JPH01123162A - Voltage detector - Google Patents

Abstract

PURPOSE:To obtain the max. AC component, by using a sampling type light detection means having a wide dynamic range even in a case using a DC light source and removing a DC component by an amplifying means. CONSTITUTION:The voltage V from an object 53 to be measured is applied to the electro-optical crystal 54 of a light modulator 40 only when a chopper circuit 10 is turned ON and, by regulating a phase compensation device 56, the CW light from a DC light source 70 is modulated by the modulator 40 and the max. AC component is outputted from the modulator 40. The luminous intensity signal from the modulator 40 is applied to a sampling type high speed light detector 11 and swept on the basis of the voltage of a repeating cycle from the object 53 to be measured by the trigger signal formed by a trigger signal generator 13 and a delay circuit 14 to be inputted to a lock-in amplifier 15. The amplifier 15 permits only the output signal of the frequency component determined on the basis of the frequency of a chopper circuit 10 to pass and the DC component of the output signal is removed and the AC component thereof is amplified to be outputted.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a voltage detection device that detects voltage with a time resolution on the order of picoseconds using an optical modulator.

[Conventional technology]

2. Description of the Related Art Devices that detect voltage using optical modulators are conventionally known.

Figures 9 and 10 are U.S. Patent No. 4,446.4, respectively.
25, Patent Application Publication No. 0,197.196, published by the European Patent Office on October 15, 1986, is a schematic configuration diagram of a conventional voltage detection device of this kind.

In the voltage detection device shown in FIG.
A short optical pulse of approximately 1000 msec is repeatedly output, and the short optical pulse is passed through a chopper 51. The optical modulator 40 inputs the measured object 531 to, for example, a photoelectric switch through the variable delay device 52, and inputs the optical modulator 40 to the optical modulator 40.
The air optical crystal 549 phase compensator 56. It is composed of an analyzer 57, and utilizes the phenomenon that an incident short pulse of light is modulated by the voltage from the object to be measured 53, and extracts a voltage waveform in the form of light intensity. More specifically, the voltage to be detected output from the object to be measured 53 in synchronization with the short light pulse is applied to the electro-optic crystal 54 of the optical modulator 40, while the short light from the pulsed light source 50 is applied to the electro-optic crystal 54. Among the pulses, a predetermined polarized light component extracted by the polarizer 55 is made incident. The electro-optic crystal 54 is made of an electro-optic material such as LiNbO3 or LiTaO3 whose refractive index changes with the application of voltage. ! Due to the above-mentioned properties of the pneumatic optical material, the short pulse of light incident on the electro-optic crystal 54 changes its polarization state and is modulated by the voltage from the object to be measured 53, and is emitted as an output light, and then passes through the phase compensator 56. and enters the analyzer 57.

The analyzer 57 extracts two orthogonal polarization components from the light emitted from the phase compensator 56, and outputs the modulated light intensity signals from the optical modulator 40 to the photodetector 58.
59. Photodetector 58.
At 59, the light intensity of each polarization component is detected, and a differential amplifier 6
0, differentially amplify the output signal from the photodetector 58°59,
Lock-in amplifier 61. The detection results are displayed on a display 63 via an averager 62.

The variable delay device 52 is used to gradually delay the timing of voltage generation from the object under test 53 to determine sampling points of the voltage waveform. Also lock-in amplifier 6
1 takes out the output from the differential amplifier 60 at a timing synchronized with the chopper 51, removes noise components, and sends the output to the averager 6.
2 averages the output of the lock-in amplifier 61.

In the voltage detection device having such a configuration, when a voltage V is applied to the electro-optic crystal 54 of the optical modulator 40, the light intensity I of the output light output from the optical modulator 40 to the photodetector 59 becomes equal to the voltage V.
In contrast, a V-1 characteristic as shown in FIG. 11(a) is obtained. When the voltage from the object to be measured 53 is not applied to the optical modulator 40 or more specifically to the electro-optic crystal 54, the light intensity (2) to the photodetector 59 is changed by changing the setting of the phase compensator 56. Here, the maximum light intensity is To
When , the light intensity to the photodetector 59 is light intensity ■. 5
If the phase compensator 56 is set so that the 11th
As can be seen from the V-1 characteristic in Figure (a), the optical modulator 40
When the 0 phase compensator 56 is set in this manner, the operating point is apparently equivalent to when the operating point voltage V/2 is applied, and the operating point is determined at the point indicated by Aπ. to the 11th
When a modulation voltage as shown in Figure (b) is applied, the analyzer 5
The light intensity ■ of the emitted light entering the photodetector 59 from 7 is the first
The result will be as shown in Figure 1 (C).

As can be seen from FIGS. 11(a) to 11(C), at operating point A, the light intensity I of the light emitted from the analyzer 57 changes most largely in proportion to the voltage change, so the AC component is the largest.

. can be obtained. On the other hand, at the operating point A, the optical intensity I includes a DC component 'DC, but by differentially amplifying the two output signals of opposite phases from the photodetectors 58 and 59 in the differential amplifier 60, component! . By removing 0, only the alternating current component IAC can be detected with high sensitivity as a voltage detection result.

In the voltage detection device shown in FIG. 10, CW light from a DC light source 70 is applied to a streak camera 71 via an optical modulator 40, and the output light from an analyzer 57 changes depending on the voltage from an object to be measured 53. The intensity was observed with a streak camera 71, and the mouth and y-quinn ambu 61. The voltage is detected by displaying it on a display 63 via an averager 62. Note that the voltage output from the device under test 53 and the operation of the lock-in amplifier 61 are synchronized with the pulses from the pulse generator 72. Further, the sweep voltage applied to the deflector (not shown) of the streak camera 71 is applied to the pulse generator 7
The timing is gradually shifted by the phase shifter 73 with respect to the pulse from 2.

In the voltage detection device having such a configuration, since the streak camera 71' is used as a detector, the operating point is set to the 11th point.
In the case of the streak camera 71, which is set as indicated by the symbol B in Figure (a), it is not possible to obtain a large dynamic range, and when the DC component IDC of the light intensity I is large, the AC component AC is observed as a signal that should be detected. Therefore, the voltage ■ applied to the optical modulator 40 is −“0”■
When Streak Camera 7! The phase compensator 56 is set so that the light intensity I is minimized, and the operating point is determined as indicated by B.

This operating point B is the DC component ■. Since C can be made extremely small, the DC component I. AC component for C,
. The modulation degree MOD, which is determined as the ratio of . Note that at the operating point B, the alternating current component ■AC is also considerably reduced compared to the operating point A, but the multiplication function of the streak camera 71 multiplies the alternating current component ■AC and makes it possible to measure it.

[Problem that the invention seeks to solve]

However, in the voltage detection device shown in FIG. 9, the operating point is set to A.
Although it is possible to obtain the maximum alternating current component 'AC' by setting it to , the light intensity I has a direct current component I. 0, it is not possible to use a streak camera as a general high-speed photodetector with a narrow dynamic range, and this creates the problem that a pulsed light source, which is expensive and difficult to handle, must be used as a light source. .

On the other hand, in the voltage detection device shown in FIG. 11, the operating point is set to B, and the DC component is set to ■. 0 can be significantly reduced, but the alternating current component (AC) also becomes small, so there is a problem in that there is a limit to obtaining highly sensitive detection results.

An object of the present invention is to provide a voltage detection device that can obtain the maximum AC component even when a DC light source is used as a light source, and can also remove the DC component.

[Means for solving problems]

The present invention provides a DC light source, a chopping means for chopping a voltage from an object to be measured, a light modulation means for modulating CW light from the DC light source with a voltage from the chopping means, and outputting the modulated light as a light intensity signal, and the light intensity A voltage detection device characterized by comprising a sampling type photodetection means for sampling and detecting a signal, and an amplification means for extracting and amplifying a frequency component determined by the chop frequency of the chopping means from the output signal sampled and detected. This improves the problems of the prior art described above.

[Effect]

In the present invention, the voltage from the object to be measured is chopped by the chopping means and applied to the optical modulation means. The CW light from the DC light source that has entered the optical modulation means is modulated by the voltage from the chopping means and output as a light intensity signal. The sampling type light detection means samples and detects the light intensity signal, and the amplification means extracts and amplifies a frequency component determined by the Chiyo-11 frequency from the sampled and detected output signal.

By the way, in the present invention, since a sampling type photodetection means having a wide dynamic range is used when a DC light source is used, the operating point of the light modulation means can be set at a point where the maximum AC component can be obtained.

At this time, a DC component is also superimposed, but this DC component is removed by the amplification means, and only the AC component is extracted and amplified.

〔Example〕

Embodiments of the present invention will be described below based on the drawings.

FIG. 1 is a configuration diagram of an embodiment of a voltage detection device according to the present invention. In FIG. 1, parts corresponding to those in FIGS. 9 and 10 are given the same reference numerals.

In the voltage detection device of this embodiment, the CW light from the DC light source 70 is
is input to the optical modulator 40, and the incident CW light is modulated by the voltage from the object to be measured 53 applied via the chop circuit 10 in the optical modulator 40, and the voltage waveform is converted into a light intensity signal to generate a sampling type high-speed signal. It is designed to be input to a photodetector 11. The voltage from the object to be measured 53 has a repeating period, is branched by the splitter 12, and is sent to the optical modulator 40 through the chop circuit 10 as described above. More specifically, the trigger signal generator 1
3. The signal is applied as a trigger signal to the sampling type high-speed photodetector 11 via the delay circuit 14. Furthermore, the output signal from the sampling type high-speed photodetector 11 is
The signal is input to a lock-in amplifier 15 that operates in synchronization with the chop frequency of the chop circuit 10.

The DC light source 70 is, for example, a He-Ne laser, a semiconductor laser, a laser diode pumped solid-state laser, or a second harmonic generation element. The sampling type high-speed photodetector 11 also sweeps the light intensity signal output from the optical modulator 40 in synchronization with the trigger signal from the delay circuit 14, and sweeps the light intensity signal from the aperture of a built-in aperture member (not shown). This is to sample and extract a part of the waveform. That is, the delay circuit 14
By gradually delaying the trigger signal, the sampling point is shifted and the light intensity waveform is sampled.

FIG. 2 is a diagram showing an example of the chop circuit 10 and the lock-in amplifier 15. In the example of FIG. 2, the chop circuit 10
is composed of a variable pulse generator 16, a gate circuit 17, and an on/off circuit 18, and the lock-in amplifier 15 is composed of a frequency counter 19, a control circuit 20, a variable bandpass filter 21, and an amplifier 22. It is configured.

In the chop circuit 10, when a pulse is generated from the variable pulse generator 16, the gate circuit 17 operates as shown in FIG. 3(a).
When the gate circuit 17 is off and no voltage is output from the gate circuit 17, the resistance of the on/off circuit 18 is as shown in FIG.
), the voltage from the object under test 53 is not applied to the optical modulator 40.On the other hand, when the gate circuit 17 is on and a voltage equal to or higher than the threshold value ■1H is output from the gate circuit 17, the voltage is turned on. The resistance of the off-circuit 18 becomes extremely small as shown in FIG. 3(b), and the voltage from the object to be measured 53 is applied to the optical modulator 40.

On the other hand, the pulses from the variable pulse generator 16 are input to the frequency counter 19 of the lock-in amplifier 15, where the pulse frequency is measured and applied to the control circuit 20.

The control circuit 20 controls the variable bandpass filter 21 so that only a signal having a frequency component of 1/2 of the pulse frequency from the variable pulse generator 16 can pass through the variable bandpass filter 21. As a result, chop circuit 1
Since only the change between the sampled light intensity signal when W118 is on and the sampled light intensity signal when it is off passes through the variable bandpass filter 21, the light intensity signal From the DC component I.

0 can be removed and only the alternating current component 'AC' can be amplified by the amplifier 22.

Note that the frequency counter 19 includes a variable pulse generator 1.
Instead of inputting the pulse from 6, the gate circuit 17
The output of gate circuit 1 is inputted to frequency counter 19.
Only the frequency component of the output of 7 is variable bandpass filter 2.
Alternatively, when chopping at a known frequency, a constant frequency output is given from the gate circuit 17 to the on/off circuit 18, and the variable bandpass filter 21 is controlled to pass a fixed bandpass. In this case, the variable pulse generator 161 frequency counter 19. The control circuit 20 becomes unnecessary.

The operation of the voltage detection device having such a configuration is shown in FIGS. 4 to 6.
This will be explained using figures.

As shown in FIG. 4(a), the voltage V from the object to be measured 53 is applied to the optical modulator 40 only when the chop circuit 10 is on.
is added to the electro-optic crystal 54. If the operating point of the optical modulator 40 is set at point A by adjusting the phase compensator 56 (see FIG. 11(a)), the CW light from the DC light source 70 will be at It is modulated by the voltage shown in FIG. 4(a), and the maximum AC component IAC as shown in FIG. 4(b) is output from the optical modulator 40. Note that by setting the operating point to A, the optical modulator 40 always outputs a DC component I. C is also output.

A light intensity signal as shown in FIG. 4(b) from the optical modulator 40 is applied to the sampling type high-speed photodetector 11. As described above, the sampling type high-speed photodetector 11 generates a trigger signal generator 13 . The light intensity signal is swept by the trigger signal generated by the delay circuit 14, and a part of the light intensity waveform is sampled from an aperture (not shown) and input to the lock-in amplifier 15. The sampling point of the sampling type high-speed photodetector 11 is moved by delaying the trigger signal and shifting the timing of the sweep. At the sampling point S1 shown in FIG. 4(C), part F1 of the light intensity waveform PG is sampled as shown in FIG. Output the output signal. Furthermore, at the sampling point S2 shown in FIG. 4(d), part F2 of the light intensity waveform F'G is shown in FIG.
As a result of sampling and repeating this, the 6th
An output signal as shown in Figure (b) is output.

Note that the sampling type high-speed photodetector 11 has a wide dynamic range, so even if a DC component Ioc is input to it, it will not saturate and will not be saturated.
. 0 can be faithfully sampled and output as shown in FIGS. 6(a) and 6(b).

The output signal sampled and extracted by the sampling type high-speed photodetector 11 in this way is input to the lock-in amplifier 15, which is connected to the chop circuit 1.
Since only the output signal of the frequency component determined by the chop frequency of 0 is passed, the DC component I of the output signal is passed. 0 is removed, and the alternating current component AC is amplified and output.

As described above, according to this embodiment, even when using the inexpensive and easy-to-handle DC light source 70, the operating point can be set so that the maximum AC component can be obtained, and the superimposed DC component can be reduced. Can be effectively removed.

In the above-described embodiment, the electro-optic crystal 54 of the optical modulator 40 is of a transmissive type, for example, in which a traveling wave line for voltage application is provided in parallel with the optical path and transmits and emits the modulated light. Alternatively, it may be a reflective type that has a reflector at the tip and reflects the modulated light and emits it.When it is a zero-reflection type, the voltage can be detected without contacting the object to be measured. Further, in order to prevent unnecessary light from being mixed in, the electro-optic crystal 54 is preferably painted black except for the paths of incident light and outgoing light.

Furthermore, in the above embodiment, the trigger signal for the sampling type high-speed photodetector 11 was generated by branching the voltage signal from the object to be measured, but as shown in FIG. A trigger signal may be generated at the same time as the voltage is generated from the object to be measured 53 by the signal from the oscillator 30. By providing the oscillator 30 separately, it becomes easier to check the operation of the entire circuit.

Further, when the object to be measured 53 is a high-speed photodetector, for example, it is necessary to give an optical pulse signal to the object to be measured 53, as shown in FIG. It is necessary to convert it into a trigger signal.

In addition, a sampling type optical off-scilloscope (003 manufactured by Hamamatsu Photonics Co., Ltd.) is used as a sampling type high-speed photodetector 11.
-01), it is possible to measure the voltage from 30I] to IGH2.

Also, when using a synchro scan photometer,
Voltages from 80MH2 to 160MH can be measured. In addition,
The frequency of the chop must be sufficiently lower than the frequency of these voltages.

〔Effect of the invention〕

As explained above, according to the present invention, even when a DC light source is used, sampling type photodetection means is used as the photodetection means, so while it is possible to obtain the maximum AC component, it is also possible to obtain the maximum AC component. The amplifying means can effectively remove the direct current component.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of an embodiment of a voltage detection device according to the present invention, Fig. 2 is a diagram showing an example of the structure of a chop circuit and a lock-in amplifier, and Fig. 3 (a) shows the output voltage of a gate circuit. Figure 3(b) is a diagram showing the resistance change of the on/off circuit,
FIG. 4(a) is a diagram showing the chopped voltage waveform applied to the optical modulator, FIG. 4(b) is a diagram showing the optical intensity signal, and FIG.
Figures (c) and (d) are sampling points S, respectively.
, S2, FIG. 5 shows the sampling point S1. S
Figure 6 shows the light intensity F and F'2 extracted in 2.
Figures (a) and (b) respectively show the sampling point S1.
Figure 7 showing the output signal sampled in S2
8 shows a modification of the trigger signal generator, and FIG. 9 shows a modified example of the trigger signal generator.
10 and 10 are schematic configuration diagrams of conventional voltage detection devices, FIG. 11(a) is a diagram showing the light intensity ■ with respect to the voltage V, and FIG. 11(b) is a diagram showing the modulated voltage from the object to be measured. figure,
FIG. 11(C) is a diagram showing the light intensity I obtained when the modulation voltage of FIG. 11(b) is applied to the operating point A of FIG. 11(a). DESCRIPTION OF SYMBOLS 10...Chop circuit, 11...Sampling type high-speed photodetector, 15...Lock-in amplifier, 40...Optical modulator, 70...DC light source patent applicant Hamamatsu Photonics Co., Ltd. agent Patent attorney Masaharu Uemoto

Claims (1)

[Claims] 1) A DC light source, a chopping means for chopping the voltage from the object to be measured, and an optical modulation means for modulating the CW light from the DC light source with the voltage from the chopping means and outputting it as a light intensity signal. , characterized in that it comprises a sampling type light detection means for sampling and detecting the light intensity signal, and an amplification means for extracting and amplifying a frequency component determined by the chop frequency of the chopping means from the sampled and detected output signal. Voltage detection device. 2) The voltage detection device according to claim 1, wherein the sampling type photodetector is a sampling type high speed photodetector. 3) The voltage detection device according to claim 1, wherein the sampling type high-speed photodetector is a sampling type optical oscilloscope or a synchro scan photometer.