JP3420978B2 - 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 electrooptic probe.

[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-optical probe 1 used when measuring signals with an EOS oscilloscope will be described with reference to FIG. In the electro-optic probe 1 shown in FIG. 7, a probe head 3 made of an insulator is provided at the tip of a probe body 2, and a metal pin 3 is provided at the center thereof.
a is fitted. 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 polarization beam splitters. Reference numeral 9 is a half-wave plate, and reference numeral 10 is a Faraday element. Reference numeral 12 is
It is a collimating lens, and reference numeral 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. 7, 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 collimating lens 12, goes straight through the polarization beam splitter 8, the Faraday element 10, the half-wave plate 9 and the polarization beam splitter 7, and further, the quarter-wave plate. 6 and 1
It enters the electro-optical element 4 through the / 2 wave plate 5. 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. 1/2
The 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.

Next, the operation of measuring the signal under measurement using the electro-optical probe 1 shown in FIG. 7 will be described.
When the metal pin 3a is brought into contact with the measuring point, the metal pin 3a
In the electro-optical element 4, the electric field propagates to the electro-optical element 4 due to the voltage applied to the birefringence index due to the Pockels effect. 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 polarization state due to the electro-optical element 4 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.

[0010]

As described above, in the signal measurement using the electro-optic probe 1, the metal pin 3 is used.
Since it is necessary to bring a into contact with the measurement point, in this case, the metal pin 3a is impacted, and as a result, the electro-optical element 4 may be damaged.

Further, in the electro-optic probe 1 described above, the reflection film 4a in which the end of the metal pin 3a is brought into contact with the laser beam is used.
Since it is configured to be incident on and reflected from,
When the position of the metal pin 3a moves, the position of the reflection film 4a and the like also shifts, and there is a problem that the function as an optical system is lost.

The present invention has been made in view of such circumstances, and an object thereof is to improve the shock resistance of the electro-optical probe by fixing the position of the metal pin with respect to the probe head.

[0013]

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, wherein an optical path is formed inside the probe main body between the base end side and the tip end side of the probe main body, and the optical path is provided at one end on the base end side of the probe main body. A laser diode is arranged, an electro-optical element is arranged at the other end of the optical path on the tip side of the probe body, and a reflection film is formed on the end surface of the electro-optical element on the tip side of the probe body. The formed 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 reflective film, and the reflected light is separated into an electric signal by the photodiode. The electro-optical element is configured to convert at least from the tip end side of the probe body by the probe head member forming the tip end portion of the probe body. Is lifting, the said probe head member, the insertion hole is formed extending to the reflective layer from an external, metal pins into the insertion hole, one end in contact with the reflective layer,
The other end is inserted in a state of protruding from the probe head, and the insertion hole is formed such that a diameter dimension on the outer side is larger than a diameter dimension on the reflection film side. I am trying.

In order to have such a structure, in this electro-optical probe, by forming one end side of the metal pin according to the shape of the insertion hole, the metal pin is fitted more than necessary into the probe head member. It is possible to prevent the electro-optical element from being damaged.

The electro-optic probe according to claim 2 is the electro-optic probe according to claim 1, wherein the insertion hole is
It is characterized in that the diameter is formed in a taper shape that gradually decreases from the outer side toward the reflective film side.

The electro-optical probe according to claim 3 is the electro-optical probe according to claim 1, wherein the insertion hole is
It is characterized in that the inner surface thereof is provided with a stepped portion whose diameter dimension decreases from the outer side toward the reflective film side.

The electro-optical probe according to claim 4 is the electro-optical probe according to any one of claims 1 to 3, wherein the one end side of the metal pin is from the other end side to the one end side. It is characterized in that it is formed as a diameter changing portion having a smaller diameter dimension toward it.

The electro-optic probe according to claim 5 is the electro-optic probe according to any one of claims 1 to 3, wherein a slit penetrating the metal pin in a diameter direction is formed on an end face of the metal pin on the one end side. It is characterized by being provided. With such a configuration, in the electro-optical probe according to the fifth aspect, one end of the metal pin can be deformed according to the shape of the insertion hole provided in the probe head member.

An electro-optical probe according to a sixth aspect is the electro-optical probe according to any of the first to fifth aspects, wherein the diameter dimension of the one end of the insertion hole is incident on the electro-optical element. It is characterized by being larger than the spot size of the incident light.

Because of such a structure, the sixth aspect of the present invention is provided.
In the electro-optical probe according to (1), the contact area between the metal pin and the reflective film is secured, and the change in the electric field that appears as the change in the polarization state in the electro-optical element can be favorably detected by the laser light.

The electro-optic probe according to claim 7 is the electro-optic probe according to any one of claims 1 to 6, 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.

The electro-optical probe according to claim 8 is the electro-optical probe according to any one of claims 1 to 6, wherein the laser diode emits continuous light as the laser light.

As described above, in the electro-optical probe according to the eighth aspect, the continuous output can be obtained from the photo diode by causing the laser diode to emit the continuous light. 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. 2 and 3 are a vertical sectional view and a plan view of an electro-optical probe 21 showing an embodiment of the present invention. The electro-optic probe 21 has a schematic structure in which an optical path 23 is formed inside a probe body 22.

The probe body 22 has a probe head member 24 at its tip 22a, and a laser diode 25 is housed at its base 22b. The laser diode 25 is located at one end 23a of the probe body 22 on the base end 22b side of the optical path 23, and is connected to an EOS oscilloscope (not shown).

On the other hand, the probe body 22 in the optical path 23
Of the electro-optical element 26 at the other end 23b on the side of the tip 22a of the
Are arranged. The electro-optical element 26 is held by the probe head member 24, and
A reflective film 28 is formed on the end surface 26a of the probe body 22 on the side of the tip 22a.

FIG. 1 shows an enlarged view of the probe head member 24 and its vicinity. As shown in the figure, an insertion hole 30 is formed in the probe head member 24, and one end 31 a of the metal pin 31 is inserted into this insertion hole 30. The metal pin 31 has an end surface 3 on the one end 31a side.
1b is in contact with the reflective film 28 from the tip side of the probe body 22, and the other end 31c is projected from the probe head member 24. As the metal pin 31, a phosphor bronze plated with nickel rhodium is used.

The shape of the insertion hole 30 is such that the end portion 3 on the outer side thereof is formed.
From 0a toward the end 30b on the reflective film 28 side, the taper shape is such that the diameter gradually decreases. Further, a taper portion (diameter changing portion) 31d is formed on the one end 31a side of the metal pin 31 such that the diameter dimension thereof gradually decreases from the other end 31c side toward the end surface 31b. The diameter dimension of the tapered portion 31d is formed to be slightly larger than the diameter dimension of the insertion hole 30, whereby the one end 31a of the metal pin 31 can be fitted and fixed in the insertion hole 30. . In addition, the end surface 31 of the metal pin 31
b is formed so that its diameter is larger than the beam diameter (spot size of incident light) of the laser beam emitted from the laser diode 25 (see FIG. 2) and reaching the reflection film 28 (see FIG. 2). ing.

On the other hand, as shown in FIG. 2, on the optical path 23, a collimating lens 33, a polarization beam splitter 34, a Faraday element 35, a polarization beam splitter 37, and a 1/4 wavelength plate 38 are arranged in this order from the right side in the figure. Are arranged.
In addition, the polarization beam splitters 34, 3 on the side of the optical path 23
Photodiodes 41 and 42 are provided at positions corresponding to 7. These photodiodes 41, 42
Is connected to the EOS oscilloscope so that incident light can be converted into an electric signal and transmitted to the EOS oscilloscope.

Further, the polarization beam splitters 34, 37
Is to function as an isolator that separates a part of the light passing through the optical path 23 and reflects it toward the photodiodes 41 and 42.

When the electro-optical probe 21 is used for signal measurement, the EOS oscilloscope is activated with the other end 31c of the metal pin 31 in contact with the measurement point. 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 33, goes straight on the optical path 23, and reaches the electro-optical element 26.
To reach.

The laser light reaching the electro-optical element 26 is
The light enters the reflection film 28 and is reflected by the light path 2
3 will proceed to the laser diode 25 side. At this time, since the electro-optical element 26 is in a state in which the refractive index changes due to the change in the electric field at the measurement point propagated through the metal pin 31, the polarization of the light when propagating through the electro-optical element 26. The state of the reflected light changes, and the reflected light is in the state where the polarization state has changed, and the polarization beam splitters 34, 3
It is separated by 7, and is collected and incident on the photodiodes 41 and 42, and is converted into an electric signal. This allows
Photodiodes 41 and 4 are used to detect changes in the polarization state of laser light.
It is possible to measure the electric signal at the measurement point by detecting as the output difference of 2.

When such a signal measurement is performed, even if the metal pin 31 is accidentally impacted when the other end of the metal pin 31 is brought into contact with the measurement point, the electro-optic probe 21 is The insertion hole 30 has a tapered shape,
Further, since the metal pin 31 is also provided with the tapered portion 31d corresponding to the shape, the metal pin 31 is prevented from being fitted into the probe head member 24 more than necessary, and the electro-optical element 26 is damaged, Alternatively, there is no concern that the position of the electro-optical element 26 is displaced and the optical system formed in the probe body 22 does not function. Therefore, the electro-optical probe 21 can ensure impact resistance during signal measurement.

Further, in the electro-optic probe 21, the diameter dimension of the end portion 30b of the insertion hole 30 on the reflection film 28 side is larger than the beam diameter of the laser beam emitted from the laser diode 25 and reaching the reflection film 28. Due to the large size, the contact area between the electro-optical element 26 and the metal pin 31 can be ensured in an amount sufficient to detect the change of the polarization state of the electro-optical element 26, and thus, as described above. Even if the hole 30 is formed in a tapered shape, this does not deteriorate the detection performance of signal measurement.

The above is an example of the embodiment of the present invention, but the present invention is not limited to the above embodiment, and changes in shape, material, etc. can be made within the scope of the invention. It is possible. For example, the metal pin 43 shown in FIG. 4 may be used instead of the metal pin 31 shown in the above embodiment. The metal pin 43 shown in FIG. 4 has a configuration in which a slit 44 penetrating the metal pin 43 in the diametrical direction is provided on the one end 43a side.

With such a structure, the metal pin 43 can be reduced in diameter at one end 43a, and can be easily fitted into the tapered insertion hole 30 shown in the above embodiment. In this case, one end 43a of the metal pin 43 is inserted into the insertion hole 3 by the repulsive force of the protrusions 43b and 43b (see FIG. 4) located on both sides of the slit 44.
0 fixed well, and in this case the metal pin 43
Even if an impact is applied from the other end 43c (see FIG. 4), the metal pin 43 is not fitted into the probe head member 24 (see FIG. 1) more than necessary. Therefore, similarly to the above-mentioned embodiment, impact resistance can be ensured. When fixing the metal pin 43 formed in this manner to the insertion hole 30, it is desirable to fill the slit 44 with a conductive material such as silver paste to eliminate the space.

In addition to this, the metal pin 4 shown in FIG.
5, one end 45a, one end 45a from the other end 45b side
Stepped portion (diameter changing portion) whose diameter is reduced toward the side a
The same effect can be obtained by adopting the one provided with 45c. In this case, the metal pin 45
The shape of the insertion hole 30 into which is inserted may be a tapered shape as in the above-mentioned embodiment, or, as shown in FIG. It may have a shape having a stepped portion 30c that is larger than the above.

Further, in the above embodiment, if continuous light is emitted from the laser diode 25, it is possible to perform signal measurement by a conventional general-purpose measuring instrument such as a real-time oscilloscope, sampling oscilloscope, spectrum analyzer, or the like. In this case, the photodiodes 41, 4
2. Instead of the EOS oscilloscope, a real-time oscilloscope, sampling oscilloscope, spectrum analyzer, etc. may be connected via a dedicated controller.

[0039]

As described above, in the electro-optic probe according to the first aspect, the diameter of the insertion hole into which the metal pin is inserted is larger on the outside side than on the reflection film side. Since it is formed like this, according to the shape of this insertion hole,
If the end portions of the metal pins are formed into a shape, there is no concern that the metal pins may be inserted into the probe head member more than necessary and damage the electro-optical element, and it is possible to realize a product having excellent impact resistance. .

In this case, as in claim 2, the shape of the insertion hole may be tapered so as to gradually become smaller from the outer side toward the reflective film side, or, as in claim 3,
The insertion hole may be provided with a step portion having a smaller diameter dimension from the outer side to the reflective film side. Corresponding to these, as in claim 4, a diameter changing portion may be provided at one end of the metal pin so that the diameter dimension decreases from the other end side to the one end, or As in claim 5,
A slit may be provided on the end face of one end of the metal pin so that the diameter can be reduced, and the one end may be fitted into the insertion hole.

Furthermore, when the diameter of one end of the insertion hole is set to be larger than the spot size of the light incident on the electro-optical element, the measurement performance can be ensured.

In the above invention, the photodiode and the laser diode are connected to the electro-optical sampling oscilloscope, and the laser light from the laser diode is pulsed based on the 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 present invention, the laser diode emits continuous light so that a 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 an enlarged sectional view of an essential part of an electro-optical probe schematically showing an embodiment of the present invention.

2 is a vertical cross-sectional view of the electro-optic probe shown in FIG.

FIG. 3 is a plan view of the same.

4A and 4B are diagrams showing another example of the metal pin used in the electro-optical probe shown in FIGS. 1 to 3, wherein FIG. 4A is a side view thereof, and FIG. FIG.

FIG. 5 is a side view showing still another example of the metal pin.

FIG. 6 is a vertical cross-sectional view showing another example of the probe head member.

FIG. 7 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 optical path 23a One end 23b the other end 24 Probe head member 25 laser diode 26 Electro-optical element 28 Reflective film 30 insertion holes 30a, 30b ends 30c step 31, 43, 45 Metal pin 31a, 43a, 45a One end 31b end face 31c, 43c, 45b The other end 31d Tapered part (diameter changing part)

─────────────────────────────────────────────────── ─── 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-A-5-267407 (JP, A) JP-A-5-40006 (JP, A) JP-A-8-129016 (JP, A) (58) Fields investigated (Int. Cl. ⁷⁾ , DB name) G01R 13/40 G01R 1/06 G01R 15/24 G01R 31/302

Claims (8)

(57) [Claims] 1. An optical path is formed inside the probe main body between a base end side and a front end side of the probe main body, and a laser diode is provided at one end of the optical path on the base end side of the probe main body. An electro-optical element is disposed at the other end of the optical path on the tip side of the probe body, and a reflection film is formed on an end surface of the electro-optical element on the tip side of the probe body. Laser light emitted from a diode is incident on the electro-optical element through the optical path, the incident light is reflected by the reflective film, and the reflected light is separated and converted into an electric signal by a photodiode. The probe head member forming the tip of the probe body holds the electro-optical element from at least the tip side of the probe body. An insertion hole from the outside to the reflection film is formed in the head member, and a metal pin is inserted into the insertion hole in a state where one end of the metal pin is in contact with the reflection film and the other end projects from the probe head. The electro-optic probe is characterized in that the insertion hole is formed such that a diameter dimension on the outer side is larger than a diameter dimension on the reflection film side. 2. The electro-optical probe according to claim 1, wherein the insertion hole is formed in a tapered shape in which a diameter dimension thereof gradually decreases from the outer side toward the reflective film side. An electro-optic probe characterized by. 3. The electro-optical probe according to claim 1, wherein the insertion hole is provided with a stepped portion whose inner surface has a diameter dimension that decreases from the outer side toward the reflective film side. An electro-optical probe having a structure. 4. The electro-optical probe according to claim 1, wherein the one end side of the metal pin has a smaller diameter dimension from the other end side toward the one end side. An electro-optical probe formed as a diameter changing portion. 5. The electro-optical probe according to claim 1, wherein a slit penetrating the metal pin in a diameter direction is provided on an end surface of the metal pin on the one end side. An electro-optical probe characterized in that 6. The electro-optical probe according to claim 1, wherein a diameter dimension of the one end of the insertion hole is larger than a spot size of incident light incident on the electro-optical element. An electro-optical probe characterized in that 7. 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. 8. The electro-optical probe according to claim 1, wherein the laser diode emits continuous light as the laser light.