Magnetic induction intensity detection device and method based on laser self-mixing interference

Abstract

The present invention discloses a magnetic induction intensity detection device based on laser self-mixing interference. The laser light emitted by the laser is split by a spectrometer and then divided into two optical paths. A polarizer, a magneto-optical crystal, and a transducer are sequentially arranged on one optical path. The transducer is electrically connected to a control module, which generates a continuous sinusoidal wave signal to continuously control the transducer. A detector is arranged on the other optical path. The detector is electrically connected to a Fourier transform module, which analyzes the laser self-mixing interference signal obtained by the detector. The magneto-optical crystal is located inside a magnetic field. The laser light emitted by the laser is reflected multiple times between the laser and the transducer, and under the action of the polarizer, laser self-mixing interference is formed. In the present invention, the laser light is reflected multiple times between the laser and the transducer, which can enhance the Faraday rotation effect. In addition, the polarizer is used as a polarizer and an analyzer, which has the advantages of not requiring an external analyzer, reducing measurement costs, and improving sensitivity.

Description

Technical Field

[0001] The present invention relates to the technical field of laser precision measurement, and in particular to a magnetic induction intensity detection device and method based on laser self-mixing interference. Background Art

[0002] Magnetic field detection technology is of great significance in fundamental scientific research, applied technology development, and practical engineering applications. It is not only a key tool for understanding fundamental physical phenomena in nature, but also plays a vital role in a variety of applied technologies, including medical imaging, data storage, navigation and positioning, industrial detection, energy management, and biomedical engineering.

[0003] One traditional method for detecting magnetic fields is to use the Faraday rotation effect, which indirectly measures magnetic induction intensity by measuring the rotation angle of the polarization direction of linearly polarized light when it passes through a medium placed in a magnetic field. This method is characterized by high sensitivity, non-invasiveness, and remote detection.

[0004] However, traditional methods for measuring the Faraday rotation effect have several limitations. Using two polarizers as a polarizer and analyzer results in increased light attenuation, which directly impacts the accuracy and reliability of the detection results. Furthermore, this configuration typically requires a complex optical system and multiple optical components, increasing system complexity and cost. Therefore, developing a new magnetic field detection technology that maintains the advantages of high sensitivity and non-invasiveness while simplifying system configuration, reducing costs, and improving measurement accuracy and reliability has become an urgent technical need. Summary of the Invention

[0005] The present invention aims to solve one of the technical problems existing in the related art at least to a certain extent.

[0006] One object of the present invention is to provide a magnetic induction intensity detection device based on laser self-mixing interference, which reduces the number of optical elements in the optical path, reduces light attenuation, and achieves more accurate, reliable and cost-effective magnetic induction intensity detection.

[0007] Another object of the present invention is to provide a method for detecting magnetic induction intensity based on laser self-mixing interference using the above-mentioned device, which uses laser self-mixing interference technology and Fourier transform analysis technology to effectively filter out background noise and improve the stability and reliability of the measurement results.

[0008] In order to achieve the above-mentioned object, the present invention provides, on one hand, a magnetic induction intensity detection device based on laser self-mixing interference, comprising a laser for emitting laser light, wherein the laser light emitted by the laser light is split by a spectrometer into two optical paths;

[0009] One of the optical paths is provided with a polarizer, a magneto-optical crystal, and a transducer in sequence; the transducer is electrically connected to a control module, and the control module generates a continuous sinusoidal wave signal to continuously control the transducer;

[0010] A detector is provided on the other optical path; the detector is electrically connected to the Fourier transform module, and the Fourier transform module analyzes the laser self-mixing interference signal obtained by the detector;

[0011] The magneto-optical crystal is located inside the magnetic field, forming a Faraday effect; the laser light emitted by the laser is reflected multiple times between the laser and the transducer, and under the action of the polarizer, laser self-mixing interference is formed.

[0012] A further preferred technical solution of the present invention is that the axis of the magneto-optical crystal is coaxial with the laser light emitted by the laser, and the axis of the magneto-optical crystal is coaxial with the normal line of the transducer surface.

[0013] Preferably, both end surfaces of the magneto-optical crystal along the axis direction are smooth surfaces, and the surface of the transducer facing the laser has mirror reflection properties.

[0014] Preferably, the polarization direction of the polarizer is the same as the polarization direction of the laser light emitted by the laser, and the polarizer serves as a polarizer and an analyzer.

[0015] Another aspect of the present invention provides a method for detecting magnetic induction intensity based on laser self-mixing interference using the above-mentioned detection device, comprising the steps of:

[0016] S1. The laser generates collimated laser light which is split into two beams by a beam splitter. One beam passes through a polarizer, a magneto-optical crystal and a transducer, and the other beam is received by a detector.

[0017] Laser light passes through a polarizer and becomes polarized light. A magneto-optical crystal is located inside the magnetic field, causing the polarization direction of the polarized light passing through the magneto-optical crystal to rotate. The polarized light after optical rotation is irradiated on the transducer surface, reflected by the transducer, and then passes through the magneto-optical crystal again, causing the polarization direction of the polarized light to rotate a second time. The polarized light after secondary optical rotation passes through the polarizer and the beam splitter and returns to the laser. The laser light is reflected multiple times between the laser and the transducer surface, forming laser self-mixing interference.

[0018] S2. The control module generates a continuous sinusoidal wave signal to drive the transducer, causing the phase of the polarized light irradiated on the transducer surface to continuously change. At the same time, the laser self-mixing interference signal is monitored by the Fourier transform module to obtain the power spectrum of the laser self-mixing interference;

[0019] S3. The power spectrum of laser self-mixing interference shows a peak attenuation phenomenon. The peak of the power spectrum is fitted to obtain the power spectrum attenuation coefficient;

[0020] S4. Changing the magnetic induction intensity, repeating steps S1-S3, recording the power spectrum attenuation coefficients at different magnetic induction intensities, and fitting the power spectrum attenuation coefficients at different magnetic induction intensities to obtain the relationship between the magnetic induction intensity and the power spectrum attenuation coefficient;

[0021] S5. Obtain the power spectrum of laser self-mixing interference under different magnetic induction intensities, calculate the attenuation coefficient of the power spectrum, and obtain the magnetic induction intensity based on the relationship between the magnetic induction intensity and the power spectrum attenuation coefficient in step S4.

[0022] Preferably, in step S2, the method for obtaining the power spectrum of laser self-mixing interference is:

[0023] The laser self-mixing interference signal after i reflections is expressed as:

[0024]

[0025] Where ζ is the coupling coefficient of the laser back to the laser; r1 and r2 are the reflectivity of the front and rear end faces of the laser, respectively; r3 is the reflectivity of the transducer; n is the total number of reflections; Δθ is the rotation angle of the laser polarization direction; is the phase of the i-th reflected laser;

[0026] The power spectrum is obtained by Fourier transforming the laser self-mixing interference signal, which is expressed as:

[0027] P(f)=|∫[P(t)·exp(-jft)]dt| 2 ;

[0028] Where P is power, f is frequency, t is time, dt represents the unit time for the laser to pass through the magneto-optical crystal, and j is the complex number sign.

[0029] Preferably, the power spectrum attenuation coefficient in step S3 is expressed as:

[0030] P(f)=a1·exp(-f / f0)+b1;

[0031] Among them, a1 and b1 are fitting coefficients.

[0032] Preferably, the relationship between the magnetic induction intensity and the power spectrum attenuation coefficient obtained in S4 is expressed as:

[0033] f0=a2·exp(-B / b2)+c2;

[0034] Among them, a2, b2, and c2 are fitting coefficients.

[0035] Beneficial effects: By using a single polarizer to act as both a polarizer and an analyzer, the present invention reduces the number of optical components in the optical path, reduces light attenuation, simplifies system configuration, and achieves more accurate, reliable, and cost-effective magnetic induction intensity detection.

[0036] The present invention utilizes laser self-mixing interference technology to enhance the ability to detect magnetic field changes, especially at low magnetic induction intensities. It also employs Fourier transform analysis technology to obtain the power spectrum of laser self-mixing interference and perform fitting analysis on the power spectra at different magnetic induction intensities, effectively filtering out background noise and improving the stability and reliability of the measurement results. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 Schematic diagram of the structure of the magnetic induction intensity detection device based on laser self-mixing interference of the present invention;

[0038] Figure 2 1 is a frequency-power relationship curve obtained by the magnetic induction intensity detection method based on laser self-mixing interference in an embodiment of the present invention;

[0039] Figure 3 This is a power spectrum attenuation coefficient fitting curve diagram obtained by the magnetic induction intensity detection method based on laser self-mixing interference in an embodiment of the present invention;

[0040] Figure 4 A fitting curve diagram of the relationship between magnetic induction intensity and power spectrum attenuation coefficient obtained by the magnetic induction intensity detection method based on laser self-mixing interference in an embodiment of the present invention. DETAILED DESCRIPTION

[0041] In order to make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with the drawings in the present invention. Obviously, the embodiments described are part of the embodiments of the present invention, not all of the embodiments, and they should not be understood as limitations on the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. In the description of the present invention, it should be understood that the terms used are only for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0042] The following combination Figures 1-4 The present invention describes a device and method for detecting magnetic induction intensity based on laser self-mixing interference.

[0043] Example 1: This example provides a magnetic induction intensity detection device based on laser self-mixing interference.

[0044] The device, such as Figure 1As shown, it includes a laser, a spectrometer, a polarizer, a magneto-optical crystal, a transducer, a control module, a detector and a Fourier transform module.

[0045] In this embodiment, a pure solid-state laser is used as the laser. The magneto-optical crystal is made of a highly transparent material to reduce optical loss during laser reflection and ensure signal transmission accuracy. In this embodiment, scandium gallium garnet (TGG) is used as the magneto-optical crystal. A piezoelectric ceramic crystal is used as the transducer. The polarization direction of the polarization plate is the same as that of the laser light emitted by the laser, and it serves as a polarizer and analyzer.

[0046] The output of the driving power supply is connected to the input of the laser, driving the laser light emitted by the laser. After being split by the beam splitter, the laser light is divided into two optical paths. The first optical path is provided with a polarizer, a magneto-optical crystal, and a transducer. The input of the transducer is connected to the input of the control module. The control module generates a continuous sinusoidal wave signal to continuously control the transducer. It can control the length of the transducer to change periodically, thereby changing the phase of the laser light and generating laser self-mixing interference. The normal of the transducer is coaxial with the laser light emitted by the laser. The coaxiality is used to ensure the accuracy of signal transmission.

[0047] A detector is placed on the second optical path. The laser illuminates the detector's input, and its output is connected to the input of a Fourier transform module, which analyzes the laser self-mixing interference signal. The Fourier transform directly displays the power spectrum of the laser self-mixing interference signal, making it easier for operators to observe the effects of changes in magnetic induction intensity.

[0048] The design principle of this embodiment's device is that laser light reflects multiple times between the laser and the transducer, causing its polarization to shift. The intensity of the deflected laser light decreases after passing through the polarizer, causing a change in the laser's self-mixing interference properties. This change is used to detect magnetic induction intensity.

[0049] The laser emitted by the laser can be reflected multiple times between the transducer and the output end face of the laser, and during the multiple reflection process, the laser passes through the magneto-optical crystal multiple times, which has the effect of enhancing the rotation of the laser polarization direction and is suitable for low magnetic induction intensity detection.

[0050] Example 2: This example provides a method for detecting magnetic induction intensity based on laser self-mixing interference, which uses the detection device of Example 1.

[0051] The specific steps of this detection method are:

[0052] S1. A pure solid-state laser generates collimated laser light, which is split into two beams by a beam splitter. One beam passes through a polarizer, a magneto-optical crystal, and a transducer before returning to the laser to form laser self-mixing interference; the other beam is received by a detector to monitor the laser self-mixing interference signal.

[0053] The laser passes through the polarizer to become polarized light, and then passes through the magneto-optical crystal. When the magnetic induction intensity of the environment in which the magneto-optical crystal is located changes, the Faraday rotation effect is generated, causing the polarization direction of the polarized light to rotate. The polarized light after optical rotation is irradiated on the transducer surface, reflected by the transducer, and then passes through the magneto-optical crystal again, causing the polarization direction of the polarized light to rotate a second time. The polarized light after secondary optical rotation passes through the polarizer and the spectrometer and returns to the laser. It is reflected multiple times between the laser and the piezoelectric ceramic surface, forming laser self-mixing interference.

[0054] S2, the control module generates a continuous sine function with a frequency of 100 Hz and an amplitude of 600 mVpp to drive the transducer, so that the phase of the polarized light irradiated on the transducer surface changes continuously. At the same time, the power spectrum of the laser self-mixing interference is observed through the Fourier transform module, as shown in Figure 2 As shown; the method for obtaining the power spectrum of laser self-mixing interference is:

[0055] The single reflection of laser light between the laser and the transducer is expressed as:

[0056] E1=ζ·r1(1-r2) 2 r3·cos(2·Δθ)·exp[-j·4π(L+l) / λ+gL]·E0;

[0057] Where g is the gain coefficient of the laser cavity, ζ is the coupling coefficient of the laser back to the laser; r1 and r2 are the reflectivity of the front and rear end faces of the laser, respectively, r3 is the reflectivity of the transducer, E0 is the initial laser, and j is the complex number sign;

[0058] -4π(L+l) is the phase change of the laser caused by the external cavity and the laser cavity, L is the distance between the laser and the transducer, and l is the length of the laser cavity;

[0059] Δθ is the rotation angle of the laser polarization direction, which is calculated as:

[0060] Δθ=V·B·d;

[0061] Where d is the length of the magneto-optical crystal, B is the magnetic induction intensity, and V is the Verdet constant of the magneto-optical crystal;

[0062] The light wave returning to the laser cavity after i reflections is expressed as:

[0063]

[0064] All reflected light between the laser and the transducer can be expressed as:

[0065]

[0066] The light inside the laser is represented as:

[0067] E L =r1r2·exp[-j·4πL / λ+gL]·E0;

[0068] For a stable laser, the light field should reach E+E L =E0; and:

[0069]

[0070] The self-mixing interference of the laser after i reflections is expressed as:

[0071]

[0072] Where, ζ is the coupling coefficient of the laser back to the inside of the laser; r1 and r2 are the reflectivity of the front and rear end faces of the laser, respectively; r3 is the reflectivity of the transducer; n is the total number of reflections; Δθ is the rotation angle of the laser polarization direction; is the phase of the i-th reflected laser;

[0073] The power spectrum is obtained by Fourier transforming the laser self-mixing interference signal, which is expressed as:

[0074] P(f)=|∫[P(t)·exp(-jft)]dt| 2 ;

[0075] Where P is power, f is frequency, t is time, dt represents the unit time for the laser to pass through the magneto-optical crystal, and j is the complex number sign.

[0076] S3. The power spectrum of laser self-mixing interference shows a peak attenuation phenomenon. The peak of the power spectrum is fitted, such as Figure 3 As shown, the power spectrum attenuation coefficient is f0 = 10.35kHz; it is expressed as:

[0077] P(f)=42.34·exp(-f / 10.35)-87.22;

[0078] S4, change the magnetic induction intensity to 0-36.11mT, repeat steps S1-S3, record the power spectrum attenuation coefficients of different magnetic induction intensities, and fit the power spectrum attenuation coefficients of different magnetic induction intensities, such as Figure 4 As shown, the relationship between magnetic induction intensity and power spectrum attenuation coefficient is obtained; it is expressed as:

[0079] f0=4.04·exp(-B / 7.70)-10.52.

[0080] S5. Obtain the power spectrum of laser self-mixing interference under different magnetic induction intensities, calculate the attenuation coefficient of the power spectrum, and obtain the magnetic induction intensity based on the relationship between the magnetic induction intensity and the power spectrum attenuation coefficient in step S4.

[0081] The principle of the detection method of this embodiment is that the power spectrum of laser self-mixing interference shows an attenuation trend, and its attenuation coefficient is related to the magnetic induction intensity, the length of the magneto-optical crystal, and the Verdet coefficient; since the change of the magnetic induction intensity in the environment of the magneto-optical crystal causes the attenuation rate of the power spectrum to change, which further causes the fitting coefficient f0 of the laser self-mixing interference power spectrum to change, the magnetic induction intensity B can be written as an expression for the power spectrum attenuation coefficient f0.

[0082] In this embodiment, the power spectrum of laser self-mixing interference shows an attenuation trend, and its attenuation coefficient is related to the magnetic induction intensity and the magneto-optical crystal. The change of the magnetic induction intensity of the magneto-optical crystal in the environment causes the attenuation rate of the power spectrum to change. The power spectrum under different magnetic induction intensities is fitted and analyzed to eliminate the influence of background noise.

[0083] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply the existence of any such actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article, or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or device. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of other identical elements in the process, method, article, or device comprising the element.

[0084] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A method for detecting magnetic induction intensity based on laser self-mixing interference using a magnetic induction intensity detection device based on laser self-mixing interference, characterized in that: The magnetic induction intensity detection device based on laser self-mixing interference includes a laser for emitting laser light, wherein the laser light emitted by the laser light is split by a spectrometer into two optical paths; One optical path is provided with a polarizer, a magneto-optical crystal, and a transducer in sequence; the transducer is electrically connected to a control module, which generates a continuous sinusoidal wave signal to continuously control the transducer; the polarization direction of the polarizer is the same as the polarization direction of the laser light emitted by the laser, and serves as a polarizer and analyzer; A detector is provided on the other optical path; the detector is electrically connected to the Fourier transform module, and the Fourier transform module analyzes the laser self-mixing interference signal obtained by the detector; The magneto-optical crystal is located inside the magnetic field, forming a Faraday effect; the laser light emitted by the laser is reflected multiple times between the laser and the transducer, and under the action of the polarizer, laser self-mixing interference is formed; the axis of the magneto-optical crystal is coaxial with the laser light emitted by the laser, and the axis of the magneto-optical crystal is coaxial with the normal of the transducer surface; the two end surfaces of the magneto-optical crystal along the axis direction are smooth surfaces, and the surface of the transducer facing the laser has mirror reflection characteristics; The detection method comprises the steps of: S1. The laser generates collimated laser light which is split into two beams by a beam splitter. One beam passes through a polarizer, a magneto-optical crystal and a transducer, and the other beam is received by a detector. Laser light passes through a polarizer and becomes polarized light. A magneto-optical crystal is located inside the magnetic field, causing the polarization direction of the polarized light passing through the magneto-optical crystal to rotate. The polarized light after optical rotation is irradiated on the transducer surface, reflected by the transducer, and then passes through the magneto-optical crystal again, causing the polarization direction of the polarized light to rotate a second time. The polarized light after secondary optical rotation passes through the polarizer and the beam splitter and returns to the laser. The laser light is reflected multiple times between the laser and the transducer surface, forming laser self-mixing interference. S2. The control module generates a continuous sinusoidal wave signal to drive the transducer, causing the phase of the polarized light irradiated on the transducer surface to continuously change. At the same time, the laser self-mixing interference signal is monitored by the Fourier transform module to obtain the power spectrum of the laser self-mixing interference; S3. The power spectrum of laser self-mixing interference shows a peak attenuation phenomenon. The peak of the power spectrum is fitted to obtain the power spectrum attenuation coefficient; S4. Changing the magnetic induction intensity, repeating steps S1-S3, recording the power spectrum attenuation coefficients at different magnetic induction intensities, and fitting the power spectrum attenuation coefficients at different magnetic induction intensities to obtain the relationship between the magnetic induction intensity and the power spectrum attenuation coefficient; S5. Obtain the power spectrum of laser self-mixing interference under different magnetic induction intensities, calculate the attenuation coefficient of the power spectrum, and obtain the magnetic induction intensity based on the relationship between the magnetic induction intensity and the power spectrum attenuation coefficient in step S4.

2. The detection method according to claim 1, wherein In step S2, the power spectrum of laser self-mixing interference is obtained by: The self-mixing interference of the laser after i reflections is expressed as: Where ζ is the coupling coefficient of the laser back to the laser; r1 and r2 are the reflectivity of the front and rear end faces of the laser, respectively; r3 is the reflectivity of the transducer; n is the total number of reflections; Δθ is the rotation angle of the laser polarization direction; is the phase of the i-th reflected laser; The power spectrum is obtained by Fourier transforming the laser self-mixing interference signal, which is expressed as: P(f)=|∫[P(t)·exp(-jft)]dt| 2 ; Where P is power, f is frequency, t is time, ft is the product of frequency and time, dt is the unit time, and j is the complex number sign.

3. The detection method according to claim 2, characterized in that The power spectrum attenuation coefficient in step S3 is expressed as: P(f)=a1·exp(-f / f0)+b1; Among them, a1 and b1 are fitting coefficients.

4. The detection method according to claim 3, characterized in that The relationship between the magnetic induction intensity and the power spectrum attenuation coefficient is obtained in S4 and is expressed as: f0=a2·exp(-B / b2)+c2; Among them, a2, b2, and c2 are fitting coefficients.

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