Method for measuring additional phase delay introduced by light source wavelength fluctuation of optical voltage transformer

Abstract

The invention provides a method for measuring additional phase delay introduced by optical voltage transformer light source wavelength fluctuation. The method comprises the following steps: S1, constructing an optical voltage transformer for realizing linear demodulation of phase delay based on an annular radial polarization grating; the optical voltage transformer comprises a light source, a polarizer, an electro-optical crystal, a quarter-wave plate, an annular radial polarization grating and a four-quadrant detector. An electric field where the electro-optical crystal is located is generated by alternating current voltage to be measured; and S2, modulating a to-be-measured AC voltage into two times of the half-wave voltage of the electro-optical crystal, and obtaining the additional phase delay introduced by the fluctuation of the central wavelength of the light source according to the light spot rotation angle measured by the optical voltage transformer. Direct linear measurement of phase delay is realized based on the annular radial polarization grating, and then additional phase delay introduced by light source center fluctuation is completely extracted and compensated, so that the problem of light source wavelength fluctuation is solved.

Description

Technical Field

[0001] The invention belongs to the technical field of optical voltage transformers, and in particular relates to a method for measuring additional phase delay introduced by wavelength fluctuation of an optical voltage transformer light source. Background Art

[0002] Optical Voltage Transducer (OVT) is mostly implemented based on the principle of Pockels electro-optical effect. It has the advantages of small size, light weight, safe and reliable insulation, green and environmental protection, and has broad application prospects. Optical voltage transformer converts the voltage (electric field) to be measured into the change of electro-optical phase delay, but the existing technical means cannot directly measure the electro-optical phase delay. Therefore, the polarization interference demodulation mode is used to convert the phase delay into the change of light intensity, and the phase delay is approximately measured by detecting the light intensity. Since this detection mode depends on the change of light intensity, the stability of the light source is crucial to the accuracy of OVT measurement. However, due to temperature drift or device aging, the central wavelength of the output light of the light source is prone to fluctuations, and an additional phase delay is introduced, which directly affects the size of the output light intensity and seriously damages the stability and reliability of OVT measurement. The additional phase delay introduced by the fluctuation of the central wavelength of the light source is coupled to the change of light intensity in a nonlinear form, which is difficult to extract and compensate in the existing nonlinear detection mode.

[0003] In order to solve the problem of light source center wavelength fluctuation, the common method is to use constant temperature and constant current control to make the light source work within a stable temperature range. However, the temperature control system introduces thermistors, refrigerators and their drive circuits, PID closed control, etc. The noise and errors of these links will increase with the increase of running time, and the long-term control effect is not ideal. At the same time, the complexity of the system is significantly increased, resulting in poor reliability and stability of optical mutual inductor measurement. Summary of the invention

[0004] The purpose of the present invention is to provide a method for measuring the additional phase delay introduced by the wavelength fluctuation of the optical voltage transformer light source, to realize direct linear measurement of the phase delay based on the annular radial polarization grating, to obtain the mathematical expression of the electro-optical phase delay of the electro-optical crystal and the additional phase delay introduced by the central fluctuation of the light source, and then to completely extract the additional phase delay and compensate for it to solve the problem of wavelength fluctuation of the light source.

[0005] To achieve the above object, the technical solution of the present invention is: a method for measuring the additional phase delay introduced by the wavelength fluctuation of the optical voltage transformer light source, comprising the following steps:

[0006] S1. Constructing an optical voltage transformer for linear demodulation of phase delay based on an annular radial polarization grating; the optical voltage transformer comprises a light source, a polarizer, an electro-optical crystal, a quarter wave plate, an annular radial polarization grating, and a four-quadrant detector; the electric field in which the electro-optical crystal is located is generated by the AC voltage to be measured;

[0007] S2. Modulate the AC voltage to be measured into twice the half-wave voltage of the electro-optical crystal, and obtain the additional phase delay introduced by the fluctuation of the central wavelength of the light source according to the light spot rotation angle measured by the optical voltage transformer.

[0008] Preferably, the optical voltage transformer realizes linear demodulation of phase delay based on annular radial polarization grating, specifically:

[0009] The light emitted by the light source passes through the polarizer to form linear polarized light, and then passes through the electro-optical crystal. Under the action of electric field modulation, the linear polarized light enters the photoelectric crystal and decomposes into two linear polarized lights o and e with orthogonal polarization directions. Due to the different refractive indices of the two polarization directions, the electro-optical phase delay generated by the o and e lights after propagating a certain distance in the photoelectric crystal is The o light and the e light are synthesized into linearly polarized light under the action of the quarter-wave plate, and the phase delay is converted into the rotation of the polarization plane of the linearly polarized light synthesized by the quarter-wave plate. The rotation angle is β and satisfies After the outgoing light of the quarter-wave plate is demodulated by the annular radial polarization grating, an annular light spot with a fixed shape is obtained, and the light spot rotates synchronously with the change of the polarization plane of the linear polarized light synthesized by the quarter-wave plate. The rotation angle of the light spot is δ=β, and the rotation period is π. The detector detects the rotation angle δ of the light spot to realize the direct measurement of the phase delay.

[0010] Preferably, S2 is specifically:

[0011] The additional phase delay introduced by the central wavelength fluctuation of the light source is

[0012] The light emitted by the light source passes through the polarizer to form linear polarized light. After the linear polarized light passes through the electro-optical crystal and the quarter-wave plate, the output light spot obtained after demodulation by the annular radial polarization grating rotates at an angle of δ+△δ; the electro-optical phase delay The corresponding rotation angle is Additional phase delay The corresponding rotation angle is

[0013] When the AC voltage to be measured is modulated to twice the half-wave voltage of the electro-optic crystal, the electro-optic phase delay Then the spot rotation angle δ corresponding to the electro-optical phase delay is π; since the spot rotation period is π, it is considered that the spot corresponding to the electro-optical phase delay has no rotation; the additional phase delay introduced by the fluctuation of the central wavelength of the light source is obtained according to the measured spot rotation angle, which is specifically calculated as follows:

[0014]

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] The present invention considers that the central wavelength fluctuation of the output light due to temperature drift or device aging of the light source will generate additional phase delay in the electro-optical crystal and the quarter-wave plate, and cannot be separated together with the electro-optical phase delay aliasing. Based on the linear demodulation mode, a linear relationship between the spot rotation angle and the phase delay (the sum of the electro-optical phase delay and the additional phase delay) can be obtained. When the AC voltage to be measured is modulated to twice the half-wave voltage of the electro-optical crystal, the electro-optical phase delay is 2π. Combined with the periodicity of the spot rotation, the spot rotation angle measured under this condition corresponds to the additional phase delay introduced by the fluctuation of the central wavelength of the light source, which can be extracted for compensation. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram of the measurement principle of the present invention;

[0018] Figure 2 Schematic diagram of the relationship between phase delay and the rotation angle of the output light spot of the present invention;

[0019] Figure 3 It is a relationship diagram between the rotation angle of the emission light spot and the additional phase delay when the voltage to be measured is the crystal half-wave voltage of the present invention. DETAILED DESCRIPTION

[0020] The following is combined with Figure 1-3 , the technical solution of the present invention is specifically described.

[0021] The existing optical voltage transformer is based on an approximately linear demodulation mode. The additional phase delay introduced by the fluctuation of the central wavelength of the light source is coupled to the light intensity change in a nonlinear form and cannot be separated and compensated.

[0022] The present invention proposes a method for measuring the additional phase delay introduced by the wavelength fluctuation of the light source of an optical voltage transformer. Based on the optical voltage transformer with a linear demodulation mode previously proposed by the applicant, the phase delay can be converted into the rotation of the output light spot. By utilizing the periodicity of the light spot rotation (the period is π), it is proposed that the additional phase delay introduced by the fluctuation of the central wavelength of the light source can be extracted and compensated by modulating the voltage to be measured to twice the half-wave voltage of the electro-optical crystal.

[0023] The present invention specifically adopts the following technical solution: a method for measuring the additional phase delay introduced by the wavelength fluctuation of the optical voltage transformer light source, comprising the following steps:

[0024] S1. Constructing an optical voltage transformer for linear demodulation of phase delay based on an annular radial polarization grating; the optical voltage transformer comprises a light source, a polarizer, an electro-optical crystal, a quarter wave plate, an annular radial polarization grating, and a four-quadrant detector; the electric field in which the electro-optical crystal is located is generated by the AC voltage to be measured;

[0025] S2. Modulate the AC voltage to be measured into twice the half-wave voltage of the electro-optical crystal, and obtain the additional phase delay introduced by the fluctuation of the central wavelength of the light source according to the light spot rotation angle measured by the optical voltage transformer.

[0026] In this embodiment, the optical voltage transformer realizes linear demodulation of phase delay based on annular radial polarization grating, specifically:

[0027] The light emitted by the light source passes through the polarizer to form linear polarized light, and then passes through the electro-optical crystal. Under the action of electric field modulation, the linear polarized light enters the photoelectric crystal and is decomposed into two linear polarized lights o and e with orthogonal polarization directions. Due to the different refractive indices of the two polarization directions, the electro-optical phase delay generated by the o and e lights after propagating a certain distance in the photoelectric crystal is φ; the o and e lights are synthesized into linear polarized light under the action of a quarter-wave plate, and the phase delay is converted into the rotation of the polarization plane of the linear polarized light synthesized by the quarter-wave plate, and the rotation angle is β and satisfies β=φ / 2; after the output light of the quarter-wave plate is demodulated by the annular radial polarization grating, an annular light spot with a fixed shape is obtained, and the light spot rotates synchronously with the change of the polarization plane of the linear polarized light synthesized by the quarter-wave plate, and the light spot rotation angle is δ=β, and the rotation period is π; the light spot rotation angle is detected by a detector to realize direct measurement of the phase delay.

[0028] In this embodiment, S2 is specifically:

[0029] The additional phase delay introduced by the fluctuation of the central wavelength of the light source is △φ; the fluctuation of the central wavelength of the light source is caused by temperature drift or device aging;

[0030] The light emitted by the light source passes through the polarizer to form linear polarized light. After the linear polarized light passes through the electro-optic crystal and the quarter-wave plate, it is demodulated by the annular radial polarization grating to obtain an output light spot rotation angle of δ+△δ. Because it is linear demodulation, the electro-optical phase delay The corresponding rotation angle is Additional phase delay The corresponding rotation angle is

[0031] When the AC voltage to be measured is modulated to twice the half-wave voltage of the electro-optic crystal, the electro-optic phase delay Then the spot rotation angle δ corresponding to the electro-optic phase delay is π; since the spot rotation period is π, it is considered that the spot corresponding to the electro-optic phase delay has no rotation (that is, the spot rotates a complete period, and it can be considered that the spot has no rotation); and the additional phase delay The resulting spot rotation angle is △δ, so the additional phase delay introduced by the central wavelength fluctuation of the light source is obtained according to the measured spot rotation angle. The specific calculation is: Thus, the additional phase delay is extracted and compensated. In summary, the problem of wavelength fluctuation of the optical voltage transformer light source is solved.

[0032] In this implementation, without considering the influence of light source wavelength fluctuation, according to Figure 1 From the optical path diagram and reference [1], we know that the output light intensity I formula of the optical voltage transformer is:

[0033]

[0034] Where A is the amplitude of the input light, t TM is the diffraction efficiency of the TM wave transmission component of the annular radial polarization grating (abbreviated as transmittance); ξ is the phase difference between the TM wave and the TE wave; δ is the azimuth angle of any grating of the annular radial polarization grating; is the electro-optic phase delay generated by the electro-optic crystal under the voltage to be measured; e is the base of the natural logarithm; j represents the imaginary unit.

[0035] In this implementation, if the wavelength fluctuation of the light source is considered, its influence on the optical voltage transformer is first analyzed. On the one hand, the wavelength fluctuation of the light source will cause the electro-optical phase delay generated by the electro-optical crystal to change, introducing additional phase delay; on the other hand, the role of the quarter-wave plate in the optical voltage transformer is to generate a phase difference of 1 / 4 wavelength, converting elliptical light into linearly polarized light. When the wavelength changes, it will also introduce additional phase difference (i.e., additional phase delay).

[0036] Described by mathematical formula: Considering the fluctuation of the central wavelength of the light source caused by temperature change or device aging, assuming that the wavelength of the light source at room temperature is λ, and the temperature coefficient of the wavelength of the light source is α, when the temperature changes by △T, the wavelength change of the light source △λ is:

[0037] Δλ=αΔT (2)

[0038] Taking the longitudinal modulation of electro-optic crystal as an example, the electro-optic phase delay according to the Pockels effect With λ, we have:

[0039]

[0040] Where n0 is the refractive index of the electro-optical crystal; γ is the electro-optic coefficient of the crystal; U π is the half-wave voltage of the electro-optical crystal, which is a certain value; U is the AC voltage to be measured.

[0041] Assume that the additional phase delay Δλ introduced by the electro-optical crystal is By taking the derivative of λ and simplifying formula (3), we can obtain:

[0042]

[0043] The role of the quarter-wave plate in the optical voltage transformer is to produce a phase difference of 1 / 4 wavelength. It can be expressed as:

[0044]

[0045] Where l is the length of the wave plate along the light transmission direction; △n is the difference in refractive index between o light and e light.

[0046] Similarly, according to equation (5), the additional birefringence introduced by Δλ in the quarter-wave plate is for:

[0047]

[0048] Wavelength fluctuations of visible light sources introduce additional phase delay into optical voltage transformers When considering When the influence of the circular radial polarization grating is applied, according to the linear demodulation mode based on the circular radial polarization grating, the demodulation result is:

[0049]

[0050] Attached Figure 2 For When the optical voltage transformer outputs a spot rotation angle δ+Δδ and The relationship between them shows that they change linearly. Because it is linear demodulation, δ is The rotation angle introduced is The additional rotation angle (i.e. error) introduced. Figure 2 It can be seen that the rotation of the output light spot after demodulation by the annular radial polarization grating is periodic, and the period is π. The AC voltage to be measured is modulated to twice the half-wave voltage of the electro-optical crystal, that is, 2U π According to formula (3), we can know Combining formula (7), we can see that The light spot rotation angle caused by this is exactly one period π (which can be considered The rotation angle of the emitted light spot is Δδ, which is The rotation angle introduced. Figure 3 As shown, when ignoring When the impact When , the dark pattern of the spot image is located in the y-axis direction; When , due to periodicity, the emitted light spot is consistent, that is, it is considered that the light spot does not rotate; when considering When affected, due to By applying AC voltage modulation, the Theoretically, the dark pattern position of the light spot is still in the y-axis direction, but due to The light spot will rotate due to the existence of , and the rotation angle is Δδ. The relationship between is shown in formula (8). Since Δδ is known at this time, the additional phase delay can be Calculate and compensate for it.

[0051]

[0052] Reference [1]: Tan Qiao, Xu Qifeng, Xie Nan. Design of optical voltage sensor for linear measurement [J]. Automation of Electric Power Systems, 2017, 41(3): 135-140.

[0053] The above are preferred embodiments of the present invention. Any changes made according to the technical solution of the present invention, as long as the resulting functions do not exceed the scope of the technical solution of the present invention, belong to the protection scope of the present invention.

Claims

1. A method for measuring additional phase delay introduced by wavelength fluctuation of an optical voltage transformer light source, characterized in that: The following steps are involved: S1. Constructing an optical voltage transformer for linear demodulation of phase delay based on an annular radial polarization grating; the optical voltage transformer comprises a light source, a polarizer, an electro-optical crystal, a quarter wave plate, an annular radial polarization grating, and a four-quadrant detector; the electric field in which the electro-optical crystal is located is generated by the AC voltage to be measured; S2. Modulate the AC voltage to be measured into twice the half-wave voltage of the electro-optical crystal, and obtain the additional phase delay introduced by the fluctuation of the central wavelength of the light source according to the light spot rotation angle measured by the optical voltage transformer.

2. The method for measuring the additional phase delay introduced by wavelength fluctuation of an optical voltage transformer light source according to claim 1, characterized in that: The optical voltage transformer realizes linear demodulation of phase delay based on annular radial polarization grating, specifically: The light emitted by the light source passes through the polarizer to form linear polarized light, and then passes through the electro-optical crystal. Under the action of electric field modulation, the linear polarized light enters the photoelectric crystal and decomposes into two linear polarized lights o and e with orthogonal polarization directions. Due to the different refractive indices of the two polarization directions, the electro-optical phase delay generated by the o and e lights after propagating a certain distance in the photoelectric crystal is The o light and the e light are synthesized into linear polarized light under the action of the quarter-wave plate, and the phase delay is converted into the rotation of the polarization plane of the linear polarized light synthesized by the quarter-wave plate. The rotation angle is β and satisfies After the outgoing light of the quarter-wave plate is demodulated by the annular radial polarization grating, an annular light spot with a fixed shape is obtained, and the light spot rotates synchronously with the change of the polarization plane of the linear polarized light synthesized by the quarter-wave plate. The rotation angle of the light spot is δ=β, and the rotation period is π. The rotation angle of the light spot is detected by the detector to realize the direct measurement of the phase delay.

3. The method for measuring the additional phase delay introduced by wavelength fluctuation of an optical voltage transformer light source according to claim 2, characterized in that: The S2 is specifically: The additional phase delay introduced by the central wavelength fluctuation of the light source is The light emitted by the light source passes through the polarizer to form linear polarized light. After the linear polarized light passes through the electro-optical crystal and the quarter-wave plate, it is demodulated by the annular radial polarization grating to obtain an output light spot with a rotation angle of δ+△δ; The electro-optical phase delay The corresponding rotation angle is δ, and Additional phase delay The corresponding rotation angle is △δ, and When the AC voltage to be measured is modulated to twice the half-wave voltage of the electro-optic crystal, the electro-optic phase delay Then the spot rotation angle δ corresponding to the electro-optic phase delay is π; since the spot rotation period is π, it is considered that the spot corresponding to the electro-optic phase delay has no rotation; according to the spot rotation angle measured at this time, the additional phase delay introduced by the central wavelength fluctuation of the light source is obtained, which is specifically calculated as follows:

Images