Testing device for multistage multi-branch optical network

Details Testing device for multistage multi-branch optical network Testing device for multistage multi-branch optical network

1998-06-18

2001-10-30

Chan, Jason (Department: 2633)

Optical: systems and elements

Deflection using a moving element

Using a periodically moving element

C359S199200, C359S199200, C359S199200, C359S199200, C359S199200, C359S199200, C356S073000

Reexamination Certificate

active

06310702

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to testing devices that perform testing on multistage multi-branch optical networks with respect to fault time, fault line and fault distance. This application is based on patent application No. Hei 9-161396 filed in Japan, the content of which is incorporated herein by reference.
2. Description of the Related Art
FIG. 7
shows an example of a testing device for a multi-branch optical network. This testing device performs fault isolation test on an optical network of 8-branch type provided in 1.31/1.55 &mgr;m wavelength multiplex transmission system. In
FIG. 7
, an OTDR measurement device
1
(where “OTDR” is an abbreviation for “Optical Time Domain Reflectometer”) generates test light (having 1.6 &mgr;m band), which is incoming to an optical line
3
via a coupler
2
. Then, the test light is subjected to branching by a star coupler
4
, from which test beams are distributed to “branch” optical fibers whose numbers range from No. 1 to No. 8. Herein, filters
41
to
48
are respectively provided on the optical fibers No. 1 to No. 8 prior to their ONUs (where “ONU” is an abbreviation for “Optical Network Unit”, which is an optical subscriber network unit). Each of the filters
41
to
48
has a specific band-pass characteristic that passes only a light signal corresponding to each of the ONUs while reflecting the test beam. Therefore, each of the test beams that progress through the optical fibers No. 1 to No. 8 respectively is reflected by each of the filters
41
to
48
. Thus, a reflection beam given from each filter is transmitted backwardly on each optical fiber. Reflection beams, transmitted backwardly on the optical fibers No. 1 to No. 8, are subjected to wave mixing by the star coupler
4
. As a result, mixed light is transmitted via the coupler
2
to the OTDR measurement device
1
as response light. So, the OTDR measurement device
1
performs analysis of the response light.
FIG. 8
shows an example of a waveform of the response light, which is supplied to the OTDR measurement device
1
. This waveform corresponds to a time-series record of the waveform of the response light, which is supplied to the OTDR measurement device
1
via the coupler
2
. In
FIG. 8
, a horizontal axis is given by multiplying a time axis by a transmission speed of the response light. That is, the horizontal axis of
FIG. 8
represents a length of the optical fiber through which the response light propagates. So, the waveform of the response light is plotted in accordance with such a horizontal axis. By the way, the reponse light corresponds to a result of wave mixing of the reflection beams reflected by the filters
41
to
48
respectively. These filters are located at different positions on the optical fibers, in other words, these filters are located with different distances from the OTDR measurement device
1
. For this reason, the reflection beams from the filters
41
to
48
, which are measured by the OTDR measurement device
1
, are not overlapped with each other on the time axis. So, they are measured as separate ones. A leftmost wave portion “R” of the waveform shown in
FIG. 8
represents a reflection beam given from the star coupler
4
. In
FIG. 8
, eight wave portions, which follow the leftmost wave portion R, are arranged from the left to the right. The eight wave portions correspond to eight reflection beams, which are transmitted backwardly on the optical fibers No. 1 to No. 8 respectively and are supplied to the OTDR measurement device
1
.
FIG.
9
A and
FIG. 9B
each show a set of three wave portions corresponding to reflection beams of the optical fibers No. 6 to No. 8, which are extracted from reflection beams measured by the OTDR measurement device
1
. Herein, the three wave portions are magnified in scale.
FIG. 9A
shows an example of the three wave portions with respect to the case where fault occurs on none of the optical fibers, while
FIG. 9B
shows another example of the three wave portions with respect to the fault-simulated case where a bending loss of 3 dB is intentionally imparted to the optical fiber No. 7. It can be observed from FIG.
9
A and
FIG. 9B
that intensity of the reflection beam is lowered due to occurrence of the simulated fault.
Thus, the testing device of
FIG. 7
is capable of performing fault detection with respect to fault that occurs on the optical fiber by analyzing the intensity of each of the reflection beams included in the response light supplied to the OTDR measurement device
1
. Incidentally, such a technology is disclosed by the paper B-846 entitled “1.6 &mgr;m-band Fault Isolation Technique for Passive Double Star Networks”, which is issued in 1994 autumn meeting of the Institute of Electronics, Information and Communication Engineers of Japan, for example.
The fault isolation test system of the multi-branch optical network, which is described above, is capable of performing fault detection only by specifying an optical line having a fault. However, this system is incapable of detecting a distance for a fault point, in other words, this system is incapable of detecting a location of a fault point. In addition, the aforementioned system provides requirement that different distances should be set from the coupler
2
to the filters
41
to
48
respectively. To achieve such a requirement, it is necessary to elongate the length(s) of the optical fiber(s) to some extent. As a result, the aforementioned system may introduce an increase of the cost for constructing the transmission system corresponding to the optical fibers. So, it is difficult to put the aforementioned system to practical use.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a testing device which is capable of detecting a fault line and a fault distance as well as a fault time with respect to a multistage multi-branch optical network.
A testing device of this invention performs testing on a multistage multi-branch optical network, which contains optical lines (such as optical fibers) that are connected together at connection points (e.g., optical couplers) in a multistage multi-branch manner. An OTDR measurement device uses software to perform fault determination with respect to the multistage multi-branch optical network. Herein, optical pulses are input to an input end of the multistage multi-branch optical network, wherein they are reflected at certain portions of the optical lines and the connection points while propagating through the optical lines. Then, reflected beams are returned to the input end and are mixed together as response light, which is measured by the OTDR measurement device. The response light is converted to a plurality of digital waveform data representing a measured waveform, which is then divided into multiple ranges on the basis of the Fresnel reflection points and connection points. Separative analysis is performed on the digital waveform data belonging to each of the ranges of the measured waveform. The separative analysis is repeated at measuring times, which are determined in advance. So, the fault determination is made by comparing results of the separative analysis, which are obtained at the measuring times respectively. By the fault determination, it is possible to determine a fault line and a fault location (or fault distance) as well as a fault time.
For example, the fault determination is made by detecting a positional shift of a spike wave on the measured waveform.


REFERENCES:
patent: 5383015 (1995-01-01), Grimes
patent: 5396569 (1995-03-01), Yanagawa et al.
patent: 5491573 (1996-02-01), Shipley
patent: 5491574 (1996-02-01), Shipley
patent: 6028661 (2000-02-01), Minami et al.
patent: 197 01 908 A1 (1997-08-01), None
patent: 0447439 (1991-09-01), None
patent: WO 90/06498 (1990-06-01), None
Hettich, Armin, “RuckstreumeBgerat OMB”, ANT Nachrichtentechnische Berichte Heft, Dec. 3, 1986, pp. 273-278.
“Electronics Letters”, Apr. 12, 1984, vol. 20, No. 8, pp. 338-340.
F. Yamamoto et al., “1.6&mgr;m-band Fault Isolation Technique for

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