JPH0783965A - Noncontact-type measuring apparatus for voltage - Google Patents

Abstract

PURPOSE:To enhance the S/N ratio of a noncontact-type voltage measuring apparatus. CONSTITUTION:An in-phase component and an antiphase component which have been separated by a polarization beam splitter 103 for a laser beam 108b which has been modulated by an EO element and by the electric field of an object to be measured are controlled by turning a half-wave plate 106, and they are made the same in amount. In addition, phases of laser beams 108d, 108e which have been separated by moving a photodetector on one side are adjusted. The difference between the laser beams 108d, 108e which have been separated and whose quantity of light and phase have been adjusted is taken. Consequently, an electrically additive circuit is not required, and also a reference signal for synchronization is not required.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-contact type voltage measuring device for non-contact measurement of a potential on an electric circuit by using a laser beam.

[0002]

2. Description of the Related Art Conventionally, a non-contact type voltage measuring device using a laser beam of this type does not apply a capacitive load to an electric circuit which is an object to be measured, as disclosed in Japanese Patent Application Laid-Open No. 3-6465. It is used for the purpose of enabling accurate waveform observation even in the high frequency region.

FIG. 3 is a block diagram showing a conventional non-contact type voltage measuring device using a laser beam. In FIG.
Reference numeral 305 is a microcell in which a gas having a Stark effect is enclosed. The frequency of the laser light emitted from the laser light source 301 is stabilized at a specific frequency. The optical path of this laser light is changed by the mirror 302, passes through the beam splitter 303, the convex lens 304, and the microcell 305, and is condensed on the electrode of the IC 306. The reflected light from this electrode passes through the microcell 305 and the convex lens 304 again to become parallel light, is reflected by the beam splitter 303, and is incident on the photodetector 310. The photodetector 310 converts a light signal into an electric signal by using a photodiode, a mercury cadmite tellurite detector, or the like.

The laser light from the laser light source 301 is generated by the oscillator 30.
8 is slightly frequency-modulated by the reference signal of 8, and the output signal of the photodetector 310 is synchronously detected by the lock-in amplifier 311 with the reference signal of the oscillator 308, and only the component synchronized with the reference signal is detected. As a result, the laser light source 30
The drift of the light intensity of 1 can be removed, and a signal with a good S / N ratio can be detected. Since the detection signal from the lock-in amplifier 311 synchronously detects the frequency-modulated laser light, it is a first derivative of the light absorption intensity. A transparent thin film electrode that is conductive and transmits light is attached to the surface of the microcell 305 from the convex lens 304, and a voltage based on the ground potential of the IC 306 is applied to this electrode by a DC amplifier 307.

The voltage of the DC amplifier 307 is the laser light source 30.
In consideration of the oscillation frequency of 1, the light absorption frequency of the gas in the microcell 305 is set so that the change in the voltage of the electrode of the IC 306 and the change in the signal output from the lock-in amplifier 311 are in proportion to each other. IC306 here
When the voltage of the upper electrode changes, the light absorption frequency of the gas in the microcell 305 changes due to the Stark effect, the light intensity detected by the photodetector 310 changes, and the output of the lock-in amplifier 311 changes.

[0006]

In this conventional non-contact type voltage measuring device using laser light, the voltage applied to the electric circuit (here, IC) which is the object to be measured is synchronized with the reference signal of the lock-in amplifier. I am letting you. That is, there is a problem that it can be applied only to the waveform observation of the signal whose frequency is known in advance in the electric circuit.

[0007]

A non-contact type voltage measuring device of the present invention is configured so that an EO element to which an electric field is applied by a voltage applied to a measurement point of an object to be tested is in phase with a laser beam passing through this EO element. A polarization beam splitter for separating into a reverse phase component, and the polarization beam when the voltage at the measuring point is in a predetermined state by adjusting the incident angle of the polarization plane of the laser light passing through the EO element with respect to the polarization beam splitter. Set the same amount of light for the in-phase and anti-phase components separated by the splitter 1
/ 2λ plate, first and second photodetectors for converting each of the in-phase and anti-phase components of the laser light separated by the polarization beam splitter into electric signals, and outputs of the first and second photodetectors And an operational amplifier that takes the difference between the two.

In the non-contact type voltage measuring device of the present invention, the phase difference of the laser light received by each of the first and second photodetectors is adjusted by moving the first or second photodetector in the direction of the optical axis. You can

[0009]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing an optical system path of an embodiment of the present invention.

In FIG. 1, the EO element 101 is incident on the EO element 101 by applying an electric field sandwiched between an electric signal at a measuring point 110 on the DUT 102 and a transparent thin film electrode 111 which is conductive and transmits light. Then, the polarization state of the laser light 108a reflected by the dielectric multilayer reflection film 112 on the reflection side end face is modulated.

As the EO element 101, for example, lithium niobate which is a uniaxial crystal is used in a vertical operation. When an electric field is applied to this EO element, the refractive index changes due to the Pockels effect, and the polarization state of the laser light passing through this EO element changes. That is, the polarization plane rotates in proportion to the applied electric field.

The mirror 109 is for guiding the laser beam 108a to the EO element 101. The convex lens 113 is a parallel laser beam 108a for measuring a minute measurement point.
Is for condensing the laser light and returning the reflected laser light back to parallel light. The ½ λ plate 106 rotates the plane of polarization of the laser beam 108b which is reflected by the dielectric multilayer reflection film 112 and passes through the convex lens 113 and is modulated in the polarization state.
Laser light 108 whose polarization plane is rotated by the 2λ plate 106
This is for separating c into in-phase and anti-phase (P polarized light, S polarized light). Photodetectors 104 and 105 are laser beams 108 d and 1 separated by the polarization beam splitter 103.
08e is an optical converter that converts the electric signal 08e into an electric signal, and the differential amplifier 107 is for detecting the signal component applied to the measurement point 110 by taking the difference between the electric signals from the photodetectors 104 and 105. .

A measurement point 110 on the object 102 to be measured is transmitted through the EO element 101 and reflected by the dielectric multilayer reflection film 112.
The laser beam 108b modulated by the electric signal of
The polarization plane is rotated by the 2λ plate 106, and the in-phase and anti-phase laser light 1 is polarized by the polarization beam splitter 103.
The photodetector 10 is separated into 08d and 108e.
4 and 105 respectively enter and are converted into an electric signal.

As a result, the measurement point 11 of the DUT 102 is measured.
Laser light 108 in a state where no electric signal is applied to 0.
Laser light 1 from the polarization beam splitter 103 of c
The separation ratio of 08d and 108e can be controlled by rotating the 1 / 2λ plate 106.
The light amounts of d and 108e can be adjusted to the same amount. That is, the bias in the initial state can be adjusted so that the detection sensitivity is higher and the electric signal output to the electric signal at the measurement point 110 of the DUT 102 is proportional.

2A and 2B show the outputs of the photodetectors 104 and 105, which are composed of the in-phase component 201 and the anti-phase component 202 of the laser light separated by the polarization beam splitter 103. The polarization beam splitter 103 is capable of steplessly adjusting the separation ratio of the amount of output light separated from the incident light, depending on the positional relationship with the polarization plane of the incident light. In the in-phase component 201 and the anti-phase component 202, the drift of the light intensity of the laser light source appears in the same phase as shown in FIG. 2, and the signal component 203 modulated by the electric signal at the measurement point 110 appears in the anti-phase.

The optical path difference is adjusted by moving one photodetector 105 in parallel with the optical axis of the laser beam 108e, and the polarization beam splitter 103 is used to adjust the laser beam 1.
Laser light 10 generated when 08c is separated into in-phase and anti-phase
The phase difference of 8d and 108e and the photodetector 104
And 105 adjust the phase difference of the electric signal generated at the time of photoelectric conversion.

The lasers separated as described above and adjusted so that the separation ratios of the laser light in the state where no electric signal is applied to the measurement point 110 of the DUT 102 are the same and the phase difference is adjusted. The lights 108d and 108e are converted into electric signals by the photodetectors 104 and 105, and are input to the differential amplifier 107 as positive and negative inputs, respectively, and when the electric signals are applied to the measurement point 110, the differential amplifier 107 is output. Outputs a signal proportional to the electric signal applied to the measurement point 110. Moreover, the differential amplifier 1
The output of 07 eliminates the light intensity drift of the laser light source,
The signal has a good S / N ratio, which compensates for the rotation of the polarization plane of the laser light due to the drift of the polarization plane and the natural birefringence of the EO element.

As the photodetector, for example, a photodiode, a photoelectric tube or the like can be used.

[0020]

As described above, since the non-contact type voltage measuring device of the present invention does not use the applied signal to the DUT as the reference signal, it is not necessary to synchronize with the measured signal. It is possible to measure even various signals and there is no need for an additional circuit for synchronizing.

Further, in order to eliminate the light intensity drift of the laser light source, the S / N ratio of the signal under measurement is improved to compensate for the polarization plane drift of the laser light source and the rotation of the polarization plane of the laser light due to the natural birefringence of the EO element. Therefore, there is an effect that the detection sensitivity of the signal under measurement is improved.

Further, by controlling the positional relationship between the plane of polarization of the laser light and the polarization beam splitter that separates the laser light into both in-phase and anti-phase components, both in-phase and anti-phase components of the laser light can be controlled. The separation ratio can be easily controlled and adjusted, and the phase difference between the in-phase and anti-phase components can be easily controlled and adjusted by moving the photo detector. When inputting both phase components to the operational amplifier, there is no need for gain adjustment and phase adjustment, and there is an effect that an electrical additional circuit for that is not required.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an optical system path of an embodiment of the present invention.

2A is a diagram showing an output of a photodetector 104 shown in FIG. 1, and FIG. 2B is a photodetector 1 shown in FIG.
It is a figure which shows the output of 05.

FIG. 3 is a configuration diagram showing an optical system path of a conventional non-contact type voltage measuring device.

[Explanation of symbols]

 Reference Signs List 101 EO element 102 DUT 103 Polarizing beam splitter 104 Photodetector 105 Photodetector 106 1 / 2λ plate 107 Differential amplifier 108a to e Laser light 109 Mirror 110 Measurement point 111 Transparent thin film electrode 112 Dielectric multilayer reflective film 113 Convex lens 201 In-phase component 202 Antiphase component 301 Laser light source 302 Mirror 303 Beam splitter 304 Convex lens 305 Microcell 306 IC formed on wafer 307 DC amplifier 308 Oscillator 309 Moving stage 310 Photodetector 311 Lock-in amplifier

Claims (2)

[Claims] 1. An EO element to which an electric field is applied by a voltage applied to a measurement point of an object to be tested, a polarization beam splitter for separating laser light passing through the EO element into in-phase and anti-phase components, and the EO element. The incident angle of the plane of polarization of the laser light passing through the polarization beam splitter is adjusted, and the light amount of the in-phase and anti-phase components separated by the polarization beam splitter when the voltage at the measurement point is in a predetermined state is equalized. ½ λ plate, first and second photodetectors for converting in-phase and anti-phase components of the laser light separated by the polarization beam splitter into electric signals, and the first and second photodetectors. A non-contact voltage measuring device, comprising: an operational amplifier that takes a difference between outputs of a photo detector. 2. The non-contact type voltage according to claim 1, wherein the phase difference of the laser light received by each of the first and second photodetectors is adjusted by moving the first or second photodetector in the direction of the optical axis. measuring device.