JP3593477B2 - Electro-optic probe - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention is an electro-optic probe that couples an electric field generated by a signal under measurement to an electro-optic crystal, makes light incident on the electro-optic crystal, and observes the waveform of the signal under measurement according to the polarization state of the incident light. In particular, the present invention relates to an electro-optic probe having an improved optical system.
[0002]
[Prior art]
An electric field generated by the signal under measurement is coupled to the 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, when the laser light is pulsed and the signal under measurement is sampled, measurement can be performed with a very high time resolution. An electro-optic sampling oscilloscope uses an electro-optic probe utilizing this phenomenon.
[0003]
This electro-optic sampling oscilloscope (hereinafter, abbreviated as “EOS oscilloscope”) is compared with a conventional sampling oscilloscope using an electric probe.
1) Since a ground wire is not required when measuring a signal, the measurement is 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. Attention has been paid to the fact that the use of optical pulses makes it possible to perform broadband measurement up to the order of GHz, which hardly disturbs the state of the measurement point.
[0004]
The configuration of a conventional electro-optic probe used when measuring signals with an EOS oscilloscope will be described with reference to FIG. In FIG. 5, reference numeral 1 denotes a probe head made of an insulator, and a metal pin 1a is fitted into the center of the probe head. Reference numeral 2 denotes an electro-optical element, and a reflective 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 8 are collimating lenses. Reference numeral 4 denotes a 波長 wavelength plate. Reference numerals 5 and 7 are polarization beam splitters. Reference numeral 6 denotes a Faraday element that rotates the plane of polarization of incident light by 45 degrees. Reference numeral 9 denotes a laser diode that emits laser light in accordance with a control signal output from a pulse generation circuit (not shown) of the EOS oscilloscope main body 19. Reference numerals 10 and 11 are collimating lenses. Reference numerals 12 and 13 denote photodiodes, which convert the input laser light into an electric signal and output it to the EOS oscilloscope main body. Reference numeral 14 denotes an isolator including the 波長 wavelength plate 4, the polarization beam splitters 5 and 7, and the Faraday element 6. Reference numeral 15 denotes a probe main body made of an insulator.
[0005]
Next, an optical path of the laser light emitted from the laser diode 9 will be described with reference to FIG. In FIG. 5, the optical path of the laser light is represented by the symbol A.
First, the laser light emitted from the laser diode 9 is converted into parallel light by the collimating lens 8, travels straight through the polarizing beam splitter 7, the Faraday element 6, and the polarizing beam splitter 5, and further passes through the 波長 wavelength plate 4. The light is condensed by the collimator lens 3 and enters the electro-optical element 2. The incident light is reflected by the reflection 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 converted into parallel light again by the collimating lens 3, passes through the 波長 wavelength plate 4, and a part of the laser light is reflected by the polarization beam splitter 5 and enters the photodiode 12. The laser light transmitted through the polarization beam splitter 5 is reflected by the polarization beam splitter 7 and enters the photodiode 13.
The quarter-wave plate 4 adjusts the intensity of the laser light incident on the photodiode 10 and the intensity of the laser light incident on the photodiode 11.
[0007]
Next, the operation of measuring the signal under measurement using the electro-optic probe shown in FIG. 5 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 9 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 12 and 13, and is converted into an electric signal.
[0008]
With the change in the voltage at the measurement point, the change in the polarization state by the electro-optical element 2 becomes the output difference between the photodiode 12 and the photodiode 13. By detecting this output difference, the electric signal applied to the metal pin 1a is converted. Can be measured. In the electro-optic probe described above, the electric signals obtained from the photodiodes 12 and 13 are input to the EOS oscilloscope and processed, but instead, the photodiodes 12 and 13 are sent to the EOS oscilloscope via a dedicated controller. By connecting a conventional measuring instrument such as a real-time oscilloscope, the signal can be measured. Thus, wideband measurement can be easily performed using the electro-optic probe.
[0009]
[Problems to be solved by the invention]
However, in the conventional electro-optical probe, the optical axes of the photodiodes 12 and 13 that receive the laser light reflected by the reflection film 2 a provided on the electro-optical element 2 are the laser light emitted by the laser diode 9. Therefore, the terminals of the photodiodes 12 and 13 must be arranged in the diametrical direction of the probe main body 15. Further, since a cable must be connected to these terminals and wired, it is necessary to provide a space in the diameter direction of the probe main body 15, resulting in a problem that the diameter of the probe main body 15 increases. Since this probe measures a signal by holding it in hand and making contact with wiring such as a printed circuit board, operability is deteriorated if the diameter of the probe body 15 is large.
[0010]
The present invention has been made in view of such circumstances, and an object of the present invention is to provide an electro-optic probe capable of reducing the diameter of an electro-optic probe main body.
[0011]
[Means for Solving the Problems]
The first aspect of the present invention provides a laser diode that emits a laser beam based on a control signal of an oscilloscope body, a first lens that converts the laser beam into parallel light, and a second lens that collects the parallel light. An electro-optical element having a reflection film on an end face; and a laser light emitted from the laser diode, provided between the first lens and the second lens, and the laser light is reflected by the reflection film. an isolator for separating the reflected light, in the first, the electro-optic probe comprising a second photodiode, the converting the reflected light separated in the isolator into electric signals, the first, second photodiode the direction of travel of incident light to the optical axis direction of the laser diode to the isolator, first, second beam to separate the reflected light, respectively A splitter, a first reflector that reflects the reflected light separated by the first beam splitter, folds in the optical axis direction of the laser diode, and enters the first photodiode, and the second beam A second reflecting section that reflects the reflected light separated by the splitter, folds the reflected light in the optical axis direction of the laser diode, and enters the second photodiode, and the first photodiode and the first photodiode. The beam splitter and the first reflecting portion of the laser diode and the second photodiode, the second beam splitter and the second reflecting portion are shifted from each other by a predetermined angle around the optical axis of the laser diode. It is characterized by being arranged .
[0012]
In the invention according to claim 2, the photodiode and the laser diode are connected to an electro-optic sampling oscilloscope, and the laser diode converts the laser light into pulse light based on a control signal from the electro-optic sampling oscilloscope. It is characterized by emitting.
The invention according to claim 3 is characterized in that the laser diode emits continuous light as the laser light.
[0013]
According to a fourth aspect of the present invention, in the electro-optic probe, the laser diode and the photodiode are provided in an oscilloscope main body, and laser light emitted from the laser diode propagates to the probe by a first optical fiber. Further, the reflected light separated by the isolator is propagated to the photodiode by a second optical fiber.
The invention described in claim 5 is characterized in that the isolator includes a parallelogram beam splitter, and the beam splitter makes the optical axes of the laser light and the reflected light parallel.
[0014]
In the invention according to claim 6, the isolator includes a cube-shaped beam splitter and a plane mirror, and the reflected light separated by the beam splitter is parallelized by the plane mirror so that the optical axes of the laser light and the reflected light are parallel to each other. It is characterized by the following.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
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. 5 are denoted by the same reference numerals, and description thereof will be omitted. The difference between the probe shown in this figure and the prior art is that the optical axis of the laser light incident on the photodiode (first photodiode) 12 and the photodiode (second photodiode) 13 is emitted by the laser diode 9. A point where the collimating lenses 10 and 11 and the photodiodes 12 and 13 are arranged so as to be parallel to the optical axis of the laser light, a parallelogram-shaped polarizing beam splitter (first beam splitter) 5a, and a polarizing beam splitter (second beam splitter). The beam splitter 7a is provided. Each of the beam splitters 5a and 7a is a beam splitter formed by combining two cube-shaped beam splitters, and can turn the separated light further by 90 degrees.
[0016]
FIG. 2 is a diagram showing a positional relationship among the polarization beam splitters 5a and 7a, the photodiodes 12 and 13, and the laser diode 9. This figure is a view of the electro-optic probe shown in FIG. As shown in FIG. 2, the polarization beam splitters 5a and 7a are arranged in a state of being shifted by 45 degrees (a predetermined angle) about the optical axis of the laser diode 9. Therefore, the photodiodes 12 and 13 are also arranged in such a manner that they are shifted by 45 degrees (predetermined angle) . Thus, the reflected lights separated by the polarization beam splitters 5a and 7a can be made incident on different photodiodes.
[0017]
Next, the optical path of the laser light emitted from the laser diode 9 will be described with reference to FIG. In FIG. 1, the optical path of the laser light is represented by reference symbol B.
First, the laser light emitted from the laser diode 9 is converted into parallel light by the collimator lens 8, travels straight through the polarization beam splitter 7 a, the Faraday element 6, and the polarization beam splitter 5 a, and further passes through the 波長 wavelength plate 4.
[0018]
Next, the parallel light transmitted through the 波長 wavelength plate 4 is condensed by the collimator lens 3 and enters the electro-optical element 2, and the reflection film 2 a formed on the end face of the electro-optical element 2 on the metal pin 1 a side Is reflected by At this time, since the collimating lens 3 is arranged at a position separated from the reflecting film 2a by the focal length from the reflecting film 2a, the laser light converted into parallel light by the collimating lens 10 Focused on a point.
[0019]
The laser light reflected by the reflection film 2a is again converted into parallel light by the collimating lens 3, passes through the quarter-wave plate 4, is reflected by the reflection surface 5b of the polarizing beam splitter 5a, and further reflected by the reflection surface ( The light is turned back by 90 degrees by the first reflecting portion 5 c, condensed by the collimating lens 10, and enters the photodiode 12. The laser beam transmitted through the polarizing beam splitter 5a is reflected by the reflecting surface 7b of the polarizing beam splitter 7a, further turned back by 90 ° by the reflecting surface (second reflecting portion) 7c, and condensed by the collimating lens 11. Then, the light enters the photodiode 13. The laser light incident on the two photodiodes 12 and 13 is converted into an electric signal, and the electric signal is sent to the EOS oscilloscope main body 19.
[0020]
As described above, since the photodiodes 12 and 13 are arranged on the same plane as the laser diode 9 and the direction in which the terminals of the photodiodes 12 and 13 protrude is defined as the length direction of the probe body 15, the diametrical direction of the probe body 15 Since there is no need for a space for wiring or the like, the diameter of the probe main body 15 can be reduced.
The arrangement of the photodiodes 12 and 13 does not necessarily have to be on the same plane as the laser diode 9 and may be arranged on the probe body 15 in the length direction.
Also, the optical axes of the light emitted from the laser diode 9 and the light incident on the photodiodes 12 and 13 are not necessarily parallel, and the direction in which the light incident on the photodiodes 12 and 13 travels depends on the arrangement of the laser diode 9. Any direction may be used.
[0021]
The polarization beam splitters 5a and 7a shown in FIG. 1 are replaced with a cube-shaped beam splitter (first beam splitter) 5, a beam splitter (second beam splitter) 7, and a plane mirror (first beam splitter) 7 as shown in FIG. May be constituted by a reflecting portion) 51 and a plane mirror (second reflecting portion) 71 . By using a plane mirror in this way, the cost of the optical components used can be reduced.
[0022]
Next, another embodiment will be described with reference to FIG.
The embodiment shown in FIG. 4 is different from the embodiment shown in FIG. 1 in that the laser diode 9 and the photodiodes 12 and 13 are arranged in the EOS oscilloscope main body 19 and the probe main body 15 and the EOS oscilloscope main body are connected by the optical fiber cable 18. 19 is connected.
[0023]
Next, an optical path of the embodiment shown in FIG. 4 will be described.
First, the laser light emitted from the laser diode 9 in the EOS oscilloscope main body 19 enters from the end 18a of the optical fiber cable. The laser light propagates through the optical fiber cable 18 and is emitted from the end 18b, and the emitted laser light is converted by the collimator lens 8 into parallel light.
The parallel light is reflected by the reflection film 2a, separated by the isolator 14, and further condensed by the collimating lenses 10 and 11, as in the optical path in FIG.
The collected reflected light enters the end 18c of the optical fiber cable 18, propagates through the optical fiber cable 18, exits from the end 18d, and is received by the photodiodes 12, 13.
[0024]
As described above, the laser diode 9 and the photodiodes 12 and 13 are arranged in the EOS oscilloscope, and only the ends 18b and 18c of the optical fiber cable are arranged in the probe main body 15. It is not necessary to provide a space for disposing the laser diode 9 and the photodiodes 12 and 13.
Further, since there is no need to wire electric signals inside the probe body 15, it is not necessary to provide an electrical shield to the probe body 15.
In the above embodiment, if continuous light is emitted from the laser diode 9, 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 12 and 13 via a dedicated controller instead of the EOS oscilloscope.
[0025]
【The invention's effect】
As described above, according to the first aspect of the present invention, the light separated by the polarization beam splitter is turned 90 degrees, and the optical axis of the light emitted from the laser diode and the optical axis of the light incident on the photodiode are parallel. By doing so, the photodiode can be arranged on the same plane as the laser diode, so that it is possible to save the space for disposing the photodiode in the diameter direction of the probe main body. Therefore, the diameter of the probe main body can be reduced.
[0026]
According to the fourth aspect of the present invention, there is no need to provide a space for arranging the laser diode and the photodiode, and furthermore, it is not necessary to provide an electrical shield on the probe main body since the inside of the probe can be made a signal by light. The effect is obtained.
[0027]
According to the fifth aspect of the present invention, the polarization beam splitter for separating the laser light emitted from the laser diode is a parallelogram beam splitter, and the reflection surface that folds the separated light by 90 degrees is integrated with the beam splitter. Thus, there is no need to newly perform optical axis alignment.
[0028]
According to the sixth aspect of the present invention, since the beam splitter for separating the laser light emitted from the laser diode is constituted by the cube-shaped beam splitter and the plane mirror, the optical components constituting the isolator can be constituted by inexpensive optical components. Is obtained.
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing a configuration of an embodiment of the present invention.
FIG. 2 is an explanatory diagram showing an arrangement of beam splitters 5a and 7a in the embodiment shown in FIG.
FIG. 3 is a configuration diagram illustrating a configuration of an embodiment in which the polarization beam splitters 5a and 7a illustrated in FIG. 1 are configured by the polarization beam splitters 5 and 7 and the plane mirrors 51 and 71.
FIG. 4 is a configuration diagram showing a configuration of another embodiment of the present invention.
FIG. 5 is a configuration diagram showing a configuration of an electro-optic probe according to the related art.
[Explanation of symbols]
1 ... probe head, 1a ... metal pin,
2 ... electro-optical element, 2a ... reflective film,
3, 8 ... collimating lens, 4 ... 1/4 wavelength plate, 5 ... beam splitter (first beam splitter), 7 ... beam splitter (second beam splitter),
5a: polarization beam splitter (first beam splitter), 7a: polarization beam splitter (second beam splitter), 5c: reflection surface (first reflection portion), 7c: reflection surface (2nd reflection part) , 6 ... Faraday element,
9 ... laser diode, 10, 11 ... collimating lens,
12: photodiode (first photodiode), 13: photodiode (second photodiode) , 14: isolator,
15: Probe body, 19: EOS oscilloscope body, 51: Plane mirror (first reflection part), 71: Plane mirror (second reflection part)

Claims (6)

A laser diode that emits laser light based on a control signal of the oscilloscope body,
A first lens that converts the laser light into parallel light;
A second lens for condensing the parallel light,
An electro-optical element having a reflective film on an end face,
An isolator that is provided between the first lens and the second lens and that passes laser light emitted by the laser diode and separates the laser light reflected by the reflection film;
First and second photodiodes for converting reflected light separated by the isolator into an electric signal;
An electro-optic probe comprising:
The direction in which the light incident on the first and second photodiodes travels is defined as the optical axis direction of the laser diode ,
A first beam splitter that separates the reflected light, and a first beam splitter that reflects the reflected light separated by the first beam splitter and folds the reflected light in an optical axis direction of the laser diode. And a second reflecting portion that reflects the reflected light separated by the second beam splitter, returns the reflected light in the optical axis direction of the laser diode, and enters the second photodiode. Having a reflection portion,
The first photodiode, the first beam splitter, and the first reflection unit, and the second photodiode, the second beam splitter, and the second reflection unit include light of the laser diode. An electro-optic probe, wherein the electro-optic probe is arranged so as to be shifted by a predetermined angle about an axis . The photodiode and the laser diode are connected to an electro-optic sampling oscilloscope,
The electro-optic probe according to claim 1, wherein 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 1, wherein the laser diode emits continuous light as the laser light. The electro-optic probe,
The laser diode and the photodiode are provided in the oscilloscope main body, laser light emitted from the laser diode is propagated to the probe by a first optical fiber, and reflected light separated by the isolator is converted to a second light. The electro-optic probe according to any one of claims 1 to 3, wherein the light propagates to the photodiode by an optical fiber. The isolator,
The electro-optic probe according to any one of claims 1 to 3, further comprising a parallelogram beam splitter, wherein the beam splitter makes an optical axis of the laser light and the reflected light parallel. . The isolator,
4. The apparatus according to claim 1, further comprising a cube-shaped beam splitter and a plane mirror, wherein the reflected light separated by the beam splitter is parallelized by the plane mirror so that the optical axes of the laser light and the reflected light are parallel to each other. The electro-optic probe according to any one of the above items.

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