Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – Using radiant energy
Reexamination Certificate
1999-10-08
2002-01-29
Metjahic, Safet (Department: 2858)
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
Using radiant energy
C324S754120, C324S754090
Reexamination Certificate
active
06342783
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a probe for an electrooptic sampling oscilloscope that couples an electrical field generated by a measurement signal and an electrooptic crystal, inputs a beam into this electrooptic crystal, and measures the waveform of the measurement signal by the state of the polarization of the input light.
This application is based on Japanese Patent Application, No. Hei 10-288547 filed in Japan, the content of which is incorporated herein by reference.
2. Description of the Related Art
It is possible to couple an electrical field generated by a measurement signal with an electrooptic crystal, input a laser beam into this electrooptic crystal, and observe the waveform of the measurement signal by the state of the polarization of the laser beam. It is possible to pulse the laser beam, and observe with an extremely high time resolution when sampling the measurement signal. The electrooptic sampling oscilloscope uses an electrooptic probe exploiting this phenomenon.
When this electrooptic sampling oscilloscope (hereinbelow, referred to as an “EOS oscilloscope”) is compared to a conventional sampling oscilloscope using an electrical probe, the following characteristics have received much attention:
1. It is easy to observe the signal because a ground wire is unnecessary.
2. Because the metal pin at the end of the electrooptic probe is not connected to the circuit system, it is possible to realize high input impedance, and as a result of this, there is almost no degradation of the state of the measurement point.
3. By using an optical pulse, broadband measurement up to the GHz order is possible.
The structure of a probe for an EOS oscilloscope in the conventional technology will be explained using FIG.
7
. In the electrooptic probe
1
shown in
FIG. 7
, a probe head
3
comprising an insulator is mounted on a tip end of a metallic probe body
2
, and a metallic pin
3
a
is fitted into the center. An electrooptic element
4
is secured to the probe head
3
. A reflecting film
4
a
is provided on an end surface of the electrooptic element
4
on the metallic pin
3
a
side, and is in contact with the metallic pin
3
a.
Reference numeral
5
denotes a ½ wavelength plate, and reference numeral
6
denotes a ¼ wavelength plate. Reference numeral
7
and
8
denote polarized beam splitters. Reference numeral
9
denotes a ½ wavelength plate, and reference numeral
10
denotes a Faraday element. Reference numeral
12
denotes a collimator lens, and reference numeral
13
denotes a laser diode. Reference numerals
14
and
15
denote condensing lenses, and reference numerals
16
and
17
denote photodiodes.
In addition, the two polarized beam splitters
7
and
8
, the ½ wavelength plate
9
, and the Faraday element
10
constitute an isolator
19
that transmits the light emitted by the laser diode
13
, in order to separate the light reflected by the reflecting film
4
a.
Next, referring to
FIG. 7
, the optical path of the laser beam emitted from the laser diode
13
is explained. In
FIG. 7
, reference letter ‘A’ denotes the optical path of the laser beam.
First, the laser beam emitted from the laser diode
13
is converted by the collimator lens
12
into a parallel beam that travels straight through the polarized beam splitter
8
, the Faraday element
10
, the ½ wavelength plate
9
, and the polarized light beam splitter
7
, and then transits the ¼ wavelength plate
6
and the ½ wavelength plate
5
, and is incident on the electrooptic element
4
. The incident light is reflected by the reflecting film
4
a
formed on the end surface of the electrooptic element
4
on the side facing the metallic pin
3
a.
The reflected laser beam then transits the ½ wavelength plate
5
and the ¼ wavelength plate
6
, one part of the laser beam is reflected by the polarized light beam splitter
7
, condensed by the condensing lens
14
, and impinges on the photodiode
16
. The laser beam that has transited the polarized light beam splitter
7
is reflected by the polarized beam splitter
8
, condensed by the condensing lens
15
, and impinges on the photodiode
17
.
Moreover, the angle of rotation of the ½ wavelength plate
5
and the ¼ wavelength plate
6
is adjusted so that the strength of the laser beam incident on the photodiode
16
and the photodiode
17
is uniform.
Next, using the electrooptic probe
1
shown in
FIG. 7
, the procedure for measuring the measurement signal is explained.
When the metallic pin
3
a
is placed in contact with a measurement point, at the electrooptic element
4
the electrical field due to the voltage applied to the metallic pin
3
a
is propagated to the electrooptic element
4
, and a phenomenon where the refractive index is altered due to the Pockels effect occurs. Due to this, the laser beam emitted from the laser diode
13
impinges on the electrooptic element
4
, and when the laser beam is propagated along the electrooptic element
4
, the polarization state of the beam changes. Then, the laser beam having this changed polarization state is reflected by the reflecting film
4
a,
condensed and impinged on the photodiode
16
and the photodiode
17
, and converted into an electrical signal.
Along with the change in the voltage at the measurement point, the change in the state of polarization by the electrooptic element
4
becomes the output difference between the photodiode
16
and the photodiode
17
, and by detecting this output difference, it is possible to measure the electrical signal applied to the metallic pin
3
a.
Moreover, in the above-described electrooptic probe
1
, the electrical signals obtained from the photodiodes
16
and
17
are input into an electrooptic sampling oscilloscope, and processed. However, instead, it is possible to measure the signals by connecting a conventional measuring device such as a real time oscilloscope to the photodiodes
16
and
17
via a dedicated controller. In this way, it is possible to carry out simply broadband measurement by using the electrooptic probe
1
.
In the manner described above, in the signal measurement using the electrooptic probe
1
, because the metallic pin
3
a
must contact the measurement point, the metallic pin
3
a
is worn by repeated measurement so that it is necessary to replace the probe head
3
. In this case, since the electrooptic element
4
which is fixed to the probe head
3
is expensive, cost is increased.
Furthermore, considering the fact that in general the type of most suitable metallic pin changes depending on the characteristics of the signal of the measurement object, then since with the abovementioned electrooptic probe
1
the metallic pin
3
a
is secured to the probe head
3
, in selecting the most suitable metallic pin
3
a
to match the characteristics of the signal to be measured, it is difficult to obtain a suitable match.
SUMMARY OF THE INVENTION
In consideration of the above described situation, it is an object of the present invention to provide an electrooptic probe which can facilitate replacement of the metallic pin.
In order to address the above problems, the present invention adopts the following means.
A first aspect of the present invention is an electrooptic probe wherein:
an optical path is formed within a probe body between a base end portion and a tip end portion of the probe body;
a laser diode is disposed at an end of the optical path on the base end portion side of the probe body;
an electrooptic element is disposed at an other end of the optical path on the tip end portion side of the probe body and retained in a probe head constituting the tip end portion of the probe body;
a metallic pin is provided in the probe head with a base end thereof connected to the electrooptic element, and a tip end thereof protruding from the probe head,
a laser beam emitted from the laser diode is incident on the electrooptic element via the optical path, and this incident beam is reflected by a re
Ito Akishige
Nagatsuma Tadao
Ohta Katsushi
Shinagawa Mitsuru
Yagi Toshiyuki
Ando Electric Co. Ltd.
Blakely & Sokoloff, Taylor & Zafman
Deb Anjan K
Metjahic Safet
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