JP2577582B2 - Voltage detector - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage detector that detects a voltage with a time resolution of the order of picoseconds using an optical modulator.

[Conventional technology]

2. Description of the Related Art Conventionally, an apparatus for detecting a voltage using an optical modulator is known.

9 and 10 are U.S. Pat. Nos. 4,446,425 and 1 respectively.
FIG. 1 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, 986.

9, the pulse light source 50 repeatedly outputs a short pulse light of about 120 femtoseconds, and this short pulse light is input to a device under test 53, for example, a photoelectric switch via a chopper 51 and a variable delay device 52. On the other hand, the light is incident on the optical modulator 40. The optical modulator 40 is composed of a polarizer 55, an electro-optic crystal 54, a phase compensator 56, and an analyzer 57, and utilizes a phenomenon that incident short pulse light is modulated by a voltage from the device under test 53, Waveforms are extracted in the form of light intensity.
More specifically, the voltage to be detected output from the device under test 53 is synchronized with the short pulse light by the electro-optic crystal of the optical modulator 40.
On the other hand, the short pulse light from the pulse light source 50 having a predetermined polarization component extracted by the polarizer 55 is incident on the electro-optic crystal 54. For the electro-optic crystal 54, an electro-optic material such as LiNbO ₃ or LiTaO ₃ whose refractive index changes by applying a voltage is used. Due to the above-described properties of the electro-optic material, the short-pulse light incident on the electro-optic crystal 54 changes its polarization state due to the voltage from the device under test 53, is modulated, and is emitted as emission light. It is incident on photon 57. The analyzer 57 extracts two orthogonal polarization components from the output light from the phase compensator 56 and outputs the modulated light intensity signals as outputs from the light modulator 40 to the photodetectors 58 and 5.
9 is incident. In the photodetectors 58 and 59,
The light intensity of each polarization component is detected, and the photodetector is
Differential amplification of the output signals from 58 and 59 and lock-in amplifier 6
1. The detection result is displayed on the display 63 via the averager 62.

Note that the variable delay unit 52 is for gradually delaying the voltage generation timing from the device under test 53 to determine the sampling point of the voltage waveform. Also lock-in amplifier 61
Extracts the output from the differential amplifier 60 at a timing synchronized with the chopper 51 to remove noise components, and the averager 62 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 emitted light output from the optical modulator 40 to the photodetector 59 becomes equal to the voltage V. On the other hand, a VI characteristic as shown in FIG. 11A is obtained. Now, when the voltage from the device under test 53 is not applied to the electro-optic crystal 54 more specifically than the optical modulator 40, the light intensity I to the photo detector 59
Is changed by changing the setting of the phase compensator 56. Here, when the maximum light intensity is set to I ₀ , if the phase compensator 56 is set so that the light intensity to the photodetector 59 becomes 50% of the light intensity I ₀ , FIG. As can be seen from the VI characteristic, the optical modulator 40 apparently has an operating point voltage _Vπ / 2
And the operating point is defined as indicated by A. When the phase compensator 56 is set in this way, when a modulation voltage as shown in FIG. 11B is applied to the optical modulator 40 from the device under test 53, the outgoing light that enters the photodetector 59 from the analyzer 57. Is as shown in FIG. 11 (c). Eleventh
As can be seen from FIGS. 7A to 7C, at the operating point A, since the light intensity I of the light emitted from the analyzer 57 changes most in proportion to the voltage change, the maximum AC component I _AC is obtained. Can be. On the other hand, at the operating point A, the DC component I
_{Although DC} is included, the photodetector 5
By differentially amplifying the two output signals having opposite phases from the signals 8, 59, the DC component I _DC can be removed and only the AC component I _AC can be detected with high sensitivity as a voltage detection result.

Further, in the voltage detection device of FIG.
The light is applied to the streak camera 71 via the optical modulator 40, and the light intensity of the light emitted from the analyzer 57, which varies with the voltage from the device under test 53, is observed by the streak camera 71. The voltage is displayed on a display 63 via 62 to detect the voltage. The voltage output from the device under test 53 and the operation of the lock-in amplifier 61 are synchronized with the pulse from the pulse generator 72. Further, the sweep voltage applied to the deflector (not shown) of the streak camera 71 has a timing gradually shifted by the phase shifter 73 with respect to the pulse from the pulse generator 72.

Since the streak camera 71 is used as the detector in the voltage detection device having such a configuration, the operating point is set to the position indicated by the reference numeral B in FIG. 11A. That is, in the streak camera 71, the dynamic range cannot be large, and if the DC component I _DC of the light intensity I is large, the AC component I _AC as a signal to be detected cannot be observed. When V is "0" V, a phase compensator is used to minimize the light intensity I to the streak camera 71.
56 is set, and the operating point is set at the position indicated by B.

Since the operating point B can make the DC component I _DC extremely small, the modulation factor MOD determined as the ratio of the _AC component I _AC to the DC component I _DC can be maximized, and the streak camera 71 having a narrow dynamic range can be obtained. Also, the AC component I _AC can be observed. The operating point B is
Although the AC component I _AC is considerably reduced as compared with the operating point A, the AC component I _AC is multiplied by the multiplication function of the streak camera 71 to enable measurement.

[Problems to be solved by the invention]

However, in the voltage detecting device shown in FIG. 9, although the operating point is set to A and the maximum AC component I _AC can be obtained, the light intensity I includes the DC component I _DC, so that the dynamic range is narrow. There is a problem that a streak camera as a typical high-speed photodetector cannot be used, and a pulse 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 of FIG. 11, although the operating point is set to B and the DC component I _DC can be remarkably reduced, the AC component I _AC is also reduced, so that a highly sensitive detection result can be obtained. There was a problem that there was a limit.

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

[Means for solving the problem]

The present invention provides a DC light source, chopping means for chopping a voltage from an object to be measured, light modulating means for modulating CW light from the DC light source with a voltage from the chopping means and outputting it as a light intensity signal, and the light intensity A voltage detecting device comprising: a sampling-type light detecting unit that samples and detects a signal; and an amplifying unit that extracts and amplifies a frequency component determined by a chop frequency of the chop unit from an output signal that is sampled and detected. It is an object of the present invention to improve the above-mentioned problems of the prior art.

[Action]

In the present invention, the voltage from the device under test is chopped by the chop means and applied to the light modulation means. The CW light from the DC light source that has entered the light modulating means is modulated by the voltage from the chop means and output as a light intensity signal. The sampling type light detecting means samples and detects the light intensity signal, and the amplifying means extracts and amplifies a frequency component determined by the chop frequency from the sampled and detected output signal.

By the way, in the present invention, even when a DC light source is used, the sampling type light detecting means having a wide dynamic range is used, so that the operating point of the light modulating means can be set to a position where the maximum AC component can be obtained. At this time, the DC component is also superimposed, but the DC component is removed by the amplifying means, and only the AC component is extracted and amplified.

〔Example〕

 Hereinafter, embodiments of the present invention will be described with reference to the drawings.

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

In the voltage detection device of the present embodiment, the CW from the DC light source 70 is made incident on the optical modulator 40, and the incident CW light is applied by the voltage from the DUT 53 applied via the chop circuit 10 in the optical modulator 40. The voltage waveform is modulated to be converted into a light intensity signal and input to the sampling type high-speed photodetector 11. The voltage from the device under test 53 is of a repetitive period, is branched by the branching device 12, and has the chopping circuit 10 as described above.
, And is applied to the sampling type high-speed photodetector 11 as a trigger signal via the trigger signal generator 13 and the delay circuit 14. Further sampling high-speed photodetector
The output signal from 11 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,
It is a laser diode pumped solid laser or a second harmonic generation element. Sampling-type high-speed photodetector 11
Converts the light intensity signal output from the optical modulator 40 into a delay circuit 14
Sweeping in synchronization with a trigger signal from the optical disk, and sampling and extracting a part of the light intensity waveform from an opening of a built-in opening member (not shown). That is, by gradually delaying the trigger signal by the delay circuit 14, 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
Variable pulse generator 16, gate circuit 17, ON / OFF
The lock-in amplifier 15 includes an OFF circuit 18, and the lock-in amplifier 15 includes a frequency counter 19, a control circuit 20, a variable bandpass filter 21, and an amplifier 22.

In the chop circuit 10, when a pulse is generated from the variable pulse generator 16, the gate circuit 17 repeats on / off with alternating pulses 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 extremely large as shown in FIG.
Does not participate. On the other hand, when the gate circuit 17 is on,
When a voltage equal to or higher than the threshold value _VTH is output from the resistor 17, the resistance of the on / off circuit 18 becomes extremely small as shown in FIG. Will be.

On the other hand, the pulse from the variable pulse generator 16 is 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 band-pass 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 band-pass filter 21. Thereby, the on / off circuit of the chop circuit 11
Since only the change between the sampled light intensity signal when 18 is on and the sampled light intensity signal when it is off passes through the variable bandpass filter 21,
The DC component I _DC can be removed from the light intensity signal, and only the AC component I _AC can be amplified by the amplifier 22. Note that instead of inputting the pulse from the variable pulse generator 16 to the frequency counter 19, the output of the gate circuit 17 is
May be controlled so that only the frequency component of the output of the gate circuit 17 can pass through the variable band-pass filter 21. When chopping at a known frequency, the gate circuit 17 supplies a constant frequency output to the on / off circuit 18 and the variable bandpass filter 21 may be changed to a fixed bandpass filter. The pulse generator 16, the frequency counter 19, and the control circuit 20 become unnecessary.

The operation of the voltage detecting device having such a configuration will be described with reference to FIGS.

The voltage V from the device under test 53 is applied to the electro-optic crystal 54 of the optical modulator 40 only when the chop circuit 10 is on, as shown in FIG. If the operating point of the optical modulator 40 is set to A by adjusting the phase compensator 56 (see FIG. 11A), the CW light from the DC light source 70 Modulated by the voltage shown in FIG.
Maximum of the alternating current component I _AC as shown in FIG. 4 (b) is outputted from the optical modulator 40. Incidentally, always DC component I _DC from the optical modulator 40 by setting the operating point A is also output.

The light intensity signal as shown in FIG. 4B from the light modulator 40 is applied to the sampling type high-speed photodetector 11. As described above, the sampling type high-speed photodetector 11 has a trigger signal generator 13,
The light intensity signal is swept by the trigger signal generated by the delay circuit 14, a part of the light intensity waveform is sampled and extracted from an aperture (not shown), and input to the lock-in amplifier 15. The sampling point of the sampling type high-speed photodetector 11 moves by delaying the trigger signal and shifting the sweep timing. When the sampling points S ₁ shown in FIG. 4 (c) is a portion F ₁ of the light intensity waveform FG as shown in Figure 5 was sampled extraction, shown in Figure 6 a result of performing repeated this (a) And output such an output signal. Further, when the sampling points S ₂ shown in FIG. 4 (d) is a portion F ₂ of the light intensity waveform FG samples extracted as shown in FIG. 5,
By repeating this, an output signal as shown in FIG. 6 (b) is output.

Since the dynamic range of the sampling type high-speed photodetector 11 is wide, even if a DC component I _DC is input thereto, the AC component I _{AC and the} DC component I _DC are not saturated without being saturated, as shown in FIGS. 6 (a) and 6 (b). As shown in (1), it is possible to faithfully sample and output.

The output signal sampled and extracted by the sampling type high-speed photodetector 11 in this manner is input to the lock-in amplifier 15, but the lock-in amplifier 15 outputs only the output signal of the frequency component determined by the chop frequency of the chop circuit 10. DC component I _DC of the output signal is removed because it passes,
The AC component I _AC is amplified and output.

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

In the above-described embodiment, the electro-optic crystal 54 of the optical modulator 40 is of a transmission type in which, for example, a traveling wave line for applying a voltage is provided in parallel with the optical path and the modulated light is transmitted and emitted. Alternatively, it may be of a reflection type having a reflecting mirror at the tip to reflect and emit modulated light. In the case of the reflection type, the voltage can be detected without contacting the measured object. The electro-optic crystal 54 is preferably painted black except for the paths of incident light and outgoing light in order to prevent unwanted light from being mixed.

Further, in the above-described embodiment, the trigger signal of the sampling type high-speed photodetector 11 is formed by branching the voltage signal from the device under test. However, as shown in FIG. A trigger signal may be generated at the same time that a voltage is generated from the device under test 53 by a signal from the device 30. The provision of the oscillator 30 makes it easier to confirm the operation of the entire circuit.

When the device under test 53 is, for example, a high-speed photodetector, it is necessary to supply an optical pulse signal to the device under test 53 as shown in FIG. To generate a trigger signal.

Furthermore, a sampling type optical oscilloscope (OOS-0 manufactured by Hamamatsu Photonics, Inc.) is used as the sampling type high-speed photodetector 11.
When using a 1) can measure the voltage 30H _Z ~1GH _Z. In the case of using the synchronous scanning photometer can measure the voltage 80MH _Z ~160MH _Z. Note that the chop frequency must be sufficiently lower than the frequency of these voltages.

〔The invention's effect〕

As described above, according to the present invention, even when a DC light source is used, the sampling type light detecting means is used as the light detecting means. DC component can be effectively removed by the amplifying means.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of one embodiment of a voltage detection device according to the present invention, FIG. 2 is a diagram showing a configuration example of a chop circuit and a lock-in amplifier, and FIG. 3 (a) shows an output voltage of a gate circuit. FIG. 3 (b) is a diagram showing a change in resistance of the ON / OFF circuit, FIG. 4 (a) is a diagram showing a chopped voltage waveform applied to the optical modulator, and FIG. 4 (b) is a light intensity Diagram showing signals,
FIGS. 4C and 4D show the sampling points S ₁ and S ₂ , respectively.
Shows a fifth figure shows the light intensity F _1, F ₂ to be extracted at the sampling points S _1, S _2, FIG. 6 (a), (b) in each sampling point S _1, S ₂ FIGS. 7 and 8 show modified examples of the trigger signal generator. FIGS. 9 and 10 show schematic configuration diagrams of a conventional voltage detection device. 11A is a diagram showing the light intensity I with respect to the voltage V, FIG. 11B is a diagram showing the modulation voltage from the DUT, and FIG. 11C is an operating point A in FIG. 11A. FIG. 11 is a diagram showing the light intensity I obtained when the modulation voltage shown in FIG. 11 (b) is applied. 10 ... Chop circuit, 11 ... Sampling-type high-speed photodetector, 15 ... Lock-in amplifier, 40 ... Optical modulator, 70 ... DC light source

Claims (3)

(57) [Claims] A DC light source; a chop means for chopping a voltage from an object to be measured; a light modulating means for modulating CW light from the DC light source with a voltage from the chop means and outputting as a light intensity signal; A voltage detecting device comprising: a sampling type light detecting means for sampling and detecting an intensity signal; and an amplifying means for extracting and amplifying a frequency component determined by the chopping frequency of the chopping means from the sampling and detected output signal. . 2. The voltage detecting apparatus according to claim 1, wherein said sampling type light detecting means is a sampling type high speed light detector. 3. The voltage detecting device according to claim 2, wherein said sampling type high-speed photodetector is a sampling type optical oscilloscope or a synchro scan photometer.