JP2742474B2 - High-speed voltage measurement device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-speed voltage measuring device using an electro-optic crystal.

[0002]

2. Description of the Related Art Conventionally, there is a high-speed voltage measuring device 1 as shown in FIG.

The high-speed voltage measuring device 1 comprises a light source 2, a light intensity modulator 4 comprising a polarizer 4A, a light modulator 4B and an analyzer 4C, a high-speed light detector 6 comprising, for example, a streak camera, and a processing device. 7 and a display device 8. Light from the light source 2 is input to the light intensity modulator 4,
The optical modulator 4B receives a change in the refractive index in response to the input electric signal to be measured, whereby the polarization state of the input light changes in the optical modulator 4B and is converted into a change in intensity by the analyzer 4C, thereby changing the speed. The light is input to the photodetector 6.

The voltage V applied to the optical modulator 4B and the voltage of the analyzer 4
As shown in FIG. 7, there is a relationship expressed by the following equation (1) between the output light intensity I input to the high-speed photodetector 6 via C.

I = I ₀ sin ² (π / 2 · V / Vπ) (1)

Here, Vπ is a half-wavelength voltage, which is determined from the performance of the optical modulator 4B.

Accordingly, the high-speed photodetector 6 detects light whose intensity is modulated by the electric signal to be measured, based on the above equation (1).

[0008]

In the conventional high-speed voltage measuring device 1 as described above, as shown in FIG.
Since the voltage V applied to the optical modulator 4B and the output light intensity I via the analyzer 4C are a function of sin ² and are not proportional, the processing device 7 needs to calculate V from I. ,
It is necessary to convert based on the output characteristics of FIG.

In this case, when V is small, there is a problem that accurate measurement is difficult because the change of I with respect to the change of V is small.

In addition, since the amount of light detected by the high-speed photodetector 6 is small, there is a problem that the S / N ratio deteriorates.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and can perform measurement easily even at a small voltage without using conversion based on input / output characteristics. It is another object of the present invention to provide a high-speed voltage measuring device having a better S / N ratio.

[0012]

SUMMARY OF THE INVENTION The present invention provides a light source for outputting polarized light, an optical modulator using an electro-optic crystal,
A polarization interferometer and a high-speed one-dimensional photodetector are arranged in this order, and an interference formed on an input surface of the photodetector in response to a change in an electric signal applied to the optical modulator. The above object is attained by a high-speed voltage measuring device, wherein the voltage of the electric signal is detected based on the amount of movement of the stripe.

The polarization interferometer may include a birefringent crystal and an analyzer in this order from the light input side.

The polarization interferometer comprises a single slit and a double slit parallel to the single slit, and polarizers having a polarization direction of + 45 ° and −45 ° with respect to the longitudinal direction of the single slit are provided. A Young interferometer provided in each slit; and a light interferometer provided on the light output side of the Young interferometer and having a polarization direction of 4 relative to the polarizer.
5 ° different analyzers.

[0015]

According to the present invention, a polarization interferometer for generating interference fringes in accordance with the polarization state of incident light and an electric signal to be measured applied to the input side of the polarization interferometer allow the incident light to be reflected. An optical modulator that changes the polarization state and outputs the light, and utilizes the fact that the interference fringes move in proportion to the voltage applied to the optical modulator.

The voltage of the electric signal to be measured can be measured by detecting the amount of movement of the interference fringes by a high-speed one-dimensional photodetector.

Since the voltage change of the electric signal to be measured and the amount of movement of the interference fringe are in a proportional relationship, unlike the conventional high-speed voltage measuring device of FIG. Voltage can be measured.

For the same reason, the linearity between the voltage and the amount of movement of the interference fringes is good, a high measurement accuracy can be obtained, and the measurement can be performed regardless of the magnitude of the half-wave voltage Vπ of the optical modulator. It has an excellent effect that it can be performed.

[0019]

Embodiments of the present invention will be described below with reference to the drawings.

As shown in FIG. 1, a high-speed voltage measuring apparatus 10 according to an embodiment of the present invention includes a light source 12 and a polarizer 14.
And an optical modulator 16 made of an electro-optic crystal to which an electric signal to be measured is applied, a polarization interferometer 18, and the polarization interferometer 1
A streak camera 20 for receiving the output light from the strobe camera 8, a processing device 22 for processing an output signal of the streak camera 20, and a display device 23 arranged in this order from the light source 12 side. The voltage of the electric signal is obtained based on the amount of movement of the interference fringes formed on the input surface of the streak camera 20 in accordance with the change in the electric signal applied to the device 16.

The polarizer 14 can be omitted when the output light from the light source 12 is polarized.

As shown in FIG. 2, the polarization interferometer 18 includes an objective lens 24, a birefringent crystal 26,
8 are arranged in this order.

The polarization direction of the analyzer 28 is arranged so as to have an angle of 45 ° with the optical axis of the crystal of the birefringent crystal 26.

As shown in FIG. 3, the streak camera 20 is set so that the entrance slit 20A crosses the interference fringes.

The processing device 22 includes the streak camera 2
The applied voltage V is obtained from the interval A between the peak values of the interference fringes obtained at 0 and the moving amount X of the peak based on the following equation (2).

Next, the operation of the above embodiment will be described.

When polarized light enters the polarization interferometer 18, it is expanded by the objective lens 24 and enters the birefringent crystal 26.

In the birefringent crystal 26, the input beam is split into two polarization states, a direction determined by the optical axis of the crystal and a direction perpendicular to the direction, and propagates through different paths.
An optical path difference will be given to the two output lights.

As described above, the analyzer 28 is arranged so that its polarization direction is at an angle of 45 ° with respect to the optical axis of the birefringent crystal 26. The two orthogonal beams interfere after passing through the analyzer 28, and their interference fringes are formed on the entrance slit 20A which is the input surface of the streak camera 20.

On the other hand, the optical modulator 16 changes the polarization state of the incident light according to the applied voltage, and outputs it to the polarization interferometer 18.

Therefore, the interference fringes formed on the input surface of the streak camera 20 by the polarization interferometer 18 move in proportion to the change of the polarization state by the optical modulator 16, that is, the change of the applied voltage.

The amount of movement X of the interference fringes at this time is given by the following equation (2), where A is the interval between the interference fringes, V is the voltage applied to the optical modulator 16, and Vπ is the half-wavelength voltage. Will be.

X = A / 2 · V / Vπ (2)

For example, FIG. 4 shows an output example of the streak camera 20 when an electric signal changing in a step function is measured. When the voltage is not applied to the optical modulator 16 (time T1), the peak positions (channels) of the output due to the interference fringes are A1 to A3 in FIG.
Indicated by Here, the vertical axis in FIG. 4 indicates time, and the horizontal axis indicates the position of the entrance slit 20A.

The processing unit 22 obtains three peak channels A1 to A3, and obtains an interference fringe interval A from the three peak channels A1 to A3.

Next, at time T2, when the electric signal to be measured is applied to the optical modulator 16, the interference fringes move.
3, the peaks B1 to B3 of the output of the streak camera 20 based on the interference fringes are obtained, and the above-described channel A1 is determined.
By comparing with A3, the moving amount X of the interference fringes can be obtained.

As described above, the voltage V can be obtained from the movement amount X, the interval A of the interference fringes, and the known Vπ.

By performing such calculations in the processing device 22 over all the times, the waveform of the electric signal to be measured can be obtained.

The streak camera 20 can measure not only a repetitive phenomenon but also an electric signal to be measured as a single event.

In the above embodiment, the angle between the polarization direction of the analyzer 28 and the optical axis of the crystal of the birefringent crystal 26 is 45 °.
However, the present invention is not limited to this, and it is sufficient if they do not coincide or are orthogonal.

In the above embodiment, the polarization interferometer 18
Includes the birefringent crystal 26, but the present invention is not limited to this, and the polarization interferometer may have another configuration.

For example, as shown in FIG. 5, a single slit 30 and a double slit 32 parallel to the single slit 30 are provided, and the polarized light is polarized at + 45 ° and −45 ° with respect to the longitudinal direction of the single slit 30. Children 34A, 34
B, and a polarization direction of the polarizer 14 provided on the light output side of the Young interferometer 36.
And an analyzer 38 having the same or orthogonal deflection direction .

The light input to the Young's interferometer 36 is
The light is diffracted and spread by the single slit 30 and enters the double slit 32.

Since the double slit 32 is provided with the polarizers 34A and 34B having polarization directions orthogonal to each other, the double slit 32 becomes light in a polarization state orthogonal to each other.
After passing through the analyzer 34B, they interfere and form interference fringes on the input surface of the streak camera 20.

When the electric signal to be measured is applied to the optical modulator 16, the phase difference between the two lights in the orthogonal polarization state changes, and the interference fringes move according to the change in the phase difference.

In the above embodiment, the polarizer 34A,
The polarization direction of 34B is not limited to + 45 ° and −45 ° with respect to the longitudinal direction of the single slit 30, and it is only necessary that both directions do not coincide .

In the above embodiment, the interference fringes are detected by the streak camera 20, but the present invention is not limited to this, and a high-speed one-dimensional photodetector that detects light at high speed is used. I just need.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a high-speed voltage measuring device according to the present invention.

FIG. 2 is a block diagram illustrating an example of a polarization interferometer according to the embodiment.

FIG. 3 is a perspective view showing a positional relationship between a streak camera and interference fringes in the apparatus of the embodiment.

FIG. 4 is a diagram showing an output example of the streak camera.

FIG. 5 is a block diagram showing another example of the polarization interferometer in the embodiment.

FIG. 6 is a block diagram showing a conventional high-speed voltage measuring device.

FIG. 7 is a diagram showing a relationship between an applied voltage to an optical modulator and an output of a photodetector in the high-speed voltage measuring device of FIG. 6;

[Description of Signs] 10: High-speed voltage measurement device, 12: Light source, 14, 34A, 34B: Polarizer, 16: Optical modulator, 18: Polarization interferometer, 20: Streak camera, 22: Processing device, 23: Display Apparatus, 26: Birefringent crystal, 28, 38: Analyzer, 30: Single slit, 32: Double slit, 36: Young's interferometer.

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-3-267766 (JP, A) JP-A-3-158704 (JP, A) JP-A-2-156166 (JP, A) JP-A-62-162 63802 (JP, A)

Claims (5)

(57) [Claims] 1. A light source for outputting polarized light, an optical modulator using an electro-optic crystal, a polarization interferometer, and a high-speed one-dimensional photodetector are arranged in this order. Detecting a voltage of the electric signal based on a moving amount of an interference fringe formed on an input surface of the high-speed one-dimensional photodetector in accordance with a change in the electric signal applied to the detector. High-speed voltage measurement device. 2. A high-speed voltage measuring apparatus according to claim 1, wherein said polarization interferometer comprises a birefringent crystal and an analyzer in this order from the light input side. 3. The polarization interferometer according to claim 1, wherein the polarization interferometer comprises a single slit and a double slit parallel to the single slit, and is + 45 ° with respect to the longitudinal direction of the single slit.
And a polarizer having a polarization direction of -45 °, a Young interferometer provided in each slit of the double slit, and provided on the light output side of the Young interferometer, the polarization direction with respect to the polarizer A high-speed voltage measuring device comprising: an analyzer that differs by 45 °. 4. The high-speed communication system according to claim 1, 2 or 3,
A high-speed voltage measuring device, wherein the two-dimensional photodetector is a streak camera. 5. The high-speed voltage measuring device according to claim 1, wherein the light source comprises a light source that outputs unpolarized light and a polarizer.