal wavelengths in the WDM optical signal, monitoring the second subportion to determine a total power level of the WDM optical signal, and generating a first electrical reference signal that represents the average power level of the signal wavelengths in the WDM signal.

36. The method of claim 35 wherein the step of monitoring the first subportion to determine a power level of the signal wavelengths in the WDM optical signal includes the steps of directing the first subportion through an optical tunable filter and sweeping the optical tunable filter so that its passband traverses each wavelength in a waveband occupied by the WDM optical signal.

37. The method of claim 34 wherein the step of monitoring the power level of the second signal wavelength comprises the steps of tapping a portion of the power from the second signal wavelength as it traverses the add port and generating a second electrical reference signal that corresponds to the tapped portion of power of the second signal wavelength.

38. The method of claim 35 wherein the step of monitoring the power level of the second signal wavelength comprises the steps of tapping a portion of the power from the second signal wavelength as it traverses the add port and generating a second electrical reference signal that corresponds to the tapped portion of power of the second signal wavelength.

39. The method of claim 34 wherein the comparing step is performed in the electrical domain.

40. The method of claim 38 wherein the comparing step includes the step of comparing the second electrical reference signal to the first electrical reference signal.

41. The method of claim 34 wherein the step of monitoring the average power level includes the steps of directing the WDM signal through an optical tunable filter and sweeping the optical tunable filter so that its passband traverses each wavelength in a waveband occupied by the WDM optical signal.

42. The method of claim 34 wherein the step of adjusting the optical attenuation is performed by an variable optical attenuator coupled to the add port.

43. The method of claim 34 wherein the step of monitoring the average power level of the signal wavelengths in the WDM signal is performed at the input port.

44. The method of claim 34 wherein the step of monitoring the average power level of the signal wavelengths in the WDM signal is performed at the output port.