JP3418578B2 - Electro-optic probe - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to coupling an electric field generated by a signal under measurement to an electro-optic crystal, injecting light into the electro-optic crystal, and observing the waveform of the signal under measurement depending on the polarization state of the incident light. The present invention relates to an electro-optic probe for

[0002]

2. Description of the Related Art It is possible to observe the waveform of a signal under measurement by coupling an electric field generated by the signal under measurement with an electro-optic crystal, injecting laser light into the electro-optic crystal, and observing the polarization state of the laser light. Here, pulse the laser light,
When the signal under measurement is sampled, it can be measured with very high time resolution. An electro-optic sampling oscilloscope uses an electro-optic probe that takes advantage of this phenomenon.

This electro-optical sampling (Electro Opt
ic Sampling) oscilloscope (hereinafter abbreviated as “EOS oscilloscope”), compared to a conventional sampling oscilloscope that uses an electric probe, 1) does not require a ground line when measuring a signal. Easy 2) Since the metal pin at the tip of the electro-optic probe is insulated from the circuit system, a high input impedance can be realized, and as a result, the state of the measured point is hardly disturbed 3) Since an optical pulse is used It has attracted attention because it has a feature that it can measure wideband up to GHz order.

The configuration of a conventional electro-optic probe 1 used when measuring signals with an EOS oscilloscope will be described with reference to FIG. In the electro-optical probe 1 shown in FIG. 2, a probe head 3 made of an insulator is provided at the tip of a metal probe body 2, and a metal pin 3a is fitted in the center of the probe head 3. Reference numeral 4 is an electro-optical element, and a reflection film 4a is provided on the end surface on the metal pin 3a side and is in contact with the metal pin 3a. Reference numeral 5 is a half-wave plate, and reference numeral 6 is a quarter-wave plate. Reference numerals 7 and 8 are
It is a polarization beam splitter. Reference numeral 9 is a half-wave plate, and reference numeral 10 is a Faraday element. Code 12
Is a collimating lens, and 13 is a laser diode. Reference numerals 14 and 15 are condenser lenses, and reference numerals 16 and 17 are photodiodes.

Two polarization beam splitters 7,
The 8, 1/2 wave plate 9 and the Faraday element 10 allow the light emitted by the laser diode 13 to pass therethrough and separate the light reflected by the reflection film 4a.
Is.

Next, the optical path of the laser light emitted from the laser diode 13 will be described with reference to FIG.
In FIG. 2, the optical path of the laser light is represented by the symbol A.

First, the laser light emitted from the laser diode 13 is converted into parallel light by the collimator lens 12, and the polarization beam splitter 8, the Faraday element 10, 1 /
Go straight through the two-wave plate 9 and the polarization beam splitter 7, and then pass through the quarter-wave plate 6 and the half-wave plate 5 to pass through the electro-optical element 4.
Incident on. The incident light is reflected by the reflection film 4a formed on the end surface of the electro-optical element 4 on the metal pin 3a side.

The reflected laser light is transmitted again to the half-wave plates 5 and 1.
A part of the laser light passing through the / 4 wavelength plate 6 is reflected by the polarization beam splitter 7, is condensed by the condenser lens 14, and is incident on the photodiode 16. On the other hand, the laser beam transmitted through the polarization beam splitter 7 is reflected by the polarization beam splitter 8, condensed by the condenser lens 15, and enters the photodiode 17.

The half-wave plate 5 and the quarter-wave plate 6 are adjusted in rotation angle with respect to their optical axes so that the laser beams incident on the photodiode 16 and the photodiode 17 have the same intensity. It

Next, the operation of measuring the signal under measurement using the electro-optical probe shown in FIG. 2 will be described. When the metal pin 3a is brought into contact with the measurement point, the electric field in the electro-optical element 4 propagates to the electro-optical element 4 due to the voltage applied to the metal pin 3a, and the phenomenon that the refractive index changes due to the Pockels effect occurs. As a result, the laser light emitted from the laser diode 13 enters the electro-optical element 4, and the polarization state of the light changes when the laser light propagates through the electro-optical element 4. Then, the laser light whose polarization state has changed is reflected by the reflection film 4a, is condensed and incident on the photodiodes 16 and 17, and is converted into an electric signal.

Along with the change in the voltage at the measuring point, the change in the polarization state by the electro-optical element 2 is changed by the photodiode 1.
6 and the output of the photodiode 17 occur, and by detecting this output difference, the metal pin 3
The electrical signal applied to a can be measured. In the electro-optical probe 1 described above, the electric signals obtained from the photodiodes 16 and 17 are input to the electro-optical sampling oscilloscope and processed.
Alternatively, a conventional measuring instrument such as a real-time oscilloscope may be connected to the photodiodes 16 and 17 via a dedicated controller to perform signal measurement. Thereby, the broadband measurement can be easily performed using the electro-optic probe 1.

[0012]

As described above, in the signal measurement using the electro-optic probe 1, the metal pin 3 is used.
It is necessary to bring a into contact with the measurement point. In this case, the contact pressure of the metal pin 3a may affect the change in the refractive index of the electro-optical element 4, so that accurate measurement is required. The contact pressure of the metal pin 3a must be kept constant, which makes the measurement time-consuming.

In addition, since the metal pin 3a must be brought into contact with the measuring point during the signal measurement, a shock is applied to the metal pin 3a, and as a result, not only the metal pin 3a but also the electro-optical element 4 is damaged. There was a concern that it would occur.

The present invention has been made in view of the above circumstances, and it is possible to make the contact pressure of the metal pin constant, and yet to ensure the safety of the metal pin and the electro-optical element. An object is to provide such an electro-optic probe.

[0015]

In order to solve the above problems, the following means are adopted in the present invention. That is,
The electro-optical probe according to claim 1, comprising a probe main body,
A probe head provided at the tip of the probe body, wherein an optical path is formed between the base end side and the tip inside the probe body, and the base end of the probe body in the optical path. A laser diode is disposed at one end of the probe side, and an electro-optical element is disposed at the other end of the optical path on the tip side of the probe body while being held by the probe head. A pin is provided such that its base end is connected to the electro-optical element and its tip projects from the probe head, and the laser light emitted from the laser diode is incident on the electro-optical element through the optical path. , The incident light is reflected by the reflection film provided on the electro-optical element, and further, the reflected light is separated and converted into an electric signal by the photodiode. The probe head is relatively displaceable in the extending direction of the optical path with respect to the tip of the probe body, and the rotational displacement about the extending direction of the optical path is restricted. It is characterized in that an elastic member, which is attached in a fixed state, is provided between the probe head and the probe main body to elastically regulate relative displacement of these optical paths in the extending direction.

Since the electro-optic probe is constructed as described above, the impact applied to the metal pin can be absorbed by the elastic member. Further, at this time, the elastic member functions so that the force acting between the probe head and the probe main body becomes almost constant. Further, at this time, the probe head is not rotationally displaced with respect to the probe body, so that the safety is high.

An electro-optical probe according to a second aspect is the electro-optical probe according to the first aspect, wherein one of the probe head and the tip of the probe body is
A long hole is formed in which the extending direction of the optical path is the longitudinal direction, and a screw that fits into the long hole is attached to the other side.

In this electro-optical probe, the relative displacement in the extending direction of the optical path between the probe head and the probe body can be allowed and the rotational displacement can be restricted by a simple structure.

An electro-optical probe according to a third aspect of the present invention is the electro-optical probe according to the first aspect, wherein the elastic member is formed in a spiral shape with the extending direction of the optical path as an axis and surrounding the optical path. It is characterized by being composed of a spring.

Due to such a structure, in this electro-optical probe, the spring may be formed to have a diameter approximately equal to the outer diameter of the probe head, and it is not necessary to downsize the spring.

The electro-optic probe according to claim 4 is the electro-optic probe according to any one of claims 1 to 3, wherein the photodiode and the laser diode are connected to an electro-optic sampling oscilloscope,
The laser diode emits the laser light as pulsed light based on a control signal from the electro-optic sampling oscilloscope.

An electro-optical probe according to a fifth aspect is the electro-optical probe according to any one of the first to third aspects, wherein the laser diode emits continuous light as the laser light.

As described above, in the electro-optic probe according to the fifth aspect, the continuous output can be obtained from the photodiode by causing the laser diode to emit the continuous light. Therefore, the photodiode is exclusively used. It is also possible to connect to a conventional general-purpose measuring instrument such as a real-time oscilloscope via the controller to perform measurement.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a vertical sectional view of an electro-optic probe 21 showing an embodiment of the present invention. The electro-optical probe 21 includes a probe body 22 and a probe head 23 provided at a tip 22 a of the probe body 22.
It is configured with and.

An optical path 24 is provided inside the electro-optical probe 21. The optical path 24 is the probe body 2
2 is provided from the base end portion 22b to the tip end 22a of the probe body 22, and the tip end 2 of the probe main body 22
2a to the inside of the probe head 23.

The base end portion 22 of the probe body 22 in the optical path 24
A laser diode 25 connected to an EOS oscilloscope (not shown) is arranged at one end 24a on the b side.
Further, the electro-optical element 26 is provided at the other end 24 b of the optical path 24 on the side of the tip 22 a of the probe body 22 and the probe head 23.
It is placed in a state where it is stored in.

A metal pin 27 is provided at the tip of the probe head 23. The metal pin 27 is held by the probe head 23, its base end 27a is connected to the electro-optical element 26, and its tip 27b.
Are projected from the probe head 23.
A reflective film 26a is formed on the end surface of the electro-optical element 26 on the tip side of the probe head 23.

Laser diode 25 and electro-optical element 26
On the optical path 24 formed between the collimator lens 29 and the polarization beam splitter 3 in order from the right side in the figure.
0, Faraday element 31, polarization beam splitter 33,
A quarter-wave plate 34 and a condenser lens 36 are arranged. In addition, the polarization beam splitters 30, 33 on the side of the optical path 24
Photodiodes 38 and 39 are provided at positions corresponding to. These photodiodes 38 and 39 are
It is connected to an EOS oscilloscope so that incident light can be converted into an electric signal and transmitted to the EOS oscilloscope.

In addition, the polarization beam splitters 30, 33
Is to function as an isolator that separates the reflected light from the electro-optical element 26 that passes through the optical path 24 and reflects it toward the photodiodes 38 and 39.

The probe head 23 is provided so as to be relatively displaceable with respect to the probe body 22 in the extending direction of the optical path 24 (direction B in the drawing). Probe head 23
Is fixed to the probe body 22 with a screw 41, but the screw hole 42 of the probe body 22 into which the screw 41 is inserted is formed as an elongated hole such that the direction B is the longitudinal direction. The probe head 23 is configured to be relatively displaceable in the B direction with respect to the probe main body 22 and has a configuration in which rotational displacement about the B direction is restricted.

A spring 44 is arranged inside the probe head 23. The spring 44 is formed in a spiral shape surrounding the optical path 24 while having the B direction as an axis, and one end 44 a of the spring 44 has the tip 2 of the probe body 22.
2a, and the other end 44b is fixed to the lens holding member 45 that is attached to the probe head 23 and holds the condenser lens 36. This spring 44
Is arranged so that its axial direction coincides with the extending direction (B direction) of the optical path 24. Therefore, the probe head 2
3 serves to elastically regulate the relative displacement of the probe body 22 in the B direction.

Next, the operation and effect will be described. When the electro-optical probe 21 is used for signal measurement, with the tip 27b of the metal pin 27 in contact with the measurement point, the EOS
Start the oscilloscope. As a result, based on the control signal emitted from the EOS oscilloscope, laser light is emitted from the laser diode 25, this laser light is converted into parallel light by the collimator lens 29, goes straight on the optical path 24, and is condensed by the condenser lens 36. The light is condensed and reaches the electro-optical element 26.

Since the condenser lens 36 is arranged at a position separated from the reflection film 26a by the focal length of the condenser lens 36, the laser light condensed by the condenser lens 36 is on the reflection film 26a. It is focused on one point. Further, this laser light is reflected by the reflection film 26a, converted into parallel light by the condenser lens 36, and the optical path 28
Will proceed to the laser diode 25 side.

At this time, the electro-optical element 26 is in a state in which the refractive index is changed by the change in the electric field at the measuring point propagated through the metal pin 27, so that the electro-optical element 2
The light propagating through 6 changes its polarization state. Therefore, the reflected light from the electro-optical element 26 is split by the polarization beam splitters 30 and 33 in the state where the polarization state has changed, and the photodiodes 38 and 39 are detected. The light is collected and incident on and converted into an electric signal. Thus, the change in the polarization state of the laser light is detected as the output difference between the photodiodes 38 and 39, and the electric signal at the measurement point is measured.

In the signal measurement as described above, it is necessary to bring the tip 27b of the metal pin 27 into contact with the measuring point. At this time, the shock acting on the metal pin 27 can be absorbed by the spring 44. . Therefore, even if a shock is accidentally applied to the metal pin 27 at the time of measurement, the metal pin 27 is not damaged, and the metal pin 27 is retracted into the probe head 23 so that the electro-optical element 26 can be removed. You can avoid taking damage. Therefore, impact resistance and operability can be improved.

Further, in this case, the spring 44 is the metal pin 2
The probe body 22 from the 7 side through the probe head 23
The contact pressure acting on the metal pin 27 can be made substantially constant at all times because the force acting on the metal pin 27 is made substantially constant, and the refractive index of the electro-optical element 26 is changed by the difference in the contact pressure of the metal pin 27. Can be prevented from being affected by changes in Therefore, accurate signal measurement can be easily performed, the measurement accuracy can be improved, and the measurement work can be facilitated. Further, since the probe head 23 is configured so that the rotational displacement about the B direction as an axis is restricted with respect to the probe main body 22, the probe head 23 is rotationally displaced by some impact on the probe head 23. Therefore, there is no concern that inconveniences such as optical axis shift will occur, and thus shock resistance and safety can be ensured.

Further, in this case, the screw 41 and the screw hole 42 easily realize the structure for allowing the relative displacement of the probe head 23 and the probe main body 22 in the B direction and restricting the relative displacement in the rotation direction. Therefore, the manufacturing can be facilitated.

Further, since the spring 44 having a constant contact pressure of the metal pin 27 is formed in a spiral shape so as to surround the optical path 24, the diameter dimension of the spring 44 is made approximately the same as the diameter dimension of the probe head 23. The spring 44 does not need to be particularly small. This makes it possible to facilitate manufacturing and reduce costs.

It should be noted that in the above embodiment, other configurations may be adopted without departing from the spirit of the present invention. For example, the spring 44 in the above embodiment
May be arranged between the probe head 23 and the probe body 22 and elastically regulate the relative displacement of the probe head 23 and the probe body 22 in the extending direction of the optical path 24. Alternatively, a cylindrical rubber member or the like may be used. Further, the spring 44 or the elastic member used in place of the spring 44 may be disposed outside the probe head 23 instead of being disposed inside the probe head 23.

Further, in the above-described embodiment, if continuous light is emitted from the laser diode 25, it is possible to perform signal measurement using a conventional general-purpose measuring instrument such as a real-time oscilloscope, sampling oscilloscope, spectrum analyzer and the like. In this case, the photodiodes 38, 3
Instead of the EOS oscilloscope, a real-time oscilloscope, a sampling oscilloscope, a spectrum analyzer, etc. may be connected via a dedicated controller.

[0041]

As described above, in the electro-optical probe according to the first aspect, the impact acting on the metal pin can be absorbed by the elastic member, and the impact may be erroneously applied to the metal pin during measurement. Even if it happens, it is possible to avoid damaging the metal pin and the electro-optical element. Therefore, it is excellent in impact resistance and has good operability. Further, since the elastic member functions to make the force acting on the probe body from the metal pin side through the probe head almost constant, the contact pressure acting on the metal pin can be made almost always constant. It is possible to prevent the change in the refractive index of the electro-optical element from being influenced by the difference in contact pressure between the metal pins. For this reason, the measurement accuracy can be improved, the measurement operation is easy, and it is particularly advantageous when measuring multiple points. Further, in this case, since the probe head is configured so that the rotational displacement about the extending direction of the optical path is restricted with respect to the probe body, the probe head is rotated by some impact on the probe head. There is no risk of displacement and inconvenience such as optical axis shift, and thus shock resistance and safety can be ensured.

In the electro-optic probe according to the second aspect of the present invention, the oblong hole and the screw allow relative displacement in the extending direction of the optical path between the probe head and the probe body, and regulate the relative displacement in the rotational direction. The invention of claim 1 can be easily realized, and manufacturing can be facilitated.

In the electro-optic probe according to the third aspect, since the elastic member is formed of a spring having a spiral shape surrounding the optical path, the diameter of the spring is about the same as the diameter of the probe head. Better, and there is no need for the spring to be particularly small. This makes it possible to facilitate manufacturing and reduce costs.

In the above invention, the photodiode and the laser diode are connected to an electro-optical sampling oscilloscope, and the laser light is pulsed from the laser diode based on a control signal from the electro-optical sampling oscilloscope. If the light is emitted as light, it is possible to perform highly accurate signal measurement in a wide band using an electro-optic sampling oscilloscope.

Further, according to the fifth aspect of the present invention, continuous light can be emitted from the laser diode, so that continuous output can be obtained from the photodiode. Therefore, the photodiode is connected to the real-time oscilloscope via the dedicated controller. It is also possible to connect to a conventional general-purpose measuring instrument such as the one described above to perform measurement, and the versatility is high.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of an electro-optical probe schematically showing an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of an electro-optical probe schematically showing a conventional technique of the present invention.

[Explanation of symbols]

21 Electro-optic probe 22 Probe body 22a tip 22b base end 23 Probe head 24 optical paths 24a One end 24b other end 25 laser diode 26 Electro-optical element 26a reflective film 27 metal pins 27a base end 27b tip 44 spring

─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Toshiyuki Yagi 4-19-7 Kamata, Ota-ku, Tokyo Ando Electric Co., Ltd. (72) Mitsuru Shinagawa 2-3-1 Otemachi, Chiyoda-ku, Tokyo Japan Telegraph and Telephone Corporation (72) Inventor Tadao Nagatsuma 2-3-1, Otemachi, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (72) Inventor Junzo Yamada 2-3-1, Otemachi, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (56) Reference JP-A-8-262117 (JP, A) JP-A-10-90371 (JP, A) JP-A-6-265606 (JP, A) JP-A-6-242152 (JP, A) JP 5-267407 (JP, A) JP 10-268003 (JP, A) JP 56-94272 (JP, A) JP 63-4571 (JP, A) US Patent 5105148 (US, A) (58) Field (Int.Cl. ^7, DB name) G01R 13/40 G01R 1/06 G01R 15/24 G01R 31/302 G01R 19/00

Claims (5)

(57) [Claims] 1. A probe main body and a probe head provided at a tip of the probe main body, wherein an optical path is formed inside the probe main body between a base end side thereof and the tip. A laser diode is disposed at one end of the optical path on the proximal side of the probe body, and an electro-optical element is disposed at the other end of the optical path on the tip side of the probe body while being held by the probe head. The probe head is provided with a metal pin, the base end of which is connected to the electro-optical element, and the tip of which is projected from the probe head, and the laser light emitted from the laser diode is supplied to the probe head. It is incident on the electro-optical element through an optical path, and the incident light is reflected by a reflective film provided on the electro-optical element,
Furthermore, the reflected light is separated and converted into an electric signal by a photodiode, the probe head is relatively displaceable in the extending direction of the optical path with respect to the tip of the probe body, and ,
It is attached in a state in which the rotational displacement about the extension direction of the optical path is regulated, and between the probe head and the probe body, elastically regulates the relative displacement in the extension direction of these optical paths. An electro-optic probe provided with an elastic member. 2. The electro-optical probe according to claim 1, wherein an elongated hole whose extension direction of the optical path is a longitudinal direction is formed in one of the tip of the probe head and the tip of the probe body. At the same time, a screw that fits into the elongated hole is attached to the other end. 3. The electro-optical probe according to claim 1, wherein the elastic member is composed of a spring formed in a spiral shape with the extending direction of the optical path as an axis and surrounding the optical path. An electro-optic probe characterized by. 4. The electro-optical probe according to claim 1, wherein the photodiode and the laser diode are
An electro-optic probe connected to an electro-optic sampling oscilloscope, wherein the laser diode emits the laser light as pulsed light based on a control signal from the electro-optic sampling oscilloscope. 5. The electro-optical probe according to claim 1, wherein the laser diode emits continuous light as the laser light.