Double-parameter temperature refractive index sensing device based on all-fiber hybrid interferometer structure

Abstract

The invention discloses a dual-parameter temperature refractive index sensing device based on an all-fiber hybrid interferometer structure. The dual-parameter temperature refractive index sensing device comprises an ASE light source, a spectrograph, a 2 * 2 coupler, a polarization controller and a polarization maintaining fiber subjected to tapering treatment, the polarization maintaining optical fiber serves as a core structure of the interferometer; the structure of the interferometer comprises a Mach-Zehnder interferometer and a Sagnac interferometer; the structure of the Mach-Zehnder interferometer is a polarization maintaining optical fiber subjected to tapering treatment, and the Sagnac interferometer realizes light splitting by adopting the polarization maintaining optical fiber subjected to tapering treatment; the diameter of the waist region of the optical fiber is changed by the tapering processed polarization maintaining optical fiber. By using a double-interferometer mixed structure, the sensitivity and the structural stability of optical fiber double-parameter detection are improved, and the detection capability of the sensing structure in different complex environments is improved.

Description

Technical Field

[0001] The present invention relates to the field of optical fiber sensing detection technology, and in particular to a dual-parameter temperature and refractive index sensing device based on an all-optical fiber hybrid interferometer structure. Background Art

[0002] The dual-parameter fiber optic sensor based on the all-fiber structure has the advantages of small size, high sensitivity, low cost, corrosion resistance and anti-electromagnetic interference, so it has practical significance in many fields such as food safety, environmental governance, and chemical production. In practical applications, the optical properties of fiber optic sensing are often affected by multiple parameters, especially temperature, refractive index and other parameters. Therefore, sensors that can realize dual-parameter detection of temperature and refractive index are increasingly valued. The all-fiber sensing structure is an effective way to achieve dual-parameter measurement. Therefore, the all-fiber hybrid interferometer structure fiber optic sensor has received widespread attention. The hybrid interference structure sensing system can effectively improve the stability of the experimental system and improve the reaction sensitivity.

[0003] Common fiber interferometers include Mach-Zehnder interferometer, Sagnac interferometer and other structures. Interferometers have been widely used in fiber optic sensing systems due to their unique structural advantages. Using a single or multiple interferometers in a sensing system can effectively enhance the interference effect. Compared with ordinary single-mode fiber (SMF), polarization-maintaining fiber (PMF) is a special fiber that can maintain the polarization state of the incident light. Tapering the polarization-maintaining fiber (PMF) can form an interference effect similar to that of the Mach-Zehnder interferometer and expand the measurement parameters. The tapered polarization-maintaining fiber (PMF) of a certain length is placed in a Sagnac loop to construct a dual interferometer structure, forming a hybrid interference spectrum combining a large envelope spectrum and fine stripes. This hybrid interference spectrum can better realize the sensitivity of the fiber structure to external sensing information and facilitate the acquisition of multi-feature parameter information. The taper operation causes a sudden change in the diameter of the fiber waist, breaking the original thermal insulation and refractive index insensitivity of the polarization-maintaining fiber (PMF), which also makes it possible to reorganize and couple the internal modes of the fiber. The two parts of the polarization-maintaining fiber that are not tapered are called transition zones. The two transition zones play the role of exciting the fundamental mode, high-order mode and recoupling modes respectively. The fiber mode propagating in the transition zone will be excited into the fundamental mode and high-order mode of orthogonal modes. The excited mode will produce an optical path difference when passing through the waist of the tapered part and recouple in the transition zone at the other end, achieving an effect similar to that of a Mach-Zehnder interferometer. The original thermal insulation of the polarization-maintaining fiber (PMF) is broken by the taper operation, which makes the polarization-maintaining fiber, which is insensitive to the refractive index, sensitive to the refractive index, so it can be used for refractive index detection. In addition, since the polarization-maintaining fiber (PMF) generates an axial tension along the stress rod direction during the preparation process, the core will produce birefringence. When the ambient temperature changes, the changes caused by the stress rods in the polarization-maintaining fiber will be more significant than the changes in the core and cladding, which will cause changes in birefringence. Temperature sensing can be achieved through the changes caused by this birefringence. Due to the high-quality characteristics of the sensing structure, the good effect of dual-parameter sensing of temperature and refractive index is achieved. Figure 1 Schematic diagram of the structure of polarization-maintaining fiber (PMF) taper.

[0004] The fiber optic sensing technology based on the all-fiber hybrid interferometer structure is a passive sensing solution that uses the fiber structure to achieve interference effects and simultaneously sense changes in external multi-parameter physical quantities. Its structure mainly includes: ASE light source, coupler, polarization controller (PC), spectrometer and other equipment. The light emitted by the ASE light source is input into the loop where the polarization-maintaining fiber (PMF) is located through the coupler. The polarization state in the loop is continuously adjusted by the polarization controller until the optimal spectral modulation depth is reached. The modulated light is input into the spectrometer after passing through the coupler for real-time detection. Figure 2 Schematic diagram of the Sagnac and MZI hybrid structure based on polarization-maintaining fiber (PMF) tapering.

[0005] Compared with traditional fiber optic sensors, the dual-parameter fiber optic sensor with an all-fiber hybrid interferometer structure has good robustness. While achieving a stable sensing structure, it can greatly reduce the volume of the sensing system and effectively improve the sensitivity of the measured parameters. It has the advantages of simple structure, convenient preparation, small size, and anti-electromagnetic interference. At the same time, the fiber optic sensing system can be placed in complex environments due to its good stability, which is of great significance for the expansion of complex environment detection. Summary of the invention

[0006] The present invention provides a dual-parameter temperature and refractive index sensing device based on an all-fiber hybrid interferometer structure. The present invention improves the sensitivity and structural stability of optical fiber dual-parameter detection by using a dual-interferometer hybrid structure, and improves the detection capability of the sensing structure in different complex environments. See the following description for details:

[0007] A dual-parameter temperature and refractive index sensing device based on an all-fiber hybrid interferometer structure, the device comprising: an ASE light source, a spectrometer, a 2×2 coupler, a polarization controller, and a tapered polarization-maintaining optical fiber;

[0008] The polarization-maintaining optical fiber is used as the core structure of the interferometer; the structure of the interferometer includes: Mach-Zehnder interferometer and Sagnac interferometer;

[0009] The structure of the Mach-Zehnder interferometer is a polarization-maintaining optical fiber after tapering, and the Sagnac interferometer uses the polarization-maintaining optical fiber after tapering to achieve light splitting; the polarization-maintaining optical fiber after tapering changes the diameter of the optical fiber waist region.

[0010] Wherein, the device comprises:

[0011] The polarization-maintaining fiber is placed in the fiber taper machine for taper processing. The first step of the taper processing is to fix the polarization-maintaining fiber in the taper machine using two movable carriers controlled by stepper motors to ensure that the taper area is placed on the heating table; the polarization-maintaining fiber is heated using a hydrogen-oxygen flame, and the movable carrier is used to achieve longitudinal heating and stretching of the polarization-maintaining fiber, ultimately making the fiber structure gradually thinner to the micron level; the diameter of the polarization-maintaining fiber after taper is 16μm;

[0012] The tapered polarization-maintaining optical fiber is subjected to coating stripping and end-face cutting, and one end of the processed polarization-maintaining optical fiber is spliced ​​with one end of the coupler that is also subjected to coating stripping and end-face cutting through the discharge operation of a fusion splicer to form a hybrid interferometer structure;

[0013] Finally, the hybrid interferometer structure is connected to the ASE light source and the spectrometer to obtain a dual-parameter temperature and refractive index sensing device with an all-fiber hybrid interferometer structure.

[0014] Among them, the sensing device uses a polarization-maintaining optical fiber that has been tapered as the sensing part. The polarization-maintaining optical fiber that has been tapered breaks the original thermal insulation and refractive index insensitivity characteristics of the polarization-maintaining optical fiber. During the preparation process, the polarization-maintaining optical fiber will generate an axial tension along the direction of the stress rod to cause the core to produce birefringence. When the ambient temperature changes, temperature sensing is achieved through the changes caused by birefringence; the transmission spectrum under arbitrary temperature and refractive index conditions is measured, and the real-time detection of temperature and refractive index is achieved using the constructed transmission matrix by measuring the offset of the central wavelength of the two trough points.

[0015] The beneficial effects of the technical solution provided by the present invention are:

[0016] 1. The present invention adopts a hybrid structure of two interferometers, Mach-Zehnder interferometer and Sagnac interferometer, to construct a sensor device. The interference effect of the hybrid interferometer structure, which is similar to the vernier effect, can effectively improve the reaction sensitivity.

[0017] 2. The present invention adopts a polarization-maintaining fiber taper structure to effectively enhance the effect of the measured parameter, and uses a dual-parameter matrix method for demodulation to achieve dual-parameter detection of temperature and refractive index. The hybrid interferometer structure effectively reduces the manufacturing cost of the sensing system. The structure is simple, reliable, and durable, which is conducive to deployment in complex environments.

[0018] 3. The present invention can simply and conveniently detect two parameters, temperature and refractive index. It has a good foundation for technical transformation and is expected to be widely used in practical applications such as industrial wastewater and environmental monitoring. The present invention can promote the promotion of optical fiber devices and achieve broad social benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Schematic diagram of the operation of taper for polarization-maintaining fiber (PMF);

[0020] Figure 2 Schematic diagram of Sagnac and MZI hybrid structure based on polarization-maintaining fiber (PMF) taper. ;

[0021] Figure 3 This is the effect diagram of the dual-parameter optical fiber sensor with all-fiber hybrid interferometer structure at different temperature values;

[0022] Among them, (a) is the spectrum measured at different temperatures; (b) is the temperature spectrum offset fitting.

[0023] Figure 4 This is the effect diagram of the dual-parameter fiber optic sensor with all-fiber hybrid interferometer structure under different refractive indices;

[0024] Among them, (a) is the spectrum diagram measured under different refractive indices; (b) is the refractive index spectrum offset fitting diagram.

[0025] In the attached figure, the list of components is as follows:

[0026] 1: Polarization-maintaining fiber taper area; 2: Light source;

[0027] 3: Spectrometer; 4: Coupler;

[0028] 5: Polarization controller; 6: Polarization-maintaining fiber;

[0029] 7: Cross-sectional structure of polarization-maintaining fiber. DETAILED DESCRIPTION

[0030] In order to make the objectives, technical solutions and advantages of the present invention more clear, the embodiments of the present invention are described in further detail below.

[0031] The embodiment of the present invention mainly utilizes the working characteristics of the passive optical fiber sensing structure, uses a combination of multiple interferometers, improves the detection effect of the interference spectrum, and realizes the dual-parameter detection of temperature and refractive index. The original temperature-sensitive property of the polarization-maintaining optical fiber can be used for temperature detection, and then the method of tapering the polarization-maintaining optical fiber is used to break the original thermal insulation of the polarization-maintaining optical fiber, so that the polarization-maintaining optical fiber is sensitive to the external refractive index, so that it can be used to detect the refractive index. After obtaining the dual-parameter information, a dual-parameter matrix is ​​used for demodulation, and finally the detection sensing of the dual parameters of temperature and refractive index is realized. This device significantly reduces the complexity of the structure and greatly improves the reliability of the optical fiber sensor in complex scenes.

[0032] Figure 1This is a schematic diagram of the polarization-maintaining fiber (PMF) taper operation. The components required for the operation include a fiber taper machine and a polarization-maintaining fiber (PMF). The main components of the fiber taper machine are two movable carriers for fixing the optical fiber and an ignition device that can control the intensity of the hydrogen-oxygen flame. Figure 1 The specific operations shown are as follows: first, Figure 2 The polarization-maintaining optical fiber 6 is placed in the optical fiber taper machine for taper processing. The first step of the taper processing is to fix the polarization-maintaining optical fiber 6 in the taper machine using two movable carriers controlled by stepper motors, ensuring that the taper area is placed on the heating table. Then the taper angle needs to be determined. Too large an angle will cause energy leakage, and too small an angle will lead to poor taper effect. Therefore, a suitable taper angle needs to be determined. In addition to the taper angle, the taper rate should also be considered.

[0033] After completing the above operations, the polarization-maintaining optical fiber 6 is heated by a hydrogen-oxygen flame, and the movable carrier is used to realize the longitudinal heating and stretching structure of the polarization-maintaining optical fiber 6, so that the fiber structure gradually becomes thinner to the micron level, and the taper effect is achieved. The diameter of the polarization-maintaining optical fiber 6 after the taper treatment is 16μm. Then, the coating layer of the taper-shaped polarization-maintaining optical fiber 6 is stripped and the end face is cut to construct the basis of the passive sensing structure. One end of the processed polarization-maintaining optical fiber 6 is spliced ​​with one end of the coupler 4 that is also stripped and the end face is cut through the discharge operation of the fusion splicer. Since the polarization-maintaining optical fiber 6 is tapered, the original adiabatic effect is broken, so that the internal mode of the polarization-maintaining optical fiber is reorganized, the fundamental mode and high-order mode inside the optical fiber are successfully excited, and the optical path difference is accumulated when passing through the waist area, and finally the recombination is achieved in the transition area to construct the MZI structure. The taper operation also breaks the original insensitivity of the polarization-maintaining fiber 6 to the refractive index. As the tapered area gradually becomes thinner, the original thermal insulation of the polarization-maintaining fiber 6 is broken, making the polarization-maintaining fiber 6 sensitive to the external refractive index, thereby realizing the detection of the refractive index.

[0034] The structural diagram of the overall sensing device is shown in Figure 2 As shown. Figure 2 The components of the sensing device include: an ASE light source 2, a spectrometer 3, a 2×2 coupler 4, a polarization controller 5, and a tapered polarization-maintaining optical fiber 6. Figure 2 The operating principle of the sensing device is as follows: the light emitted by the light source 2 is divided into two beams after passing through a 2×2 coupler 4. The two beams propagate in opposite directions. The polarization-maintaining optical fiber 6 after tapering is connected to the two ends of the coupler 4 to form a Sagnac loop. The light propagating in the loop is modulated by the polarization controller 5. Figure 2) is to ensure that the interference spectrum obtains the maximum modulation depth. The polarization-maintaining optical fiber 6 in the loop that has been subjected to tapering is used as the sensing part to realize temperature and refractive index detection. The light after interference in the loop is then input into the spectrometer 3 through the coupler 4 for real-time detection. Before performing the temperature and refractive index dual parameter detection, the polarization controller 5 must be continuously adjusted to change the polarization state inside the Sagnac loop until a better spectral modulation depth is obtained. The state of the polarization controller 5 is maintained before dual parameter detection can be performed.

[0035] Since the polarization-maintaining fiber itself is sensitive to temperature, different temperatures will cause the interference spectrum to shift. Therefore, the temperature can be detected by comparing the relationship between the spectrum shift and the interference dip at different temperatures. During the temperature detection process, the temperature control box can be used to control the real-time temperature of the sensing part 6. Each time the data collection operation is performed, it must be ensured that the heating process has reached a constant state. Figure 3 The spectrum shown in Figure (a) above shows that by selecting any two trough points in the spectrum and performing linear fitting on the relationship between the central wavelength and temperature, the following equation can be obtained: Figure 3 The middle figure (b) shows the fitting line and two different temperature detection sensitivities. Since the polarization-maintaining fiber 6 is tapered, the original thermal insulation of the fiber structure is broken, making the polarization-maintaining fiber sensitive to changes in the refractive index, thereby causing interference spectrum shift and realizing refractive index sensing. When detecting the refractive index, by dropping a solution with a known refractive index on the sensing structure, the refractive index is changed, and the following can be obtained: Figure 4 In the spectrum shown in Figure (a), two trough points corresponding to the temperature measurement are selected, and the relationship between the central wavelength and the refractive index is fitted again, and the following can be obtained: Figure 4 The middle figure (b) shows the fitting line and two different refractive index detection sensitivities. Finally, the transmission matrix is ​​constructed using the two temperature sensitivities and two refractive index sensitivities obtained above to measure the transmission spectrum under arbitrary temperature and refractive index conditions. By measuring the offset of the central wavelength of the two trough points, the constructed transmission matrix can be used to achieve real-time detection of temperature and refractive index, and at the same time, it can effectively overcome the detection error caused by the cross-sensitivity of the optical fiber sensor device.

[0036] Unless otherwise specified, the models of the components in the embodiments of the present invention are not limited, and any device that can perform the above functions may be used.

[0037] Those skilled in the art can understand that the accompanying drawing is only a schematic diagram of a preferred embodiment, and the serial numbers of the embodiments of the present invention are only for description and do not represent the advantages and disadvantages of the embodiments.

[0038] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A dual-parameter temperature and refractive index sensing device based on an all-fiber hybrid interferometer structure, characterized in that: The device comprises: an ASE light source, a spectrometer, a 2×2 coupler, a polarization controller, and a tapered polarization-maintaining optical fiber; The polarization-maintaining optical fiber is used as the core structure of the interferometer; the structure of the interferometer includes: Mach-Zehnder interferometer and Sagnac interferometer; The structure of the Mach-Zehnder interferometer is a polarization-maintaining optical fiber after tapering, and the Sagnac interferometer uses the polarization-maintaining optical fiber after tapering to achieve light splitting; the polarization-maintaining optical fiber after tapering changes the diameter of the optical fiber waist region.

2. The dual-parameter temperature and refractive index sensing device based on the all-fiber hybrid interferometer structure according to claim 1 is characterized in that: The device comprises: The polarization-maintaining fiber is placed in the fiber taper machine for taper processing. The first step of the taper processing is to fix the polarization-maintaining fiber in the taper machine using two movable carriers controlled by stepper motors to ensure that the taper area is placed on the heating table; the polarization-maintaining fiber is heated using a hydrogen-oxygen flame, and the movable carrier is used to achieve longitudinal heating and stretching of the polarization-maintaining fiber, ultimately making the fiber structure gradually thinner to the micron level; the diameter of the polarization-maintaining fiber after taper is 16μm; The tapered polarization-maintaining optical fiber is subjected to coating stripping and end-face cutting, and one end of the processed polarization-maintaining optical fiber is spliced ​​with one end of the coupler that is also subjected to coating stripping and end-face cutting through the discharge operation of a fusion splicer to form a hybrid interferometer structure; Finally, the hybrid interferometer structure is connected to the ASE light source and the spectrometer to obtain a dual-parameter temperature and refractive index sensing device with an all-fiber hybrid interferometer structure.

3. The dual-parameter temperature and refractive index sensing device based on an all-fiber hybrid interferometer structure according to claim 1 is characterized in that: The sensing device uses a polarization-maintaining optical fiber that has been subjected to a taper treatment as a sensing part. The polarization-maintaining optical fiber that has been subjected to a taper treatment breaks the original thermal insulation and refractive index insensitivity characteristics of the polarization-maintaining optical fiber. During the preparation process, the polarization-maintaining optical fiber generates an axial tension along the direction of the stress rod to cause the fiber core to generate birefringence. When the ambient temperature changes, temperature sensing is achieved through the change caused by the birefringence. The transmission spectrum under arbitrary temperature and refractive index conditions is measured. By measuring the shift of the central wavelength of the two trough points, the constructed transmission matrix is ​​used to achieve real-time detection of temperature and refractive index.

Images