Six-path optical fiber electric field vector sensing system

Abstract

The utility model relates to a six-path optical fiber electric field vector sensing system, which comprises a light source, a modulation module, an isolation optical fiber and a sensing unit module which are sequentially arranged along a light path, the sensing unit module comprises a non-polarization beam splitter NPBS1-NBPS5, a plurality of 1 / 4 wavelength plates and a polarization analyzer. Incident light passes through the non-polarization beam splitter, the 1 / 4 wavelength plate and the polarization analyzer and is divided into six paths of different light beams to be output. The sensing system not only can measure the direction of the electric field at the sensing crystal, but also can synchronously measure the electrogenerated phase difference in direct proportion to the intensity of the electric field at the position. When the sensing unit module is used for the electric field measurement type optical fiber voltage transformer, under the conditions that the geometric position relation between the sensing unit module and the high-voltage electrode is fixed firmly and is not interfered by an external electric field, if the direction of the measured electric field is changed, partial discharge occurs near the sensing unit module, space charges are generated, and the distribution of the near electric field is changed. Therefore, the synchronous monitoring of the electric field direction can ensure the reliability of the measurement result of the electric field measurement type optical fiber voltage transformer.

Description

Technical Field

[0001] The utility model relates to a six-channel optical fiber electric field vector sensing system, belonging to the technical field of optical fiber sensing. Background Art

[0002] Passive fiber optic voltage sensor uses optical fiber and crystal with Pockels electro-optic effect to measure high voltage waveform information. Since optical fiber plays the role of optical isolation and insulation, it not only ensures the safety of secondary low voltage equipment and personnel, but also ensures that high voltage information is not affected by electromagnetic interference during transmission; and since both optical fiber and Pockels crystal are not affected by electromagnetic interference, the accuracy of voltage measurement is ensured. As an optical voltage meter, it will provide accurate and safe measurement equipment for high voltage amplitude and waveform information of power system.

[0003] In specific applications, the electro-optical crystal of the sensing unit can be placed in the electric field generated by the high-voltage electrode, or the measured voltage can be divided and then directly applied to the electro-optical crystal in the sensing unit, that is, the electric field measurement type and the voltage division type.

[0004] The basic sensing principle is the electro-optical Pockels effect, i.e., the electro-induced birefringence effect. This determines that the stability of the optical fiber sensing system depends on the polarization characteristics of the optical fiber-transmitted light, and is very sensitive to changes in the polarization characteristics of the optical fiber-transmitted light. At any point on the optical fiber's light wave transmission path, such as external mechanical vibration, or changes in ambient temperature, or even the relocation and movement of the sensing system, the polarization state of the transmitted light will change, making this sensing system inevitably a time-varying system. Other components of the system, such as the light source, the optical fiber connector, and the coupling ratio between the light and the optical fiber collimator, all have certain time-varying characteristics. Utility Model Content

[0005] In order to overcome the above problems, the utility model provides a six-channel optical fiber electric field vector sensing system and a measurement method. The sensing system can not only measure the electric field direction at the sensing crystal, but also synchronously measure the electro-induced phase difference which is proportional to the electric field strength at that location, while also eliminating the influence of the system's time-varying characteristics on the measurement accuracy.

[0006] The technical solution of the utility model is as follows:

[0007] A six-channel optical fiber electric field vector sensing system comprises a light source, a modulation module, an isolation optical fiber and a sensing unit module arranged in sequence along an optical path;

[0008] The sensing unit module includes a non-polarization beam splitter NPBS1, which splits the incident light into a first incident light and a second incident light;

[0009] The non-polarization beam splitter NPBS5 splits the first incident light into a third incident light and a fourth incident light;

[0010] The third incident light passes through the 1 / 4 wavelength plate and the analyzer in sequence and is output as a BXQ system;

[0011] The fourth incident light is output as a BXZ system after passing through the analyzer;

[0012] The second incident light is reflected after passing through the Pockels crystal and enters the non-polarization beam splitter NPBS1, and is split into a twelfth incident light and a fifth incident light by the non-polarization beam splitter NPBS1;

[0013] The fifth incident light is split into a sixth incident light and a seventh incident light by the non-polarization beam splitter NPBS2;

[0014] The sixth incident light is split into an eighth incident light and a ninth incident light by the non-polarization beam splitter NPBS3;

[0015] The eighth incident light passes through the quarter wavelength plate and the analyzer in sequence and is output as the AXQ system;

[0016] The ninth incident light is output as an AXZ system after passing through the analyzer;

[0017] The seventh incident light is split into a tenth incident light and an eleventh incident light by the non-polarization beam splitter NPBS4;

[0018] The tenth incident light passes through the 1 / 4 wavelength plate and the analyzer in sequence and is output as an A0Q system;

[0019] The eleventh incident light is output as an A0Z system after passing through the polarizer.

[0020] Furthermore, one side of the Pockels crystal is coated with a total reflection film.

[0021] Furthermore, the angle between the fast axis of the quarter wavelength plate through which the tenth incident light passes and the y-axis of the Pockels crystal is 45°; the angle between the fast axis of the wavelength plate through which the third incident light and the eighth incident light pass and the y-axis of the Pockels crystal is 90°.

[0022] Furthermore, the light transmission direction Ψ of the polarizer through which the tenth incident light and the eleventh incident light pass is A =0°; the light transmission direction Ψ of the analyzer through which the third incident light, the fourth incident light, the eighth incident light and the ninth incident light pass A =45°.

[0023] The utility model has the following beneficial effects:

[0024] The utility model can not only measure the electric field direction at the sensing crystal, but also synchronously measure the electro-induced phase difference which is proportional to the electric field intensity at the sensing crystal.

[0025] In the case of an electric field measurement type optical fiber voltage transformer, the geometric position relationship between the sensor unit module of the utility model and the high-voltage electrode is fixed firmly and is not interfered by the external electric field. If the measured electric field direction changes, it indicates that local discharge has occurred near the sensor unit module, generating space charge, causing the nearby electric field distribution to change. Therefore, the synchronous monitoring of the electric field direction can ensure the reliability of the measurement results of the electric field measurement type optical fiber voltage transformer. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a module schematic diagram of an embodiment of the utility model.

[0027] Figure 2 Schematic diagram of the optical path of the sensor unit module according to an embodiment of the present utility model.

[0028] Figure 3 This is the optical path of the third-order polarimeter.

[0029] Figure 4 is the spatial relationship between the intrinsic function of the optical path of the third-order polarimeter and the phase difference.

[0030] Figure 5 is the spatial relationship between the intrinsic function of the optical path of the third-order polarimeter and the phase difference on the XZ plane.

[0031] Figure 6 This is the optical path of the second-order polarimeter.

[0032] Figure 7(a) and 7(b) is the spatial relationship between the intrinsic function of the optical path of the second-order polarimeter and the phase difference.

[0033] Figure 8 is the intrinsic function vector rotation caused by the electro-phase difference in the optical path of the second-order polarimeter.

[0034] Fig. 9 Schematic diagram of the optical path of the 4-channel sensor unit module.

[0035] Figure 10(a) , 10(b) , 11(a) and 11(b) are the relationships between the intrinsic functions of the 4-channel sensor unit module and the direction of the analyzer.

[0036] Figure 12(a) and 12(b) This is the relationship between the intrinsic function of the 4-channel sensor unit module and the direction of the polarizer and the main axis.

[0037] Figure 13(a) and 13(b)1 is the relationship between the intrinsic function of the sensor unit module and the direction of the polarizer and the main axis direction of the embodiment.

[0038] Fig.14 FIG. 4 is the relationship between the intrinsic function of the sensor unit module and the phase difference on the XZ plane of the embodiment. DETAILED DESCRIPTION

[0039] The utility model is described in detail below with reference to the accompanying drawings and specific embodiments.

[0040] A six-channel optical fiber electric field vector sensing system comprises a light source, a modulation module, an isolation optical fiber and a sensing unit module arranged in sequence along an optical path;

[0041] The sensing unit module includes a non-polarization beam splitter NPBS1, which splits the incident light into a first incident light and a second incident light;

[0042] The non-polarization beam splitter NPBS5 splits the first incident light into a third incident light and a fourth incident light;

[0043] The third incident light passes through the 1 / 4 wavelength plate and the analyzer in sequence and is output as a BXQ system;

[0044] The fourth incident light is output as a BXZ system after passing through the analyzer;

[0045] The second incident light is reflected after passing through the Pockels crystal and enters the non-polarization beam splitter NPBS1, and is split into a twelfth incident light and a fifth incident light by the non-polarization beam splitter NPBS1;

[0046] The fifth incident light is split into a sixth incident light and a seventh incident light by the non-polarization beam splitter NPBS2;

[0047] The sixth incident light is split into an eighth incident light and a ninth incident light by the non-polarization beam splitter NPBS3;

[0048] The eighth incident light passes through the quarter wavelength plate and the analyzer in sequence and is output as the AXQ system;

[0049] The ninth incident light is output as an AXZ system after passing through the analyzer;

[0050] The seventh incident light is split into a tenth incident light and an eleventh incident light by the non-polarization beam splitter NPBS4;

[0051] The tenth incident light passes through the 1 / 4 wavelength plate and the analyzer in sequence and is output as an A0Q system;

[0052] The eleventh incident light is output as an A0Z system after passing through the polarizer.

[0053] In one implementation of the utility model, one side of the Pockels crystal is coated with a total reflection film.

[0054] In one embodiment of the utility model, the angle between the fast axis of the 1 / 4 wavelength plate through which the tenth incident light passes and the y-axis of the Pockels crystal is 45°; the angle between the fast axis of the wavelength plate through which the third incident light and the eighth incident light pass and the y-axis of the Pockels crystal is 90°.

[0055] In one embodiment of the present invention, the light transmission direction Ψ of the polarizer through which the tenth incident light and the eleventh incident light pass is A =0°; the light transmission direction Ψ of the analyzer through which the third incident light, the fourth incident light, the eighth incident light and the ninth incident light pass A =45°.

[0056] refer to Figure 3 , the general light intensity formula of the modulation polarimeter is:

[0057]

[0058] Among them, γ(t) is the total effect of the transmittance of each unit on light, I0(t) is the light intensity emitted by the light source, (Ψ P -Ψ M ) is the optical axis of the polarizer Ψ P OPM spindle with phase modulator Ψ M The angle, θ M is the phase modulation amount of OPM, η and ξ are the intrinsic functions of the basic optical path, and α and β are constants determined by the directional angles of each adjacent vector device.

[0059] The polarizer P and analyzer A are respectively determined by their light transmission direction Ψ P and A is described by the fast axis position Ψ V and the electro-induced phase difference θ V To describe, t is the time, the isolation fiber S is at its entrance, the fast axis position Ψ s1 , the total phase delay of the optical fiber θ s and the fast axis orientation Ψ at the exit s2 to describe.

[0060] From the above, we can get the intrinsic function ξ of the modulated third-order polarimeter:

[0061] ξ=sin2(Ψ s2 -Ψ V )cos2(Ψ V -Ψ A )·sin(θ s)+·sin2(Ψ V -Ψ A )·sin(θ V )cos(θ s )+cos2(Ψ s2 -Ψ V )sin2(Ψ V -Ψ A )·cos(θ V )sin(θ s )

[0062] The intrinsic function ξ is calculated according to the angle Ψ between the fast axis of the electro-optic crystal and the optical axis of the analyzer. V -Ψ A After transformation, the intrinsic function expression of the modulation polarimeter is obtained:

[0063] ξ=ξ T ·cos2(Ψ V -Ψ A )+ξ RT ·sin2(Ψ V -Ψ A )

[0064] ξ T = sin2(Ψ s2 -Ψ V )·sin(θ s )

[0065] ξ RT = cos2(Ψ s2 -Ψ V )·sin(θ s )cos(θ V )+cos(θ s )sin(θ V )

[0066] Let the equivalent phase difference of the isolation fiber be Θ, and take

[0067] K·sin(Θ)=ξ RS = cos2(Ψ s2 -Ψ V )·sin(θ s )

[0068] K·cos(Θ)=ξ R4 =cos(θ s )

[0069] and

[0070]

[0071] The conversion can obtain the following intrinsic function

[0072] ξ RT = cos2(Ψ s2 -Ψ V )·sin(θ s )cos(θ V )+cos(θ s )sin(θ V )

[0073] =K·sin(θ+θ V )

[0074] ξ RS =K·sin(Θ)

[0075] And the radius K of the intrinsic function has the following relationship:

[0076] K 2 =ξ 2 RS +ξ 2 R4 =[cos2(Ψ s2 -Ψ V )·sin(θ s )] 2 +cos 2 (θ s )

[0077] =1-[sin2(Ψ s2 -Ψ V )·sin(θ s )] 2 =1-ξ 2 t

[0078] Through the above test, the intrinsic function ξ and the electro-induced phase difference θ can be V The spatial vector relationship between the equivalent phase difference θ of the isolation fiber is shown in Figure 4 middle.

[0079] like Figure 5 As shown, in the XZ plane, the electro-induced phase difference θ V The increase or decrease of the equivalent phase difference θ with the isolation fiber will cause the intrinsic function vector to rotate by K.

[0080] Figure 6 It is the second-order polarimeter optical path of the modulated polarimeter without passing through the Pockels electro-optical crystal. The intrinsic function ξ of the optical path can be obtained from the light intensity expression of the optical path. N for:

[0081] ξ N = sin2(Ψ s2 -Ψ A )·sin(θs )

[0082] Decomposing the above formula, it can be transformed into:

[0083] ξ N = sin[2(Ψ s2 -Ψ V )+2(Ψ V -Ψ A )]·sin(θ s )

[0084] =ξ T ·cos2(Ψ V -Ψ A )+ξ RS ·sin2(Ψ V -Ψ A )

[0085] Therefore, the optical paths before and after the Pockels electro-optical crystal have the same intrinsic function expression of the modulation polarimeter:

[0086] ξ=ξ T ·cos2(Ψ V -Ψ A )+ξ RT ·sin2(Ψ V -Ψ A )

[0087] ξ N =ξ T ·cos2(Ψ V -Ψ A )+ξ RS ·sin2(Ψ V -Ψ A )

[0088] Due to the orientation of the main axis of electro-birefringence Ψ in the electro-optical crystal of the voltage sensing module V is fixed, in order to remove the unknown ξ T , set the light transmission direction of the polarizer of each optical path A The direction of the main axis of electro-birefringence V The angle is fixed at Ψ V -Ψ A =45°, and using the phase adjustment function of the 1 / 4 wavelength plate for pairing, the following four groups of intrinsic function groups of the optical path can be obtained:

[0089] ξ RT =K·sin(θ+θ V )

[0090] ξ RR =K·cos(θ+θ V )

[0091] ξ RS =K·sin(Θ)

[0092] ξ R4 =K·cos(θ)

[0093] according to Figure 7(a) , 7(b) From 8, we can know that the intrinsic function group detected by the four-way optical system constitutes the rotation of the intrinsic function vector, and its rotation angle is the electro-induced phase difference θ V , its measurement range is [-π,+π].

[0094] The overall optical path diagram of the voltage sensing module unit in the prior art is as follows: Fig. 9 As shown. The fiber collimator is used to emit the incident light transmitted by the isolation optical fiber, and to receive the light and inject it into the return optical fiber. The non-polarization beam splitter NPBS is an optical system used to split the incident light into two beams to form multiple optical paths. Taking the fast axis direction generated by the electric field at the sensor element (Pockels element) as the reference direction, the transmittance axis direction of the polarizer of each optical path is set to 45 degrees. The fast axis direction of the 1 / 4 wavelength plate is set to be in the same direction as the electro-fast axis direction, and an additional π / 2 phase difference is introduced to the corresponding optical path, so that the optical path forms a complementary phase difference with the other optical path.

[0095] The main unknown measurements of the fiber optic electric field meter sensing system are: (1) the direction of the electric field, i.e., Ψ V -Ψ A ; (2) Electroinduced phase difference θ V and (3) the equivalent phase difference Θ of the isolation fiber.

[0096] For each orientation of the analyzer, there is a pair of two optical paths with complementary phase differences, and their modulation polarimeter intrinsic function expressions are:

[0097] ξ1=ξ T ·cos2(Ψ V -Ψ A )+ξ RT ·sin2(Ψ V -Ψ A )

[0098] ξ2=ξ T ·cos2(Ψ V -Ψ A )+ξ RR ·sin2(Ψ V -Ψ A )

[0099] ξ1-ξ2=(ξ RT -ξ TR )·sin2(Ψ V -ΨA )

[0100] Depend on Figure 10(a) , 10(b) , 11(a) and 11(b), we can see that Ψ V -Ψ A That is, the deflection angle of the electric field direction relative to the light transmission axis of the analyzer. Since the analyzer has only one pair of effective orthogonal polarization positions Ψ A , and its other effective direction is Ψ A2 =Ψ A +45°; for this analyzer position Ψ A2 The intrinsic function expression of a pair of optical paths with complementary phase differences is:

[0101] ξ3=ξ T ·sin2(Ψ V -Ψ A )+ξ RT ·cos2(Ψ V -Ψ A )

[0102] ξ4=ξ T ·sin2(Ψ V -Ψ A )+ξ RR ·cos2(Ψ V -Ψ A )

[0103] ξ3-ξ4=(ξ RT -ξ RR )·cos2(Ψ V -Ψ A )

[0104] From the above formula, we can see that the difference between each set of intrinsic functions removes the unknown ξ T The influence of Figure 12(a) and 12(b) As shown in the figure, the difference of the intrinsic functions of the phase difference complementary optical path of this pair of orthogonal polarizers, ξ1-ξ2 and ξ3-ξ4, respectively constitute the two orthogonal components of the electric field deflection angle of the sensing optical fiber, and the electric field deflection angle Ψ can be obtained from them. V -Ψ A The range is a semicircle [-90°, +90°].

[0105] A method for measuring an optical fiber electric field vector, which measures an optical fiber electric field vector through the six-channel optical fiber electric field vector sensing system of the utility model, comprises the following steps:

[0106] Measure the AXZ system light intensity, AXQ system light intensity, A0Z system light intensity and A0Q system light intensity, and calculate the intrinsic function ξ of the AXZ system, AXQ system, A0Z system and A0Q systemAXZ , ξ AXQ , ξ A0Z , and ξ A0Z ; and there is the following relationship:

[0107] ξ AXZ = ξ T ·cos2(Ψ V - Ψ A ) + ξ RT ·sin2(Ψ V - Ψ A );

[0108] ξ AXQ = ξ T ·cos2(Ψ V - Ψ A ) + ξ RR ·sin2(Ψ V - Ψ A );

[0109] ξ A0Z = ξ T ·sin2(Ψ V - Ψ A ) + ξ RT ·cos2(Ψ V - Ψ A );

[0110] ξ A0Q = ξ T ·sin2(Ψ V - Ψ A ) + ξ RR ·cos2(Ψ V - Ψ A );

[0111] Among them, Ψ V - Ψ A is the electric field deflection angle, Ψ V is the azimuth of the fast axis of the Pockels crystal, Ψ A is the azimuth of the analyzer;

[0112] ξ T = sin2(Ψ s2 - Ψ V )·sin(θ s );

[0113] ξ RT = K·sin(Θ + θ V );

[0114] ξ RR = K·cos(Θ + θ V );

[0115] Among them, s2 is the fast axis orientation at the exit of the isolation fiber, θ s is the overall phase delay of the isolation fiber; K is the intrinsic function radius of the optical fiber electric field vector sensing system, and Θ is the equivalent phase difference of the isolation fiber.

[0116] The electric field deflection angle Ψ is obtained from the difference between the two sets of intrinsic functions. V -Ψ A :

[0117] (ξ AXZ -ξ AXQ )=[ξ RT -ξ RR ]·sin2(Ψ V -Ψ A );

[0118] (ξ A0Z -ξ A0Q )=[ξ RT -ξ RR ]·cos2(Ψ V -Ψ A ).

[0119] The BXZ system light intensity and the BXQ system light intensity are measured, their respective intrinsic functions are calculated, and the following equation is solved to obtain the equivalent phase difference θ of the isolation optical fiber:

[0120] ξ BXZ = K·sin(Θ);

[0121] ξ BXQ = K·cos(θ);

[0122] Solve the following equation to get ξ RT and RR :

[0123]

[0124] According to RT , RR Solve the following equation with the equivalent phase difference θ to obtain the electro-induced phase difference θ V :

[0125] ξ RT =K·sin(θ+θ V );

[0126] ξ RR =K·cos(θ+θ V ).

[0127] The above description is only an embodiment of the present invention, and does not limit the patent scope of the present invention. Any equivalent structure made using the contents of the specification and drawings of the present invention, or directly or indirectly used in other related technical fields, is also included in the patent protection scope of the present invention.

Claims

1. A six-channel optical fiber electric field vector sensing system, characterized in that: It includes a light source, a modulation module, an isolation optical fiber and a sensor unit module which are sequentially arranged along the optical path; The sensing unit module includes a non-polarization beam splitter NPBS1, which splits the incident light into a first incident light and a second incident light; The non-polarization beam splitter NPBS5 splits the first incident light into a third incident light and a fourth incident light; The third incident light passes through the 1 / 4 wavelength plate and the analyzer in sequence and is output as a BXQ system; The fourth incident light is output as a BXZ system after passing through the analyzer; The second incident light is reflected after passing through the Pockels crystal and enters the non-polarization beam splitter NPBS1, and is split into a twelfth incident light and a fifth incident light by the non-polarization beam splitter NPBS1; The fifth incident light is split into a sixth incident light and a seventh incident light by the non-polarization beam splitter NPBS2; The sixth incident light is split into an eighth incident light and a ninth incident light by the non-polarization beam splitter NPBS3; The eighth incident light passes through the quarter wavelength plate and the analyzer in sequence and is output as the AXQ system; The ninth incident light is output as an AXZ system after passing through the analyzer; The seventh incident light is split into a tenth incident light and an eleventh incident light by the non-polarization beam splitter NPBS4; The tenth incident light passes through the 1 / 4 wavelength plate and the analyzer in sequence and is output as an A0Q system; The eleventh incident light is output as an A0Z system after passing through the polarizer.

2. The six-channel optical fiber electric field vector sensing system according to claim 1, characterized in that: One side of the Pockels crystal is coated with a total reflection film.

3. The six-channel optical fiber electric field vector sensing system according to claim 1, characterized in that: The angle between the fast axis of the quarter wavelength plate through which the tenth incident light passes and the y-axis of the Pockels crystal is 45°; the angle between the fast axis of the wavelength plate through which the third incident light and the eighth incident light pass and the y-axis of the Pockels crystal is 90°.

4. The six-channel optical fiber electric field vector sensing system according to claim 1, characterized in that: The light transmission direction Ψ of the analyzer through which the tenth incident light and the eleventh incident light pass A =0°; the light transmission direction Ψ of the analyzer through which the third incident light, the fourth incident light, the eighth incident light and the ninth incident light pass A =45°.

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