High-sensitivity magnetic field sensor based on coupled optoelectronic oscillator

Abstract

The invention discloses a high-sensitivity magnetic field sensor based on a coupled optoelectronic oscillator. Comprising a first circulator, a magnetostriction piece used for sensing changes of external magnetic field intensity, a first sensing unit arranged on the magnetostriction piece, a coupler, a photoelectric detector, an electric filter, an electric power divider, an electro-optical modulator, a spectrum analyzer, a second circulator and a second sensing unit, the second end is connected with the first sensing unit, the third end is connected with the input end of the coupler, the first output end of the coupler is connected with the input end of the electric power divider through the photoelectric detector and the electric filter in sequence, and the two output ends of the electric power divider are connected with the electrooptical modulator and the spectrum analyzer respectively; the second output end of the coupler is connected with the first end of the second circulator, the second end of the second circulator is connected with the second sensing unit, and the third end of the second circulator is connected with the electro-optical modulator. The system is high in sensitivity and strong in anti-interference capability.

Description

Technical Field

[0001] The invention belongs to the field of microwave photon sensing, and in particular relates to a high-sensitivity magnetic field sensor based on a coupled photoelectric oscillator. Background Art

[0002] The magnetic field is one of nature's most fundamental vector fields. With the advancement of science and technology, the need for more precise magnetic field measurements is increasing. Current research on magnetic field measurements can be categorized into three main categories: weak magnetic fields, strong magnetic fields, and ultra-strong magnetic fields. The measurement of weak magnetic fields has garnered widespread attention due to its significant implications for military defense, resource exploration, biomedicine, and aerospace.

[0003] However, current magnetic field sensors generally have low sensitivity, making it difficult to meet the requirements for high-sensitivity measurements, and their measurement accuracy is reduced in electromagnetic interference environments. Therefore, providing a highly sensitive magnetic field measurement device suitable for electromagnetic interference environments is a necessity for the continuous development of science and technology. Summary of the Invention

[0004] The present invention provides a high-sensitivity magnetic field sensor based on a coupled photoelectric oscillator to solve the problems of low sensitivity and weak anti-interference ability of current magnetic field sensors.

[0005] According to a first aspect of an embodiment of the present invention, a high-sensitivity magnetic field sensor based on a coupled optoelectronic oscillator is provided, comprising a first circulator, a magnetostrictive element for sensing changes in external magnetic field intensity, a first sensing unit disposed on the magnetostrictive element, a coupler, a photodetector, an electrical filter, an electric power splitter, an electro-optical modulator, a spectrum analyzer, a second circulator, and a second sensing unit. The first end of the first circulator is used to input a laser signal and is connected to the output end of the electro-optical modulator, the second end is connected to the first sensing unit, and the third end is connected to the input end of the coupler. The first output end of the coupler is connected to the input end of the electric power splitter via the photodetector and the electrical filter in sequence. The two output ends of the electric power splitter are respectively connected to the electrical signal input end of the electro-optical modulator and the spectrum analyzer. The second output end of the coupler is connected to the first end of the second circulator, the second end of the second circulator is connected to the second sensing unit, and the third end is connected to the optical signal input end of the electro-optical modulator.

[0006] Optionally, after receiving the laser signal, the first circulator transmits the laser signal to the first sensing unit. When the magnetostrictive element deforms under the action of the magnetic field strength, the wavelength of the first reflected light reflected from the first sensing unit thereon and returned to the first circulator drifts. The first circulator transmits the first reflected light to the coupler. The coupler splits the first reflected light into two paths. One path of the first reflected light is sequentially subjected to photoelectric conversion by the photodetector and filtering by the electrical filter to form a modulated electrical signal. The electrical power splitter splits the modulated electrical signal into two paths, one path being transmitted to the spectrum analyzer and the other being transmitted to the electro-optical modulator.

[0007] Another path of the first reflected light is transmitted to the second sensing unit through the second circulator. The second sensing unit filters a portion of the received first reflected light, causing the optical power of the second reflected light transmitted back to the second circulator to change. The second circulator transmits the second reflected light to the electro-optical modulator. The second reflected light is formed by superimposing the initial second reflected light and the first reflected light remaining after filtering. Compared with the first reflected light, the wavelength of the second reflected light has drifted. The initial second reflected light is the second reflected light transmitted back by the second sensing unit in the absence of a magnetic field.

[0008] The electro-optical modulator modulates the second reflected light according to the modulating electrical signal, so that the second reflected light is mode-locked. The second reflected light passes through the first circulator, the first sensing unit, the coupler, the photodetector, the electrical filter and the electrical power divider in sequence, and is transmitted to the spectrum analyzer. The magnetic field strength is determined according to the oscillation frequency shift of the signal in the spectrum analyzer.

[0009] Optionally, after the first reflected light is transmitted to the second sensing unit, a portion of the first reflected light that does not overlap with the initial second reflected light is filtered out;

[0010] As the magnetic field intensity changes, the wavelength of the first reflected light drifts to varying degrees, the corresponding portion of the first reflected light filtered out by the second sensing unit changes, and the optical power and wavelength drift of the second reflected light also change to varying degrees;

[0011] After being mode-locked, the second reflected light sequentially passes through the first circulator, the first sensing unit, the coupler, the photodetector, the electrical filter, and the electrical power divider, and is converted into a modulated electrical signal. The electro-optical modulator modulates the loss of the mode-locked laser circuit according to the modulated electrical signal, thereby causing the wavelength of the mode-locked laser circuit to shift. After the second reflected light is mode-locked and converted into a modulated electrical signal, and the loss modulation of the mode-locked laser circuit is completed, the magnetic field strength is determined based on the oscillation frequency shift of the signal in the spectrum analyzer. In this case, the oscillation frequency shift is determined by the wavelength shift of the first reflected light and the wavelength shift of the mode-locked laser circuit.

[0012] The optical power variation ΔP of the second reflected light is proportional to the wavelength drift Δλ of the first reflected light. The stronger the magnetic field intensity, the greater the wavelength drift Δλ of the first reflected light, and the greater the optical power variation ΔP of the second reflected light. The greater the wavelength drift Δλ1 of the mode-locked laser circuit or the wavelength drift of the second reflected light caused by the optical power variation of the second reflected light. The electro-optical modulator, the first circulator, the magnetostrictive sensing unit, the coupler, the second circulator, the second sensing unit and the electro-optical modulator constitute a mode-locked laser circuit.

[0013] Alternatively, the sum of wavelength shifts Δλ′ is expressed as:

[0014]

[0015] Wherein, Δλ represents the wavelength drift of the first reflected light under the corresponding magnetic field strength, Δλ1 represents the wavelength drift of the mode-locked laser circuit caused by the optical power change of the second reflected light, λ1 is the initial characteristic wavelength of the first sensing unit, P e is the elastic-optical coefficient of the single-mode optical fiber, k is the magnetostrictive coefficient of the material corresponding to the magnetostrictive element, P T is the starting power threshold of the optoelectronic oscillator, η is the proportional coefficient of the optical power change ΔP of the second reflected light to the wavelength drift Δλ of the first reflected light, and ΔH is the change in magnetic field intensity;

[0016] The magnetostrictive element and the first sensing unit constitute a magnetostrictive sensing unit, and the electro-optical modulator, the first circulator, the magnetostrictive sensing unit, the coupler, the photoelectric detector, the electric filter, the electric power divider and the electro-optical modulator constitute an optoelectronic oscillator circuit.

[0017] Optionally, after the second reflected light is mode-locked, the oscillation frequency shift Δf′ of the signal in the spectrum analyzer is expressed as:

[0018]

[0019] Where D is the dispersion coefficient of the first sensing unit, L e is the length of the first sensing unit, t0 is the time delay from the coupler to the electro-optical modulator in the mode-locked laser circuit, N is the number of oscillations of the first reflected light in the optoelectronic oscillator before the second reflected light is mode-locked, and N is an integer greater than 0.

[0020] Optionally, an optical delay device is also included, which is arranged between the second output end of the coupler and the first end of the second circulator, and is used to match the lengths of the two paths from the two output ends of the coupler to the electrical signal input end and the optical signal input end of the electro-optical modulator, respectively, to achieve second reflected light mode locking.

[0021] Optionally, a polarization controller is further included, and the polarization controller is arranged between the third end of the second circulator and the optical signal input end of the electro-optical modulator.

[0022] Optionally, it also includes a first optical amplifier, a second optical amplifier, a third optical amplifier and an electrical amplifier, wherein the first optical amplifier is arranged between the first end of the first circulator and the output end of the electro-optical modulator, for inputting the laser signal; the second optical amplifier is arranged between the third end of the first circulator and the input end of the coupler; the third optical amplifier is arranged between the third end of the second circulator and the polarization controller, and the electrical amplifier is arranged between the electrical filter and the electrical power divider.

[0023] Optionally, both the first sensing unit and the second sensing unit are fiber gratings, and their reflection spectra match, that is, the characteristic wavelength of one fiber grating is located at the falling edge of the characteristic wavelength of the other fiber grating.

[0024] Optionally, the optical delay device is an adjustable optical delay device. By adjusting the delay length of the adjustable optical delay device, the number of oscillations N of the first reflected light within the optoelectronic oscillator before the second reflected light is mode-locked is adjusted, thereby adjusting the oscillation frequency shift Δf′ of the signal in the spectrum analyzer. The magnetostrictive element and the first sensing unit constitute a magnetostrictive sensing unit, and the electro-optical modulator, first circulator, magnetostrictive sensing unit, coupler, photodetector, electric filter, electric power divider, and electro-optical modulator constitute an optoelectronic oscillator circuit.

[0025] The beneficial effects of the present invention are:

[0026] 1. The present invention provides an optoelectronic oscillator circuit comprising an electro-optical modulator, a first circulator, a magnetostrictive sensor unit, a coupler, a photodetector, an electric filter, an electric power divider, and an electro-optical modulator; and a mode-locked laser circuit comprising the electro-optical modulator, the first circulator, the magnetostrictive sensor unit, the coupler, the second circulator, the second sensor unit, and the electro-optical modulator. The optoelectronic oscillator circuit and the mode-locked laser circuit share the electro-optical modulator, the first circulator, the magnetostrictive sensor unit, and the coupler. Under the influence of an external magnetic field, the wavelength of first reflected light reflected by the first sensor unit in the magnetostrictive sensor unit shifts. When the wavelength shift of the first reflected light varies, the first reflected light is transmitted to the second sensor unit, where corresponding portions of the first reflected light are filtered out by the second sensor unit. When the magnetic field is absent, the initial second reflected light reflected by the second sensor unit overlaps with the remaining first reflected light after filtering. In addition, a second reflected light is formed, and the optical power of the second reflected light changes, thereby causing the wavelength of the second reflected light to drift, that is, the difference in the change in magnetic field intensity will cause the wavelength drift of the second reflected light to be different from that of the first reflected light. It can be seen that the change in magnetic field intensity will cause two wavelength drifts in the present invention. Compared with the prior art, under the same change in magnetic field intensity, the wavelength drift of the present invention is larger, and the oscillation frequency shift of the signal in the spectrum analyzer is also larger. Therefore, when determining the magnetic field intensity based on the oscillation frequency shift, the sensitivity is higher and the demodulation resolution is higher; the present invention applies microwave photon sensing technology to magnetic field measurement, first converts the change in magnetic field intensity into an optical sensing signal, and then converts the optical sensing signal into a microwave electrical signal. When determining the magnetic field intensity, it is based on the microwave electrical signal, so the anti-interference ability is stronger; the present invention only needs to demodulate the magnetic field intensity according to a single formula, so the demodulation speed is faster;

[0027] 2. In addition to the wavelength drift of the first and second reflected lights, in the present invention, after the second reflected light is mode-locked at the electro-optical modulator, it passes through the first circulator, the first sensing unit, the coupler, the photodetector, the electrical filter, and the electrical power divider in sequence, and is converted into a modulated electrical signal. The electro-optical modulator then modulates the loss of the mode-locked laser circuit according to the modulated electrical signal, thereby causing the wavelength of the mode-locked laser circuit to drift. These three wavelength drift processes collectively reflect the change in magnetic field intensity. When the present invention uses the second reflected light for mode locking, the oscillation frequency shift of the signal immediately obtained by the spectrum analyzer is used to determine the magnetic field intensity. Compared with the prior art, the magnetic field measurement sensitivity of the present invention is improved. However, when the second reflected light is mode-locked and converted into a modulated electrical signal, and the loss of the mode-locked laser circuit is modulated, the magnetic field intensity is determined based on the oscillation frequency shift of the signal in the spectrum analyzer. Compared with the previous method for determining magnetic field intensity of the present invention, the magnetic field measurement sensitivity of this method for determining magnetic field intensity is further significantly improved.

[0028] 3. The present invention can adjust the cavity length of the mode-locked laser circuit by setting an adjustable optical delay line, so that the cavity lengths of the optoelectronic oscillator circuit and the mode-locked laser circuit are more closely matched, thereby improving the mode-locking efficiency;

[0029] 4. The present invention provides a polarization controller between the third end of the second circulator and the optical signal input end of the electro-optical modulator. First, the polarization control can ensure optimal polarization matching between the second reflected light and the electro-optical modulator by adjusting the polarization direction of the second reflected light, thereby maximizing modulation efficiency and reducing insertion loss. Second, the polarization controller can be used to select specific polarization mode oscillations, effectively suppressing mode competition and improving frequency stability. Third, the polarization adjustment capability of the polarization controller can optimize the response efficiency of the photodetector, because the sensitivity of the photodetector is generally polarization-dependent.

[0030] 5. The present invention can maintain the loop gain of the optoelectronic oscillator and compensate for signal loss by providing the first optical amplifier, the second optical amplifier, the third optical amplifier and the electrical amplifier. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a schematic structural diagram of an embodiment of a high-sensitivity magnetic field sensor based on a coupled photoelectric oscillator according to the present invention;

[0032] Figure 2 This is the filtering principle of the second sensing unit of the present invention;

[0033] Figure 3 1 is a schematic structural diagram of another embodiment of a high-sensitivity magnetic field sensor based on a coupled photoelectric oscillator according to the present invention;

[0034] Figure 4 This is a schematic diagram of the electric spectrum response of a magnetic field sensor based on a single FBG to a magnetic field, as well as the fitting of the electric spectrum frequency and the magnetic field;

[0035] Figure 5 It is a schematic diagram of the electric spectrum response of the magnetic field sensor based on dual FBGs to the magnetic field and the fitting of the electric spectrum frequency and the magnetic field. DETAILED DESCRIPTION

[0036] In order to enable those skilled in the art to better understand the technical solutions in the embodiments of the present invention and to make the above-mentioned purposes, features and advantages of the embodiments of the present invention more obvious and easy to understand, the technical solutions in the embodiments of the present invention are further described in detail below with reference to the accompanying drawings.

[0037] In the description of the present invention, unless otherwise specified and limited, it should be noted that the term "connection" should be understood in a broad sense. For example, it can be a mechanical connection or an electrical connection, or it can be the internal connection between two elements. It can be a direct connection or an indirect connection through an intermediate medium. For ordinary technicians in this field, the specific meaning of the above terms can be understood according to the specific circumstances.

[0038] See also Figure 1 , which is a schematic diagram of the structure of an embodiment of a high-sensitivity magnetic field sensor based on a coupled optoelectronic oscillator according to the present invention. The magnetic field sensor may include a first circulator CIR1, a magnetostrictive element 1 for sensing changes in the external magnetic field intensity, a first sensing unit FBG1 provided on the magnetostrictive element 1, a coupler OC, a photodetector PD, an electric filter EF, an electric power divider ED, an electro-optical modulator MZM, a spectrum analyzer ESA, a second circulator CIR2, and a second sensing unit FBG2. The first end of the first circulator CIR1 is used to input a laser signal and is connected to the output end of the electro-optical modulator MZM, and the second end is connected to the first sensing unit FBG1. , the third end is connected to the input end of the coupler OC, the first output end of the coupler OC is connected to the input end of the electric power divider ED through the photodetector PD and the electric filter EF in sequence, the two output ends of the electric power divider ED are respectively connected to the electrical signal input end of the electro-optical modulator MZM and the spectrum analyzer ESA; the second output end of the coupler OC is connected to the first end of the second circulator CIR2, the second end of the second circulator CIR2 is connected to the second sensor unit FBG2, and the third end is connected to the optical signal input end of the electro-optical modulator MZM.

[0039] In this embodiment, after receiving the laser signal, the first circulator CIR1 transmits the laser signal to the first sensor unit FBG1. When the magnetostrictive element 1 deforms under the action of the magnetic field strength, the wavelength of the first reflected light reflected back to the first circulator CIR1 by the first sensor unit FBG1 shifts. The first circulator CIR1 transmits the first reflected light to the coupler OC. The coupler OC splits the first reflected light into two paths. One path of the first reflected light undergoes photoelectric conversion by the photodetector PD and filtering by the electric filter EF to form a modulated electrical signal. The electric power divider ED splits the modulated electrical signal into two paths, one path being transmitted to the spectrum analyzer ESA and the other to the electro-optical modulator MZM. The other path of the first reflected light is transmitted to the second sensor unit FBG2 through the second circulator CIR2. The second sensor unit FBG2 filters out part of the received first reflected light and transmits it back to the second circulator. The optical power of the second reflected light of the filter CIR2 changes, and the second circulator CIR2 transmits the second reflected light to the electro-optical modulator MZM; the second reflected light is formed by the superposition of the initial second reflected light and the first reflected light remaining after filtering. Compared with the first reflected light, the wavelength of the second reflected light has drifted. The initial second reflected light is the second reflected light reversely transmitted back by the second sensing unit FBG2 when there is no magnetic field; the electro-optical modulator MZM modulates the second reflected light according to the modulated electrical signal, so that the second reflected light is mode-locked. The second reflected light passes through the first circulator CIR1, the first sensing unit FBG1, the coupler OC, the photodetector PD, the electric filter EF, and the electric power divider ED in sequence, and is transmitted to the spectrum analyzer ESA. The magnetic field strength is determined according to the oscillation frequency shift of the signal in the spectrum analyzer ESA. At this time, the oscillation frequency shift is determined by the wavelength drift of the first reflected light and the wavelength drift of the second reflected light.

[0040] The magnetostrictive element 1 and the first sensing unit FBG1 can form a magnetostrictive sensing unit MA-FBG1 (when the sensing unit is a fiber Bragg grating, the magnetostrictive sensing unit can be a magnetostrictive fiber Bragg grating). The electro-optical modulator MZM, the first circulator CIR1, the magnetostrictive sensing unit MA-FBG1, the coupler OC, the photodetector PD, the electric filter EF, the electric power divider ED, and the electro-optical modulator MZM can form an optoelectronic oscillator (OEO) circuit. The electro-optical modulator MZM, the first circulator CIR1, the magnetostrictive sensing unit MA-FBG1, the coupler OC, the second circulator CIR2, the second sensing unit FBG2, and the electro-optical modulator MZM can form a mode-locked laser circuit Laser. Under the influence of a magnetic field, strain occurs within the magnetostrictive element 1, causing the magnetostrictive material to elongate. Due to the deformation of the magnetostrictive element 1, the first sensing unit attached to its surface is also subjected to stress, causing the characteristic wavelength of the first sensing unit to shift. The strain ε of the magnetostrictive element 1 is M The wavelength shift Δλ of the first reflected light reflected back by the first sensing unit FBG1 satisfies the following relationship:

[0041] ε M =kΔH

[0042] Δλ=λ1(1-P e )kΔH

[0043] Where ΔH is the change in magnetic field strength, P e is the elastic-optical coefficient of the single-mode optical fiber, k is the magnetostriction coefficient of the material corresponding to the magnetostrictive element; λ1 is the initial characteristic wavelength of the first sensing unit.

[0044] When only the magnetostrictive sensing unit MA-FBG1 is added without the second sensing unit FBG2, that is, only the optoelectronic oscillator OEO is set without the mode-locked laser circuit Laser, after the optoelectronic oscillator OEO self-oscillates, the oscillation frequency shift Δf of the signal in the spectrum analyzer ESA can be expressed as:

[0045]

[0046] Where D is the dispersion coefficient of the first sensing unit FBG1 in the optoelectronic oscillator OEO loop, L e is the length of the first sensing unit FBG1 in the optoelectronic oscillator (OEO) loop, t0 is the time delay from the coupler to the electro-optical modulator in the mode-locked laser loop, λ1 is the initial characteristic wavelength of the first sensing unit FBG1, and N is the number of oscillations of the first reflected light in the optoelectronic oscillator (OEO) before the second reflected light is mode-locked, where N is an integer greater than 0.

[0047] It can be seen from the above formula that the oscillation frequency shift Δf′ is linearly related to the change in magnetic field intensity ΔH, and the magnetic field sensing sensitivity is related to the dispersion coefficient D and dispersion length L of the first sensing unit. e , it is related to the magnetostrictive coefficient k of the corresponding material of the magnetostrictive component.

[0048] When the magnetostrictive sensing unit MA-FBG1 and the second sensing unit FBG2 are added at the same time, that is, the optoelectronic oscillator OEO and the mode-locked laser circuit Laser are set at the same time, the combination Figure 2 As shown, in the absence of a magnetic field, the magnetostrictive sensing unit MA-FBG1 reversely transmits back the initial first reflected light, the wavelength position of the initial first reflected light is shown by the red line in the figure. After receiving the first reflected light, the second sensing unit FBG2 reversely transmits back the initial second reflected light, the wavelength position of the initial second reflected light is shown by the blue line in the figure. Under the action of the external magnetic field strength, the magnetostrictive sensing unit MA-FBG1 reversely transmits back the test first reflected light, the wavelength position of the test first reflected light is shown by the green line, and the test first reflected light shown by the green line has a wavelength shift compared to the initial first reflected light shown by the red line. After the first reflected light is transmitted to the second sensing unit FBG2, the portion of the first reflected light that does not overlap with the initial second reflected light is filtered out, as shown by the yellow dotted line in the figure. As a result, the initial second reflected light and the remaining first reflected light after filtering are superimposed to form a second reflected light. Compared with the first reflected light, the optical power of the second reflected light has changed and the wavelength of the second reflected light has shifted.

[0049] As the magnetic field intensity changes, the wavelength of the first reflected light, shown by the green line, drifts to varying degrees. The corresponding portion of the first reflected light filtered out by the second sensing unit changes, and the optical power and wavelength drift of the second reflected light also change to varying degrees. It can be seen that the optical power change ΔP of the second reflected light is proportional to the wavelength drift Δλ of the first reflected light. Assuming the proportionality coefficient between the two is η, the relationship between the two can be expressed as: ΔP = ηΔλ.

[0050] In addition, after being mode-locked, the second reflected light passes through the first circulator, the first sensing unit, the coupler, the photodetector, the electrical filter, and the electrical power divider in sequence, and is converted into a modulated electrical signal. The electro-optical modulator modulates the loss of the mode-locked laser circuit according to the modulated electrical signal, thereby causing the wavelength of the mode-locked laser circuit to drift. After the second reflected light is mode-locked and converted into a modulated electrical signal, and the loss modulation of the mode-locked laser circuit is completed, the magnetic field strength is determined based on the oscillation frequency shift of the signal in the spectrum analyzer. At this time, the oscillation frequency shift is determined by the wavelength drift of the first reflected light and the wavelength drift of the mode-locked laser circuit.

[0051] It can be seen that in addition to the wavelength drift of the first reflected light and the second reflected light in the present invention, after the second reflected light is mode-locked at the electro-optical modulator, it passes through the first circulator, the first sensing unit, the coupler, the photodetector, the electrical filter, and the electrical power divider in sequence, and is converted into a modulated electrical signal. Thereafter, the electro-optical modulator also modulates the loss of the mode-locked laser circuit according to the modulated electrical signal, thereby causing the wavelength of the mode-locked laser circuit to drift. These three wavelength drift processes jointly reflect the change in magnetic field intensity. When the present invention uses the second reflected light to lock the mode, the oscillation frequency shift of the signal immediately obtained by the spectrum analyzer is used to determine the magnetic field intensity. Compared with the prior art, the magnetic field measurement sensitivity of the present invention is improved. However, when the second reflected light is mode-locked and converted into a modulated electrical signal to complete the loss modulation of the mode-locked laser circuit, the magnetic field intensity is determined based on the oscillation frequency shift of the signal in the spectrum analyzer. Compared with the previous magnetic field intensity determination method of the present invention, the magnetic field measurement sensitivity of this magnetic field intensity determination method is further significantly improved.

[0052] The stronger the magnetic field, the greater the wavelength shift Δλ of the first reflected light, the greater the optical power change ΔP of the second reflected light, and the greater the wavelength shift Δλ1 of the mode-locked laser circuit or the wavelength shift of the second reflected light caused by the optical power change of the second reflected light. The first sensing unit FBG1 and the second sensing unit FBG2 form a tunable filter.

[0053] In the frequency domain, the output wavelength is determined by the wavelength-dependent losses. It is the supermode with the least loss that acquires the most energy and subsequently oscillates. Therefore, variations in optical power caused by magnetic field intensity also affect the wavelength of the laser loop. The wavelength shift Δλ1 of the mode-locked laser loop caused by variations in the optical power of the second reflected light can be expressed as:

[0054]

[0055] Where λ1 is the initial characteristic wavelength of the first sensing unit, ΔP is the optical power change of the second reflected light, and P T is the starting power threshold of the optoelectronic oscillator, Δλ is the wavelength drift of the first reflected light, and η is the proportional coefficient of the optical power change ΔP of the second reflected light to the wavelength drift Δλ of the first reflected light.

[0056] Therefore, the effect of the external magnetic field strength causes the wavelength of the first reflected light transmitted back by the first sensing unit FBG1 to drift. The second sensing unit FBG2 filters out part of the first reflected light it receives, causing the optical power of the second reflected light transmitted back to change, thereby causing the wavelength of the second reflected light to drift compared to the first reflected light. The sum of the two wavelength drifts Δλ′ can be expressed as:

[0057]

[0058] Wherein, Δλ represents the wavelength drift of the first reflected light under the corresponding magnetic field strength, Δλ1 represents the wavelength drift of the mode-locked laser circuit caused by the optical power change of the second reflected light, λ1 is the initial characteristic wavelength of the first sensing unit, P e is the elastic-optical coefficient of the single-mode optical fiber, k is the magnetostrictive coefficient of the material corresponding to the magnetostrictive element, P T is the starting power threshold of the optoelectronic oscillator, η is the proportional coefficient of the optical power change ΔP of the second reflected light and the wavelength drift Δλ of the first reflected light, and ΔH is the change in magnetic field intensity.

[0059] At this time, after the second reflected light is mode-locked, the oscillation frequency shift Δf′ of the signal in the spectrum analyzer ESA can be expressed as:

[0060]

[0061] Where D is the dispersion coefficient of the first sensing unit FBG1 in the optoelectronic oscillator OEO loop, L e is the length of the first sensing unit FBG1 in the optoelectronic oscillator OEO loop, t0 is the time delay from the coupler to the electro-optical modulator in the mode-locked laser loop, λ1 is the initial characteristic wavelength of the first sensing unit FBG1, N is the number of oscillations of the first reflected light in the optoelectronic oscillator OEO before the second reflected light is mode-locked, N is an integer greater than 0, λ1 is the initial characteristic wavelength of the first sensing unit, P e is the elastic-optical coefficient of the single-mode optical fiber, k is the magnetostrictive coefficient of the material corresponding to the magnetostrictive element, P T is the starting power threshold of the optoelectronic oscillator, and η is the proportional coefficient of the optical power variation ΔP of the second reflected light to the wavelength drift Δλ of the first reflected light.

[0062] In one example, the first sensing unit FBG1 and the second sensing unit FBG2 can both be fiber gratings (e.g., fiber Bragg gratings), with their reflection spectra matched, meaning the characteristic wavelength of one fiber grating lies on the falling edge of the characteristic wavelength of the other. The electro-optical modulator can be a Mazin modulator, which plays a key role in signal modulation, frequency control, and phase noise optimization. The MZM influences the output characteristics of the OEO through different bias point operating modes: in quadrature bias mode, the MZM can efficiently generate a fundamental microwave signal, while in zero bias mode, it outputs a frequency-doubled signal. Combined with an electrical divider, the fundamental signal can be recovered to construct a stable oscillation loop. Furthermore, the MZM significantly optimizes phase noise in zero bias mode, with its noise floor approximately 3dB lower than in quadrature bias mode, while maintaining a stable interval between oscillation modes. The spectrum analyzer is a crucial testing and characterization device, primarily used for real-time monitoring and precise analysis of key characteristics of the system's output electrical signal. It can intuitively display the spectral distribution of microwave signals, including the amplitude of the main oscillation frequency, harmonic components, and spurious signals, providing a direct basis for evaluating signal purity. By setting a precise passband frequency range, the electrical filter effectively suppresses the broadband noise generated by the photodetector, significantly improving the signal-to-noise ratio of the output signal. Secondly, the electrical filter can accurately select the target oscillation mode, suppress competition between adjacent modes, and ensure that the system operates at a single stable main oscillation frequency, which is crucial for maintaining frequency stability and reducing phase noise.

[0063] As can be seen from the above embodiments, the present invention provides an optoelectronic oscillator circuit composed of an electro-optical modulator, a first circulator, a magnetostrictive sensor unit, a coupler, a photodetector, an electrical filter, an electrical power divider, and an electro-optical modulator; and a mode-locked laser circuit composed of the electro-optical modulator, the first circulator, the magnetostrictive sensor unit, the coupler, the second circulator, the second sensor unit, and the electro-optical modulator. The optoelectronic oscillator circuit and the mode-locked laser circuit share the electro-optical modulator, the first circulator, the magnetostrictive sensor unit, and the coupler. When the intensity of the external magnetic field is exerted on the first sensor unit in the magnetostrictive sensor unit, the wavelength of the first reflected light reflected back shifts. When the wavelength shift of the first reflected light is different, after the first reflected light is transmitted to the second sensor unit, the corresponding different portions of the first reflected light are filtered out by the second sensor unit. When the magnetic field is not present, the initial second reflected light reflected back by the second sensor unit differs from the first reflected light remaining after filtering. The incident light is superimposed to form a second reflected light, and the optical power of the second reflected light changes, thereby causing the wavelength of the second reflected light to drift. That is, the difference in the change in magnetic field intensity will cause the wavelength drift of the second reflected light to be different from that of the first reflected light. It can be seen that the change in magnetic field intensity will cause two wavelength drifts in the present invention. Compared with the existing technology, under the same change in magnetic field intensity, the wavelength drift of the present invention is larger, and the oscillation frequency shift of the signal in the spectrum analyzer is also larger. Therefore, when determining the magnetic field intensity based on the oscillation frequency shift, the sensitivity is higher and the demodulation resolution is higher; the present invention applies microwave photon sensing technology to magnetic field measurement, first converts the change in magnetic field intensity into an optical sensing signal, and then converts the optical sensing signal into a microwave electrical signal. When determining the magnetic field intensity, it is based on the microwave electrical signal, so the anti-interference ability is stronger; the present invention only needs to demodulate the magnetic field intensity according to a single formula, so the demodulation speed is faster.

[0064] See also Figure 3 , is a structural diagram of another embodiment of a high-sensitivity magnetic field sensor based on a coupled photoelectric oscillator of the present invention. Figure 3 and Figure 1The difference between the illustrated embodiments is that the magnetic field sensor may further include an optical delay device TODL, disposed between the second output end of the coupler OC and the first end of the second circulator CIR2, for matching the lengths of the two paths from the two output ends of the coupler OC to the electrical signal input end and the optical signal input end of the electro-optical modulator MZM, respectively, to achieve mode locking of the second reflected light. The optical delay device may be an adjustable optical delay device. By adjusting the delay length of the adjustable optical delay device, the number of oscillations N of the first reflected light within the optoelectronic oscillator before the second reflected light is mode-locked is adjusted, thereby adjusting the oscillation frequency shift Δf′ of the signal in the spectrum analyzer. The magnetostrictive element and the first sensing unit constitute a magnetostrictive sensing unit, and the electro-optical modulator, the first circulator, the magnetostrictive sensing unit, the coupler, the photodetector, the electrical filter, the electrical power divider, and the electro-optical modulator constitute an optoelectronic oscillator circuit. The present invention can adjust the cavity length of the mode-locked laser circuit by setting an adjustable optical delay line, so that the cavity lengths of the optoelectronic oscillation circuit and the mode-locked laser circuit are more matched, thereby improving the mode-locking efficiency.

[0065] Figure 3 and Figure 1 The difference between the illustrated embodiments is that the magnetic field sensor can also include a polarization controller PC, which is disposed between the third end of the second circulator CIR2 and the optical signal input end of the electro-optical modulator MZM. The present invention provides a polarization controller between the third end of the second circulator and the optical signal input end of the electro-optical modulator. First, polarization control adjusts the polarization direction of the second reflected light to ensure optimal polarization matching between the second reflected light and the electro-optical modulator, thereby maximizing modulation efficiency and reducing insertion loss. Second, the PC can be used to select specific polarization mode oscillations, effectively suppressing mode competition and improving frequency stability. Third, the PC's polarization adjustment capability can optimize the response efficiency of the photodetector, as the sensitivity of the photodetector is generally polarization-dependent.

[0066] in addition, Figure 3 and Figure 1The difference between the illustrated embodiments is that the magnetic field sensor can also include a first optical amplifier EDFA1, a second optical amplifier EDFA2, a third optical amplifier EDFA3, and an electrical amplifier EA. The first optical amplifier EDFA1 is arranged between the first end of the first circulator CIR1 and the output end of the electro-optical modulator MZM, for inputting the laser signal; the second optical amplifier EDFA2 is arranged between the third end of the first circulator CIR1 and the input end of the coupler OC; the third optical amplifier EDFA3 is arranged between the third end of the second circulator CIR2 and the polarization controller PC; and the electrical amplifier EA is arranged between the electrical filter EF and the electrical power divider ED. By providing the first, second, and third optical amplifiers, and the electrical amplifier, the present invention can maintain the gain of the optoelectronic oscillator loop and compensate for signal loss.

[0067] As can be seen from the above embodiments, the present invention provides an optoelectronic oscillator circuit composed of an electro-optical modulator, a first circulator, a magnetostrictive sensor unit, a coupler, a photodetector, an electrical filter, an electrical power divider, and an electro-optical modulator; and a mode-locked laser circuit composed of the electro-optical modulator, the first circulator, the magnetostrictive sensor unit, the coupler, the second circulator, the second sensor unit, and the electro-optical modulator. The optoelectronic oscillator circuit and the mode-locked laser circuit share the electro-optical modulator, the first circulator, the magnetostrictive sensor unit, and the coupler. When the intensity of the external magnetic field is exerted on the first sensor unit in the magnetostrictive sensor unit, the wavelength of the first reflected light reflected back shifts. When the wavelength shift of the first reflected light is different, after the first reflected light is transmitted to the second sensor unit, the corresponding different portions of the first reflected light are filtered out by the second sensor unit. When the magnetic field is not present, the initial second reflected light reflected back by the second sensor unit differs from the first reflected light remaining after filtering. The incident light is superimposed to form a second reflected light, and the optical power of the second reflected light changes, thereby causing the wavelength of the second reflected light to drift. That is, the difference in the change in magnetic field intensity will cause the wavelength drift of the second reflected light to be different from that of the first reflected light. It can be seen that the change in magnetic field intensity will cause two wavelength drifts in the present invention. Compared with the existing technology, under the same change in magnetic field intensity, the wavelength drift of the present invention is larger, and the oscillation frequency shift of the signal in the spectrum analyzer is also larger. Therefore, when determining the magnetic field intensity based on the oscillation frequency shift, the sensitivity is higher and the demodulation resolution is higher; the present invention applies microwave photon sensing technology to magnetic field measurement, first converts the change in magnetic field intensity into an optical sensing signal, and then converts the optical sensing signal into a microwave electrical signal. When determining the magnetic field intensity, it is based on the microwave electrical signal, so the anti-interference ability is stronger; the present invention only needs to demodulate the magnetic field intensity according to a single formula, so the demodulation speed is faster.

[0068] The present invention significantly improves the sensitivity of magnetic field measurement (by 49.8 times) by combining microwave photon sensing technology with a tunable filter composed of dual sensing units (i.e., dual fiber gratings (FBGs)). Figure 4 and Figure 5 As shown, the magnetic field measurement sensitivity of a single fiber Bragg grating (FBG) is 161 Hz / mT, while that of a dual-FBG is 8.02 kHz / mT. The dual-FBG experiment improves sensitivity by approximately 49.8 times compared to a single-FBG experiment, and its measurement accuracy is improved by up to four orders of magnitude compared to a spectrometer. This invention provides a solution for magnetic field measurement and has important scientific significance and application value.

[0069] Other embodiments of the present invention will readily occur to those skilled in the art after considering the specification and practicing the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of the present invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein. The description and examples are to be considered as exemplary only, with the true scope and spirit of the invention being indicated by the following claims.

[0070] It will be appreciated that the present invention is not limited to the precise construction that has been described above and shown in the accompanying drawings, and that various modifications and variations can be made without departing from its scope, which is governed solely by the appended claims.

Claims

1. A high-sensitivity magnetic field sensor based on a coupled optoelectronic oscillator, characterized in that: The invention comprises a first circulator, a magnetostrictive element for sensing changes in the external magnetic field intensity, a first sensing unit arranged on the magnetostrictive element, a coupler, a photodetector, an electric filter, an electric power splitter, an electro-optical modulator, a spectrum analyzer, a second circulator and a second sensing unit. The first end of the first circulator is used to input a laser signal and is connected to the output end of the electro-optical modulator, the second end is connected to the first sensing unit, and the third end is connected to the input end of the coupler. The first output end of the coupler is connected to the input end of the electric power splitter through the photodetector and the electric filter in sequence. The two output ends of the electric power splitter are respectively connected to the electric signal input end of the electro-optical modulator and the spectrum analyzer. The second output end of the coupler is connected to the first end of the second circulator, the second end of the second circulator is connected to the second sensing unit, and the third end is connected to the optical signal input end of the electro-optical modulator.

2. The high-sensitivity magnetic field sensor based on coupled optoelectronic oscillator according to claim 1, characterized in that: After receiving the laser signal, the first circulator transmits the laser signal to the first sensing unit. When the magnetostrictive element deforms under the action of the magnetic field strength, the wavelength of the first reflected light reflected from the first sensing unit to the first circulator shifts. The first circulator transmits the first reflected light to the coupler. The coupler splits the first reflected light into two paths. One path of the first reflected light undergoes photoelectric conversion by the photodetector and filtering by the electric filter to form a modulated electrical signal. The electric power splitter splits the modulated electrical signal into two paths, one path being transmitted to the spectrum analyzer and the other to the electro-optical modulator. Another path of the first reflected light is transmitted to the second sensing unit through the second circulator. The second sensing unit filters a portion of the received first reflected light, causing the optical power of the second reflected light transmitted back to the second circulator to change. The second circulator transmits the second reflected light to the electro-optical modulator. The second reflected light is formed by superimposing the initial second reflected light and the first reflected light remaining after filtering. Compared with the first reflected light, the wavelength of the second reflected light has drifted. The initial second reflected light is the second reflected light transmitted back by the second sensing unit in the absence of a magnetic field. The electro-optical modulator modulates the second reflected light according to the modulating electrical signal, so that the second reflected light is mode-locked. The second reflected light passes through the first circulator, the first sensing unit, the coupler, the photodetector, the electrical filter and the electrical power divider in sequence, and is transmitted to the spectrum analyzer. The magnetic field strength is determined according to the oscillation frequency shift of the signal in the spectrum analyzer.

3. The high-sensitivity magnetic field sensor based on coupled optoelectronic oscillator according to claim 2, characterized in that: After the first reflected light is transmitted to the second sensing unit, the portion of the first reflected light that does not overlap with the initial second reflected light is filtered out; As the magnetic field intensity changes, the wavelength of the first reflected light drifts to varying degrees, the corresponding portion of the first reflected light filtered out by the second sensing unit changes, and the optical power and wavelength drift of the second reflected light also change to varying degrees; After being mode-locked, the second reflected light sequentially passes through the first circulator, the first sensing unit, the coupler, the photodetector, the electrical filter, and the electrical power divider, and is converted into a modulated electrical signal. The electro-optical modulator modulates the loss of the mode-locked laser circuit according to the modulated electrical signal, thereby causing the wavelength of the mode-locked laser circuit to shift. After the second reflected light is mode-locked and converted into a modulated electrical signal, and the loss modulation of the mode-locked laser circuit is completed, the magnetic field strength is determined based on the oscillation frequency shift of the signal in the spectrum analyzer. In this case, the oscillation frequency shift is determined by the wavelength shift of the first reflected light and the wavelength shift of the mode-locked laser circuit. The optical power variation ΔP of the second reflected light is proportional to the wavelength drift Δλ of the first reflected light. The stronger the magnetic field intensity, the greater the wavelength drift Δλ of the first reflected light, and the greater the optical power variation ΔP of the second reflected light. The greater the wavelength drift Δλ1 of the mode-locked laser circuit or the wavelength drift of the second reflected light caused by the optical power variation of the second reflected light. The electro-optical modulator, the first circulator, the magnetostrictive sensing unit, the coupler, the second circulator, the second sensing unit and the electro-optical modulator constitute a mode-locked laser circuit.

4. The high-sensitivity magnetic field sensor based on a coupled optoelectronic oscillator according to claim 3, characterized in that: The total wavelength shift Δλ′ is expressed as: Wherein, Δλ represents the wavelength drift of the first reflected light under the corresponding magnetic field strength, Δλ1 represents the wavelength drift of the mode-locked laser circuit caused by the optical power change of the second reflected light, λ1 is the initial characteristic wavelength of the first sensing unit, P e is the elastic-optical coefficient of the single-mode optical fiber, k is the magnetostrictive coefficient of the material corresponding to the magnetostrictive element, P T is the starting power threshold of the optoelectronic oscillator, η is the proportional coefficient of the optical power change ΔP of the second reflected light to the wavelength drift Δλ of the first reflected light, and ΔH is the change in magnetic field intensity; The magnetostrictive element and the first sensing unit constitute a magnetostrictive sensing unit, and the electro-optical modulator, the first circulator, the magnetostrictive sensing unit, the coupler, the photoelectric detector, the electric filter, the electric power divider and the electro-optical modulator constitute an optoelectronic oscillator circuit.

5. The high-sensitivity magnetic field sensor based on coupled optoelectronic oscillator according to claim 4, characterized in that: After the second reflected light is mode-locked, the oscillation frequency shift Δf′ of the signal in the spectrum analyzer is expressed as: Where D is the dispersion coefficient of the first sensing unit, L e is the length of the first sensing unit, t0 is the time delay from the coupler to the electro-optical modulator in the mode-locked laser circuit, N is the number of oscillations of the first reflected light in the optoelectronic oscillator before the second reflected light is mode-locked, and N is an integer greater than 0.

6. The high-sensitivity magnetic field sensor based on a coupled optoelectronic oscillator according to any one of claims 1 to 5, characterized in that: It also includes an optical delay device, which is arranged between the second output end of the coupler and the first end of the second circulator, and is used to match the lengths of the two paths from the two output ends of the coupler to the electrical signal input end and the optical signal input end of the electro-optical modulator, respectively, to achieve second reflected light mode locking.

7. The high-sensitivity magnetic field sensor based on a coupled optoelectronic oscillator according to claim 6, characterized in that: It also includes a polarization controller, which is arranged between the third end of the second circulator and the optical signal input end of the electro-optical modulator.

8. The high-sensitivity magnetic field sensor based on coupled optoelectronic oscillator according to claim 7, characterized in that: It also includes a first optical amplifier, a second optical amplifier, a third optical amplifier and an electrical amplifier. The first optical amplifier is arranged between the first end of the first circulator and the output end of the electro-optical modulator, and is used to input the laser signal; the second optical amplifier is arranged between the third end of the first circulator and the input end of the coupler; the third optical amplifier is arranged between the third end of the second circulator and the polarization controller, and the electrical amplifier is arranged between the electrical filter and the electrical power divider.

9. The high-sensitivity magnetic field sensor based on a coupled optoelectronic oscillator according to claim 1 or 2, characterized in that: The first sensing unit and the second sensing unit are both fiber gratings, and their reflection spectra match, that is, the characteristic wavelength of one fiber grating is located at the falling edge of the characteristic wavelength of the other fiber grating.

10. The high-sensitivity magnetic field sensor based on coupled optoelectronic oscillator according to claim 6, characterized in that: The optical delay device is an adjustable optical delay device. By adjusting the delay length of the adjustable optical delay device, the number of oscillations N of the first reflected light in the optoelectronic oscillator before the second reflected light is mode-locked is adjusted, thereby adjusting the oscillation frequency shift Δf′ of the signal in the spectrum analyzer. The magnetostrictive element and the first sensing unit constitute a magnetostrictive sensing unit, and the electro-optical modulator, the first circulator, the magnetostrictive sensing unit, the coupler, the photodetector, the electric filter, the electric power divider, and the electro-optical modulator constitute an optoelectronic oscillator circuit.

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