Devices and methods for characterization of distributed fiber bend and stress

1. A polarization-sensitive optical frequency domain reflectometer device for measuring a distributed fiber bend or stress based on optical polarization sensing, comprising:

a light source that produces probe light that is at least partially coherent;

an optical unit that includes different optical ports positioned relative to the probe light from the light source and relatively to a fiber link under test, couples the probe light from the light source into the fiber link under test in an input state of polarization (I-SOP), and receives reflected probe light from the fiber link under test in an output state of polarization (O-SOP) to produce first and second optical signals in two different optical polarizations from the reflected probe light;

an optical coupler that couples a portion of the probe light as an optical local oscillator light;

an optical detection unit that includes different receiving ports, the optical detection unit coupled to receive the optical local oscillator light and the first and second optical signals and configured to mix the optical local oscillator light with the first and second optical signals to perform coherent detection of the first and second optical signals; and

a signal processor that processes information from the coherent detection of the first and second optical signals to compute a difference in measurements of an optical parameter in reflected probe light from two different locations in the fiber under test and compute a polarization-dependent property of a fiber bend or stress from the computed difference at different positions along a fiber path in the fiber link under test to provide an assessment of the fiber bend or stress in the fiber link under test.

2. An optical time domain reflectometer (OTDR) device, comprising:

a light source that produces probe light at different optical wavelengths;

a light routing device that includes different ports that are positioned relative to the light source and a fiber link under test, directs the probe light from the light source to the fiber link under tests, and receives reflected probe light from the fiber link under test;

an optical detector coupled to receive the reflected probe light from the light routing device to produce detector signals; and

a signal processor that processes information from the detector signals to perform:

computing a first optical power difference in reflected optical signals from two different locations in the fiber link under test at each of two or more different optical wavelengths;

computing a second optical power difference in reflected optical signals from each of the two different locations in the fiber link under test at the two different optical wavelengths;

using information on the first and second optical power differences to obtain optical loss caused by a fiber bend or stress present in the fiber link under test; and

using the optical loss caused by a fiber bend or stress present in the fiber link under test to determine a parameter of the fiber bend or stress.

3. The device as in claim 2 , wherein the light source includes a tunable light source that tunes to the different optical wavelengths.

4. The device as in claim 2 , further comprising a sampling and averaging unit that processes the detector signals to produce output signals to be processed by the signal processor.

5. The device as in claim 2 , further comprising a control unit that is coupled to the light source to control generation of the probe light at the different optical wavelengths and is further coupled to the signal processor.

6. The device as in claim 2 , wherein the parameter of the fiber bend or stress includes a fiber bend length.

7. The device as in claim 2 , wherein the parameter of the fiber bend or stress includes a fiber bend radius.

8. The device as in claim 2 , wherein the parameter of the fiber bend or stress includes a fiber type of the fiber under test.

9. The device as in claim 2 , wherein the light source includes different light sources at different wavelengths.

10. The device as in claim 9 , wherein the light routing device includes an optical coupler.

11. The device as in claim 9 , wherein the light routing device includes an optical backreflection extractor.

12. A method for using optical time domain reflectometer (OTDR) to measure a fiber link under test, comprising:

operating a light source to produce probe light at different optical wavelengths;

directing the probe light into a fiber link under test;

directing reflected probe light from the fiber link under test into an optical detector to produce detector signals;

processing information from the detector signals to determine a fiber bend or stress present in the fiber link under test, wherein the processing includes:

computing a first optical power difference in reflected optical signals from two different locations in the fiber link under test at each of two or more different optical wavelengths;

computing a second optical power difference in reflected optical signals from each of the two different locations in the fiber link under test at the two different optical wavelengths;

using information on the first and second optical power differences to obtain optical loss caused by a fiber bend or stress present in the fiber link under test; and

using the optical loss caused by a fiber bend or stress present in the fiber link under test to determine a parameter of the fiber bend or stress.

13. The method as in claim 12 , wherein the parameter of the fiber bend or stress includes a fiber bend length.

14. The method as in claim 12 , wherein the parameter of the fiber bend or stress includes a fiber bend radius.

15. The method as in claim 12 , wherein the parameter of the fiber bend or stress includes a fiber type of the fiber under test.