CN110161295B - Probe of reflective optical fiber electric field sensor and assembling and adjusting method thereof - Google Patents
Probe of reflective optical fiber electric field sensor and assembling and adjusting method thereof Download PDFInfo
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- GQYHUHYESMUTHG-UHFFFAOYSA-N lithium niobate Chemical compound [Li+].[O-][Nb](=O)=O GQYHUHYESMUTHG-UHFFFAOYSA-N 0.000 claims abstract description 47
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N silicon dioxide Inorganic materials O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims abstract description 31
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- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
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- G01R15/14—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks
- G01R15/24—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks using light-modulating devices
- G01R15/241—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks using light-modulating devices using electro-optical modulators, e.g. electro-absorption
- G01R15/242—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks using light-modulating devices using electro-optical modulators, e.g. electro-absorption based on the Pockels effect, i.e. linear electro-optic effect
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Abstract
The invention discloses a probe of a reflective optical fiber electric field sensor and an assembling and adjusting method thereof, belonging to the field of electromagnetic field measurement, wherein the reflective optical fiber electric field sensor comprises a laser, a polarization-maintaining optical fiber, a three-port circulator and a photoelectric detector, wherein the polarization-maintaining optical fiber is accessed from a first port of the three-port circulator, and the photoelectric detector is arranged at a third port of the three-port circulator; the probe includes: the fixing device is provided with a groove structure, and a polarizing plate, a lithium niobate crystal, an 1/8 wave plate and a reflecting plate which are sequentially arranged are fixed in the groove structure; and one end of the quartz sleeve is inserted with a collimating lens, the other end of the quartz sleeve is sleeved with a quartz cylinder, the fixing device is fixed in the middle of the quartz sleeve, and the collimating lens is connected with the second port of the three-port circulator. The probe structure in the reflective optical fiber electric field sensor is adjusted, the adverse effect caused by the defects of each element is reduced, the optimization of the relative position of each element is realized, and the measurement sensitivity and stability are improved.
Description
Technical Field
The invention relates to the field of electromagnetic field measurement, in particular to a probe of a reflection type optical fiber electric field sensor and an assembling and adjusting method thereof.
Background
With the continuous increase of the power transmission capacity of the power system, the transmission voltage grade is continuously improved, and the long-distance power transmission is continuously increased, so that the requirement on the measurement accuracy of the working voltage is higher and higher. Currently available voltage sensors include electromagnetic voltage sensors, capacitive voltage sensors, and optical voltage sensors. The two methods are the first two methods which are most widely used and have relatively mature technologies at present, but the method cannot meet the increasing voltage measurement requirements due to overlarge volume, complex insulation and the like. The optical voltage sensor is more and more favored by researchers in various countries due to the factors of good insulation property, small packaging volume and the like.
The electric field measurement includes the measurement of various physical quantities such as current, voltage and the like, and an optical fiber electric field sensor for measuring voltage is called an optical fiber voltage sensor. Most of the fiber-optic voltage sensors for measuring electric field at present are based on a transmission type structure of linear electro-optical effect, and comprise a polaroid, an electro-optical crystal and a quarter wave plate. A conventional transmissive optical fibre electric field sensor structure is shown in figure 1.
Chinese patent publication No. CN106093599A discloses an optical probe and an electromagnetic field measuring device and their measuring methods, in which the probe is sequentially assembled in a quartz glass tube according to the order of a collimator, a polarizer, a quartz wave plate, an electro-optic crystal and a high-reflectivity dielectric plate, and an incident optical fiber is connected to the collimator and fixed on the wall of the glass tube. The reflective optical probe has the advantages of small volume, high integration level, small interference on a measured electromagnetic field and the like, but the current problems still exist, namely poor stability, and how to improve the stability can be started from a special assembling and adjusting method.
Transmission-type optical fiber electric field sensor probe structure incident needs to connect the light source, and the emergence needs to connect photoelectric detector and data acquisition equipment, and both ends all will connect equipment to lead to the flexibility to reduce, are unfavorable for surveying the electric field in narrow and small space. Compared with a transmission type, the reflection type probe needs fewer optical elements, is higher in integration level, and due to the adoption of a reflection structure, the electro-optical crystal with the same length can achieve twice the effective length, and is higher in sensitivity. But how to adjust the relative angular and positional relationships between the optical elements to achieve optimal performance still needs to be explored.
One factor affecting the measurement stability of the fiber optic electric field sensor is the natural birefringence of the electro-optic crystal and the thermoelectric effect, both of which are temperature dependent. When the light beam is precisely aligned along the crystal optical axis, natural birefringence is not generated, and the pyroelectric effect can be greatly reduced. But the criterion of ensuring the accuracy of the optical axis of the crystal and the direction of the light beam is difficult. Minor errors can cause temperature instability of the sensor.
Another factor affecting the measurement stability of the fiber optic electric field sensor is the wave plate. When the optical fiber voltage sensor carries out intensity modulation on a large signal, the Bessel function analysis can find that a light intensity modulation wave is distorted, and besides a linear term, a large amount of harmonic components are generated and are related to the phase of a wave plate which plays a role in biasing. Therefore, the quality and the position angle of the wave plate have great influence on the measurement accuracy of the optical fiber electric field sensor probe.
Disclosure of Invention
The invention aims to provide a probe of a reflection type optical fiber electric field sensor and an assembling and adjusting method thereof, which solve the problem of assembling and adjusting the probe structure in the reflection type optical fiber electric field sensor, reduce the adverse effect caused by the defects of each element, realize the optimization of the relative position of each element and improve the measurement sensitivity and stability.
In order to achieve the above object, in one aspect, the present invention provides a probe of a reflective fiber optic electric field sensor, wherein the reflective fiber optic electric field sensor includes a laser, a polarization maintaining fiber, a three-port circulator and a photodetector, the polarization maintaining fiber is accessed from a first port of the three-port circulator, and the photodetector is disposed at a third port of the three-port circulator; the probe includes:
the fixing device is provided with a groove structure, and a polarizing plate, a lithium niobate crystal, an 1/8 wave plate and a reflecting plate which are sequentially arranged are fixed in the groove structure;
one end of the quartz sleeve is inserted with a collimating lens, the other end is sleeved with a quartz cylinder, the fixing device is fixed in the middle of the quartz sleeve, and the collimating lens is connected with the second port of the three-port circulator.
In the technical scheme, light emitted by the laser sequentially passes through the three-port circulator, the collimating lens, the polaroid, the lithium niobate crystal and the 1/8 wave plate, is reflected back by the reflector plate and then is emitted from the three ports of the three-port circulator after passing through the 1/8 wave plate, the lithium niobate crystal, the polaroid and the collimating lens again, and is measured by the photoelectric detector to convert output light intensity into current or voltage so as to be convenient for measurement and analysis. The measured electric field is loaded into the light path in a phase difference mode through the pockel effect of the lithium niobate crystal, the effective length of the lithium niobate crystal is doubled through reflection, and the sensitivity is obviously improved.
Preferably, the extinction ratio of the polarizing plate is at least 40 dB. In the whole probe structure, the extinction ratio of the polaroid needs to be ensured to be more than 40dB, the accurate position of the electro-optic crystal is convenient to determine in the assembling and adjusting process, and meanwhile, the measurement sensitivity can be improved in measurement. The transmission axis of the polaroid is along the horizontal direction.
In the whole probe structure, the optical axis of the electro-optical crystal needs to be accurately aligned with the direction of a light beam, so that natural birefringence cannot be generated, and meanwhile, the thermoelectric effect can be greatly reduced. The natural birefringence effect can reduce the probe measurement sensitivity, and the natural birefringence and pyroelectric effects can cause the temperature dependence of the electro-optic crystal. According to the linear electro-optical effect coupled wave theory, the accurate relation between the optical axis of the electro-optical crystal and the direction of the light beam can be obtained. Preferably, the optical axis of the lithium niobate crystal is parallel to the direction of the laser beam.
Preferably, the transmission axis of the polarizer and the fast axis of the 1/8 wave plate are at an angle of 45 °. The light path passes through the 1/8 wave plate twice through the reflector plate, so that 90-degree phase delay is generated, the probe works in a linear region, the linear relation between the voltage to be measured and the output light intensity is realized, and the measurement sensitivity is improved.
In order to improve the quality of the 1/8 wave plate and reduce the introduction of a large amount of harmonic components, thereby improving the detection sensitivity, preferably, the 1/8 wave plate is plated with an antireflection film to ensure that the fast axis is along the diagonal direction when the 1/8 wave plate is produced.
In order to ensure that the reflection loss of the reflective sheet is small, it is preferable that the reflective sheet is coated with a highly reflective film corresponding to the wavelength of the laser light emitted from the laser. The center wavelength of the currently used laser is 1550nm, so that the reflectivity of the reflecting sheet in the 1550 waveband is more than 98% by coating (such as an HR film) required by the reflecting sheet.
On the other hand, the probe adjusting method of the reflection type optical fiber electric field sensor provided by the invention comprises the following steps:
1) the laser emits laser, the laser is transmitted through the polarization-maintaining optical fiber, and is emitted from the second port after passing through the first port of the three-port circulator and enters the collimating lens, the collimating lens is fixed by the six-dimensional adjusting frame, and the groove structure is fixed by the clamp, so that the laser emitted by the collimating lens passes through the center of the groove;
2) putting the polaroid into a groove structure, rotating the collimating lens by using a six-dimensional adjusting frame, adjusting the polaroid at the same time until the minimum optical power is below-40 dB, adjusting the optical power penetrating through the polaroid to be maximum, and fixing the polaroid;
3) fixing a reflector plate at the other end of the groove structure by using a three-dimensional adjusting frame, and adjusting the reflector plate until the optical power measured from a third port of the three-port circulator is maximum;
4) fixing an 1/4 wave plate between the polaroid and the reflector by using a 360-degree rotatable adjusting frame, and rotating a 1/4 wave plate until the optical power measured by the third port is less than-40 dB and then fixing;
5) putting the lithium niobate crystal into a groove structure, so that the transmitted and reflected laser can pass through the lithium niobate crystal, poking the lithium niobate crystal by using an optical fiber until the optical power measured by the third port is less than-40 dB, and solidifying the lithium niobate crystal under the condition of ensuring that the optical power is less than-40 dB;
6) and adhering the reflector plate on the three-dimensional adjusting frame by using heat-conducting silicone grease, adjusting the three-dimensional adjusting frame until the laser power reflected back to the third port is maximum, and adjusting the three-dimensional adjusting frame until the reflector plate is moved into the groove while observing the laser power change of the third port. Subsequently, an 1/8 waveplate was placed between the crystal and the mirror, and the 1/8 waveplate was adjusted to see if the third port laser power was exactly halved (compared to the laser power before the 1/8 waveplate was not placed). If the halving is successful, removing the 1/8 wave plate and curing the reflector plate; if the 1/8 wave plate cannot be adjusted to successfully reduce the laser power by half (larger or smaller), the 1/8 wave plate is removed, the reflector plate is finely adjusted, then the 1/8 wave plate is placed into the reflector plate to see whether the laser power can be reduced by half, and the laser power reflected by the reflector plate can be successfully reduced by half after multiple adjustments are carried out until the 1/8 wave plate is placed into the reflector plate (the judgment standard is that the laser power reflected by the reflector plate is reduced by half as much as possible after the 1/8 wave plate is added). After the reflector plate is adjusted, the 1/8 wave plate is taken off, and the reflector plate is solidified;
7) placing an 1/8 wave plate between the lithium niobate crystal with the groove structure and the reflector plate, adjusting the position of the 1/8 wave plate until the laser power of the third port is half of that before the wave plate, and then fixing;
8) placing the groove structure with the polarizer, the lithium niobate crystal, the 1/8 wave plate and the reflector fixed well in the middle of the sleeve, sleeving the lens end of the collimating lens in the end part of the quartz sleeve, exposing one end of the connecting optical fiber outside, rotating the six-dimensional adjusting frame and adjusting the groove structure until the optical power measured from the third port is the same as the optical power after the 1/8 wave plate is fixed in the step 7), and then fixing;
9) the other end of the quartz sleeve is sealed by a small quartz cylinder.
Preferably, all elements in the groove structure and all elements in the quartz sleeve are adhered by ultraviolet glue and are fixed by irradiation of an ultraviolet lamp.
Compared with the prior art, the invention has the beneficial effects that:
the probe of the reflective optical fiber electric field sensor and the assembling and adjusting method thereof solve the assembling and adjusting problem of the probe structure of the reflective optical fiber voltage sensor, reduce the adverse effect generated by the defects of each element, realize the optimization of the relative position of each element and improve the measurement sensitivity and stability.
Drawings
FIG. 1 is a schematic structural diagram of a conventional transmission-type optical fiber electric field sensor in the background art of the present invention;
FIG. 2 is a schematic structural diagram of a reflective optical fiber electric field sensor according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of a probe according to an embodiment of the present invention;
FIG. 4 is a diagram showing the polarization state change of light after passing through optical elements in the optical path for adjusting the optical axis of the lithium niobate crystal in the embodiment of the present invention, including the polarization state (1) after the laser light emitted from the second port of the circulator passes through the collimating lens and the polarizer; the laser continues to pass through the polarization state (2) of the lithium niobate crystal; the polarization state (3) of the laser after passing through the 1/4 wave plate is continued; the polarization state (4) of the laser reflected from the reflector plate; the polarization state (5) of the laser light after being reflected back from the reflector plate and passing through the 1/4 wave plate; the polarization state (6) of the laser reflected back from the reflector plate and passing through the 1/4 wave plate and the lithium niobate crystal;
FIG. 5 is a diagram showing a simulation of the change comsol in the polarization state of light after passing through each optical element in the optical path for adjusting the optical axis of the lithium niobate crystal in the embodiment of the present invention;
FIG. 6 is a diagram showing the relationship between the deflection angle of the optical axis of the lithium niobate crystal and the direction of the light beam and the temperature stability in the embodiment of the present invention, wherein (a) the diagram simulates the relationship between the temperature and the relative output light intensity in the orthogonal polarization system when the deflection angle is 1.8 degrees, 18 degrees, 90 degrees, and the measured electric field is 20000V; (b) the graph simulates the relationship between the deflection angle of the lithium niobate crystal and the temperature stability in an orthogonal polarization system when the measured electric field is 0-18 degrees.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be further described with reference to the following embodiments and accompanying drawings.
Examples
Referring to fig. 2 and 3, the reflective optical fiber electric field sensor according to the embodiment of the present invention includes a laser 001, a polarization maintaining optical fiber 002, a three-port circulator 003, and a photodetector 004, where the polarization maintaining optical fiber 002 is accessed from a first port of the three-port circulator 003, and the photodetector 004 is disposed at a third port of the three-port circulator.
The probe includes:
the fixing device 005 is provided with a groove structure, and a polarizing plate 3, a lithium niobate crystal 4, an 1/8 wave plate 5 and a reflecting plate 6 which are sequentially arranged are fixed in the groove structure through ultraviolet glue;
the one end of quartz sleeve 006 is inserted and is equipped with collimating lens 2 to glue fixedly through the ultraviolet, and the other end cover seals has quartz cylinder 1, glues fixedly through the ultraviolet equally, and fixing device 005 glues fixedly through the ultraviolet in the middle part of quartz sleeve 006, and collimating lens 2 connects the second port of three-port circulator 003.
Light emitted by the laser 001 sequentially passes through the three-port circulator 003, the collimating lens 2, the polarizing plate 3, the lithium niobate crystal 4 and the 1/8 wave plate 5, is reflected back through the reflecting plate 6, passes through the 1/8 wave plate 5, the lithium niobate crystal 4, the polarizing plate 3 and the collimating lens 2 again, and then is emitted from a third port of the three-port circulator 003, and is measured by the photoelectric detector 004 to convert output light intensity into current or voltage so as to be convenient for measurement and analysis. The measured electric field is loaded into the light path in a phase difference mode through the pockel effect of the electro-optical crystal, the effective length of the lithium niobate crystal is doubled through reflection, and the sensitivity is obviously improved.
In the whole probe structure, the extinction ratio of the polaroid 3 is ensured to reach more than 40dB, the accurate position of the lithium niobate crystal 4 is convenient to determine in the assembling and adjusting process, and meanwhile, the measurement sensitivity can be improved in the measurement. The transmission axis of the polarizing plate 3 is in the horizontal direction.
In the whole probe structure, the optical axis of the lithium niobate crystal 4 is ensured to be accurately aligned with the beam direction, so that natural birefringence is not generated, and the thermoelectric effect can be greatly reduced. The natural birefringence effect decreases the probe measurement sensitivity, and the natural birefringence and the pyroelectric effect cause the temperature dependence of the lithium niobate crystal 4. According to the linear electro-optical effect coupled wave theory, the accurate relation between the optical axis of the electro-optical crystal and the direction of the light beam can be obtained. FIG. 6 is a graph of the relationship between the crystal optic axis and the beam off-angle and temperature stability. When the measured electric field is 0, a certain relation exists between the deflection angle and the temperature stability. To ensure both natural birefringence and small pyroelectric effects, it is desirable to make the crystal optical axis as parallel as possible to the beam direction.
In whole probe structure, guarantee that 3 printing opacity axles of polaroid and 1/8 wave plate 5's fast axle contained angle is 45, the light path can pass through 1/8 wave plates twice through the reflector plate to produce 90 phase delays, thereby let probe work in the linear region, realize the linear relation between the voltage that awaits measuring and the output light intensity, improve measuring sensitivity. Furthermore, the wave plate requires high quality, otherwise a large amount of harmonic components are introduced, reducing the detection sensitivity. 1/8 wave plate production ensures the fast axis is along the diagonal direction, plating the antireflection coating.
In the whole probe structure, the reflection loss of the reflector plate 6 is ensured to be very small, and the surface of the reflector plate 6 is plated with a high-reflection film corresponding to the laser wavelength.
The probe assembling and adjusting method of the reflection type optical fiber electric field sensor comprises the following steps:
the S100 laser 001 emits laser, the laser is transmitted through the polarization maintaining optical fiber 002, and is emitted out of the second port after passing through the first port of the three-port circulator 003 to enter the collimating lens 2, the collimating lens 2 is fixed by the six-dimensional adjusting frame, and the groove structure is fixed by the clamp, so that the laser emitted from the collimating lens 2 approximately passes through the center of the groove structure.
And (2) adhering a small amount of ultraviolet glue at one end of the S200 groove structure, placing the polaroid 3, rotating the collimating lens 2 by using a six-dimensional adjusting frame, finely adjusting the polaroid 3, adjusting the light power penetrating through the polaroid 3 to be maximum after determining that the minimum light power is below-40 dB, keeping the positions of the collimating lens 2 and the polaroid 3 unchanged, irradiating and curing by using an ultraviolet lamp, and heating and curing.
S300 a reflector plate 6 is fixed with a three-dimensional adjusting jig about 10cm behind the groove structure, and the reflector plate 6 is adjusted until the optical power measured from the third port of the three-port circulator 003 is maximum.
An 1/4 wave plate 5 is fixed between the S400 groove structure and the reflector plate 6 by a 360-degree rotatable adjusting frame, the 1/4 wave plate 5 is rotated, and the maximum value and the minimum value (the minimum value needs to be less than-40 dB) of the optical power measured by the third port are determined; the 1/4 wave plate was rotated until the 3 port was fixed after measuring less than-40 dB of optical power.
S500, adhering a small amount of ultraviolet glue on the polarizing film 3 on the groove structure, placing the lithium niobate crystal 4, enabling the transmitted and reflected laser to pass through the lithium niobate crystal 4, poking the lithium niobate crystal 4 by using an optical fiber until the optical power measured by the third port is less than-40 dB, irradiating and curing by using an ultraviolet lamp while observing the fluctuation condition of the optical power, and curing the lithium niobate crystal 4 under the condition of ensuring that the optical power is always less than-40 dB, and then thermally curing.
S600, adhering a small amount of ultraviolet glue at the tail end of the groove, adhering the reflector plate 6 on the three-dimensional adjusting frame by using heat-conducting silicone grease, fixing and adjusting the three-dimensional adjusting frame at a position which is 5mm away from the groove until the laser power reflected back to the third port is maximum; the three-position adjusting bracket is adjusted while observing the laser power change of the third port until the reflector plate 6 is moved into the groove. Subsequently, an 1/8 waveplate was placed between the crystal and the mirror, and the 1/8 waveplate was adjusted to see if the third port laser power was exactly halved (compared to the laser power before the 1/8 waveplate was not placed). If the halving is successful, removing the 1/8 wave plate and curing the reflector plate; if the 1/8 wave plate cannot be adjusted to successfully reduce the laser power by half (larger or smaller), the 1/8 wave plate is removed, the reflector plate is finely adjusted, then the 1/8 wave plate is placed into the reflector plate to see whether the laser power can be reduced by half, and the laser power reflected by the reflector plate can be successfully reduced by half after multiple adjustments are carried out until the 1/8 wave plate is placed into the reflector plate (the judgment standard is that the laser power reflected by the reflector plate is reduced by half as much as possible after the 1/8 wave plate is added). After the reflector plate is adjusted, the 1/8 wave plate is removed, and the laser beam is irradiated by an ultraviolet lamp and heated for curing, wherein the process ensures that the laser power of the third port is maximum.
And (3) adhering a small amount of ultraviolet glue between the lithium niobate crystal and the reflecting plate in the S700 groove, placing 1/8 wave plate 5, adjusting the position of the wave plate until the laser power of the third port is half of that before the wave plate is placed, determining that the included angle between the transmission axis of the polaroid 3 and the fast axis of the 1/8 wave plate 5 is 45 degrees, irradiating and curing by using an ultraviolet lamp, and heating and curing.
S800, coating a layer of ultraviolet glue on the middle and one end in the quartz sleeve 006, adhering the groove structures on which the polarizing plate 3, the lithium niobate crystal 4, the 1/8 wave plate 5 and the reflecting plate 6 are fixed to the ultraviolet glue in the middle of the quartz sleeve 006, adhering the lens end of the collimating lens 2 to the edge of the quartz sleeve 006, exposing one end of the connecting optical fiber outside, rotating the six-dimensional adjusting frame and finely adjusting the groove structures until the optical power measured from the third port is the same as the optical power of the fixed wave plate in the step S700, and irradiating, curing and heating the collimating lens 2 and the groove structures by using the ultraviolet lamp.
S700, after all the steps are completed, the inner wall of the opening end of the quartz sleeve 006 is coated with uv glue, the quartz cylinder 1 is fixed therein to achieve a sealing effect, and the quartz cylinder is cured by irradiation with an ultraviolet lamp and heated.
In the assembly step of the probe structure in the reflective optical electric field sensor, the lithium niobate crystal 4 needs to be adjusted to the state that the optical axis of the crystal is parallel to the propagation direction of the laser, so that the natural birefringence effect can not occur and the lithium niobate crystal is divided into o light and e light, thereby enabling more light to participate in the calibration of signals and improving the sensitivity. In order to judge whether the crystal optical axis is parallel to the laser propagation direction, an optical path needs to be established: the collimating lens-polarizer-lithium niobate crystal-1/4 wave plate-reflector plate is characterized in that the transmission axes of the polarizers are parallel or vertical, and the fast axis of the 1/4 wave plate forms an angle of 45 degrees with the horizontal direction and the vertical direction. If the transmission axis of the polaroid is along the x direction, the polarization direction of the laser is along the x axis after the laser passes through the collimating lens and the polaroid, and is shown in figure 4 (1); if the optical axis direction of the lithium niobate crystal is parallel to the laser propagation direction, the polarized light will not be divided into o light and e light after passing through the crystal, and the polarization direction is still along the x axis, as shown in fig. 4 (2); the included angles between the fast axis and the x and y axes of the 1/4 wave plate are both 45 degrees, so that light is changed from linear polarization into circular polarization after passing through the wave plate, as shown in fig. 4 (3); the light reflected from the reflector is still circularly polarized, as shown in fig. 4 (4); then the light passes through 1/4 wave plate and is changed from circular polarization into linear polarization along y axis, as shown in figure 4 (5); because the optical axis direction of the lithium niobate crystal is parallel to the propagation direction of the laser, the light passing through the crystal is still linearly polarized along the y-axis, as shown in fig. 4 (6); the transmission axis of the polarizer is along the x-axis, so that the reflected polarized light cannot pass through the polarizer, and the optical power measured from the third port is 0. Here, the condition that the optical power measured at the third port is 0 is that the optical axis of the lithium niobate crystal is parallel to the light propagation direction. If the optical axis of the crystal is not parallel to the light propagation direction, the light is split into o and e light after passing through the crystal, so that a part of the reflected light must pass through the polarizer, and the optical power measured at the third port cannot be 0. This is the basis for determining whether the crystal optical axis is parallel to the light propagation direction.
Fig. 5 is a simulation diagram of change comsol in polarization state of light after passing through each optical element in an optical path for adjusting the optical axis of the lithium niobate crystal in the embodiment of the present invention. The theoretical accuracy is verified just like the theoretical polarization state of fig. 4.
FIG. 6 is a graph showing the relationship between the crystal optic axis and the beam deflection angle and the temperature stability according to the embodiment of the present invention. (a) The graph simulates the relationship curve of temperature and relative output light intensity in an orthogonal polarization system when the deflection angle is 1.8 degrees, 18 degrees and 90 degrees, and the measured electric field is 20000V. (b) The graph simulates the relationship between the crystal deflection angle and the temperature stability in an orthogonal polarization system when the deflection angle is 0-18 degrees and the measured electric field is 0. The horizontal axis is the deviation angle of the crystal and the light beam direction, the vertical axis is the deviation of the output and input light intensity ratio to the temperature, and the closer the value is to 0, the better the temperature stability is. When the maximum light intensity is 10mW, the minimum output light intensity reaches below-41 dBm under the condition of ensuring that the deflection angle is less than 4 degrees, and the deflection angle can be ensured to be below 0.45 degrees.
Claims (7)
1. A probe of a reflective optical fiber electric field sensor comprises a laser, a polarization-maintaining optical fiber, a three-port circulator and a photoelectric detector, wherein the polarization-maintaining optical fiber is accessed from a first port of the three-port circulator, and the photoelectric detector is arranged at a third port of the three-port circulator; characterized in that the probe comprises:
the fixing device is provided with a groove structure, and a polarizing plate, a lithium niobate crystal, an 1/4 wave plate and a reflecting plate which are sequentially arranged are fixed in the groove structure;
one end of the quartz sleeve is inserted with a collimating lens, the other end of the quartz sleeve is sleeved with a quartz cylinder, the fixing device is fixed in the middle of the quartz sleeve, and the collimating lens is connected with the second port of the three-port circulator;
the probe assembling and adjusting method comprises the following steps:
1) the laser emits laser, the laser is transmitted through the polarization-maintaining optical fiber, and is emitted from the second port after passing through the first port of the three-port circulator and enters the collimating lens, the collimating lens is fixed by the six-dimensional adjusting frame, and the groove structure is fixed by the clamp, so that the laser emitted by the collimating lens passes through the center of the groove;
2) putting the polaroid into a groove structure, rotating the collimating lens by using a six-dimensional adjusting frame, adjusting the polaroid at the same time until the minimum optical power is below-40 dB, adjusting the optical power penetrating through the polaroid to be maximum, and fixing the polaroid;
3) fixing a reflector plate at the other end of the groove structure by using a three-dimensional adjusting frame, and adjusting the reflector plate until the optical power measured from a third port of the three-port circulator is maximum;
4) fixing an 1/4 wave plate between the polaroid and the reflector by using a 360-degree rotatable adjusting frame, and rotating a 1/4 wave plate until the optical power measured by the third port is less than-40 dB and then fixing;
5) putting the lithium niobate crystal into a groove structure, so that the transmitted and reflected laser can pass through the lithium niobate crystal, poking the lithium niobate crystal by using an optical fiber until the optical power measured by the third port is less than-40 dB, and solidifying the lithium niobate crystal under the condition of ensuring that the optical power is less than-40 dB;
6) adhering the reflector plate to the three-dimensional adjusting frame by using heat-conducting silicone grease, adjusting the three-dimensional adjusting frame until the laser power reflected back to the third port is maximum, and adjusting the three-dimensional adjusting frame until the reflector plate is moved into the groove while observing the laser power change of the third port; subsequently, 1/4 wave plates are placed between the lithium niobate crystal and the reflecting plate, 1/4 wave plates are adjusted to see whether the laser power of the third port is halved compared with the laser power before 1/4 wave plates are not placed, and if halved, 1/4 wave plates are removed and the reflecting plate is solidified; if the 1/4 wave plate cannot be adjusted to reduce the laser power by half successfully, the 1/4 wave plate is removed, the reflector plate is finely adjusted, and then the 1/4 wave plate is placed into the reflector plate to reduce the laser power by half or not, and the laser power is adjusted for multiple times until the laser power is reduced by half successfully after the 1/4 wave plate is placed into the reflector plate; after the reflector plate is adjusted, the 1/4 wave plate is taken off, and the reflector plate is solidified;
7) placing 1/4 wave plate between the groove-structured lithium niobate crystal and the reflector plate, adjusting the position of 1/4 wave plate until the laser power of the third port is half of that before the 1/4 wave plate, and then fixing;
8) placing the groove structure with the polarizer, the lithium niobate crystal, the 1/4 wave plate and the reflector fixed well in the middle of the quartz sleeve, sleeving the lens end of the collimating lens in the end part of the quartz sleeve, exposing one end of the connecting optical fiber outside, rotating the six-dimensional adjusting frame and adjusting the groove structure until the optical power measured from the third port is the same as the optical power of the 1/4 wave plate fixed in the step 7), and then fixing;
9) the other end of the quartz sleeve is sealed by a small quartz cylinder.
2. The probe of claim 1 wherein the polarizer has an extinction ratio of at least 40 dB.
3. The probe of claim 1 wherein the optical axis of said lithium niobate crystal is parallel to the direction of the laser beam.
4. The probe of claim 1 wherein the transmission axis of the polarizer is at an angle of 45 ° to the fast axis of the 1/4 waveplate.
5. The probe of claim 1, wherein the 1/4 wave plate is coated with an anti-reflective coating.
6. The probe of claim 1, wherein the reflective sheet is coated with a high reflective film corresponding to a wavelength of a laser emitted from the laser.
7. The probe of claim 1, wherein the elements in the groove structure and the elements in the quartz sleeve are adhered by ultraviolet glue and fixed by irradiation of an ultraviolet lamp.
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| CN111239500A (en) * | 2020-02-20 | 2020-06-05 | 云南电网有限责任公司电力科学研究院 | Transformer inner space electric field measurement system |
| CN111751595B (en) * | 2020-06-01 | 2023-03-24 | 贵州江源电力建设有限公司 | Miniaturized optical fiber voltage sensor and information processing system |
| CN113341236B (en) * | 2021-05-31 | 2024-03-01 | 昆明理工大学 | Polarization maintaining fiber coupling type electrooptical crystal electric field sensor |
| CN116930629B (en) * | 2023-09-15 | 2023-12-22 | 清华大学 | Electric field sensing device and method |
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