Method of evaluating fiber PMD using polarization optical time domain reflectometry

• US 20040084611A1
• Filed: 11/05/2002
• Published: 05/06/2004
• Est. Priority Date: 11/05/2002
• Status: Active Grant

• Current Assignee: Corning Incorporated
• Original Assignee: Corning Incorporated
• Inventors: Chen, Xin, Mozdy, Eric J., Heron, Nicol A., Hunt, Timothy L., Stainer, Darren A.
• Granted Patent: US 6,946,646 B2
• Time in Patent Office: Days
• US Class Current: 250/225
• CPC Class Codes: G01M 11/3181 Reflectometers dealing with polarisation

Abstract

A method for screening fiber polarization mode dispersion using a polarization optical time domain reflectometer. A pulse radiation is emitted into the fiber under test, and the backscattered radiation is measured by the POTDR and used to obtain a POTDR trace. The POTDR trace is then analyzed to compare the variation of signals along the length of the fiber, the variation in signals relating to the level of PMD along the length of the fiber. Because high levels of PMD correspond to localized levels of low variability, by setting the variability of signal threshold sufficiently low, fibers having unacceptably high localized PMD can be identified and removed.

Claims

1. A method for measuring polarization mode dispersion in an optical fiber comprising:

emitting a pulse of radiation into a length of optical fiber;

measuring radiation which is backscattered back through the fiber from said pulse radiation;

analyzing the variation of intensity level of said measured backscattered radiation and relating the level of variation of intensity level to the polarization mode dispersion in said fiber.

2. The method of claim 1, wherein said variation of intensity level is used to determine whether a region along the length of the fiber exhibits PMD which is above a predetermined threshold value for PMD.

3. The method of claim 1, wherein said analyzing step comprises assessing the variability in said backscattered intensity level along the length of said fiber, and using the variation to identify areas of higher or lower polarization mode dispersion along the length of said fiber.

4. The method of claim 1, wherein said pulse radiation is emitted from an OTDR, and said measured radiation is measured with an OTDR.

5. The method of claim 4, wherein the emitted radiation is polarized and the measured radiation which is backscattered is directed through a polarization analyzing component prior to returning to the OTDR.

6. The method of claim 1, wherein said analyzing step comprises analyzing a sliding window of data within which a standard deviation is calculated over said window, and moving said window of data lengthwise along the length of the fiber to produce information related to the local variation along the length of the fiber.

7. The method of claim 6, wherein said standard deviation is calculated in log scale.

8. The method of claim 1, wherein variation of signals are plurality of optical fibers having varying degrees of PMD, and the variation of signals is mapped against polarization mode dispersion levels for said fibers, and a level of variation of signals is selected above or below which the optical fiber passes or fails.

9. The method of claim 6, wherein a VOS threshold is set below which the fiber is said to have unacceptably high PMD.

10. The method of claim 1, wherein said method comprises emitting said pulse radiation into a length of optical fiber which is already installed into a telecommunications system.

11. The method of claim 1, wherein the pulse radiation in said emitting step comprises a pulse width between about 5 and 200 ns.

12. The method of claim 1, wherein the pulse radiation in said emitting step comprises a pulse width between about 30 and 150 ns.

13. The method of claim 1, wherein said pulse radiation is emitted into a length of fiber greater than 15 km, to thereby provide PMD information in said fiber which is a distance greater than 15 km from the source of the emitted radiation.