JP2000171488A - Electrooptical probe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrooptical probe for preventing unneeded reflection light being generated in optical parts in a probe from entering a photodiode. SOLUTION: An irregular surface 61a and a slope 91a are provided on the lower surface of polarization beam splitters 61 and 91, and the optical axis of light being reflected on reflection surfaces 61b and 91b is inclined. Also, by providing a slope 17a and an irregular surface 17b on the inner surface of a probe body 17, the optical axis of light being reflected on the reflection surfaces 61b and 91b is inclined so that light does not enter photodiodes 14 and 15, thus preventing unneeded reflection light from entering the photodiodes 14 and 15 and hence improving the S/N ratio of a signal being outputted from the photodiodes 14 and 15.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric field generated by a signal to be measured is coupled to an electro-optic crystal, light is incident on the electro-optic crystal, and the waveform of the signal to be measured is observed based on the polarization state of the incident light. More particularly, the present invention relates to an electro-optic probe having an improved optical system.

[0002]

2. Description of the Related Art An electric field generated by a signal under measurement is coupled to an electro-optic crystal, a laser beam is incident on the electro-optic crystal, and the waveform of the signal under measurement can be observed based on the polarization state of the laser beam. Here, the laser light is pulsed,
When the signal under measurement is sampled, it can be measured with a very high time resolution. An electro-optic sampling oscilloscope uses an electro-optic probe utilizing this phenomenon.

The electro-optic sampling (Electro Opt)
ic Sampling) oscilloscopes (hereafter abbreviated as “EOS oscilloscopes”) do not require a ground wire when measuring signals, as compared to conventional sampling oscilloscopes that use electrical probes. Easy 2) Since the metal pin at the tip of the electro-optic probe is insulated from the circuit system, high input impedance can be realized, and as a result, the state of the measured point is hardly disturbed. 3) Since optical pulses are used. It has attracted attention because of its feature that it can perform broadband measurement up to GHz order.

FIG. 2 shows the configuration of a conventional electro-optic probe used when measuring signals with an EOS oscilloscope.
This will be described with reference to FIG. In FIG. 2, reference numeral 1 denotes a probe head made of an insulator.
a is fitted. Reference numeral 2 denotes an electro-optical element, and a reflection film 2a is provided on an end face 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, and reference numeral 5
Is a 波長 wavelength plate. Reference numerals 6 and 9 are polarization beam splitters. Reference numeral 7 denotes a half-wave plate, and reference numeral 8 denotes a Faraday element that rotates the plane of polarization of incident light by 45 degrees. Reference numeral 11 denotes a laser diode that emits laser light according to a control signal output from an EOS oscilloscope main body (not shown). Symbols 12 and 13
Is a collimating lens. Reference numerals 14 and 15 are photodiodes that convert the input laser light into an electric signal and output the electric signal to the EOS oscilloscope main body. Code 16
Is an isolator comprising １ ／ wavelength plates 4 and 7, １ ／ wavelength plate 5, polarization beam splitters 6 and 9, and Faraday element 8. Reference numeral 17 denotes a probe main 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 reference symbol A. First,
The laser light emitted from the laser diode 11 is converted into parallel light by the collimating lens 10, goes straight through the polarizing beam splitter 9, the Faraday element 8, the 波長 wavelength plate 7, and the polarizing beam splitter 6, and further passes through the ４ wavelength plate. 5,
After passing through the half-wave plate 4, the light is condensed by the collimator lens 3 and enters the electro-optical element 2. The incident light is
The light is reflected by the reflective film 2a formed on the end face of the electro-optical element 2 on the metal pin 1a side.

[0006] The reflected laser light is applied to a collimating lens 3.
The laser light is again converted into parallel light, passes through the half-wave plate 4 and the quarter-wave plate 5 again, and a part of the laser light is reflected by the polarizing beam splitter 6 and further condensed by the collimating lens 12 to be photodiode. 14 is incident. The laser light transmitted through the polarizing beam splitter 6 is reflected by the polarizing beam splitter 9, further condensed by a collimator lens 13, and enters the photodiode 15. The quarter-wave plate 4 adjusts the intensity of the laser light incident on the photodiode 14 and the intensity of the laser light incident on the photodiode 15. Also, a half-wave plate 4
Is for adjusting the plane of polarization of light incident on the electro-optical element 2, and the half-wave 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-optic probe shown in FIG. 2 will be described. When the metal pin 1a is brought into contact with the measurement point, the voltage applied to the metal pin 1a causes the electric field of the electro-optical element 2 to propagate to the electro-optical element 2, and the birefringence changes due to the Pockels effect. Thereby, the laser light emitted from the laser diode 11 enters the electro-optical element 2, and the polarization state of the light changes when the laser light propagates through the electro-optical element 2. 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.

[0008] With the change in the voltage at the measurement point, the change in the polarization state due to the electro-optical element 2 is changed by the photodiode 14.
And the output difference of the photodiode 15. By detecting this output difference, the electric signal applied to the metal pin 1 a can be measured. In the electro-optic probe described above, the electric signals obtained from the photodiodes 14 and 15 are input to the EOS oscilloscope and processed.
A conventional measuring instrument such as a real-time oscilloscope may be connected to each of the devices 4 and 15 via a dedicated controller to perform signal measurement. Thus, wideband measurement can be easily performed using the electro-optic probe.

[0009]

However, in the prior art electro-optical probe, the optical path B shown in FIG.
As shown in C, in the laser light emitted from the laser diode 11, a part of the light to be transmitted is reflected on the reflection surfaces 6b and 9b due to the poor extinction ratio of the polarization beam splitters 6 and 9. This reflected light further
The light is reflected on the inner surface of the probe main body 17, is incident on the photodiodes 14 and 15, becomes noise light, and is converted into an electric signal, thereby deteriorating the S / N ratio.
There is a problem that it appears as a measurement error of the S oscilloscope.

The polarization beam splitter 6 to be used,
It is difficult to improve the extinction ratio of No. 9 and there is a problem that the cost of the optical components increases.

The present invention has been made in view of such circumstances, and reduces unnecessary reflected light in a probe to reduce S / S.
An object of the present invention 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 of an oscilloscope body, a collimating lens for converting the laser beam into a parallel beam, and a reflection film on an end surface. An electro-optical element in which an electric field is propagated through a metal pin provided on an end surface on the reflection film side to change optical characteristics, and the electro-optical element is provided between the collimator lens and the electro-optical element, An isolator having a polarizing beam splitter for passing a laser beam emitted by a laser diode and separating the reflected beam reflected by the reflection film, and converting the reflected beam separated by the isolator into an electric signal In an electro-optic probe including a photodiode, the electro-optic probe faces the photodiode with the polarization beam splitter interposed therebetween. 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-optic sampling oscilloscope, and the laser diode outputs the laser light based on a control signal from the electro-optic sampling oscilloscope. It emits as pulsed light. The invention according to 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 section has an irregular surface having no regularity.

The invention according to claim 5 is characterized in that the anti-reflection section has a surface which is not perpendicular to the optical axis while the light emitted from the polarizing beam splitter enters the photodiode. .

According to a sixth aspect of the present invention, there is provided a laser diode for emitting a laser beam based on a control signal of an oscilloscope main body, a collimating lens for collimating the laser beam, and a reflection film on an end face. An electro-optical element in which an electric field is propagated through a metal pin provided on an end surface on the film side to change optical characteristics, and a laser provided between the collimating lens and the electro-optical element, and emitted by the laser diode. An electrical device comprising: an isolator having a polarizing beam splitter that transmits light and separates the reflected light reflected by the reflection film from the laser light; and a photodiode that converts the reflected light separated by the isolator into an electric signal. In the optical probe, the polarization beam splitter has a direction opposite to a 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-optic sampling oscilloscope, and the laser diode outputs the laser light based on a control signal from the electro-optic sampling oscilloscope. It emits as pulsed light. The invention according to claim 8 is characterized in that the laser diode emits continuous light as the laser light. According to a ninth aspect of the present invention, the processing surface of the polarization beam splitter is a surface processed into an irregular surface having no regularity.

According to a tenth aspect of the present invention, the processing surface of the polarization beam splitter is a surface processed to be not perpendicular to an optical axis when light emitted from the polarization beam splitter enters the photodiode. It is characterized by being.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an electro-optic probe (hereinafter, referred to as a probe) according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a configuration of the embodiment. In FIG. 1, the same portions as those of the conventional probe shown in FIG. 2 are denoted by the same reference numerals, and description thereof will be omitted. The probe shown in this figure is different from the prior art in that a polarizing beam splitter 61 having an uneven surface 61a having irregularities on the lower surface and a polarizing beam splitter 91 having an inclined surface 91a on the lower surface are provided. And an anti-reflection portion 17a having an inclined surface and an anti-reflection portion 17b having an uneven surface on the inner surface of the probe main 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 reference symbol D. First,
The laser light emitted from the laser diode 11 is converted into parallel light by the collimator lens 10, and goes straight through the polarizing beam splitter 91, the Faraday element 8, the half-wave plate 7, and the polarizing beam splitter 61, and further, a quarter-wave plate. 5, pass 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 is incident on the electro-optical element 2, and is formed on the end face of the electro-optical element 2 on the metal pin 1a side. The light is reflected by the reflection film 2a. Since the collimating lens 3 is arranged at a position separated from the reflecting film 2a by only the focal length of the collimating lens 3, the laser light converted into parallel light by the collimating lens 10 is
The light 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 collimating lens 3, and further passes through the half-wave plate 4, the quarter-wave plate 5, and
Separated by the polarizing beam splitters 61 and 91,
The light enters the photodiodes 14 and 15 and is converted into an electric signal.

Next, an optical path in which the laser light emitted from the laser diode 11 is reflected on 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 is thus reflected on the inner surface of the probe main body 17. Does not enter the photodiode 14. Further, the probe body 17 has an antireflection portion 17 having an inner surface at a position facing the photodiode 14 with the polarization beam splitter 61 interposed therebetween, the surface being 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
It is possible to prevent the light (reference numeral E in FIG. 1) reflected on at the photodiode 14 from entering the photodiode 14 even if the light goes straight.

The angle of inclination of the antireflection portion 17a having the inclined surface is obtained by geometrically tracing the optical path of the light emitted from the polarizing beam splitter 61, and
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.

The laser light reflected on the reflection 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 therefrom. 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, light temporarily reflected on the reflecting surface 91b (FIG. 1)
Even if the symbol F) goes straight, the intensity of light incident on the photodiode 15 can be reduced because the light 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 geometrically tracing the optical path of the light emitted from the polarization beam splitter 91. What is necessary is just to set from the output angle which does not enter into the range of an element (not shown), and the refractive index of the material of this polarizing beam splitter 91.

As described above, the polarization beam splitter 61,
By providing an uneven surface 61a and an inclined surface 91a on the lower surface of the probe 91, tilting the optical axis of the light emitted from the lower surface of the polarizing beam splitter, and providing the antireflection portions 17a and 17b on the inner surface of the probe main body 17, unnecessary. Since the reflected light can be prevented from entering the photodiodes 14 and 15, the S / N ratio can be improved as a result.

The configuration shown in FIG. 1 includes an uneven surface 61 a provided on the lower surface of the polarizing beam splitter 61, an inclined surface 91 a provided on the lower surface of the polarizing beam splitter 91, and an inclined surface provided on the inner surface of the probe main body 17. Surface 17a and uneven surface 1
Although the example in which all the elements 7b are provided is shown, at least one of these elements may be provided. For example, the antireflection portions 17a and 17b may not be provided on the inner surface of the probe main body 17, and only the concave and convex surfaces 61a or the inclined surfaces 91a may be provided on the polarization beam splitters 61 and 91. Further, the polarization beam splitters 61 and 91 use the cube-shaped polarization beam splitters 6 and 9 shown in FIG.
The anti-reflection portion 17a having an inclined surface or the anti-reflection portion 17b having an uneven surface may be provided only on the inner surface.

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

[0029]

As described above, claims 1, 4, 5
According to the invention, the anti-reflection portion is provided on the inner surface of the probe main body. Therefore, even if light to be transmitted through the polarization beam splitter is reflected, the optical axis of the reflected light is tilted by the anti-reflection portion, which is unnecessary for the photodiode. Incident light can be avoided, and as a result, the S / N ratio of the signal can be improved.

According to the sixth, ninth and tenth aspects of the present invention, even if the light to be transmitted through the polarizing beam splitter is reflected and emitted by processing the light emitting surface of the polarizing beam splitter, the optical axis of the light is maintained. Since the light is tilted, even if this light is reflected by the probe main body, it can be prevented from being incident on the photodiode. As a result, an effect is obtained that the S / N ratio of the signal output from the photodiode can be improved.

[Brief description of the 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-optic probe according to the related art.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Probe head 1a Metal pin 2 Electro-optical element 2a Reflective film 3 Collimating lens 4 1/2 wavelength plate 5 1/4 wavelength plate 7 1/2 wavelength 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 section 17b Antireflection section 61 Polarization beam splitter 91 Polarization beam splitter

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Katsushi Ota 4-19-7 Kamata, Ota-ku, Tokyo Inside Ando Electric Co., Ltd. (72) Inventor Toshiyuki Yagi 4-197-7 Kamata, Ota-ku, Tokyo Ando Inside Electric Corporation (72) Inventor Mitsuru Shinagawa 2-3-1 Otemachi, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (72) Tadao Nagatsuma 2-3-1 Otemachi, Chiyoda-ku, Tokyo (72) Inventor Junzo Yamada 2-3-1 Otemachi, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation

Claims (10)

[Claims] 1. A laser diode that emits a laser beam based on a control signal of an oscilloscope main body, a collimating lens that converts the laser beam into parallel light, a reflecting film on an end face, and the reflecting film is provided on an end face on the reflecting film side. An electro-optical element in which an electric field is propagated through a metal pin to change optical characteristics, and a laser beam provided between the collimating lens and the electro-optical element, the laser beam emitted by the laser diode being passed therethrough. An electro-optic probe comprising: an isolator provided with a polarizing beam splitter that separates reflected light reflected by the reflective film; and a photodiode that converts reflected light separated by the isolator into an electric signal. An anti-reflection portion is provided at a position facing the photodiode with a beam splitter interposed therebetween. Electro-optic probe. 2. The method according to claim 1, wherein the photodiode and the laser diode are connected to an electro-optic sampling oscilloscope, and the laser diode emits the laser light as pulse light based on a control signal from the electro-optic sampling oscilloscope. 2. The electro-optic probe according to claim 1, wherein 3. The electro-optical probe according to claim 1, wherein the laser diode emits continuous light as the laser light. 4. The apparatus according to claim 1, wherein the antireflection section has an irregular surface having no regularity.
4. The electro-optic probe according to any one of items 1 to 3, 5. The anti-reflection unit according to claim 1, wherein the anti-reflection unit has a surface that is not perpendicular to an optical axis while the light emitted from the polarization beam splitter is incident on the photodiode. An electro-optic probe according to any of the above items. 6. A laser diode that emits a laser beam based on a control signal of an oscilloscope main body, a collimator lens that converts the laser beam into parallel light, and a reflection film on an end surface, which is provided on the end surface on the reflection film side. An electro-optical element in which an electric field is propagated through a metal pin to change optical characteristics, and a laser beam provided between the collimating lens and the electro-optical element, the laser beam emitted by the laser diode being passed therethrough. An isolator provided with a polarizing beam splitter that separates the reflected light reflected by the reflection film; and a photodiode that converts the reflected light separated by the isolator into an electric signal. The plane of the polarizing beam splitter opposite to the direction in which the diodes are arranged exits from this plane. An electro-optic probe, wherein an optical axis of light to be emitted is processed so as not to be parallel to an optical axis when light emitted from the polarizing beam splitter enters the photodiode. 7. The photodiode and the laser diode are connected to an electro-optic sampling oscilloscope, and the laser diode emits the laser light as pulse light based on a control signal from the electro-optic sampling oscilloscope. The electro-optic probe according to claim 6, wherein 8. The electro-optic 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 processing surface of the polarization beam splitter is a surface processed into a non-regular uneven surface. 10. The processing surface of the polarization beam splitter is a surface processed into a surface that is not perpendicular to an optical axis when light emitted from the polarization beam splitter enters the photodiode. An electro-optic probe according to any one of claims 6 to 8.