RU2579541C1 - Voltage meter based on pockels effect - Google Patents

Abstract

FIELD: electric power engineering.

SUBSTANCE: invention relates to power engineering and can be used in high-voltage measuring equipment. In disclosed voltage meter based on Pockels effect, processing unit is connected via a fibre-optic line to a sensor. Sensor includes a quartz column with end film electrodes and a forty five-degree Faraday rotator, a collimator and a spherical mirror. Column consists of a pair of identical single-crystal cylinder ends and coaxially coupled so that their electrical axes X are anti-collinear, and like optical axes Y and Z are orthogonal. Line is made from optical fibre, which maintains polarisation. Module comprises a programmable computer connected to laser light source unit and an analogue-to-digital converter at input and photodetectors. Fibre-optic line 2 extends to photodetectors and via circulator and a polarisation divider. Module measures intensity of reflected radiation entering photodetectors, and calculates phase shift between polarisation modes in quartz column, by which determines voltage applied to end electrodes of quartz column. Line is built-in with a modulator of phase shift and fibre-optic delay element, shifting reflected radiation on phase modulation.

EFFECT: technical result of invention is improving accuracy of measurements.

2 cl, 2 dwg

Description

Technical field

The invention relates to the field of electric power and may find application in high-voltage measurement technology.

State of the art

Known optical meters (sensors, sensors) of stresses using the Pockels effect [RU 2121147, RU 2539130, US 8233754, JP 4102106, EP 682261].

Patent EP 682261 was chosen as a prototype, because it, like in the proposed solution, uses a double passage (direct and reflected) of a laser beam through an electro-optical element having the Pockels effect.

The prototype contains a measuring module with two photodetectors connected via fiber optic lines with a sensor on an electro-optical (EO) crystal, to the ends of which an electric voltage is applied. A reflecting mirror is installed on one of the ends of the EO of the sensor crystal, and optical elements are placed on the other end of the crystal, which divide the reflected radiation into two polarization modes recorded by the photodetectors of the measuring module.

The disadvantage of the prototype is a large measurement error caused by its own birefringence in the elements of the optical path of the prototype: optical fibers and EO crystal.

Disclosure of invention

The technical result of the invention is improving the accuracy of measurements.

This drawback is eliminated in the proposed solution, due to the fact that it compensates for the intrinsic birefringence of both the electro-optical element and the fiber-optic line connecting the sensor to a photodetector remote from it.

The set of features of a voltage meter based on the Pockels effect, which provides the indicated technical result, includes a processing module connected through a fiber optic line with a sensor, which includes a quartz column with end electrodes, a 45 ° Faraday rotator, a collimator and a spherical mirror mounted on opposite ends of the quartz column, which consists of at least one pair of identical single-crystal cylinders coaxially compressed by the ends so that their electric axes a are collinear and optical axes of the same name are orthogonal, while the fiber optic line is made of polarization-preserving fiber, and the processing module contains a computing unit and a laser radiation source connected to it, an analog-to-digital converter with two photodetectors at the input, to which it is possible to separate two polarizing The radiation mode is equipped with a fiber optic line, and is configured to measure the intensities of the reflected radiation arriving at these photodetectors, and calculate tatam this measurement the phase shift between polarization modes of the radiation in the quartz column and determining the electrical voltage applied to the end of quartz column electrodes in accordance with the calculated phase shift.

The proposal has a development related to particular cases of its implementation, which consists in the fact that the meter can be equipped with a phase raid modulator built into the specified fiber optic line and a fiber optic delay element that shifts the reflected radiation along the modulation phase.

Brief Description of the Drawings

In FIG. 1 shows the optical circuit of the meter. In FIG. 2 - sensor structure.

The implementation of the invention in view of its development

In the diagram of FIG. 1 shows a processing module 1 coupled through a fiber optic line 2 to a sensor 3.

The composition of the sensor 3 (Fig. 2) includes a quartz column 4 with end film electrodes 5 and 6, a forty-five-degree Faraday rotator 7 and a collimator 8, through which one (left in Fig. 2) end face 9 of column 4 is paired with fiber optic line 2, and a spherical mirror 10 mounted on the other end 11 of the column 4. Column 4 consists of at least one pair of identical single-crystal cylinders 12 and 13, coaxially conjugated by the ends so that their electrical axes X are anticollinear and the optical axes of the same name Y and Z are orthogonal. Despite the small EO, the constant crystalline quartz is selected as the material of cylinders 12 and 13 due to its abundance, high electrical resistance, chemical neutrality, and suitable physical properties. An aluminum mirror 10 is formed by sputtering at the end surface of the column 4 farthest from the collimator 8. The film electrodes 5 and 6 are glued to its end surfaces.

Line 2 (Fig. 1) is made of polarized optical fiber. Module 1 contains a laser radiation source 15 connected to the programmable computing unit 14 and two photodetectors 16 and 17, connected to the unit 14 through an analog-to-digital converter (ADC) 18. Fiber optic line 2 is connected to the photodetectors 16 and 17 with the separation of polarization modes between them, which is performed using a circulator 19 and a polarizing divider 20.

Module 1 is configured to measure the intensities of the reflected radiation arriving at the photodetectors 16 and 17, calculate, based on the results of this measurement, the phase shift between the polarization modes of radiation in the quartz column 4 and determine the voltage corresponding to the calculated phase shift, applied to the end electrodes 5 and 6 of the quartz column four.

The meter is equipped with a phase-shift modulator 21 integrated in line 2 between the polarization modes of radiation and the fiber-optic delay element 22, which shifts the reflected radiation along the modulation phase.

The device operates as follows.

From the source 15, partially polarized radiation, oriented along the fast axis of the optical fiber, passes through the circulator 19, which supports only one polarization mode of the fiber, to the corresponding output of the polarization divider 20. Thus, the output of the divider 20 is linearly polarized.

The fiber of line 2 is welded to the output of the polarization divider 20. The axis of the fibers of line 2 is rotated by an angle of 45 degrees, which ensures uniform excitation in line 2 of both polarization modes of its fiber.

The radiation passing through line 2 is directed by the collimator 8 along the geometric axis of the sensor 3, which coincides with the electrical axis X of the cylinders 12 and 13. In this case, the optical axis of the fiber of line 2 is oriented at an angle of 45 degrees to the optical axes of the crystals of the cylinders 12 and 13, so that, taking into account A 45-degree rotation by rotator 7, each polarization radiation mode propagated in the planes of the optical axes of the cylinders (the Y axis of one cylinder and the Z axis of the other cylinder parallel to it).

Using the conductive electrodes 5 and 6, a measured voltage is applied to the ends of the cylinders 12 and 13, which acts on the crystals of the cylinders 12 and 13 along their electric axes X.

The principle of operation of the sensor 3 is based on measuring the ellipticity of the polarization of the light beam when passing through a crystal with a linear electro-optical Pockels effect. Cylinders 12 and 13 are made of crystalline quartz, which has a small EO effect, providing a modulation depth substantially less than the wavelength of the light source. In order to exclude the influence of optical losses on the fiber of line 2, the state of light polarization is directly transmitted through it, while the phase incursion of the polarization angle of the reflected radiation transmitted to photodiodes 16 and 17 carries the measurement information. The anticollinearity of the electric axes X of cylinders 12 and 13 provides compensation for the effect the inverse piezoelectric effect (changing the size of quartz cylinders under the action of an applied voltage) by the magnitude of the phase incursion.

An optical fiber preserving polarization is used to transmit polarized radiation and to form a light beam with a given polarization in line 2.

To compensate for the intrinsic birefringence of fiber of line 2, a Faraday rotator 7 is installed in front of the sensor 4, which rotates the beam polarization plane by 45 degrees. The beam polarization plane rotator 7 rotates 45 degrees twice (with direct passage and after reflection by the mirror 10), as a result of which the polarization modes in the forward and reverse passage of the fiber line 2 are interchanged. The radiation traveling from module 1 to sensor 3 in the fast polarizing mode of line 2 fiber will run back in the slow mode. Thus, the delay between the intrinsic polarization modes of line 2 fiber is fully compensated.

When voltage is applied to the column 4 between the polarization modes of radiation, an additional delay appears, which is not compensated by the reverse passage of the radiation reflected by the mirror 10. The polarization of this radiation from linear to elliptical, and the degree of ellipticity is determined by the phase incursion in the crystals of cylinders 12 and 13, which depends on the applied voltage.

Own birefringence in the crystals of cylinders 12 and 13 leads to a similar delay between polarization modes and to additional polarization ellipticity (shift of the “working point” of the interference signal). The total phase delay should not exceed the coherence length of the radiation source, otherwise the radiation reflected back becomes completely depolarized.

The radiation that returned to the receiving module through the fiber of line 2 welded with a 45 degree rotation is divided into polarization modes by a polarizing divider 20. One polarizing component (mode) is detected by the photodetector 17 directly at the output of the polarizing divider 20, the second enters the photodetector 16 through the circulator 19. The total optical radiation power at both photodetectors, minus losses in the optical path, is proportional to the radiation intensity of source 1.

Since the sensor pair of crystals 12 and 13 has its own birefringence, a useful signal is observed against the background of a constant phase shift (shift of the “working point”). To measure and compensate for this displacement, a phase modulator 21 is used, which is made on a piece of fiber wound on a piezoceramic cylinder. The intrinsic static birefringence in the modulator 21 is compensated by the Faraday rotator 7 similarly to the compensation of the intrinsic birefringence in the fiber of line 2. Modulator 21 provides harmonic high-frequency modulation of the phase incursion between the polarization modes propagating along the fiber of line 2. Due to the delay line 22 built into line 2, the radiation returns in another phase of high frequency modulation.

The signals from the photodetectors 16 and 17 are digitized by the ADC 18 and their further digital processing is carried out in a programmable computing unit 14.

It can be seen from the foregoing that the proposed meter allows one to obtain the indicated technical result by compensating for the intrinsic birefringence of both the electro-optical sensor and the fiber-optic line connecting the sensor with a measuring module remote from it.

Claims (2)

1. A voltage meter based on the Pockels effect, comprising a processing module coupled through a fiber optic line with a sensor, which includes a quartz column with end electrodes, a 45 ° Faraday rotator, a collimator and a spherical mirror mounted on opposite ends of the quartz column, which consists of at least one pair of identical single-crystal cylinders coaxially compressed by the ends so that their electric axes are anticollinear and the optical axes of the same name are orthogonal, with optical fibers the line is made of polarization-preserving fiber, and the processing module contains a computing unit and a laser radiation source connected to it, an analog-to-digital converter with two photodetectors at the input, to which a fiber-optic line is connected with the possibility of separating two polarization radiation modes, and is configured to measuring the intensities of the reflected radiation arriving at the indicated photodetectors, calculating, based on the results of this measurement, the phase incursion between the polarization modes of radiation silica column and determining the electrical voltage applied to the end of quartz column electrodes in accordance with the calculated phase shift. 2. The meter according to claim 1, characterized in that it is equipped with a phase raid modulator built into said fiber optic line and a fiber optic delay element that shifts the reflected radiation along the modulation phase.

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