CN218002459U - Optical fiber strain sensor based on vernier effect - Google Patents

Abstract

The utility model discloses an optical fiber strain sensor based on a vernier effect, which comprises a reference interferometer and a sensing interferometer arranged in parallel, the reference interferometer and the sensing interferometer are Mach-Zehnder interferometers; the reference interferometer The instrument and the sensing interferometer include the first single-mode fiber, the second single-mode fiber, the few-mode fiber and the third single-mode fiber which are fused in sequence; the light beam is excited into a high-order mode and a fundamental mode through the second single-mode fiber; the few-mode The optical fiber transmits the high-order mode and the fundamental mode to the third single-mode optical fiber; the high-order mode and the fundamental mode interfere in the third single-mode optical fiber; the utility model simultaneously monitors the transmission spectrum of the reference interferometer that is only affected by temperature changes Wavelength drift, the wavelength drift of the large envelope of the parallel signal affected by both strain and temperature changes can demodulate temperature and strain, which not only greatly improves the strain sensitivity of the sensor, but also eliminates the influence of temperature.

Description

A Fiber Optic Strain Sensor Based on Vernier Effect

technical field

The utility model belongs to the technical field of optical fiber sensing, in particular to an optical fiber strain sensor based on the cursor effect.

Background technique

Compared with traditional electronic sensors, fiber optic sensors are favored by many scholars and researchers because of their simple structure, small size, light weight, anti-electromagnetic interference, and high sensitivity. In recent years, in order to further improve the measurement sensitivity of Mach-Zehnder sensors, the vernier effect has entered the sight of researchers. The vernier effect was first applied to vernier caliper barometers to improve the accuracy of measurement, and was later applied to optical device sensing systems to amplify the shift of spectral resonant peaks and improve the sensitivity of photonic devices. The Mach-Zehnder interference principle is widely used in optical interference testing because of its simple and stable characteristics in various interference principles. The single physical parameters measured according to the Mach-Zehnder interference principle can be temperature, refractive index, pressure, etc. , Strain, etc.

However, most sensors based on the Mach-Zehnder interference principle have multi-parameter responses, and it is difficult to accurately measure a single parameter, so synchronous sensing of strain and temperature is one of the ways to achieve accurate measurement. At present, more and more researchers are beginning to study the dual-parameter measurement sensor, while the traditional multi-parameter sensor realizes the simultaneous measurement of temperature and strain through the sensitivity measurement matrix. However, the sensor envelope based on the vernier effect is a single-frequency signal. Simultaneous measurement of temperature and strain cannot be achieved using the aforementioned sensitivity matrix, eliminating temperature cross-sensitivity.

Utility model content

The purpose of the utility model is to provide a fiber optic strain sensor based on the vernier effect, which improves the strain sensitivity of the sensor and eliminates the influence of temperature.

In order to solve the above problems, the utility model adopts the following technical scheme: a fiber optic strain sensor based on the vernier effect, including a reference interferometer and a sensing interferometer arranged in parallel, and the reference interferometer and the sensing interferometer are Mach-Zeng Del interferometer; the reference interferometer and the sensing interferometer include the first single-mode fiber, the second single-mode fiber, the few-mode fiber and the third single-mode fiber which are fused in sequence; the light beam is excited into a high-order mode by the second single-mode fiber and the fundamental mode; the few-mode fiber transmits the high-order mode and the fundamental mode to the third single-mode fiber; the high-order mode and the fundamental mode interfere in the third single-mode fiber.

Further, the second single-mode fiber includes a splicing ball A and a splicing ball B. When the light beam is transmitted to the splicing ball A through the first single-mode fiber, it is excited into a high-order mode of the cladding in the second single-mode fiber; the light beam passes through When splicing ball A is transmitted to splicing ball B, it is excited as the fundamental mode in the fiber core.

Further, the reference interferometer and the sensing interferometer are connected in parallel through two 3dB couplers.

Further, the free spectral range FSR _envelope produced by the optical fiber strain sensor is:

Among them, FSR _s represents the free spectral range of the sensing interferometer; FSR _r represents the free spectral range of the reference interferometer.

Further, the vernier effect sensitivity amplification factor M of the optical fiber strain sensor is:

Further, when the external temperature changes, the transmission spectrum wavelength of the reference interferometer drifts, and the calculation formula of the drift Δλ of the reference interferometer is:

Δλ=k _1T ΔT

In the formula, k _1T is the temperature sensitivity of the sensor interferometer, and ΔT is expressed as the temperature change value.

Further, when the external temperature and strain change, the wavelength of the transmission spectrum of the sensing interferometer will also change accordingly, and the calculation formula of the transmission spectrum wavelength shift Δλ _envelope of the sensing interferometer is:

Δλ _envelope = k _2T ΔT+k _2ε Δε

In the formula, k _2T is the temperature sensitivity of the sensing interferometer; k _2ε is the strain sensitivity of the sensing interferometer, and Δε is the strain change value.

Compared with the prior art, the beneficial effects achieved by the utility model are:

On the one hand, the utility model adopts the reference interferometer and the sensing interferometer arranged in parallel, and the reference interferometer and the sensing interferometer are Mach-Zehnder interferometers; Wavelength drift, the wavelength drift of the large envelope of the parallel signal affected by strain and temperature changes can demodulate temperature and strain, make the optical fiber strain sensor produce a vernier effect and calibrate, not only greatly improve the sensor strain sensitivity, but also eliminate affected by temperature.

On the other hand, the second single-mode fiber described in the present invention includes a fusion splice ball A and a fusion splice ball B. When the light beam is transmitted to the fusion splice ball A through the first single-mode fiber, it is excited into a higher-order mode of the cladding in the second single-mode fiber; When the light beam passes through the splicing ball A and is transmitted to the splicing ball B, it is excited as the fundamental mode in the fiber core; the second single-mode optical fiber ensures that interference can still occur after increasing the propagation distance.

Description of drawings

Fig. 1 is a schematic structural diagram of an optical fiber strain sensor based on the vernier effect provided by an embodiment of the present invention;

In the figure: 1-the first single-mode fiber; 2-the second single-mode fiber; 21-the fusion ball A; 22-the fusion ball B; 3-the few-mode fiber; 4-the third single-mode fiber.

detailed description

The utility model will be further described below in conjunction with the accompanying drawings. The following examples are only used to illustrate the technical solution of the utility model more clearly, but not to limit the protection scope of the utility model.

In describing the present utility model, it should be understood that the terms "center", "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", The orientations or positional relationships indicated by "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. are based on the orientation or positional relationships shown in the drawings, and are only for the convenience of describing the present invention. Novel and simplified descriptions do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore should not be construed as limiting the utility model.

In addition, in the description of the present utility model, unless otherwise specified, "plurality" means two or more.

In the description of the present utility model, it should be noted that, unless otherwise clearly stipulated and limited, the terms "installation", "connection" and "connection" should be understood in a broad sense, for example, it can be a fixed connection or a flexible connection. Detachable connection, or integral connection; it can be mechanical connection or electrical connection; it can be direct connection or indirect connection through an intermediary, and it can be the internal communication of two components. Those of ordinary skill in the art can understand the specific meanings of the above terms in the present invention through specific situations.

As shown in Figure 1, the embodiment of the utility model provides a kind of optical fiber strain sensor based on the vernier effect, including the reference interferometer and the sensing interferometer arranged in parallel, the reference interferometer and the sensing interferometer are Mach-Zeng Del interferometer; the reference interferometer and the sensing interferometer include the first single-mode fiber 1, the second single-mode fiber 2, the few-mode fiber 3 and the third single-mode fiber 4 which are fused in sequence; the first single-mode The output end of the optical fiber 1 is connected to the input end of the second single-mode optical fiber 2; the second single-mode optical fiber 2 includes a fusion splice ball A21 and a fusion splice ball B22, and when the light beam is transmitted to the fusion splice ball A21 through the first single-mode optical fiber 1, the excitation It is the high-order mode of the cladding in the second single-mode fiber 2; when the light beam passes through the fusion ball A21 and is transmitted to the fusion ball B22, it is excited as the fundamental mode in the core, and the few-mode fiber 3 transmits the high-order mode and the fundamental mode to the The third single-mode optical fiber 4; the high-order mode and the fundamental mode interfere in the third single-mode optical fiber 4, and the second single-mode optical fiber 2 ensures that the interference can still occur after increasing the propagation distance.

The optical signal in the sensing interferometer is superimposed with the optical signal in the reference interferometer to produce a vernier effect, resulting in a large interference envelope; the optical fiber strain sensor is connected to the isolator; keep the sensor strain-free, only when the temperature changes , the temperature sensitivity k _1T of the reference interferometer is calibrated by computer, and the temperature sensitivity k _1T of the reference interferometer is obtained by fitting the temperature change-transmission spectrum trough wavelength shift curve; keep the sensor without strain, only when the temperature changes, Calibrate the temperature sensitivity k _2T of the parallel signal envelope of the fiber optic strain sensor, and obtain the temperature sensitivity k _2T of the parallel signal envelope of the fiber optic strain sensor by fitting the temperature change-envelope valley wavelength shift curve; keep the initial temperature of the sensor remains unchanged, only when the strain acts on the sensing interferometer, the strain sensitivity k _2ε of the parallel signal envelope of the fiber optic strain sensor is calibrated, and the parallel signal envelope is obtained by fitting the strain-envelope valley wavelength shift curve Strain sensitivity k _2ε .

The free spectral range FSR _envelope that described optical fiber strain sensor produces is:

Among them, FSR _s represents the free spectral range of the sensing interferometer; FSR _r represents the free spectral range of the reference interferometer.

The vernier effect sensitivity amplification factor M of the optical fiber strain sensor is:

When the external temperature changes, the transmission spectrum wavelength of the reference interferometer drifts, and the calculation formula of the drift Δλ of the reference interferometer is:

Δλ=k _1T ΔT

In the formula, k _1T is the temperature sensitivity of the sensor interferometer, and ΔT is expressed as the temperature change value.

When the external temperature and strain change, the wavelength of the transmission spectrum of the sensing interferometer will also change accordingly, and the calculation formula of the transmission spectrum wavelength drift Δλ _envelope of the sensing interferometer is:

Δλ _envelope = k _2T ΔT+k _2ε Δε

In the formula, k _2T is the temperature sensitivity of the sensing interferometer; k _2ε is the strain sensitivity of the sensing interferometer, and Δε is the strain change value.

The preparation of the sensing interferometer and the reference interferometer comprises the following steps:

After removing the coating layer from the first single-mode optical fiber 1 and the second single-mode optical fiber 2, wipe it clean with alcohol, then cut out 2 cm of uncoated optical fiber with a cutting knife, and separate the first single-mode optical fiber 1 and the second single-mode optical fiber 1 and the second single-mode optical fiber. The cutting surfaces at both ends of the single-mode optical fiber 2 are cut smoothly;

Place a well-cut single-mode optical fiber at one end of the fusion splicer for discharge; since the discharge power during manual discharge will be greater than the power of ordinary fusion splicing, the cut surface of the optical fiber will melt and shrink, and then present a spherical state . Two small balls that have been welded separately are placed on both ends of the welding machine at the same time for manual discharge to form welded ball A21 and welded ball B22;

Cut off the redundant structure of the second single-mode optical fiber 2, and only keep the splicing ball A21 and the splicing ball B22;

After removing the coating layer from the few-mode optical fiber 3 , wipe it clean with alcohol, cut out a 25.8 cm fiber without the coating layer with a cutting knife, and cut the cut surfaces at both ends flat. One end of the few-mode fiber 3 is fused to the core of the fusion ball B22, and the other end is fused to the third single-mode fiber 4; the fabricated sensing interferometer and reference interferometer are packaged and protected.

In the embodiment of the utility model, two sensing interferometers and reference interferometers with similar but not identical FSRs are connected in parallel to generate a vernier effect, which greatly improves the strain sensitivity of the parallel sensors; The wavelength shift of the transmission spectrum of the instrument, and the wavelength shift of the large envelope of the parallel signal affected by the strain and temperature changes can demodulate the temperature and strain, which not only greatly improves the strain sensitivity of the sensor, but also eliminates the influence of temperature.

The above description is only a preferred example of the utility model, and is not intended to limit the utility model. Although the utility model has been described in detail with reference to the aforementioned embodiments, for those skilled in the art, it can still be used for the aforementioned items. The technical schemes recorded in the examples are modified, or some technical features are equivalently replaced. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present utility model shall be included in the protection scope of the present utility model.

Claims (5)

1. The optical fiber strain sensor based on the vernier effect is characterized by comprising a reference interferometer and a sensing interferometer which are arranged in parallel, wherein the reference interferometer and the sensing interferometer are Mach-Zehnder interferometers; the reference interferometer and the sensing interferometer comprise a first single-mode fiber, a second single-mode fiber, a few-mode fiber and a third single-mode fiber which are sequentially welded; the light beam is excited into a high-order mode and a fundamental mode by the second single-mode fiber; the few-mode fiber transmits a high-order mode and a fundamental mode to the third single-mode fiber; the higher-order mode and the fundamental mode interfere in the third single-mode fiber.

2. The vernier effect based optical fiber strain sensor as claimed in claim 1, wherein the second single mode fiber comprises a fusion ball a and a fusion ball B, and the light beam is excited into a high-order mode of a cladding in the second single mode fiber when being transmitted to the fusion ball a through the first single mode fiber; the beam is excited into a fundamental mode in the core as it passes through the solder ball a to the solder ball B.

3. A vernier effect based fibre optic strain sensor as claimed in claim 1 or 2 wherein the reference and sensing interferometers are connected in parallel by two 3dB couplers.

4. The vernier effect based fiber optic strain sensor of claim 1, wherein the free spectral range FSR generated by the fiber optic strain sensor is _envelope Comprises the following steps:

wherein, FSR _s Representing the free spectral range of the sensing interferometer; FSR _r Representing the free spectral range of the reference interferometer.

5. The vernier effect based optical fiber strain sensor according to claim 4, wherein the vernier effect sensitivity amplification factor M of the optical fiber strain sensor is:

Images