JPH01121764A - Voltage detecting device - Google Patents

Abstract

PURPOSE:To set an operation point freely and to obtain a large S/N by composing a voltage detecting device of an optical modulating means which outputs a light intensity signal corresponding to a voltage to be detected and a sampling type fast photodetecting means which detects the light intensity signal. CONSTITUTION:The voltage detecting device consists of the optical modulator 1 which modulates light from a DC light source 70 with a voltage from a body 53 to be measured and outputs the light intensity signal corresponding to the voltage and the light type fast photodetector 2 which detects the light intensity signal. Here, an He-Ne laser or semiconductor laser is used as the light source 70 and the optical modulator 1 consists of a polarizer 55 which extracts a prescribed polarized component, a Pockel's cell 54 which varies the polarization state with the voltage from a body 53 to be measured and generates projection light, a phase compensator 3 which adjusts the phase of the projection light, and an analyzer 3 which extracts a specific polarized component from the projection light to generate the light intensity signal. Thus, the light intensity waveform the projection light is extracted by a detector 2 and the voltage waveform of the body 53 to be measured is observed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention uses an optical modulator to resolve time-resolved images on the order of picoseconds.
Quantize the voltage detection device that detects the voltage.

[Conventional technology]

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

Figures 5 and 6 are respectively U.S. Patent No. 4.446.42.
5 is a schematic configuration diagram of a conventional voltage detection device of this kind disclosed in Patent Application Publication No. 0.197.196 issued by the European Patent Office on October 15, 1986.

In the voltage detection device shown in FIG.
A short optical pulse of about 1000 seconds is outputted electrically, and this short optical pulse is sent to the chopper 51. The measured object 531 is inputted to, for example, a photoelectric switch via the variable delay device 52, and is also inputted to the optical modulator 40. The optical modulator 40 includes a polarizer 55 .
Pockels cell 541 phase compensator 56. It consists 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, while applying the voltage to be detected output from the object to be measured 53 in synchronization with the short optical pulse to the Pockels cell 54 of the optical modulator 40,
A predetermined polarized light component extracted by a polarizer 55 among the short light pulses from the pulsed light source 50 is made incident on the Pockels cell 54 . The Pockels cell 54 has, for example, L' i N b O3 whose refractive index changes with the application of voltage.
Electro-optic materials such as °L*T a O3 are used. Due to the above-mentioned properties of the electro-optic material, the short optical pulse incident on the Pockels cell 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. 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°5
9 detects the light intensity of each polarization component, and a differential amplifier 60
differentially amplify the output signals from the photodetectors 58, 59, and lock-in amplifiers 161. 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 is the chopper 51 of the output from the differential amplifier 60.
It is designed to amplify and extract only the frequency component determined by the frequency of , thereby reducing noise. Further, the averager 62 is configured to average the output of the lock-in amplifier 61.

In a voltage detection device having such a configuration, when a voltage V is applied to the Pockels cell 54 of the optical modulator 40, the light intensity I of the emitted light output from the optical modulator 40 to the photodetector 59 is different from the voltage V. As a result, a VI characteristic as shown in FIG. 7(a) is obtained. Now, the voltage across the object to be measured 53 is applied to the optical modulator 40. More specifically, the light intensity I to the photodetector 59 when not connected to the Pockels cell 54 is changed by changing the settings of the phase compensator 56. Here, ■ its maximum light intensity. and! At this time, the light intensity to the photodetector 59 is the light intensity I.

When the phase compensator 56 is set to 50% of the optical modulator 4, as can be seen from the VI characteristic in FIG.
When the 0 phase compensator 56 is set in this manner, the operating point is apparently equivalent to when the operating point voltage v7/2 is applied, and the operating point is determined at the location indicated by A. 53 to the change pressure V as shown in Fig. 7(b).
, the light intensity I of the emitted light entering the photodetector 59 from the analyzer 57 becomes as shown in FIG. 7(C).

As can be seen from FIGS. 7(a) to (C), at the 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 maximum AC component ■AC
4! -Can be obtained. On the other hand, at operating point A, the light intensity ■
■ DC component. However, by differentially amplifying the two output signals of mutually opposite phases from the photodetectors 58 and 59 in the differential amplifier 60, the DC component! . By removing 0, only the alternating current component IAC can be detected with high sensitivity as a voltage detection result. Further, the output from the differential amplifier 60 is applied to the lock-in amplifier 61, and only the frequency component determined by the frequency of the chopper 51, for example, IKH7, is amplified, thereby making it possible to reduce noise.

Further, in the voltage detection device shown in FIG.
The W light is applied to the streak camera 71 via the optical modulator 40, and the analyzer 5 changes depending on the voltage from the object to be measured 53.
The intensity of the light emitted from the lock-in amplifier 61.7 is observed with a streak camera 71. The voltage is detected by displaying it on a display 63 via an averager 62.

Note that the voltage output from the device to be measured 111ff53 and the operation of the lock-in amplifier 61 are synchronized with the pulse from the pulse generator 72. Also streak camera 71
The timing of the sweep voltage applied to the deflector (not shown) is gradually shifted from the pulse from the pulse generator 72 by a phase shifter 73.

In the voltage detection device having such a configuration, since the streak camera 71 is used as a detector, the operating point is determined as shown in FIG.
In a), set the location indicated by the symbol B. That is, the streak camera 71 cannot have a large dynamic range, and if the DC component IDC of the light intensity ■ is large, the alternating current component AC as a signal to be detected cannot be observed. The phase compensator 56 is set so that the light intensity I to the streak camera 71 is minimized when "Onv", and the operating point is determined as indicated by B.

This operating point B is the DC component I. Since C can be made extremely small, the DC component I. AC component for C■A
Since the modulation degree MOD determined as the ratio of C can be maximized, the alternating current component AC can be observed even with the streak camera 71 having a narrow dynamic range. Note that at operating point B, the alternating current component IAC is also significantly reduced compared to operating point A, but the multiplication function of the streak camera 71 multiplies the alternating current component IAC to enable measurement.

[Problem that the invention seeks to solve]

However, in the voltage detection device shown in Fig. 5, the operating point is set to A.
Although it is possible to obtain the maximum alternating current component 'AC' by setting it to , there is a direct current component (■) in the light intensity I. Because C is also included, it is not possible to use a streak camera as a general high-speed photodetector with a narrow dynamic range, and as a result, a pulsed light source that is expensive and difficult to handle must be used as a light source. . - On the other hand, in the voltage detection device of FIG. 6, the operating point is set to B, and the DC component I. 0 is significantly reduced, it is possible to combine the DC light source 70 and the streak camera 71. However, since a general streak camera with a narrow dynamic range is used, the operating point is fixed at B. There was a problem in that it was not possible to configure settings freely and lacked flexibility.

In addition, although the voltage detection devices shown in Figs. 5 and 6 can obtain the maximum alternating current component (AC) or maximize the modulation degree MOD, they do not take into consideration maximizing the S/N ratio. The problem was that it was not done.゛Furthermore, in the voltage detection device shown in Fig. 5, the lock-in anti-6
1 can reduce noise from the output of the differential amplifier 60, but the differential amplifier 60 has a slow response speed.
8. Take the difference between the output signals of 59 and lock-in amplifier 61
Therefore, the signal to be detected will be considerably deformed when it is input to the lock-in amplifier 61, and the lock-in anti 61 cannot accurately amplify the modulated signal, that is, the alternating current component 'AC. There was a problem. Further, the lock-in amplifier 61 has a sampling frequency as low as 100KH7 due to its time constant, and there is a problem in that it is not possible to further reduce noise, especially 1/f noise, by increasing the sampling frequency.

゛An object of the present invention is to provide a flexible voltage detection device that allows the operating point to be freely set.

A further object of the present invention is to provide a voltage detection device capable of maximizing the S/N ratio and obtaining highly accurate detection results.

Another object of the present invention is to provide a voltage detection device that can accurately measure the signal to be detected and further reduce noise.

[Means for solving problems]

The present invention is characterized in that it includes a light modulation means that outputs a light intensity signal corresponding to the voltage to be detected, and a sampling type high-speed light detection means that detects the light intensity signal from the light modulation means. The voltage detection device improves the problems of the prior art described above. [Operation] In the present invention, when the voltage of the axis to be measured is applied to the optical modulation means,
The polarization state of the incident light is changed and modulated, and a light intensity signal corresponding to the magnitude of the voltage is outputted from the light modulation means and inputted to the sampling type high speed detection means. The sampling-type high-speed light detection means samples and extracts this light intensity signal, observes it as a light intensity waveform, and detects the voltage of the object to be measured based on this. By the way, the sampling type high-speed optical detection means has a wide dynamic range, so even if the optical intensity signal from the optical modulation means contains a DC component, it is possible to observe the AC component as the signal to be detected. The operating point of the light modulation means can be freely set at a desired location. In particular, if the operating point is set so that the S/N ratio is maximized, shot noise can be reduced and detection accuracy can be improved. Further, a chopper and a lock-in amplifier are not required, and 1/f noise can be further reduced.

〔Example〕

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

FIG. 1 is a partial schematic diagram of an embodiment of a voltage detection device according to the present invention. In FIG. 1, parts corresponding to those in FIGS. 5 and 6 are given the same reference numerals.

The voltage detection device of this embodiment includes a DC light source 70 and an optical modulator 1 that modulates CW light from the DC light source 70 with a voltage from an object to be measured 53 and outputs a light intensity signal corresponding to the voltage.
and a sampling type high-speed photodetector 2 that detects a light intensity signal. The DC light source 70 is, for example, He-Ne.
These are lasers and semiconductor lasers. Further, the optical modulator 1 has a CW
A polarizer 55 that extracts a predetermined polarized component from light, and a Pockels cell 54 that changes the polarization state of the light from the polarizer 55 using a voltage from the object to be measured 53 and outputs it as emitted light.
, a phase compensator 3 that adjusts the phase of the light emitted from the Pockels cell 54, and an analyzer 57 that extracts a predetermined polarization component from the light emitted from the phase compensator 3 and uses it as a light intensity signal. The phase compensator 3 is, for example, a Babinet-Soleil compensator, and is adapted to change the phase and move the operating point of the optical modulator 1.

FIG. 2 is a configuration diagram of the sampling type high-speed photodetector 2. As shown in FIG.

Referring to FIG. 2, the sampling type high-speed photodetector 2 includes a lens 10 that collects the emitted light from the analyzer 57, a photocathode 11 that converts the emitted light into electrons corresponding to the intensity of the emitted light, and an accelerating type [i12, a deflector 13 that sweeps accelerated electrons in the direction of arrow F, an aperture member 15 provided with an aperture 14, and an electron multiplier into which the swept electrons that have passed through the aperture 14 are incident. 16.

In such a sampling type high-speed photodetector 2, by gradually shifting the timing of the deflection voltage applied to the deflector 13, a part of the light intensity signal of the emitted light that repeatedly enters the photocathode 11 is sequentially transmitted from the aperture 14. It is designed to be extracted and sampled.

The electron multiplier 16 may be a group of dynodes that directly multiplies the electrons that have passed through the aperture 14, or may include a fluorescent surface that emits light upon the incidence of electrons that have passed through the aperture 14, and an electron multiplier that converts the light emitted from the fluorescent surface into electrons. It may also be combined with a photomultiplier tube that converts and multiplies the electrons again.

In this sampling type high-speed photodetector 2, an electron multiplier 1
6 inputs only a portion of the electrons that have passed through the aperture 14, so it has a wider dynamic range than the general streak camera 71 used in the voltage detection device shown in FIG. There is a direct current component I in the light intensity I of the emitted light. Even if 0 is included, this causes the AC component IAC
It is possible to prevent the '$ situation where it becomes impossible to observe.

In the voltage detection device having such a configuration, the phase compensator 3 is adjusted to set the operating point of the optical modulator 1 to a desired position.

The CW light from the DC light source 70 enters the Pockels cell 54 through the polarizer 55, where its polarization state changes depending on the voltage of the object to be measured 53, and is sent to the phase compensator 3 as output light. , adjusts the phase of the emitted light, extracts the emitted light with a predetermined polarization component in the analyzer 57, and inputs it to the sampling type high-speed photodetector 2.

The sampling type high-speed photodetector 2 observes the voltage waveform of the object to be measured 53 by sampling the light intensity waveform of the emitted light incident on the photocathode 11 . By the way, since the sampling type high-speed photodetector 2 has a wide dynamic range as mentioned above, the light intensity I of the emitted light has a direct current component I.

Even if 0 is included, a minute AC component I superimposed on this
AC can be observed.

This eliminates the need to fix the operating point at B as in the device shown in FIG.
It can be set freely between

Now, consider setting the operating point of the optical modulator 1 so as to obtain the maximum S/N ratio.

The light intensity I of the light emitted from the analyzer 57 is I = I o
S + n C(x/2) ・(v/vx
) As shown in (1), it is changed by adjusting the phase compensator 3 to change the voltage V that determines the operating point, and it is similar to that shown in Fig. 7(a) above. Gives VI characteristics. In addition, Io is the light intensity of the emitted light incident on the analyzer 57, and 2 is the half-wave voltage.

π The AC component IAC included in this light intensity ■, that is, the signal to be detected is obtained by differentiating equation (1) with respect to the voltage ■, as follows:■ =π・■・(ΔV/V)・A
COπ sin C(π/2) ・(V/V) )
・π cos ((π/2)−(V/V)) ・
=・ (2) Given as π. Here, ΔV is a modulated voltage from the object to be measured 53. Assuming that the light intensity I of the light emitted from the analyzer 57 has a waveform as shown in FIG. 3, the S/N ratio is: I AC/Ft = πJI, (Δ■/V, r)
・cos ((π/2)・(V/V)) /π 1+π (ΔV/V) /lan C(π/2)
・π (V/V))
・(3)π, where the noise component is E for the light intensity I
It was assumed that the noise was shot noise with a size of 1.

On the other hand, the modulation degree MOD is IAo/(2・■oo×AC) π・(ΔV/V) sin ((π/2)・π (V/V)) cos ((π/2)・π ( V/V) ) / (2sin 2π ((V/2)・(V/V,)) 1π・π (AV/V) sin ((π/2)−π (V/V)] cos (: (π/2)
・π (V/V)] 1 π.

Figures 4(a) to (C) represent equations (1) to (3), respectively.
) AC component I S/N ratio calculated based on formula.

It is a diagram showing AC/modulation degree MOD. In addition, in FIGS. 4(a) to (C), the horizontal axis is the voltage V/V normalized by the half-wave voltage Va. As shown in FIGS. 4(a) and (C), The component IAC becomes maximum when the voltage V that determines the operating point is set at the operating point A shown in FIG. It becomes maximum when it is set at the operating point B shown in FIG. 7(a), that is, when ■="0". Regarding these, referring to FIG. 4(b),
The S/N ratio reaches its maximum when ■/V is 10-1,
This operating point π is between operating points A and B in FIG. 7(a).

By the way, as a practical matter, the DC component IDC of the light intensity ■
Since dark light is superimposed on
exists.

Therefore, the actual DC component Ir of the light intensity I is 1 =
I oc 1 d・= ”・(5) “ The S/N ratio at this time is I Ac/ I , + I t, c= πJgo7
(ΔV/V, r)・cos ((π/2)・(V/
V ))/π (6) If we find the operating point at which the S/N ratio is maximum from equation (6), we get V/V = 10, which is the same as when there is no dark light.
It will be at -1. As a result, even when dark light is taken into account, the operating point that provides the maximum S/N ratio remains the same, and the phase compensator 3 can be appropriately adjusted to reduce shot noise and achieve a good S/N ratio. Detection results can be obtained.

Furthermore, to simplify the explanation, if a pulsed light source is used instead of the DC light source 70, a short-pulse light intensity signal will be input to the sampling type high-speed photodetector 2, and this short-pulse light intensity signal will be sampled. The sampling frequency (I M H
(can be set to z or higher), the optical intensity signal is narrowband amplified in synchronization with the sampling frequency. In other words, the sampling type high-speed photodetector 2 has a function similar to that of a lock-in amplifier.

Furthermore, since the sampling frequency of IMH1 or higher is considerably higher than the maximum synchronous frequency of 100KH7 of a normal lock-in amplifier, the sampling-type high-speed photodetector 2 can eliminate noise, especially L
/f noise can be further reduced.

In this way, in the voltage detection device of this embodiment, by setting the operating point of the optical modulator to a point that provides the maximum S/N ratio, it is possible to significantly reduce not only shot noise but also 1/f noise at the same time. As a result, extremely accurate detection results can be obtained.

In the above embodiment, the light source was mainly the DC light source 70, which is inexpensive and easy to handle. However, even if a pulsed light source is used, highly accurate detection results can be obtained using the sampling type high-speed photodetector 2. Can be done. Further, as the sampling type high-speed photodetector 2, a sampling type optical oscilloscope (for example, 00S-01 manufactured by Hamamatsu Photonics Co., Ltd.), a synchro scan photometer, etc. can be used.

〔Effect of the invention〕

As explained above, according to the present invention, since the optical intensity signal from the optical modulation means is detected by the sampling type high-speed detection means, the operating point of the optical modulation means can be freely set, resulting in significant flexibility. 1/f noise can be significantly reduced. Furthermore, if the operating point of the optical modulation means is set to the point that gives the maximum S/N ratio, 1
/f noise and shot noise can be reduced at the same time, making it possible to obtain extremely highly accurate detection results.

[Brief explanation of the drawing]

FIG. 1 is a partial schematic configuration diagram of an embodiment of a voltage detection device according to the present invention, FIG. 2 is a configuration diagram of a sampling type streak camera, and FIG. 3 is a diagram showing an example of the light intensity waveform of emitted light.
FIGS. 4(a) to (C) are AC components I S
Figures 5 and 6 are schematic configuration diagrams of conventional voltage detection devices, respectively, and Figure 7 (a) shows the light intensity vs. voltage V. Figure 7(b) is a diagram showing the modulation voltage ΔV from the object under test, and Figure 7(C) shows the change in Figure 7(b) at operating point A in Figure 7(a). FIG. 3 is a diagram showing the light intensity I obtained when a 7A voltage ΔV is applied. DESCRIPTION OF SYMBOLS 1... Optical modulator, 2... Sampling type high-speed photodetector, 53... Measured object, 54... Boggels cell, 55... Polarizer,
57...Analyzer, 70...DC light source No. 2
figure

Claims (1)

[Scope of Claims] 1) A light modulation means for outputting a light intensity signal corresponding to the voltage to be detected, and a sampling type high-speed light detection means for detecting the light intensity signal from the light modulation means. A voltage detection device featuring: 2) The voltage detection device according to claim 1, wherein the optical modulation means has an operating point set such that the S/N ratio is maximized. 3) The voltage detection device according to claim 1, wherein the sampling type high-speed optical detection means is composed of a streak tube having a sampling slit and has a large dynamic range. 4) The voltage detection device according to claim 1, wherein the sampling type high-speed optical detection means is a sampling type optical oscilloscope. 5) The voltage detection device according to claim 1, wherein the sampling type high-speed light detection means is a synchro scan photometer.