Reflection-type lithium niobate crystal alternating current or direct current integrated strong electric field sensor

Abstract

The invention discloses a reflective lithium niobate crystal alternating current or direct current integrated strong electric field sensor. Light transmission paths of the input polarization-maintaining optical fiber collimator, the polarizer, the quarter-wave plate, the electro-optical crystal, the hollow roof reflector, the polarization splitting prism, the total reflection mirror, the first polarization analyzer, the second polarization analyzer, the first output single-mode optical fiber collimator and the second output single-mode optical fiber collimator are coaxially arranged in parallel; and the LED light source is coupled in the packaging shell through insulating glue. The invention develops a reflective lithium niobate crystal alternating current or direct current integrated strong electric field sensor for measurement of an alternating current / direct current electric field in a mode of combining a polarization splitting prism and a lithium niobate crystal to rotate a shielding electrode.

Description

Technical Field

[0001] The invention belongs to the technical field of optical electric field sensing, and in particular relates to a reflective lithium niobate crystal AC or DC integrated strong electric field sensor. Background Art

[0002] With the development of modern science and technology, electric power resources have become an indispensable energy source in human life. However, in my country and even in the world, the distribution of electric power resources is extremely unbalanced. In order to reasonably distribute my country's electric power resources to various regions, it is often necessary to build some cross-regional and long-distance transmission projects. These transmission projects often use ultra-high voltage AC and DC shared transmission corridors to achieve long-distance transmission. Therefore, in order to ensure the stable operation of the power system, it is necessary to monitor the surface electric field of high-voltage equipment or transmission corridors in real time.

[0003] Electric field sensors are mainly divided into two categories: electrical electric field sensors and optical electric field sensors. Optical electric field sensors have attracted extensive attention from the international community due to their advantages such as high electric field isolation, non-contact, small size, sensitive response and wide bandwidth, and researchers from various countries have continued to follow up on them.

[0004] Although optical electric field sensors have made some progress after years of development, they still cannot achieve AC and DC hybrid integrated measurement in complex AC and DC hybrid power grids. Therefore, designing and studying an optical electric field sensor that can simultaneously measure AC and DC hybrid electric fields has good development and application prospects. Summary of the invention

[0005] In view of the deficiencies of the prior art, the present invention designs a reflective lithium niobate crystal AC or DC integrated strong electric field sensor, which has the advantages of small size, sensitive response and simultaneous measurement of AC and DC electric fields.

[0006] To achieve the above-mentioned object, the present invention provides the following scheme: The present invention provides a reflective lithium niobate crystal AC or DC integrated strong electric field sensor, the sensor comprising: an input polarization-maintaining fiber collimator, a polarizer, a quarter-wave plate, an electro-optical crystal, a shielding electrode, a hollow roof reflector, a polarization beam splitter, a total reflector, a first analyzer, a second analyzer, a first output single-mode fiber collimator, a second output single-mode fiber collimator and a packaging shell;

[0007] The light paths of the input polarization-maintaining fiber collimator, polarizer, quarter-wave plate, electro-optic crystal, hollow roof reflector, polarization beam splitter, total reflector, first analyzer, second analyzer, first output single-mode fiber collimator, and second output single-mode fiber collimator are all coaxially arranged in parallel, and are coupled in the packaging shell by insulating glue;

[0008] The surface of the shielding electrode is arranged parallel to the surface of the electro-optical crystal;

[0009] The light wave output by the tunable laser is input into the input polarization-maintaining fiber collimator through the optical fiber and converged into a parallel light beam, which is converted into linearly polarized light through the polarizer. The polarization direction of the linearly polarized light is 45 degrees to the slow axis of the quarter-wave plate. After passing through the quarter-wave plate, the light wave is converted into circularly polarized light. The circularly polarized light is injected into the electro-optical crystal for electro-optical modulation. The output light wave after electro-optical modulation is reflected by the hollow roof reflector and enters the electro-optical crystal again for electro-optical modulation. The modulated light wave is divided into light wave one and light wave two by the polarization beam splitter prism.

[0010] The first oscilloscope and the second oscilloscope are used to display the information of the measured electric field.

[0011] In a possible design, light wave 1 is polarized by the first polarizer and then input into the second photodetector by the first output single-mode fiber collimator for photoelectric conversion. The electric signal converted by the second photodetector is transmitted by the radio frequency cable to the second oscilloscope to display the information of the measured electric field.

[0012] Light wave 2 is input into the second polarizer by the total reflection mirror for polarization analysis, and then input into the first photodetector through the optical fiber by the second output single-mode fiber collimator for photoelectric conversion. The electrical signal converted by the first photodetector is transmitted to the first oscilloscope by the radio frequency cable to display the information of the measured electric field.

[0013] In a possible design, the input polarization-maintaining fiber collimator, the first output single-mode fiber collimator and the second output single-mode fiber collimator are all cylindrical glass types, and the output ends are all flat, with a diameter of 2 mm and a length of 8 mm.

[0014] In a possible design, the first analyzer, the second analyzer and the polarizer are all made of square optical glass with a volume of 3mm×3mm×3mm; the quarter-wave plate is made of cylindrical optical glass with a radius of 1.5mm and a thickness of 1mm.

[0015] In a possible design, the electro-optical crystal is a custom-made optical-grade rectangular lithium niobate crystal with a volume of 25 mm×8 mm×2 mm.

[0016] In a possible design, the total reflector and the hollow roof reflector are both optical-grade gold-plated glass with a height of 6 mm; the shielding electrode is made of aluminum and consists of three sectors with a central angle of 60°, a radius of 25 mm, and a thickness of 1 mm.

[0017] In one possible design, the transmission axis of the polarizer is set parallel to the y-axis of the electro-optical crystal, the slow axis of the quarter-wave plate is set at 45° to the y-axis of the electro-optical crystal, the transmission axes of the first and second analyzers are set at 90° to the y-axis of the electro-optical crystal, and the transmission axis of the second analyzer is set at 45° to the y-axis of the electro-optical crystal.

[0018] In a possible design, the surface of the shielding electrode is arranged parallel to the x-axis of the electro-optical crystal.

[0019] In one possible design, the packaging shell is made of acrylic material and has grooves inside that are compatible with the input polarization-maintaining fiber collimator, polarizer, quarter-wave plate, electro-optical crystal, rotating shielding electrode, hollow roof reflector, polarization splitter prism, total reflector, first analyzer, second analyzer, first output single-mode fiber collimator, and second output single-mode fiber collimator.

[0020] In a possible design, the shielding electrode is controlled to rotate by an external power supply, thereby periodically shielding the length of the electro-optic crystal acting on the DC electric field. The electro-optic modulation length of the periodic shielding can be expressed as:

[0021]

[0022] Wherein, L is the length of the electro-optic crystal, h represents the distance between the electro-optic crystal and the rotation axis of the shielding electrode, T=2π / ωn is the period of the L(t) function, and n is the number of opening petals.

[0023] Compared with the prior art, the present invention has the following effects: The present invention provides a reflective lithium niobate AC / DC integrated optical electric field sensor. By using a polarization beam splitter and a lithium niobate crystal in combination with a rotating shielding electrode, a reflective lithium niobate crystal AC or DC integrated strong electric field sensor is developed for the measurement of AC / DC electric fields. The sensor can be used for the measurement of AC / DC electric fields. A new design scheme is provided for the development of lithium niobate crystal electric field sensors. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0025] Figure 1 It is a top view schematic diagram of a reflective lithium niobate crystal AC or DC integrated strong electric field sensor of the present invention;

[0026] Figure 2 It is a side view schematic diagram of a reflective lithium niobate crystal AC or DC integrated strong electric field sensor of the present invention.

[0027] Among them: 1. shielding electrode; 2. electro-optic crystal; 3. hollow roof reflector; 4. quarter wave plate; 5. polarization beam splitter; 6. total reflector; 7. polarizer; 8. first analyzer; 9. second analyzer; 10. input polarization-maintaining fiber collimator; 11. first output single-mode fiber collimator; 12. second output single-mode fiber collimator; 13. packaging shell; 14. sensor; 15. optical fiber; 16. tunable laser; 17. first photodetector; 18. second photodetector; 19. first oscilloscope; 20. radio frequency cable; 21. second oscilloscope. DETAILED DESCRIPTION

[0028] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0029] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0030] like Figure 1-2 As shown, the present invention provides a reflective lithium niobate crystal AC or DC integrated strong electric field sensor 14, including a tunable laser 16, a first oscilloscope 19 and a second oscilloscope 21 of exactly the same model, a plurality of optical fibers 15, an input polarization-maintaining fiber collimator 10, a first output single-mode fiber collimator 11, a second output single-mode fiber collimator 12, an electro-optical crystal 2 (lithium niobate crystal), a polarizer 7, a first analyzer 8, a second analyzer 9, a hollow roof reflector 3, a total reflector 6, a polarization splitter prism 5 for splitting light, a shielding electrode 1, a first photodetector 17, a second photodetector 18, and a plurality of radio frequency cables 20.

[0031] The light wave outputted by the tunable laser 16 is converted into linear polarized light by the polarizer 7. The polarization direction of the linear polarized light is 45° with the slow axis of the quarter wave plate 4 and enters the quarter wave plate 4. After passing through the quarter wave plate 4, the output light wave is converted into circular polarized light and enters the electro-optic crystal 2. When the AC / DC electric field in space is decomposed into two directions, x and y, due to the characteristics of the lithium niobate crystal itself, the DC electric field in the y direction is offset by the reverse electric field inside the crystal. The rotating shielding electrode used in the x direction is used to realize the measurement of the DC electric field. The output light wave after passing through the electro-optic crystal carries the electric field information. After being reflected by the hollow roof reflector 3, it enters the electro-optic crystal 2 again for electro-optic modulation. After the secondary electro-optic modulation, the light wave is divided into light wave 1 and light wave 2 by the polarization beam splitter 5. Among them, light wave 1 is polarized by the first analyzer 8 and then input into the second photodetector 18 by the first output single-mode fiber collimator 11 for photoelectric conversion. Finally, the information of the measured electric field is displayed by the second oscilloscope 21. The light wave 2 is input by the total reflection mirror 6 into the second polarizer 9 for polarization analysis. The polarized light wave is input by the second output single-mode fiber collimator 12 into the first photodetector 17 for photoelectric conversion. Finally, the first oscilloscope 19 displays the information of the measured electric field.

[0032] The working principle of the present invention is as follows: When the reflective lithium niobate crystal AC or DC integrated strong electric field sensor provided by the present invention is used to measure the electric field, the vibration direction of the linear polarized light output through the polarizer 7 is aligned with the y-axis of the electro-optical crystal 2. At this time, the electric vector of the output polarized light after passing through the polarizer 7 can be Jones's proof J 1 It is expressed as:

[0033]

[0034] When the slow axis of the λ / 4 wave plate 4 is set at 45° to the y-axis of the electro-optical crystal 2, its Jones matrix J 2 It can be expressed as

[0035]

[0036] Jones matrix J of electro-optical crystal 2 3 It can be expressed as

[0037]

[0038] The transmission axis of the first polarizer 8 and the second polarizer 9 is 90° to the y-axis, and its Jones matrix J 4 for

[0039]

[0040] Therefore, after the light wave passes through the polarizer 7, the λ / 4 wave plate 4, the electro-optical crystal 2 and the first analyzer 8 in sequence, the electric vector of the output light wave can be expressed as

[0041]

[0042] The light intensity I output by the first polarizer 8 is out1 for

[0043]

[0044] When the transmission axis of the second analyzer 9 is 45° to the x-axis, the Jones matrix of the second analyzer 9 is J 5 It can be expressed as

[0045]

[0046] Then, after the light wave passes through the polarizer 7, the λ / 4 wave plate 4, the electro-optical crystal 2 and the second analyzer 9 in sequence, the electric vector of the output light wave can be expressed as

[0047]

[0048] The light intensity I output by the second polarizer 9 is out2 for

[0049]

[0050] According to the electro-optic effect of lithium niobate crystal, when the AC / DC electric field in space is decomposed into the x and y directions, the electric field in the x and y directions will rotate the refractive index ellipsoid of the lithium niobate crystal by 45° and 0° respectively. According to formula (6) and formula (9), we can get

[0051]

[0052] It can be seen that the output light of the first polarizer 8 and the second polarizer 9 corresponds to the detection of the electric field in the y and x directions respectively. According to the electro-optical effect of lithium niobate crystal, after the phase modulation of the spatial electric field, the phase difference of the polarized light caused is:

[0053]

[0054] Where: L is the length of the crystal, E AC+DC is the AC / DC electric field strength in the external space, λ is the wavelength of the incident light, n o is the refractive index of o light, ( 22 is the electro-optic coefficient of lithium niobate crystal.

[0055] When φ is very small, sinφ≈φ, so further substituting formula (11) into formula (10) yields

[0056]

[0057] Due to the characteristics of lithium niobate crystals, the DC electric field in the y direction is offset by the reverse electric field inside the crystal. Therefore, the output light wave is mainly used to detect the AC electric field. The DC electric field is measured by using a rotating shielding electrode in the x direction. Therefore, formula (12) can be further written as

[0058]

[0059] From equation (13), we can see that the two optical wave signals output by the sensor are linearly related to the external DC electric field and AC electric field respectively.

[0060] The embodiments described above are only descriptions of the preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A reflective lithium niobate crystal AC or DC integrated strong electric field sensor, characterized in that: The sensor (14) comprises: an input polarization-maintaining fiber collimator (10), a polarizer (7), a quarter-wave plate (4), an electro-optical crystal (2), a shielding electrode (1), a hollow roof reflector (3), a polarization beam splitter (5), a total reflector (6), a first polarizer (8), a second polarizer (9), a first output single-mode fiber collimator (11), a second output single-mode fiber collimator (12), and a packaging shell (13); The light paths of the input polarization-maintaining fiber collimator (10), the polarizer (7), the quarter-wave plate (4), the electro-optical crystal (2), the hollow roof reflector (3), the polarization beam splitter (5), the total reflector (6), the first polarizer (8), the second polarizer (9), the first output single-mode fiber collimator (11), and the second output single-mode fiber collimator (12) are all arranged in coaxial parallel and are coupled in the packaging shell (13) by means of insulating glue; The surface of the shielding electrode (1) is arranged parallel to the surface of the electro-optical crystal (2); The light wave outputted by the tunable laser (16) is inputted into the input polarization-maintaining fiber collimator (10) through the optical fiber (15) and converged into a parallel light beam, which is then converted into linearly polarized light through the polarizer (7), wherein the polarization direction of the linearly polarized light is 45 degrees to the slow axis of the quarter-wave plate (4), and the light wave is converted into circularly polarized light after passing through the quarter-wave plate (4), and the circularly polarized light is injected into the electro-optic crystal (2) for electro-optical modulation, and the output light wave after electro-optical modulation is reflected by the hollow roof reflector (3) and then enters the electro-optic crystal (2) again for electro-optical modulation, and the modulated light wave is divided into light wave one and light wave two by the polarization beam splitter (5); The first oscilloscope (19) and the second oscilloscope (21) are used to display information of the measured electric field.

2. A reflective lithium niobate crystal AC or DC integrated strong electric field sensor according to claim 1, characterized in that: Light wave 1 is polarized by a first polarizer (8) and then input into a second photodetector (18) through a first output single-mode optical fiber collimator (11) for photoelectric conversion. The electric signal converted by the second photodetector (18) is transmitted to a second oscilloscope (21) through a radio frequency cable (20) to display information of the measured electric field. Light wave 2 is inputted into a second polarizer (9) by a total reflection mirror (6) for polarization analysis, and then inputted into a first photodetector (17) through an optical fiber (15) by a second output single-mode optical fiber collimator (12) for photoelectric conversion. The electric signal converted by the first photodetector (17) is transmitted to a first oscilloscope (19) by a radio frequency cable (20) to display information of the measured electric field.

3. A reflective lithium niobate crystal AC or DC integrated strong electric field sensor according to claim 2, characterized in that: The input polarization-maintaining optical fiber collimator (10), the first output single-mode optical fiber collimator (11) and the second output single-mode optical fiber collimator (12) are all cylindrical glass types, and the output ends are all flat, with a diameter of 2 mm and a width of 8 mm.

4. A reflective lithium niobate crystal AC or DC integrated strong electric field sensor according to claim 2, characterized in that: The first analyzer (8), the second analyzer (9) and the polarizer (7) are all made of square optical glass with a volume of 3 mm×3 mm×3 mm; the quarter wave plate (4) is made of cylindrical optical glass with a radius of 1.5 mm and a width of 1 mm.

5. The reflective lithium niobate crystal AC or DC integrated strong electric field sensor according to claim 2, characterized in that: The electro-optical crystal (2) is a custom-made optical-grade rectangular lithium niobate crystal with a volume of 25 mm×8 mm×2 mm.

6. A reflective lithium niobate crystal AC or DC integrated strong electric field sensor according to claim 5, characterized in that: The total reflector (6) and the hollow roof reflector (3) are both optical grade gold-plated glass with a height of 6 mm. The shielding electrode (1) is made of aluminum and consists of three sectors with a central angle of 60°, a radius of 25 mm, and a width of 1 mm.

7. A reflective lithium niobate crystal AC or DC integrated strong electric field sensor according to claim 6, characterized in that: The light transmission axis of the polarizer (7) is arranged parallel to the y-axis of the electro-optical crystal (2); the slow axis of the quarter-wave plate (4) is arranged at 45° to the y-axis of the electro-optical crystal (2); the light transmission axes of the first analyzer (8) and the second analyzer (9) are arranged at 90° to the y-axis of the electro-optical crystal (2); and the light transmission axis of the second analyzer (9) is arranged at 45° to the y-axis of the electro-optical crystal (2).

8. The reflective lithium niobate crystal AC or DC integrated strong electric field sensor according to claim 1, characterized in that: The surface of the shielding electrode (1) is arranged parallel to the x-axis of the electro-optical crystal (2).

9. A reflective lithium niobate crystal AC or DC integrated strong electric field sensor according to claim 8, characterized in that: The packaging shell (13) is made of acrylic material and has grooves therein adapted to the input polarization-maintaining optical fiber collimator (10), the polarizer (7), the quarter-wave plate (4), the electro-optical crystal (2), the rotating shielding electrode (1), the hollow roof reflector (3), the polarization beam splitter (5), the total reflector (6), the first polarizer (8), the second polarizer (9), the first output single-mode optical fiber collimator (11), and the second output single-mode optical fiber collimator (12).

10. A reflective lithium niobate crystal AC or DC integrated strong electric field sensor according to any one of claims 1 to 9, characterized in that: The shielding electrode (1) is controlled to rotate by an external power supply, thereby periodically shielding the length of the electro-optical crystal acting on the DC electric field. The electro-optical modulation length of the periodic shielding can be expressed as: Wherein, L is the length of the electro-optic crystal, h represents the distance between the electro-optic crystal and the rotation axis of the shielding electrode, T=2π / ωn is the period of the L(t) function, and n is the number of opening petals.

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