Sensor and method of sensing

1. A sensor, suitable for sensing one or more properties of one or more structures, the sensor comprising:

a first optical propagation path which is configurable to cooperate with a structure whose properties are to be sensed;

a second optical propagation path which is configurable to cooperate with a structure whose properties are to be sensed;

a third optical propagation path;

an amplifier for amplifying a signal which propagates in the third optical propagation path, so that the signal is amplified before it begins propagation along the second optical propagation path;

a circulator configured to prevent the propagation of signals from the second optical propagation path to the third optical propagation path;

a means to prevent the propagation of signals from the first optical propagation path to the second optical propagation path, wherein the means to prevent the propagation of signals from the first optical propagation path to the second optical propagation path is further configured to allow the propagation of signals, from the second optical propagation path to the first optical propagation path and from the third optical propagation path to the second optical propagation path, and

an analyser configured to provide a first pump signal to the first optical propagation path and a second pump signal to the third optical propagation path,

wherein a first end of the first optical propagation path is connected to said analyser, and a second opposite end of the first optical propagation path is connected to said circulator, and

wherein a first end of the third optical propagation path is connected to said analyser, and a second opposite end of the third optical propagation path is connected to said circulator, such that:

the second pump signal propagates from the first end of the third optical propagation path in a direction towards the second opposite end of the third optical propagation path; and

the first pump signal propagates from the first end of the first optical propagation path towards the second opposite end of the first optical propagation path.

2. A sensor according to claim 1 wherein the means to prevent the propagation of signals from the second optical propagation path to the third optical propagation path comprises a circulator circuit.

3. A sensor according to claim 1 wherein the third optical propagation path is configurable to be arranged remote to the one or more structures so that a signal propagating in the third optical propagation path is unaffected by properties of the one or more structures.

4. A sensor according to claim 1 , wherein the signal generator is further configured to provide a first pump signal to the first optical propagation path, a second pump signal to the third optical propagation path, and a probe signal to the second optical propagation path, so that one or more distributed sensing techniques may be carried out to determine properties of the one or more structures.

5. A sensor according to claim 4 wherein the first pump signal is configured to have a higher power than the second pump signal.

6. A sensor according to claim 1 , further comprising a coupler configured to divide a main pump signal to provide the first pump signal and second pump signal.

7. A sensor according to claim 1 wherein, the third optical propagation path is configured such that the time for a signal to propagate along the length of the third optical propagation path is equal to, or greater than, the time for a signal to propagate along the length of the first optical propagation path.

8. A method of sensing properties of one or more structures, using a sensor according to claim 1 , comprising the steps of:

arranging the first optical propagation path in cooperation with a structure whose properties are to be sensed;

arranging the second optical propagation path in cooperation with a structure whose properties are to be sensed;

propagating a first pump signal along the first optical propagation path in a direction from the first end of the first optical propagation path towards the second opposite end of the first optical propagation path, and propagating a second pump signal along the third optical propagation path in a direction from the first end of the third optical propagation path towards the second opposite end of the third optical propagation path;

amplifying the second pump signal only such that the second pump signal is amplified before the second pump signal propagate along the second propagation path;

providing a probe signal which propagates along the second optical propagation path, and along said first optical propagation path in a direction from the second end of the first optical propagation path towards the first end of the first optical propagation path to stimulate Brillouin scattering in both the first pump signal which propagates in the first optical propagation path and in the second pump signal which propagates in the second optical propagation path;

preventing the propagation of the probe signal along the third optical propagation path; and

using a backscattered signal which has resulted from the Brillouin scattering, to determine properties of the one or more structures.

9. The method according to claim 8 further comprising the step of, blocking the propagation of signals from the first optical propagation path to the second optical propagation path.

10. The method according to claim 8 further comprising the step of, delaying the propagation of the second pump signal in the third optical propagation path.

11. The method according to claim 8 further comprising the step of, dividing a main pump signal to provide the first and second pump signal.

12. The method according to claim 8 further comprising the step of, remotely controlling the amplification of the second pump signal.

13. The method according to claim 8 further comprising the step of, providing a control signal which controls the amplification provided by an amplifier which is operable to amplify a pump signal.

14. A sensor, suitable for sensing one or more properties of one or more structures, the sensor comprising:

a first optical propagation path which is configurable to cooperate with a structure whose properties are to be sensed;

a second optical propagation path which is configurable to cooperate with a structure whose properties are to be sensed;

a third optical propagation path;

a means for amplifying a signal which propagates in the third optical propagation path, so that the signal is amplified before it begins propagation along the second optical propagation path;

a means to prevent the propagation of signals from the second optical propagation path to the third optical propagation path,

a means for providing a first pump signal to the first optical propagation path and a second pump signal to the third optical propagation path, and

a means for providing a probe signal to the second optical propagation path, so that one or more distributed sensing techniques may be carried out to determine properties of the one or more structures, wherein:

a first end of the first optical propagation path is connected to the means for providing a pump signal to the first optical propagation path and a second opposite end of the first optical propagation path is connected to said means to prevent the propagation of signals from the second optical propagation path to the third optical propagation path, and

a first end of the third optical propagation path is connected to the means for providing a second pump signal to the third optical propagation path and a second opposite end of the third optical propagation path is connected to said means to prevent the propagation of signals from the second optical propagation path to the third optical propagation path, such that:

a pump signal provided in the third optical propagation path, by said means for providing a pump signal, to propagate from the first end of the third optical propagation path in a direction towards the second, opposite end of the third optical propagation path; and

a pump signal provided in the first optical propagation path, by said means for providing a pump signal, to propagate from the first end of the first optical propagation path towards the second, opposite, end of the first optical propagation path, wherein the sensor further comprises, a means to prevent the propagation of signals from the first optical propagation path to the second optical propagation path; and

wherein the means to prevent the propagation of signals from the first optical propagation path to the second optical propagation path, is further configured to allow the propagation of signals, from the second optical propagation path to the first optical propagation path and from the third optical propagation path to the second optical propagation path.

15. A method of sensing properties of one or more structures, using a sensor according to claim 14 , comprising the steps of:

arranging the first optical propagation path in cooperation with a structure whose properties are to be sensed;

arranging the second optical propagation path cooperation a structure whose properties are to be sensed;

propagating a first pump signal along the first optical propagation path in a direction from the first end of the first optical propagation path towards the second, opposite, end of the first optical propagation path, and propagating a second pump signal along the third optical propagation path in a direction from the first end of the third optical propagation path towards the second, opposite, end of the third optical propagation path;

amplifying the second pump signal only such that the second pump signal is amplified before the second pump signal propagate along the second propagation path; providing a probe signal which propagates along the second optical propagation path, and along said first optical propagation path in a direction from the second end of the first optical propagation path towards the first end of the first optical propagation path, to stimulate Brillouin scattering in both the first pump signal which propagates in the first optical propagation path and in the second pump signal which propagates in the second optical propagation path;

preventing the propagation of the probe signal along the third optical propagation path; and

using a backscattered signal which has resulted from the Brillouin scattering, to determine properties of the one or more structures.