Data processing: measuring – calibrating – or testing – Measurement system in a specific environment – Chemical analysis
Reexamination Certificate
1998-09-25
2001-07-10
Hilten, John S. (Department: 2854)
Data processing: measuring, calibrating, or testing
Measurement system in a specific environment
Chemical analysis
C356S073100
Reexamination Certificate
active
06259993
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an optical fiber characteristic evaluation system for evaluating the transmission characteristics of many optical fibers forming optical transmission lines in a communication system or the like, and a computer-readable recording medium on which a computer program used for the system is recorded.
Recently, optical fibers have been widely used as signal transmission lines in communication systems and the like in place of conventional metal lines.
To lay and manage such optical fibers, a test on an optical fiber transmission line and evaluation of the test result must be periodically performed.
Assume that one optical fiber includes a plurality of optical fibers connected in series.
Conventionally, optical fibers are tested by using an optical time-domain reflectometer (OTDR) like the one shown in FIG.
10
.
In this OTDR, an optical pulse from an optical pulse generator
10
is input to one end of one of optical fibers
2
1
to
2
n
of an optical multi-fiber cable
1
through a directional coupler
11
and an optical path switch
12
, and a photodetector
13
detects the intensity of light (backward scattered light or reflected light) returning to the one end side of the optical fiber. An A/D converter
14
then converts the photodetection signal output from the photodetector
13
into a data signal, and inputs it to a signal processor
15
. The signal processor
15
processes a series of data signals until a predetermined period of time elapses after the incident timing of the optical pulse, and stores the distance versus received light intensity characteristic data in a characteristic data memory
16
.
After the characteristic data of the optical fiber forming one transmission line are acquired, the optical path switch
12
is switched to connect another optical fiber to the directional coupler
11
, thus storing the characteristic data of the optical fibers
2
1
to
2
n
in the characteristic data memory
16
.
The transmission characteristics of each optical fiber are evaluated as follows. The characteristic data stored in the characteristic data memory
16
is selectively output to an image display unit or printer (not shown) to display a waveform on the coordinate plane defined by the distance axis and the received light intensity axis, as shown in FIG.
11
. Variations in attenuation value and the presence/absence of a disconnection or the like are checked from the slope of the displayed waveform, local level changes, and the like.
To detect the overall characteristics of the optical multi-fiber cable
1
as a bundle of optical fibers
2
1
to
2
n
or evaluate the characteristics of one optical fiber in contrast to the characteristics of the overall transmission line, instead of independently evaluating each of the optical fibers
2
1
to
2
n
all the characteristic data stored in the characteristic data memory
16
must be displayed on the same coordinate plane and evaluated.
In tests on optical fibers using the above OTDR, the characteristic data obtained from optical fibers having the same characteristics vary due to variations in the wavelength of an optical pulse and variations in connection loss in the optical path switch
12
.
If, therefore, the waveforms of the characteristic data obtained by this OTDR are displayed on the same coordinate plane, the displayed waveforms greatly shift from each other in the vertical direction than the variations of the characteristic data, even though the optical fibers have almost the same characteristics. For this reason, it is very difficult to detect the overall characteristics of the cable and evaluate the characteristics of one optical fiber in contrast to the characteristics of the overall transmission line.
Generally, one transmission line is made by connecting a plurality of optical fibers each having a length of several km.
In this case, amounts of connection losses between fibers greatly vary due to variations in connection points and transmission lines.
Since the variations in connection losses are accumulated in the transmission line having a plurality of connection points, if using optical fibers having the same characteristics, the characteristics of the overall transmission line differ from every transmission lines.
In evaluating a characteristic of a certain connection point in a certain transmission line in the overall transmission line, the characteristic data of the near portion of the certain connection point greatly varies due to accumulating variations in the connection loss and accumulated variations in connection loss in the optical path switch
12
.
For this reason it is very difficult to evaluate the characteristic of the certain connection point only.
In recent years, with an increase in the number of optical fibers of the optical fiber cable
1
, the OTDR can acquire the characteristics of several ten to several thousand optical fibers. This makes it more difficult to perform evaluation.
BRIEF SUMMARY OF THE INVENTION
It is an object of the present invention to provide an optical fiber characteristic evaluation apparatus which can easily detect the overall characteristics of a cable and evaluate the characteristics of one optical fiber in contrast to characteristics of the overall transmission line by solving the above problems in the prior art.
It is another object of the present invention to provide an optical fiber characteristic evaluation method which can easily detect the overall characteristics of a cable and evaluate the characteristics of one optical fiber in contrast to characteristics of the overall transmission line by solving the above problems in the prior art.
It is still another object of the present invention to provide a computer-readable recording medium on which a computer program is recorded, which is used for an optical fiber characteristic evaluation system which can easily detect the overall characteristics of a cable and evaluate the characteristics of one optical fiber in contrast to characteristics of the overall transmission line by solving the above problems in the prior art.
In order to achieve the above objects, according to an aspect of the present invention, there is provided an optical fiber characteristic evaluation apparatus comprising:
characteristic data storage means for storing a plurality of characteristic data each indicating a change in distance versus characteristic value of an optical fiber, which is obtained by inputting an optical pulse to one end of the optical fiber and detecting an intensity of light returning to the one end as a characteristic value, the characteristic data storage means storing a plurality of characteristic data obtained by measuring one optical fiber a plurality of number of times at time intervals or a plurality of characteristic data obtained by measuring a plurality of optical fibers;
an output unit for displaying waveforms of the plurality of characteristic data;
waveform display control means for causing the output unit to display the waveforms of the plurality of characteristic data on an orthogonal coordinate plane defined by a distance axis and a characteristic value axis;
reference point designation means for designating an arbitrary reference point in the orthogonal coordinate plane;
calculation means for calculating a difference between a characteristic value axis coordinate value of the reference point designated by the reference point designation means and a characteristic value axis coordinate value of each of the characteristic data at a distance axis coordinate value substantially equal to a distance axis coordinate value of the reference point; and
offset means for offsetting the characteristic data in a characteristic value axis direction by amounts corresponding to the differences calculated by the calculation means to make waveforms of the characteristic data displayed by the waveform display control means pass through the reference point.
According to another aspect of the present invention, there is provided an optical fiber characteristic evaluation
Anritsu Corporation
Frishauf, Holtz Goodman, Langer & Chick, P.C.
Hilten John S.
Tran Mylinh T
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