JPH0344563A - Method and device for measuring photoelectric field - Google Patents

Abstract

PURPOSE:To reduce an effect due to a background light or an ambient temperature and to make a result of measurement highly precise by taking out angular frequency signals being the same and twice as large as an alternating-current electric field acting on a Pockels element and by determining the electric field and a generation source voltage from the relative ratio between them. CONSTITUTION:A light from a light-emitting unit 24 is made to enter a sensor head unit 10 from a fiber collimator 18, transmitted through a polarizer 14, a Pockels element 12 having a means 25 for impressing an alternating-current voltage to be measured, a phase member 13 and an analyzer 16 and emitted from a fiber collimator 20. Receiving the light through an optical fiber 26, a light-receiving unit 28 supplies an electric signal E corresponding to the intensity of the light to an identical angular frequency component detector 30 and a double angular frequency component detector 32. A divider 34 subjects signal components from the detectors 32 and 30 to division and an alternating-current voltage V to be measured is measured from a signal ET thus obtained. Accordingly, the signal ET is made free from an error in measurement due to the quantity of emitted light, a transmission loss of an optical transmission line or a change in the amplitude of the signal E.

Description

Detailed Description of the Invention (Technical Field) The present invention relates to a novel optical electric field measurement method and apparatus for measuring an alternating current electric field or an alternating current voltage that generates the alternating electric field by utilizing the light modulation effect due to the Pockels effect. It is related to.

(Background technology) In recent years, the light modulation effect due to the Pockels effect has been used as a method for measuring electric fields (voltages) on power transmission lines and distribution lines, etc. in the power field, as it provides excellent insulation reliability and resistance to electromagnetic induction. The optical electric field measurement method has been attracting attention.

Therefore, when measuring an alternating current electric field (voltage) using the Pockels effect, conventionally a polarizer and an analyzer are placed in series before and after the light transmission direction of a Pockels element having the Pockels effect. and transmitting the light emitted from the light emitting part to the sensor part configured such that the transmitted light is modulated by the electric field acting on the Pockels element, and forming the light emitting part.
A light receiving section that outputs the transmitted light that has passed through the sensor section receives the light to be transmitted through the sensor section, and from the output signal of the light receiving section, the DC component (E l1lc) of the signal is detected.
and a signal component (Eω) with the same angular frequency as the AC electric field acting on the Pockels element, and calculate their relative ratio (
The AC electric field to be measured, that is, the AC electric field acting on the Pockels element or the AC voltage that generates it, has been determined from Eω/Enc).

To this end, conventional optical electric field measurement methods that utilize the Pockels effect employ a light propagation method that uses optical fibers or the like to receive only the light emitted from the light emitting part at the light receiving part. There is no problem if the The alternating current electric field (voltage) is
There was a problem that an error occurred in the measurement results.

On the other hand, in conventional optical electric field measurement devices that employ the optical electric field measurement method described above, the relational expression for determining the AC electric field (voltage) to be measured, that is, the DC component (E
oc) and the AC component (Eω), the half-wave voltage of the Pockels element with temperature dependence; V
In order to solve the problem of unavoidable errors in the measurement results of the alternating current electric field (voltage) due to the environmental temperature at the installation position of the Pockels element, since π is included, Although various methods have been considered, it has not yet been possible to fully solve this problem, or the method to solve the problem is complicated or the equipment is large-scale. There were circumstances in which it lacked practicality.

(Problem to be solved) The present invention has been made against the background of the above-mentioned circumstances, and the problem to be solved is that even if a space where background light exists is used as a light propagation path, The object of the present invention is to provide a photoelectric measurement method and apparatus in which the measurement results are hardly affected by the background light in the light propagation space even when a light propagation method is adopted, and even when a Pockels element is installed. An object of the present invention is to provide a photoelectric external measurement method and device that can satisfactorily suppress measurement errors caused by changes in environmental temperature even if the environmental temperature at a location changes, and can stably obtain highly accurate measurement results. .

(Solution Means) In order to solve this problem, in the present invention, a polarizer and an analyzer are arranged in series before and after the light transmission direction of the Pockels element, and the electric field acting on the Pockels element is A light emitting part that transmits the light emitted from the light emitting part to a sensor part configured to modulate the transmitted light, and a light receiving part that outputs the transmitted light that has passed through the sensor part.
The light to be transmitted through the sensor section is received, and from the output signal of the light receiving section, a signal component (Eω) having the same angular frequency as the AC electric field acting on the Pockels element and a signal component (Etω) having twice the angular frequency as the AC electric field acting on the Pockels element are determined. ), find their relative ratio, and from that relative ratio, find the alternating current electric field acting on the Pockels element or the alternating current voltage that generates the alternating electric field.

Further, in order to solve the above problems, the present invention apparatus includes (i) a Pockels element, a polarizer and an analyzer arranged in series in front and behind the light transmission direction of the Pockels element, and (11) a sensor section configured such that transmitted light is modulated by an electric field acting on a Ponkers element;
a light emitting unit that emits light to be transmitted to the sensor unit;
(l!i) a light emitting section that receives light to be transmitted through the sensor section; a light receiving section that outputs the transmitted light that has passed through the sensor section; (v) a first extraction means for extracting a signal component (Eω) having the same angular frequency as the AC electric field acting on the Pockels element; It was decided to include a second extracting means for extracting the signal component (aXω), and a relative ratio detecting means for determining the relative ratio of the signal components extracted by the first and second extracting means. .

In addition, in the method and device of the present invention described above, if a retarder is provided in series with the Pockels element to provide an optical bias ψ that satisfies the following equation between the polarizer and the analyzer of the sensor section, it can be used regardless of the environmental temperature. First, it becomes possible to stably obtain highly accurate measurement results.

≦1 × 10 [However, ■π: π: Pockels half-wavelength voltage Vπ. : Half-wave voltage T conversion ratio ψ of the Pockels element at room temperature. Optical bias at room temperature using a two-phase shifter (specific configuration/examples) The present invention will be explained in more detail below with reference to drawings showing some examples of the present invention.

First, FIG. 1 shows an example of the photoelectric external measuring device according to the present invention, in which 10 is a sensor head part as a measuring part, which is arranged in series with each other in the light transmission direction. A polarizer 14 and an analyzer 16 are arranged in series before and after the Pockels element 2 and the retarder (phase difference element) 13, and a fiber collimator is arranged further before and after the polarizer 14 and the analyzer 16. 18.20
It has a structure in which these are arranged in series. Then, a fiber collimator 1 on the front side of the sensor head IO
A light emitting section 24 is connected to the light emitting section 8 via an optical fiber 22, and the light emitted from the light emitting section 24 is guided to a fiber collimator 18 by the optical fiber 22. The light incident on the polarizer 14. The light passes through the Pockels element 12, the phase shifter 13, and the analyzer 16 in this order, and is emitted from the fiber collimator 20. As is clear from this, here, the light emitting section 2
Only the light emitted from the fiber collimator 4 is transmitted to the Pockels element 12, and only the light that has passed through the Pockels element 12 is emitted from the fiber collimator 20.

Note that the Pockels element 12 is made of LiNb0i.

LiTaO5+81+zSiOzo+81+zG80z
The retarder 13 is made of various optical materials having a Pockels effect, such as o+CdMnTe, and quartz+
81+zSiOzo+81+zGeO□. It is possible to employ various optical materials having birefringence, such as, for example.

In FIG. 1, reference numeral 25 is connected to electrodes 27 and 27 disposed on opposing surfaces of the Pockels element 12, and is used to apply an AC voltage to be measured to the Pockels element 12. It is a means.

An optical fiber 26 is connected to the fiber collimator 2o that emits the light that has passed through the sensor head section 10, and the transmitted light that is emitted from the sensor head section lo through the fiber collimator 20 is transmitted through the optical fiber 26 to a photodiode, etc. The light is guided to the light receiving section consisting of the following. The light emitting section and the sensor section are configured to output an electrical signal E corresponding to the intensity P of the light received through the optical fiber 26, and the electrical signal E is The signal is supplied to an angular frequency component detector 30 and a double angular frequency component detector 32, respectively.

The same angular frequency component detector 30 detects a signal component Eω having the same angular frequency ω as the AC voltage to be measured: V applied to the Pockels element 12 by the AC voltage applying means 25 to be measured.
The light emitting section and the sensor section are used to extract the output signal E from the transmitting section 28. It is composed of an electric filter, a phase detection circuit, etc., and the light emitting section and the sensor section are connected to the transmitting section 28. A signal component Eω having the same angular frequency ω as the AC voltage to be measured: V is detected from the electric signal E of the day, and the detected signal component Eω is supplied to the divider 34. Further, the double angular frequency component detector 32 detects a signal component: E2 with an angular frequency: 2ω that is twice the AC voltage to be measured: V.
This is for extracting ω, and like the angular frequency component detector 30, it is composed of an electric filter, a phase detection circuit, etc., and has a light emitting section and a transmitting section that outputs the output signal of the second day. A signal component: Etω having an angular frequency: 2ω that is twice the AC voltage to be measured: V is detected from :E, and the detected signal component; E2ω is supplied to the divider 34. Then, the divider 34 is divided into the double angular frequency division detector 3
Signal component from 2: I! 2ω is divided by the signal component from the same angular frequency component detector 30: Eω, and the divided signal is:
It is designed to output Ey (=Ezω/Eω),
Here, the AC voltage to be measured: ■ is measured from the divided signal: E.

- As is clear from the above description, here, the same angular frequency component detector 3o and the double angular frequency component detector 32 constitute the first extraction means and the second extraction means, respectively. Furthermore, the divider 34 constitutes relative ratio detection means.

Next, the measurement principle of the AC voltage to be measured: (2) of this device will be explained.

That is, in the above device, the polarizer 14 and the analyzer 1
Relative angle of 6: When θ is Oo, AC voltage to be measured applied by AC voltage applying means 25; Optical phase difference induced in transmitted light of Pockels element 12 by ■:
φ is given as shown in equation (1) below.

φ=(π/Vπ)・V...(1) [
However, Vπ: half-wave voltage of the Pockels element 12] Here, the light received by the light emitting section and the sensor section 28 by the transmitting section 28 is only the light emitted from the light emitting section 24, as is clear from the above explanation. Therefore, the intensity of light received by the light emitting section, the sensor section, and the transmitting section 28: P is given as shown in equation (2) below, and is output from the light emitting section, the sensor section, and the transmitting section 28. The electrical signal: E is given as shown in equation (3) below.

P = c P ocO5” [(φ+ψ)/2) )=
cPocos” ([(π/Vz)V+ψ)/2] [However, C: proportionality constant Po: output light intensity ψ from the light emitting unit 24: optical bias due to the phase shifter 13 Vo: amplitude of the AC voltage to be measured (V) ω: Angular frequency t of AC voltage to be measured (V): Time A=(π/■π)・Vo] [However, Eo: Amplitude of electrical signal (E)] Here, the same angular frequency component detector 30 Signal component extracted: Eω
The signal component E2ω extracted by the double angular frequency component detector 32 is the electrical signal E from the light receiving unit 28 expressed by the above equation (3). Based on the above, the following (5),
Therefore, the divider 34 outputs a division signal: ET expressed by the following equation (7).

O E = = (1+cos(^sinωt+ψ))-5i
n(A sinωt) ・sinψ)+2Ja(A)si
n4ωt+ − ゛) cosψ (2,L (A) sinωt+2Jz(A) sin3ω
t+ ・ ・) sinψ] ・(4) E Q) = Eo ' Jt(＾) ・sinψ
・(5) E2ω= Eo−Jt(A) ・cosψ ・(6) Eo ・Jt(A) ・sinψ Here, if A(=(π/■π)・VO) is smaller than 1, the above Equation (7) can be rearranged as shown in (8) 2 below.

'1-cotψ In other words, the division signal Et output from the divider 34 is
As is clear from equation (8), the AC voltage to be measured:
The amplitude of V is a value proportional to ■o, therefore,
According to the device shown in FIG. 1, the DC component (
E DC) and the same angular frequency component (Eω) as the AC voltage to be measured (V), and calculate their relative ratio (Eω/E
Similar to the optical electric field measurement device that calculates the amplitude (VO>) of the AC voltage (V) to be measured from oc), the divided signal:
The AC voltage to be measured: v (amplitude: Vo) applied to the Pockels element 12 can be determined from ET, and the electric field strength applied to the Pockels element 12 can be determined from the amplitude: Vo. It is.

Note that here, as is clear from the above equation (8).

Since the divided signal E does not include the amplitude Eo of the electrical signal E, which varies depending on the amount of light emitted in the light emitting section 24, the transmission loss of the optical propagation path, or the detection sensitivity of the light receiving section 28, these light emitted It also has the advantage of not producing measurement errors due to fluctuations in the amount of light emitted by the section 24, transmission loss in the optical propagation path, or detection sensitivity of the light receiving section 24.

By the way, in the upper optical electric field measurement device, the polarizer 14. which constitutes the sensor section. Pockels element 12, phase shifter 1
3 and the analyzer 16, and only the transmitted light is received by the light receiving section 28. Therefore, the light emitting section and the sensor section are connected to the transmitting section 2.
The intensity 2P of the light received at 8 is expressed as in equation (2) above, and therefore, the electric signal E output from the light emitting section and the sensor section from the transmitting section 2 is also expressed as in equation (3) above. However, when the light propagation path is a space where background light exists, such as an outdoor space or an indoor space with lighting, as in the device shown in Figure 2, the light receiving section The intensity 2P of the light received in 2 days is affected by the background light in the light propagation space and is expressed as the following equation (2). Therefore, the electric signal output from the light receiving section 28 is: E is also expressed as the following equation (3)°.

・ ・ ・(2)′ [However, P,: the intensity of the background light received by the light receiving section 2B] [However, E,: the electrical signal corresponding to the background light intensity (P s)] Here, the background light intensity :P, the electric signal corresponding to :El can be regarded as a DC component, so when the equation (3) is expanded using the Bessel function, it is expressed as the equation (4) below, which is the same as Measured AC voltage extracted by the angular frequency component detector 30 and double angular frequency component detector 32:
As is clear from equation (4) 1, the signal component with the same angular frequency as Eo and the signal component with twice the angular frequency as E2ω are the same as in the case of the device shown in FIG. 1, respectively.
5) and (6). Therefore, the division signal output from the divider 34: ET (=E2ω
/Eω) is also expressed by the above (8) 2, as in the device shown in FIG. becomes.

+ 2J a (A) s i n4ωt+=lcos
ψ(2Jl(^)sinωt+2J3(A)sin3ω
L+・・)sinψ】・・・・(4) In other words, even if the background light in the light propagation space is received by the light receiving unit 28 together with the light emitted from the light emitting unit 24, the background light in the light propagation space is not measured. It does not affect the measurement results of AC voltage: ■ (amplitude: ■.), and therefore it is possible to stably obtain highly accurate measurement results without errors caused by background light. be.

Incidentally, in a conventional optical electric field measuring device that uses a space where background light exists as a light propagation path, the light emitting section and the sensor section are connected to the output signal of the transmitting section 28. The DC component extracted from E; Eoc is as follows. It is expressed as equation (9), and the angular frequency component Eo, which is the same as the AC electric field to be measured: V, is expressed as follows (5)
Since it is expressed as the following equation, the electrical signal 2E corresponding to the background light intensity 2P is also included in the relational expression representing their relative ratio; Therefore, it was inevitable that errors caused by the background light in the light propagation space would occur in the measurement results of the AC voltage to be measured: v(vo).

2 Eω"'Eo・J+(A)・sinωt [However, ψ=
90° ] Eω Eo/2− As1nωt Ebc Etl+ Ea/2 ・(5) In the optical electric field measuring device shown in FIG.
The polarizer 14 and analyzer 16, which together with the Pockels element 12 and the retarder 13 constitute a sensor section, are composed of a Pockels element 12, a retarder 13, and a reflecting mirror 36 provided behind the retarder 13. The light receiving section 24 and the light receiving section 28 are provided in the main body 38 of the device. As is clear from FIG. 2, the light emitted from the light emitting section 24 is transmitted through the polarizer 14. Pockels element 12. The light passes through the phase shifter 13, is reflected by the reflecting mirror 36, passes through the phase shifter 13 and Pockels element 12 again, and is received by the light receiving section 28 via the analyzer 16.

Next, in the optical electric field measuring device shown in FIG. , AC voltage to be measured: ■ (amplitude: Vo) can always be stably measured with high accuracy, and the reason why such an effect can be obtained will be explained.

・ ・ ・01) Temperature change rate ψ. : Optical bias due to the phase shifter 13 at room temperature, that is, optical bias due to the phase shifter 13: φ and optical phase difference of the Pockels element 12: A at φ (=(π
/Vπ)·Vo) can be expressed as in the following equations 021 and 03), taking into consideration the respective temperature characteristics.

=ψ. 10Δψ...02) [However, ψ. Optical bias at room temperature due to the two-phase shifter 13 = 60+ΔA [However, A o =(π/Vπ.)·V.

■π0: Half-wave voltage at Pockels element 1・Room temperature at zero support 2 Therefore, the relative ratio between the signal component of the same angular frequency as the AC voltage to be measured: Eω and the signal component of twice the angular frequency: E2ω: The above equation (8) expressing El can be expressed as the following equation 04) by considering the temperature characteristics of A at the optical bias: ψ due to the retarder 13 and the optical phase difference: φ of the Pockels element 12. .

Here, if , then such a formula can be expressed as ・ ・ ・0, and in such 05) 2, 8. 5in2ψ.

That is, if ・(11) Then, the formula 09 further becomes, It can be organized as follows.

Then, the nonlinear term in this equation 00: (A2/24
> is an extremely small value and can be virtually ignored, so the equation (8), that is, the division signal 2ET from the divider 34, can be expressed as the following equation o'7).

・ ・ ・0′7) In other words, the retarder 13
If the optical bias: ψ is set, as is clear from the equation 07), the division signal from the divider 34: E7
The relational expression representing is substantially unaffected by the temperature at the installation position of the Pockels element 12, and therefore,
According to the optical electric field measuring device equipped with the retarder 13 between the Pockels element 12 and the analyzer 16 such that the optical bias ψ satisfies the above formula (11), the optical bias ψ is caused by the environmental temperature at the installation position of the Pockels element 12. It is possible to stably obtain error-free measurement results, and the configuration itself is extremely simple.

Note that it is actually extremely difficult to make the left and right sides of the above formula 00 completely equal, so the optical bias ψ due to the phase shifter 13 must be set to a size that completely satisfies the above formula (11). However, in order to minimize measurement errors due to changes in environmental temperature, the following (
11) More preferably, the following (!
+) It is desirable to set the optical bias: ψ of the retarder 13 so as to satisfy the formula.Here, the following (II)
The retarder 13 is
Optical bias: If ψ is set, the temperature difference will be 100
When used in an environment where the temperature is °C, measurement errors due to environmental temperature can be suppressed to 1% or less and 0.1% or less, respectively.

・ ・ ・(11) “ ・ ・ ・ (II) '″ In this way, between the Pockels element 12 and the analyzer 16, the above formula (I 1) (in practice, the above (It)
By intervening the phase shifter 13 that gives an optical bias: ψ that satisfies the equation '), it is possible to extremely suppress errors caused by environmental temperature and to stably obtain highly accurate measurement results. However, such an effect can be obtained even if a similar retarder 13 is interposed between the polarizer 14 and the Pockels element 12, or if the total optical bias: ψ is Even if a plurality of retarders are arranged in series between the polarizer 14 and the analyzer 16 so as to satisfy the above conditions, it is possible to obtain the same effect.

In addition, in the structure for obtaining the temperature characteristic compensation effect as described above, that is, between the polarizer 14 and the analyzer 16, the above-mentioned (
11) The configuration in which a retarder is installed to provide an optical bias that satisfies the formula ψ is applied to an optical electric field measurement device using a light propagation method that uses a space where background light exists as a light propagation path, as shown in Figure 2. However, in that case, it is necessary to install the retarder 13 in the same temperature environment as the Pockels element 12.

Furthermore, although the above explanation is based on the assumption that the light emitted from the light emitting section 24 has a single wavelength, the light emitted from the light emitting section 24 may be light having a wide wavelength range, for example, white light.
According to the present invention, by setting conditions based on the same discussion as above, it is possible to obtain the same effect as when using a single wavelength light source. In addition to monochromatic light sources,
It is also possible to use a white light source that is inexpensive and has a large amount of light. In other words, by employing a white light source or the like, measurement accuracy can be improved by increasing the amount of light emitted from the light emitting section 24, and device costs can be reduced.

(Effect of the invention) As is clear from the above explanation, according to the method of the present invention,
Even when using a light propagation method that uses a space where background light exists as a light propagation path, the influence of the background light in the light propagation space on measurement results is extremely well suppressed, resulting in high reliability. Measurement results can be stably obtained, and measurement errors caused by changes in environmental temperature at the installation position of the Pockels element can be effectively suppressed with a simple configuration. According to the apparatus of the present invention, these methods can be suitably implemented.

[Brief explanation of drawings]

FIG. 1 and FIG. 2 are system diagrams each showing an example of a photoelectric external measuring device according to the present invention. 10: Sensor head section 12: Pockels element 13: Retarder 14: Polarizer 16: Analyzer 22, 26: Optical fiber 24: Light emitting section 28: Light receiving section 30: Same angular frequency component detector 32: Double angular frequency component detector 34: Divider

Claims (4)

[Claims] (1) A light emitting section is attached to a sensor section configured such that a polarizer and an analyzer are arranged in series before and after the light transmission direction of the Pockels element, and the transmitted light is modulated by the electric field acting on the Pockels element. A light receiving section that outputs a signal corresponding to the received light transmits the light emitted from the sensor section, and receives the transmitted light that has passed through the sensor section, and acts on the Pockels element from the output signal of the light receiving section. Extract the signal component (Eω) with the same angular frequency as the alternating current electric field and the signal component (E_2ω) with twice the angular frequency, find their relative ratio,
A method for measuring an optical electric field, which comprises determining an alternating current electric field acting on the Pockels element or an alternating current voltage that generates the alternating electric field from the relative ratio thereof. (2) Claim (1) wherein the sensor section is a retarder that provides an optical bias: ψ that satisfies the following formula and is provided in series with the Pockels element between the polarizer and the analyzer. ) optical electric field measurement method described. Vπ_0・d(1/Vπ)/dT・sin2ψ_0−2
dψ/dT≦1×10^-^4 However, Vπ: Half-wave voltage of Pockels element Vπ_0: Half-wave voltage of Pockels element at room temperature d(1/Vπ)/dT: Temperature change rate of half-wave voltage ψ_0: Optical bias dψ/dT at room temperature due to phase shifter: Temperature change rate of optical bias (3) including a Pockels element, a polarizer and an analyzer arranged in series in front and behind the light transmission direction of the Pockels element,
a sensor section configured such that transmitted light is modulated by an electric field acting on the Pockels element; a light emitting section that emits light to be transmitted to the sensor section; and a light emitting section that receives the transmitted light that has passed through the sensor section. a light receiving section that outputs a signal corresponding to the received light, and a first extraction means that extracts a signal component (Eω) having the same angular frequency as the alternating current electric field acting on the Pockels element from the output signal of the light receiving section. , a second extraction means for extracting a signal component (E_2ω) having an angular frequency twice that of the alternating current electric field acting on the Pockels element from the output signal of the light receiving section; An optical electric field measuring device comprising: relative ratio detection means for determining the relative ratio of signal components. (4) Claim (3) wherein the sensor unit includes a retarder in series with the Pockels element that provides an optical bias: ψ that satisfies the following equation between the polarizer and the analyzer. The optical electric field measuring device described. Vπ_・d(1/Vπ)/dT・sin2ψ_0−2d
ψ/dT≦1×10^-^4 However, Vπ: Half-wave voltage of Pockels element Vπ_0: Half-wave voltage of Pockels element at room temperature d(1/Vπ)/dT: Temperature change rate of half-wave voltage ψ_0: Optical bias dψ/dT at room temperature due to phase shifter: Temperature change rate of optical bias