JPH04213081A - Optical sampling apparatus - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] This invention relates to ultrahigh-speed electronic devices (
This invention relates to improvements in optical sampling devices that measure high-speed electrical signals and high-speed optical pulse waveforms in GaAs ICs, InPICs, etc.

0002

[Background Art] GaAs, which is a recent high-speed electronic device,
The oscillation frequency of MESFET exceeds 100GHz,
20 for InGaAs/AlGaAs modulated doped FETs.
Characteristics of 0 GHz or higher have been obtained. The characteristics of these high-speed electronic devices cannot be measured using conventional sampling oscilloscopes or the like for the following two reasons. (b) Lack of measurement bandwidth The characteristics of modern high-speed electronic devices are
exceeds the measurement band of the analyzer. (b) Measurement by contact In general, as the speed of an element increases, it becomes more susceptible to the effects of parasitic capacitance depending on its arrangement, which becomes a cause of impediments to higher speeds. Conventional sampling oscilloscopes have a probe in contact with the element during measurement, which affects the characteristics of the element.

Conventionally, sampling methods have been used to measure high-speed phenomena. Figure 5 shows the principle of the sampling method. That is, N consecutive signals under measurement as shown in (A) are measured while shifting the gate time little by little, and the results are combined to obtain a measured value as shown in (B). Therefore, even a high-speed phenomenon can be treated as a low-speed phenomenon. In this technique, the sampling width determines the time resolution of the measurement results. To increase the measurement bandwidth,
It is necessary to shorten this sampling width. On the other hand, Ray
In recent years, it has become possible to obtain optical pulses of several ps to several fs in this field. Therefore, by using this optical pulse as a sampling gate pulse, it is now possible to measure high-speed signals that could not be measured using conventional electrical methods. Since there is no need to do this, it is now possible to perform measurements without affecting the device.

FIG. 6 shows a conventional example of a measuring device that uses optical pulses for sampling as described above. This device is a Ga
Since the As substrate has an electro-optic effect, the polarization plane of the returned light changes depending on the magnitude of the electric field, which is utilized. The output light of the YAG laser 1 is converted to ps by the pulse compression section 2.
It is compressed to a pulse width of about 100 mL, and is irradiated to the circuit under test 5 via the polarizer 3 and the wave plate 4. Here, the circuit under test 5 is G
Assuming that the circuit is made of an aAs integrated circuit or a material with an electro-optic effect such as InP, when the circuit is in operation, the polarization plane of the irradiated light changes due to the generated electric field. Therefore, the reflected return light has a polarization plane different from that of the incident light. After the polarized components are separated by a polarizer 3, their intensity is measured by a light receiving element 6, and a measured voltage waveform is displayed on a display section 8. By sequentially sampling the repetition frequency of the drive circuit 7 that drives the circuit under test 5 by slightly shifting it from the repetition frequency of the pulses of the YAG laser 1, a high-speed phenomenon can be treated as a low-speed phenomenon, as explained in FIG. The internal voltage waveform of the circuit under test 5 can be measured using the same principle as the sampling technique described above. According to this device ps
Measurements can be made at sampling rates of the order of magnitude.

[0005] Conventionally, an SHG correlator using an autocorrelation method has been used as a means for measuring high-speed optical pulses. The pulse width of the light can be determined by dividing the measured optical pulse into two optical paths, giving an optical path difference and making it incident on the SHG crystal, and measuring the intensity of the second harmonic generated from the SHG crystal while changing the optical path difference. can be measured.

[0006]

However, the apparatus shown in FIG. 6 has a problem in that the time resolution is degraded due to jitter between the measurement signal and the sampling pulse. That is, when the jitter becomes larger than the pulse width of light, it becomes equivalent to sampling with light having a pulse width comparable to the jitter, and the time resolution is determined by the jitter rather than the pulse width. Since such jitter of about 0.1 ps always exists, the time resolution is limited. Furthermore, since the above-mentioned apparatus uses a time series sampling method, measurement cannot be performed unless the same waveform is repeated, and a single phenomenon cannot be measured. On the other hand, the above-mentioned SHG correlator has the following problems, which limits its use. (a) Only repeated optical pulses can be measured; measurement of single optical pulses is essentially impossible. (b) Since it is an autocorrelation method, the shape of the pulse cannot be measured. Therefore, even if the pulse width is the same, if the pulse shape is different, the pulse width will be measured differently. (c) Since the configuration uses a SHG crystal to generate second harmonics, the efficiency is poor, and measurement cannot be performed if the intensity of the light to be measured is low.

The present invention was made to solve the above-mentioned problems, and its purpose is to realize an optical sampling device that is not affected by jitter, has high time resolution, and can measure even single phenomena. .

[0008]

[Means for Solving the Problems] The first optical sampling device according to the present invention includes a first optical pulse generating means for irradiating an output optical pulse onto a circuit under test, and an output of the first optical pulse generating means. a second optical pulse generating means that outputs a temporally shorter optical pulse in synchronization with the light; and a second optical pulse generating means that outputs a temporally shorter optical pulse in synchronization with the light, and a spatial time difference between the return light from the circuit under test and the optical pulse from the second optical pulse generating means. It includes a nonlinear optical material that is irradiated crosswise within the nonlinear optical material so that the light is generated, and a line sensor that converts the spatial distribution of light generated from the nonlinear optical material into an electrical signal. It is characterized by being configured to measure the voltage waveform of the measurement circuit. A second aspect of the optical sampling device according to the present invention includes a light source to be measured that outputs light to be measured, a light pulse generating means that outputs a temporally shorter light pulse in synchronization with the light source to be measured, and A nonlinear optical material in which the output light and the light pulse from the light pulse generation means intersect and are irradiated with each other so that a spatial time difference occurs, and a spatial distribution of the light generated from this nonlinear optical material. The present invention is characterized in that it includes a line sensor that converts into an electrical signal, and is configured to measure changes over time in the intensity of the light pulse output from the light source to be measured based on the output of the line sensor.

[0009]

[Operation] When the return optical pulse from the circuit under test and the short optical pulse from the second optical pulse generation means intersect on the nonlinear optical material, a spatial time difference occurs, which is detected by the line sensor as a second harmonic. Since the return light pulse is sampled with the short light pulse,
Measurement voltage waveform can be measured. In addition, when the light pulse to be measured and the short light pulse from the light pulse generating means intersect on the nonlinear optical material, a spatial time difference occurs, and the line sensor detects the light emitted from the nonlinear optical material. Since the light pulse is sampled with the short light pulse, it is possible to measure the temporal change in the intensity of the light pulse to be measured.

0010

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be explained in detail below with reference to the drawings. FIG. 1 shows an embodiment of an optical sampling device according to the present invention. In Fig. 1, 11 is a pulse laser such as a YAG laser.
12 is a Pockels cell 1 constituting a shutter that controls the passage of light pulses output from the pulse laser 11;
3 is a half mirror that constitutes a separation means that divides the light output from the Pockels cell into two optical paths; 14 is a mirror that changes the direction of the light that has passed through half mirror 13; and 15 is a mirror that is reflected by mirror 14. 16 is a polarizer that reflects the light that has passed through the delay line 15; 17 is a device to be measured consisting of a GaAs integrated circuit that is irradiated with the reflected light from the polarizer 16; It is a circuit. 1
8 is a pulse compressor that reduces the pulse time width of the light reflected by the half mirror 13; 20 is a nonlinear optical material;
A nonlinear optical crystal such as KTP or BBO, which is arranged so that the light enters from one side through the pulse compressor 18 and the output light of the pulse compressor 18 enters from the other, intersects inside.
Reference numeral 21 denotes a line sensor that is provided facing the nonlinear crystal 20 and close to the rear thereof, and receives the second harmonic generated by the nonlinear crystal.
22 is a calculation display unit that calculates and displays the signal voltage waveform of the circuit under test 17 based on the output of the line sensor 21, and 23 is the circuit under test. 17, a scan signal for the line sensor 21, a timing signal for the pulse laser 11, and a drive signal for the Pockels cell 12. Here, the Pockels cell is a type of optical switch that uses the Pockels effect, which is an electro-optic effect. The pulse laser 11, the Pockels cell 12, and the half mirror 13 constitute a first optical pulse generating means that generates an optical pulse to irradiate the circuit under test 17.
The laser 11, Pockels cell 12, half mirror 13, and pulse compressor 18 constitute a second optical pulse generating means that outputs a temporally shorter optical pulse in synchronization with the output light of the first optical pulse generating means. do.

The operation of the above device will now be explained. The pulsed laser 11 generates a train of light pulses, of which only one light pulse passes through the Pockels cell 12. A part of this light pulse passes through the half mirror 13 and passes through the mirror 1.
4 and the delay line 15, the light is reflected by the polarizer 16 and irradiated onto the circuit under test 17. The circuit under test 17 is G
Since aAs has an electro-optic effect, it changes the plane of polarization of the irradiated light when the circuit is in operation. That is, the reflected return light has a polarization plane different from that of the incident light. The amount of change in this plane of polarization is proportional to the internal electric field strength, so when this polarized wave component is separated by the polarizer 16, this light becomes the change in the electric field strength inside the circuit under test converted into light intensity. . On the other hand, the optical pulse reflected by the half mirror 13 is compressed by the pulse compressor 18, and the pulse width becomes narrower.

The optical pulse from the circuit under test 17 and the optical pulse compressed by the pulse compressor 18 are incident on the nonlinear optical crystal 20 at equal angles, as shown in FIG. Furthermore, since the optical path difference between the two optical pulses is adjusted by the delay line 15, they arrive at the nonlinear optical crystal 20 at the same time. At this time, the two incident lights have polarization planes that are orthogonal to each other. When two lights are incident simultaneously, the nonlinear optical crystal 20 generates a second harmonic of the incident light, that is, light whose wavelength is 1/2. The line sensor 21 receives only this second harmonic. As shown in FIG. 2, the optical pulse from the circuit under test 17 and the compressed optical pulse enter the nonlinear optical crystal 20 so as to intersect with each other, so that they are incident in the horizontal axis direction of the nonlinear optical crystal 20, that is, in the X-axis direction in the figure. A time difference occurs between the two optical pulses, and the horizontal axis direction corresponds to the time difference. 2 at points a, b, and c inside the nonlinear optical crystal 20 in FIG.
Figure 3 (A), (B), (
C). Here, the light from the circuit under test 17 is represented by 31, and the pulse-compressed light is represented by 32. Since the nonlinear optical crystal 20 generates a second harmonic of the incident light when two lights are incident at the same time, the intensities of the two lights are multiplied. That is, in the horizontal direction of FIG. 2, the light from the circuit under test 17 is sampled with pulse-compressed light. Specifically, in FIG. 2, pulse compressed light 3
2 intersects the returned light 31 temporally in the order of point c, point b, and point a, so the sampling of the returned light was performed in the order shown in FIGS. 3(C), 3(B), and 3(A). As a result, the conventional time-series sampling can be replaced with spatial sampling. The signal detected by the scan of the line sensor 21 is displayed as a waveform on the time axis on the calculation display section 22, and the operating voltage of the circuit under test 17 is measured.

[0013] According to the optical sampling device having such a configuration, a first optical pulse having an intensity proportional to the characteristic on the time axis of the circuit under test, and a second optical pulse having a narrower pulse width. are arranged so that a spatial time difference occurs, and the product of their intensities is obtained using a nonlinear optical crystal, which has the following advantages. stomach. It is possible to measure not only repeated phenomena but also single phenomena. B. Since there is no need to sample multiple periods, unlike conventional sampling devices, there is no restriction on time resolution due to jitter between the drive signal of the circuit under test and the optical pulse, and an optical sampling device with high time resolution can be realized.

Note that the circuit to be measured is not limited to a GaAs integrated circuit, but can be applied to a circuit made of any material having an electro-optic effect such as InP. Further, in each of the above embodiments, the case where the object to be measured is made of an electro-optic material, such as a GaAs integrated circuit, has been described, but the present invention can also be applied to a material that does not have an electro-optic effect, such as silicon. In this case, LiTaO3 is placed close to the object to be measured such as silicon.
A material with an electro-optic effect such as a (lithium tantalate) single crystal is placed, and the LiTaO3 single crystal is irradiated with light to produce an electro-optic effect due to the leakage electric field from the circuit under test made of silicon etc. do it. Further, in the above embodiment, a change in the plane of polarization due to the electro-optic effect is detected, but the present invention is not limited to this, and a physical quantity such as a change in absorption spectrum due to a change in the carrier density of a semiconductor may be detected. In this case, instead of using an electro-optic material, a semiconductor material is placed within the electric field of the circuit under test, its light absorption rate is changed by the electric field from the circuit under test, and pulsed light is incident on it to increase its light intensity. Modulate. Furthermore, instead of detecting the reflected light of the circuit under test, transmitted light may be detected. Furthermore, two different light sources may be used to synchronize the light pulses irradiated onto the circuit under test and the pulse-compressed light pulses. Furthermore, materials other than crystals can also be used as the nonlinear optical material 20. Further, in FIG. 2, the efficiency is maximized when the return light pulse and the compressed light pulse are incident on the nonlinear optical crystal 20 at the same angle, but they may be incident on the nonlinear optical crystal 20 at different angles.

FIG. 4 is a block diagram showing another embodiment of the optical sampling apparatus according to the present invention, which measures the temporal change in the intensity of high-speed optical pulses. The same parts as in FIG. 1 are given the same symbols and detailed explanations are omitted. In the figure,
The pulsed light to be measured outputted from the light source to be measured 40 becomes parallel light and enters the nonlinear optical crystal 20 . Pulsed light source 1
The pulsed light outputted from 1 passes through Pockels cell 12, pulse compressor 18, and delay line 15, and enters nonlinear optical crystal 20. As in the case of FIG. 2, the two lights are arranged so as to intersect inside the nonlinear optical crystal. The delay line 15 has two optical pulses connected to the nonlinear optical crystal 2.
This is provided to adjust the optical path difference so that they arrive at zero at the same time. A line sensor 21 is provided at the rear of the nonlinear optical crystal 20 and receives the second harmonic generated by the nonlinear optical crystal 20. The output of the line sensor 21 is guided to a calculation display section 22. Pulsed light source 11, Pockels cell 12
, line sensor 21, calculation display section 22, and light source to be measured 40 are driven by a synchronous drive section 23. The pulse laser 11, Pockels cell 12, and pulse compressor 18 constitute a light pulse generating means that outputs a temporally shorter light pulse in synchronization with the light source to be measured.

The operation of the apparatus in FIG. 4 is similar to that in FIG. Optical pulse 42 pulse-compressed by pulse compressor 18
is sufficiently thinner than the optical pulse 41 from the light source 40 to be measured, and the optical pulse 41 is sampled with the optical pulse 42 in the same operation as shown in FIGS. 2 and 3. As a result, the light pulses from the light source to be measured 40 are calculated and displayed on the display unit 2.
2, it can be displayed as a waveform on the time axis.

According to the optical sampling device having such a configuration, a light pulse from the light source to be measured and a narrower light pulse are arranged so that a spatial time difference occurs, and the product of their intensities is calculated using nonlinear optics. Since it is structured to obtain crystals, it has the following advantages. (a) It is possible to measure even if the optical pulse to be measured is not a repeated phenomenon but a single phenomenon. (b) Unlike conventional autocorrelation measurements, the shape of the pulse can be measured. (c) Measurement is possible even when the power of the light to be measured is weak. This is because even if the light pulse from the light source to be measured is weak, if the intensity of the other light pulse is made strong enough, the intensity of the light generated by the nonlinear effect can be increased to a sufficient intensity for measurement. It is.

In each of the above embodiments, since the wavelengths of the two optical pulses are the same, the line sensor receives the second harmonic; however, when the wavelengths are different, the sum frequency, difference frequency,
Nonlinear optical materials (KTP,
It is also possible to generate light of a wavelength different from (at least one) of the incident light from a BBO (BBO is also possible), and detect this with a line sensor.

[0019]

Effects of the Invention As specifically explained based on the embodiments above, according to the present invention, an optical sampling device that is not affected by jitter, has high time resolution, and can measure even a single phenomenon can be easily constructed. It can be realized with a configuration.

[Brief explanation of the drawing]

FIG. 1 is a configuration block diagram showing an embodiment of an optical sampling device according to the present invention.

FIG. 2 is an operation explanatory diagram showing the operation of the circuit in FIG. 1;

FIG. 3 is another operation explanatory diagram showing the operation of the circuit in FIG. 1;

FIG. 4 is a configuration block diagram showing another embodiment of the optical sampling device according to the present invention.

FIG. 5 is a principle diagram of a conventional sampling technique.

FIG. 6 is a configuration block diagram showing a conventional example of an optical sampling device.

[Explanation of symbols]

11 Pulsed laser 12 Pockelsel 13 Half mirror 15 Delay line 17 Circuit under test 18 Pulse compressor 20 Nonlinear optical materials 21 Line sensor 40 Light source to be measured

Claims (2)

[Claims] 1. A first optical pulse generating means for irradiating an output optical pulse onto a circuit under test; and a first optical pulse generating means for outputting a temporally shorter optical pulse in synchronization with the output light of the first optical pulse generating means. a nonlinear optical material on which the return light from the circuit under test and the optical pulse from the second optical pulse generating means intersect and are irradiated therein so as to create a spatial time difference; and a line sensor that converts the spatial distribution of light generated from the nonlinear optical material into an electrical signal, and is configured to measure the voltage waveform of the circuit under test based on the output of the line sensor. Optical sampling device. 2. A light source to be measured that outputs light to be measured; a light pulse generating means that outputs a temporally shorter light pulse in synchronization with the light source to be measured; output light from the light source to be measured; A nonlinear optical material to which light pulses from a pulse generating means cross each other so as to create a spatial time difference, and a line that converts the spatial distribution of light generated from this nonlinear optical material into an electrical signal. What is claimed is: 1. A light sampling device comprising: a sensor, and configured to measure a temporal change in the intensity of a light pulse output from a light source to be measured based on the output of the line sensor.