A high-sensitivity magnetic-sensitive optical fiber with special-shaped core

Abstract

The application discloses a high-sensitivity special-shaped core magnetic sensitive optical fiber and belongs to the technical field of optical fibers. The special-shaped core magnetic sensitive optical fiber comprises a cladding and a special-shaped core embedded in the cladding. The cross section of the special-shaped core is a chord-shaped structure composed of a circular arc and a chord, and the radian of the circular arc is greater than pi. The cladding is an air layer except the special-shaped core. The material of the special-shaped core is a rare earth metal element terbium doped magneto-optical glass. The special-shaped core magnetic sensitive optical fiber can generate a significant non-reciprocal magneto-optical effect under the action of a magnetic field, can be used for high-sensitivity magnetic field detection, can realize high-sensitivity, high-stability, miniaturization and high-bandwidth optical fiber magnetic field sensing, and has great significance in the development in the field of magnetic field measurement.

Description

Technical Field

[0001] This invention belongs to the field of optical fiber technology, and particularly relates to a high-sensitivity irregular-shaped core magnetic sensitive optical fiber. Background Technology

[0002] In recent years, magnetic field sensing has been widely used in applications such as precision submarine exploration, earthquake prediction, and geomagnetic matching navigation. Developing highly stable, highly sensitive, high-bandwidth, and miniaturized magnetic field sensors is one of the main ways to meet these needs. Fiber optic magnetic field detection technology is a major development direction for miniaturized magnetic field measurement, possessing unique advantages such as high sensitivity, small size, high bandwidth, corrosion resistance, and electromagnetic interference resistance, and has always been a research hotspot in various countries. Current fiber optic magnetic field sensors struggle to overcome the technical bottleneck of high-stability measurement, making it difficult to achieve a magnetic field sensing system that integrates high sensitivity, high stability, and miniaturization. The main reasons are the insufficiently advanced magnetic sensing mechanism, the inherent instability of the measurement structure, and the large size of the demodulation system, which limits its engineering applications. Researching new high-sensitivity, high-stability, miniaturized, and high-bandwidth magnetic field sensors is of great significance to the development of fields such as magnetic field measurement.

[0003] Currently, the most widely used fiber optic magnetic field sensors include magnetostriction, magnetohydrodynamic tunable refractive index (MZ / McG) methods, and Faraday magneto-optical (FAO) methods. Magnetostriction is based on MZ or Michelson interferometer structures. It utilizes the stretching and deformation of magnetic materials fixed to optical fibers or gratings caused by changes in the external magnetic field, resulting in strain in the fiber or grating on the measuring arm. The change in the external magnetic field is measured by measuring the phase or spectral changes of the interferometer. However, magnetostrictive materials exhibit residual magnetization, which is detrimental to repeated detection; and eddy currents can occur under high-frequency magnetic fields. Magnetohydrodynamic tunable refractive index methods are based on the characteristic that the refractive index of magnetohydrodynamic fluids changes under the influence of a magnetic field. They utilize FP cavities, MZ structures, or Sagnac structures to measure the intensity or spectrum of coherent light, thus measuring the external magnetic field. However, magnetohydrodynamic fluids are prone to volatility and condensation, easily saturate in the magnetic field, and are significantly affected by ambient temperature. FAO methods utilize the high magneto-optical coefficient of magneto-optical crystals. When the magnetic field is parallel to the direction of light propagation, the polarization state of linearly polarized light propagating in the crystal is deflected. The angle of deflection is linearly related to the magnitude of the magnetic field, the magneto-optical coefficient, and the length of the crystal. The magnetic field is measured by measuring the deflection angle of the polarized light. However, optical paths cannot achieve common-path measurement, making it difficult to solve the system stability problem caused by the temperature sensitivity of optical devices. In summary, existing magnetic detection technologies cannot simultaneously meet the requirements of sensitive, stable, and miniaturized magnetic field detection in complex environments, necessitating a more suitable magnetic field sensing system solution. Summary of the Invention

[0004] The purpose of this invention is to address the difficulty of achieving high sensitivity, high stability, large bandwidth, and miniaturization simultaneously in current mainstream optical magnetic field sensor research schemes. This invention proposes a high-sensitivity irregularly shaped core magnetic-sensitive optical fiber that detects magnetic fields through the non-reciprocal magneto-optical effect.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A highly sensitive irregularly shaped core magnetic-sensitive optical fiber includes a cladding and an irregularly shaped core embedded within the cladding. The cross-section of the irregularly shaped core is a chordal structure composed of arcs and chords, with the arc degree being greater than π. The cladding, except for the irregularly shaped core, consists of an air layer. The irregularly shaped core is made of magneto-optical glass doped with the rare-earth metal element terbium.

[0007] Preferably, the cladding is made of glass.

[0008] Preferably, the irregularly shaped core magnetic-sensitive optical fiber exhibits only single-mode transmission, and the refractive index of the irregularly shaped core is greater than that of the cladding, with the refractive difference between the two satisfying the condition. Where 'a' is the radius of the irregular fiber core, 'n1' is the refractive index of the irregular fiber core, 'n2' is the refractive index of the cladding, and 'λ' is the operating wavelength. This condition ensures that the irregular-core magnetic-sensitive fiber only supports single-mode transmission. Furthermore, it is necessary to control the diameter and height of the irregular fiber core to suppress higher-order modes and achieve single-mode transmission. Preferably, the diameter of the irregular fiber core cross-section is 6–10 μm, the height is 3–7 μm, and the diameter of the cladding cross-section is 120–130 μm. Here, the height refers to the distance between the chord center and the arc center on the irregular fiber core cross-section, and the height should be greater than the fiber core radius.

[0009] Preferably, the height of the irregular fiber core cross section should be selected to maximize the difference in propagation constants.

[0010] Preferably, the formula for calculating the difference in propagation constants is as follows:

[0011]

[0012] Where ω is the spatial angular frequency, ε0 ​​is the vacuum permittivity, n is the refractive index of the shaped fiber core, λ is the transmission wavelength, V is the Wilder constant, B is the magnitude of the applied magnetic field, and E y E z These are the mode field components of the fundamental mode quasi-TM in the magnetically sensitive fiber. For E y The conjugate of complex numbers, To extract the imaginary part of a complex number.

[0013] Preferably, the operating wavelength of the irregularly shaped core magnetic sensitive optical fiber is between 1060nm and 1550nm.

[0014] The application of the aforementioned highly sensitive irregular-shaped core magnetic optical fiber in magnetic field detection.

[0015] Preferably, in application, the irregularly shaped core magnetic-sensitive optical fiber is wound into an optical fiber ring, and the magnetic field is detected based on the non-reciprocal magneto-optical effect, wherein the direction of the magnetic field is parallel to the interface between the irregularly shaped core and the air layer.

[0016] The beneficial effects of this invention are:

[0017] For irregularly shaped core magnetic-sensitive optical fibers, a non-reciprocal magneto-optical effect occurs under the influence of a small magnetic field in a specified direction, generating a phase difference to detect the external magnetic field. Compared to magnetostrictive magnetic field sensing schemes, this invention does not use magnetostrictive materials, effectively avoiding the problems of residual magnetization in magnetostrictive materials, which hinders repeated detection, as well as the stability issues of the fixed connection between magnetostrictive materials and optical fibers. Compared to magnetofluidic tunable refractive index magnetic field sensing schemes, this invention overcomes the shortcomings of magnetofluids in magnetic field sensing, such as easy volatility, easy deposition, and difficult fabrication, and has advantages in terms of service life, sensitivity, and integration. Compared to Faraday magneto-optical effect magnetic field sensing schemes, this invention is easier to integrate and miniaturize than magneto-optical crystals, and has advantages in terms of service life, sensitivity, and integration, providing new research ideas for future fiber-optic magnetic field sensors. Furthermore, optical fiber itself, as a sensitive transmission element, has significant advantages over traditional magnetic sensors, such as low volume dependence, ease of miniaturization design, strong resistance to environmental interference, and high reliability. This invention enables high-sensitivity, high-stability, miniaturized, and wide-bandwidth magnetic field sensing, which is of great significance to the development of fields such as magnetic field measurement.

[0018] In summary, compared with the prior art, the present invention has the following obvious and prominent substantive features:

[0019] 1. High sensitivity. The irregularly shaped core of the magnetically sensitive fiber uses terbium-doped magneto-optical glass, which has a very high Wilder constant. Under non-reciprocal magneto-optical interaction, it will generate a large phase difference, which is convenient for detection.

[0020] 2. High stability. The irregular structure of the core of the magnetically sensitive fiber can effectively maintain the polarization state of the light wave, thus avoiding polarization attenuation caused by birefringence in single-mode fiber and maintaining good stability.

[0021] 3. High bandwidth. The irregularly shaped core magnetic sensitive fiber is made of magneto-optical glass, which does not bring about the eddy current effect caused by magnetostrictive materials under the action of high-frequency magnetic fields, and can realize the detection of AC magnetic fields with a high bandwidth.

[0022] 4. Miniaturization. Irregularly shaped core magnetic sensitive optical fibers are small in size and easy to couple into optical fiber magnetic sensing units, which facilitates the integration of optical fiber magnetic field sensing systems and provides a new method for high-sensitivity measurement of magnetic fields. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the cross-section of an irregularly shaped core magnetic-sensitive optical fiber.

[0024] Figure 2 This is a schematic diagram of the magnetic field sensing direction of an irregularly shaped fiber core magnetic sensitive optical fiber.

[0025] Figure 3 This is a schematic diagram of the mode field distribution of the fundamental modes Re(Ey) and Im(Ez) of the quasi-TM magnetically sensitive fiber with irregular core.

[0026] In the diagram, 1-Irregular fiber core, 2-Air, 3-Clad layer. Detailed Implementation

[0027] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0028] Reference Figure 1 The irregularly shaped core magnetic-sensitive fiber of the present invention comprises an irregularly shaped core 1, air 2, and cladding 3. Light waves are concentrated in the irregularly shaped core 1 for transmission, with a very small amount of light waves attenuated in air 2 and cladding 3. The irregularly shaped core 1 is made of terbium-doped magneto-optical glass with a refractive index of 1.74–1.75 at 1060 nm; the cladding 3 is made of other glass materials with a refractive index of 1.73–1.74 at 1060 nm. The outer diameter of cladding 3 is 120–130 μm, the diameter of irregularly shaped core 1 is 6–10 μm, and its height is 3–7 μm. The materials and refractive indices described above are only examples, and other options can be used. The diameter of irregularly shaped core 1 should ensure the single-mode transmission characteristics of the magnetic-sensitive fiber; the height of irregularly shaped core 1 should ensure the optimal value of the propagation constant difference of the magnetic-sensitive fiber; the diameter of cladding 3 generally follows common single-mode fiber parameters, but can be appropriately adjusted according to requirements.

[0029] The magnetically sensitive optical fiber in this invention uses a core with a special structure and special materials, which differs from the core of conventional optical fibers in the following ways:

[0030] Conventional optical fiber cores have a complete circular cross-section and are made of homogeneous quartz. In contrast, the core of the magnetic-sensitive optical fiber in this invention is structurally chord-shaped (a perfect circle with its arc removed, resulting in a chord composed of arcs and chords), and it utilizes terbium-doped magneto-optical glass, possessing a high Wilder constant. Furthermore, to ensure single-mode transmission in the magnetic-sensitive optical fiber, a minimal refractive index difference between the core and cladding must be maintained, and the refractive indices of both must satisfy certain conditions. Where a is the radius of the irregular fiber core 1, n1 is the refractive index of the irregular fiber core 1, n2 is the refractive index of the cladding 3, and λ is the operating wavelength. To enhance the non-reciprocal magneto-optical effect generated by the magnetosensitive fiber, the height of the irregular fiber core needs to be optimized to obtain the optimal propagation constant difference.

[0031] Reference Figure 2 Let x, y, and z form a rectangular coordinate system. The x and y planes are parallel to the cross-section of the magnetic fiber, and the z direction is parallel to the optical axis of the magnetic fiber. The magnetic fiber in this invention... Figure 2 The magnetic field in the x-direction (i.e., parallel to the interface between the irregular fiber core 1 and air 2) exhibits high sensitivity. The working principle of this invention for magnetic field detection is as follows: Based on the approximate scalar method in linear polarization modes, there are two independent propagation modes in special optical fibers: a transverse magnetic mode (quasi-TM mode) and a transverse electric mode (quasi-TE mode). The magnetic field component of the quasi-TM mode is perpendicular to the propagation direction of the light wave, while the electric field component of the quasi-TE mode is perpendicular to the propagation direction of the light wave. That is, the quasi-TM mode has no magnetic field component in the propagation direction of the light wave, and the quasi-TE mode has no electric field component in the propagation direction of the light wave. When a magnetic field acts on the magnetically sensitive optical fiber, both the forward-propagating (+z) and reverse-propagating (-z) light waves will generate propagation constants. The propagation constants generated by the quasi-TE mode light in the forward and reverse propagating light waves are the same, resulting in a zero difference in propagation constants. However, the propagation constants generated by the quasi-TM mode light in the forward and reverse propagating light waves are different, resulting in a propagation constant difference Δβ, expressed as formula... Where ω is the spatial angular frequency, ε0 ​​is the vacuum permittivity, n is the refractive index of the shaped fiber core, λ is the transmission wavelength, V is the Wilder constant, and B is the magnitude of the applied magnetic field. y E z These are the mode field components of the fundamental mode quasi-TM in the magnetically sensitive fiber. For E y The conjugate of complex numbers.

[0032] Reference Figure 3 Simulation results show that the values ​​of Im(Ey) and Re(Ez) being zero have no effect; the propagation constant difference Δβ is determined by Re(Ey) and Im(Ez). Simultaneously, the propagation constant difference Δβ is linearly positively correlated with the magnetic field B, allowing for effective detection of external magnetic fields. Materials with higher Wilder constants V can also be used as the core material for irregularly shaped fibers to enhance the non-reciprocal magneto-optical effect of the magnetically sensitive fiber. If the fiber of this invention is wound into a fiber ring and connected to a phase detection system, such as a Sagnac interferometer structure, the non-reciprocal phase difference between two beams of light with an inherent relationship to the external magnetic field strength can be detected, enabling precise measurement of the external magnetic field. As a novel magnetic field detection scheme, it has advantages such as low operating environment requirements and high detection accuracy, and has broad application prospects in biomedicine, industrial inspection, and other fields.

[0033] Example 1:

[0034] The magnetically sensitive fiber consists of three parts: a shaped core 1, air 2, and a cladding 3. The shaped core 1 is a terbium-doped magneto-optical glass with a diameter of 3 μm and a height of 3.8 μm. The cladding material is another glass material with an outer diameter of 125 μm. Its refractive index difference with the shaped core at a wavelength of 1064 nm is 0.01, ensuring that only single-mode light waves propagate in the magnetically sensitive fiber. Under the influence of a directional magnetic field (parallel to the interface between the shaped core 1 and air 2), the non-reciprocal magneto-optical effect results in a propagation constant difference Δβ of 0.0234 rad / μm, enabling highly sensitive magnetic field sensing.

[0035] Example 2:

[0036] The magnetically sensitive fiber consists of three parts: a shaped core (1), air (2), and cladding (3). The shaped core (1) is a terbium-doped magneto-optical glass with a diameter of 3 μm and a height of 5.0 μm. The cladding is made of other glass materials with an outer diameter of 130 μm. Its refractive index difference with the shaped core at a wavelength of 1064 nm is 0.01, ensuring that only single-mode light waves propagate in the magnetically sensitive fiber. Under the influence of a directional magnetic field, the non-reciprocal magneto-optical effect results in a propagation constant difference Δβ of 0.0231 rad / μm, enabling highly sensitive magnetic field sensing.

[0037] For the purposes of illustration and description, the foregoing illustrative examples relating to the invention are provided. This is not intended to be an exhaustive description of the invention or to limit it to the precise forms described; modifications and variations can be made based on the foregoing description. The embodiments were chosen and described to explain the principles of the invention and as practical applications thereof, enabling those skilled in the art to use the invention in various embodiments and to make various modifications for specific purposes. All variations that can be directly derived or conceived by those skilled in the art from the disclosure of this invention should be considered within the scope of protection of this invention.

Claims

1. The application of a highly sensitive irregularly shaped magnetic core optical fiber in magnetic field detection, characterized in that, The irregularly shaped core magnetic-sensitive fiber includes a cladding (3) and an irregularly shaped core (1) embedded in the cladding (3). The cross-section of the irregularly shaped core (1) is a chordal structure composed of arcs and chords, with the arc degree being greater than π. Except for the irregularly shaped core (1), the rest of the cladding (3) is an air layer. The irregularly shaped core (1) is made of magneto-optical glass doped with the rare earth metal element terbium. The cladding (3) is made of glass. When detecting the magnetic field, the irregularly shaped core magnetic sensitive fiber is wound into an optical fiber ring, and the magnetic field direction is parallel to the interface between the irregularly shaped core (1) and the air layer. The measurement of the external magnetic field is achieved by detecting the non-reciprocal phase difference between the two beams of light with the inherent relationship with the external magnetic field strength.

2. The application of the high-sensitivity irregularly shaped magnetic fiber core according to claim 1 in magnetic field detection, characterized in that, The refractive index of the shaped fiber core (1) is greater than that of the cladding (3), and the refractive indices of both satisfy the condition. Where a is the radius of the shaped fiber core (1), n1 is the refractive index of the shaped fiber core (1), n2 is the refractive index of the cladding (3), and λ is the working wavelength.

3. The application of the high-sensitivity irregularly shaped magnetic fiber core according to claim 1 in magnetic field detection, characterized in that, The irregularly shaped magnetic fiber only supports single-mode transmission.

4. The application of the high-sensitivity irregularly shaped magnetic fiber according to claim 1 in magnetic field detection, characterized in that, The diameter of the cross section of the irregular fiber core (1) is 6-10 μm and the height is 3-7 μm, and the diameter of the cross section of the cladding (3) is 120-130 μm.

5. The application of the high-sensitivity irregularly shaped magnetic fiber core according to claim 4 in magnetic field detection, characterized in that, The height of the cross section of the irregular fiber core (1) should be selected to maximize the difference in propagation constant.

6. The application of the high-sensitivity irregularly shaped magnetic fiber core according to claim 5 in magnetic field detection, characterized in that, The formula for calculating the difference in propagation constants is as follows: Where ω is the spatial angular frequency, ε0 ​​is the vacuum permittivity, n is the refractive index of the shaped fiber core, λ is the transmission wavelength, V is the Wilder constant, B is the magnitude of the applied magnetic field, and E y E z These are the mode field components of the fundamental mode quasi-TM in the magnetically sensitive fiber. For E y The conjugate of complex numbers, This refers to extracting the imaginary part of a complex number.

7. The application of the high-sensitivity irregularly shaped magnetic fiber according to claim 1 in magnetic field detection, characterized in that, The operating wavelength of the irregularly shaped core magnetic sensitive optical fiber is between 1060nm and 1550nm.

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