A dual-transmission-path magneto-optical Faraday rotation measurement system

Abstract

The invention discloses a dual-transmission optical path magneto-optical Faraday rotation measurement system. The multi-transmission magneto-optical Faraday rotation measurement system mainly consists of a base plate, a power supply, a detector, a laser, a prism, a polarizing plate 1, a spiral coil, a polarizing plate 2, a mirror 1, a mirror 2 and the like. The transmitted light can be transmitted multiple times in a magneto-optical glass, thereby increasing the optical path, thereby increasing the Faraday rotation angle by multiple times, greatly improving the sensitivity of the sensing system, and does not require a strong Faraday magneto-optical effect of a sample to be measured and a large V value or applying a particularly large magnetic field. The system can measure samples with large Faraday rotation angles as well as samples with small Faraday rotation angles, with an error rate of 0.00003%. The sensitivity of the magneto-optical sensing system is 0.00022±0.00001min / Oe, with high measurement accuracy, simple construction, low cost, and a wide range of applicable samples, and can be used in the field of magneto-optical sensing.

Description

Technical Field

[0001] The invention belongs to the technical field of magneto-optical sensing, and in particular relates to a double-transmission light path magneto-optical Faraday rotation measurement system. Background Art

[0002] In recent years, with the advancement of photonic and optical technologies, the demand for glass-based non-reciprocal magneto-optical effect elements in photonic devices such as optical sensing and optical communications has been increasing. Among them, magneto-optical glass with magneto-optical Faraday effect has attracted widespread attention in the fields of laser optics, optical fiber communication systems, sensing technology and current sensing due to its good magneto-optical rotation and anti-electromagnetic interference performance, high precision, fast response and low cost. The huge potential applications of magneto-optical glass include rotators based on Faraday effect, isolators, optical switches, modulators, magneto-optical current sensors, magneto-optical biosensors, etc.

[0003] Currently, magneto-optical sensors still use rare earth-doped single crystal materials, because the magneto-optical Verdet constant V of rare earth single crystals can reach 0.35-0.4 min / G.cm 633nm; however, due to the high cost of rare earth and single crystal materials, and the large change of V with temperature, the sensitivity of the equipment is greatly restricted by the ambient temperature in practical applications, thus affecting its practicality and sensitivity; and magneto-optical glass (whether paramagnetic or diamagnetic) has low cost and the Field constant V is not affected by temperature, but the Field constant V is lower than that of rare earth-doped single crystal materials, which cannot meet the needs of high-performance magneto-optical devices, and the sensitivity of the sensor cannot be guaranteed. A larger magnetic field must be used to meet the requirements of Faraday rotation.

[0004] To solve the problem of low sensitivity of magneto-optical sensors based on magneto-optical glass and the need to use a large magnetic field, a common method is to prepare magneto-optical glass with a strong Faraday magneto-optical effect and a large V value; rare earth-doped paramagnetic glass increases the concentration of rare earth ions to increase the magneto-optical properties of the glass (0.25-0.3 min / G.cm 633nm), but the doping of a large amount of rare earth greatly reduces the thermal and mechanical stability of the glass, and it is expensive; therefore, a research team has studied diamagnetic glass based on heavy metal oxides, but the current magneto-optical Felton constant that can be achieved is a V value of 0.12-0.22 min / G.cm 633nm.

[0005] At present, there are few innovative studies on magneto-optical Faraday rotation measurement at home and abroad, and they mainly use traditional Faraday rotation test methods. Figure 1As shown, this method can obtain a more obvious Faraday rotation angle θf for materials with good Faraday rotation performance and a larger V, such as magneto-optical single crystals; while for magneto-optical glass with a smaller V, since its Faraday rotation angle θf is small, it is very easy to be disturbed by the surrounding ambient light signals, so in many cases θf cannot be accurately obtained, or even cannot be obtained; and the current magneto-optical sensing systems based on Faraday rotation, including magneto-optical current sensors or magneto-optical biosensors, are all based on traditional Faraday measurement methods, so a large magnetic field must be used as a whole to obtain a more obvious Faraday rotation angle θf and a more sensitive sensing system, so its cost and sensitivity are greatly limited in practical applications. Summary of the invention

[0006] According to the Faraday rotation theory, when a magnetic field is applied to magneto-optical glass, a Faraday effect is induced in the optical fiber, and the rotation angle of the polarization plane depends on the applied magnetic field and the length of light propagating in the glass, θf= VBL, where θf is the Faraday rotation angle, B is the magnetic field, L is the induction length of the magnetization direction, and V is the Verdet constant of the optical fiber; for a given magneto-optical glass, its Field constant is constant within a certain temperature and wavelength range, so under a certain magnetic field, the larger the sample length, the larger the Faraday rotation angle, and the greater the magneto-optical sensitivity of the device. According to the above principle, under the conditions of certain magneto-optical properties and magnetic field intensity, increasing the propagation optical path of the laser in the magneto-optical glass is a breakthrough in realizing a highly magneto-optically sensitive device. Because the Faraday effect is a non-reciprocal phenomenon, it is not affected by the propagation direction of light and is only related to the direction of the magnetic field, so the magneto-optical effect caused by the optical fiber length of the propagation optical path of the transmitted light in the magneto-optical glass can play a superposition and enhancement effect. Therefore, the present invention improves the sensitivity of the Faraday rotation angle measurement of the magneto-optical device by increasing the optical path of the transmitted light.

[0007] In order to overcome the technical defects of high cost and low sensitivity in the traditional Faraday rotation test process, the present invention designs a dual-transmission light path magneto-optical Faraday rotation measurement system, the structure of which is as follows: it includes a base plate and a detector, the detector is composed of a probe and a processor, the probe and the processor are connected by a wire, the processor and the power supply are fixed on the base plate from left to right, two parallel slide rails are arranged on one side of the base plate, a laser, a prism, a polarizing plate 1, a spiral coil, a polarizing plate 2, and a mirror are slidably arranged on the outer slide rail from left to right, a probe and a mirror are slidably arranged on the inner slide rail from left to right, the laser and the probe are located in the same plane perpendicular to the base plate, the mirror 1 is placed at an angle a, and the mirror 2 is placed at an angle φ, a and φ are the incident angles of the laser on the mirror surface, respectively, and 2 ◦ <a<5 ◦ , 35 ◦ <φ<48 ◦, the laser, the processor and the spiral coil are respectively connected to the power supply through wires;

[0008] Preferably, a backup power supply is also provided on the bottom plate;

[0009] Preferably, the bottom plate is a magnetic steel plate;

[0010] Preferably, the laser, prism, polarizer 1, spiral coil, polarizer 2, mirror 1, probe, and mirror 2 are connected to corresponding slide rails through sliders, and each of the components is threadedly connected to the corresponding sliders;

[0011] Preferably, the magnetic field applied by the spiral coil is 220-500G.

[0012] In the process of constructing and implementing a dual-transmission optical path magneto-optical Faraday rotation measurement system, there are three important parameters that affect the accuracy of the measurement results, specifically:

[0013] 1) Setting the spatial fixed position of mirror 1: Because the transmitted light first passes through the glass and then irradiates the mirror surface, according to the reflection principle, it is necessary to ensure that the transmitted light can still pass through the glass after reflection, so the setting of the mirror angle is very critical; without considering the linear birefringence and internal circular birefringence in the glass, according to the Jones formula for the setting and calculation of the longitudinal and transverse polarization vectors, the angle between the mirror and the longitudinal axis should be 2 to 5 degrees, which can ensure that cos(a)≈1, thereby ensuring that the phase shift and optical path generated by the first and second transmitted light in the glass are roughly the same, so that the Faraday rotation angles generated by the two transmitted light in the glass can be roughly the same;

[0014] 2) Setting the spatial fixed position of mirror 2: Because the transmitted light first passes through the glass and then irradiates the mirror surface, according to the reflection principle, it is necessary to ensure that the transmitted light can still pass through the glass after reflection. Based on the mirror width d, without considering the linear birefringence and internal circular birefringence in the glass, the longitudinal and transverse polarization vectors are set and calculated according to the Jones formula (such as Figure 2 Assume that the angle between mirror 2 and the longitudinal axis is φ, and according to the Jones matrix corresponding to the reflection of mirror 2, set Figure 2 The x and y axes of transmitted light 3 and 4 remain unchanged, and the range of φ is calculated to be 35-48 degrees, ensuring that the second transmitted light enters the glass after being reflected on the second surface of the mirror, and the phase shift and optical path of the generated transmitted light 3 and transmitted light 4 are roughly the same, so that the Faraday rotation angles generated by the four transmitted lights in the glass are roughly the same;

[0015] 3) The intensity of polarized light after the fourth transmission: According to the non-reciprocal nature of the magneto-optical Faraday effect, when the fourth transmitted light is received by the photodetector, its polarization intensity is also the superposition of the four polarization intensities, which can be expressed as , where θf is the polarization rotation angle of the first transmitted light in the glass. According to the intensity I of the light obtained from the detector, the Faraday rotation angle of the glass can be inferred, and then the Felton constant of the sample can be calculated according to θ=VBL.

[0016] Beneficial effects achieved by the present invention:

[0017] The present invention is based on a design concept different from that of the existing measurement system, improves the existing magneto-optical Faraday rotation measurement system, makes the transmitted light transmit multiple times in the magneto-optical glass, increases the optical path, and thus increases the Faraday rotation angle by multiple times, greatly improves the sensitivity of the sensing system, and does not require the Faraday magneto-optical effect of the sample to be measured to be strong and the V value to be large or to apply a particularly large magnetic field. It can measure samples with large Faraday rotation angles as well as samples with small Faraday rotation angles, with an error rate of 0.00003%. The sensitivity of the magneto-optical sensing system is 0.00022±0.00001min / Oe, has high measurement accuracy, is simple to construct, is low in cost, is applicable to a wide range of samples, and can be used in the field of magneto-optical sensing. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a schematic diagram of the optical platform for traditional magneto-optical Faraday rotation testing;

[0019] Figure 2 It is a cross-sectional view of the mirror angle design in the present invention;

[0020] Figure 3 Schematic diagram of the dual-transmission optical path magneto-optical Faraday rotation measurement system in Example 1;

[0021] Figure 4 A physical diagram of the dual-transmission optical path magneto-optical Faraday rotation measurement system designed for the present invention;

[0022] Figure 5 This is a physical picture of the pure quartz glass sample used in Example 1 and Example 2. DETAILED DESCRIPTION

[0023] The present invention will be further described below by means of specific examples.

[0024] Example 1

[0025] like Figure 3 and Figure 4As shown, a dual-transmission optical path magneto-optical Faraday rotation measurement system includes a base plate and a detector, the detector is composed of a probe and a processor, the probe and the processor are connected by a wire, the base plate is a magnetic steel plate, the processor, power supply, and backup power supply are fixed on the base plate from left to right, two parallel slide rails are arranged on one side of the base plate, a laser, a prism, a polarizer 1, a spiral coil, a polarizer 2, and a mirror 1 are slidably arranged on the outer slide rail from left to right, the probe and the mirror 2 are slidably arranged on the inner slide rail from left to right, the laser and the probe are located in the same plane perpendicular to the base plate, and the mirror 1 is at an angle a=2 ◦ Place the mirror at an angle of φ=35 ◦ Placed, a and φ are the incident angles of the laser on the mirror respectively, the laser, processor and spiral coil are connected to the power supply through wires respectively; the laser, prism, polarizer 1, spiral coil, polarizer 2, mirror 1, probe and mirror 2 are connected to the corresponding slide rails through sliders respectively, and the various devices are respectively connected to the corresponding slider threads.

[0026] The specifications of the laser are: wavelength of 532nm, 633nm, 750nm, 1032nm, output power of 5-10mW, numerical aperture of 0.28, emission efficiency of 29%, output spot diameter of 1mm;

[0027] The polarization extinction ratio of polarizer 1 and polarizer 2 is >1:5000;

[0028] The power supply is a DC power supply with an output voltage of 5V and an output current of 20mA;

[0029] The specifications of the spiral coil are: PTFE tube inner radius r1 = 11.5 mm, outer radius r2 = 17 mm, length 19 cm, copper wire diameter 2 mm, wound into 180 turns;

[0030] The pure quartz glass sample has a size of 10 mm × 30 mm × 40 mm, a surface smoothness of ≈ 100 µm, a Felton constant V of 0.01352 min / G.cm, and a wavelength of 633 nm;

[0031] The detector is a BPX65 PIN diode, an AD8015 transimpedance amplifier, and a 1 mm 2 Sensing area, 240 MHz bandwidth.

[0032] The magneto-optical glass sample is fixed in the center of the spiral coil. The laser is turned on 15 minutes in advance to stabilize the incident light output. The laser beam is focused on the sample surface after passing through the polarizer. After the transmitted light passes through the sample, it is reflected multiple times by a mirror placed at a specific angle, and finally passes through the sample and the polarizer and enters the detector to obtain optical information. Because the Faraday effect is a non-reciprocal phenomenon and does not depend on the propagation direction, the light propagates four times in the magneto-optical medium in the applied longitudinal magnetic field and experiences four times the rotation polarization angle. Because the mirror is at an angle a=2 ◦ Placed, its cos(a)≈1, and the mirror 2 is at an angle of φ=35 ◦ Placed, it can be considered that the optical path of the four-times transmitted light is approximately equal to L; therefore, the Faraday rotation angle of the sample after the total phase shift is θf = θf1 + θf2 + θf3 + θf4; since the optical length is the same (L), θf1 = θf2 = θf3 = θf4, the total phase shift is θf = 4θf1 = 4VBL (V is the Felton constant, B is the magnetic field intensity, and L is the sample length); According to this method, four times the Faraday rotation angle can be measured, and the error rate of the magneto-optical sensing system can be calculated based on the ratio of the rotation angle or Verdet constant calculated by measurement to the known Verdet constant of pure quartz glass, and the error rate E = V 测量 / V 已知 .

[0033] The measurement parameters of Example 1 of the present invention are shown in Table 1. The error rate of the double-transmission light path magneto-optical Faraday rotation measurement system is 0.00003%, and the sensitivity of the magneto-optical sensing system is 0.00022±0.00001min / Oe.

[0034] Table 1

[0035]

[0036] Example 2

[0037] The difference between this embodiment and embodiment 1 is that the mirror is at an angle a=5 ◦ Place the mirror at an angle of φ=48 ◦ Placement, other things are the same, the measurement parameters are shown in Table 2, the error rate of the double transmission light path magneto-optical Faraday rotation measurement system is 0.00003%, and the sensitivity of the magneto-optical sensing system is 0.00022±0.00001min / Oe.

[0038] Table 2

[0039]

[0040] The above specific implementation modes are used to explain the present invention rather than to limit the present invention. Any modification and change made to the present invention within the spirit of the present invention and the protection scope of the claims shall fall within the protection scope of the present invention.

Claims

1. A dual-transmission optical path magneto-optical Faraday rotation measurement system, characterized in that: The invention comprises a bottom plate and a detector, wherein the detector is composed of a probe and a processor, and the probe and the processor are connected by a wire. The processor and the power supply are fixed on the bottom plate from left to right in sequence, and two parallel slide rails are arranged on one side of the bottom plate. The laser, prism, polarizing plate 1, spiral coil, polarizing plate 2, and mirror 1 are arranged on the outer slide rail from left to right in sequence, and the probe and mirror 2 are arranged on the inner slide rail from left to right in sequence, and the laser and the probe are located in the same plane perpendicular to the bottom plate, and the mirror 1 is placed at an angle a, and the mirror 2 is placed at an angle φ, where a and φ are the incident angles of the laser on the mirror surface, respectively, and 2 ◦ <a<5 ◦ , 35 ◦ <φ<48 ◦ , the laser, processor and spiral coil are respectively connected to the power supply through wires.

2. The system according to claim 1, characterized in that A backup power supply is also provided on the bottom plate.

3. The system according to claim 1, characterized in that The bottom plate is a magnetic steel plate.

4. The system according to claim 1, characterized in that The laser, prism, polarizer 1, spiral coil, polarizer 2, mirror 1, probe, and mirror 2 are respectively connected to corresponding slide rails through sliders, and each of the components is respectively threadedly connected to the corresponding sliders.

5. The system according to claim 1, characterized in that The magnetic field applied by the spiral coil is 220-500G.

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