High-stability optical electric field sensor based on Fabry-Perot structure

Abstract

The invention provides a high-stability optical electric field sensor based on a Fabry-Perot structure, and relates to the technical field of electric field sensors, a temperature compensation crystal with a negative thermo-optic coefficient or a negative thermal expansion coefficient is added in a Fabry-Perot resonant cavity to offset the positive thermo-optic effect and the thermal expansion effect of an electro-optical crystal. The device specifically comprises a laser, a polarizer, two groups of reflectors, an electro-optical crystal, a temperature compensation crystal and a photoelectric detector, wherein the laser, the polarizer, the reflecting mirror, the electro-optical crystal, the temperature compensation crystal, the reflecting mirror and the photoelectric detector are sequentially arranged along the direction of a light path, and the two groups of reflecting mirrors form a Fabry-Perot resonant cavity; the polarizer, the two groups of reflectors, the electro-optical crystal and the temperature compensation crystal are packaged into a sensor probe; the sensor probe is connected with the laser and the photoelectric detector through optical fiber jumpers. According to the scheme, the temperature stability of the optical electric field sensor can be improved, and the application scene of the optical electric field sensor is widened.

Description

Technical Field

[0001] The invention relates to the technical field of electric field sensors, and in particular to a high-stability optical electric field sensor based on a Fabry-Perot structure. Background Art

[0002] Electric field measurement is widely used in many disciplines and engineering fields, including corona electric field measurement, electromagnetic environment monitoring of transmission lines, and electric field distribution verification of power equipment. The traditional electric field measurement method is based on the principle of electromagnetic induction, and measures the electric field through the induced charge on the metal probe. This method is simple in principle, but the insulation resistance of the sensor is weak, and the measurement frequency band is narrow, which has gradually failed to meet the needs of modern electric field measurement, especially for the power field with a more complex electromagnetic environment, and its measurement accuracy cannot meet the measurement requirements.

[0003] In order to solve the above problems, technicians in this field have proposed an optical electric field sensor, which uses crystal material as the sensing medium and realizes the measurement of the electric field based on Pockels' linear electro-optical effect. It has the characteristics of wide response band, all-dielectric structure and strong resistance to electromagnetic interference, and has obvious advantages in the field of wide-field and strong electric field measurement.

[0004] Electro-optical sensors can be divided into polarization modulation sensors, phase modulation sensors and amplitude modulation sensors according to the electro-optical modulation method. Amplitude modulation sensors can use Fabry-Perot resonant cavity to improve the sensitivity of the sensor. However, in practical applications, optical electric field sensors based on this principle are most easily affected by environmental factors such as temperature and have poor stability, which seriously limits their application scenarios. Summary of the invention

[0005] In view of this, in order to address the above shortcomings, it is necessary to propose a high-stability optical electric field sensor based on a Fabry-Perot structure to solve the problem of poor stability of the electric field sensor caused by temperature.

[0006] The present invention provides a high-stability optical electric field sensor based on a Fabry-Perot structure, in which a temperature compensation crystal with a negative thermo-optic coefficient or a negative thermal expansion coefficient is added to the Fabry-Perot resonant cavity to offset the positive thermo-optic effect and thermal expansion effect of the electro-optic crystal itself.

[0007] Preferably, the optical electric field sensor specifically includes: a laser, a polarizer, two groups of reflectors, an electro-optical crystal, a temperature compensation crystal and a photodetector; wherein the laser, the polarizer, the reflector, the electro-optical crystal, the temperature compensation crystal, the reflector and the photodetector are arranged in sequence along the optical path direction, and the two groups of reflectors constitute a Fabry-Perot resonant cavity; the polarizer, the two groups of reflectors, the electro-optical crystal and the temperature compensation crystal are packaged as a sensor probe; the sensor probe is connected to the laser and the photodetector through an optical fiber jumper; the laser is used to generate a laser signal and transmit it into the sensor probe; the photodetector is used to convert the laser signal received from the sensor probe after being acted on by the electric field to be measured into an electrical signal, and determine the electric field strength of the electric field to be measured based on the electrical signal.

[0008] Preferably, the photoelectric detector is used to determine the electric field strength of the electric field to be measured according to the following calculation formula:

[0009]

[0010] η i =α i +β i (n i -1)

[0011] Among them, φ is used to characterize the phase change of light in the Fabry-Perot resonant cavity, φ0 is used to characterize the inherent phase of the Fabry-Perot resonant cavity, λ is the wavelength of the laser, i=1,2, corresponding to the electro-optical crystal and the temperature compensation crystal respectively, n i Characterizes the refractive index of the corresponding crystal i, l i Characterizes the length of the light transmission direction of the corresponding crystal i, η i Characterizes the reduced thermal coefficient of the material corresponding to crystal i, α i Characterizes the material thermo-optic coefficient corresponding to crystal i, β i It characterizes the thermal expansion coefficient of the material of the corresponding crystal i, T is used to characterize the ambient temperature, γ is used to characterize the electro-optic coefficient of the electro-optic crystal, E is used to characterize the electric field strength of the electric field to be measured, and L is the cavity length of the Fabry-Perot resonant cavity.

[0012] Preferably, the length of the temperature compensation crystal is calculated by the formula Calculated.

[0013] Preferably, the polarization direction of the polarizer is the same as a characteristic polarization direction of the electro-optical crystal.

[0014] Preferably, the two groups of reflectors are formed by quartz glass plates with reflective films coated on the inner walls, the two quartz glass plates and the quartz glass lining plate located at the bottom form a U-shaped structure, and the electro-optical crystal and the temperature compensation crystal are arranged in the U-shaped groove.

[0015] Preferably, the reflectivity of the two groups of reflectors is not less than 90%, and the distance between the two groups of reflectors is 15 cm.

[0016] Preferably, the photodetector includes a photodiode and a processor; the photodiode is used to convert the laser signal output by the sensor probe into a current signal in proportion to a conversion coefficient, and the processor sets the working point at 3 / 4 of the maximum light transmittance intensity to obtain maximum sensitivity.

[0017] Preferably, the optical electric field sensor also includes a first fiber optic collimator and a second fiber optic collimator, which are respectively integrated in the laser and the sensor probe; the parameters of the first fiber optic collimator and the second fiber optic collimator are: a projection wavelength of 1550nm, a diameter of 1mm, a length of 30mm, a material of quartz glass, and a fiber optic connector for coupling the laser in the fiber optic jumper into spatial light, or coupling the spatial light into the fiber optic jumper.

[0018] Preferably, the temperature compensation crystal is organic glass PMMA.

[0019] It can be seen from the above technical scheme that in the high-stability optical electric field sensor based on the Fabry-Perot structure provided by this scheme, a temperature compensation crystal with a negative thermo-optic coefficient or a negative thermal expansion coefficient is added to the Fabry-Perot resonant cavity, which can compensate for the positive thermal expansion effect and positive thermo-optic effect of the electro-optical crystal, thereby improving the temperature stability of the optical electric field sensor and broadening the application scenarios of the optical electric field sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 A schematic diagram of a high-stability optical electric field sensor based on a Fabry-Perot structure provided in an embodiment of the present invention.

[0021] Figure 2 The output temperature characteristic curve of FP electro-optical sensor under different reflectivity. DETAILED DESCRIPTION

[0022] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0023] The optical electric field sensor based on Fabry-Perot FP is very sensitive to phase changes and has high sensitivity, but at the same time, environmental factors such as temperature also have a great impact on the sensor output. When light propagates in an electro-optic crystal, it is affected by both the thermo-optic effect and the electro-optic effect, and the two cannot be separated. This problem is common in existing electro-optic sensors of various structures. If you want to improve the temperature stability of the sensor, you must reduce the proportion of the temperature term in the total phase. Therefore, this scheme considers introducing a term with a negative temperature effect to offset the positive temperature effect term of the electro-optic crystal itself, that is, setting a crystal with a negative thermo-optic coefficient or a negative thermal expansion coefficient in the optical path to compensate for the positive thermal expansion effect and positive thermo-optic effect of the electro-optic crystal.

[0024] Specifically, Figure 1 As shown, the optical electric field sensor may include: a laser, a polarizer, two groups of reflectors, an electro-optical crystal, a temperature compensation crystal and a photodetector; wherein the laser, the polarizer, the reflector, the electro-optical crystal, the temperature compensation crystal, the reflector and the photodetector are arranged in sequence along the optical path direction, and the two groups of reflectors constitute a Fabry-Perot resonant cavity; the polarizer, the two groups of reflectors, the electro-optical crystal and the temperature compensation crystal are packaged as a sensor probe; the sensor probe is connected to the laser and the photodetector through an optical fiber jumper; the laser is used to generate a laser signal and transmit it into the sensor probe; the photodetector is used to convert the laser signal received from the sensor probe after being acted on by the electric field to be measured into an electrical signal, and determine the electric field strength of the electric field to be measured based on the electrical signal.

[0025] In this embodiment, the phase φ is the phase change of light passing through a cavity in the FP cavity. If a negative thermal effect term is to be introduced, the temperature compensation crystal and the electro-optical crystal must be set in the FP cavity. The polarization direction of the polarizer should be the same as a characteristic polarization direction of the electro-optical crystal. When the incident polarization direction is linearly polarized along a characteristic direction of the electro-optical crystal, the change in the crystal refractive index caused by the electric field will change the transmission coefficient of the Fabry-Perot standard distance, thereby causing a change in the amplitude of the light beam, thereby enabling electric field detection. Both sets of reflectors should be formed by quartz glass plates coated with reflective films on the opposite inner walls, and the two quartz glass plates and the quartz glass lining plate at the bottom form a U-shaped structure. The electro-optical crystal and the temperature compensation crystal are set in the U-shaped groove to form a FP structure together.

[0026] It should be pointed out that the quartz glass constituting the U-shaped structure should be a material with weak thermo-optical effect and good light transmittance, and the electro-optical crystal should be coated with an anti-reflection film. In addition, the reflectivity of the two sets of reflectors after being coated with the reflective film should be no less than 90%.

[0027] In this embodiment, the laser may be a DFB (Distributed Feedback Laser) laser, which is used to generate a laser with a wavelength of 1550nm, a line width of 10kHz, an output optical power of 100mW, and an output optical frequency that is adjustable within a range of -30GHz to +30GHz from the center frequency. The DFB laser has the characteristics of narrow line width, large and stable output optical power, and adjustable output optical frequency, so that it can generate a laser with a wavelength of 1550nm, a line width of 10kHz, a power of 100mW, and adjustable frequency.

[0028] In addition, the DFB laser has a pigtail and emits a stable single-frequency laser to provide a high-quality seed light source for the electro-optical crystal. The DFB laser can also be integrated with a first fiber collimator, the parameters of which are a projection wavelength of 1550nm, a diameter of 1mm, a length of 30mm, a material of quartz glass, and a fiber connector for coupling the laser in the fiber jumper into spatial light, that is, coupling the laser light source into the fiber jumper. Of course, the sensor probe should also integrate a second fiber collimator, the parameters of which are a projection wavelength of 1550nm, a diameter of 1mm, a length of 30mm, a material of quartz glass, and a fiber connector for coupling spatial light into the fiber jumper. For example, the light output end of the sensor probe integrates a second fiber collimator to couple the spatial light propagated from the Fabry-Perot standard distance into the fiber jumper so that it can be propagated from the fiber jumper to the photodetector.

[0029] The pigtail of the laser is connected to the input end of the sensor probe through an optical fiber jumper, which is used to transmit the laser signal received from the DFB laser to the sensor probe. The sensor probe is packaged by a polarizer, two sets of reflectors, an electro-optical crystal and a temperature compensation crystal, and the order of each component along the optical path is polarizer, reflector, electro-optical crystal, temperature compensation crystal and reflector. The sensor probe is used to convert the electric field effect into a change in the output optical signal. The optical signal is proportional to the output line electrical signal, and then the output of the electrical signal and the determination of the electric field intensity are realized through the photoelectric detector. The polarizer can be a PBS polarization beam splitter prism with a transmission wavelength of 1550nm, a size of 5mm wide, 5mm long and 5mm high, and is used to convert lasers of any polarization state into linear polarization.

[0030] The laser passes through three media in the FP cavity: air, electro-optic crystal, and temperature compensation crystal. The cavity length of the entire FP cavity is constant at L, which can be 15 cm. The expansion of the temperature compensation crystal and the electro-optic crystal with the increase of temperature will shorten the propagation path of the laser in the air. The total phase of the FP cavity can be written as:

[0031]

[0032] Considering the thermo-optical effect and thermal expansion effect of the temperature compensation material and electro-optical crystal, the phase φ can be written as:

[0033]

[0034] η i =α i +β i (n i -1)

[0035] Among them, φ is used to characterize the phase change of light in the Fabry-Perot resonant cavity, φ0 is used to characterize the inherent phase of the Fabry-Perot resonant cavity, λ is the wavelength of the laser, i=1,2, corresponding to the electro-optical crystal and the temperature compensation crystal respectively, n i Characterizes the refractive index of the corresponding crystal i, l i Characterizes the length of the light transmission direction of the corresponding crystal i, η i Characterizes the reduced thermal coefficient of the material corresponding to crystal i, α i Characterizes the material thermo-optic coefficient corresponding to crystal i, β i Characterizes the thermal expansion coefficient of the material of the corresponding crystal i, T is used to characterize the ambient temperature, γ is used to characterize the electro-optic coefficient of the electro-optic crystal, E is used to characterize the electric field strength of the electric field to be measured, and L is the cavity length of the Fabry-Perot resonant cavity. That is, the photodetector can determine the electric field strength of the electric field to be measured according to the above calculation formula.

[0036] In this embodiment, the smaller the second term η1l1+η2l2 is, the better the temperature stability of the FP sensor is, that is, the theoretical length of the temperature compensation crystal can be calculated by the formula: Calculated.

[0037] For temperature compensation crystals, since composite polymers generally have negative thermo-optic coefficients and no photoelectric effect, and their thermo-optic coefficients are linearly related to thermal expansion coefficients, the greater the negative thermo-optic coefficient, the greater the thermal expansion coefficient of the material, so the effects of different polymers are not much different. Considering the performance of temperature compensation crystal materials, PMMA, which has good light transmittance and is easy to process, is selected.

[0038] For the electro-optical crystal, a LiNbO3 crystal with a volume of 5mm×5mm×5mm and a refractive index of 2.13 may be used. The refractive index n will change with the external electric field, thereby enabling the detection of the electric field.

[0039] For the optical fiber jumper, it can adopt a structure of 25μm diameter quartz core, 3mm tight sleeve, 10m length, and FC-PC optical fiber connector, which is used to transmit the laser emitted by the DFB laser to the sensor probe, and transmit the laser emitted by the sensor probe to the photodetector.

[0040] In one embodiment, the photodetector may include a photodiode and a processor; the photodiode is used to convert the second laser signal into a current signal in proportion to the conversion coefficient, and the processor sets the operating point at 3 / 4 of the maximum light transmission intensity to obtain maximum sensitivity.

[0041] In this embodiment, the parameters of the photodiode are 1550nm detection wavelength, 0.5A / W conversion coefficient, 100mW optical damage threshold, and coupled with a single-mode pigtail package, which is used to convert the laser signal into a current signal in proportion to the conversion coefficient. It uses a fast-response silicon photodiode with an operating range of 700-1800nm ​​and a response time of 1ns. In order to obtain maximum sensitivity, it is considered that the processor sets the operating point at 3 / 4 of the maximum light intensity.

[0042] In one embodiment, the photodetector may further include a current-voltage conversion circuit, wherein the current-voltage conversion module includes a DC bias voltage and a sampling resistor, wherein the DC bias voltage is applied to the photodiode, and the sampling resistor is used to convert the current generated by the photodiode into a voltage.

[0043] The following is an explanation of the effect of this solution in conjunction with specific experiments. Figure 2 Shown is the output temperature characteristic curve of the FP optical electric field sensor under different reflectivities.

[0044] The peak value of the temperature characteristic curve represents the maximum output of the sensor without temperature influence, and represents the maximum sensitivity of the sensor. The half-width of the curve represents the temperature variation range corresponding to the electro-optical signal being more than half of the maximum value. The larger the half-width, the better the temperature stability of the sensor. As the reflectivity increases, the peak value of the sensor electro-optical signal increases significantly, but the temperature characteristic curve of the sensor output also becomes narrower and the half-width decreases. The temperature compensation structure can significantly increase the half-width of the temperature characteristic curve and improve the temperature stability of the sensor. Among them, at each reflectivity, the figure on the left is the temperature characteristic curve without adding a temperature compensation structure, and the figure on the right is the temperature characteristic curve after adding a temperature compensation structure based on this solution.

[0045] Moreover, the temperature compensation structure increases the half-width of the sensor output temperature characteristic curve by about 30 times, significantly weakening the impact of temperature on the sensor output, improving the temperature stability of the FP electro-optical sensor, and helping to expand the application scenarios of the sensor.

[0046] In summary, the high-stability optical electric field sensor designed by the present invention based on the Fabry-Perot structure has at least the following beneficial effects:

[0047] (1) Adding a negative thermo-optic coefficient material into the FP cavity can offset the positive thermo-optic effect and thermal expansion effect of the electro-optic crystal itself, thus weakening the influence of temperature changes on the sensor output.

[0048] (2) The higher the reflectivity of the FP cavity, the greater the maximum sensitivity of the electro-optical sensor and the worse the temperature stability. The half-width of the temperature characteristic curve of the sensor output represents the temperature stability of the sensor. The half-width can be increased by 30 times through the temperature compensation method, significantly improving the temperature stability of the sensor.

[0049] The modules or units in the device of the embodiment of the present invention can be combined, divided and deleted according to actual needs. The above disclosure is only the preferred embodiment of the present invention, and of course it cannot be used to limit the scope of the rights of the present invention. Those skilled in the art can understand that all or part of the processes of the above embodiment are implemented, and the equivalent changes made according to the claims of the present invention still fall within the scope of the invention.

Claims

1. A high-stability optical electric field sensor based on a Fabry-Perot structure, characterized in that: A temperature compensation crystal with a negative thermo-optic coefficient or a negative thermal expansion coefficient is added to the Fabry-Perot resonant cavity to offset the positive thermo-optic effect and thermal expansion effect of the electro-optic crystal itself.

2. The high stability optical electric field sensor based on Fabry-Perot structure according to claim 1, characterized in that: The optical electric field sensor specifically includes: a laser, a polarizer, two groups of reflectors, an electro-optical crystal, a temperature compensation crystal and a photodetector; wherein the laser, the polarizer, the reflector, the electro-optical crystal, the temperature compensation crystal, the reflector and the photodetector are arranged in sequence along the optical path direction, and the two groups of reflectors constitute a Fabry-Perot resonant cavity; the polarizer, the two groups of reflectors, the electro-optical crystal and the temperature compensation crystal are packaged as a sensor probe; the sensor probe is connected to the laser and the photodetector through an optical fiber jumper; the laser is used to generate a laser signal and transmit it into the sensor probe; the photodetector is used to convert the laser signal output by the sensor probe after being acted on by the electric field to be measured into an electrical signal, and determine the electric field strength of the electric field to be measured based on the electrical signal.

3. The high stability optical electric field sensor based on Fabry-Perot structure according to claim 2, characterized in that: The photoelectric detector is used to determine the electric field strength of the electric field to be measured according to the following calculation formula: or i =a i +b i (n i -1) Among them, φ is used to characterize the phase change of light in the Fabry-Perot resonant cavity, φ0 is used to characterize the inherent phase of the Fabry-Perot resonant cavity, λ is the wavelength of the laser, i=1,2, corresponding to the electro-optical crystal and the temperature compensation crystal respectively, n i Characterizes the refractive index of the corresponding crystal i, l i Characterizes the length of the light transmission direction of the corresponding crystal i, η i Characterizes the reduced thermal coefficient of the material corresponding to crystal i, α i Characterizes the material thermo-optic coefficient corresponding to crystal i, β i It characterizes the thermal expansion coefficient of the material of the corresponding crystal i, T is used to characterize the ambient temperature, γ is used to characterize the electro-optic coefficient of the electro-optic crystal, E is used to characterize the electric field strength of the electric field to be measured, and L is the cavity length of the Fabry-Perot resonant cavity.

4. The high stability optical electric field sensor based on Fabry-Perot structure according to claim 3, characterized in that: The length of the temperature compensation crystal is calculated by Calculated.

5. The high stability optical electric field sensor based on Fabry-Perot structure according to claim 2, characterized in that: The polarization direction of the polarizer is the same as a characteristic polarization direction of the electro-optical crystal.

6. The high stability optical electric field sensor based on Fabry-Perot structure according to claim 2, characterized in that: The two groups of reflectors are both formed by quartz glass plates with reflective films coated on the inner walls. The two quartz glass plates and the quartz glass lining plate at the bottom form a U-shaped structure. The electro-optical crystal and the temperature compensation crystal are arranged in the U-shaped groove.

7. The high-stability optical electric field sensor based on Fabry-Perot structure according to claim 6, characterized in that: The reflectivity of the two groups of reflectors is not less than 90%, and the distance between the two groups of reflectors is 15 cm.

8. The high stability optical electric field sensor based on Fabry-Perot structure according to claim 2, characterized in that: The photodetector includes a photodiode and a processor; the photodiode is used to convert the laser signal output by the sensor probe into a current signal in proportion to a conversion coefficient, and the processor sets the working point at 3 / 4 of the maximum light transmission intensity to obtain maximum sensitivity.

9. The high-stability optical electric field sensor based on Fabry-Perot structure according to claim 2, characterized in that: The optical electric field sensor also includes a first fiber optic collimator and a second fiber optic collimator, which are respectively integrated in the laser and the sensor probe; the parameters of the first fiber optic collimator and the second fiber optic collimator are: a projection wavelength of 1550nm, a diameter of 1mm, a length of 30mm, a material of quartz glass, and a fiber optic connector for coupling the laser in the fiber optic jumper into spatial light, or coupling the spatial light into the fiber optic jumper.

10. The high-stability optical electric field sensor based on a Fabry-Perot structure according to any one of claims 1 to 9, characterized in that: The temperature compensation crystal is organic glass PMMA.

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