DBF fiber laser bend sensor and optical heterodyne microphone
Methods and systems using one or more distributed feedback (DFB) lasers for capturing changes in the lasing environment are disclosed. Specifically, a sensor for measuring a measurand, such as pressure or temperature, or changes in a measurand, includes a fiber with at least one core, at least one fiber laser cavity formed by a single fiber grating in the core, wherein the laser operates on at least two modes along at least part of its length. The DFB laser includes a section that is bent into a non-linear shape and at least one pump laser connected to the fiber laser cavity. When the DFB laser experiences a perturbation or measurand change that changes the spacing of the modes, a change in an RF beat note is generated. This beat note can then be measured and related to the measurand change.
1. A sensor to sense a measurand, the sensor comprising:
a fiber comprising a fiber core;
a fiber laser cavity formed by a single fiber grating in the fiber core, the fiber laser cavity having at least two modes along at least part of its length, the fiber laser cavity including a first section that is bent in a non-linear shape, the non-linear shape having a radius of curvature (R), a change in the measurand causing a shift in a RF beat note (Δv), the Δv being a function of (1/R) 2 ; and
at least one pump laser connected to the fiber laser cavity.
2. The sensor of claim 1 , further comprising a structure connected to the fiber that converts a change in the measurand into a change of the non-linear shape of the first section of the fiber laser cavity.
3. The sensor of claim 1 , the sensor comprising a RF detector connected to the fiber laser cavity.
4. The sensor of claim 1 , wherein the single fiber grating is a distributed feedback laser.
5. The sensor of claim 1 , wherein the fiber laser cavity has a fiber cross-section with anisotropic pressure properties that cause radially asymmetric strain of the fiber which cause the fiber to bend by itself as a result of changing pressure or vibrations.
6. The sensor of claim 4 , further comprising an optical detector connected to the distributed feedback laser.
7. The sensor of claim 1 , wherein the fiber laser cavity has a slow axis and a fast axis of birefringence along at least part of its length.
8. The sensor of claim 1 , wherein the measurand is a pressure or a temperature or a vibration or a chemical reaction.
9. The sensor of claim 6 , further comprising a frequency demodulator connected to the optical detector.
10. The sensor of claim 1 , wherein the sensor is part of an optical heterodyne microphone.
11. A method of sensing a measurand with a sensor, the method comprising:
exciting a fiber laser cavity with a pump laser; and
exposing the sensor to a perturbation, the sensor comprising a fiber, the fiber comprising a fiber core, the sensor further comprising a fiber laser cavity formed by a single fiber grating in the fiber core, the fiber laser cavity having at least two modes along at least part of its length, the fiber laser cavity including a first section that is bent in a non-linear shape, the non-linear shape having a radius of curvature (R), a change in the measurand causing a shift in a RF beat note (Δv), the Δv being a function of (1/R) 2 , the sensor further comprising a pump laser connected to the fiber laser cavity.
12. The method of claim 11 , wherein the perturbation is applied to a structure connected to the sensor.
13. The method of claim 11 , comprising detecting a RF beat note generated by the perturbation with a RF detector connected to the fiber laser cavity.
14. The method of claim 11 , wherein the fiber laser cavity has a fiber cross-section with anisotropic pressure properties that cause radially asymmetric strain of the fiber which cause the fiber to bend by itself as a result of changing pressure or vibrations.
15. The method of claim 11 , wherein the fiber laser cavity has a slow axis and a fast axis of birefringence along at least part of its length.
16. The method of claim 11 , wherein the perturbation is a pressure or a temperature or a vibration or a chemical reaction.
17. The method of claim 11 , wherein a frequency demodulator demodulates a signal from the fiber laser cavity.
18. The method of claim 11 , wherein the sensor is part of an optical heterodyne microphone.
19. A sensor to sense a measurand, the sensor comprising:
a fiber having a radius of curvature (R);
a first core located in the fiber, the first core supporting a first distinct mode, the first distinct mode having a first propagation constant, the first distinct mode being characterized by a first beat note;
a first distributed feedback laser in the first core, the first distributed feedback laser being subject to a perturbation, the perturbation causing a first shift in the first propagation constant, the first shift causing a first change in the first beat note, the first change being a function of (1/R) 2 ;
a second core located in the fiber, the second core supporting a second distinct mode, the second distinct mode having a second propagation constant, the second propagation constant being different from the first propagation constant, the second distinct mode being characterized by a second beat note, the second beat note being different from the first beat note,
a second distributed feedback laser in the second core, the second distributed feedback laser being subject to the perturbation, the perturbation causing a second shift in the second propagation constant, the second shift causing a second change in the second beat note; and
a RF detector connected to the fiber, the RF detector for detecting the first beat note, the RF detector further for detecting the second beat note.
20. The sensor of claim 19 , further comprising one or more additional distributed feedback lasers located in the fiber.