JP2827264B2 - Physical quantity measurement device using light - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an apparatus for measuring a physical quantity using light,
In particular, the present invention relates to a physical quantity measuring device using light capable of measuring a high-speed phenomenon.

<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 high-speed phenomena by such a high-speed electronic device, a sampling oscilloscope is usually used. FIG. 5 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, the plane of polarization of the return light changes depending on the magnitude of the flowing current.
Utilizing this phenomenon, a measuring device using light has been developed. FIG. 6 shows the configuration of a measuring apparatus using such light. The output of the YAG laser 1 is compressed to a pulse width of about ps by the pulse compression unit 2 and the GaAs is transmitted through the polarizer 3 and the wave plate 4
Input to the integrated circuit 5. The return light is transmitted through the wave plate 4.
, The light is reflected by the polarizer 3, its intensity is measured by the light receiving element 6, and is displayed on the display unit 8. When the current flowing through the GaAs integrated circuit 5 is changed by the drive circuit 7, the plane of polarization of the return light changes, and the intensity of light incident on the light receiving element 6 changes by the polarizer 3. The driving circuit 7 synchronizes the timing of the output light of the YAG laser 1 with the timing of flowing the current to the GaAs integrated circuit 5 and shifts the phase difference little by little, so that the same as the sampling technique described in FIG. The operation of the GaAs integrated circuit 5 can be measured in principle.

<Problems to be Solved by the Invention> However, in the sampling oscilloscope of FIG. 5, the sampling width is limited by the speed of the step recovery diode, and is limited to about 25 ps. There was a problem that there was.

In addition, although the measurement device can measure in the order of ps using the light shown in FIG. 6, it is difficult to increase the S / N ratio because the intensity of light incident on the light receiving element 6 is weak. There was also a problem that signal processing such as averaging processing had to be performed.

<Object of the Invention> An object of the present invention is to provide a physical quantity measuring device using light that can measure a high-speed phenomenon with a high S / N ratio.

<Means for Solving the Problem> In order to solve the problem, according to the present invention, the first optical pulse generating means is irradiated on the object to be measured, and the return light thereof and the time required for the second optical pulse generating means to be more time-consuming. The pulse light having a short width is multiplexed, and the multiplexed light is incident on harmonic light generating means made of a non-linear material to generate harmonic light. The intensity is measured, and one of the return light and the output light of the second optical pulse generating means is delayed by a delay means, and the delay amount is continuously changed.

Further, instead of delaying the light, the phase of the timing of driving the device under test and the timing of the timing of driving the second optical pulse generating means are continuously shifted.

<Operation> By generating harmonic light proportional to the product of the intensity of the return light and the intensity of the reference light by the harmonic light generation means, a physical quantity can be measured at a high S / N ratio.

<Embodiment> Fig. 1 shows an embodiment of a physical quantity measuring device using light according to the present invention. In FIG. 1, reference numeral 10 denotes a pulse laser, which corresponds to a first optical pulse generating means, and its output light is polarized perpendicularly to the plane of the drawing (indicated by a circle). Reference numeral 11 denotes a half mirror to which the output light of the pulse laser 10 is incident and splits the light into two. Reference numeral 12 denotes a pulse compressor, which receives one of the lights split by the half mirror 11 and temporally compresses the pulse width. The pulse laser 10 and the pulse compressor 12 constitute a second optical pulse generating means. Reference numeral 14 denotes a light delay line, and the output light of the pulse compressor 12 reflected by the mirror 13 enters. The delay line 14 includes a mirror 141 and a corner cube 142, and the incident light is reflected by the mirror 141 to reach the corner cube 142, the direction is reversed by the corner cube 142, reflected again by the mirror 141, and output.
Accordingly, by moving the corner cube 142 in the direction of the arrow to change the distance between the mirror 141 and the corner cube 142, the delay amount can be changed. Reference numeral 15 denotes a polarizer to which the output light of the delay line 14 is incident. Reference numeral 16 denotes a polarizer, and the other output light of the pulse laser 10 split by the half mirror 11 is incident and transmitted. The transmitted light passes through the λ / 4 and λ / 2 wavelength plates 17, is focused by the objective lens 18, and irradiates the object 19 to be measured. The DUT 19 is, for example, Ga
An As integrated circuit, which is driven by the drive unit 20. The GaAs integrated circuit has an electro-optic effect, and changes the plane of polarization of irradiated light and reflects it. Since the change in the polarization plane changes depending on the current flowing through the object to be measured, which is a GaAs integrated circuit, the current flowing through the object to be measured 19 can be measured by measuring the change. The return light from the device under test 19 is incident on the polarizer 16. The polarizer 16 reflects only light polarized in the plane of the paper (represented by |). The wave plate 17 is adjusted so that the return light is maximized. The light reflected by the polarizer 16 is incident on the polarizer 15, and is multiplexed with the output light of the delay line 14 which is separately incident. Reference numeral 21 denotes a harmonic light generating means, which receives the light multiplexed by the polarizer 15 and outputs a second harmonic of the incident light. Reference numeral 22 denotes a filter, to which the output light of the harmonic light generating means 21 is incident, and transmits only the second harmonic. Reference numeral 23 denotes a light receiving element, which converts the light intensity of light transmitted through the filter 22 into an electric signal. Numeral 24 denotes a calculation / display unit, which receives the output of the light receiving element 23, calculates the magnitude of the current flowing through the device under test 19 from this signal, and displays it.

Next, the operation of this embodiment will be described. The GaAs integrated circuit as the device under test 19 has an electro-optic effect. Therefore, when the integrated circuit is in the operating state, the polarization plane of the return light is different from that of the incident light according to the flowing current. The physical quantity of the DUT 19 is measured using this property. Therefore, a current is caused to flow through the device under test 19 by the drive unit 20 and the pulse laser 10 is operated to output light polarized perpendicular to the plane of the drawing. This light is split into two by a half mirror 11, one of which is converged by an objective lens 18 and irradiates an object 19 to be measured. Of the returned light, only the polarized light in the plane of the paper is reflected by a polarizer 16. Is incident on the polarizer 15.
Therefore, the intensity of light incident on the polarizer 15 changes depending on the current flowing through the device under test 19. The other light split by the half mirror 11 has its pulse width temporally compressed by the pulse compressor 12 and is incident on the delay line 14 to be given a predetermined delay. The two lights incident on the polarizer 15 are linearly polarized waves orthogonal to each other. Therefore, the output light has a time relationship as shown in FIG. In FIG. 2, reference numeral 30 denotes return light from the device under test 19, and reference numerals 31 and 32 denote output lights of the delay line 14. 31 corresponds to the case where the delay amount of the delay line 14 is small, and 32 corresponds to the case where it is large. By moving the corner cube 142 to change the amount of delay, the phase difference with the return light 30 can be changed.
Can be scanned over the entire area.

For example, when the output light of the delay line 14 rises at the same time when the return light 30 rises when the delay amount is “0”, the corner cube 142 is moved to gradually increase the delay amount, thereby 2 moves from the output light 31 to the output light 32 in FIG. 2, so that the entire area of the return light 30 can be scanned. The light multiplexed by the polarizer 15 is converted into high-frequency light generating means 21.
Is incident on. The harmonic light generating means 21 is made of a KDP crystal, and its optic axis is set at about 59 ° with respect to the light incident direction. The harmonic light generating means 21 generates a second harmonic of the incident light, and its intensity P follows the following equation (1).

_{P = r 123 · E 1 ·} E 2/2 ......... (1) where, E _1, E ₂ the intensity of the return light from the object to be measured 19 is at each point of the harmonic light generating means 21 and the delay line 14
Is the output light intensity, and r ₁₂₃ is a constant representing the likelihood of the nonlinear effect. Therefore, the second harmonic is generated only in a portion where these lights overlap in time. Only the second harmonic portion of the output of the harmonic light generating means 21 is extracted by the filter 22 and is incident on the light receiving element 23, where the light intensity is converted into an electric signal. Since the phase difference between the return light of the device under test 19 and the output light of the pulse compressor 12 is continuously changed by the delay line 14, the temporal change of the second harmonic measured by the light receiving element 23 is equal to the delay line. Assuming that the output light intensity of 14 is constant, a temporal distribution of the return light intensity of the device under test 19 is obtained. Therefore, it is possible to measure the current flowing through the DUT 19, that is, the temporal change in the distribution of the physical quantity. Also,
As can be seen from the above equation (1), by increasing the light intensity of the pulse compressor 12, it is possible to increase the intensity of the second harmonic even if the intensity of the return light from the device under test 19 is low. S / N ratio can be improved.

FIG. 3 shows another embodiment of the present invention. The same elements as those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted. In this embodiment, the insertion position of the delay line 14 is changed. That is, the delay line 14 is inserted in the optical path of the return light of the device 19 reflected by the polarizer 16, and the delay time of the return light is changed. The output light of the pulse compressor 12 reflected by the mirror 13 is made to directly enter the polarizer 15.
In the present invention, since the phase difference between the output light of the second pulse generating means and the return light from the device under test 19 may be changed, the same object can be achieved even in such a case.

FIG. 4 shows still another embodiment. The same elements as those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted. In this embodiment, the pulse laser 10 is also driven in the drive unit 20 without using the delay line 14, and the phase difference from the timing for driving the device under test 19 is gradually changed. That is, a current is caused to flow through the GaAs integrated circuit, which is the device under test 19, and after the elapse of the time Δt, the pulse laser 10 is driven to generate an optical pulse. By gradually increasing Δt, a series of changes in the physical quantity of the DUT 19 can be observed. In the configuration of this embodiment, the output light of the pulse compressor 12, that is, the output of the second optical pulse generating means is irradiated to the device under test 19, and the return light and the pulse laser
10, ie, the output light of the first optical pulse generation means may be multiplexed.

In these embodiments, the output light of the pulse laser 10, which is the first optical pulse generating means, is temporally compressed by the pulse compressor 12 to form the second optical pulse generating means. You may do so.

In these embodiments, a GaAs integrated circuit having an electro-optic effect has been described as an object to be measured. However, silicon and the like having no electro-optic effect can be measured. In this case, a LiTaO ₃ single crystal having an electro-optical effect may be brought close to silicon, and the electric field generated there may be measured by the electro-optical effect of the LiTaO ₃ single crystal.

Further, in these embodiments, the wavelengths of the output light of the first and second optical pulse generating means are the same, but the intensity of the light of the sum or difference frequency may be measured by changing the wavelength. Good. In this case, the characteristics of the filter 22 may be changed so that light of the sum or difference frequency is transmitted.

Furthermore, instead of the second harmonic light, third or higher harmonic light may be used.

<Effects of the Invention> As described above in detail based on the embodiments, the present invention uses a wide light pulse and a narrow light pulse, irradiates one of the object to be measured with its return light and the other light. The light was multiplexed, and the physical quantity was measured from the intensity of the harmonic light. Therefore, even if the return light from the DUT is weak, the signal intensity can be increased by increasing the intensity of the combined light.
There is an effect that good measurement of N ratio can be performed.

In addition, since light is used, there is an effect that non-contact measurement can be performed, and high-speed measurement can be performed essentially.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a physical quantity measuring device using light according to the present invention, FIG. 2 is a characteristic curve diagram for explaining the operation thereof, and FIGS. FIG. 5 is a diagram showing the principle of the sampling technique, and FIG. 6 is a diagram showing the configuration of a conventional measuring device using light. Reference numeral 10: pulse laser, 12: pulse compressor, 14: delay line, 15, 16: polarizer, 19: device under test, 21: harmonic light generating means, 22: filter, 23: light receiving element.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G01R 19/00 G01R 15/24 G01R 31/308

Claims (3)

(57) [Claims] A first light pulse generating means for irradiating an object to be measured with the output light; and a second light pulse for outputting a pulse light having a shorter time width than the output light of the first light pulse generating means. Optical pulse generating means; delay means inserted into the path of output light of the second optical pulse generating means for delaying these lights for a predetermined time; output light of the delay means and return light from the device under test Multiplexing means for multiplexing; harmonic light generating means for receiving the output light of the multiplexing means and generating harmonic light of the incident light by a non-linear optical effect; and A light, comprising: a filter that transmits only light having a wavelength; and a light receiving element that receives the output light of the filter and converts the light intensity into an electric signal, wherein a delay amount of the delay unit is varied. Physical quantity measurement using Apparatus. A first light pulse generating means for irradiating the object with the output light; and a second light pulse for outputting a pulse light having a shorter time width than the output light of the first light pulse generating means. Optical pulse generating means; delay means inserted into the path of return light of the device under test for delaying the light by a predetermined time; and combining the delayed light and output light of the second optical pulse generating means. A multiplexing means, a harmonic light generating means for receiving the output light of the multiplexing means and generating a harmonic light of the incident light by a nonlinear optical effect, and a light of a specific wavelength to which the output light of the harmonic light generating means is incident And a light-receiving element for receiving the output light of the filter and converting the light intensity into an electric signal, wherein the delay amount of the delay means is made variable. Physical quantity measurement device. 3. A first light pulse generating means, a second light pulse generating means for outputting pulse light having a shorter time width than an output light of the first light pulse generating means, and the first light A pulse generating unit and a driving unit for driving the device under test; and an output light of one of the output lights of the first or second optical pulse generating device that is not irradiated to the device under test and a return light of the device under test. Multiplexing means for multiplexing the multiplexed light, harmonic light generating means for receiving the output light of the multiplexing means and generating harmonic light of the incident light by a non-linear optical effect, output light of the harmonic light generating means being incident and specifying And a light-receiving element that receives the output light of the filter and converts the light intensity into an electric signal. The other output light of the first or second light pulse generating means is provided. When the object is irradiated, First physical quantity measuring device using light, characterized in that to be able to change the phase difference between the drive timing of the object to be measured and the driving timing of the light pulse generating means.