Vernier effect based optical fiber line intra-cascade Fabry-Perot cavity sensor induced by femtosecond laser

Abstract

The invention puts forward an interferometer cascaded by two Fabry-Perot cavities on the basis of an optical fiber line. The interferometer comprises a broadband light source, a circulator, a sensinghead and a spectrum analyzer, wherein the sensing head is manufactured by a single-mode optical fiber or a multimode optical fiber. The interferometer is characterized in that femtosecond laser is used for inscribing four reflecting mirror surfaces which vertically penetrate through a fiber core and have the same size, wherein the end surface of the optical fiber is cut into a wedge shape to eliminate end surface reflection interference, and all reflecting mirrors and the optical fiber form the sensing head of the Fabry-Perot cavity interferometer. Light from the broadband light source is received by the circulator and is transmitted to the sensing head, then, the sensing head returns the light to the circulator, and the light is transmitted to the spectrum analyzer through the circulatorso as to form the cascade Fabry-Perot cavity interferometer. The interferometer has the characteristics of being simple in structure, simple in manufacture, low in cost, high in sensitivity and the like.

Description

technical field [0001] The invention provides an optical fiber in-line cascaded Fabry-Perot cavity interferometer based on a vernier effect, which belongs to the technical field of optical fiber sensing. Background technique [0002] Optical fiber strain sensors have the advantages of light weight, small size, durability, anti-electromagnetic interference, flexible operation, and good stability. They are widely used in aerospace, environmental monitoring, civil engineering and other fields. The structural types of optical fiber strain sensors include: Bragg grating (FBG), long period grating (LFBG), hollow photonic crystal fiber (PCF), dislocation fusion, tapered, built-in cavity, and optical waveguide, etc. However, the sensitivity of strain sensors fabricated from a single structure is relatively low, usually below 10 pm / με. The vernier effect can effectively improve the sensitivity. This method is not to track the shift of a single fringe in the spectrum, but to monitor ...

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Problems solved by technology

However, these structures have some limitations: cascaded Mach-Zehnder interferometers usually work in the transmission mode, which is not convenient for remote sensing; cascaded Signac interferometers are not suitable for measuring physical quantities that change along one-dimensional axes; The structure of the instrument is complicated and difficult to manufacture; while the more popular cascaded Fabry-Perot cavity interferometer usually fuses different types of optical fibers or capillaries together. Although the structure is relatively simple, the Fabry-Perot cavity interferometer The position of the cavity will change during the welding process, resulting in the failure to achieve the expected cascade amplification effect

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