CN106403833A - Method utilizing fiber core mismatch interference structure to measure strain - Google Patents

Abstract

The present invention provides a method for measuring strain by using a fiber core mismatch interference structure, the method comprising the following steps: a) building a fiber core dislocation welding interference structure, the fiber core dislocation welding interference structure including sequentially connected pumping sources , wavelength division multiplexer, gain fiber, the first single-mode fiber, the second single-mode fiber, the third single-mode fiber and spectrum analyzer; b) to the first single-mode fiber, the second single-mode fiber and the third single-mode fiber c) measure the external strain of the temperature control device to be tested: combine the first single-mode optical fiber, the second single-mode optical fiber and the third single-mode optical fiber with the temperature control device, and under the condition of strain change Next, cause the interferometer to bend, by gradually increasing the size of the strain, record the moving length of the comb spectrum, and obtain the change curve of the comb spectrum with the strain, according to the drift amount, the strain amount can be inferred by the following formula: Y=aX±b , where X is the strain, Y is the changing wavelength, and a, b are constants.

Description

A Method for Measuring Strain Using Core Mismatch Interferometric Structure

technical field

The invention relates to the field of optical communication, in particular to a method for measuring strain by using a fiber core mismatch interference structure.

Background technique

The all-fiber sensor has the advantages of compact structure, long service life, sensitivity to test volume, and multiple transmission channels, and is widely used in optical fiber sensing, optical fiber communication, optical processing and other fields. Through the micro-machining technology of the fiber end face or building an all-fiber sensor with an interference structure, under the action of the pump source, an interference spectrum curve with a comb-like spectrum pattern is output. The thin-core optical fiber Mach-Zehnder optical fiber sensor has a simple structure and is easy to implement. The structure consists of a thin-core optical fiber welded to two relatively thick core-diameter doped rare-earth optical fibers. The doped rare-earth optical fiber is also used as the gain medium of the sensor. . With the development of optical fiber sensing technology, there are many kinds of optical fiber sensors for measuring strain. In 2011, Fan Linyong et al. designed a Mach-Zehnder interferometer based on dual-core optical fiber, which is applied to the measurement of temperature and strain, and interference fringes The width-to-surface ratio is about 10dBm, and the fringe interval is about 2nm. In 2013, Zou Hui et al. used two 3dB couplers to make a Mach-Zehnder interferometer system, combined with a dual-core optical fiber, to form a Mach-Zehnder interferometer with a dual-stage structure. The fringe-to-width ratio is about 30dBm. Optical fiber Mach-Zehnder interferometer has the advantages of simple structure, high fringe contrast, and dense comb spectrum, and is often used in the field of optical fiber sensing. But these fiber optic sensors have disadvantages, which are limited in practical application.

Contents of the invention

In order to solve the above problems, the present invention provides a method for measuring strain using a core mismatch interference structure, the method includes the following steps: a) building a core misalignment fusion fusion interference structure, the fiber core misalignment fusion fusion interference structure includes sequentially Connected pump source, wavelength division multiplexer, gain fiber, first single-mode fiber, second single-mode fiber, third single-mode fiber and spectrum analyzer; b) for the first single-mode fiber, the second single-mode The optical fiber and the third single-mode optical fiber are dislocated and welded; c) measuring the external strain of the temperature control device to be tested: combining the first single-mode optical fiber, the second single-mode optical fiber and the third single-mode optical fiber with the temperature control device, Under the condition of strain change, the interferometer is caused to bend. By gradually increasing the strain, the length of the comb spectrum movement is recorded, and the change curve of the comb spectrum with strain is obtained. The wavelength of the measurement point is selected, and the spectral wavelength curve drifts at this time. , According to the amount of drift, the amount of strain can be deduced by the following formula: Y=aX±b, where X is the strain, Y is the changing wavelength, and a and b are constants.

Preferably, the calculation in step c) is to read the measured wavelength of the core mismatch structure according to the relationship curve between the calibrated wavelength shift of the fiber core mismatch structure and the strain suffered by the susceptor The corresponding external strain.

Preferably, the relationship curve between the wavelength shift and the strain change of the core mismatch structure is calibrated by placing the core mismatch structure under known strain conditions.

Preferably, the output end of the first single-mode optical fiber is connected to the input end of the second single-mode optical fiber through a dislocation fusion splicing structure, and the output end of the second single-mode optical fiber is connected to the input end of the third single-mode optical fiber through a dislocation fusion splicing structure .

Preferably, the radial misalignment distance of the single-mode optical fiber in the step b) is 3-4 μm.

Preferably, the radial misalignment distance of the single-mode optical fiber is 3.6 μm.

Preferably, the length of the second single-mode optical fiber is 9 cm.

It should be understood that both the foregoing general description and the following detailed description are exemplary illustrations and explanations, and should not be used as limitations on the claimed content of the present invention.

Description of drawings

With reference to the accompanying drawings, more objects, functions and advantages of the present invention will be clarified through the following description of the embodiments of the present invention, wherein:

FIG. 1 is a schematic diagram of a fiber core mismatch structure;

2 is a schematic diagram of a core mismatch interferometer for measuring strain according to the present invention;

Figure 3 is an image of a single-mode optical fiber dislocation fusion splicing;

Figure 4 is a transmission spectrum diagram of a single-mode optical fiber with different dislocations;

Figure 5 is a schematic diagram of the red-shift or blue-shift of the fiber comb spectrum during the calibration process;

Fig. 6 is a curve of the fiber comb spectrum changing with strain during the calibration process.

detailed description

Core mismatch is the core mismatch during fiber splicing. According to the principle of core mismatch, the core mismatch interference structure is a special Mach-Zehnder interferometer. In the single-mode-multimode-singlemode (Single mode-Multi mode-Singlemode, SMS) structure (as shown in Figure 1), the single-mode fiber at the input end couples the incident light into the single-mode fiber with a dislocated core. After the optical fiber is modulated, the incident light is drawn out through the single-mode fiber at the output end, and the light wave mode is transmitted along the optical fiber. In the transmission direction, the light intensity will change periodically with the change of the length of the multimode fiber, even in the multimode fiber. The light field distribution is almost the same as the incident light field. This is the mode interference effect in multimode fiber, also called intermode interference. Since the interference between multiple modes can be realized in one fiber, the optical path is simplified and the structure It is more compact, and has low loss and is free from external interference, so it has a good development prospect.

Fig. 2 shows a schematic diagram of a core mismatch interferometer structure using a core mismatch interference structure to measure strain according to the present invention. A core mismatch interferometer 200 as shown in Fig. 2 is built, including sequentially connected pumps Source 201 , wavelength division multiplexer (WDM) 202 , gain fiber 203 , first single mode fiber (SMF) 204 , second single mode fiber 205 , third single mode fiber 206 and optical spectrum analyzer 207 . The output end of the pumping source 201 is connected to the wavelength division multiplexer (WDM) 202 and the gain fiber 203 in turn, the gain fiber 203 is connected to the input end of the first single-mode fiber 204, and the output end of the first single-mode fiber 204 is connected to the second The input end of the single-mode optical fiber 205 is connected by a dislocation fusion splicing structure, the output end of the second single-mode optical fiber 205 is connected with the input end of the third single-mode optical fiber 206 by a dislocation fusion splicing structure, and the output end of the third single-mode optical fiber 206 is connected with the spectral analysis Meter 207 is connected.

According to the present invention, the working principle of the fiber core mismatch interference structure for measuring strain by using the fiber core mismatch interference structure is as follows:

Firstly, the first single-mode optical fiber 204 , the second single-mode optical fiber 205 and the third single-mode optical fiber 206 are spliced with optical fiber dislocation. Figure 3 is an image of a single-mode optical fiber dislocation fusion splicing. When the optical fiber dislocation is spliced, the dislocation amount is gradually adjusted in the order from small to large. Figure 4 is the transmission spectrum of different dislocation amounts. Observing the transmission spectrum, it is found that when the dislocation amount is too small, there is no obvious inter-mode interference phenomenon, such as As shown in Figure 4a, this is because when the transmitted light is coupled into the second single-mode fiber (9cm in length) by the first single-mode fiber, most of the light propagates through the core, and only a small part is coupled into the cladding. The interference effect is not obvious when they meet in the third single-mode fiber; when the dislocation amount is appropriate, the mode in the fiber will change, and the mode change will lead to different interference results. With the increase of the dislocation amount, the interference phenomenon is gradually obvious; when When the misalignment is too large, due to the large loss at the fiber fusion joint, the inter-mode interference phenomenon is also not obvious, as shown in Figure 4c. The size of the fiber core/cladding of the optical fiber that adopts among the present invention is 10/125 μ m, when dislocation is few, the light that is injected in the cladding of rear end by front-end fiber core is weaker, and interference phenomenon is not obvious; When dislocation is bigger, The light injected from the front core into the back cladding is strong, but the light in the core is weak, and the interference phenomenon is affected; when the radial misalignment distance is 3-4 μm, the light injected from the front core into the back cladding and the core The light intensity is similar, so it has the best effect, as shown in Figure 4b. The best experimental effect is obtained when the fusion splice distance between the first single-mode fiber and the second single-mode fiber is the same as the fusion splice distance between the second single-mode fiber and the third single-mode fiber.

Secondly, the temperature calibration of the core mismatch interference structure is carried out. The calibration process is as follows: the first single-mode fiber, the second single-mode fiber and the third single-mode fiber are combined with the strain control device. Under the condition of strain change, Causes the interferometer to bend, resulting in a change in the optical path of the two arms of the interference, resulting in a red shift or blue shift in the comb spectrum (as shown in Figure 5). According to the change of the wavelength value at the trough under different strain intensities, Sensitivity of the sensor to changes in external strain conditions,

As the strain increases, that is, the axial microstress increases, the transmission spectrum of the comb filter shifts to the short-wave or long-wave direction. By gradually increasing the magnitude of the strain and recording the length of the comb spectrum movement, the change curve of the comb spectrum with strain is obtained, as shown in Figure 6. The wavelength of the measurement point is selected, and the spectral wavelength curve drifts at this time. According to the drift amount, the strain amount can be inferred by the following formula:

Y=aX±b,

Among them, X is the strain, Y is the changing wavelength, and a and b are constants.

Finally, the applied temperature is measured through the relationship curve between spectral line shift and strain. Using the strain calibration curve, determine the strain experienced by the sensor.

Other embodiments of the invention will be readily apparent to and understandable to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. The description and examples are considered exemplary only, with the true scope and spirit of the invention defined by the claims.

Claims (7)

1. A method utilizing a fiber core mismatch interference structure to measure strain, said method comprising the steps of: a) Building a fiber core dislocation fusion splicing interference structure, the fiber core dislocation fusion splicing interference structure includes a pump source connected in sequence, a wavelength division multiplexer, a gain fiber, a first single-mode fiber, a second single-mode fiber, and a third single-mode fiber. Mode fiber and optical spectrum analyzer; b) Perform optical fiber dislocation fusion splicing on the first single-mode optical fiber, the second single-mode optical fiber and the third single-mode optical fiber; c) Measure the external strain of the temperature control device to be tested: Combining the first single-mode fiber, the second single-mode fiber and the third single-mode fiber with the temperature control device, the interferometer is caused to bend under the condition of strain change, and the comb spectrum is recorded by gradually increasing the strain Move the length of the comb to get the change curve of the comb spectrum with the strain. Select the wavelength of the measurement point. At this time, the spectral wavelength curve drifts. According to the drift amount, the strain amount can be inferred by the following formula: Y=aX±b, Among them, X is the strain, Y is the changing wavelength, and a and b are constants. 2. The method according to claim 1, wherein the calculation in the step c) is based on the relational curve between the calibrated wavelength drift of the mismatched core structure and the strain suffered by the susceptor, and reads the The measured external strain corresponding to the wavelength of the core-mismatched structure. 3. The method of claim 2, wherein the relationship between wavelength shift and strain change of the core mismatched structure is calibrated by subjecting the core mismatched structure to a known strain condition. 4. The method according to claim 1, wherein the output end of the first single-mode fiber is connected to the input end of the second single-mode fiber by a dislocation fusion splicing structure, and the output end of the second single-mode fiber is connected to the third single-mode fiber The input end of the optical fiber is connected by a dislocation fusion splicing structure. 5. The method according to claim 1, wherein the radial displacement distance of the single-mode optical fiber in the step b) is 3-4 μm. 6. The method of claim 1, wherein the radial misalignment distance of the single-mode fiber is 3.6 μm. 7. The method of claim 1, wherein the second single-mode optical fiber has a length of 9 cm.