Temperature and strain insensitive optical fiber vector torsion sensor
By adopting cascaded Machzendel interference technology in fiber torsion sensors, the torsion angle measurement is achieved using the envelope peak wavelength change in the fiber sensing unit, and the existing fiber torsion sensors are solved, which is large in size, complex structure, high cost and sensitive to temperature and strain, and a compact, easy-to-integrate and strong anti-interference ability of fiber vector torsion sensors are realized.
Patent Information
- Application Number
- CN202421768695.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-07-25
- Publication Date
- 2025-04-22
- Estimated Expiration
- 2034-07-25
AI Technical Summary
Existing fiber torsion sensors have large size, complex structure, high cost and sensitive to temperature and strain, which limit their application in civil engineering, mechanical manufacturing and other fields.
An optical fiber torsion sensor based on cascade Mach Zengdel interference is used to form an SMF-PMF-FMF-SMF sensing unit through sequentially connected wide-spectral light source, single-mode fiber, polarization-controlled fiber, small-mode fiber and spectrometer, and torsion angle measurement is achieved using the envelope peak wavelength change of the Mach Zengdel interferometer.
It realizes a fiber vector torsion sensor with compact structure, easy production, high repeatability, and insensitive to temperature and strain, with strong anti-interference ability and easy integration.
Smart Images
Figure CN222784124U_ABST
Abstract
Description
Technical Field
[0001] The utility model relates to an optical fiber torsion sensor technology, in particular to an optical fiber torsion sensor based on cascaded Mach-Zehnder interference, in particular to an optical fiber vector torsion sensor which is insensitive to temperature and strain. Background Art
[0002] Torsion is an important indicator for judging the health of a structure. Torsion sensors play a very important role in civil engineering, mechanical manufacturing, and biorobotics. However, for traditional electronic torsion sensors, the disadvantages of large size, complex structure, and high cost make torsion measurement a technical problem.
[0003] Fiber optic sensors are small in size and easy to be twisted, so they can be easily buried inside structures. Research based on fiber optic sensors has gradually become a hot research direction for scholars at home and abroad. At present, there are two main types of fiber optic torsion sensors. One is based on grating devices such as long-period fiber gratings and tilted fiber Bragg gratings, but the preparation equipment is complicated and expensive, and the refractive index modulation type sensor has low sensitivity; the other is based on inter-mode interference type sensors. For example, Ruan Tiantian disclosed a torsion sensor based on Sagnac rings. This torsion sensor has a simple structure and is easy to make, but this sensor is easily affected by temperature; Lu Ping et al. disclosed a high-sensitivity fiber optic torsion device with no temperature cross-sensitivity by tapering on a thin-core optical fiber, but these taper structures make the optical fiber fragile and have low mechanical strength, which limits the scope of practical application.
[0004] Therefore, it is of high application value to study and provide a torsion sensor which has a simple structure, is easy to manufacture, has high repeatability, is insensitive to temperature and strain, and has strong anti-interference ability. Utility Model Content
[0005] The utility model aims to provide a temperature and strain insensitive optical fiber vector torsion sensor to address the deficiencies of the prior art. The sensor has a compact structure, is easy to manufacture, has high repeatability, is insensitive to temperature and strain, has strong anti-interference ability, and is easy to integrate.
[0006] The technical solution to achieve the purpose of this utility model is:
[0007] A temperature and strain insensitive optical fiber vector torsion sensor comprises a broadband source BBS (BBS), a first single-mode fiber SMF (SMF), a polarization maintaining optical fiber PMF (PMF), a few-mode fiber FMF (FMF), a second single-mode optical fiber SMF and an optical spectrum analyzer OSA (OSA) connected in sequence, wherein the sensing unit is formed by SMF-PMF-FMF-SMF fusion splicing, and the two ends of the sensing unit are respectively connected to the broadband source BBS and the spectrometer OSA to form a sensing system, wherein the broadband source BBS emits a light source into the first single-mode optical fiber SMF, and forms a first Mach-Zehnder interferometer MZI (Mach-Zehnder Interferometer, MZI for short); in the sensing unit SMF-PMF-FMF-SMF, the few-mode fiber FMF and the polarization-maintaining fiber PMF are staggered in the fast axis direction with a stagger of 12 μm. The few-mode fiber FMF is staggered along the fast axis direction of the PMF to form a second MZI in the few-mode fiber FMF; the second single-mode fiber SMF is connected to the spectrometer OSA.
[0008] The broadband light source BBS is incident from the first single-mode optical fiber SMF of the sensing unit SMF-PMF-FMF-SMF. The core diameter of the first single-mode optical fiber SMF is 9 μm, and the core diameter of the polarization-maintaining optical fiber PMF is 6.5 μm. When the light passes through the polarization-maintaining optical fiber PMF, it is divided into two parts and transmitted along the core and cladding of the polarization-maintaining optical fiber PMF respectively, forming the first MZI.
[0009] The polarization-maintaining fiber PMF and the few-mode fiber FMF are staggered and spliced. The broadband light source emitted from the BBS is divided into two parts when passing through the polarization-maintaining fiber FMF, and is transmitted forward along the core and cladding of the few-mode fiber FMF respectively, and converges to the core of the second single-mode fiber SMF to form the second MZI. Finally, the spectral information is collected by the spectrometer OSA.
[0010] The free spectral widths of the two MZIs generated in the polarization-maintaining fiber PMF and the few-mode fiber FMF are expressed as:
[0011] , (i is the input fast axis or slow axis polarization mode),
[0012] Among them, λ represents the wavelength, △n p,i and △n fThey represent the effective refractive index difference in the polarization-maintaining fiber PMF and the few-mode fiber FMF, Lp and Lf represent the interference length in the polarization-maintaining fiber PMF and the few-mode fiber FMF, respectively.
[0013] Then the free spectral width of the envelope formed by the two MZIs is expressed as:
[0014] .
[0015] When the sensor performs torsion measurement, the torsion angle measurement can be achieved by monitoring the wavelength change of the envelope peak in the SMF-PMF-FMF-SMF sensing unit.
[0016] By adjusting the lengths of PMF and FMF in the SMF-PMF-FMF-SMF structure, a higher quality envelope can be obtained. The optimized lengths of PMF and FMF are L PMF =3cm, L FMF =3cm.
[0017] Since the torsion process will cause elliptical birefringence in the sensor unit structure, the sensor unit structure will produce differences when twisted in different directions. By detecting the wavelength drift direction of the fitted envelope, the torsion direction of the sensor can be determined, and the sensor can realize vector torsion measurement.
[0018] This sensor has a compact structure, is easy to manufacture, has high repeatability, is insensitive to temperature and strain, has strong anti-interference ability, and is easy to integrate. BRIEF DESCRIPTION OF THE DRAWINGS
[0019] Figure 1 A schematic diagram of the system structure of the sensor in the embodiment;
[0020] Figure 2 It is a schematic diagram of the cross-sectional view of the offset welding of PMF and FMF in the embodiment;
[0021] Figure 3 Schematic diagram of the sensing structure spectrum and fitted envelope peak in the embodiment;
[0022] Figure 4 Schematic diagram of the cascaded MZI envelope peak in the embodiment, wherein Figure (a) is a schematic diagram of the wavelength change of the clockwise envelope peak of the cascaded MZI envelope peak, and Figure (b) is a schematic diagram of the wavelength change of the counterclockwise envelope peak of the cascaded MZI envelope peak.
[0023] In the figure, 1. broadband light source 2. first single-mode optical fiber 3. polarization-maintaining optical fiber 4. few-mode optical fiber 5. second single-mode optical fiber 6. spectrometer. DETAILED DESCRIPTION
[0024] The content of the utility model is further explained below in conjunction with the drawings and embodiments, but the utility model is not limited thereto.
[0025] Example:
[0026] Reference Figure 1 A temperature and strain insensitive optical fiber vector torsion sensor comprises a broadband light source BBS, a first single-mode optical fiber SMF, a polarization-maintaining optical fiber PMF, a few-mode optical fiber FMF, a second single-mode optical fiber SMF and a spectrometer OSA which are connected in sequence. The broadband light source BBS emits a light source into the first single-mode optical fiber SMF, and forms a first Mach-Zehnder interferometer MZI in the polarization-maintaining optical fiber PMF; the few-mode optical fiber FMF is spliced with a 12 μm offset along the fast axis direction of the PMF, and a second MZI is formed in the few-mode optical fiber FMF; the second single-mode optical fiber SMF is connected to the spectrometer OSA, and a sensing unit is formed by SMF-PMF-FMF-SMF fusion splicing, and two ends of the sensing unit are respectively connected to the broadband light source BBS and the spectrometer OSA to form a sensing system.
[0027] In the sensing unit SMF-PMF-FMF-SMF, the fast axis directions of the few-mode fiber FMF and the polarization-maintaining fiber PMF are staggered and spliced, wherein the stagger amount is 12 μm, such as Figure 2 shown.
[0028] The broadband light source BBS is incident from the first single-mode optical fiber SMF of the sensing unit SMF-PMF-FMF-SMF. The core diameter of the first single-mode optical fiber SMF is 9 μm, and the core diameter of the polarization-maintaining optical fiber PMF is 6.5 μm. Due to the mismatch of mode field diameters, the light is divided into two parts when passing through the polarization-maintaining optical fiber PMF, and is transmitted along the core and cladding of the polarization-maintaining optical fiber PMF respectively, to form the first MZI.
[0029] The polarization-maintaining fiber PMF and the few-mode fiber FMF are staggered and spliced, so the wide-spectrum light source emitted from the BBS is divided into two parts when passing through the polarization-maintaining fiber FMF, and is transmitted forward along the core and cladding of the few-mode fiber FMF respectively, and converges to the core of the second single-mode fiber SMF to form a second MZI, and finally the spectral information is collected by the spectrometer OSA.
[0030] The free spectral widths of the two MZIs generated in the polarization-maintaining fiber PMF and the few-mode fiber FMF are expressed as:
[0031] , (i is the input fast axis or slow axis polarization mode),
[0032] Among them, λ represents the wavelength, △n p,i and △n fThey represent the effective refractive index difference in the polarization-maintaining fiber PMF and the few-mode fiber FMF, Lp and Lf represent the interference length in the polarization-maintaining fiber PMF and the few-mode fiber FMF, respectively.
[0033] Then the free spectral width of the envelope formed by the two MZIs is expressed as:
[0034] .
[0035] When the sensor performs torsion measurement, the torsion angle measurement can be achieved by monitoring the wavelength change of the envelope peak in the SMF-PMF-FMF-SMF sensing unit.
[0036] By adjusting the lengths of PMF and FMF in the SMF-PMF-FMF-SMF structure, a higher quality envelope can be obtained. In this example, the lengths of PMF and FMF are L PMF =3cm, L FMF =3cm, the fitted envelope image is as follows Figure 3 As shown in FIG. 1 , since the torsion process causes elliptical birefringence in the sensor unit structure, the sensor unit structure will have differences when it is twisted in different directions, such as Figure 4 As shown, by detecting the wavelength drift direction of the fitted envelope, the torsion direction of the sensor can be determined, and the sensor realizes vector torsion measurement.
[0037] In this example, the PMF is spliced with the FMF at 12μm along the fast axis direction, and the rest of the optical fibers are core-fused. When working, the light emitted by the broadband light source 1 passes through the first single-mode optical fiber, and is divided into two beams in the PMF, which are transmitted along the core and cladding of PMF3 respectively, forming the first MZI; after passing the offset point, the light is transmitted along the core and cladding of FMF4 respectively, and converges in the second single-mode optical fiber 5, forming the second MZI; when the sensor is twisted, the polarization state (SOP) evolves due to the elliptical birefringence induced by the PMF-FMF twist. This elliptical refraction changes the SOP of the core mode and the cladding mode, causing the effective refractive index between the two to change. As a result, the fitted tilt envelope wavelength offset direction is different, allowing the sensor to achieve torsion measurement and distinguish the torsion direction.
Claims
1. A temperature and strain insensitive optical fiber vector torsion sensor, characterized in that: The invention comprises a broadband light source BBS, a first single-mode optical fiber SMF, a polarization-maintaining optical fiber PMF, a few-mode optical fiber FMF, a second single-mode optical fiber SMF and a spectrometer OSA which are connected in sequence. The sensing unit is formed by SMF-PMF-FMF-SMF fusion splicing. Two ends of the sensing unit are respectively connected to the broadband light source BBS and the spectrometer OSA to form a sensing system. The broadband light source BBS emits light into the first single-mode optical fiber SMF to form a first Mach-Zehnder interferometer MZI in the polarization-maintaining optical fiber PMF. In the sensing unit SMF-PMF-FMF-SMF, the few-mode optical fiber FMF and the polarization-maintaining optical fiber PMF are spliced in a staggered manner in the fast axis direction, with a stagger of 12 μm. The few-mode optical fiber FMF is spliced in a staggered manner along the fast axis direction of the PMF to form a second MZI in the few-mode optical fiber FMF. The second single-mode optical fiber SMF is connected to the spectrometer OSA.
2. The temperature and strain insensitive optical fiber vector torsion sensor according to claim 1, characterized in that: The broadband light source BBS is incident from the first single-mode optical fiber SMF of the sensing unit SMF-PMF-FMF-SMF. The core diameter of the first single-mode optical fiber SMF is 9 μm, and the core diameter of the polarization-maintaining optical fiber PMF is 6.5 μm. When the light passes through the polarization-maintaining optical fiber PMF, it is divided into two parts and transmitted along the core and cladding of the polarization-maintaining optical fiber PMF respectively, forming the first MZI.
3. The temperature and strain insensitive optical fiber vector torsion sensor according to claim 1, characterized in that: The polarization-maintaining fiber PMF and the few-mode fiber FMF are staggered and spliced. The broadband light source emitted from the BBS is divided into two parts when passing through the polarization-maintaining fiber FMF, and is transmitted forward along the core and cladding of the few-mode fiber FMF respectively, and converges to the core of the second single-mode fiber SMF to form the second MZI. Finally, the spectral information is collected by the spectrometer OSA.