JP2893921B2 - Optical sampling device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for measuring a high-speed electric signal, and more particularly to an optical sampling device with improved S / N.

<Prior Art> Recently, many high-speed electronic devices have been developed. For example, HEMT (High Electron Mobility Trans
istor), the gate delay time is about 10 ps, and the direct modulation band of a semiconductor laser used for optical communication and the like has reached several tens of GHz. In order to measure a high-speed phenomenon by such a high-speed electronic device, a sampling oscilloscope is usually used. FIG. 4 shows the principle of the sampling oscilloscope. That is, the measurement is performed while gradually shifting the gate time for N consecutive signals to be measured as in (A), and the results are combined to obtain a measurement value as in (B). In this technique, the sampling width becomes the resolution of the measurement result.

On the other hand, since the GaAs substrate has an electro-optic effect, when irradiated with light, the plane of polarization of the reflected return light changes according to the magnitude of the electric field. Utilizing this phenomenon, a measuring device using light has been developed. FIG. 5 shows the configuration of a measuring apparatus using such light. The output light of the YAG laser 1 is compressed to a pulse width of about ps by the pulse compression unit 2 and is input to the GaAs integrated circuit 5 via the polarizer 3 and the wavelength plate 4. The return light passes through the wave plate 4 and is reflected by the polarizer 3. The intensity of the returned light is measured by the light receiving element 6 and displayed on the display unit 8. When the electric field generated by the GaAs integrated circuit 5 is changed by the drive circuit 7, the plane of polarization of the returned light changes, and the intensity of light incident on the light receiving element 6 by the polarizer 3 changes. By the drive circuit 7,
Timing of output light of YAG laser 1 and GaAs integrated circuit 5
The operation of the GaAs integrated circuit 5 can be measured according to the same principle as the sampling technique described with reference to FIG. 4 by synchronizing the timing for driving the GaAs integrated circuit and gradually shifting the phase difference.

<Problems to be solved by the invention> However, in the sampling oscilloscope of FIG. 4, the sampling width is limited by the speed of the step recovery diode, and is limited to about 25 ps, and even the optical oscilloscope using optical pulses is limited to about 10 ps. There was a problem that.

Although the measurement apparatus using light shown in FIG. 5 can measure in the order of ps, it is difficult to increase the S / N ratio because the intensity and signal intensity of the light incident on the light receiving element 6 are weak. There was a problem that was.

<Object of the Invention> The present invention has been made to solve the above problems, and has as its object to realize an optical sampling device capable of measuring a high-speed measurement signal at a high S / N ratio.

<Means for Solving the Problems> According to the present invention, the state of the plane of polarization of an optical pulse is changed in accordance with the operating voltage of the circuit under test, and the change in the plane of polarization is detected to measure the voltage waveform of the circuit under test. The present invention relates to an optical sampling device, which is characterized by an optical pulse generating means for outputting an optical pulse, a polarization plane modulating means for modulating the state of the plane of polarization of the output light of the optical pulse generating means, and a polarization plane An electro-optical element that changes the plane of polarization by an electric field corresponding to the operating voltage of the circuit to be measured by receiving the output light of the modulating means,
Detecting means for detecting a change in the plane of polarization in the output light of the electro-optical element, and synchronous detecting means for synchronously detecting the output of the detecting means; and detecting the voltage waveform of the circuit under test based on the output of the synchronous detecting means. The point is that it is configured to measure.

<Operation> The polarization-modulated optical pulse is applied to the electro-optical element to which the electric field of the circuit to be measured is applied, and after rotating the plane of polarization, synchronous detection is performed to increase the operating voltage of the circuit to be measured.
It can be measured by ratio.

<Embodiment> FIG. 1 shows an embodiment of an optical sampling apparatus according to the present invention. The same parts as those in FIG. 5 are denoted by the same reference numerals.
Reference numeral 11 denotes a polarization plane modulator that modulates the polarization plane of the transmitted light output of the polarizer 3 and is composed of a phase modulator using an element having an electro-optic effect such as LiNbO ₃ , and 12 denotes an output of the polarization plane modulator 11. GaAs integrated circuit 5 which is the circuit to be measured when the emitted light is incident
Λ / 2 plate (half-wave plate), 13 is a λ / 2 plate 12, a polarization modulator 11 and a polarizer 3 for reflecting light reflected by the GaAs integrated circuit 5.
A lock-in amplifier for inputting an output electric signal of the light-receiving element 6 after entering the light-receiving element 6 through the optical amplifier 6, a display device 14 for inputting an output of the lock-in amplifier 13, and a polarization modulator 11
This is an oscillator that outputs the modulated signal of FIG. 1 and a signal serving as a reference signal of the lock-in amplifier 13. The polarizer 3 and the light receiving element 6 constitute detection means for detecting a change in the plane of polarization.

The operation of the apparatus having the above configuration will be described below. Figure 2 shows the first
It is an operation explanatory view for explaining the operation of the main part of the figure. Figure 3 shows the output of the oscillator 15 and the polarization modulator 11 is a polarization modulator of the incident light.
Electric field component (Y-axis component) perpendicular to 11 main axes (X-axis)
5 is a time chart showing a phase difference and output of the light-receiving element 6 given to the first embodiment. In the figure, A1 to G2 indicate the state of the polarization plane when the GaAs integrated circuit 5 is viewed from the polarizer 3, and the suffix 1 indicates when the output of the oscillator 15 is Lo, and the suffix 2 indicates when the output of the oscillator 15 is Hi. Corresponding. The incident light transmitted through the polarizer 3 becomes linearly polarized light (A1, A2), and enters the polarization plane modulator 11. The principal axis of the polarization modulator 11 is 22.5 ° with respect to the axis of the polarizer 3 (the same applies hereinafter).
It is rotating, 90 ° when the output of oscillator 15 is Lo, 27 when it is Hi
Gives a 0 ° phase difference. Therefore, in the former case, clockwise elliptically polarized light (B1), and in the latter case, counterclockwise elliptically polarized light (B2)
Becomes Next, when passing through the λ / 2 plate 12, the major axis of the elliptically polarized light
The angle formed by the major axis of the refractive index ellipsoid of the GaAs integrated circuit 5 is 45 °. For this purpose, when the major axis of the refractive index ellipsoid of the GaAs integrated circuit 5 and the axis of the polarizer 3 coincide with each other, the direction of the main axis of the λ / 2 plate 12 is adjusted in advance to 33.75 °. It should be left. As a result, the light transmitted through the λ / 2 plate 12 becomes left-handed elliptically polarized light and right-handed elliptically polarized light in the major axis direction of 45 ° (C1, C2). Since the GaAs integrated circuit 5 has an electro-optic effect, if the circuit is in an operating state, the plane of polarization of the irradiated light is changed according to the electric field intensity. Therefore, the light incident on the GaAs integrated circuit 5 changes its polarization plane state in accordance with the change in the operating voltage (corresponding to the electric field intensity) of the GaAs integrated circuit 5. Assume now that the main axis XY of the GaAs integrated circuit 5 is as shown in the figure, and the phase of the electric field of the Y-direction component is slightly delayed with respect to the electric field of the X-direction component of the incident light. In this case, when the left-handed elliptically polarized light (C1) is incident, the reflected light has a smaller ellipticity (D1), and the right-handed elliptically polarized light (C2) has a larger ellipticity (D2) (according to the GaAs integrated circuit 5). When the phase difference is small). This reflected light passes through the λ / 2 plate 12 again (E1, E2),
The light passes through the polarization modulator 11 and becomes linearly polarized light (F1, F2).
At this time, the angle of the plane of polarization with respect to the axis of the polarizer 3 changes depending on the ellipticity, and the magnitude of the angle corresponds to the magnitude of the ellipticity.
For example, when the ellipticity is 1 / tan 22.5 ° (when the state of the polarization plane does not change in GaAs), the angle is 45 °. The light emitted from the polarization plane modulator 11 further enters the polarizer 3, and only the polarization component in the vertical direction enters the light receiving element 6 (G1, G2). The output of the light receiving element 6 increases when the output of the oscillator 15 is Lo, and decreases when it is Hi (FIG. 3C). The output of the light receiving element 6 is synchronously detected by the lock-in amplifier 13 using the output of the oscillator 15 as a reference signal, and an output corresponding to the operating voltage of the GaAs integrated circuit 5 is obtained.
Based on this output, the voltage waveform of the circuit under test 5 is displayed on the display device.
Displayed at 14.

According to the optical sampling device having such a configuration, since the state of the polarization plane is modulated and the output of the light receiving element is synchronously detected by the lock-in amplifier to obtain a signal, the transmission noise bandwidth can be theoretically increased as much as possible. It can be reduced and S / N is improved. Also, if the modulation frequency is adjusted to a band where the noise of the light source mainly composed of 1 / f noise is small, the S / N is further improved.

Also, by modulating the state of the polarization plane, the change in the state of the polarization plane due to the operating voltage of the circuit under test, that is, the signal intensity incident on the light receiving element is equivalently doubled and detected, so that the sensitivity and S / N are reduced. improves.

In these examples, the case where the object to be measured is a GaAs integrated circuit, that is, the case where the object to be measured itself is made of an electro-optical material has been described, but a material having no electro-optical effect such as silicon may be used. Applied. In this case, placing a material having an electro-optic effect, such as proximity to LiTaO ₃ single crystal to be measured such as silicon, by irradiating light to the LiTaO ₃ single crystal, the measurement circuit is generated composed of silicon or the like An electro-optic effect may be generated by the generated electric field.

In the above embodiment, the polarization plane modulator was used, and the state of the polarization plane was modulated by changing the phase difference to 90 ° and 270 °. However, the number of modulators, the angle of the axis, and the phase difference are not limited to this. Instead, any combination can be used as long as the state of the plane of polarization is modulated and the intensity of light incident on the light receiving element is modulated.

Alternatively, transmitted light may be detected instead of detecting a change in the state of the plane of polarization of reflected light from the GaAs integrated circuit.

<Effects of the Invention> As described above in detail based on the embodiments, according to the present invention, it is possible to realize an optical sampling device capable of measuring a high-speed measurement signal at a high S / N ratio with a simple configuration. Can be.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of an optical sampling device according to the present invention, FIG. 2 is an explanatory diagram for explaining the operation of the FIG. 1 device, and FIG. FIG. 4 is a time chart for explanation, FIG. 4 is a principle diagram of a sampling technique, and FIG. 5 is a configuration diagram of a conventional optical sampling device. 1 ... optical pulse generation means, 5 ... measured circuit, 6 ... detection means, 11 ... polarization plane modulation means, 13 ... synchronous detection means.

Claims (1)

(57) [Claims] An optical sampling apparatus for changing the state of the plane of polarization of an optical pulse in accordance with the operating voltage of a circuit to be measured, detecting the change in the plane of polarization, and measuring the voltage waveform of the circuit to be measured. An optical pulse generating means for outputting an optical pulse; a polarization plane modulating means for modulating the state of the plane of polarization of the output light from the optical pulse generating means; An electro-optical element that changes the plane of polarization by a corresponding electric field; detecting means for detecting a change in the plane of polarization in the output light of the electro-optical element; and synchronous detecting means for synchronously detecting the output of the detecting means. An optical sampling device characterized in that a voltage waveform of a circuit to be measured is measured based on an output of a detection means.