JP3420977B2 - 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-optical probe having an improved optical system.

[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.

FIG. 2 shows the configuration of a conventional electro-optical probe used when performing signal measurement with an EOS oscilloscope.
Will be described with reference to. In FIG. 2, reference numeral 1 is a probe head made of an insulator, and a metal pin 1 is provided at the center of the probe head.
a is fitted. Reference numeral 2 is an electro-optical element, and a reflection film 2a is provided on the end surface on the metal pin 1a side and is in contact with the metal pin 1a. Reference numerals 3 and 10 are collimating lenses. Reference numeral 4 is a half-wave plate, reference numeral 5
Is a quarter-wave plate. Reference numerals 6 and 9 are polarization beam splitters. Reference numeral 7 is a half-wave plate, and reference numeral 8 is a Faraday element that rotates the polarization plane of incident light by 45 degrees. Reference numeral 11 is a laser diode that emits laser light in accordance with a control signal output from an EOS oscilloscope body (not shown). Reference numerals 12 and 13
Is a collimating lens. Reference numerals 14 and 15 denote photodiodes that convert the input laser light into an electric signal and output it to the EOS oscilloscope body. Code 16
Is an isolator including half-wave plates 4 and 7, quarter-wave plate 5, polarization beam splitters 6 and 9, and a Faraday element 8. Reference numeral 17 is a probe body.

Next, the optical path of the laser light emitted from the laser diode 11 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 11 is converted into parallel light by the collimator lens 10, goes straight through the polarization beam splitter 9, the Faraday element 8, the half-wave plate 7, and the polarization beam splitter 6, and further, the quarter-wave plate. 5,
After passing through the half-wave plate 4, it is condensed by the collimator lens 3 and enters the electro-optical element 2. The incident light is
It is reflected by the reflection film 2a formed on the end surface of the electro-optical element 2 on the metal pin 1a side.

The reflected laser light is collimated by the collimator lens 3
A part of the laser beam is reflected by the polarization beam splitter 6 and further collected by the collimator lens 12 to be collimated by the photodiode. It is incident on 14. The laser light that has passed through the polarization beam splitter 6 is reflected by the polarization beam splitter 9, is further condensed by the collimator lens 13, and enters the photodiode 15. The quarter-wave plate 4 is adjusted so that the laser beams incident on the photodiode 14 and the photodiode 15 have the same intensity. Also, the half-wave plate 4
Is for adjusting the polarization plane of the light incident on the electro-optical element 2, and the ½ wavelength plate 7 is for aligning the axes of the polarization beam splitters 6 and 9.

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 1a is brought into contact with the measurement point, the electric field of the electro-optical element 2 propagates to the electro-optical element 2 due to the voltage applied to the metal pin 1a, and the phenomenon that the birefringence changes due to the Pockels effect occurs. As a result, the laser light emitted from the laser diode 11 is incident on the electro-optical element 2, and when the laser light propagates through the electro-optical element 2, the polarization state of the light changes. Then, the laser light whose polarization state has changed is reflected by the reflection film 2a, enters the photodiodes 14 and 15, and is converted into an electric signal.

Along with the change in the voltage at the measuring point, the change in the polarization state caused by the electro-optical element 2 is changed by the photodiode 14
And the output difference of the photodiode 15, and the electric signal applied to the metal pin 1a can be measured by detecting this output difference. In the electro-optical probe described above, the electric signals obtained from the photodiodes 14 and 15 are input to the EOS oscilloscope and processed, but instead of this, the photodiode 1
It is also possible to connect a conventional measuring instrument such as a real-time oscilloscope to 4 and 15 via a dedicated controller to perform signal measurement. This allows easy broadband measurements using the electro-optic probe.

[0009]

However, in the conventional electro-optic probe, the optical path B shown in FIG.
As in C, the laser light emitted from the laser diode 11 is partially reflected by the reflecting surfaces 6b and 9b due to the poor extinction ratio of the polarization beam splitters 6 and 9. This reflected light is
Since the light is reflected on the inner surface of the probe main body 17 and enters the photodiodes 14 and 15 to be converted into noise light and converted into an electric signal, the S / N ratio is deteriorated, resulting in EO.
There is a problem that it appears as a measurement error of the S oscilloscope.

Further, the polarization beam splitter 6 to be used,
It is difficult to improve the extinction ratio of 9 and there is a problem that the cost of the optical component is increased.

The present invention has been made in view of such circumstances, and reduces unnecessary reflected light in the probe to reduce S / S.
An object is to provide an electro-optic probe that can improve the N ratio.

[0012]

According to a first aspect of the present invention, there is provided a laser diode for emitting a laser beam based on a control signal from an oscilloscope body, a collimating lens for collimating the laser beam, and a reflecting film on an end face. And an electro-optical element whose electric characteristics are changed by propagating an electric field through a metal pin provided on the end surface on the side of the reflection film, and provided between the collimator lens and the electro-optical element. An isolator having a polarization beam splitter that allows the laser light emitted from the laser diode to pass therethrough and separates the reflected light reflected by the reflective film, and the reflected light separated by the isolator is converted into an electrical signal. In an electro-optical probe including a photodiode, the polarization beam splitter is sandwiched between the photodiode and the photodiode. Characterized by providing an anti-reflection portion in position.

According to a second aspect of the present invention, the photodiode and the laser diode are connected to an electro-optical sampling oscilloscope, and the laser diode outputs the laser light based on a control signal from the electro-optical sampling oscilloscope. It is characterized by emitting as pulsed light. The invention described in claim 3 is characterized in that the laser diode emits continuous light as the laser light. The invention according to claim 4 is characterized in that the antireflection portion is provided with an uneven surface having no regularity.

According to a fifth aspect of the present invention, the antireflection section is provided with a surface that is not perpendicular to the optical axis while the light emitted from the polarization beam splitter is incident on the photodiode. .

According to a sixth aspect of the present invention, there is provided a laser diode which emits a laser beam based on a control signal from the oscilloscope body, a collimating lens which collimates the laser beam, and a reflection film on an end face. A laser emitted from the laser diode, which is provided between the electro-optical element in which an electric field is propagated through a metal pin provided on the end face on the film side and optical characteristics change, and the collimator lens and the electro-optical element. Electricity consisting of an isolator having a polarization beam splitter that allows light to pass therethrough and separate the reflected light reflected by the reflective film, and a photodiode that converts the reflected light separated by the isolator into an electrical signal In the optical probe of the polarization beam splitter opposite to the direction in which the photodiode is arranged. The optical axis of the light emitted from this surface, the light emitted from the polarization beam splitter and wherein the processed so as not to be parallel to the optical axis when incident on the photodiode.

According to a seventh aspect of the present invention, the photodiode and the laser diode are connected to an electro-optical sampling oscilloscope, and the laser diode outputs the laser light based on a control signal from the electro-optical sampling oscilloscope. It is characterized by emitting as pulsed light. The invention described in claim 8 is characterized in that the laser diode emits continuous light as the laser light. The invention described in claim 9 is characterized in that the processing surface of the polarization beam splitter is a surface processed into an uneven surface having no regularity.

According to a tenth aspect of the present invention, the processed surface of the polarization beam splitter is a surface that is not perpendicular to the optical axis when the light emitted from the polarization beam splitter enters the photodiode. Is characterized in that.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION An electro-optic probe (hereinafter referred to as a probe) according to an embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing the configuration of the same embodiment. In FIG. 1, the same parts as those of the conventional probe shown in FIG. 2 are designated by the same reference numerals and the description thereof will be omitted. The probe shown in this figure is different from the prior art in that a polarization beam splitter 61 having an uneven surface 61a having irregularities provided on the lower surface and a polarization beam splitter 91 having an inclined surface 91a provided on the lower surface are provided. The point is that an antireflection portion 17a having an inclined surface and an antireflection portion 17b having an uneven surface are provided on the inner surface of the probe body 17.

Next, the optical path of the laser light emitted from the laser diode 11 will be described with reference to FIG.
In FIG. 1, the optical path of the laser light is represented by the symbol D. First,
The laser light emitted from the laser diode 11 is converted into parallel light by the collimator lens 10, goes straight through the polarization beam splitter 91, the Faraday element 8, the half-wave plate 7, the polarization beam splitter 61, and further, the quarter-wave plate. 5 and passes through the half-wave plate 4.

Next, the parallel light transmitted through the half-wave plate 4 is condensed by the collimator lens 3 and enters the electro-optical element 2, and is formed on the end face of the electro-optical element 2 on the metal pin 1a side. It is reflected by the reflective film 2a. Since the collimator lens 3 is arranged at a position separated from the reflection film 2a by the focal length of the collimator lens 3, the laser light converted into parallel light by the collimator lens 10 is
It is focused on one point on the reflection film 2a.

The laser light reflected by the reflection film 2a is converted into parallel light again by the collimator lens 3, and further passes through the half-wave plate 4 and the quarter-wave plate 5,
Separated by the polarization beam splitters 61 and 91,
The light enters the photodiodes 14 and 15 and is converted into an electric signal.

Next, the optical path of the laser light emitted from the laser diode 11 reflected by the reflection surfaces 61b and 91b of the polarization beam splitters 61 and 91 will be described. First, the laser light reflected on the reflection surface 61b of the polarization beam splitter 61 is emitted as scattered light by the uneven surface 61a provided on the lower surface of the polarization beam splitter 61, and thus is reflected on the inner surface of the probe body 17. However, it does not enter the photodiode 14. Further, in the probe body 17, the antireflection portion 17 has an inner surface at a position facing the photodiode 14 with the polarization beam splitter 61 interposed therebetween, and having a surface that is not perpendicular to the optical axis of the light reflected by the reflection surface 61b.
a is provided. As a result, the reflection surface 61b
Even if the light (reference numeral E in FIG. 1) reflected at (1) goes straight, it can be prevented from entering the photodiode 14.

The inclination angle of the antireflection portion 17a having the inclined surface is obtained by tracing the optical path of the light emitted from the polarization beam splitter 61 geometrically and optically,
The angle may be set so that this light ray does not enter the range of the light receiving element (not shown) in the photodiode 14.

Further, the laser light reflected by the reflecting surface 91a of the polarization beam splitter 91 is refracted by the inclined surface 91a provided on the lower surface of the polarization beam splitter 91 and emitted, so that it is reflected by the inner surface of the probe body 17. Even if it does, it does not enter the photodiode 15. Further, an antireflection portion 17b having an uneven surface is provided on the inner surface at a position facing the photodiode 15 with the polarization beam splitter 91 interposed therebetween. As a result, the light temporarily reflected on the reflecting surface 91b (see FIG.
Even if the symbol F) of (3) goes straight, the intensity of light incident on the photodiode 15 can be weakened because it is diffusely reflected by the uneven surface of the antireflection portion 17b.

The inclination angle of the inclined surface 91a of the polarization beam splitter 91 is obtained by tracing the optical path of the light emitted from the polarization beam splitter 91 geometrically and optically, and this light ray is received by the photodiode 15. It suffices to set it based on the exit angle that does not enter the range of the element (not shown) and the refractive index of the material of this polarization beam splitter 91.

In this way, the polarization beam splitter 61,
Unnecessary by providing the uneven surface 61a and the inclined surface 91a on the lower surface of 91 to incline the optical axis of the light emitted from the lower surface of the polarization beam splitter, and by providing the antireflection portions 17a and 17b on the inner surface of the probe body 17. Since such reflected light can be prevented from entering the photodiodes 14 and 15, the S / N ratio can be improved as a result.

The structure shown in FIG. 1 has an uneven surface 61a provided on the lower surface of the polarization beam splitter 61, an inclined surface 91a provided on the lower surface of the polarization beam splitter 91, and an inclined surface provided on the inner surface of the probe body 17. Surface 17a and uneven surface 1
Although an example including all 7b is shown, at least one of them may be included. For example, the antireflection portions 17a and 17b may not be provided on the inner surface of the probe body 17, and only the uneven surface 61a or the inclined surface 91a may be provided on the polarization beam splitters 61 and 91. In addition, the polarization beam splitters 61 and 91 use the cube-shaped polarization beam splitters 6 and 9 shown in FIG.
It is also possible to provide only the antireflection portion 17a having an inclined surface or the antireflection portion 17b having an uneven surface on the inner surface.

Further, the antireflection portions 17a and 17b are not provided with an inclined surface or a concavo-convex surface, but the probe body 17
The black paint may be applied to the inner surface or the inner surface may be made of a porous material. In the above embodiment, if continuous light is emitted from the laser diode 11, it is possible to perform signal measurement using a conventional general-purpose measuring instrument such as a real-time oscilloscope, a sampling oscilloscope, and a spectrum analyzer. In this case, instead of the EOS oscilloscope, the photodiodes 14 and 15 may be connected to a real-time oscilloscope, a sampling oscilloscope, a spectrum analyzer, etc. via a dedicated controller.

[0029]

As described above, according to the first, fourth, and fifth aspects.
According to the invention, since the antireflection portion is provided on the inner surface of the probe main body, even if the light to be transmitted through the polarization beam splitter is reflected, the optical axis of the reflected light is tilted by the antireflection portion, which is unnecessary for the photodiode. It is possible to avoid the incidence of such light, and as a result, it is possible to improve the S / N ratio of the signal.

According to the sixth, ninth and tenth aspects of the present invention, the output surface of the polarization beam splitter is processed so that even if the light to be transmitted through the polarization beam splitter is reflected and emitted, its optical axis is Since it is tilted, even if this light is reflected by the probe body, it can be prevented from entering the photodiode. This has the effect of improving the S / N ratio of the signal output from the photodiode.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a configuration of an embodiment of the present invention.

FIG. 2 is a configuration diagram showing a configuration of an electro-optical probe according to a conventional technique.

[Explanation of symbols]

1 probe head 1a metal pin 2 Electro-optical element 2a reflective film 3 Collimating lens 4 1/2 wave plate 5 1/4 wave plate 7 1/2 wave plate 8 Faraday element 10 Collimating lens 11 Laser diode 12 Collimating lens 13 Collimating lens 14 Photodiode 15 photodiode 16 Isolator 17 Probe body 17a Antireflection part 17b Antireflection part 61 Polarizing beam splitter 91 Polarizing beam splitter

─────────────────────────────────────────────────── ─── 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 61-140802 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G01R 13/40 G01R 15 / 24 G01R 19/00 G01R 11/00-11/30 102

Claims (10)

(57) [Claims] 1. A laser diode that emits a laser beam based on a control signal of an oscilloscope body, a collimating lens that collimates the laser beam, and a reflecting film on an end face, which is provided on the end face on the reflecting film side. An electro-optical element whose electric characteristics are changed by propagating an electric field through a metal pin, and a laser beam which is provided between the collimator lens and the electro-optical element and which allows the laser beam emitted by the laser diode to pass therethrough. An electro-optical probe comprising: an isolator having a polarization beam splitter for separating the reflected light reflected by the reflective film; and a photodiode for converting the reflected light separated by the isolator into an electric signal, wherein the polarized light A special feature is that an antireflection section is provided at a position facing the photodiode with the beam splitter in between. Electro-optic probe to collect. 2. The photodiode and the laser diode are connected to an electro-optical sampling oscilloscope, and the laser diode emits the laser light as pulsed light based on a control signal from the electro-optical sampling oscilloscope. The electro-optical probe according to claim 1. 3. The electro-optical probe according to claim 1, wherein the laser diode emits continuous light as the laser light. 4. The antireflection portion is provided with an uneven surface having no regularity.
The electro-optical probe according to any one of items 1 to 3. 5. The antireflection unit comprises a surface which is not perpendicular to an optical axis during which the light emitted from the polarization beam splitter is incident on the photodiode. The electro-optic probe according to the section. 6. A laser diode that emits a laser beam based on a control signal of an oscilloscope body, a collimating lens that collimates the laser beam, and a reflecting film on an end face, and the collimating lens is provided on the end face on the reflecting film side. An electro-optical element whose electric characteristics are changed by propagating an electric field through a metal pin, and a laser beam which is provided between the collimator lens and the electro-optical element and which allows the laser beam emitted by the laser diode to pass therethrough. Is an isolator having a polarization beam splitter for separating the reflected light reflected by the reflective film, and a photodiode for converting the reflected light separated by the isolator into an electric signal, The surface of the polarization beam splitter opposite to the direction in which the diode is arranged is projected from this surface. An electro-optical probe, characterized in that the optical axis of the emitted light is processed so as not to be parallel to the optical axis when the light emitted from the polarization beam splitter enters the photodiode. 7. The photodiode and the laser diode are connected to an electro-optical sampling oscilloscope, and the laser diode emits the laser light as pulsed light based on a control signal from the electro-optical sampling oscilloscope. The electro-optical probe according to claim 6. 8. The electro-optical probe according to claim 6, wherein the laser diode emits continuous light as the laser light. 9. The electro-optic probe according to claim 6, wherein the processed surface of the polarization beam splitter is a surface processed into an irregular surface having no regularity. 10. The processed surface of the polarization beam splitter is a surface processed not to be perpendicular to the optical axis when the light emitted from the polarization beam splitter enters the photodiode. The electro-optical probe according to any one of claims 6 to 8.