Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – Using radiant energy
Reexamination Certificate
1999-11-23
2002-04-09
Metjahic, Safet (Department: 2858)
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
Using radiant energy
C324S750010, C356S369000, C355S067000
Reexamination Certificate
active
06369562
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to electro-optical probes used for oscilloscopes that use electro-optical crystals to measure waveforms of signals based on electro-optical effects, and particularly to electro-optical probes used for electro-optic sampling oscilloscopes.
This application is based on Patent Application No. Hei 10-333309 filed in Japan, the content of which is incorporated herein by reference.
2. Description of the Related Art
In general, the electro-optic sampling oscilloscopes operate as follows:
Electric fields being caused to occur due to measured signals are connected with electro-optical crystals, on which laser beams are incident. Using polarization states of the laser beams in the electro-optical crystals, it is possible to detect the measured signals. Herein, the laser beams are formed in a pulse-like form, so that it is possible to measure waveforms of the signals with a very high resolution with respect to time. The electrooptic sampling oscilloscopes use electro-optical probes, which work based on the known electro-optical phenomenon.
As compared with the conventional sampling oscilloscopes using probes of an electric type, the electro-optic sampling oscilloscopes (abbreviated by “EOS” oscilloscopes) draw considerable attention of scientists and engineers because of some advantages, as follows:
(1) It is easy to perform measurement on the waveforms of the signals because the EOS oscilloscopes do not require ground lines when measuring the signals.
(2) A metal pin provided at a tip end of the electro-optical probe is insulated from the circuitry, so it is possible to realize high input impedance. Therefore, it is possible to perform measurement without substantially disturbing states of measuring points.
(3) The EOS oscilloscope uses optical pulses for the measurement. So, it is possible to perform the measurement in a broad band, a frequency range of which is increased up to Giga-Hertz (GHz) order.
Now, a description will be given with respect to an example of the EOS oscilloscope with reference to FIG.
3
. Specifically,
FIG. 3
shows a probe unit
15
of the EOS oscilloscope, which is equipped with a probe head
1
made of an insulator. A metal pin
1
a
is installed at a center of the probe head
1
. An electro-optical element (i.e., electro-optical crystal)
2
is equipped with a reflector (or reflection mirror)
2
a
, which is formed at a terminal surface facing with an end of the metal pin
1
a
and is brought into contact with the metal pin
1
a
. The probe unit
15
contains collimator lenses
3
,
10
, half-wavelength (or ½ wavelength) plates
4
,
7
, a quarter-wavelength (or ¼ wavelength) plate
5
, polarizing beam splitters
6
,
9
, and a Faraday rotator
8
, which rotates a polarizing plane of incident light by 45 degrees. In addition, the probe unit
15
contains a laser diode
11
, which radiates laser beams in response to a control signal output from a main body of the EOS oscilloscope (not shown), as well as photodiodes
12
,
13
, which convert incoming laser beams to electric signals. Those electric signals are output to the main body of the EOS oscilloscope. Incidentally, the probe unit
15
contains an optical isolator
14
a
, which is configured by the half-wavelength plates
4
,
7
, quarter-wavelength plate
5
, beam splatters
6
,
9
and Faraday rotator
8
.
Next, an optical path of the laser beams radiated from the laser diode
11
will be described with reference to
FIG. 3
, wherein it is denoted by a reference symbol “C”.
The collimator lens
10
converts the laser beams output from the laser diode
11
to parallel beams, which propagate straight through the polarizing beam splitter
9
, Faraday rotator
8
, half-wavelength plate
7
and polarizing beam splitter
6
sequentially in a forward direction. They also pass through the quarter-wavelength plate
5
and half-wavelength plate
4
sequentially. Thereafter, the parallel beams are converged together by the collimator lens
3
and are then incident on the electro-optical element
2
as its incoming beams. The incoming beams of the electro-optical element
2
are reflected by the reflector
2
a
, which is formed at the terminal surface of the electro-optical element
2
facing with the metal pin
1
a.
Then, reflected beams are converted to parallel beams by the collimator lens
3
. The parallel beams propagate through the half-wavelength plate
4
and quarter-wavelength plate
5
in a backward direction. A part of the parallel beams is reflected by the polarizing beam splitter
6
and is incident on the photodiode
12
. In contrast, the parallel beams that transmit through the polarizing beam splitter
6
are reflected by the polarizing beam splitter
9
and are incident on the photodiode
13
.
The quarter-wavelength plate
4
is provided to make adjustment such that strength of incoming laser beams of the photodiode
12
coincides with strength of incoming laser beams of the photodiode
13
. In addition, the half-wavelength plate
4
is provided to adjust a polarizing plane of an incoming beam of the electro-optical element
2
.
Next, a description will be given with respect to a series of measuring operations to perform measurement on signals by using the aforementioned probe of the EOS oscilloscope shown in FIG.
3
.
When a human operator brings the metal pin
1
a
in contact with a measuring point (not shown), an electric voltage is applied to the metal pin
1
a
to form an electric field. Such an electric field spreads and is connected with the electro-optical element
2
. Due to Pockel's effect, there is caused to occur a phenomenon in which a birefringence index changes. The laser diode
11
radiates laser beams, which are incident on the electro-optical element
2
. Due to the aforementioned phenomenon, the incoming laser beams that propagate in the electro-optical element
2
change in polarization states. Then, the laser beams whose polarization states are changed are reflected by the reflector
2
a
and are incident on the photodiodes
12
,
13
respectively. The photodiodes
12
,
13
convert the incoming beams thereof to electric signals.
Accompanied with changes of the voltage applied to the metal pin
1
a
at the measuring point, changes occur with respect to the polarization states of the beams in the electro-optical element
2
. Those changes bring differences between outputs of the photodiodes
12
,
13
. By detecting such output differences, it is possible to measure an electric signal being applied to the metal pin
1
a.
Incidentally, the electric signals produced by the photodiodes
12
,
13
of the EOS probe are input to the EOS oscilloscope, in which they are processed. Instead of using the EOS oscilloscope, it is possible to use some conventional measurement devices such as the real-time oscilloscope. Herein, the measurement device is connected to the photodiodes
12
,
13
by way of a dedicated controller so as to perform measurement on signals. That is, the EOS probe can be widely used for the measurement devices to enable broad-band measurement on the signals with ease.
The aforementioned EOS oscilloscope is designed to separate the incoming beams of the electro-optical element
2
, which are brought by the optical isolator
14
a
, from the reflected beams which are reflected by the reflector
2
a
. Such a design causes a problem in which a number of optical parts constructing the optical isolator
14
a
is increased.
Due to an increased number of optical parts, “unnecessary” reflected beams are produced by some optical parts. This causes another problem in which an amount of noise component is increased while a S/N ratio in signal processing is reduced. In addition, there is a still another problem in which the incoming beams of the two photodiodes
12
,
13
need to be adjusted in intensities by rotation of the optical parts.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an electro-optical probe used for an electro-optic sampling oscilloscope, which i
Ito Akishige
Nagatsuma Tadao
Ohta Katsushi
Shinagawa Mitsuru
Yagi Toshiyuki
Ando Electric Co. Ltd.
Blakely & Sokoloff, Taylor & Zafman
Metjahic Safet
Nguyen Vincent Q.
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