U.S. patent application number 09/772083 was filed with the patent office on 2001-11-29 for optical signal switching apparatus.
Invention is credited to Hayashi, Yuki, Kakizaki, Sunao, Kuwano, Shinichi, Tsushima, Hideaki.
Application Number | 20010046344 09/772083 |
Document ID | / |
Family ID | 18662469 |
Filed Date | 2001-11-29 |
United States Patent
Application |
20010046344 |
Kind Code |
A1 |
Hayashi, Yuki ; et
al. |
November 29, 2001 |
Optical signal switching apparatus
Abstract
Variable (coupling ratio) optical couplers 3-0 and 6-0 each have
ports of two inputs and two outputs, and the coupling ratio of
inputted light is variably controlled by drive circuits 4-1 and
7-1. In the optical 1+1 switching structure, the coupling ratio of
the variable (coupling ratio) optical coupler 3-0 is controlled to
be 50%:50%. The variable (coupling ratio) optical coupler 6-0 is
controlled to have the coupling ratio of 100%:0% or 0%:100%. In the
optical 1:1 switching structure, the coupling ratios of the
variable (coupling ratio) optical couplers 3-0 and 6-0 are
controlled to be 100%:0% or 0%:100%. When a performance monitor (0)
9-0 detects signal degradation, signal interruption, and the like,
the system controller 1-0 sends an instruction signal and the
control circuits 20-0 and 21-0 output control signals for
controlling coupling ratios of the variable (coupling ratio)
optical couplers 3-0 and 6-0, respectively. The coupling ratios of
the variable (coupling ratio) optical couplers 3-0 and 6-0 change
gradually.
Inventors: |
Hayashi, Yuki; (Fujisawa,
JP) ; Kakizaki, Sunao; (Kawasaki, JP) ;
Tsushima, Hideaki; (Komae, JP) ; Kuwano,
Shinichi; (Yokohama, JP) |
Correspondence
Address: |
ANTONELLI TERRY STOUT AND KRAUS
SUITE 1800
1300 NORTH SEVENTEENTH STREET
ARLINGTON
VA
22209
|
Family ID: |
18662469 |
Appl. No.: |
09/772083 |
Filed: |
January 30, 2001 |
Current U.S.
Class: |
385/15 ; 385/24;
398/140 |
Current CPC
Class: |
H04Q 2011/0083 20130101;
H04Q 11/0005 20130101; H04Q 2011/0015 20130101; H04Q 2011/0081
20130101; H04Q 2011/0039 20130101; H04Q 2011/0024 20130101 |
Class at
Publication: |
385/15 ; 385/24;
359/154 |
International
Class: |
G02B 006/26 |
Foreign Application Data
Date |
Code |
Application Number |
May 29, 2000 |
JP |
2000-157922 |
Claims
What is claimed is:
1. An optical switching apparatus comprising: a first optical
transmitter that converts an electric signal to be transmitted to
an optical signal; a first variable (coupling ratio) optical
coupler having first and second input ports and first and second
output ports, in which the optical signal outputted from said first
optical transmitter is inputted to the first or second input port,
and said first variable (coupling ratio) optical coupler outputs
the optical signal inputted to the first or second input port, to
the first and second output ports connected respectively to first
and second optical transmission lines corresponding respectively to
working and protection systems, at a first coupling ratio set by a
first drive signal; a second variable (coupling ratio) optical
coupler having third and fourth input ports and third and fourth
output ports, in which the optical signal transmitted through the
first and second optical transmission lines is inputted
respectively to the third and fourth input ports, and the second
variable (coupling ratio) optical coupler outputs the optical
signal inputted to the third and fourth input ports, to the third
and fourth output ports at a second coupling ratio set by a second
drive signal; a first optical receiver that converts the optical
signal received from the third output port of said second optical
coupler, to an electrical signal; a first performance monitor that
monitors performance of the electric signal received by said first
optical receiver; a system controller that outputs instruction
signals for switching or connecting said first and second optical
transmission lines from the working system to the protection system
or inversely, when degradation or interruption of the received
signal is detected based on the performance detected by said first
performance monitor; control circuits that output first and second
control signals for controlling the first and second coupling
ratios of said first and second optical couplers, based on the
instruction signals received from said system controller,
respectively; and drive circuits that output the first and second
drive signals for instructing the first and second coupling ratios
of said first and second optical couplers based on the first and
second control signals received from said control circuits,
respectively.
2. The optical signal switching apparatus according to claim 1,
further comprising: a second optical receiver connected to the
fourth output port of said second optical coupler; and a second
performance monitor that monitors performance of an electric signal
received by said second optical receiver; wherein, said system
controller outputs the instruction signals based on the
performances detected by said first and second performance
monitors.
3. The optical signal switching apparatus according to claim 1,
wherein: the performance monitored by said first or second
performance monitor is a symbol error rate, signal degradation, or
signal interruption.
4. The optical signal switching apparatus according to claim 2,
wherein: the performance monitored by said first or second
performance monitor is a symbol error rate, signal degradation, or
signal interruption.
5. The optical signal switching apparatus according to claim 1,
wherein: each of said control circuits comprises: reference value
generators for generating a plurality of reference values used for
setting the coupling ratios of said first and second optical
couplers correspondingly to first and second states; a selector
that selects one of the reference values generated by said
reference value generators, in accordance with a selector control
signal; a processor for calculating the first or second control
signal for gradually changing the first or second coupling ratio at
which an input from each input port is outputted to the output
ports of the first or second optical coupler when the first state
changes into the second state, said calculation being performed in
accordance with a processor control signal; and a control signal
generator that outputs the selector control signal for controlling
said selector's selection of the reference value to said selector
and the processor control signal for controlling a time and
quantity of change when the first or second coupling ratio is
changed to said processor, in accordance with the instruction
signal from said system controller.
6. The optical signal switching apparatus according to claim 2,
wherein: each of said control circuits comprises: reference value
generators for generating a plurality of reference values used for
setting the coupling ratios of said first and second optical
couplers correspondingly to first and second states; a selector
that selects one of the reference values generated by said
reference value generators, in accordance with a selector control
signal; a processor for calculating the first or second control
signal for gradually changing the first or second coupling ratio at
which an input from each input port is outputted to the output
ports of the first or second optical coupler when the first state
changes into the second state, said calculation being performed in
accordance with a processor control signal; and a control signal
generator that outputs the selector control signal for controlling
said selector's selection of the reference value to said selector
and the processor control signal for controlling a time and
quantity of change when the first or second coupling ratio is
changed to said processor, in accordance with the instruction
signal from said system controller.
7. The optical signal switching apparatus according to claim 1,
wherein: an optical amplifier is provided in a stage subsequent to
said first optical coupler and/or a stage subsequent to said second
optical coupler.
8. The optical signal switching apparatus according to claim 2,
wherein: an optical amplifier is provided in a stage subsequent to
said first optical coupler and/or a stage subsequent to said second
optical coupler.
9. The optical signal switching apparatus according to claim 5,
wherein: said reference value generators further have a variable
reference value setting function.
10. The optical signal switching apparatus according to claim 6,
wherein: said reference value generators further have a variable
reference value setting function.
11. The optical signal switching apparatus according to claim 5,
wherein: said reference value generators generate at least three
reference values for setting the coupling ratio between the first
output port and the second output port as 100%:0%, 0%:100%, and
50%:50%.
12. The optical signal switching apparatus according to claim 6,
wherein: said reference value generators generate at least three
reference values for setting the coupling ratio between the first
output port and the second output port to 100%:0%, 0%:100%, and
50%:50%.
13. The optical signal switching apparatus according to claim 1,
wherein: in optical 1+1 switching structure, and with respect to
said first optical coupler, said drive circuits and/or said control
circuits control the coupling ratio of an optical signal inputted
to the first input port to be "the first output port:the second
output port=50%:50%.
14. The optical signal switching apparatus according to claim 2,
wherein: in optical 1+1 switching structure, and with respect to
said first optical coupler, said drive circuits and/or said control
circuits control the coupling ratio of an optical signal inputted
to the first input port to be "the first output port:the second
output port=50%:50%.
15. The optical signal switching apparatus according to claim 1,
wherein: in an optical 1:1 switching structure, and with respect to
said first optical coupler, in the first state, said drive circuits
and/or said control circuits control the coupling ratio of an
optical signal inputted to the first input port to be "the first
output port:the second output port=100%:0%", and control the
coupling ratio of an optical signal inputted to the second input
port to be "the first output port:the second output port=0%:100%",
and on the other hand, in the second state, said drive circuits
and/or said control circuits control the coupling ratio of an
optical signal inputted to the first input port to be "the first
output port:the second output port=0%:100%", and control the
coupling ratio of an optical signal inputted to the second input
port to be "the first output port:the second output
port=100%:0%".
16. The optical signal switching apparatus according to claim 2,
wherein: in an optical 1:1 switching structure, and with respect to
said first optical coupler, in the first state, said drive circuits
and/or said control circuits control the coupling ratio of an
optical signal inputted to the first input port to be "the first
output port:the second output port=100%:0%", and control the
coupling ratio of an optical signal inputted to the second input
port to be "the first output port:the second output port=0%:100%",
and on the other hand, in the second state, said drive circuits
and/or said control circuits control the coupling ratio of an
optical signal inputted to the first input port to be "the first
output port:the second output port=0%:100%", and control the
coupling ratio of an optical signal inputted to the second input
port to be "the first output port:the second output
port=100%:0%".
17. The optical signal switching apparatus according to claim 1,
wherein: in an optical 1+1 switching structure and an optical 1:1
switching structure, and with respect to said second optical
coupler, in the first state, said drive circuits and/or said
control circuits control the coupling ratio of an optical signal
inputted to the third input port to be "the third output port:the
fourth output port=100%:0%"; and on the other hand, in the second
state, said drive circuits and/or said control circuits control the
coupling ratio of an optical signal inputted to the third input
port to be "the third output port:the fourth output
port=0%:100%".
18. The optical signal switching apparatus according to claim 2,
wherein: in an optical 1+1 switching structure and an optical 1:1
switching structure, and with respect to said second optical
coupler, in the first state, said drive circuits and/or said
control circuits control the coupling ratio of an optical signal
inputted to the third input port to be "the third output port:the
fourth output port=100%:0%"; and on the other hand, in the second
state, said drive circuits and/or said control circuits control the
coupling ratio of an optical signal inputted to the third input
port to be "the third output port:the fourth output port=0%:100%".
Description
[0001] This application claims a priority based on Japanese Patent
Application No. 2000-157922 filed on May 29, 2000, the entire
contents of which are incorporated herein by reference for all
purposes.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to an optical signal switching
apparatus, and particularly to an optical signal switching
apparatus having an optical protection function.
[0003] First, structures for realizing an optical protection
function, i.e., the optical 1+1 switching structure and the optical
1:1 switching structure will be described (See Japanese Unexamined
Patent Laid-Open No. 6-244796 and Tong-Ho Wu, "Fiber Network
Service Survivability", Artech House (1992), pp. 88-93).
[0004] FIG. 5 is a block diagram showing the conventional optical
1+1 switching structure. The optical 1+1 switching structure
includes an optical transmitter 1001, an optical coupler (splitter)
1002, a working optical fiber 1003, a protection optical fiber
1004, an optical switch 1005, and an optical receiver 1006. On the
transmitting side, an optical signal outputted from the optical
transmitter 1001 is split by the optical coupler (splitter) 1002,
and outputted to the working and protection optical fibers 1003 and
1004. On the receiving side, either of the working and protection
optical fibers 1003 and 1004 is selected by the optical switch
1005, and the optical signal is received by the optical receiver
1006.
[0005] FIG. 6 shows a block diagram showing the conventional
optical 1:1 switching structure. The optical 1:1 switching
structure includes a working optical transmitter 1011, a protection
optical transmitter 1021, an optical switch 1012, a working optical
fiber 1013, a protection optical fiber 1014, an optical switch
1015, a working optical receiver 1016, and a protection optical
receiver 1026. On the working transmitting side, an optical signal
(data) outputted from the working optical transmitter 1011 is
switched by the optical switch 1012, and usually outputted to the
working optical fiber 1013. On the working receiving side, the
working optical fiber 1013 is selected by the optical switch 1015,
and the optical signal is received by the working optical receiver
1016. On the other hand, also in the protection system, an optical
signal (extra data) outputted from the protection optical
transmitter 1021 is switched by the optical switch 1012, and
usually outputted to the protection optical fiber 1014. The
protection optical fiber 1014 is selected by the optical switch
1015, and the optical signal is received by the protection optical
receiver 1026.
[0006] Further, in the case of trouble with the working optical
fiber 1013, the optical switches 1012 and 1015 are switched so that
data outputted from the working optical transmitter 1011 is
received by the working optical receiver 1016 through the
protection optical fiber 1014. In any case, the optical receivers
1006, 1016 and 1026 receive an optical signal and convert it to an
electric signal.
[0007] In the above-described techniques, when the optical 1+1
switching structure is changed (expanded) to the optical 1:1
switching structure, it is necessary to replace the optical coupler
(splitter) with the optical switch. Further, these switching
structures tend to generate rapid fluctuation of optical power, at
the time of switching optical signals (changeover of the optical
switches). In particular, when an optical amplifier is connected in
a subsequent stage to an optical switch, there may arise (a)
excessive optical output (optical surge), or (b) effects
(disturbances) on optical signals of other wavelengths at the time
of general amplification of multiple wavelengths.
SUMMARY OF THE INVENTION
[0008] In consideration of the above problems, the present
invention provides an optical signal switching apparatus whose
hardware can be commonly used for the 1+1 switching structure
(splitting on the sending side and switching on the receiving side)
and the 1:1 switching structure (switching on the sending side and
switching on the receiving side). Further, the present invention
provides an optical signal switching apparatus that has
sending-side and receiving side switches having the same structure,
and thus is suitable for unifying and integrating sending and
receiving components. Further, conventionally, an optical coupler
should be replaced with an optical switch, and accordingly
in-service transformation is difficult. On the other hand,
according to the present invention, in-service transformation from
the 1+1 switching structure to the 1:1 switching structure and
in-service transformation from the 1:1 switching structure to the
1+1 switching structure are possible.
[0009] Further, according to the present invention, the control
circuits are provided, and accordingly, it is possible to suppress
rapid optical power fluctuation accompanying optical signal
switching. In particular, the present invention can suppress (a)
cause of excessive optical output (generation of optical surge),
(b) effect (disturbance) on optical signals of other wavelengths at
the time of general amplification of multiple wavelengths, etc. in
an optical amplifier.
[0010] Further, conventionally, when generation of optical signal
interruption (LOS) or the like is detected at the time of switching
from working system to protection system, malfunction can occur.
However, according to the present invention, switching can be
performed without generating optical signal interruption.
[0011] In the present invention, in particular, a variable
(coupling ratio) optical coupler is applied to a switch of an
optical signal switching apparatus. At the time of the 1+1
switching structure, the sending side is made to have a splitting
structure (coupling ratio=50%:50%) and the receiving side is made
to have a switching structure (coupling ratio=100%:0%, or 0%:100%).
At the time of the 1:1 switching structure, the sending side is
made to have a switching structure (coupling ratio=100%:0%, or
0%:100%) and the receiving side is made to have a switching
structure (coupling ratio=100%:0%, or 0%:100%).
[0012] Further, the present invention can realize an optical signal
switching function without rapid optical power fluctuation, by
combining a variable (coupling ratio) optical coupler with a
control circuit that gradually (continuously) controls the coupling
ratio of the coupler.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] Preferred embodiments of the present invention will now be
described in conjunction with the accompanying drawings, in
which:
[0014] FIG. 1 is a block diagram of a 1+1 optical signal switching
apparatus;
[0015] FIG. 2 is a block diagram of a 1:1 optical signal switching
apparatus;
[0016] FIG. 3 is a block diagram showing a control circuit;
[0017] FIGS. 4A to 4F are an explanation of control operation by
the control circuit;
[0018] FIG. 5 is a block diagram of the conventional optical 1+1
switching structure; and
[0019] FIG. 6 is a block diagram of the conventional optical 1:1
switching structure.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0020] FIG. 1 is a block diagram of a 1+1 optical signal switching
apparatus. The 1+1 optical signal switching apparatus comprises an
optical transmitter (0) 2-0, a variable (coupling ratio) optical
coupler 3-0, an optical amplifier (0) 30-0, an optical amplifier
(1) 30-1, optical fibers 5-0 and 5-1, a variable (coupling ratio)
optical coupler 6-0, an optical amplifier (2) 31-0, an optical
receiver (0) 8-0, a performance monitor (0) 9-0, a system
controller 1-0, control circuits 20-0 and 21-0, and drive circuits
4-0 and 7-0.
[0021] The optical transmitter (0) 2-0 converts an electric signal
to an optical signal 2-2. Each of the variable (coupling ratio)
optical couplers 3-0 and 6-0 has ports of two inputs (for example,
IN1 and IN2) and two outputs (for example, OUT1 and OUT2), and the
coupling ratio at which input light from the inputs IN1 or IN2 is
outputted to the outputs OUT1 and OUT2 can be variably controlled
by the drive circuit 4-0 or 7-0. For example, when the coupling
ratio for input light from the input IN1 is OUT1:OUT2=100%:0%, the
coupling ratio for input light from the input IN2 becomes
OUT1:OUT2=0%:100%. Further, when the coupling ratio for input light
from the input IN1 is OUT1:OUT2=70%:30%, the coupling ratio for
input light from the input IN2 becomes OUT1:OUT2=30%:70%. As the
variable (coupling ratio) optical couplers 3-0 etc., may be used an
optical element that has ports of at least two inputs and two
outputs, and its optical coupling ratio between the input ports and
the output ports can be variably controlled. As such an optical
element, a directional coupler type optical switch using lithium
niobate (LiNbO.sub.3) as a medium for an optical waveguide (LN
optical switch), a Mach-Zender interferometer type optical switch
using a silica glass waveguide (Planar Light wave Circuit (PLC)
optical switch), a Y-branch type optical switch using a polymer
waveguide (polymer optical switch), and a micromachine type optical
switch to which micromachine techniques are applied
(Micro-Electro-Mechanical System (MEMS) optical switch) may be
mentioned, for example. These are generally called optical
switches, and can be applied to the variable (coupling ratio)
optical coupler of the present invention. Japanese Unexamined
Patent Laid-Open No. 2000-019471 describes application examples
such as a variable optical attenuator and an optical power
adjuster.
[0022] The optical 1+1 switching structure controls the coupling
ratio of the variable (coupling ratio) optical coupler 3-0, so that
the output ratio becomes OUT1:OUT2=50%:50%. Further, the variable
(coupling ratio) optical coupler 6-0 outputs input light from the
input IN1, so that the output ratio becomes OUT1:OUT2=100%:0% or
OUT1:OUT2=0%:100%. Similarly, input light from the input IN2 is
outputted at the output ratio OUT1:OUT2=0%:100% or
OUT1:OUT2=100%:0%. Thus, the variable (coupling ratio) optical
coupler 6-0 is controlled in its coupling ratio such that one
optical signal is selectively received (as an output signal 6-2 of
the variable (coupling ratio) optical coupler) out of the optical
fiber output signals 5-2 and 5-3. This function of the variable
(coupling ratio) optical coupler 6-0 is equivalent to an optical
switching function. When this system is used oppositely, the
variable (coupling ratio) optical couplers 3-0 and 6-0 may be used
integratedly on the sending and receiving side.
[0023] The optical amplifier (0) 30-0 optically amplifies a
variable (coupling ratio) optical coupler output signal 3-2, and
the optical amplifier (1) 30-1 optically amplifies a variable
(coupling ratio) optical coupler output signal 3-3. The optical
fibers 5-0 and 5-1 are optical fiber transmission lines, and may
include wavelength multiplexers in addition to the optical fibers.
The optical amplifier (2) 31-0 optically amplifies an optical
signal propagated through the optical fiber transmission
lines/lossy media. The optical receiver (0) 8-0 converts an optical
signal to an electric signal 8-2. The performance monitor (0) 9-0
monitors performance of the received electric signal, constantly or
periodically. As an example of the performance monitoring, a symbol
error rate is monitored to detect signal degradation/signal
interruption. Here, the monitored performance may include, for
example, LOS (Loss of Signal), LOF (Loss of Frame), AIS (Alarm
Indication Signal), BER (Bit Error Rate), etc. The system
controller is advised of the detected performance monitor
information as a performance monitor (information) signal 9-2. To
the system controller 1-0, is inputted a system setup signal 150.
The system setup signal sets, for example, the optical 1+1
switching structure or the optical 1:1 switching structure, and is
determined by a system maintenance person/administrator, etc. In
accordance with the system setup signal 150 inputted by the system
maintenance person/administrator, the system controller 1-0 gives
(transmits) setup information (instruction signals) 1-1 and 1-2 on
the coupling ratios of the variable (coupling ratio) optical
couplers 3-0 and 6-0 to the respective control circuits 20-0 and
21-0. Further, the system controller 1-0 monitors (receives) the
performance monitor (information) signal 9-2 of the performance
monitor (0) 9-0 that monitors the performance of the received
signal. When signal degradation/interruption, etc. of the received
signal is detected, the system controller 1-0 sends the control
circuits 20-0 and 21-0 instruction signals 1-1 and 1-2 for
switching from the main (working) optical transmission line to the
spare (protection) optical transmission line, or from the spare
optical transmission line to the main optical transmission
line.
[0024] In accordance with the system controller output signal 1-1,
the control circuit 20-0 outputs a control signal 20-1 for changing
(controlling) the coupling ratio of the variable (coupling ratio)
optical coupler 3-0. Similarly, in accordance with the system
controller output signal 1-2, the control circuit 21-0 output a
control signal 21-1 for changing (controlling) the coupling ratio
of the variable (coupling ratio) optical coupler 6-0. In accordance
with the control circuit output signal 20-1, the drive circuit 4-0
outputs a drive signal (drive circuit output signal) 4-1 for
changing the coupling ratio of the variable (coupling ratio)
optical coupler 3-0. In accordance with the control circuit output
signal 21-1, the drive circuit 7-0 outputs a drive signal (drive
circuit output signal) 7-1 for changing the coupling ratio of the
variable (coupling ratio) optical coupler 6-0.
[0025] Next, flow of data will be described. On the transmitting
side, an optical signal outputted from the optical transmitter (0)
2-0 is split by the variable (coupling ratio) optical coupler 3-0,
to be outputted to the working and protection optical fibers 5-0
and 5-1. On the receiving side, either of the working and
protection optical fibers 5-0 and 5-1 is selected by the variable
(coupling ratio) optical coupler 6-0, and the selected optical
signal is received by the optical receiver (0) 8-0 through the
optical amplifier (2) 31-0. The variable (coupling ratio) optical
coupler 6-0 selects the optical fiber 5-0 at the working time, and
selects the optical fiber 5-1 at the protection time.
[0026] FIG. 2 is a block diagram of a 1:1 optical signal switching
apparatus. The 1:1 optical signal switching apparatus comprises an
optical transmitter (0) 2-0, an optical transmitter (1) 2-1, a
variable (coupling ratio) optical coupler 3-0, an optical amplifier
(0) 30-0, an optical amplifier (1) 30-1, optical fibers 5-0 and
5-1, a variable (coupling ratio) optical coupler 6-0, an optical
amplifier (2) 31-0, an optical amplifier (3) 31-1, an optical
receiver (0) 8-0, an optical receiver (1) 8-1, a performance
monitor (0) 9-0, a performance monitor (1) 9-1, a system controller
1-0, control circuits 20-1 and 21-0, and drive circuits 4-0 and
7-0.
[0027] Further, the system controller 1-0 monitors (receives)
respective performance monitor (information) signals 9-2 and 9-3 of
the performance monitors (0) 9-0 and (1) 9-1 that monitor
performance of received signals. When degradation/interruption of
the received signal is detected, the system controller 1-0 sends
the control circuits 20-0 and 21-0 instruction signals 1-1 and 1-2
for switching from the main (working) optical transmission line to
the spare (protection) optical transmission line, or from the spare
optical transmission line to the main optical transmission line.
The optical transmitters (0) 2-0 and (1) 2-1 convert an electric
signal to an optical signal. The variable (coupling ratio) optical
coupler 3-0 has ports of two inputs (for example, IN1 and IN2) and
two outputs (for example, OUT1 and OUT2). In the optical 1:1
switching structure, input light from the input IN1 is controlled
so that the coupling ratio becomes OUT1:OUT2=100%:0%, or 0%:100%.
And, correspondingly, input light from the input IN2 is controlled
so that the coupling ratio becomes OUT1:OUT2=0%:100%, or
100%:0%.
[0028] The variable (coupling ratio) optical coupler 6-0 has ports
of two inputs (for example, IN1 and IN2) and two outputs (for
example, OUT1 and OUT2). In the optical 1:1 switching structure,
input light from the input IN1 is controlled so that the coupling
ratio becomes OUT1:OUT2=100%:0%, or 0%:100%. And, correspondingly,
input light from the input IN2 is controlled so that the coupling
ratio becomes OUT1:OUT2=0%:100%, or 100%:0%.
[0029] The optical amplifiers (2) 31-0 and (3) 31-1 optically
amplify optical signals propagated through the optical fiber
transmission lines/lossy media. The optical receivers (0) 8-0 and
(1) 8-1 convert optical signals to electric signals 8-2 and 8-3.
The performance monitors (0) 9-0 and (1) 9-1 monitor performance of
received electric signals constantly or periodically. As an example
of the performance monitoring, a symbol error rate is monitored to
detect signal degradation/signal interruption. The system
controller is advised of the detected performance monitor
information as performance monitor (information) signals 9-2 and
9-3. The other configuration is similar to FIG. 1.
[0030] Next, flow of data will be described. On the transmission
side of the working system, an optical signal (data) outputted from
the working optical transmitter 2-0 is switched by the variable
(coupling ratio) optical coupler 3-0 to be usually outputted to the
working optical fiber 5-0. On the receiving side of the working
system, the working optical fiber 5-0 is selected by the variable
(coupling ratio) optical coupler 6-0, and the optical signal is
received by the working optical receiver (0) 8-0 through the
optical amplifier (2) 31-0. On the other hand, also in the case of
the protection system, an optical signal (extra data) outputted
from the protection optical transmitter (1) 2-1 is switched by the
variable (coupling ratio) optical coupler 3-0 to be usually
outputted to the protection optical fiber 5-1. The protection
optical fiber 5-1 is selected by the variable (coupling ratio)
optical coupler 6-0, and the optical signal is received by the
protection optical receiver (1) 8-1 through the optical amplifier
(3) 31-1. Further, in the case of trouble with the working optical
fiber 5-0, the variable (coupling ratio) optical couplers 3-0 and
6-0 are switched so that data outputted from the working optical
transmitter (0) 2-0 is transmitted to the protection optical fiber
5-1 and received by the working optical receiver (0) 8-0 through
the optical amplifier (2) 31-0.
[0031] Next, FIG. 3 is a block diagram showing a control circuit.
The control circuit 100-0 corresponds to the control circuit 20-0
or 21-0 of the above-mentioned 1+1 optical signal switching
apparatus or 1:1 optical signal switching apparatus. The control
circuit 100-0 comprises a control signal generator 90-0, a
reference voltage generators (1) 40-0, (2) 40-1 and (3) 40-2, a
selector 41-0, an A/D converter 42-0, a processor 43-0, and a D/A
converter 44-0.
[0032] To the control signal generator 90-0, is inputted a system
controller output signal 60-0 from the system controller 1-0. This
signal corresponds to the system controller output signal 1-1 or
1-2 of FIG. 1 or 2. The control signal generator 90-0 outputs a
selector control signal 90-1 and an processor control signal 90-2
in accordance with the system controller output signal 60-0. The
selector control signal 90-1 is a control signal for controlling
selection/switching in the selector 41-0. On the other hand, the
processor control signal 90-2 is a control signal for setting and
controlling timing at which the processor starts the operation and
for setting and controlling a time of controlling a coupling ratio
of a variable (coupling ratio) optical coupler.
[0033] The reference voltage generator (1) 40-0 generates a
reference voltage for obtaining a coupling ratio OUT1:OUT2=50%:50%
of a variable (coupling ratio) optical coupler. The reference
voltage generator (2) 40-1 generates a reference voltage for
obtaining a coupling ratio OUT1:OUT2=100%:0% of a variable
(coupling ratio) optical coupler. The reference voltage generator
(3) 40-2 generates a reference voltage for obtaining a coupling
ratio OUT1:OUT2=0%:100% of a variable (coupling ratio) optical
coupler. These reference voltage generators from (1) 40-0 to (3)
40-2 may have a variable setting function with respect to their
reference voltages (outputs), making their outputs adjustable. The
selector 41-0 selects and outputs one of three reference voltage
signals 40-3, 40-4 and 40-5, in accordance with the selector
control signal 90-1. The A/D converter 42-0 converts the reference
voltage signal (analog signal) selected by the selector to an n-bit
digital signal. Here, the present invention may use suitable
reference values, not limited to the reference voltages.
[0034] The processor 43-0 has the following functions.
[0035] (1) The processor 43-0 outputs (holds) a digital signal of
the previous state.
[0036] (2) The processor 43-0 calculates a difference between an
A/D converter output digital signal 42-1 (n bits), which
corresponds to the next state, and a processor output digital
signal 43-1 (n bits), which corresponds to the previous state, in
accordance with the processor control signal 90-2. And, the
processor 43-0 calculates and outputs successively and stepwise
such that the processor output digital signal 43-1 coincides with
the next state by m bits/T (period) each time. Further, by making
it possible to variably set m bits and T (period), the times of
controlling the coupling ratios of the variable (coupling ratio)
optical couplers 3-0 and 6-0 can be set at any values. The D/A
converter 44-0 converts the processor output digital signal 43-1 to
an analog signal, to output a control circuit output signal (drive
circuit input signal) 70-0. The control circuit output signal 70-0
corresponds to the control signal 20-1 or 21-1 of FIG. 1 or FIG. 2,
and is inputted to the drive circuit 4-0 or 7-0.
[0037] FIGS. 4A to 4F are an explanation of control operation by
the control circuit. FIG. 4A shows a waveform of the control
circuit output signals (drive circuit input signals) 70-0, 20-1,
and 21-1 in the case that the control circuits 100-0, 20-0 and 21-0
do not exist, as in the conventional technique. In this case, at
the time of switching, the output changes rapidly. FIG. 4B shows an
optical waveform of the output of the variable (coupling ratio)
optical couplers 3-0 and 6-0 (the input to the optical amplifiers
30-0, 30-1, 31-0 and 31-1 in FIG. 4A. FIG. 4C shows an output
optical waveform of the optical amplifiers 30-0, 30-1, 31-0 and
31-1 in FIG. 4A. As shown in this figure, excessive optical output
is generated in the conventional technique. FIG. 4D shows a
waveform of the control circuit output signals (drive circuit input
signals) 70-0, 20-1 and 21-1 in the case that the control circuits
100-0, 20-0 and 21-1 shown in FIG. 3 are provided. In this case,
the output changes gradually at the time of switching. FIG. 4E
shows an optical waveform of the output of the variable (coupling
ratio) optical couplers 3-0 and 6-0 (the input to the optical
amplifiers 30-0, 30-1, 31-0, 31-1) in FIG. 4D. FIG. 4F shows an
output optical waveform of the optical amplifiers 30-0, 30-1, 31-0
and 31-1 in FIG. 4D. Thus, according to the present invention,
occurrence of excessive optical output is suppressed at the time of
switching.
[0038] As described above, the present invention can provide an
optical signal switching apparatus whose hardware can be commonly
used for the 1+1 switching structure (splitting on the sending side
and switching on the receiving side) and the 1:1 switching
structure (switching on the sending side and switching on the
receiving side) for realizing the optical protection function.
Further, the present invention can provide an optical signal
switching apparatus that has sending-side and receiving-side
switches having the same structure, and thus is suitable for
unifying and integrating sending and receiving components. Further,
conventionally, an optical coupler should be replaced with an
optical switch, and accordingly in-service transformation is
difficult. On the other hand, according to the present invention,
in-service transformation from the 1+1 switching structure to the
1:1 switching structure and in-service transformation from the 1:1
switching structure to the 1+1 switching structure are possible.
Further, according to the present invention, the control circuits
are provided, and accordingly, it is possible to suppress rapid
optical power fluctuation accompanying optical signal switching. In
particular, the present invention can suppress (a) cause of
excessive optical output (generation of optical surge), (b) effect
(disturbance) on optical signals of other wavelengths at the time
of general amplification of multiple wavelengths, etc. in an
optical amplifier. Further, conventionally, when generation of
optical signal interruption (LOS) or the like is detected at the
time of switching from working system to protection system,
malfunction can occur. However, according to the present invention,
switching can be performed without generating optical signal
interruption.
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