Method and apparatus for controlling a variable optical attenuator in an optical network

• US 20040109661A1
• Filed: 05/19/2003
• Published: 06/10/2004
• Est. Priority Date: 12/05/2002
• Status: Active Grant

• Current Assignee: WSOU Investments, LLC (WSOU Holdings, LLC)
• Original Assignee: 6766285 Canada Incorporated d/b/a Divvali Lighting Inc.
• Inventors: Donnelly, Victoria, Bierman, Robert Michael, Moharram, Omayma
• Granted Patent: US 6,987,922 B2
• Time in Patent Office: Days
• US Class Current: 385/140
• CPC Class Codes: H04B 10/077 using a supervisory or additional signal
• 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

Abstract

This invention describes a method for controlling attenuation for a variable optical attenuator (VOA) inserted in an optical path of an optical signal propagating in an optical network, comprising the steps of measuring power of the optical signal at the VOA; comparing the measured power with a target power; and if the measured power differs from the target power, changing the attenuation of the VOA in one or more variable size intervals (VSI) so that the power of the optical signal substantially equals to the target power, wherein the VSI being a function of the measured power and target power. The method further comprises the step of comparing the measured power with a Loss-of-signal (LOS) power threshold, and if the measured power is less than the LOS power threshold, changing the attenuation of the VOA in one or more variable size intervals so that the power of the optical signal substantially higher than the LOS power threshold, wherein the size of the variable interval being a function of the measured power and the LOS power threshold. The method dynamically computes a VSI, updates the VOA setting by said VSI, and manages a combination of open and closed VOA control loops to maintain the target power attenuation of the VOA The corresponding apparatus for controlling the VOA is also provided.

Claims

1. A method for controlling attenuation for a variable optical attenuator (VOA) inserted in an optical path of an optical signal propagating in an optical network, the method comprising the steps of:

measuring power of the optical signal {Pmeas} at the VOA;

comparing the measured power {Pmeas) with a target power {Ptarget}; and

if the measured power {Pmeas} differs from the target power {Ptarget}, changing the attenuation of the VOA in one or more variable size intervals (VSI) so that the power of the optical signal substantially equals to the target power {Ptarget}, the size of the variable interval being a function of the {Pmeas} and {Ptarget}.

2. A method as described in claim 1, further comprises the step of comparing the measured power {Pmeas) with a LOS power threshold {Pthres}, and if the measured power {Pmeas} is less than the LOS power threshold {Pthres}, changing the attenuation of the VOA in one or more variable size intervals (VSI) so that the power of the optical signal substantially higher than the LOS power threshold {Pthres}, wherein the size of the variable interval being a function of the {Pmeas} and {Pthres}.

3. A method as described in claim 2, wherein the step of measuring power of the optical signal {Pmeas} at the VOA comprises measuring the optical signal power at an input to the VOA {Pinput}.

4. A method as described in claim 2, wherein the step of measuring power of the optical signal {Pmeas} at the VOA comprises measuring the optical signal power at an output of the VOA {Poutput}.

5. A method as described in claim 2, wherein the step of measuring power of the optical signal {Pmeas} at the VOA comprises measuring the optical signal power at an input to the VOA {Pinput} and at an output of the VOA {Poutput}.

6. A method as described in claim 2, wherein the step of changing the attenuation of the VOA further comprising the steps of adjusting and updating the VOA attenuation in variable size intervals (VSI) if the measured power {Pmeas} is initially below the LOS power threshold {Pthres} and changes to a level higher and lower than the target power {Ptarget}.

7. A method as described in claim 2, wherein the step of changing the attenuation of the VOA comprises determining the variable size interval (VSI), wherein the VSI being a function of VOA attenuation setting parameters and network operating requirements including a pre-calibrated manufacturing default insertion loss {Δ

} and commissioned network operating requirements factors {α

(i), wherein, i=1, 2, . . . , n}.

8. A method as described in claim 7, wherein the step of changing the attenuation of the VOA comprises determining the VSI as one or more of the following:

a linear function of the parameters {Δ

, α

, Pmeas, Pthres, Ptarget};

a nonlinear function of said parameters; and

a combination of linear and nonlinear functions of said parameters.

9. A method as described in claim 3, wherein the step of determining the VSI for changing the attenuation of the VOA comprises computing the VSI, wherein the VSI is given by one or more of the following formulae:

10. A method as described in claim 4, wherein the step of determining the VSI for changing the attenuation of the VOA comprises computing the VSI, wherein the VSI is given by one or more of the following formulae:

11. A method as described in claim 5, wherein the step of determining the VSI for changing the attenuation of the VOA comprises computing the VSI, wherein the VSI is given by the following formula:

12. An apparatus for controlling attenuation for a variable optical attenuator (VOA) inserted in an optical path of an optical signal propagating in an optical network, the apparatus comprising:

a means for measuring power of the optical signal {Pmeas} at the VOA;

a means for comparing the measured power {Pmeas) with a target power {Ptarget}; and

means for changing the attenuation of the VOA in one or more variable size intervals (VSI) so that the power of the optical signal substantially equals to the target power {Ptarget}.

13. An apparatus as described in claim 12, further comprises a means for comparing the measured power {Pmeas} with a LOS power threshold {Pthres} and means of changing the attenuation of the VOA in one or more variable size intervals (VSI) so that the power of the optical signal substantially higher than the LOS power threshold {Pthres}.

14. An apparatus as described in claim 13, wherein the means for changing the attenuation of the VOA further comprising means for adjusting and updating the VOA attenuation in variable size intervals (VSI) if the measured power {Pmeas} is initially below the LOS power threshold {Pthres} and changes to a level higher and lower than the target power {Ptarget}.

15. An apparatus as described in claim 13, wherein the means for changing the attenuation of the VOA comprises a means for determining the variable size intervals (VSI).

16. An apparatus as described in claim 15, wherein the means for determining the variable size intervals (VSI) further comprises a means for computing the VSI as one or more of the following:

a linear function of the parameters {Δ

, α

, Pmeas, Pthres, Ptarget};

a nonlinear function of said parameters; and

a combination of linear and nonlinear functions of said parameters.

17. An apparatus as described in claim 16, wherein the means for computing the variable size intervals (VSI) further comprises a means for storing the VSI for adjusting and updating the VOA attenuation.

18. An apparatus as described in claim 13, wherein the means for measuring power of the optical signal at the VOA comprises one or more of the following:

a means for measuring the optical signal power at an input to the VOA;

a means for measuring the optical signal power at an output of the VOA; and

means for measuring the optical signal power at an input to the VOA and at an output of the VOA.

19. An apparatus as described in claim 18, wherein the means for measuring power of the optical signal at the VOA comprises a tap coupler for detecting the power of the optical signal at the VOA and a tap monitor for measuring the power of the optical signal at the VOA.

20. An apparatus as described in claim 13, wherein the means for changing the attenuation of the VOA comprises a smart microcontroller for determining a VSI, computing the VSI, and storing said VSI for adjusting and updating the VOA attenuation whenever the measured signal power is below a LOS power threshold and whenever the change in measured signal power is higher and lower than the target power.