Optical fiber sensing based on changes in laser emission wavelength
A sensor includes a light emitter capable of producing stimulated emission. The sensor includes an optical fiber comprising at least one fiber Bragg grating. A first end of the optical fiber is optically coupled to a first emitting end of the light emitter. The fiber Bragg grating is located at a measurement region of the optical fiber away from the first end. A change in wavelength of the laser emission in the optical fiber is induced by a change in peak reflectivity of the fiber Bragg grating. The change in the peak reflectivity occurs in response to an environmental change at the measurement region, e.g., which changes a physical periodicity and/or the refractive index of the grating. The sensor includes an optical detector coupled to the optical fiber or the light emitter that detects the change in the wavelength.
1 . A sensor comprising:
a light emitter capable of producing stimulated emission, the light emitter comprising a laser diode having multiple longitudinal modes;
an optical fiber comprising at least one fiber Bragg grating, a first end of the optical fiber optically coupled to a first emitting end of the light emitter, the fiber Bragg grating located at a measurement region of the optical fiber away from the first end, a change in wavelength of the laser emission in the optical fiber being induced by a change in peak reflectivity of the fiber Bragg grating, the change in the peak reflectivity occurring in response to an environmental change at the measurement region; and
an optical detector coupled to the optical fiber or the light emitter, the optical detector detecting the change in the wavelength wherein the change in the wavelength comprises a discrete change in the wavelength due to mode hopping, the change in the wavelength indicative of the environmental change.
2 . The sensor of claim 1 , wherein the laser diode comprises a Fabry-Perot laser diode.
3 . The sensor of claim 1 , wherein the first emitting end of the light emitter has an optical reflectivity of less than 5%.
4 . The sensor of claim 3 , wherein the light emitter comprises a semiconductor optical amplifier or reflective semiconductor optical amplifier.
5 . The sensor of claim 3 , wherein the change in the wavelength of the laser emission is continuous.
6 . The sensor of claim 1 , wherein the optical detector is coupled to a second end of the optical fiber opposite the first end of the optical fiber.
7 . The sensor of claim 1 , wherein the optical detector is coupled to a second emitting end of the light emitter opposite the first emitting end of the light emitter.
8 . The sensor of claim 1 , wherein the environmental change comprises at least one of a change in temperature of the optical fiber and a change in strain of the optical fiber.
9 . The sensor of claim 1 , wherein the at least one fiber Bragg grating comprises two or more fiber Bragg gratings, each of the two or more fiber Bragg gratings longitudinally spaced apart in the optical fiber along respective two or more measurement regions, each of the two or more fiber Bragg gratings tuned to affect a different wavelength of the laser emission.
10 . The sensor of claim 9 , wherein changes in the different wavelengths are used by the optical detector to respectively determine environmental changes at the two or more measurement regions.
11 . The sensor of claim 1 , wherein the light emitter and the optical detector are physically co-located.
12 . The sensor of claim 1 , wherein the optical detector is coupled to the optical fiber between the first end of the optical fiber and a second end of the optical fiber opposite to the first end of the optical fiber.
13 . A method comprising:
causing stimulated emission of light from a light emitter into an optical fiber that comprises at least one fiber Bragg grating, the light emitter comprising a laser diode having multiple longitudinal modes, the fiber Bragg grating located at a measurement region of the optical fiber away from the emitter, a change in wavelength of laser emission in the optical fiber being induced by a change in peak reflectivity of the fiber Bragg grating, the change in peak reflectivity occurring in response to an environmental change at the measurement region;
detecting the change in the wavelength by an optical detector, wherein the change in the wavelength comprises a discrete change in the wavelength due to mode hopping; and
measuring the environmental change in response to the change in the wavelength by a monitoring apparatus coupled to the optical detector.
14 . The method of claim 13 , wherein the environmental change comprises at least one of a change in temperature of the optical fiber and a change in strain of the optical fiber.
15 . The method of claim 13 , wherein the at least one fiber Bragg grating comprises two or more fiber Bragg gratings, each of the two or more fiber Bragg gratings longitudinally spaced apart in the optical fiber along respective two or more measurement regions, each of the two or more fiber Bragg gratings tuned to affect a different wavelength of the laser emission, and wherein changes in the different wavelengths are detected by the optical detector and used by the monitoring apparatus to respectively determine environmental changes at the two or more measurement regions.