Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – Using radiant energy
Reexamination Certificate
1999-09-30
2002-02-19
Nguyen, Vinh P. (Department: 2858)
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
Using radiant energy
Reexamination Certificate
active
06348787
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 measured signal and an electrooptic crystal, inputs a beam into this electrooptic crystal, and measures the waveform of the measured light signal by the state of the polarization of the input light.
This application is based on Japanese Patent Application, No. Hei 10-294567 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 measured signal with an electrooptic crystal, input a laser beam into this electrooptic crystal, and observe the waveform of the measured signal by the state of the polarization of the laser beam. It is possible pulse the laser beam, and observe with an extremely high time resolution when sampling the measured 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 measured 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 the end terminal of the metallic probe body
2
, and a metallic pin
3
a
is fit into the center. Reference numeral
4
is an electrooptic element, a reflecting film
4
a
is provided on the end surface on the metallic pin
3
a
side, and is in contact with the metallic pin
3
a
. Reference numeral
5
is a ½ wavelength plate, and reference numeral
6
is a ¼ wavelength plate. Reference numeral
7
and
8
ate polarized beam splitters. Reference numeral
9
is a ½ wavelength plate, and reference numeral
10
is a Faraday element. Reference numeral
12
is a collimator lens, and reference numeral
13
is a laser diode. Reference numerals
14
and
15
are condensing lenses, and reference numerals
16
and
17
are photodiodes.
In addition, the two polarized beam splitters
7
and
8
, the ½ wavelength plate
9
, and the Faraday element
10
comprise an isolator
19
that transmits the light emitted by the laser diode
13
, in order to split 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 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 incident 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 incident 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 measured signal is explained. When the metallic pin
3
a
is placed in contact with the measurement point, due to the voltage applied to the metallic pin
3
a
, at the electrooptic element
4
this electrical field is propagated to the electrooptic element
4
, and the phenomenon of the altering of the refractive index due to the Pockels effect occurs. Thereby, the laser beam emitted from the laser diode
13
is incident on the electrooptic element
4
, and when the laser beam is propagated along the electrooptic element
4
, the polarization state of the beam changes. Additionally, the laser beam having this changed polarization state is reflected by the reflecting film
4
a
, condensed and incident 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 observe 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, but instead, it is possible to connect a conventional measuring device such as a real time oscilloscope at the photodiodes
16
and
17
via a dedicated controller. Thereby, 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 a metallic pin
3
a
must contact the measurement point, in this case, a shock is applied to the metallic pin
3
a
, and as a result, there is the concern that damage may occur to the electrooptic element
4
.
In addition, the electrooptic probe
1
described above has a structure wherein a laser beam is incident on the reflecting film
4
a
, with which the metallic pin
3
a
is in contact, and is then reflected, and thus when the position of the metallic pin
3
a
is moved, the position of the reflecting film
4
a
, etc., shifts, and there is the problem that its function as an optical system is lost.
SUMMARY OF THE INVENTION
In consideration of the above described problems, it is an object of the present invention to solve this problem by improving the shock resistance of the electrooptic probe by anchoring the position of the metallic pin with respect to the probe head.
In order to solve the above problem, the following means are used.
A first aspect of the present invention is an electrooptic probe wherein:
a light path between a base terminal and an end terminal of the probe body is formed within the probe body;
at the end of the light path on the base terminal side of the probe body, a laser diode is disposed;
at the other end of the light path on the end terminal side of the probe body, an electrooptic element is disposed;
at the end surface of the electrooptic element on the end terminal side of the probe body, a reflecting film is formed;
the laser beam emitted from the laser diode is incident on the electrooptic element via the optical path, this incident beam is reflected by the reflecting film, and furthermore, this reflected light is separated and converted into an electric signal; and wherein
the electrooptic element is supported at least from the end terminal side of the probe body by a probe head member that serves as the end terminal of the probe body;
an insertion hole from the outside to the r
Ito Akishige
Nagatsuma Tadao
Ohta Katsushi
Shinagawa Mitsuru
Yagi Toshiyuki
Ando Electric Co. Ltd.
Blakely & Sokoloff, Taylor & Zafman
Nguyen Vinh P.
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