JPH02150776A - Voltage detecting device - Google Patents

Abstract

PURPOSE:To improve the detecting sensitivity of the title device by providing an optical probe which is brought nearer to a part to be measured and contains an electrooptic material and an electric field concentrating electrode which concentrates electric lines of force from the part to be measured to the optical probe. CONSTITUTION:Probe light modulated by means of an electric field at an optical probe 46 is adjusted by means of a Soleli-Babinet compensator 52 so that its bias quantity can become 1/4 wavelength to obtain a linear response and maximum voltage sensitivity after the probe light is reflected by a half mirror 51 and made incident on an analyzer 50. The output light of the analyzer 50 is detected by means of a pair of photodiodes 42 and 44 and detecting signals of the diodes 42 and 44 are displayed on a display device 57 after the signals are processed by means of a sampling detecting device 56 incorporating a differential amplifier 56A and lock-in amplifier 56B. An optical delaying device 54 is actuated synchronously to the sampling detecting device 56 when the device 56 is operated. Therefore, a time-voltage display of an unknown electric signals can be made.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a voltage detection device that detects the voltage by electro-optic conversion using an electro-optic material whose refractive index changes depending on the voltage of a predetermined portion of a measured object. The present invention relates to a high voltage detection device.

[Conventional technology]

The electric field (electric field lines) in a predetermined part of a high-speed device that operates on the picosecond order, such as an ultra-high-speed transistor such as a MODFET, a superlattice photodetector, or a high-speed integrated circuit, has a time resolution on the picosecond order and a microvolt order. As a technique for non-contact, high-speed measurement with sensitivity of An electric field detection device has been developed that detects the change in the electric field by placing the electro-optic material between a polarizer and an analyzer whose polarization directions are orthogonal to each other. Electric field detection devices that utilize this Pockels effect include, for example, an electrode type in which an electrode is provided on a plate-shaped electro-optic material and connected to the electrode of the object to be measured, and an electrode-type device in which an electrode is provided on a plate-shaped electro-optic material and connected to the electrode of the object to be measured.
There is a probe type that allows easy access to any part to be measured from the outside. The former is, for example, U.S. Pat.
603293, US Patent No. 4,618,819, European Patent Application Publication No. 197196, IEEE Jo
Urnat of Quantun E Iec
tronics, vol, QE-22. No, 1. Jan, 1986 PP69-78. On the other hand, the latter 10-B type is, for example, CLBO[7PP
352-353, L L E Review. Vol, 32. Juby-sep, 1987 PP
158-163. In the latter case, the optical probe that approaches the part to be measured is CLEO”8.
7 As shown in FIG. 11, a chip-shaped LiTaO3 crystal 14 in the shape of a four-sided pyramid is attached to the tip of the silica support 12 to the PPs 352 to 353, and a light beam 18 for detection is reflected on the bottom surface of the LiTaO3 crystal 14. An optical probe 10 on which a total reflection mirror 16 made of a dielectric multilayer film is deposited is disclosed. 22 are arranged two-dimensionally, an electric field represented by lines of electric force exists on the circuit surface between the t i #122. Therefore, if the tip of the optical probe 10 approaches the object to be measured 20, Li
Since the refractive index of the TaO3 crystal 14 changes, the light beam 18 is thereby modulated. Therefore, the electric field generated between the electrodes 22 of the object to be measured 20 can be detected by converting it into a change in the amount of transmitted light using a polarizer and an analyzer. Further, as another example of the optical probe 10, LLERevi
ev, Vol, 32, July-3ep,
1987 PP 158-163 discloses a device that eliminates the need for a reflective film on the bottom surface of the crystal by totally reflecting the light beam 18 three times on the inner surface of the LiTaO3 crystal 30 to change the beam direction, as shown in FIG. . In this optical probe 10, a LiTa0a crystal 30
near the bottom surface of the LiTaO3 due to an electric field parallel to the Z axis.
The refractive index of crystal 30 is modulated.

[What the invention aims to accomplish! ! ! ] However, since LiTaO3 crystal, which is an electro-optical material, has a dielectric constant ε of 40, which is larger than air, when this crystal is brought close to the object to be measured, the electrode 22 of the object to be measured 20
The problem is that the electric field E generated by the electric field changes and becomes weaker as E=D/ε (D is the electric flux density). That is, when there is no crystal, the electric field on the object to be measured 20 as shown in FIG.
14, the electric field on the object to be measured 20 changes so that its isoelectric field lines avoid the crystal 32. Therefore, the electric field generated in the crystal 32 is smaller than in the case where there is no crystal. That is, since a voltage is applied to the crystal 32 and the crystal 32 becomes unstable, the voltage of the object to be measured cannot be detected efficiently with the light beam made of such an electro-optic material, and the detection sensitivity cannot be improved. It had the problem of being difficult. In order to solve these problems, IEICE Transactions CVol, J71-CNo. 7 (July 1988)
month) PP1076-1077 contains LiTa0. It has been disclosed that adding an electric field concentration plate to the crystal to improve sensitivity is for measuring spatial electric fields, and as in the present invention, for example, high-speed integrated circuits, etc. It did not concern a beam of light for measuring the voltage of an object. The present invention was made to solve the above-mentioned conventional problems, and an object of the present invention is to provide a probe-type voltage detection device with high detection sensitivity. Means for Accomplishing the Object The present invention provides a voltage detection device that uses an electro-optic material whose refractive index changes depending on the voltage at a predetermined portion of the object to be measured, and detects the voltage by electro-optical conversion. The above object is achieved by providing an optical probe containing an electro-optic material for approaching the measurement part, and providing the optical probe with an electric field concentration electrode that concentrates the lines of electric force from the object to be measured. It is. Further, at least a portion of the electric field concentration electrode is provided in contact with the surface of the electro-optic material. Further, a part of the electric field concentration electrode is provided so as to protrude into the air from the surface of the electro-optic material. a pulsed light source as an incident light source to the light beam 10;
It is designed to perform sampling detection. Further, the photodetector for the light emitted from the optical probe is a high-speed photodetector with high temporal resolution. Further, the high-speed photodetector described above is a high-speed photodetector to which streak camera technology is applied.

[Effect]

First, the present invention will be described in detail by taking as an example the case of a horizontal modulator for detecting a horizontal electric field, in which the traveling direction of light and the direction of the electric field (direction perpendicular to equipotential lines) are perpendicular. In this lateral modulator, in the conventional example which does not have an electric field concentration electrode, the equipotential line is between the crystal 32 and the
At the top of the crystal, the distance between them is wide and the applied voltage is small. On the other hand, if the electric field concentration electrode 34 is provided in contact with the side surface of the crystal 32 as in the first embodiment of the optical probe according to the present invention shown in FIG. Therefore, a uniform electric field is obtained up to the top of the crystal 32, the number of equipotential lines in the crystal increases, and the electric field in the crystal 32 is strengthened. Therefore, detection sensitivity is improved compared to the conventional example shown in FIG. Furthermore, if the tip of the electric field concentration t'Ii 34 is made to protrude into the air from the surface of the crystal 32 as in the second embodiment of the optical probe shown in FIG. Since the composite dielectric constant ε' is smaller than that of the first embodiment, and the electric field E becomes stronger as D/ε', the detection sensitivity is further improved. Next, let's take the case of a vertical modulator in which the direction of light travel and the direction of the electric field are parallel to each other to detect a vertical electric field.
The present invention will be described in detail. In the case of this vertical modulator, as shown in FIG. 5, in the conventional example without an electric field concentration electrode, the equipotential lines cross the bottom surface of the crystal 32, so the number of equipotential lines in the crystal 32 is small.
The electric field cannot be detected efficiently.In contrast, if an electric field concentration electrode 34 is provided in contact with the bottom surface of the crystal 32 as in the third embodiment of the optical globe according to the present invention shown in FIG. Since the potential lines are parallel to and confined to the bottom surface of the crystal 32, the number of equipotential lines in the crystal 32 increases and the electric field is strengthened. Therefore, detection sensitivity is improved compared to the conventional example shown in FIG. Furthermore, as in the fourth embodiment of the optical probe shown in FIG. 6, if the crystal 32 is made thinner and the electrode 34 is made to protrude into the air, the dielectric constant of the optical probe becomes f! Since it is determined by the portion above 34 (crystal 32 and air), its composite dielectric constant ε' is smaller than that of the third embodiment. At this time,
Since the electric field E becomes stronger as E=D/ε', detection sensitivity is further improved. Furthermore, as in the fifth embodiment of the optical probe shown in FIG. 7, if the tip of the crystal 32 is made sharper, the electric field will be more concentrated.
Detection sensitivity is further improved. As explained above, by providing the electric field concentrating electrode 34 on the crystal 32, it becomes possible to concentrate the equipotential field lines in the crystal of the optical probe, and the detection sensitivity of the optical probe can be improved.

【Example】

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a voltage measuring device in which an optical probe according to the present invention is employed as a modulator using an electro-optic effect will be described in detail with reference to the drawings. The first embodiment of the present invention utilizes an electro-optical (E-0) sampling measurement method, and as shown in FIG.
For example, a repetition rate of 100M1 (70 fpm pulses in z) is used and a conventional pair of photodiodes (eg PIN photodiodes) 42.44 are used as detectors. The optical modulator is shown in Fig. 1, Fig. 3, Fig. 4, Fig. 6, or Fig. 7.
Optical probe 46 made of electro-optic material as shown in the figure
, a pair of polarizers 48, an analyzer 50, and an optical element for applying an optical bias, such as a Soleil-Babinet compensator 52. The object to be measured 20 has a built-in photodetector (not shown), for example, and this photodetector scans the light emitted from the CPM laser 40 and after it passes through the half mirror 53 by changing the amount of delay. The object to be measured 20 is excited by a trigger light beam 55 that has passed through an optical delay 54 . In this way, the object to be measured 20 is brought into operation in synchronization with the CPM laser 40. Note that the object to be measured 20
trigger light beam 55 without incorporating a photodetector into the
By irradiating the gap between the gate of the object 20 and the common electrode, the gate may be momentarily switched to ground. On the other hand, after being emitted from the CPM laser 40 and reflected by a half mirror 53, the light beam 10 passes through a polarizer 48 set at a polarization direction of 45 degrees with respect to the optical axis of the beam 46.
- The optical beam 47 for the probe is focused on the optical probe 46 . The probe light modulated by the electric field in the optical probe 46 is reflected by the half mirror 51, and then sent to the Soleil-Babinet compensator 52, where the bias amount is adjusted to 1/4 wavelength in order to obtain a linear response and maximum voltage sensitivity. It is adjusted so that it becomes incident on the analyzer 50. The output light from the analyzer 50 is transmitted to a pair of photodiodes 4.
2.44, and the detection signal is sent to the differential amplifier 5.
6A, a lock-in amplifier 56B, a signal averaging circuit 56C for improving the S/N as necessary, and a delay amount control circuit 56D for controlling the optical delay 54. An output waveform is displayed on a display device (for example, a CRT) 57, where is the delay amount (ie, optical path difference) of the optical delay 54 and the vertical axis is the detection signal. At this time, the optical delay 54 and sampling detector 256 operate synchronously. This allows time-voltage representation of unknown electrical signals. Note that the signal averaging circuit 56C can also be omitted. Next, with reference to FIG.
Examples will be described in detail. In this second embodiment, the optical modulator is similar to that in the first embodiment, but the light source is, for example, He-Ne.
A continuous (CW) laser light source such as a laser 70 is used, and a high-speed photodetector 72 using streak camera technology, for example, is used as a detector. Further, as the high-speed photodetector 72, for example, the one proposed by the applicant in Japanese Patent Application No. 116732/1988 can also be used. The other configurations and operations are the same as those in the first embodiment, so their explanations will be omitted. In this embodiment, since an optical delay, a sampling detection device, a photodiode, etc. are not required, the configuration is simple. Next, a third embodiment of a voltage measuring device using a laser diode and an electrical delay will be described in detail with reference to FIG. In this third embodiment as well, the optical modulator is the same as in the first embodiment, but a laser diode 80 is used as the light source. This laser diode 80 is pulse-driven by a drive circuit 82 in synchronization with the drive of the object to be measured 20 . An electric delay 84 is provided between the drive circuit 82 and the laser diode 80, so that the timing of both, that is, the scanning timing can be sequentially shifted. The output light is detected by a photodetector such as a photodiode 42, 44, processed by a sampling detection device 56 similar to the first embodiment, and then displayed as an output waveform on a display device 57. At this time, the electrical delay 84 and the sampling detection device 56 operate synchronously. Other points are the same as those in the first embodiment, so detailed explanation will be omitted.

【Effect of the invention】

As explained above, according to the present invention, in a voltage detection device that utilizes an electro-optic effect, an electro-optic material used for a probe for detecting an electric field, such as LiTaO3, is used.
Since the electric field concentration electrode is provided on the crystal, the electric field generated by the object to be measured can be efficiently detected. Therefore,
The minimum detectable sensitivity can be improved. Furthermore,
This has excellent effects such as being able to widen the distance between the optical probe and the object to be measured, and preventing accidents such as accidentally bringing the optical probe into contact with the object and damaging both.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing the configuration of a first embodiment of an optical probe according to the present invention, FIG. 2 is a cross-sectional view showing a conventional example of a lateral modulator, and FIG. 3 is a cross-sectional view of the optical probe according to the present invention. FIG. 4 is a cross-sectional view showing the second embodiment, FIG. 5 is a cross-sectional view showing the third embodiment, and FIG.
6 is a sectional view showing a conventional example of a vertical modulator; FIG. 6 is a sectional view showing a fourth embodiment of the optical probe according to the present invention; FIG. 7 is a sectional view showing a fifth embodiment; The diagram is
A block diagram showing the configuration of a first embodiment of a voltage measuring device employing an optical probe according to the present invention, FIG. 9 is a block diagram showing the configuration of a second embodiment, and FIG. FIG. 11 is a block diagram showing the configuration of the third embodiment; FIG. 11 is a sectional view showing a conventional example of an optical probe;
This figure is a perspective view showing another conventional example of an optical probe, and FIGS. 13 and 14 are diagrams comparing and showing changes in electric field due to the combination of electro-optic materials. 20...Measurement object, 22...Electrode, 32=Li'ra Oa crystal, 34...Electric field concentration electrode, 40...CPM laser, 42.44...Photodiode, 46...Light 10-wave, 47... 10-wave light beam, 48... Polarizer, 50... Analyzer, 52... Soleil-Babinet compensator, 54... Optical delay, 55... Trigger light beam, 56... Sampling detection device, 57... Display device, 0... He-Ne laser, 2... High speed photodetector, 0... Laser diode, 2... Drive Circuit, 4... Electrical delay.

Claims (6)

[Claims] (1) In a voltage detection device that uses an electro-optic material whose refractive index changes depending on the voltage at a predetermined portion of the object to be measured, and detects the voltage by electro-optical conversion, an electro-optic material is used to approach the measured portion. 1. A voltage detection device comprising: an optical probe containing a material; and an electric field concentrating electrode for concentrating lines of electric force from an object to be measured. (2) The voltage detection device according to claim 1, wherein at least a portion of the electric field concentration electrode is provided in contact with a surface of the electro-optic material. (3) The voltage detection device according to claim 2, wherein a part of the electric field concentration electrode is provided to protrude into the air from the surface of the electro-optic material. (4) The voltage detection device according to claim 1, wherein the light source incident on the optical probe is a pulsed light source, and sampling detection is performed. (5) The voltage detection device according to claim 1, wherein the photodetector for the light emitted from the optical probe is a high-speed photodetector. (6) The voltage detection device according to claim 5, wherein the high-speed photodetector is a high-speed photodetector to which streak camera technology is applied.