Temperature or strain distribution sensor comprising a coherent receiver to determine a temperature or a strain associated with a device under test

1. A temperature or strain distribution sensor comprising:

a first laser source to emit a first laser beam;

a second laser source to emit a second laser beam;

a photodiode to acquire a beat frequency between the first laser beam and the second laser beam, wherein the beat frequency is used to maintain

a predetermined offset frequency shift between the first laser beam and the second laser beam, wherein the predetermined offset frequency shift is relative to a predetermined frequency of either the first laser beam or the second laser beam, or

a constant optical frequency for the first laser beam and the second laser beam;

a modulator to modulate the first laser beam, wherein the modulated first laser beam is to be injected into a device under test (DUT); and

a coherent receiver to acquire a backscattered signal from the DUT, wherein the backscattered signal results from the modulated first laser beam injected into the DUT, and wherein

the coherent receiver is to use the second laser beam as a local oscillator to determine a Brillouin trace with respect to the DUT based on the predetermined offset frequency shift between the first laser beam and the second laser beam, wherein the Brillouin trace is used to determine a Brillouin frequency shift and a Brillouin power for the DUT to implement an absolute referencing of a Rayleigh reference trace, and

the coherent receiver is to determine, relative to the Rayleigh reference trace, a further Brillouin frequency shift and a Rayleigh frequency shift to determine a temperature or a strain associated with the DUT.

2. The temperature or strain distribution sensor of claim 1 , wherein the predetermined offset frequency shift for determination of the Brillouin trace is approximately 10.8 GHz.

3. The temperature or strain distribution sensor of claim 1 , wherein the predetermined offset frequency shift for determination of the Brillouin trace is selected from a range of approximately 10.0 GHz to approximately 13.0 GHz.

4. The temperature or strain distribution sensor of claim 1 , wherein

the coherent receiver is to use the second laser beam as the local oscillator to determine a Rayleigh trace with respect to the DUT based on the constant optical frequency for the first laser beam and the second laser beam, wherein the Rayleigh trace is used to determine the Rayleigh frequency shift for the DUT to determine the temperature or the strain associated with the DUT.

5. The temperature or strain distribution sensor of claim 1 , wherein the DUT is an optical fiber.

6. The temperature or strain distribution sensor of claim 1 , further comprising:

a polarization beam splitter (PBS) of the coherent receiver to

receive the backscattered signal, and

divide the backscattered signal into two different polarization states, wherein

a divided portion of the backscattered signal corresponding to a first polar state is to be mixed with the second laser beam at the first polar state, and a divided portion of the backscattered signal corresponding to a second polar state is to be mixed with the second laser beam at the second polar state to determine the Brillouin trace with respect to the DUT.

7. A method for temperature or strain determination, the method comprising:

maintaining a predetermined offset frequency shift between a first laser beam and a second laser beam, wherein the predetermined offset frequency shift is relative to a predetermined frequency of either the first laser beam or the second laser beam;

modulating the first laser beam, wherein the modulated first laser beam is to be injected into a device under test (DUT);

acquiring a backscattered signal from the DUT, wherein the backscattered signal results from the modulated first laser beam injected into the DUT, and wherein the second laser beam is to be used as a local oscillator;

determining, based on the acquired backscattered signal from the DUT, a Brillouin trace for the DUT;

determining, based on the Brillouin trace, a Brillouin frequency shift and a Brillouin power for the DUT to implement an absolute referencing of a Rayleigh reference trace;

determining, relative to the Rayleigh reference trace, a further Brillouin frequency shift and a Rayleigh frequency shift; and

determining, based on the further Brillouin frequency shift and the Rayleigh frequency shift, a temperature or a strain associated with the DUT.

8. The method for temperature or strain determination according to claim 7 , further comprising:

maintaining a constant optical frequency for the first laser beam and the second laser beam;

determining, based on the constant optical frequency for the first laser beam and the second laser beam, a Rayleigh trace with respect to the DUT; and

determining, based on the Rayleigh trace with respect to the DUT, the Rayleigh frequency shift for the DUT.

9. The method for temperature or strain determination according to claim 7 , further comprising:

repeating the acquisition of the backscattered signal from the DUT for a plurality of frequency shifts;

sampling, based on the repeated acquisitions corresponding to the plurality of frequency shifts and the acquisition of the backscattered signal from the DUT, a distributed Brillouin spectra; and

determining, based on the sampling of the distributed Brillouin spectra, the Brillouin frequency shift along the DUT to implement the absolute referencing of the Rayleigh reference trace.

10. The method for temperature or strain determination according to claim 9 , further comprising:

determining, based on the sampling of the distributed Brillouin spectra, the Brillouin power by performing an integration operation with respect to the Brillouin frequency shift along the DUT to implement the absolute referencing of the Rayleigh reference trace.

11. The method for temperature or strain determination according to claim 7 , wherein the DUT is an optical fiber.

12. The method for temperature or strain determination according to claim 7 , wherein the predetermined offset frequency shift for determination of the Brillouin trace is approximately 10.8 GHz.

13. The method for temperature or strain determination according to claim 7 , wherein the predetermined offset frequency shift for determination of the Brillouin trace is selected from a range of approximately 10.0 GHz to approximately 13.0 GHz.

14. A method for temperature or strain determination, the method comprising:

maintaining a constant optical frequency for a first laser beam and a second laser beam;

modulating the first laser beam, wherein the modulated first laser beam is to be injected into a device under test (DUT);

acquiring a backscattered signal from the DUT, wherein the backscattered signal results from the modulated first laser beam injected into the DUT, and wherein the second laser beam is to be used as a local oscillator;

determining, based on the acquired backscattered signal from the DUT, a Rayleigh trace for the DUT;

maintaining a predetermined offset frequency shift between the first laser beam and the second laser beam, wherein the predetermined offset frequency shift is relative to a predetermined frequency of either the first laser beam or the second laser beam;

modulating the first laser beam that includes the predetermined offset frequency shift, wherein the modulated first laser beam that includes the predetermined offset frequency shift is to be injected into the DUT;

acquiring a further backscattered signal from the DUT, wherein the further backscattered signal results from the modulated first laser beam that includes the predetermined offset frequency shift injected into the DUT, and wherein the second laser beam is to be used as the local oscillator;

determining, based on the acquired further backscattered signal from the DUT, a Brillouin trace for the DUT;

determining, based on the Brillouin trace, a Brillouin frequency shift and a Brillouin power for the DUT to implement an absolute referencing of a Rayleigh reference trace;

determining, relative to the Rayleigh reference trace, a further Brillouin frequency shift and a Rayleigh frequency shift, wherein the Rayleigh frequency shift is determined based on the Rayleigh trace for the DUT; and

determining, based on the further Brillouin frequency shift and the Rayleigh frequency shift, a temperature or a strain associated with the DUT.

15. The method for temperature or strain determination according to claim 14 , further comprising:

repeating the acquisition of the further backscattered signal from the DUT for the predetermined offset frequency shift; and

averaging, during scanning of the first laser beam and the second laser beam over a wavelength range with the predetermined offset frequency shift between the two laser beams, the repeated acquisitions of the further backscattered signal from the DUT for the predetermined offset frequency shift to reduce coherent fading noises.

16. The method for temperature or strain determination according to claim 14 , wherein the DUT is an optical fiber.

17. The method for temperature or strain determination according to claim 14 , wherein the predetermined offset frequency shift for determination of the Brillouin trace is approximately 10.8 GHz.

18. The method for temperature or strain determination according to claim 14 , wherein the predetermined offset frequency shift for determination of the Brillouin trace is selected from a range of approximately 10.0 GHz to approximately 13.0 GHz.

19. The method for temperature or strain determination according to claim 14 , further comprising:

determining, based on sampling of a distributed Brillouin spectra, the Brillouin power by performing an integration operation with respect to the Brillouin frequency shift for the DUT to implement the absolute referencing of the Rayleigh reference trace.

20. The method for temperature or strain determination according to claim 14 , further comprising:

repeating the acquisition of the further backscattered signal from the DUT for a plurality of frequency shifts;

sampling, based on the repeated acquisitions corresponding to the plurality of frequency shifts and the acquisition of the further backscattered signal from the DUT, a distributed Brillouin spectra; and

determining, based on the sampling of the distributed Brillouin spectra, the Brillouin frequency shift to implement the absolute referencing of the Rayleigh reference trace.