Claims
- 1. A polarization mode dispersion measurement system for measuring a fiber under test comprising:
at least one incoherent light source emitting light at a first wavelength and at a second wavelength; an optical polarizer adjustable to at least three polarization states; two bandpass filters passing light respectively at said first and second wavelengths and being insertable in a light path between said at least one light source and said optical polarizer, light output from said polarizer being received by said fiber under test; and a polarimeter receiving an optical output of said fiber under test and measuring a polarization state of light received from said fiber under test.
- 2. The system of claim 1,
wherein the at least one light source comprises a first and a second light emitting diode emitting respectively at said first and second wavelengths and the first and second bandpass filters receive respective optical outputs of the first and second light emitting diodes, and further comprising a first light switch having two first switch inputs receiving respective outputs of said first and second bandpass filter and selectively connectable to a first switch output, the polarizer receiving the first switch output.
- 3. The system of claim 2, further comprising:
a second optical switch comprising
a second switch input receiving the light output from the fiber under test, and at least two second switch outputs selectively connectable to the second switch input, an output of a first of the switch outputs being received by the polarimeter; and an optical detector receiving an output of a second of the second switch outputs.
- 4. The system of claim 3, further comprising a laser emitting within a bandwidth associated with the first and second light emitting diodes and wherein the first switch includes a third first switch input receiving an output of the laser and being selectively connectable to the first switch output.
- 5. The system of claim 3, further comprising a visible laser emitting at a visible wavelength and wherein the first switch includes a fourth switch input receiving an output of the visible laser and being selectively connectable to the first switch output.
- 6. The system of claim 1, further comprising:
an optical switch comprising
a switch input receiving the light output from the fiber under test, and at least two switch output selectively connectable to the switch input, an output of a first of the switch outputs being received by the polarimeter; and an optical detector receiving an output of a second of the switch outputs.
- 7. The system of claim 1, further comprising:
a laser emitting within a bandwidth associated with the first and second wavelengths; and a switch including at least two inputs receiving respective outputs of the laser and the two bandpass filters and being selectively connectable to an output providing light to the fiber under test.
- 8. The system of claim 1, further comprising:
a visible laser emitting light emitting light at a visible wavelength; and a switch including at least two inputs receiving respective outputs of the laser and the two bandpass filters and being selectively connectable to an output providing light to the fiber under test.
- 9. The system of claim 1, further comprising a twist unit able to induce a selected amount of twist along the fiber under test.
- 10. The system of claim 1, further comprising a load cell able to induce a selected load upon the fiber under test.
- 11. A method of measuring a birefringent property in an optical fiber comprising the steps of:
(a) passing incoherent light through a bandpass filter to form probing light; (b) setting a state of polarization for the probing light; (c) passing the probing light with set state of polarization through a fiber under test; (d) detecting a state of polarization for the probing light with set state of polarization after exiting the fiber; and (e) from repeated sequences of steps (a) through (d) determining the birefringent property of the fiber under test.
- 12. The method of claim 11 further comprising aligning the fiber under test with coherent light.
- 13. The method of claim 11, wherein the determining step uses polarization states measured for two optical wavelengths passed by two bandpass filters and three sets of polarization states.
- 14. The method of claim 13, wherein the determining step uses Jones matrix analysis.
- 15. The method of claim 11, wherein the birefringent property is a differential group delay.
- 16. The method of claim 11 further comprising:
(f) twisting the fiber under test to a twist value, wherein the determining step determines the birefringent property value corresponding to the twist value.
- 17. The method of claim 16 further comprising:
(g) repeating steps (a) through (f) for a plurality of twist values; and (h) selecting a birefringent property representative of the fiber under test from the plurality of birefringent property values.
- 18. The method of claim 17, wherein the selected birefringent property is a differential group delay.
- 19. The method of claim 18, wherein the selected differential group delay is a maximum value determined from the plurality of differential group delay values.
- 20. The method of claim 11, further comprising applying a plurality of loads to the fiber under test and measuring the birefringent property for each of the loads.
- 21. The method of claim 11, wherein said birefringent property is a differential group delay.
- 22. A method of measuring polarization mode dispersion comprising the steps of:
(a) passing light from an incoherent light source through a bandpass filter, having a transmission peak at a transmission wavelength, to a polarization system passing a selectable polarization state of light; (b) passing light from the polarization system through a fiber under test; (c) measuring a polarization state of light output from the fiber under test; (d) performing steps (a) through (c) at least six times for all combinations of three polarization states of light of said polarization system and for two transmission wavelengths; and (e) calculating a polarization mode dispersion from the six polarization states measured in step (d).
- 23. The method of claim 22, including aligning the fiber under test with a source of laser light incident upon said polarization system and an optical detector receiving an output from the fiber under test.
- 24. A method of qualifying a spool of at least 4 km of fiber comprising:
cutting a length of no more than 5 m of fiber from the spool, the 5 m of fiber forming a fiber under test; measuring a polarization mode dispersion of the fiber under test; and associating the polarization mode dispersion measured for the fiber under test with the fiber remaining on the spool through an empirically derived mapping.
- 25. The method of claim 24 wherein the empirically derived mapping comprises:
(a) from a first fiber wrapped on a first spool containing at least 4 km of fiber, cutting a length of at least 100 m of the first fiber; (b) measuring a first value of polarization mode dispersion on the at least 100 m fiber; (c) cutting a length of no more than 5 m of the first fiber; (d) measuring a second value polarization mode dispersion on the no more than 5 m of fiber; (e) associating the first value of polarization mode dispersion with the second value of polarization mode dispersion; and (f) repeating steps (a) through (e) on other spools of fiber to thereby form a mapping between said first and second values of polarization mode dispersion.
- 26. The method of claim 25, wherein the step (b) of measuring the first value of
polarization mode dispersion includes externally twisting the fiber under test to a sequence of twists and measuring respective twist values of polarization mode dispersion; and selecting for the first value of polarization mode dispersion a value derived from the respective twist values associated with a predetermined amount of twist internally experienced in the fiber.
- 27. The method of claim 26, wherein the selected value is a maximum value derived from the respective twist values.
- 28. The method of claim 27, where the selecting step includes fitting the respective twist values to a relationship describable with a number of parameters less than the number of respective twist values and calculating the first value of polarization dispersion from the parameters.
Parent Case Info
[0001] This application is a Divisional Application of U.S. patent application Ser. No. 09/512,724, which claims priority to and the benefit of U.S. Provisional Patent Application No. 60/127,107, filed Mar. 31, 1999.
Provisional Applications (1)
|
Number |
Date |
Country |
|
60127107 |
Mar 1999 |
US |
Divisions (1)
|
Number |
Date |
Country |
Parent |
09512724 |
Feb 2000 |
US |
Child |
10039919 |
Oct 2001 |
US |