Electric Field Sensor

Abstract

To provide an electric field sensor that achieves a simplified device configuration without reducing measurement accuracy.SOLUTION: The electric field sensor includes a first light source for emitting light including a first wavelength, a second light source for emitting light including a second wavelength different from the first wavelength, an electro-optic crystal to which an electric field to be measured is applied and into which the light emitted from the first and second light sources is input, a detection unit for detecting an amount of phase change of the light of the first and second wavelengths through the electro-optic crystal, and a signal processing device for obtaining an electric field to be measured from amounts of phase changes of the light of the first and second wavelengths detected in the detection unit using calibration curves showing the relationship between the electric field applied to the electro-optic crystal and the ambient temperature and the amounts of phase changes of the light of the first and second wavelengths via the electro-optic crystal.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an electric field sensor. [Background technology]

[0002] Conventionally, electric field sensors using the electro-optic effect have been used. The electro-optic effect is an effect in which, when an electric field is applied to an electro-optic crystal, the refractive index of the electro-optic crystal changes depending on the electric field strength. The change in refractive index causes a phase change in the light wave passing through the electro-optic crystal. An electric field sensor measures the electric field applied to the electro-optic crystal by measuring the change in phase (see, for example, Patent Document 1).

[0003] Because the characteristics of electro-optic crystals change significantly with temperature, the accuracy of measuring an electric field is easily reduced by the ambient temperature. For this reason, there are techniques for correcting measured values ​​according to the ambient temperature (see, for example, Patent Documents 2 and 3). The technique described in Patent Document 2 detects the ambient temperature using a thermometer and corrects the measured value based on the detected value. The technique described in Patent Document 3 calculates the temperature based on the resonant wavelength obtained using a resonator structure and a spectrum analyzer, and corrects the measured value using the calculated value. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2020-118498 [Patent Document 2] Patent No. 4851000 [Patent Document 3] Japanese Patent Application Laid-Open No. 2008-216035 Summary of the Invention [Problem to be solved by the invention]

[0005] However, an electric field sensor that corrects the measurement value requires a device for measuring temperature, which makes the device configuration complicated.

[0006] An object of one aspect of the present invention is to provide an electric field sensor that can simplify the device configuration without reducing measurement accuracy. [Means for solving the problem]

[0007] In order to achieve the above object, an electric field sensor (100, 200, 300, 400) according to one embodiment of the present invention is an electric field sensor that measures an electric field to be measured by utilizing an electro-optic effect, and includes: a first light source (first laser light source 101) that emits light including a first wavelength; a second light source (second laser light source 103) that emits light including a second wavelength different from the first wavelength; an electro-optic crystal (106) to which the electric field to be measured is applied and into which the light emitted from the first and second light sources is incident; a detection unit (120, 220, 320) that detects the amount of phase change of the light of the first and second wavelengths that passes through the electro-optic crystal; and a signal processing device (123, 323) that determines the electric field to be measured from the amount of phase change of the light of the first and second wavelengths detected by the detection unit using a calibration curve that shows the relationship between the electric field applied to the electro-optic crystal, the ambient temperature, and the amount of phase change of the light of the first and second wavelengths that passes through the electro-optic crystal.

[0008] In an electric field sensor according to one embodiment of the present invention, the signal processing device may use as the calibration curves a first calibration curve showing the relationship between the electric field applied to the electro-optic crystal, the ambient temperature, and the amount of phase change of light of the first wavelength passing through the electro-optic crystal, and a second calibration curve showing the relationship between the electric field applied to the electro-optic crystal, the ambient temperature, and the amount of phase change of light of the second wavelength passing through the electro-optic crystal.

[0009] In an electric field sensor according to one embodiment of the present invention, the detection unit may include a separation optical system (125, 225) that separates the light that has passed through the electro-optic crystal into light of the first wavelength and light of the second wavelength; a first detection unit (126) that separates the light of the first wavelength separated by the separation optical system into two lights with different polarization states and detects the amount of phase change of the light of the first wavelength from the amplitude ratio of the separated lights; and a second detection unit (127) that separates the light of the second wavelength separated by the separation optical system into two lights with different polarization states and detects the amount of phase change of the light of the second wavelength from the amplitude ratio of the separated lights.

[0010] In an electric field sensor according to one embodiment of the present invention, the separation optical system may include a first filter (108) that selectively transmits light of the first wavelength from light that has passed through the electro-optic crystal, and a second filter (113) that selectively transmits light of the second wavelength from light that has passed through the electro-optic crystal.

[0011] In the electric field sensor according to one aspect of the present invention, the separation optical system may include a wavelength separation element (207) that separates the light that passes through the electro-optic crystal into light of the first wavelength and light of the second wavelength.

[0012] In the electric field sensor according to one aspect of the present invention, the first detection unit includes a first polarization separation element (110) that separates the light of the first wavelength separated by the separation optical system into two lights with different polarization states, a first light receiving element (111) that receives one of the lights separated by the first polarization separation element and outputs a first received light signal, a second light receiving element (112) that receives the other light separated by the first polarization separation element and outputs a second received light signal, and a first calculator (121) that calculates a difference between the first received light signal and the second received light signal. ), and the second detection unit may include a second polarization separation element (115) that separates the light of the second wavelength separated by the separation optical system into two lights with different polarization states, a third light receiving element (116) that receives one of the lights separated by the second polarization separation element and outputs a third light receiving signal, a fourth light receiving element (117) that receives the other light separated by the second polarization separation element and outputs a fourth light receiving signal, and a second calculator (122) that calculates the difference between the third light receiving signal and the fourth light receiving signal.

[0013] The electric field sensor according to one aspect of the present invention further includes a first modulator (301) that modulates the light of the first wavelength at a first frequency, and a second modulator (302) that modulates the light of the second wavelength at a second frequency, and the detection unit includes a polarization separation element (304) that separates the light that has passed through the electro-optic crystal into two lights with different polarization states, a first light receiving element (305) that receives one of the lights separated by the polarization separation element and outputs a first received light signal, a first lock-in amplifier (307) that performs lock-in detection on the first received light signal using the first frequency to obtain a first signal, and a second lock-in amplifier (308) that performs lock-in detection on the first received light signal using the second frequency. a second lock-in amplifier (308) that performs lock-in detection on the second light received signal using the first frequency to obtain a second signal, a second light receiving element (306) that receives the other light separated by the polarization separation element and outputs a second received light signal, a third lock-in amplifier (309) that performs lock-in detection on the second received light signal using the first frequency to obtain a third signal, a fourth lock-in amplifier (310) that performs lock-in detection on the second received light signal using the second frequency to obtain a fourth signal, a first calculator (321) that calculates the difference between the first signal and the third signal, and a second calculator (322) that calculates the difference between the second signal and the fourth signal. [Effects of the Invention]

[0014] According to one aspect of the present invention, it is possible to provide an electric field sensor that can simplify the device configuration without reducing measurement accuracy. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a diagram illustrating a configuration example of an electric field sensor according to a first embodiment. [Figure 2] FIG. 4 is a diagram illustrating an example of wavelength transmission characteristics of a first filter. [Figure 3] FIG. 10 is a diagram illustrating another example of the wavelength transmission characteristics of the first filter. [Figure 4] FIG. 10 is a diagram illustrating an example of wavelength transmission characteristics of a second filter. [Figure 5] FIG. 10 is a diagram illustrating another example of the wavelength transmission characteristics of the second filter. [Figure 6]FIG. 1 is a diagram showing a step flow of a calibration method. [Figure 7] FIG. 10 is a diagram illustrating a configuration example of an electric field sensor according to a second embodiment. [Figure 8] FIG. 10 is a diagram illustrating a configuration example of an electric field sensor according to a third embodiment. [Figure 9] FIG. 10 is a diagram illustrating a configuration example of an electric field sensor according to a fourth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, electric field sensors according to embodiments of the present invention will be described in detail with reference to the drawings. First, an overview of the embodiments of the present invention will be described, and then the details of the embodiments of the present invention will be described.

[0017] 〔overview〕 The present invention simplifies the device configuration without reducing measurement accuracy, specifically, it is possible to suppress fluctuations in the measured electric field value due to fluctuations in ambient temperature without complicating the device configuration.

[0018] The above-mentioned Patent Document 1 discloses an example of an electric field sensor that utilizes the electro-optic effect (EO effect). This electric field sensor measures the electric field to be measured applied to an electro-optic crystal by detecting the amount of phase change of light that passes through the electro-optic crystal to which the electric field to be measured is applied. Such an electric field sensor has the characteristics of a wide bandwidth, low disturbance, and high speed.

[0019] However, because electro-optic crystals have a large temperature characteristic, the measurement value fluctuates with fluctuations in the ambient temperature. Therefore, when the measurement value of an electric field sensor fluctuates, it is not possible to distinguish whether the fluctuation is due to the change in the electric field to be measured applied to the electro-optic crystal or the change in the ambient temperature, resulting in a deterioration in measurement accuracy. To prevent this deterioration in measurement accuracy, the temperature characteristic of the electro-optic crystal is corrected.

[0020] The above-mentioned Patent Document 2 proposes a method of simultaneously measuring the ambient temperature using a thermometer and correcting the measurement value. However, this method requires a separate thermometer, which makes the sensor configuration complicated. Also, the above-mentioned Patent Document 3 proposes a method of calculating the temperature by measuring the resonant wavelength using a resonator structure and a spectrum analyzer. However, this method requires a separate resonator structure and the like, which makes the configuration complicated.

[0021] In an embodiment of the present invention, two lights with different wavelengths (light including a first wavelength and light including a second wavelength) are incident on an electro-optic crystal to which an electric field to be measured is applied, and the amount of phase change of the light of the first and second wavelengths that passes through the electro-optic crystal is detected. Then, using a calibration curve that shows the relationship between the electric field applied to the electro-optic crystal, the ambient temperature, and the amount of phase change of the light of the first and second wavelengths that passes through the electro-optic crystal, the electric field to be measured is calculated from the detected amount of phase change of the light of the first and second wavelengths. This makes it possible to eliminate the influence of ambient temperature without measuring the ambient temperature, thereby simplifying the device configuration without reducing measurement accuracy.

[0022] First Embodiment [Electric field sensor] 1 is a diagram showing an example of the configuration of an electric field sensor 100 according to the first embodiment. As shown in Fig. 1, the electric field sensor 100 includes a first laser light source 101 (first light source), a first λ / 4 wave plate 102, a second laser light source 103 (second light source), a second λ / 4 wave plate 104, a wavelength mixer 105, an electro-optic crystal 106, a detection unit 120, and a signal processing device 123.

[0023] The detection unit 120 includes a separation optical system 125 , a first detection unit 126 , and a second detection unit 127 . The separation optical system 125 includes a beam splitter 107 (separation unit), a first filter 108, a first λ / 2 wave plate 109, a second filter 113, and a second λ / 2 wave plate 114. The first detection unit 126 includes a first polarization separation element 110, a first light receiving element 111 (first light receiving unit), a second light receiving element 112 (second light receiving unit), and a first amplifier 121 (first computing unit). The second detection unit 127 includes a second polarization separation element 115, a third light receiving element 116 (third light receiving unit), a fourth light receiving element 117 (fourth light receiving unit), and a second amplifier 122 (second computing unit).

[0024] The arrangement of the optical components of the electric field sensor 100 will be described. The first λ / 4 wave plate 102 is disposed between the first laser light source 101 and the wavelength mixer 105. The second λ / 4 wave plate 104 is disposed between the second laser light source 103 and the wavelength mixer 105. The wavelength mixer 105 is disposed between the first λ / 4 wave plate 102 and the electro-optic crystal 106, and between the second λ / 4 wave plate 104 and the electro-optic crystal 106. The electro-optic crystal 106 is disposed between the wavelength mixer 105 and the beam splitter 107. The beam splitter 107 is disposed between the electro-optic crystal 106 and the first filter 108, and between the electro-optic crystal 106 and the second filter 113. The first filter 108 is disposed between the beam splitter 107 and the first λ / 2 wave plate 109. The first λ / 2 wave plate 109 is disposed between the first filter 108 and the first polarization separation element 110. The second filter 113 is disposed between the beam splitter 107 and the second λ / 2 wave plate 114. The second λ / 2 wave plate 114 is disposed between the second filter 113 and the second polarization separation element 115.

[0025] The connection relationships of the electrical components of the electric field sensor 100 will be described. The output terminal of the first light receiving element 111 is connected to a first input terminal of a first amplifier 121. The output terminal of the second light receiving element 112 is connected to a second input terminal of the first amplifier 121. The output terminal of the first amplifier 121 is connected to a signal processing device 123. The output terminal of the third light receiving element 116 is connected to a first input terminal of a second amplifier 122. The output terminal of the fourth light receiving element 117 is connected to a second input terminal of the second amplifier 122. The output terminal of the second amplifier 122 is connected to the signal processing device 123.

[0026] The first laser light source 101 and the second laser light source 103 include, for example, semiconductor lasers. The first laser light source 101 and the second laser light source 103 are driven by a laser driver (not shown) to emit light.

[0027] Fig. 2 is a diagram showing an example of the wavelength transmission characteristics of the first filter 108. Fig. 3 is a diagram showing another example of the wavelength transmission characteristics of the first filter 108. As shown in Figs. 2 and 3, the light from the first laser light source 101 has a spectrum S1 whose peak value is at a wavelength λ1 (first wavelength). The light from the second laser light source 103 has a spectrum S2 whose peak value is at a wavelength λ2 (second wavelength) that is greater than the wavelength λ1.

[0028] 2 and 3, the transmission wavelength ranges R11 and R12 of the first filter 108 include the wavelength λ1 but do not include the wavelength λ2. Therefore, most of the light beam from the first laser light source 101 can pass through the first filter 108, but almost no light beam from the second laser light source 103 can pass through the first filter 108.

[0029] The transmission wavelength range R11 of the first filter 108 shown in Fig. 2 is set to a wide range that includes a low wavelength range. The first filter 108 is, for example, a short-pass filter. The transmission wavelength range R12 of the first filter 108 shown in Fig. 3 is set to a narrow range with a wavelength λ1 as a center value. The first filter 108 is, for example, a band-pass filter.

[0030] Fig. 4 is a diagram showing an example of the wavelength transmission characteristics of second filter 113. Fig. 5 is a diagram showing another example of the wavelength transmission characteristics of second filter 113. 4 and 5, the transmission wavelength ranges R21 and R22 of the second filter 113 do not include the wavelength λ1 but include the wavelength λ2. Therefore, most of the light from the first laser light source 101 cannot pass through the second filter 113, but most of the light from the second laser light source 103 can pass through the second filter 113.

[0031] The transmission wavelength range R21 of the second filter 113 shown in Fig. 4 is set to a wide range that includes a long wavelength range. The second filter 113 is, for example, a long-pass filter. The transmission wavelength range R22 of the second filter 113 shown in Fig. 5 is set to a narrow range with the wavelength λ2 as the center value. The second filter 113 is, for example, a band-pass filter.

[0032] The first filter 108 may employ the wavelength transmission characteristics shown in Fig. 2 or may employ the wavelength transmission characteristics shown in Fig. 3. The second filter 113 may employ the wavelength transmission characteristics shown in Fig. 4 or may employ the wavelength transmission characteristics shown in Fig. 5.

[0033] As shown in FIG. 1, the wavelength mixer 105 may be a WDM filter, a dichroic mirror, or the like. The electro-optic crystal 106 is, for example, LiNbO3, LiTaO3, Bi 12 SiO 20 (BSO), Bi 12 GeO 20 (BGO), ADP, KDP, etc. The optical axis of the first λ / 2 wave plate 109 is arranged at an angle that allows the first polarization separation element 110 to separate the light beam into P waves and S waves. The optical axis of the second λ / 2 wave plate 114 is arranged at an angle that allows the second polarization separation element 115 to separate the light beam into P waves and S waves.

[0034] The signal processing device 123 includes, for example, a processing unit and a storage unit. The processing unit includes a calculation unit and a control unit. The control unit controls the start and end of electric field generation by the electric field generation source 130, the electric field strength, etc.

[0035] [Electric field measurement method] Next, a method for measuring an electric field using the electric field sensor 100 will be described. Electric field sensors have temperature characteristics, so their measured values ​​fluctuate with changes in ambient temperature. The temperature coefficient varies depending on the wavelength of the detection light used for measurement. The input / output characteristics also change depending on the wavelength of the detection light used for measurement.

[0036] The electric field sensor 100 can acquire signals for each of the wavelengths λ1 and λ2 independently. Therefore, by calculating each signal, it is possible to distinguish between fluctuations in the output value due to temperature characteristics and fluctuations in the output value due to changes in the input value, thereby achieving highly accurate measurements.

[0037] (Creating a calibration curve) Fig. 6 shows a step flow of a method for calibrating input / output characteristics and temperature characteristics. As shown in Fig. 6, after checking whether calibration has been completed (step S1), if calibration has not been completed, a calibration curve is created as follows.

[0038] 1, to create a calibration curve, for example, electric field generation source 130, temperature adjustment device 131, and sensor 132 are used. Electric field generation source 130 generates an electric field and can apply an arbitrary input signal to electro-optic crystal 106. Sensor 132 detects a signal due to the electric field applied to electro-optic crystal 106. Temperature adjustment device 131 can set the ambient temperature of electro-optic crystal 106 as desired.

[0039] The calibration curve uses the signal amplitude of the input signal to electro-optic crystal 106 and the ambient temperature as explanatory variables, and the signal amplitude of the output signal from amplifiers 121 and 122 as a target variable. The amount of phase change of light passing through electro-optic crystal 106 can be detected as the signal amplitude of the output signal. The signal amplitude of the input signal is referred to as the "input signal amplitude." The signal amplitude of the output signal is referred to as the "output signal amplitude."

[0040] The calculation unit calculates the output signal amplitude V as follows: out A loop process is performed to repeatedly obtain the above (steps S2 to S6). For an input signal of wavelength λ1, at ambient temperature T1, sample 1 (input signal amplitude V in1 ), Sample 2 (input signal amplitude V in2 ), sample n (input signal amplitude V inn ) output signal amplitude V out Similarly, at ambient temperature T2, sample 1 (input signal amplitude V in1 ), Sample 2 (input signal amplitude V in2 ), sample n (input signal amplitude V inn ) output signal amplitude V out Similarly, calculate the ambient temperature T m In sample 1 (input signal amplitude V in1 ), Sample 2 (input signal amplitude V in2 ), sample n (input signal amplitude V inn ) output signal amplitude V out Ask for.

[0041] n is an integer of 2 or more. m is an integer of 2 or more. n and m may be any numbers of 2 or more, but the larger the numbers, the higher the measurement accuracy. Signal amplitude V in1 ~V inn are different from each other. Ambient temperatures T1 to T m are different from each other.

[0042] In this way, for an input signal of wavelength λ1, n input signal amplitudes V in and for m ambient temperatures T, the output signal amplitude V out That is, V of n patternsin and m patterns of T for V out This will determine the input signal amplitude V in and the ambient temperature T, the n × m output signal amplitude V out Get.

[0043] For the input signal of wavelength λ2, n input signal amplitudes V in and for m ambient temperatures T, the output signal amplitude V out That is, V of n patterns in and m patterns of T for V out This will determine the input signal amplitude V in and the ambient temperature T, the n × m output signal amplitude V out Get.

[0044] An n×m table is created for the input signal of wavelength λ1 and stored in the storage unit.An n×m table is also created for the input signal of wavelength λ2 and stored in the storage unit (step S7).

[0045] The calculation unit uses the above-mentioned table to create a calibration curve (first calibration curve) shown in the following equation (1) for the input signal of wavelength λ1 (step S8). out1 is the output signal amplitude for wavelength λ1. V out1 =f(V in ,T) (1) This calibration curve shows the relationship between the electric field applied to electro-optic crystal 106, the ambient temperature, and the amount of phase change of light passing through electro-optic crystal 106 for wavelength λ1.

[0046] The calculation unit uses the above-mentioned table to create a calibration curve (second calibration curve) shown in the following equation (2) for the input signal of wavelength λ2 (step S8). out2 is the output signal amplitude for wavelength λ2. V out2 =g(V in ,T) (2) This calibration curve shows the relationship between the electric field applied to electro-optic crystal 106, the ambient temperature, and the amount of phase change of light passing through electro-optic crystal 106 for wavelength λ2.

[0047] These calibration curves can be created as needed using linear approximation, polynomial approximation, etc. The calculation unit stores the calibration curves in the storage unit.

[0048] (Light incidence on electro-optic crystal) The first laser light source 101 emits light having a peak value at wavelength λ1 (first wavelength). The second laser light source 103 emits light having a peak value at wavelength λ2 (second wavelength) that is greater than wavelength λ1 (see FIGS. 2 to 5).

[0049] First λ / 4 wave plate 102 circularly polarizes the light beam incident from first laser light source 101 and outputs it. Second λ / 4 wave plate 104 circularly polarizes the light beam incident from second laser light source 103 and outputs it. It can be said that first λ / 4 wave plate 102 and second λ / 4 wave plate 104 optically bias the light incident on electro-optic crystal 106.

[0050] The light beam that has passed through the first λ / 4 wave plate 102 and the light beam that has passed through the second λ / 4 wave plate 104 are made incident on the wavelength mixer 105. These light beams are combined in the wavelength mixer 105 to become one circularly polarized light beam.

[0051] Electro-optic crystal 106 changes the polarization state due to a change in birefringence that corresponds to the strength of the applied electric field. The circularly polarized light beam from wavelength mixer 105 is modulated by the electric field in electro-optic crystal 106. As a result, the light beam emerges from electro-optic crystal 106 as an elliptically polarized light beam with an ellipticity that corresponds to the strength of the electric field.

[0052] (Detection of phase change amount) The light beam that passes through electro-optic crystal 106 is split into two by beam splitter 107. The first of the two light beams is incident on first filter 108 (see FIGS. 2 and 3). First filter 108 selectively transmits light beams in the wavelength range (peak wavelength λ1) of first laser light source 101.

[0053] The light beam (light with wavelength λ1) that has passed through the first filter 108 passes through a first λ / 2 wave plate 109 and enters a first polarization separation element 110. The first polarization separation element 110 separates the light beam into two lights with different polarization states (more specifically, P waves and S waves).

[0054] The first light receiving element 111 receives the P wave (one light) incident from the first polarization separation element 110, converts it into an electrical signal, and outputs the converted electrical signal of the P wave component (first received light signal) to a first input terminal of the first amplifier 121. The second light receiving element 112 receives the S wave (the other light) incident from the first polarization separation element 110, converts it into an electrical signal, and outputs the converted electrical signal of the S wave component (second received light signal) to a second input terminal of the first amplifier 121.

[0055] The first amplifier 121 amplifies the electrical signals of the P wave component and the S wave component and outputs them to the signal processing device 123. The output signal from the first amplifier 121 is a signal (output signal of wavelength λ1) in the wavelength range (peak wavelength λ1) of the first laser light source 101. The first amplifier 121 calculates the difference between the first received light signal and the second received light signal. The first amplifier 121 can detect the amount of phase change in the light of wavelength λ1 from the amplitude ratio between the P wave and the S wave based on the first received light signal and the second received light signal.

[0056] The second of the two beams split by the beam splitter 107 is incident on the second filter 113 (see FIGS. 4 and 5). The second filter 113 selectively transmits the beam in the wavelength range (peak wavelength λ2) of the second laser light source 103.

[0057] The light beam (light with wavelength λ2) that has passed through the second filter 113 passes through the second λ / 2 wave plate 114 and enters the second polarization separation element 115. The second polarization separation element 115 separates the light beam into two lights with different polarization states (more specifically, P waves and S waves).

[0058] The third light receiving element 116 converts the P wave incident from the second polarization separation element 115 into an electric signal and outputs the converted electric signal of the P wave component (third received light signal) to a first input terminal of the second amplifier 122. The fourth light receiving element 117 converts the S wave incident from the second polarization separation element 115 into an electric signal and outputs the converted electric signal of the S wave component (fourth received light signal) to a second input terminal of the second amplifier 122.

[0059] The second amplifier 122 amplifies the electrical signals of the P wave component and the S wave component and outputs them to the signal processing device 123. The output signal from the second amplifier 122 is a signal (output signal of wavelength λ2) in the wavelength range (peak wavelength λ2) of the second laser light source 103. The second amplifier 122 finds the difference between the third received light signal and the fourth received light signal. The second amplifier 122 can detect the amount of phase change in the light of wavelength λ2 from the amplitude ratio between the P wave and the S wave based on the third received light signal and the fourth received light signal.

[0060] (Measurement of the electric field to be measured) Measurement value when the ambient temperature T is unknown (output signal amplitude V out1 ,V out2 ) is obtained (step S9). out1 ,V out2 are substituted into equations (1) and (2) to obtain the following equations (3) and (4) (step S10). V in =f'(T) (3) V in = g'(T) (4)

[0061] Equations (3) and (4) are expressed in terms of two unknowns (input signal amplitude V in and ambient temperature T), the input signal amplitude V inIn this way, the input signal amplitude can be determined from the measured value (output signal amplitude). This completes the measurement (step S11). In electric field sensor 100, the electric field (electric field to be measured) applied to electro-optic crystal 106 can be determined based on the calculated input signal amplitude.

[0062] [Effects of the electric field sensor according to the embodiment] The electric field sensor 100 is equipped with a signal processing device 123 that calculates the amplitude of the input signal from the measured value using a calibration curve, enabling highly accurate measurements. This makes it possible to prevent a decrease in measurement accuracy. Furthermore, the electric field sensor 100 can determine the amplitude of the input signal without measuring the ambient temperature T, eliminating the need for a device for measuring temperature. This simplifies the device configuration of the electric field sensor 100.

[0063] The electric field sensor 100 uses a first calibration curve relating to the phase of light of wavelength λ1 and a second calibration curve relating to the phase of light of wavelength λ2, and therefore can improve the accuracy of measuring the light of wavelengths λ1 and λ2.

[0064] Electric field sensor 100 separates light that has passed through electro-optic crystal 106 into light of wavelength λ1 and light of wavelength λ2 using separation optical system 125. The separated light of wavelengths λ1 and λ2 are then separated into P waves and S waves by first detection unit 126 and second detection unit 127, respectively, and the amount of phase change is detected from the amplitude ratio of the separated light. This allows the amount of phase change to be measured with high accuracy.

[0065] The electric field sensor 100 uses a first filter 108 (see Figures 2 and 3) that selectively transmits light of wavelength λ1 and a second filter 113 (see Figures 4 and 5) that selectively transmits light of wavelength λ2, so that light of the target wavelengths (wavelength λ1 and wavelength λ2) can be obtained with high accuracy.

[0066] The electric field sensor 100 obtains the difference between the first and second received light signals in the first amplifier 121, and obtains the difference between the third and fourth received light signals in the second amplifier 122. This makes it possible to accurately detect the amount of phase change in light of each wavelength from the amplitude ratio between two lights (P waves and S waves) with different polarization states.

[0067] Second Embodiment [Electric field sensor] 7 is a diagram showing an example of the configuration of an electric field sensor 200 according to the second embodiment. Components common to other embodiments are given the same reference numerals and descriptions thereof will be omitted.

[0068] As shown in FIG. 7, the electric field sensor 200 differs from the electric field sensor 100 shown in FIG. The detection unit 220 includes a separation optical system 225 , a first detection unit 126 , and a second detection unit 127 . The separation optical system 225 includes a wavelength separation element 207 and a second λ / 2 wave plate 114. The wavelength separation element 207 is, for example, a dichroic mirror.

[0069] [Electric field measurement method] Next, a method for measuring an electric field using the electric field sensor 200 will be described.

[0070] (Light incidence on electro-optic crystal) A light beam from first laser light source 101 is incident on wavelength mixer 105 via first λ / 4 wave plate 102. A light beam from second laser light source 103 is incident on wavelength mixer 105 via second λ / 4 wave plate 104. These light beams are combined in wavelength mixer 105 and incident on electro-optic crystal 106.

[0071] (Detection of phase change amount) The light beam that has passed through electro-optic crystal 106 is incident on wavelength separation element 207. Wavelength separation element 207 separates the light beam into a light beam in the wavelength range of first laser light source 101 (peak wavelength λ1) and a light beam in the wavelength range of second laser light source 103 (peak wavelength λ2).

[0072] The light with wavelength λ1 obtained by wavelength separation element 207 passes through first λ / 2 wave plate 109 and enters first polarization separation element 110. First polarization separation element 110 separates the light beam into two lights with different polarization states (more specifically, P waves and S waves). The first light receiving element 111 receives the P wave (one light) incident from the first polarization separation element 110, converts it into an electrical signal, and outputs the converted electrical signal of the P wave component (first received light signal) to a first input terminal of the first amplifier 121. The second light receiving element 112 receives the S wave (the other light) incident from the first polarization separation element 110, converts it into an electrical signal, and outputs the converted electrical signal of the S wave component (second received light signal) to a second input terminal of the first amplifier 121. The first amplifier 121 amplifies the electrical signals of the P wave component and the S wave component and outputs them to the signal processing device 123. The first amplifier 121 calculates the difference between the first and second received light signals. Based on the first and second received light signals, the first amplifier 121 can detect the amount of phase change in the light of wavelength λ1 from the amplitude ratio between the P wave and the S wave.

[0073] The light with wavelength λ2 obtained by wavelength separation element 207 passes through second λ / 2 wave plate 114 and enters second polarization separation element 115. Second polarization separation element 115 separates the light beam into two lights with different polarization states (more specifically, P waves and S waves). The third light receiving element 116 converts the P wave incident from the second polarization separation element 115 into an electric signal and outputs the converted electric signal of the P wave component to a first input terminal of the second amplifier 122. The fourth light receiving element 117 converts the S wave incident from the second polarization separation element 115 into an electric signal and outputs the converted electric signal of the S wave component to a second input terminal of the second amplifier 122. The second amplifier 122 amplifies the electrical signals of the P wave component and the S wave component and outputs them to the signal processing device 123. The second amplifier 122 calculates the difference between the third and fourth received light signals. Based on the third and fourth received light signals, the second amplifier 122 can detect the amount of phase change in the light of wavelength λ2 from the amplitude ratio between the P wave and the S wave.

[0074] The measurement of the electric field to be measured is the same as in the first embodiment.

[0075] [Effects of the electric field sensor according to the embodiment] Electric field sensor 200 is equipped with signal processing device 123 that calculates the amplitude of the input signal from the measured value using a calibration curve, allowing for highly accurate measurements. This makes it possible to prevent a decrease in measurement accuracy. Furthermore, since the amplitude of the input signal can be determined without measuring the ambient temperature T, there is no need to use equipment for temperature measurement. This simplifies the device configuration of electric field sensor 200.

[0076] In the electric field sensor 200, the wavelength separation element 207 is used, so that light of the target wavelengths (wavelength λ1 and wavelength λ2) can be obtained with high precision.

[0077] <Third embodiment> [Electric field sensor] 8 is a diagram showing an example of the configuration of an electric field sensor 300 according to the third embodiment. Components common to other embodiments are given the same reference numerals and descriptions thereof will be omitted.

[0078] As shown in FIG. 8, the electric field sensor 300 includes a first modulator 301, a first laser light source 101 (first light source), a first λ / 4 wave plate 102, a second modulator 302, a second laser light source 103 (second light source), a second λ / 4 wave plate 104, a wavelength mixer 105, an electro-optic crystal 106, a detection unit 320, a first lock-in amplifier 307, a second lock-in amplifier 308, a third lock-in amplifier 309, a fourth lock-in amplifier 310, a first amplifier 321 (first computing unit), a second amplifier 322 (second computing unit), and a signal processing unit 323.

[0079] The detection section 320 includes a λ / 2 wave plate 303, a polarization separation element 304, a first light receiving element 305 (first light receiving section), and a second light receiving element 306 (second light receiving section).

[0080] The first modulator 301 modulates the light from the first laser light source 101 to a first frequency f1. The second modulator 302 modulates the light from the second laser light source 103 to a second frequency f2. The second frequency f2 is different from the first frequency f1.

[0081] [Electric field measurement method] Next, a method for measuring an electric field using the electric field sensor 300 will be described.

[0082] (Light incidence on electro-optic crystal) A light beam from first laser light source 101 is incident on wavelength mixer 105 via first λ / 4 wave plate 102. A light beam from second laser light source 103 is incident on wavelength mixer 105 via second λ / 4 wave plate 104. These light beams are combined in wavelength mixer 105 and incident on electro-optic crystal 106.

[0083] (Detection of phase change amount) The light beam that has passed through electro-optic crystal 106 passes through λ / 2 wave plate 303 and enters polarization separation element 304. Polarization separation element 304 separates the light beam into two lights with different polarization states (specifically, P wave and S wave). The first light receiving element 305 converts the P wave incident from the polarization separation element 304 into an electrical signal, and outputs the converted electrical signal of the P wave component (first received light signal) to the first lock-in amplifier 307 and the second lock-in amplifier 308. The second light receiving element 306 converts the S wave incident from the polarization separation element 304 into an electrical signal, and outputs the converted electrical signal of the S wave component (second light receiving signal) to the third lock-in amplifier 309 and the fourth lock-in amplifier 310.

[0084] The first lock-in amplifier 307 obtains a first signal by locking in and detecting the first received light signal using a first frequency f1 based on the signal from the first modulator 301. The second lock-in amplifier 308 obtains a second signal by locking in and detecting the second received light signal using a second frequency f2 based on the signal from the second modulator 302.

[0085] The third lock-in amplifier 309 obtains a third signal by locking in and detecting the third received light signal using the first frequency f1 based on the signal from the first modulator 301. The fourth lock-in amplifier 310 obtains a fourth signal by locking in and detecting the fourth received light signal using the second frequency f2 based on the signal from the second modulator 302.

[0086] The first amplifier 321 determines the difference between the first and third received light signals. The first amplifier 321 can detect the amount of phase change in the light of wavelength λ1 based on the first and third received light signals. The second amplifier 322 determines the difference between the second and fourth received light signals. The second amplifier 322 can detect the amount of phase change in the light of wavelength λ2 based on the second and fourth received light signals.

[0087] The measurement of the electric field to be measured is the same as in the first embodiment.

[0088] [Effects of the electric field sensor according to the embodiment] Electric field sensor 300 is equipped with signal processing device 323 that calculates the amplitude of the input signal from the measured value using a calibration curve, enabling highly accurate measurements. This makes it possible to prevent a decrease in measurement accuracy. Furthermore, since the amplitude of the input signal can be determined without measuring the ambient temperature T, there is no need to use equipment for temperature measurement. This simplifies the device configuration of electric field sensor 300.

[0089] When detecting the amount of phase change of light, the electric field sensor 300 can detect P-wave and S-wave signals without wavelength separation using a filter, a wavelength separation element (dichroic mirror), etc. This has the advantage that the wavelength of the target light can be selected arbitrarily without being restricted by the wavelength separation performance of a filter, etc.

[0090] <Fourth embodiment> 9 is a diagram showing an example of the configuration of an electric field sensor 400 according to the fourth embodiment. Components common to other embodiments are given the same reference numerals and descriptions thereof will be omitted. 9, electric field sensor 400 shows the configuration of electro-optic crystal 106 and its preceding stage. Electric field sensor 400 differs from electric field sensor 100 shown in FIG. 1 in that it does not include first λ / 4 wave plate 102 and second λ / 4 wave plate 104. Other configurations may be similar to those of electric field sensor 100 shown in FIG. 1.

[0091] In the first embodiment, the light beams from the laser light sources 101 and 103 are converted into circularly polarized light by the λ / 4 wave plates 102 and 104 (see FIG. 1), but electric field measurement without using the λ / 4 wave plates 102 and 104 is also possible. 9, light beams from laser light sources 101 and 103 are incident as linearly polarized light on electro-optic crystal 106. Electric field sensor 400 does not include λ / 4 wave plates 102 and 104, and therefore the device configuration can be simplified.

[0092] Although the present invention has been described above using embodiments, the present invention is not limited to these embodiments, and various modifications and substitutions can be made without departing from the spirit of the present invention. For example, in the electric field sensor 100 shown in Fig. 1, the electric field to be measured is determined from the amount of phase change using two calibration curves for light of two wavelengths, but the number of wavelengths used and the number of calibration curves may be any number equal to or greater than two. [Explanation of symbols]

[0093] 100, 200, 300, 400... electric field sensor, 101... first laser light source (first light source), 103... second laser light source (second light source), 106... electro-optic crystal, 108... first filter, 110... first polarization separation element, 111... first light receiving element, 112... second light receiving element, 113... second filter, 115... second polarization separation element, 116... third light receiving element, 117... fourth light receiving element, 120, 220, 320... detection unit, 121, 321... first amplifier (first computing unit) ), 122, 322...second amplifier (second computing unit), 123, 323...signal processing device, 125, 225...separation optical system, 126...first detection unit, 127...second detection unit, 207...wavelength separation element, 301...first modulator, 302...second modulator, 304...polarization separation element, 305...first light receiving element, 306...second light receiving element, 307...first lock-in amplifier, 308...second lock-in amplifier, 309...third lock-in amplifier, 310...fourth lock-in amplifier.

Claims

1. An electric field sensor that measures an electric field to be measured by utilizing an electro-optic effect, a first light source that emits light having a first wavelength; a second light source that emits light having a second wavelength different from the first wavelength; an electro-optic crystal to which the electric field to be measured is applied and to which the light emitted from the first and second light sources is incident; a detector for detecting a phase change amount of the light of the first and second wavelengths transmitted through the electro-optic crystal; a signal processing device that uses a calibration curve that indicates the relationship between the electric field applied to the electro-optic crystal, the ambient temperature, and the phase change amount of the light of the first and second wavelengths that has passed through the electro-optic crystal, and determines the electric field to be measured from the phase change amount of the light of the first and second wavelengths detected by the detection unit; a first modulator that modulates the light of the first wavelength emitted by the first light source itself with a first frequency; a second modulator that modulates the light of the second wavelength emitted by the second light source itself with a second frequency; Equipped with The detection unit a polarization separation element that separates the light that has passed through the electro-optic crystal into two lights with different polarization states; a first light receiving element that receives one of the lights split by the polarization split element and outputs a first light receiving signal; a first lock-in amplifier that performs lock-in detection on the first received light signal using the first frequency to obtain a first signal; a second lock-in amplifier that performs lock-in detection on the first received light signal using the second frequency to obtain a second signal; a second light receiving element that receives the other light separated by the polarization separation element and outputs a second light receiving signal; a third lock-in amplifier that performs lock-in detection on the second received light signal using the first frequency to obtain a third signal; a fourth lock-in amplifier that performs lock-in detection on the second received light signal using the second frequency to obtain a fourth signal; a first computing unit that calculates a difference between the first signal and the third signal; a second computing unit that calculates a difference between the second signal and the fourth signal; An electric field sensor comprising:

2. the signal processing device includes a first calibration curve indicating a relationship between an electric field applied to the electro-optic crystal, an ambient temperature, and a phase change amount of the light of the first wavelength passing through the electro-optic crystal; a second calibration curve showing the relationship between the electric field applied to the electro-optic crystal, the ambient temperature, and the phase change amount of the light of the second wavelength passing through the electro-optic crystal; 2. The electric field sensor according to claim 1, wherein the following is used as the calibration curve:

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