Method for characterizing polarization transformers

• US 6,661,936 B2
• Filed: 02/12/2001
• Issued: 12/09/2003
• Est. Priority Date: 02/11/2000
• Status: Expired due to Fees

• Current Assignee: Xieon Networks S.A.R.L. (Infinera Corp.)
• Original Assignee: Siemens AG
• Inventors: Noe, Reinhold
• Primary Examiner(s): Stafira, Michael P.
• Assistant Examiner(s): Valentin, II, Juan D
• Application Number:
  US09/781,849
• Publication Number:
  US 20010038486A1
• Time in Patent Office: 1,030 Days
• Field of Search: 385/11, 385/31, 359/501, 359/499
• US Class Current: 385/11
• CPC Class Codes: G02F 1/0136 for the control of polarisation, e.g. state of polarisation [SOP] control, polarisation scrambling, TE-TM mode conversion or separation G02F1/0353 takes precedence
• CPC Class Codes: G02F 1/035 in an optical waveguide structure
• CPC Class Codes: G02F 1/05 with ferro-electric properties G02F1/035, G02F1/055 take precedence
• CPC Class Codes: H04B 10/2569 due to polarisation mode dispersion [PMD]

Abstract

For characterizing polarization transformers or PMD compensators, a polarization transformer to be characterized is operated as a mode converter with full mode conversion and variable orientation. A polarization control sees to it that a further polarization transformer assures the desired, overall polarization transformation. Conclusions about the precision with which the polarization transformer to be characterized works can be drawn from the nature and strength or, too, from the absence of changes of control signals of this further polarization transformer, and this can be improved. The method is particularly suited for the automatic follow-up of DC drift in polarization transformers or PMD compensators with lithium niobate components.

Claims

1. A method for characterizing a polarization transformer, which is traversed by an optical signal, with a control function, said method comprising the steps of:

providing a first polarization transformer to be characterized;

providing a further polarization transformer that lies before or after the first polarization transformer in a light path of the optical signal and connected to said first polarization transformer, both said first polarization transformer and said further polarization transformer being traversed by the optical signal;

performing a characterization of the first polarization transformer during implementation of one of polarization transformation and compensation of polarization mode dispersion of the optical signal by said further polarization transformer so that the control function is not negatively affected.

2. A method as claimed in claim 1, further comprising the step of:

characterizing a plurality of polarization transformers by alternating characterization of one polarization transformer and implementing a desired polarization transformation by the one polarization transformer.

3. A method as claimed in claim 1, wherein one of said first polarization transformer and said further polarization transformer acts as an elliptical retarder with a delay.

4. A method as claimed in claim 1, wherein at least a part of one of said first polarization transformer and said further polarization transformer acts as a mode converter with selectable delay and selectable orientation.

5. A method as claimed in claim 4, wherein said selectable delay and said selectable orientation provide a phase difference between converted and non-converted signals.

6. A method as claimed in claim 4, wherein at least a part of one of said first polarization transformer and said further polarization transformer acts as a Soleil-Babinet analog with said selectable delay and said selectable orientation with mode conversion between TE and TM modes.

7. A method as claimed in claim 4, wherein at least a part of one of said first polarization transformer and said further polarization transformer acts as a Soleil-Babinet compensator with said selectable delay and said selectable orientation with mode conversion between circular polarizations.

8. A method as claimed in claim 4, further comprising the step of:

operating the mode converter to be characterized with full mode conversion.

9. A method as claimed in claim 8, wherein the full mode conversion includes a delay equal to an odd-numbered multiple of the value π

and variable orientation.

10. A method as claimed in claim 8, further comprising the step of:

providing a further mode converter functionally following the mode converter to be characterized, the further mode converter experiencing changes of its orientation that correspond to approximately twice a change of the orientation of the mode converter to be characterized.

11. A method as claimed in claim 8, further comprising the step of:

providing a polarization transformer functionally preceding the mode converter to be characterized, the polarization transformer experiencing no substantial change of its control parameters.

12. A method as claimed in claim 1, further comprising the step of:

operating the polarization transformer to be characterized with a delay equal to an even-numbered multiple of the value 2π and

a variable orientation.

13. A method as claimed in claim 1, further comprising the step of:

operating the polarization transformer to be characterized with a variable delay.

14. A method as claimed in claim 1, further comprising the step of:

detecting changes of polarization transformation of the optical signal caused by parameter variation of the polarization transformer to be characterized.

15. A method as claimed in claim 14, further comprising the step of:

changing other parameters of the polarization transformer to be characterized as a function of an output signal of said detecting step.

16. A method as claimed in claim 15, wherein said changing ensues for a purpose of minimizing an output signal in said detecting step.

17. A method as claimed in claim 15, wherein said changing ensues for a purpose of maximizing an output signal in said detecting step.

18. A method as claimed in claim 14, further comprising the steps of:

supplying an output signal of said detecting step to a controller; and

at least partially compensating by another polarization transformer for changes of the polarization transformation.

19. A method as claimed in claim 18, further comprising the step of:

undertaking a change of other parameters of the polarization transformer to be characterized as a function of the change of parameters of said further polarization transformer.

20. A method as claimed in claim 19, wherein said step of undertaking ensues for minimizing the change of parameters of said further polarization transformer.

21. A method as claimed in claim 19, wherein said step of undertaking ensues for maximizing the change of parameters of said further polarization transformer.

22. A method as claimed in claim 1, wherein the polarization transformer to be characterized is part of a polarization transformer that one of:

generates a fixed polarization from every arbitrary polarization of the optical signal, and

serves for receiver-side PMD compensation; and

further comprising the steps of;

providing polarization transformers functionally preceding the polarization transformer to be characterized in a beam path preceding the polarization transformer to be characterized; and

providing polarization transformers that functionally follow in the beam path behind the polarization transformer to be characterized.

23. A method as claimed in claim 1, wherein the polarization transformer to be characterized is part of a polarization transformer that one of:

generates any arbitrary polarization from a fixed polarization of the optical signal; and

serves for transmission-side PMD compensation; and

further comprising the steps of;

providing polarization transformers functionally preceding the polarization transformer to be characterized in the beam path following the polarization transformer to be characterized; and

providing polarization transformers that functionally follow in the beam path preceding the polarization transformer to be characterized.

24. A method as claimed in claim 1, further comprising the step of:

operating the first polarization transformer with voltages opposite those for an implementation of desired polarization transformation at times wherein the further polarization transformer at least approximately assures implementation of the desired polarization transformation or compensation of polarization mode dispersion of the optical signal.