JPH04148874A - Optical sampling device - Google Patents

Abstract

PURPOSE:To enable a high-speed voltage waveform to be measured without adversely affecting a circuit to be measured by measuring a voltage waveform of the circuit to be measured based on an output of a calculation circuit. CONSTITUTION:This device is provided with a pulse generation means 10 which outputs optical pulses, a separation means 11 which separates this output light into two parts, a pulse compressor 12 which compresses one output light, and an electric optical element 31 which allows that output light to enter and change a polarization surface by an electric field corresponding to operation voltage of a circuit to be measured 16. Change in the polarization surface of returning light from an element 31 is converted to a change in light intensity by a polarization means 13, other output light of a separation means 11 is frequency-shifted by an optical acoustic modulator 20, both are synthesized by a synthesizing means 24, and the light is received by a light-receiving element 25. A waveform of the circuit to be measured 16 is calculated by a calculation circuit 26 based on an output of the element 25, thus enabling a voltage waveform of the circuit to be measured 16 to be measured.

Description

[Detailed Description of the Invention] <Field of Application in Industry> This invention is an ultrahigh-speed electronic device (GaAs IC)
The present invention relates to a device for measuring high-speed electrical signals such as 1, nP ICs, etc., and particularly relates to an optical sampler device that reduces the influence on the circuit under test.

<Prior Art> Recently, many high-speed electronic devices have been developed. For example, HE M 'l' (lligh 1
lectr.

n14obilily Transistor), the gate delay time is about 1. , Ops, and the direct modulation band of semiconductors used in optical communications has reached several i G )-(z. Measurement of high-speed phenomena using such high-speed electronic devices is A sampler oscilloscope is usually used. Figure 71 shows the principle of the sampler oscilloscope.
For N consecutive signals under test like A, ),
Goo 1 - Measure the time by slightly changing it by 7,
The results are combined to obtain a measurement value like (Y3).

In this technique, the sampling width becomes the resolution of the measurement results.

However, in the sunblink oscilloscope shown in Fig. 4, the sampling width is limited by the speed of the step recovery diode, and the limit is about 25 ps, and even for an optical oscilloscope that uses optical pulses, the sampling width is about 25 ps or less. There was a drawback in terms of speed.

On the other hand, since the GaAs substrate has an electro-optic effect, the polarization plane of the returned light changes depending on the magnitude of the electric field. Measurement devices using light have been developed to take advantage of this phenomenon. FIG. 5 shows the configuration of a measuring device using such light. The output light of the YAG laser 1 is compressed by the pulse compressor 2.
The pulse width is compressed to about s, and the polarizer 3, wave plate 1
The signal is input to the G a AS integrated circuit 5 via the G a AS integrated circuit 5 . Also,
The returned light passes through the wavelength plate 4, is reflected by the polarizer 3, and its intensity is measured by the light receiving element 6 and displayed on the display section 8.

When the drive circuit 7 changes the electric field generated by the GaAs integrated circuit 5, the polarization plane of the returned light changes, and the polarizer 3 changes the intensity of the light incident on the light receiving element 6. By synchronizing the timing of the output light of the YAG laser 1 and the timing of driving the GaAs integrated circuit 5 using the IS section circuit 7, and gradually shifting the phase difference, the timing explained in FIG. 4 is achieved. The internal voltage waveform of the GaAs integrated circuit 5 can be measured using the same principle as the sample link technique. According to this device, measurement can be performed at a sampling speed on the order of ps.

<Problem to be solved by the invention> However, in the apparatus shown in Fig. 5, the optical power of the optical pulse incident on the circuit under test is not small enough, and the generated photoelectrons and reverse electro-optic effect adversely affect the circuit operation. There is a problem. Also, it is difficult to measure small signals because the S/N ratio cannot be obtained sufficiently.

<Purpose of the Invention> This invention was made to solve the above-mentioned problems, and by improving the S/N ratio, minute measurement signals can be measured, and high-speed measurement can be performed without adversely affecting the circuit under test. The purpose is to realize an optical sampling device that can measure signals.

Means for Solving the Problems> The present invention changes the state of the polarization plane of an optical pulse according to the operating voltage of the circuit under test, detects the change in the polarization plane, and measures the voltage waveform of the circuit under test. It is a type of optical sampling device for the purpose of A pulse compressor that converts one output light into narrow optical pulses, an electro-optical element that receives the output light of this pulse compressor and changes the polarization plane by an electric field corresponding to the operating voltage of the circuit under test, and this electro-optical element. a polarization stage that converts a change in the plane of polarization of the returned light into a change in light intensity; a photoacoustic modulator that frequency-shifts the other output light of the separation means; It includes a multiplexing means for multiplexing the output light of the modulator, a light receiving element for receiving the output light of the multiplexing means, and an arithmetic circuit for calculating the voltage waveform of the circuit under test based on the output of the light receiving element. Another advantage is that the voltage waveform of the circuit under test is determined based on the output of the arithmetic circuit.

After the optical pulse output from the optical pulse generating means is narrowed by a pulse compressor, the plane of polarization is rotated in an electro-optic element to which the electric field of the circuit under test is applied, and the optical frequency of the optical pulse generating means is changed. It is possible to amplify the signal isometrically by inputting it into a light receiving element together with local oscillation light shifted by a photoacoustic modulator and performing optical frequency heterodyne detection.

<Embodiment> FIG. 1 shows an embodiment of an optical sampler device according to the present invention.

In FIG. 1, 10 is an optical pulse generating means with an optical frequency fID that outputs a light pulse with a repetition frequency f.mode 1:l! A half mirror 112 constitutes a separating means for separating the output light of the optical pulse generating means 10 into two light beams.
13 is a polarizer that transmits the output light of the pulse compressor 12, 14 is a wavelength plate that adjusts the plane of polarization of the output light of the polarizer 13, and 15 is a wavelength plate. Ga
The back side of the pattern of the circuit under test 16 consisting of an As integrated circuit (
(described later) is a lens that focuses light on the 17 is a high frequency oscillator that drives the optical pulse generator ρ stage 10 with a sine wave signal having a repetition frequency f of optical pulses, and 18 is a high frequency oscillator that drives the circuit under test 16 at a frequency that is slightly different from the frequency 11+j of the oscillator 17 by a minute frequency Δf. A driving circuit 20 is a photoacoustic modulator that shifts the optical frequency of the reflected light from the half mirror 11 by Δf in order to generate local oscillation light, 21.22
．． 23 is a mirror constituting an optical path length adjustment means for adjusting the optical path length of the output light of the photoacoustic modulator 20; 24 is a mirror that directs the reflected light from the circuit under test 16 through a lens 15. A half mirror 125 constituting a combining means that combines the light reflected from the mirror 23 via the wavelength plate 14 and the polarization 13 is a light receiving element into which the output light of the half mirror 24 enters, and 26 is the electrical output of the light receiving element 25. This is a calculation display circuit that calculates and displays the internal voltage waveform of the circuit under test 16 based on.

The operation of the apparatus having the configuration 1- will now be described.

The optical pulse generating means 10 generates optical pulses in synchronization with the output of the oscillator 17. This light pulse is passed through the Huff mirror 11 into two
The transmitted light is further made into narrow light pulses by a pulse compressor 12, and transmitted through a polarized light r13 and a wavelength plate 14.
A lens] 5 focuses on the circuit under test 16. As shown in FIG. 2, this incident light enters from the back surface of the circuit under test 16, passes through the GaAs substrate 31,
The light is reflected by the back surface of the IC pattern 32 on the front surface of the substrate 6, passes through the GaAs substrate 31 in the opposite direction, and is emitted from the back surface. The plane of polarization of this reflected light is GaA of the circuit under test 16.
The s-substrate is an electro-optic element having an electro-optic effect,
For the polarization plane of the incident optical pulse, 1. It changes according to the electric field strong wind generated at M51° in the electrical signal 4 on the C pattern. This reflected light pulse passes through the lens 15 in the opposite direction, and after the plane of polarization is adjusted by the wave plate 14, the polarizer 1
When reflected at 3, the light intensity is modulated according to its plane of polarization. On the other hand, after the light reflected by the half mirror 11 changes its optical path direction by the mirror 19, the optical frequency is frequency-shifted by Δf1o by the photoacoustic modulator 20.

The output light is adjusted to have the same optical path length as the light that passes through the pulse compressor 12 via mirrors 21 to 23, and is combined with the light reflected by the polarizer 13 and the half mirror 24 as locally oscillated light. After that, the light is detected by the light-receiving element 25, and optical heat detection 17 is performed on the section where both lights overlap, as will be described later. Pulse compressor 1
Since the light passing through the photoacoustic modulator 20 has a narrower optical pulse than the light passing through the photoacoustic modulator 20, the two lights can be completely overlapped. The calculation display circuit 266J displays the internal signal waveform of the circuit under test 16 based on the output of the light receiving probe 25.

The above heterotine detection will be explained below using a formula. For example, assuming that the optical frequency of the optical pulse photon means 10 is ω1, the optical output from the optical pulse photon means 10 is expressed by Elsin's 1t,
Assuming that the optical frequency of the optical output from the photoacoustic modulator 20 is ω2, E2sz11ω21. It is expressed as When these two lights are combined by the half mirror 24, the combined light on the light receiving part of the light receiving element 25 is expressed by the formula (Els i nω1t, +E2 s i nω2t,
)...<1) becomes. +7 after being converted into an electrical signal by the photodetector r-25
- The signal after passing through the bus filter and D□ka1~ circuit is ElHE2 cos (ω1 6.+2) t,
□++ (2). Here, ω1 ω27−2πΔf11) (3). In equation (2), El contains useful information corresponding to the internal voltage signal of the circuit under test 16, but usually,
-- Since it is constant, El<<El.E2, and isometrically the signal) is amplified by a factor of E2, and it is clear that the S/N ratio is improved. Therefore, even if the optical power incident on the circuit under test 16 is made smaller than that of the conventional example, it is possible to obtain an S/N equal to or higher than that of the conventional example.

In addition, in order to use the sampling technique, the fundamental frequency f of the drive signal of the circuit under test 16 output from the drive circuit 18 is
, is expressed as fd=N−fp+Δf (4). Here N=1.2.3. ...1, Δf is a minute frequency. Due to the presence of Δf in equation (4), the signal under test in the circuit under test 16 can be sunblinked with an optical pulse by shifting f Tachikawa by t, and a high-speed phenomenon can be treated as a low-speed phenomenon. J is coming. s
The difference in explanation is that the high frequency fd of the object surface to be measured is converted to a low frequency Δf.

According to Japan's leading optical sampler devices such as , and -, by using optical header I7 dyne detection for the sampling light, it is possible to reduce the power that enters the circuit under test. It is possible to reduce the reverse electro-optic effect and lessen the adverse effect on the operation of the circuit under test.

In the above embodiment, a mode +7 solid state laser was used as the light source, but the light source is not limited to this, and a semiconductor laser or the like may also be used.

FIG. 3 shows a modification of the device shown in FIG. 1, and is a block diagram of the main part of the apparatus, but does not show an arrangement in which the detection section is of a differential configuration in order to further improve the S/N ratio. The same parts as in Figure 1 are marked with the same archery. The optical output from the pulse compressor 12 is transmitted through the polarizer 337 rotating 7'-37 and the polarizer ] 3, and is incident on the wave plate 14. The output light from the wavelength plate 14 is separated by the polarizer 13 and the polarizer 33 in terms of the X and Y direction components of its polarization plane, and is output. Each of the separated lights is combined with the output light from the optical path length adjustment mirror by half mirrors 24, 38, respectively. Each of the multiplexed lights is detected by the light receiving probes 35 and 3.1, respectively, and subtracted from each other by the subtracter 36. Since the polarization plane of the optical pulse is modulated in the circuit under test 16 with X and Y direction components or with opposite polarities, the optical system's 7゜ line members 1 to 10 are arranged so that the opposite phase components are equally incident on the light receiving elements 34 and 35. If this is done, the noise of the light source itself is unrelated to the phase, so the light receiving elements 34 and 35 have the same phase and are canceled out by subtraction, and the signal component of the detected light that has received modulation C-t in the circuit under test 16 has an opposite phase. and are added together by subtraction. Therefore, the SIN ratio is further improved.

Note that in each of the above embodiments, if the object to be measured is a GaAs integrated circuit, the object to be measured itself is electro-optical + 4 + 2.
Although the present invention will be described with reference to a case in which the present invention is configured with a single electro-optical effect, the present invention is also applicable to materials that do not have an electro-optic effect, such as silicon. In this case, a material with an electro-optic effect such as a 1-7hTaO3 single crystal is placed close to the object to be measured, such as silicon, and the iTa033 crystal is irradiated with light. It is only necessary to shift so that an electro-optical effect is produced by the electric field generated by the circuit under test.

Furthermore, instead of detecting a change in the state of the polarization plane of the reflected light from the circuit under test, transmitted light may be detected [7].

Furthermore, when a light source with high 1-minute coherency is used, the optical path length adjusting means can be omitted.

<Effects of the Invention> 2. As specifically explained based on the embodiments, according to the present invention, a very small measurement signal can be measured by improving the S/N ratio, and it can be applied to the circuit under test. Optical sampling device that can measure pre-J at high speed without adverse effects.
It is possible to realize 4= with a simple fit configuration.

[Brief explanation of the drawing]

Figure 1 shows an example of the optical sampler device (M'-) according to Akira Kiguto. 1 and 3 do not show the modified example of the device opening shown in FIG.
FIG. 5, which is a diagram of the principle of printer technology in the fourth country, shows the configuration of a conventional optical printer device.

Claims (1)

[Scope of Claim] An optical sampling device that changes the state of the polarization plane of a light pulse according to the operating voltage of the circuit under test, and measures the voltage waveform of the circuit under test by detecting the change in the polarization plane, comprising: An optical pulse generating means for outputting a pulse; a separating means for separating the output light of the optical pulse generating means into two; a pulse compressor for converting one output light of the separating means into a narrow optical pulse; An electro-optical element that receives output light and changes the plane of polarization using an electric field corresponding to the operating voltage of the circuit under test; and a polarizer that converts the change in the plane of polarization of the return light from the electro-optic element into a change in light intensity. a photoacoustic modulator for frequency shifting the output light from the other of the separating means; a combining means for combining the output light of the polarizing means and the output light of the photoacoustic modulator; It is equipped with a light-receiving element that receives output light, and an arithmetic circuit that calculates the voltage waveform of the circuit under test based on the output of the light-receiving element, and is configured to measure the voltage waveform of the circuit under test based on the output of the arithmetic circuit. An optical sampling device characterized by: