U.S. patent application number 10/058781 was filed with the patent office on 2003-02-06 for optical switching apparatus with optical reflection monitor and reflection monitoring system.
Invention is credited to Fukashiro, Yasuyuki, Kakizaki, Sunao, Kitajima, Sigeki, Tushima, Hideaki.
Application Number | 20030026524 10/058781 |
Document ID | / |
Family ID | 19068867 |
Filed Date | 2003-02-06 |
United States Patent
Application |
20030026524 |
Kind Code |
A1 |
Kakizaki, Sunao ; et
al. |
February 6, 2003 |
Optical switching apparatus with optical reflection monitor and
reflection monitoring system
Abstract
Practical utilization of an optical signal processor configured
by combining a plurality of optical components requires
configurations and methods by which reflected light arising in the
processor during assembly, installation, or operation thereof can
be detected reliably and immediately to enable switching of optical
signal paths and recovery actions (maintenance) such as replacement
and repair of components, thereby improving the reliability,
availability, and service ability of the processor. The present
invention provides an optical switching system configured as a
combination of optical components, including multistage-connected
optical switching devices each having a plurality of optical
reflection monitoring functions. These functions enable reliable
and immediate detection and notification of reflected light arising
in the optical switching system. The invention also provides a
method of monitoring and reporting reflection.
Inventors: |
Kakizaki, Sunao; (Kawasaki,
JP) ; Tushima, Hideaki; (Tokyo, JP) ;
Kitajima, Sigeki; (Kawasaki, JP) ; Fukashiro,
Yasuyuki; (Yokohama, JP) |
Correspondence
Address: |
ANTONELLI TERRY STOUT AND KRAUS
SUITE 1800
1300 NORTH SEVENTEENTH STREET
ARLINGTON
VA
22209
|
Family ID: |
19068867 |
Appl. No.: |
10/058781 |
Filed: |
January 30, 2002 |
Current U.S.
Class: |
385/16 ;
385/18 |
Current CPC
Class: |
H04Q 2011/0049 20130101;
G02B 6/3588 20130101; H04Q 2011/0083 20130101; H04Q 11/0005
20130101; H04Q 2011/0045 20130101; H04Q 2011/0039 20130101; G02B
6/3512 20130101; H04Q 2011/0035 20130101; G02B 6/4222 20130101;
G02B 6/356 20130101; G02B 6/3586 20130101 |
Class at
Publication: |
385/16 ;
385/18 |
International
Class: |
G02B 006/35 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 6, 2001 |
JP |
2001-237856 |
Claims
What is claimed is:
1. An optical switching device having a plurality of optical input
ports and a plurality of optical output ports, comprising: a
plurality of optical reflection monitors for monitoring optical
reflection, disposed between the plurality of input ports and the
plurality of output ports.
2. The optical switching device according to claim 1, wherein the
optical reflection monitors detect reflected light on a path
transmitting an optical signal input to the optical switching
device, and locate positions of reflection on the paths.
3. An optical switching system configured by multistage-connecting
a plurality of optical switching devices, wherein the optical
switching device comprises a plurality of optical reflection
monitors with an optical reflection monitoring function, the
optical reflection monitors detecting reflected light on a path
transmitting an optical signal input to the optical switching
device, and locating positions of reflection on the path.
4. The optical switching system according to claim 3, wherein each
of the optical reflection monitors comprises an optical branching
circuit that separates the optical signal or the reflected light,
and an optical detector that monitors the optical signals or the
reflected light.
5. The optical switching system according to claim 3, wherein the
optical reflection monitors comprise an optical isolator that
passes only the optical signal and blocks the reflected light; an
optical branching circuit that separates the reflected light of the
optical signal; and an optical detector that monitors the reflected
light.
6. The optical switching system according to claim 3, wherein the
optical reflection monitors comprise an optical circulator that
allows the passage of the optical signal and circulates or blocks
the reflected light of the optical signal, and an optical detector
that monitors the reflected light.
7. A reflected light measuring system, comprising a terminal
provided with optical reflection measuring software; an optical
switching system with an optical switching unit that controls
switching of optical signals; a reflected light meter that measures
reflected light of the optical signals; and a port selector that
selects an optical signal input path to the optical switching unit;
wherein the terminal is operable by executing the software, to
control the operation of the reflected light meter, the port
selector, and the optical switching unit, to measure the reflected
light of the optical signals, and locate the reflecting
positions.
8. The reflected light measuring system according to claim 7,
wherein the terminal is a portable personal computer; the reflected
light meter includes a control and monitoring unit that monitors
the reflected light, a light source including a laser diode, and an
optical detector that detects the reflected light; the port
selector includes a selector that selects ports for optical signals
and a control unit that controls the selectors; and the optical
switching system includes a system control and monitoring unit and
optical switching units.
9. The reflected light measuring system according to claim 8,
wherein the system control and monitoring unit includes a switching
information memory unit that stores information about switched
paths of the optical switching unit, and an optical reflection
alarm information memory unit that stores reflected light alarm and
other types of information transferred from the reflected light
meter.
10. The reflected light measuring system according to claim 8,
wherein the software is storable not only in the terminal but also
in the control and monitoring unit in the reflected light meter
and/or in the system control and monitoring unit in the optical
switching system.
11. An optical switching method enabling detection of reflected
light, the method comprising the steps of: making a setting for
switching an optical switch and storing optical interconnection
relationships; making a selection of a circuit board on which
optical switching devices are mounted according to a command from
an operation control unit and storing an optical reflection alarm
information; and locating positions of reflection according to the
optical interconnection relationships and the optical reflection
alarm information being stored.
12. The optical switching method according to claim 11, wherein the
step of storing the optical interconnection relationships includes
steps of transmitting a switching command to multistage-connected
optical switching devices according to a command from an operation
control unit; after completing the necessary settings for switching
of the optical switching devices, updating the contents of the
optical interconnection relationships being stored based on
switching information transferred from the optical switching
device.
13. The optical switching method according to claim 11, wherein the
step of storing the optical reflection alarm information includes
steps of transferring the optical reflection alarm information from
the optical switching device to the operation control unit after
transmitting an optical reflection alarm acquisition request to the
optical switching device mounted on the selected circuit board by
the CPU; and updating the contents of the optical reflection alarm
information being stored based on the optical reflection alarm
information by the CPU.
14. The optical switching method according to claim 11, wherein the
step of locating the positions of reflection includes steps of
detecting an alarm position according to the optical reflection
alarm information that has been stored, when optical reflection
alarm information is present; searching the optical interconnection
relationships being stored; selecting a suspected abnormal optical
interconnection path; and after determining a rearmost connection
among interconnected points at which reflected light occurs,
notifying the operation control unit of the rearmost
connection.
15. A method of setting switching information and optical
reflection alarm information in the optical switching device, the
method comprising the steps of: performing a settings for switching
of optical switches and setting a switching information register by
a switching control unit in an optical switching device; and after
selecting an optical reflection monitor circuit by the CPU,
performing A/D conversion of a monitored signal from the optical
reflection monitor circuit, transferring the converted monitored
signal to a monitoring and control unit, and setting an optical
reflection monitoring register therein.
16. The method according to claim 15, wherein the step of
performing a setting includes a step of setting the optical switch
switching information into the switching information register.
17. The method according to claim 15, wherein the step of setting
an optical reflection monitoring register further includes the step
of setting the optical reflection monitoring register so that a
comparison is made between the A/D converted monitored signal value
and a threshold stored in the monitoring and control unit for use
in processing; writing a "1" into a memory in the monitoring and
control unit is made to indicate an abnormal condition when the
monitored signal value is smaller than the threshold; and writing a
"0" into the memory is made to indicate a normal condition when the
monitored signal value is larger than the threshold.
18. A method of measuring an optical reflection position in an
optical switching unit by using an optical reflecting measuring
system, comprising the steps of: transmitting a switching command
to a port selector under control of a portable terminal;
transmitting the switching command to the optical switching unit
under control of the portable terminal; requesting acquisition of a
reflected light measurement value by a reflected light meter; and
searching an optical reflection alarm control table and an
interconnection control table and locating an abnormal alarm
position.
19. The method according to claim 18, wherein the step of
requesting acquisition of the reflected light measurement value
further includes steps of comparing the reflected light measurement
value transferred from the reflected light meter with a threshold
stored in an optical reflection alarm information memory in a
control and monitoring unit; and updating the optical reflection
alarm information memory by writing a "1" into a memory in the
monitoring and control unit to indicate an abnormal condition when
the reflected light measurement value is smaller than the threshold
and by writing a "0" into the memory to indicate normality when the
reflected light measurement value is larger than the threshold.
20. The method according to claim 18, wherein the step of locating
an abnormal alarm position includes the steps of searching the
optical reflection alarm control table and detecting an alarm
position when information stored in the optical reflection alarm
information memory indicates an abnormal condition, further
includes the steps of searching the interconnection control table;
selecting an interconnection with a suspected abnormal optical
fiber; and determining a rearmost connection among interconnected
positions at which reflected light occurs.
21. An optical switching device comprising optical reflection
monitors each having a plurality of optical reflection functions
disposed between a plurality of optical input ports and a plurality
of optical output ports, for monitoring reflected light arising at
certain positions on optical transmission paths provided between
the plurality of optical input ports and the plurality of optical
output ports for the optical signal input via the optical input
port, thereby enabling immediate notification of abnormal
conditions in optical connection cables on the optical transmission
paths.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to the structure of an optical
switching system including an optical reflection measuring system.
More particularly, the invention relates to an optical switching
system that enables immediate detection and notification of
reflected light occurring on a plurality of optical signal
transmission paths, and an optical reflection measuring system for
measuring the reflected light.
BACKGROUND OF THE INVENTION
[0002] In order to keep up with rapid increases in data traffic as
typified by the Internet and in demands for multimedia
communications combining image, voice, and data, the speed and
capacity of transmission paths and communication nodes that form
networks are being improved, and optical communication systems
using optical fibers and optical signals are being brought into
use. In addition, as an alternative to conventional communication
equipment in which optical signals are processed through
optical-to-electrical conversion, optical signal processors such as
the optical cross-connect (referred to as an OXC below) and optical
add drop multiplexer (referred to as an OADM below), in which
switching operations such as transmission path switching and
circuit switching are carried out without such conversion, are
under consideration for practical use.
[0003] The OXCs and OADMs mentioned above are configured by
selectively using optical amplifiers, optical couplers, optical
isolators and other optical components as required and combining
(interconnecting) them with optical fibers and connectors. As can
typically be seen in optical switches and other optical devices, it
is difficult to increase their capacity as matters now stand, so
high-capacity optical switching systems are generally implemented
by combining a number of low-capacity optical components. A
higher-capacity optical switch, for example, can be implemented by
multistage-connecting low-capacity optical switches, such as
2.times.2 or 8.times.8 optical switches that are already in
commercial use.
[0004] As described above, an optical switching system is
implemented by interconnecting a number of optical components and
optical fibers with connectors and splices, so optical signals
passing through the system suffer degradation due to optical loss
in the components, and to various conditions at the connecting
points, such as dirt, axial deviation, and open connection ends,
which may give rise to the departure of part of an optical signal
from the proper course. In particular, reflection in the direction
opposite to the proper direction of propagation causes degradation
of the optical signal.
[0005] Some optical signal processors and optical components that
detect optical reflection have already been introduced. optical
switches such as the one disclosed in JP-A-358261/2000 have been
suggested, which comprises a reflected light detector at the input
terminal thereof and a reflector at the output terminal thereof,
and checks internal paths by confirming that an optical signal
input from the input terminal is reflected back to the input
terminal.
[0006] In optical signal processors configured by combining a
plurality of optical components such as optical amplifiers, optical
switches, optical couplers, and optical isolators as mentioned
above, light reflected at a connection point of another optical
component, resulting in multiply reflected light.
[0007] This multiply reflected light becomes a delayed version of
the intended optical signal, so it interferes with the intended
optical signal (causing degradation of the optical signal). Recent
studies by the present inventor(s) have resulted in the discovery
that degradation of optical signals caused by such multiply
reflected light has a major effect on the operation of optical
signal processors configured by combining a plurality of optical
components.
[0008] More specifically, it was discovered that, in the optical
switching system 300 in FIG. 2, when an optical (digital) signal
370 transmitted through optical fibers 310-1 to 310-N proceeds from
an input port 330-N to an output port 340-N, multiply reflected
light 375 that has been delayed at a reflecting point 1 indicated
by reference numeral 350 and a reflecting point 2 indicated by
reference numeral 360 may superimpose itself on the optical signal
370, causing coherent crosstalk, or interference between the
optical signal and the multiply reflected light may form a
resonator that is not actually present in the system. If a
wavelength multiplexed signal is processed optically in an optical
signal processor configured by combining a plurality of optical
components, various types of optical degradation due to multiply
reflected light may occur on a random basis: for example, (1)
wavelength-dependent variations in optical-loss characteristics,
(2) occurrence of signal amplitude noise due to wavelength
fluctuations of an intended signal, and (3) wavelength dispersion.
It has been found that these effects have a major effect on the
operation of the system.
[0009] Therefore, practical utilization of an optical signal
processor configured by combining a plurality of optical components
requires configurations and methods by which reflected light
arising in the processor during assembly, installation, or
operation thereof can be detected reliably and immediately to
enable alteration of optical signal paths and recovery actions
(maintenance) such as replacement and repair of components, thereby
improving the reliability, availability, and serviceability of the
processor.
[0010] The document mentioned above describes a configuration for
detecting singly reflected light, but it does not provide
configurations and methods for implementing systems that address
the problems of multiply reflected light in an optical signal
processor configured by combining a plurality of optical
components.
SUMMARY OF THE INVENTIION
[0011] An object of the present invention is to solve the above
problems of optical switching systems configured by combining a
plurality of optical components, by providing an optical switching
system with functions enabling reliable and immediate detection and
notification of reflected light, and providing methods enabling
reliable and immediate detection and notification of reflected
light arising in an optical switching system.
[0012] Another object of the present invention is to provide a more
highly reliable, available, and serviceable optical switching
system by providing a simplified configuration enabling reliable
and immediate detection and notification of reflected light arising
therein, thus enabling the replacement of optical signal paths and
recovery actions (maintenance) such as replacement and repair of
the optical components.
[0013] Another object of the present invention is to provide a
method comprising simplified procedural steps for reliable and
immediate detection and notification of reflected light arising in
an optical switching system, thereby improving the reliability,
availability, and serviceability thereof.
[0014] Another object of the present invention is to provide an
optical switching device with a plurality of optical input ports
and a plurality of optical output ports, comprising optical
reflection monitors with optical reflection monitoring functions
provided between the plurality of optical input ports and the
plurality of optical output ports.
[0015] Another object of the present invention is to provide an
optical switching system configured by multistage-connecting a
plurality of optical switching devices, wherein each optical
switching device comprises a plurality of optical reflection
monitors having optical reflection monitoring functions, and the
optical reflection monitors can detect reflected light on paths
followed by optical signals input to the optical switching device
and use the optical reflection monitoring function to locate the
point of reflection on the path.
[0016] Another object of the present invention is to provide a
reflected light measuring system comprising a terminal with
reflected light measuring software, an optical switching system
including optical switching units that control switching of optical
signals, reflected light meters that measure reflected light of
optical signals, and port selectors that select the input path of
an optical signal input to the optical switching unit, wherein the
software can be executed to control the operation of the reflected
light meters, port selectors, and optical switching system, and
thereby measure the reflected light of the optical signal to locate
reflection positions.
[0017] Another object of the present invention is to provide an
optical switching method capable of detecting reflected light,
comprising steps of performing settings for switching of an optical
switch and storing optical interconnection relationships; selecting
a circuit board equipped with the optical switching device
according to a command from an operation control unit and storing
optical reflection alarm information; and locating a position at
which reflection is occurring according to the stored optical
interconnection relationships and optical reflection alarm
information.
[0018] Another object of the present information is to provide a
method of setting optical switching information and optical
reflection alarm information in an optical switching device,
comprising steps in which a switching control unit in the optical
switching device performs settings for switching of an optical
switch and settings of a switching information register, and a CPU
selects an optical reflection monitoring circuit, then transfers a
signal from the optical reflection monitoring circuit, after
analog-to-digital conversion, to a monitoring and control unit, and
sets an optical reflection monitoring register therein.
[0019] Another object of the present invention is to provide a
reflection position measuring method using an optical reflection
measuring system in an optical switching unit, comprising steps of
transmitting a switching command to a port selector under control
of a portable terminal; transmitting the switching command to an
optical switching unit under control of the portable terminal;
requesting a measured value from a reflected light meter; and
searching in an optical reflection alarm control table and an
interconnection control table to determine an abnormal alarm
position.
[0020] Another object of the present invention is to provide an
optical switching device comprising a plurality of optical
reflection monitors with optical reflection monitoring functions
disposed between a plurality of optical input ports and a plurality
of optical output ports, that receives an optical signal input
through an optical input port and uses the optical reflection
monitors to monitor reflected light arising at certain points along
the transmission paths between the plurality of optical input ports
and the plurality of optical output ports, thereby enabling
immediate notification of abnormal conditions in connecting cables
along the optical transmission paths.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is a drawing showing an example of the structure of a
communication network equipped with an optical switching system
according to the present invention;
[0022] FIG. 2 is a drawing explaining the effects of reflected
light arising in optical switching systems;
[0023] FIG. 3 is a drawing showing an example in which a reflection
alarm is issued in an optical switching system with
multistage-connected optical switching devices according to the
present invention;
[0024] FIG. 4 is a drawing showing another example in which a
reflection alarm is issued in an optical switching system with
multistage-connected optical switching devices according to the
present invention;
[0025] FIG. 5 is a drawing showing an exemplary block diagram of an
optical switching device according to the present invention;
[0026] FIG. 6 is a block diagram of an optical switching system
with an external measuring instrument for measuring reflected light
in the switching system and an external port selector;
[0027] FIG. 7 is a drawing showing an example of the structure of
an optical branching unit and optical detector in an optical
switching device according to the present invention;
[0028] FIG. 8 is a drawing showing an example of the structure of
an optical branching unit, optical isolator, and optical detector
in an optical switching device according to the present
invention;
[0029] FIG. 9 is a drawing showing an example of the structure of
an optical circulator and optical detector in an optical switching
device according to the present invention;
[0030] FIG. 10 is a diagram showing the flow of operations based on
the system configuration shown in FIGS. 3 and 4 according to the
present invention;
[0031] FIG. 11 is a flow diagram of operations based on the
exemplary structure shown in FIG. 4 according to the present
invention;
[0032] FIG. 12 is a flow diagram of operations based on the
exemplary structure shown in FIG. 5 according to the present
invention;
[0033] FIGS. 13A and 13B are drawings showing an optical reflection
alarm information table according to the present invention; and
[0034] FIG. 14 is a drawing showing an interconnection control
table according to the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0035] Embodiments illustrating the structure of optical signal
switching apparatus according to the present invention and the use
thereof will be described with reference to the attached drawings,
in which like parts are indicated by like reference characters in
FIGS. 3 and 4. FIG. 1 is a drawing of a network configuration that
will be used as an example of a communication network adopting
optical signal switching apparatus according to the present
invention. Optical signal switching apparatus 100 (100-1 to 100-9)
is interconnected with optical fibers 200 (200-1 to 200-12, and
others) to form a communication network. A more specific embodiment
includes a pair of optical cross-connects (each referred to as an
OXC below: 100-1 and 100-2) that switch and output multiplexed
optical signals received from the optical fibers (200-1 to 200-5
and others) to appropriate destination optical fibers, and optical
add drop multiplexers (each referred to as an OADM below: 100-3 to
100-9) that separate an optical signal from or insert an optical
signal into the multiplexed optical signals received from the
optical fibers (200-5 and 200-9) as required by the devices
connected thereto and transmit and receive optical signals to and
from the optical fibers (200-6 to 8, and 200-10 to 12). A
communication network is constructed by connecting the optical
signal switching apparatus according to the present invention and
these optical fibers having proper multiplexing degrees and
transmission rates, as required.
[0036] An optical signal switching system according to the present
invention simplifies network construction by enabling proper
selective use of components to construct flexible communication
networks capable of supporting various optical signal transmission
rates and multiplexing degrees. For example, the system can handle
both optical signals with transmission rates exceeding the STM-0
(51.84 MHz) level established by an ITU-T Recommendation or
unmodulated (dc) light, and places no limitations on the presence
or absence of wavelength division multiplexing and the number of
multiplexed wavelengths. An optical signal switching system
providing 8 paths with 32 multiplexed wavelengths requires an OXC
capable of 256.times.256 switching. In this case, it becomes
impossible to implement a compact signal switching system by using
electronic circuits, so the present invention provides a
significant effect.
[0037] FIGS. 3 and 4 are block diagrams of an optical switching
system 300 with multistage-connected optical switches.
[0038] A system control and monitoring unit 405 comprises an
interconnecting structure with a bus 436, an I/O unit 410 that
communicates with an operation control unit 400, a CPU 415 that
controls the overall system control and monitoring unit 405, a
switching information memory 420, an optical reflection alarm
information memory 425, and an I/O unit 430 that interconnects
multistage-connected circuit boards (CBs) 700-1 to 700-6 with
conducting wire 435. Each of the CBs includes a circuit board
control and monitoring unit 440-N that controls and monitors the
CB, an optical reflection monitor 460-X-N that monitors reflected
light in the CB, and an optical switching unit 465-N that switches
optical paths in the CB. The switching information memory unit 420
stores an interconnection control table shown in FIG. 14; the
optical reflection alarm information memory 425 stores an optical
reflection alarm control table shown in FIGS. 12(a) and (b).
[0039] The CPU 415 accesses these control tables to control
switching and other processing of the circuit boards 700-1 to
700-6. The operation control unit 400 collects circuit board status
information from the multistage-connected circuit boards 700-1 to
700-6, switching status information from the optical switching
unit, alarm information provided from the optical reflection
monitors when reflection occurs, and other information through the
I/O unit 430 and relays switching settings and other commands to
each of the circuit boards. The multistage-connected circuit boards
700-1 to 700-6 are used for optical transmission and switching. The
multistage connection structure includes several redundant paths,
providing alternative detour paths in the case of a failure in a
circuit board.
[0040] In the example of the system structure shown in FIGS. 3 and
4, an optical signal 690-1, for example, is transmitted on a
transmission path sequentially from an input port 455-1-1, through
the optical switching unit 465-1, an output port 475-1-1 of the
circuit board 700-1, an input port 455-3-1, the optical switching
unit 465-3, an output port 475-3-1 of the circuit board 700-3, an
input port 455-5-1, and the optical switching unit 465-5, to an
output port 475-5-1 of the circuit board 700-5.
[0041] In the example of FIG. 3, when there is a reflecting point
in the input port 455-3-1 of CB700-3 and reflected light is
monitored in optical reflection monitors 470-1-1 and 460-1-1, a
value indicating an abnormal condition is written into both ingress
and egress columns under CB1 in the optical reflection alarm
control table shown in FIG. 13A. Based on the monitoring results,
maintenance or other personnel can replace optical cables and
circuit boards with new ones at the position where the reflection
is occurring.
[0042] FIG. 5 is a block diagram showing the details of one of the
circuit boards 700-1 to 700-6 included in the optical switching
system described with reference to FIGS. 3 and 4. In FIG. 5, an I/O
unit 710, a CPU 715, a switching information register unit 720, an
optical reflection monitoring register 725, a switch control unit
730 that controls switching of switches in an optical switching
unit 465-X, a monitoring control unit 765, analog-to-digital (A/D)
converters 735 and 770, and a driver 755 that drives the optical
switching unit are interconnected via a bus 713, forming a circuit
board control and monitoring unit 440-X that is controlled by the
CPU 715. The monitoring control unit 765 monitors digital signals
obtained through detection of reflected light in the optical
detectors 750-1 to 750-N and 775-1 to 775-N and A/D conversion of
the detected reflected light in A/D converters 735 and 770.
[0043] The optical detectors 750-1 to 750-N and 775-1 to 775-N
monitor reflected light of an optical signal that has been branched
out from the optical signal in optical branching circuits 745-1 to
745-N and 780-1 to 780-N, each of which comprises an optical
coupler and other optical components, and transmits it to the A/D
converters 735 and 770 as a monitored signal. The behaviors of the
switching information register unit 720 and the optical reflection
monitoring register unit 725 will be described later with reference
to the flow diagram shown in FIG. 11.
[0044] The driver 755 and the switching control unit 730 set
optical transmission paths from the input ports 455-X-1 to 455-X-N
to the output ports 475-X-1 to 475-X-N of the optical switching
units 465-X.
[0045] Circuits 460-X-1 to 460-X-N and 470-X-1 to 470-X-N (shown in
the boxes enclosed with a broken line in FIG. 5), which are
combinations of optical branching circuits 745-1 to 745-N and 780-1
to 780-N and optical detectors 750-1 to 750-N and 775-1 to 755-N
respectively correspond to the optical reflection monitor circuits
(or optical reflection monitors) 460-1-1 to 460-6-N and 470-1-1 to
470-6-N in each circuit board shown in FIGS. 3 and 4. Each optical
reflection monitor can detect reflected light on an optical
transmission path followed by an optical signal input to the
optical switching device mounted on the circuit board, and locate
the reflecting positions along the path.
[0046] FIGS. 7 to 9 show specific examples of the structure of the
optical detector 750 and an optical branching circuit that form the
optical reflection monitor connected to the optical switching
devices mounted on CB 700 in FIG. 5 described above.
[0047] The optical reflection monitor shown in FIG. 7 comprises an
optical detector 1010 for monitoring optical power of an optical
signal 1015-1 input to an optical branching circuit 1000 (provided
to separate the optical signal and reflected light thereof), and an
optical detector 1005 that monitors reflected light 1020-1 or
1020-2 of the optical signal 1015-1 or 1015-2 at the optical
connector. This structure makes it possible to determine the amount
of reflection loss accurately as the ratio of input power to
reflected light power.
[0048] FIG. 8 shows an optical reflection monitor with a structure
comprising a combination of an optical isolator 1100, an optical
branching circuit 1105 that separates reflected light of optical
signals, and an optical detector 1110. The optical isolator 1100
allows an optical signal 1115-1 to pass but blocks the reflected
light 1120-1 that arises at the optical connector. Providing the
optical isolator 1100 can prevent reflected light from proceeding
beyond the optical detector 1110 (toward the left in the drawing).
The optical detector 1110 monitors reflected light 1120-3 as
described with reference to FIG. 7.
[0049] FIG. 9 shows an optical reflection monitor with a structure
comprising a combination of an optical circulator 1200 that allows
the passage of an optical signal and circulates or blocks reflected
light thereof and an optical detector 1205. An optical signal
1210-1 is passed through the optical circulator 1200 to the optical
connector and other components, while reflected light 1215-2 that
arises in the optical connector is circulated clockwise in the
optical circulator 1200 and transmitted to the optical detector
1205 to be monitored. The optical circulator 1200 has an advantage
in that it produces less reflection loss than occurs in the optical
coupler used in the optical branching circuit described above, and
consequently never weakens the reflected light power.
[0050] FIG. 10 is a flow diagram showing the procedures for
switching operations, collecting optical reflection alarms, and
locating abnormal conditions. OPERATION 1 shows a procedure of
switching operation, OPERATION 2 shows a procedure for collecting
optical reflection alarms, and OPERATION 3 shows a procedure of
finding and calculating optical reflection alarm positions and
other operations.
[0051] In OPERATION 1, the CPU 415 performs settings for switching
optical switches as commanded by the operation control unit 400 in
FIGS. 3 and 4 (Step S10); transfers the switching command to an
optical switching device mounted on one of the multistage-connected
circuit boards concerned (Step S11); and completes required setting
for the switching of the optical switch (Step S12). Then the CPU
415 updates the contents of the interconnection control table shown
in FIG. 14, which is stored in the switching information memory
420, in accordance with switching information transferred from the
optical switching device (Step S13), and if all settings for
switching of optical switches required are completed, terminates
OPERATION 1, or otherwise, returns to Step S10 and repeats the
switching setting operation in accordance with the switching
command from the operation control unit 400.
[0052] In OPERATION 2, the CPU 415 selects a circuit board (CB)
(Step S30) and requests optical reflection alarm acquisition (Step
S31); then the optical reflection alarm information is transferred
from an optical switching device mounted on the selected CB to the
operation control unit 400 through the CPU 415 (Step S32). At the
same time, the contents of the optical reflection alarm information
table shown in FIGS. 13A and 13B, which is stored in the optical
reflection alarm information memory 425, are updated (Step S33).
For example, if there is an optical reflection alarm, "1" is
written into the optical reflection information table in the
optical reflection alarm information memory 425 to indicate the
presence of an optical reflection alarm. If the monitoring of all
circuit boards in OPERATION 2 is completed, the CPU 415 terminates
OPERATION 2; otherwise, it returns to Step S30 to repeat the
procedure.
[0053] Finally, in OPERATION 3, if no optical reflection alarm has
been generated through OPERATIONs 1 and 2, the CPU 415 terminates
the operation. If there is an optical reflection alarm, the optical
reflection alarm control table shown in FIGS. 13A and 13B is
searched (Step S20), all alarm positions are detected (Step S21),
the interconnection control table shown in FIG. 14 is searched
(Step S22), a suspected abnormal optical interconnection path is
selected (Step S23), the rearmost interconnection of the connecting
path on which reflected light is arising is determined and the
reflection position is reported to the operation control unit 400
(Step S24). If the rearmost interconnections for all optical
reflection alarms have been found and reported, then the CPU 415
terminates operations in OPERATION 3; otherwise, it repeats the
procedure of OPERATION 3.
[0054] FIG. 11 is a flow diagram of the operation of the CPU 715,
the switching control unit 730, the monitoring and control unit
765, the switching information register unit 720, and the optical
reflection monitoring register 725 in FIG. 5 showing the details of
each circuit board in the system structure shown in FIGS. 3 and
4.
[0055] In OPERATION 1, the switching control unit 730 performs
settings for required switching of an optical switch in an optical
switching unit (Step S40), the CPU 715 sets the switching
information register unit 720 in accordance with the switching
information (Step S41), and if switching for all the settings is
completed (Step S42), then terminates the operation, or otherwise,
returns to Step S40 and repeats the procedure. These operations and
settings can be executed directly by the system control and
monitoring unit 405.
[0056] In OPERATION 2, the CPU 715 selects an optical reflection
monitoring circuit (Step S50); compares an A/D-converted output
value from a designated optical reflection monitoring circuit to a
threshold stored in the CPU 715, the monitoring and control unit
765, or the optical reflection monitoring register 725 (Step S51);
writes "1" for an abnormal condition and "0" for a normal condition
into a memory in the monitoring control unit 765 and sets the
optical reflection monitoring register 725 (Step S52); and if the
settings for all the optical reflection monitoring circuits are
completed (Step S53), then terminates OPERATION 2, or otherwise,
returns to Step S50 and repeats the procedure.
[0057] FIGS. 13A and 13B show optical reflection alarm control
tables. The tables are stored in the optical reflection alarm
information memory 425 shown in FIGS. 3 and 4, and indicate the
presence or absence of reflected light arising at the ingress and
egress ports 1 to N of each of the circuit boards (CB1 to CB6) on
which the multistage-connected optical switching units are mounted
in the system structures (FIGS. 3 and 4) of the optical switching
system 300, as abnormal or normal condition information. In these
tables, CB1, CB3, and CB5 correspond to circuit boards 700-1,
700-3, and 700-5; CB2, CB4, and CB6 correspond to circuit boards
700-2, 700-4, and 700-6.
[0058] The condition information (normal or abnormal) at the input
and output ports 1 to N of each circuit board is monitored in the
CPU 415 shown in FIGS. 3 and 4, and switching of the optical
switching unit in the circuit board is carried out in accordance
with the condition information. The control table shown in FIG. 13A
indicates that there is a reflecting point at the input port
455-3-1 of circuit board 700-3 in the system structure in FIG. 3
and the reflected light has been monitored. The control table shown
in FIG. 13B indicates that there is a reflecting point in the
optical switching unit 465-3 of circuit board 700-3 in the system
structure in FIG. 4 and the reflected light has been monitored.
[0059] The interconnection control table in FIG. 14 is stored in
the switching information memory 420 shown in FIGS. 3 and 4, which
indicates the input-to-output port interconnection information
within each of the circuit boards CB1 to CB6 described with
reference to FIGS. 13A and 13B and CB-to-CB port interconnection
information. For example, the table shows interconnection between
input port 1 and output port 1 and between input port N and output
port 1 within CB1. The CB-to-CB interconnection column indicates
CB1-to-CB3 or CB4, CB2-to-CB3 or CB4, CB3-to-CB5 or CB6, and
CB4-to-CB5 or CB6 interconnection information.
[0060] Interconnecting conditions indicated by the interconnection
control table conform to the optical cabling of CB1 to CB6 shown in
FIGS. 3 and 4. The content of this interconnection control table is
also monitored by the CPU 415 shown in FIGS. 3 and 4 as is the case
with the optical reflection alarm information table shown in FIGS.
13A and 13B.
[0061] In the structure shown in FIG. 3, it is possible to use the
optical reflection alarm control table (FIG. 13A) and the
interconnection control table (FIG. 14) in accordance with the flow
diagram (FIG. 10) to locate reflecting points. Specifically, FIG.
13A indicates an alarm from the optical reflection monitors 460-1-1
and 470-1-1 of CB1 and no alarm from the optical reflection monitor
460-3-1. Reference to the interconnection control table in FIG. 14
shows that there may be abnormal conditions in the optical fiber
from CB1 output port 1 to CB3 input port 1 or in the connectors of
this optical fiber. In the case of FIG. 4, the table in FIG. 13B
also indicates an alarm from optical reflection monitor 460-3-1 of
CB3. Reference to the interconnection control table in FIG. 14
shows there may be an abnormal condition in the connection path
from input port 1 to output port 1 within CB3. In this way, the
optical reflection alarm control table and interconnection control
table can be used in accordance with the procedure of the flow
diagram shown in FIG. 10 to identify failures. As a result of
identifying the failures, alarms can be issued and signals can be
switched over to paths that are still normal.
[0062] FIG. 6 is a block diagram of a structure for providing a
reflected light measuring function by combining a personal computer
(PC) 801 that operates as a portable terminal with stored software
such as a reflected light measuring program 870, an optical
switching system 300, outboard devices including a reflected light
meter 800 and a port selector 830. The personal computer 801
executes the reflected light measuring program 870 using an I/O
cable 877-1 to send a reflected light measuring command to the
optical switching system 300, the port selector 830, and the
reflected light meter 800 through a bus 877 to measure reflected
light.
[0063] The reflected light meter 800 includes a laser diode or
other electronic device as a light source 820 for generating test
light. The optical signal 880-2 is transferred to the optical
switching unit through a port 925-1, for example, which is selected
in the port selector 830. The port selector 830 receives reflected
light 885-1 from a port 930-1 of the optical switching unit, and
transmits it back to a reflected light separating unit 825 in the
reflected light meter 800 via a port 915.
[0064] A control unit 840 in the port selector 830 controls the
port selecting unit that selects a port in accordance with command
information sent via a bus 877; an I/O unit 835 is connected to the
system control and monitoring unit 850 and reflected light meter
800 via the bus 877.
[0065] A control and monitoring unit 810 in the reflected light
meter 800 monitors reflected light 885-4 that has been separated in
the reflected light separating unit 825 in the optical detector
815, and supervises the monitored signal. The control and
monitoring unit 810 controls inside the reflected light meter 800
in accordance with the command information sent via the bus 877,
and it can also store the reflected light measuring program
870.
[0066] The system control and monitoring unit 850 in the optical
switching system 300 comprises an I/O unit 855 that sends
measurement commands to the reflected light meter 800 and the port
selector 830 that are outboard equipment, an I/O unit 899 that
sends switching commands to the optical switching unit 851 in the
optical switching system 300, a CPU 860 that globally controls the
optical switching system 300, a switching information memory 865
that stores the optical interconnection relationships in the
optical switching unit, and the optical reflection alarm
information memory 875 that stores the optical reflection alarm
control table shown in FIGS. 13A and 13B and stores alarm
information on reflected light that is transmitted from the
reflected light meter; these elements are interconnected via a bus
856 etc. If the optical switching unit 851 is equivalent to the
unit comprising a plurality of circuit boards shown in FIGS. 3 and
4, the switching information memory 865 stores the interconnection
control table shown in FIG. 14. The reflected light measuring
program 870, including a testing program for measuring reflected
light, can also be provided within the optical switching system
300. In that case, the program issues measuring commands to be
executed by the port selector 830 and the reflected light meter 800
to be executed and controls the optical switching unit with
reference to the test results obtained from the reflected light
meter 800 via bus 877. Output ports 935-1 to 935-4 of the optical
switching unit are terminated in the optical isolator and other
components during measurement.
[0067] FIG. 12 shows a flow diagram of operations in each block
that operates under control of the CPU 860 in the reflected light
measuring system shown in FIG. 6. In an environment in which the
reflected light measuring program is executed on the personal
computer 801, the CPU 860 in the optical switching system 300
transfers a switching command to the port selector 830 (Step S60);
transfers the switching command to the optical switching unit (Step
S61); sends the reflected light meter 800 a request to acquire a
reflected light measurement value (Step S62); receives the
reflected light measurement value transferred from the reflected
light meter (Step S63); then compares the reflected light
measurement value with the threshold stored in the optical
reflection alarm information memory 875 or the CPU 860 (Step S64);
if the measurement value is smaller than the threshold, writes "1"
indicating an abnormal condition, or otherwise, writes "0"
indicating a normal condition into the optical reflection alarm
information memory 875, thereby updating the memory (Step S65); if
measurements have been completed for all paths in the optical
switching unit (Step S66), references the optical reflection alarm
information memory 875; and if there is a reflection alarm, sets a
reflection alarm indication (Step S67), or otherwise, returns to
the starting point. After that, the CPU 860 searches a table
similar to the optical reflection alarm control table in FIGS. 13A
and 13B that indicate the conditions (indicated as normal or
abnormal) of reflected light on each input and output port of the
optical switching unit 851 (FIG. 6) (Step S68), detects all optical
reflection alarm positions in the abnormal conditions (Step S69),
searches a table similar to the interconnection control table in
FIG. 14 that indicates interconnection status on each input and
output port of the optical switching unit 851 (FIG. 6) (Step
S70),selects suspected abnormal cable connections (Step S71), and
determines the rearmost interconnection having reflection in its
connection cable (Step S72). If searching of all optical reflection
alarms is completed, the CPU 860 terminates the operation;
otherwise, it returns to Step S67.
[0068] As described above, the present invention simplifies the
detection of optical reflection causing degradation of signals, and
consequently simplifies the installation and maintenance of the
system. In addition, it becomes possible to provide functions
enabling reliable and immediate detection and notification of
reflected light in optical switching system configured by combining
a plurality of optical components. Furthermore, the invention
provides a method of reliable and immediate detection and
notification of reflection in an optical switching system.
[0069] It also becomes possible to provide optical switching
systems with higher reliability, availability, and serviceability
in a simplified configuration in which reliable and immediate
detection and notification of reflected light makes possible the
switching of optical signal paths and recovery actions
(maintenance) including replacement and repair of components.
[0070] It also becomes possible to provide a method enabling
reliable and immediate detection and notification of reflected
light arising in an optical switching system with simpler
procedures, and improve the reliability, availability, and
serviceability of the system.
[0071] Furthermore, combination with an optical reflection
prevention circuit (isolator) makes it possible to confine
reflecting positions within a certain range, and the use of
circulators can improve utilization efficiency and facilitate
design of optical power monitors.
[0072] In addition, if a circulator is used, it can also function
as a reflection prevention circuit.
* * * * *