Method and system for optical fiber sensing

1. A method of optical sensing, comprising:

coupling an excitation optical signal into a first optical fiber to induce Rayleigh backscattering, thereby providing a backscattered signal;

coupling said backscattered signal into a second optical fiber, spatially separated from said first optical fiber; and

optically amplifying said backscattered signal in said second optical fiber, thereby generating a sensing signal;

wherein said optically amplifying comprises introducing a pump light beam into said second fiber, wherein said pump light beam and said backscattered signal enter said second fiber from the same end thereof.

2. The method according to claim 1 , further comprising transmitting said sensing signal into a signal analyzer, for analyzing said sensing signal so as to identify a change in at least one property along said first fiber.

3. The method according to claim 2 , wherein said at least one property is selected from the group consisting of a mechanical property, a thermal property and a chemical property.

4. The method according to claim 1 , further comprising transmitting said sensing signal into a signal analyzer, for analyzing said sensing signal so as to identify a spatially-resolved change in at least one property along said first fiber.

5. The method according to claim 1 , wherein said optically amplifying comprises employing Brillouin amplification or Raman amplification.

6. The method according to claim 1 , wherein said excitation optical signal is a pulsed optical signal.

7. The method according to claim 6 , wherein a characteristic duty cycle of said pulsed optical signal is less than 10%.

8. The method according to claim 1 , wherein said optical amplification is an on-resonance optical amplification.

9. The method according to claim 1 , wherein said optical amplification is an off-resonance optical amplification.

10. The method according to claim 9 , wherein a detuning frequency of said off-resonance optical amplification is from about 0.1X to about 0.9X, where X is a characteristic on-resonance bandwidth of said optical amplification.

11. A method of optical sensing, comprising:

coupling an excitation optical signal into an optical fiber to induce Rayleigh backscattering, thereby providing a backscattered signal;

optically amplifying said backscattered signal in said optical fiber, thereby generating a sensing signal;

wherein said optically amplifying is by pump light beam at intensity I satisfying gI≥K+2α, said α being a Rayleigh scattering coefficient characteristic to said fiber, said g being a gain coefficient characteristic to said fiber, and said K being a predetermined variation rate which larger than −0.01 m −1 .

12. The method according to claim 11 , wherein said K is larger than −0.001 m −1 .

13. The method according to claim 11 , wherein said intensity I satisfies gI≥2α.

14. A system for optical sensing, comprising:

a light source system configured for generating an excitation optical signal selected to induce Rayleigh backscattering, and a pump light beam selected to amplify said Rayleigh backscattering;

an arrangement of optical couplers arranged for coupling said excitation optical signal into a first optical fiber thereby providing a backscattered signal, and for coupling said backscattered signal and said pump light beam into a second optical fiber, spatially separated from said first optical fiber, to thereby generate an optically amplified sensing signal, wherein said pump light beam and said backscattered signal enter said second fiber from the same end thereof; and

a signal analyzer, for analyzing said sensing signal so as to identify a change in at least one property along said first fiber.

15. The system according to claim 14 , wherein said signal analyzer is configured for analyzing said sensing signal so as to allow identifying a spatially-resolved change in at least one property along said first fiber.

16. The system according to claim 14 , wherein said at least one property is selected from the group consisting of a mechanical property, a thermal property and a chemical property.

17. The system according to claim 14 , wherein said pump light beam is selected to amplify said Rayleigh backscattering by Brillouin amplification.

18. The system according to claim 14 , wherein said wherein said pump light beam is selected to amplify said Rayleigh backscattering by Raman amplification.

19. The system according to claim 14 , wherein said excitation optical signal is a pulsed optical signal.

20. The system according to claim 19 , wherein a characteristic duty cycle of said pulsed optical signal is less than 10%.

21. The system according to claim 14 , wherein said pump light beam is selected to induce an on-resonance optical amplification.

22. The system according to claim 14 , wherein said pump light beam is selected to induce an off-resonance optical amplification.

23. The system according to claim 22 , wherein a detuning frequency of said off-resonance optical amplification is from about 0.1X to about 0.9X, where X is a characteristic on-resonance bandwidth of said optical amplification.

24. A system of optical sensing, comprising:

a light source system configured for generating an excitation optical signal selected to induce Rayleigh backscattering, and a pump light beam selected to amplify said Rayleigh backscattering;

an optical coupler arranged for coupling said excitation optical signal and said pump light beam into an optical fiber to thereby generate an optically amplified sensing signal; and

a signal analyzer, for analyzing said sensing signal so as to identify a change in at least one property along said fiber;

wherein said pump light beam has intensity I satisfying gl≥K+2α, said α being a Rayleigh scattering coefficient characteristic to said fiber, said g being a gain coefficient characteristic to said fiber, and said K being a predetermined variation rate which larger than −0.01 m −1 .

25. The system according to claim 24 , wherein said K is larger than −0.001 m −1 .

26. The system according to claim 24 , wherein said intensity I satisfies gI≥2α.