U.S. patent application number 09/778774 was filed with the patent office on 2001-08-30 for bi-directional wavelength switching device and wavelength demultiplexing/multiplexing device.
Invention is credited to Terahara, Takafumi.
Application Number | 20010017960 09/778774 |
Document ID | / |
Family ID | 12015766 |
Filed Date | 2001-08-30 |
United States Patent
Application |
20010017960 |
Kind Code |
A1 |
Terahara, Takafumi |
August 30, 2001 |
Bi-directional wavelength switching device and wavelength
demultiplexing/multiplexing device
Abstract
An optical device has an optical switching unit and a variable
filter. The optical switching unit connects a pair of single
direction optical transmission lines to a bi-directional optical
transmission line carrying optical signals of different wavelengths
in different directions relative to the optical switching unit. The
single direction optical transmission lines carry optical signals
in single different directions relative to the optical switching
unit. The variable filter has first and second opposing terminal
pairs such that optical signals of different wavelengths input to
one terminal of one terminal pair are filtered with a portion of
the different wavelengths being output to one terminal of the
opposing terminal pair and the remainder of the different
wavelengths being output to the other terminal of the opposing
terminal pair. The bi-directional optical transmission line is
coupled to one terminal of the variable filter. The optical
switching unit may include an optical circulator. The variable
filter may be an acousto-optic tunable filter. The optical device
have a pair of optical switching units respectively connecting two
pairs of single direction optical transmission lines to two
opposing terminals of the variable filter through two
bi-directional optical transmission lines.
Inventors: |
Terahara, Takafumi;
(Kawasaki-shi, JP) |
Correspondence
Address: |
STAAS & HALSEY LLP
700 11TH STREET, NW
SUITE 500
WASHINGTON
DC
20001
US
|
Family ID: |
12015766 |
Appl. No.: |
09/778774 |
Filed: |
February 1, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09778774 |
Feb 1, 2001 |
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09087635 |
May 29, 1998 |
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6211980 |
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Current U.S.
Class: |
385/24 ; 385/16;
398/82; 398/83 |
Current CPC
Class: |
H04J 14/0209 20130101;
H04J 14/0206 20130101; H04J 14/0213 20130101; H04J 14/0217
20130101; H04J 14/0221 20130101; H04J 14/0216 20130101; H04J 14/021
20130101; H04J 14/0212 20130101 |
Class at
Publication: |
385/24 ; 385/16;
359/128 |
International
Class: |
G02B 006/293 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 30, 1998 |
JP |
HEI 10-020033 |
Claims
What is claimed is:
1. An optical device comprising: an optical switching unit
connecting a pair of single direction optical transmission lines to
a bi-directional optical transmission line carrying optical signals
of different wavelengths in different directions relative to the
optical switching unit, the single direction optical transmission
lines carrying optical signals in single different directions
relative to the optical switching unit; and a variable filter
having first and second opposing terminal pairs such that optical
signals of different wavelengths input to one terminal of one
terminal pair are filtered with a portion of the different
wavelengths being output to one terminal of the opposing terminal
pair and the remainder of the different wavelengths being output to
the other terminal of the opposing terminal pair, the
bi-directional optical transmission line being coupled to one
terminal of the variable filter.
2. An optical device according to claim 1, wherein the optical
switching unit includes an optical circulator.
3. An optical device according to claim 1, wherein the variable
filter is an acousto-optic tunable filter.
4. An optical device according to claim 1, wherein the optical
device has a pair of optical switching units respectively
connecting two pairs of single direction optical transmission lines
to two opposing terminals of the variable filter through two
bi-directional optical transmission lines.
5. An optical device according to claim 4, wherein each optical
switching unit includes an optical circulator.
6. An optical device according to claim 1, wherein the optical
device has a four optical switching units respectively connecting
four pairs of single direction optical transmission lines to the
first and opposing terminal pairs of the variable filter through
four bi-directional optical transmission lines.
7. An optical device according to claim 6, wherein each optical
switching unit includes an optical circulator.
8. An optical device according to claim 6, further comprising an
optical switch having two inputs and two outputs, each of the two
inputs being connected to one single direction optical transmission
line such that the two inputs are linked to the terminals of one
opposing terminal pair of the variable filter, the outputs of the
optical switch being switchable between the terminals linked
thereto.
9. An optical switch according to claim 1, further comprising a
main add line carrying optical signals toward the variable filter;
a demultiplexer to split the main add line into two single
direction sub-add lines leading respectively to the opposing
terminal pairs of the variable filter; a sub-drop lines carrying
optical signals away from the opposing terminal pairs of the
variable filter; and a multiplexer to combine the sub-drop lines
into a main drop line.
10. An optical device comprising: an acousto-optic tunable filter
having first and second sides; a bi-directional optical
transmission line connected to one side of the acousto-optic
tunable filter; and an optical switching unit connecting the
bi-directional optical transmission line and two single direction
optical transmission lines such that an optical signal travelling
from the acousto-optic tunable filter is output to one of the
single direction optical transmission lines and an optical signal
travelling to the acousto-optic tunable filter is input from the
other of the single direction optical transmission lines.
11. An optical device according to claim 10, wherein the optical
switching unit includes an optical circulator.
12. An optical device according to claim 10, wherein the optical
device has a pair of optical switching units respectively
connecting two pairs of single direction optical transmission lines
to the first and second sides of the acousto-optic tunable filter
through two bi-directional optical transmission lines.
13. An optical device according to claim 12, wherein each optical
switching unit includes an optical circulator.
14. An optical device according to claim 10, wherein a terminal
pair is provided on each of the first and second sides of the
acousto-optic tunable filter, and the optical device has a four
optical switching units respectively connecting four pairs of
single direction optical transmission lines to the terminal pairs
provided on the and second sides of the acousto-optic tunable
filter through four bi-directional optical transmission lines.
15. An optical device according to claim 14, wherein each optical
switching unit includes an optical circulator.
16. An optical device according to claim 14, further comprising an
optical switch having two inputs and two outputs, each of the two
inputs being connected to one single direction optical transmission
line such that the two inputs are linked to the terminals of one
terminal pair, the outputs of the optical switch being switchable
between the terminals linked thereto.
17. An optical switch according to claim 10, further comprising a
main add line carrying optical signals toward the acousto-optic
tunable filter; a demultiplexer to split the main add line into two
single direction sub-add lines leading respectively to the first
and second sides of the acousto-optic tunable filter; a sub-drop
lines carrying optical signals away from the first and second sides
of the acousto-optic tunable filter; and a multiplexer to combine
the sub-drop lines into a main drop line.
18. A wavelength division multiplexed transmission system
comprising: a pair of transmit/receive terminal stations
communicating to each other; a multiplexing device provided within
a communication line between the pair of optical transmit/receive
terminal stations, comprising: an acousto-optic tunable filter
having first and second sides; a pair of bi-directional optical
transmission lines connected respectively to the first and second
sides of the acousto-optic tunable filter; and a pair of optical
switching units each connecting one of the bi-directional optical
transmission lines to two single direction optical transmission
lines such that for each optical switching unit, an optical signal
travelling from the acousto-optic tunable filter is output to one
of the single direction optical transmission lines and an optical
signal travelling to the acousto-optic tunable filter is input from
the other of the single direction optical transmission lines.
19. A wavelength division multiplexed transmission system according
to claim 18, wherein each switching unit includes an optical
circulator.
20. A wavelength division multiplexed transmission system according
to claim 18, wherein the pair of transmit/receive terminal stations
communicate to each other through the single direction optical
transmission lines such that each transmit/receive terminal station
is linked to one side of the acousto-optic tunable filter.
21. A wavelength division multiplexed transmission system according
to claim 20, wherein the multiplexing device further comprises: a
second pair of bi-directional optical transmission lines connected
respectively to the first and second sides of the acousto-optic
tunable filter; and a second pair of optical switching units each
connecting one of the second pair of bi-directional optical
transmission lines to two single direction optical transmission
lines, and the transmission system further comprises a terminal
station linked to the second pair of bi-directional optical
transmission lines through the second pair of optical switching
units and single direction optical transmission lines.
22. A wavelength division multiplexed transmission system according
to claim 20, wherein each switching unit includes an optical
circulator.
23. A wavelength division multiplexed transmission system according
to claim 19, wherein the pair of transmit/receive terminal stations
communicate to each other through bi-directional optical
transmission lines linked respectively to the first and second
sides of the acousto-optic tunable filter, and the device further
comprises a terminal station linked to the single direction optical
lines such that optical signals travelling from the acousto-optic
tunable filter serve as dropped signals and optical signals
travelling to the acousto-optic tunable filter serve as added
signals.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to Japanese patent
application number 10-020033, filed Jan. 30, 1998 in Japan, which
is incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a bi-directional wavelength
switching device and a wavelength demultiplexing/multiplexing
device suitable for use in the wavelength division multiplexed
transmission system.
[0004] 2. Description of the Related Art
[0005] Accompanied with the recent advanced developments and
intricacies in communication technology, wavelength division
multiplexed ("WDM") transmission has been proposed as a way to
transmit large amounts of information on optical fibers. FIG. 20 is
a block diagram generally illustrating a proposed wavelength
division multiplexed transmission system. The WDM transmission
system 100' shown in FIG. 20 employs wavelength
demultiplexing/multiplexing devices 1'-a and 1'-b to be integrated
into a WDM network.
[0006] The transmission line usually employs more than one pair of
optical fibers 7'. One pair will be considered. The other pairs may
provide for additional information transmission or provide for
backups. One of the optical fibers 8'-a in the pair is used for the
upstream communication line, and another optical fiber 8'-b is used
for the downstream communication line. Optical amplifier repeaters
9'-a are placed in order to compensate for losses in the optical
fibers 8'-a and 8'-b on the upstream and downstream communication
lines. One optical amplifier repeater 9'-a is provided with at
least two optical amplifiers 9'-b (more than two amplifiers for
more fibers) for the upstream and downstream communication lines.
From each of the terminal stations 50a', 50b', 50c', and 60', a
plurality of optical signals (WDM signals) respectively having
different wavelengths are transmitted into one optical fiber. The
WDM signals are split into the various transmission lines according
to wavelength by the wavelength demultiplexing/multiplexing devices
1'-a and 1'-b to thereby be transmitted to the terminal stations
50a', 50b', 50c', and 60'.
[0007] The wavelength demultiplexing/multiplexing devices 1'-a,
1'-b used for the WDM network each include a combination of OADM
(optical add-drop multiplexer) circuits.
[0008] FIG. 21 is a chart to explain the basic character of an OADM
circuit. The OADM circuit 30'a drops only the optical signals
having selected wavelengths from the WDM signals having a plurality
of wavelengths (.lambda.1, .lambda.2, . . . , .lambda.n)
propagating in a trunk system transmission fiber 8'-c. These
optical signals are dropped to a drop transmission fiber 8'-e. The
OADM circuit 30a' adds optical signals input from an add
transmission fiber 8'-d to the optical signals travelling on trunk
system fiber 8'-c. The added optical signals and the signals not
dropped are output onto a trunk system transmission fiber 8'-f.
Usually, the same wavelength is selected for the wavelength of the
optical signal to be dropped and the wavelength of the optical
signal to be added.
[0009] In the WDM optical communication system, normally one or
more optical fiber pairs are used for the upstream and downstream
transmission lines. Accordingly, the wavelength
demultiplexing/multiplexing devices 1'-a and 1'-b are comprised of
more than two of the OADM circuits shown in FIG. 21. The wavelength
demultiplexing/multiplexing device 1'-a (1'-b) is constructed such
that an OADM circuit 30'a intervenes in each trunk system optical
fiber 8'-a and 8'-b, with each OADM circuit connected to a separate
drop and add optical fibers 8-g and 8-h, as shown in FIG. 22.
[0010] Further, to give the OADM circuit the capability of
selecting the wavelength to be dropped or added, it is conceivable
to use an acoustic-optic tunable filter (hereunder, referred to as
"AOTF") capable of varying the permeability for the OADM circuit.
The AOTF is a device in which an acousto-optical effect is applied,
which can be used effectively as an optical filter that can vary
the filtered wavelength. The construction of the AOTF has been
proposed in several types, however, the basic operational principle
is the same.
[0011] FIG. 23 shows an example of an AOTF. The AOTF 30' employs a
radio frequency ("RF") signal, which is input to an electrode 30'-1
(IDT, hereunder referred to as a transducer) through a control port
30-7 to thereby produce a surface acoustic wave ("SAW"). The SAW
propagates in an SAW cladding 30'-2, and is absorbed by an SAW
absorber 30'-3. On the other hand, the optical signals come in from
an optical input port 01, and are polarized and split by a
Polarization Beam Splitter ("PBS") 30'-4 into two optical
waveguides. The SAW and the optical signals overlap and interfere,
to polarize only the optical signals having a wavelength
corresponding to the frequency of the SAW. This is due to the
acousto-optical effect. The selectively polarized optical signals
are split off by a PBS 30'-5 at the output. The polarized optical
signals are output from the optical output port 02', and the
non-polarized optical signals are output from an optical output
port 01'. At the same time, other optical signals are introduced at
optical input port 02. There is a one-to-one correspondence between
the frequency of the RF signal frequency, namely the frequency of
the SAW, and the wavelength of the optical signal to be polarized,
under a constant temperature. In other words, it is possible to
select the wavelength of an optical signal to be output by varying
the RF signal frequency.
[0012] When the AOTF 30' is used as in an OADM, the optical input
port 01 is usually used as the main input port, the optical input
port 02 as the add light input port, the optical output port 01' as
the main output port and the optical output port 02' as the drop
light input port. When the RF signal is supplied to the transducer,
it is possible to simultaneously add and drop optical signals
having a wavelength corresponding to the frequency of the RF
signal. Further, if a plurality of RF signals of different
frequencies are supplied to the electrodes, it is possible to
select optical signals having a plurality of wavelengths
respectively corresponding to those RF signals. That is, the
foregoing construction is very effective for use with an OADM
filter that simultaneously adds and drops optical signals having a
plurality of wavelengths. The AOTF is bi-directional in principle,
and to replace the input port with the output and vice versa will
maintain the same operation.
[0013] The AOTF 30' shown in FIG. 24 may be used in the wavelength
demultiplexing/multiplexing device shown in FIG. 22. However, the
construction shown in FIG. 22 requires two AOTFs, and moreover,
requires two RF signal sources and two driving circuits to drive
the two AOTFs. Accordingly, the device becomes complicated, and
this is a problem.
SUMMARY OF THE INVENTION
[0014] Accordingly, it is an object of the present invention to
switch optical signals to and from an optical fiber in a wavelength
division multiplexed transmission system.
[0015] It is further object of the present invention to switch
optical signals from a bi-directional transmission line.
[0016] It is another object of the present invention to optionally
select wavelength of the switched signals.
[0017] It is a still further object of the present invention to
reduce the number of devices required to switch signals from a
bi-directional optical fiber.
[0018] These and other objects are accomplished by providing an
optical device having an optical switching unit and a variable
filter. The optical switching unit connects a pair of single
direction optical transmission lines to a bi-directional optical
transmission line carrying optical signals of different wavelengths
in different directions relative to the optical switching unit. The
single direction optical transmission lines carry optical signals
in single different directions relative to the optical switching
unit. The variable filter has first and second opposing terminal
pairs such that optical signals of different wavelengths input to
one terminal of one terminal pair are filtered with a portion of
the different wavelengths being output to one terminal of the
opposing terminal pair and the remainder of the different
wavelengths being output to the other terminal of the opposing
terminal pair. The bi-directional optical transmission line is
coupled to one terminal of the variable filter.
[0019] Alternatively, an optical device may have an acousto-optic
tunable filter having first and second sides, a bi-directional
optical transmission line connected to one side of the
acousto-optic tunable filter, and an optical switching unit. The
optical switching unit connects the bi-directional optical
transmission line and two single direction optical transmission
lines such that an optical signal travelling from the acousto-optic
tunable filter is output to one of the single direction optical
transmission lines and an optical signal travelling to the
acousto-optic tunable filter is input from the other of the single
direction optical transmission lines.
[0020] Alternatively, a wavelength division multiplexed
transmission system includes a multiplexing device and a pair of
transmit/receive terminal stations. The transmit/receive terminal
stations communicate to each other The multiplexing device is
provided within a communication line between the pair of optical
transmit/receive terminal stations. The multiplexing device has an
acousto-optic tunable filter having first and second sides, a pair
of bi-directional optical transmission lines connected respectively
to the first and second sides of the acousto-optic tunable filter,
and a pair of optical switching units. Each of the optical
switching units connect one of the bi-directional optical
transmission lines to two single direction optical transmission
lines such that for each optical switching unit, an optical signal
travelling from the acousto-optic tunable filter is output to one
of the single direction optical transmission lines and an optical
signal travelling to the acousto-optic tunable filter is input from
the other of the single direction optical transmission lines.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] The invention will now be described in more detail in
connection with the attached drawings in which like reference
characters represent like elements, wherein:
[0022] FIG. 1 is a block diagram illustrating a WDM transmission
system employing a wavelength demultiplexing/multiplexing device
related to a first embodiment of the invention;
[0023] FIG. 2 is a block diagram illustrating a first modification
to the WDM transmission system shown in FIG. 1;
[0024] FIG. 3 is a block diagram illustrating a WDM transmission
system employing a wavelength demultiplexing/multiplexing device
related to a second embodiment of the present invention;
[0025] FIG. 4 is a block diagram illustrating a first modification
to the WDM transmission system shown in FIG. 3;
[0026] FIG. 5 is a block diagram illustrating a second modification
to the WDM transmission system shown in FIG. 3;
[0027] FIG. 6 is a block diagram illustrating a WDM transmission
system employing a wavelength demultiplexing/multiplexing device
related to a third embodiment of the present invention;
[0028] FIGS. 7(a) and 7(b) are block diagrams illustrating the
operation of a switch of the WDM transmission system shown in FIG.
6;
[0029] FIG. 8 is a block diagram illustrating a WDM transmission
system employing a wavelength demultiplexing/multiplexing device
related to a fourth embodiment of the present invention;
[0030] FIG. 9 is a chart illustrating a wavelength arrangement of
the WDM transmission system shown in FIG. 8;
[0031] FIG. 10 is a block diagram to illustrating an application of
the WDM transmission system shown in FIG. 8;
[0032] FIG. 11 is a chart illustrating a wavelength arrangement of
the WDM transmission system shown in FIG. 10;
[0033] FIG. 12 is a block diagram illustrating a modification to
the WDM transmission system shown in FIG. 8;
[0034] FIG. 13 is a chart illustrating a wavelength arrangement of
the WDM transmission system shown in FIG. 12;
[0035] FIG. 14 is a block diagram illustrating a WDM transmission
system employing a wavelength demultiplexing/multiplexing device
related to a fifth embodiment of the present invention;
[0036] FIG. 15 is a block diagram illustrating an application of
the WDM transmission system shown in FIG. 14;
[0037] FIGS. 16(a), 16(b) are block diagrams illustrating the
operation of a switch relating of the WDM transmission system shown
in FIG. 15;
[0038] FIG. 17 is a block diagram illustrating a bi-directional
wavelength switching device related to a sixth embodiment of the
invention;
[0039] FIG. 18 is a block diagram illustrating a modification to
the bi-directional wavelength switching device shown in FIG.
17;
[0040] FIG. 19 is a block diagram illustrating an application of
the bi-directional wavelength switching device shown in FIG.
17;
[0041] FIG. 20 is a block diagram illustrating a generally proposed
wavelength division multiplexed transmission system;
[0042] FIG. 21 is a block diagram illustrating an OADM circuit;
[0043] FIG. 22 is a block diagram illustrating a wavelength
demultiplexing/multiplexing device employing OADM circuits;
[0044] FIG. 23 is a top view of an AOTF; and
[0045] FIG. 24 is a block diagram illustrating a wavelength
demultiplexing/multiplexing device using AOTFs.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0046] The invention will now be described in detail with reference
to the accompanying drawing and preferred embodiments given by way
of example only, and not limitation.
[0047] (a) First Embodiment
[0048] FIG. 1 is a block diagram to illustrate a WDM transmission
system in which a wavelength demultiplexing/multiplexing device 1
relating to the first embodiment of the invention is applied. A WDM
transmission system 100 shown in FIG. 1 is constructed such that an
optical fiber pair 7 (trunk system transmission line) as a
bi-directional optical signal transmission means connects optical
transmit/receive terminal stations 50a and 50b to transmit and
receive wavelength division multiplexed signals. The wavelength
demultiplexing/multiplexing device 1 is positioned between the
optical transmit/receive terminal stations 50a and 50b.
[0049] The optical fiber pair 7 contains one optical fiber 8
serving as the upstream line and another optical fiber 9 serving as
the downstream line.
[0050] The wavelength demultiplexing/multiplexing device 1 drops
only selected wavelength optical signals from the WDM signals
(.lambda.1, .lambda.2, . . . , .lambda.n) transmitted by the
optical transmit/receive terminal station 50a, propagating through
the trunk system transmission fiber 8 into a transmission fiber 15.
Also, the wavelength demultiplexing/multiplexing device 1 adds
optical signals input from a transmission fiber 25, to the rest of
the optical signals. The device outputs the added optical signals
to the trunk system transmission fiber 8 leading to the optical
transmit/receive terminal station 50b.
[0051] Here, the wavelength demultiplexing/multiplexing device 1 is
connected to a branch terminal station 60 through the
bi-directional transmission fibers 15, 25. Usually, an identical
wavelength is selected for the wavelength of the optical signal to
be dropped and the wavelength of the optical signal to be
added.
[0052] In order to accomplish the foregoing, the wavelength
demultiplexing/multiplexing device 1 is configured with an
acousto-optical tunable filter (hereunder, referred to as "AOTF")
30, a first switching unit 10, and a second switching unit 20. The
AOTF 30 (equivalent to the AOTF 30' in FIG. 24) is a device in
which the acousto-optic effect is applied, and is able to control
the output optical signals based on the RF signal supplied to a
control port 30-7. The AOTF 30 executes a switch control so as to
output the optical signals at terminals 01, 02, 01', 02', from a
desired one of terminals 01, 02, 01', 02'. The following Table 1
illustrates the switch control of the input/output signals by the
AOTF 30.
1TABLE 1 output terminal of light input terminal of input
signal/output signal optical signal signal RF signal present RE
signal not present 01 .lambda.-1, .lambda.'-1 01'/.lambda.'-1
01'/.lambda.-1, .lambda.'-1 02'/.lambda.-1 02 .lambda.-3,
.lambda.'-3 01'/.lambda.-3 02'/.lambda.-3, .lambda.'-3
02'/.lambda.'-3 01' .lambda.-2, .lambda.'-2 01/.lambda.'-2
01/.lambda.-2, .lambda.'-2 02/.lambda.-2 02' .lambda.-4,
.lambda.'-4 01/.lambda.-4 02/.lambda.-4, .lambda.'-4
02/.lambda.'-4
[0053] In the Table, the input terminal and the output terminal
each signify an terminal. The optical signals propagating through
the trunk optical fibers 8, 9 are input to the terminals 02, 02',
and are output from the terminals 02, 02'. On the other hand, the
optical signals propagating through the optical fiber 25 are input
and output from the terminal 01, and the optical signals
propagating through the optical fiber 15 are input and output to
and from terminal 01'.
[0054] Further, since the light wavelength at which the
acousto-optic effect is generated (the SAW frequency generated by
the transducer) corresponds to a known RF signal frequency under a
constant temperature, the AOTF 30 is able to select the optical
signals to be output from the terminals 01, 02, 01', 02' by varying
the RF signal frequency.
[0055] As shown in Table 1, for example, when the WDM signals
.lambda.-3, .lambda.'-3 are input to terminal 02 from the optical
transmit/receive terminal station 50a and the RF signal is ON and
input to the control port 30-7, the AOTF 30 outputs, as a drop
optical signal of a desired wavelength, the optical signal
.lambda.-3 into the optical fiber 15 as the bi-directional
transmission line leading to the branch terminal station 60 from
terminal 01'. Further, when the AOTF 30 receives the optical
signals .lambda.-1, .lambda.'-1 propagating through the optical
fiber 25 as the bi-directional transmission line, through the
terminal 01, from the branch terminal station 60, the AOTF 30
outputs a desired optical signal .lambda.-1 as an added optical
signal from the terminal 02'.
[0056] When the WDM signals .lambda.-3, .lambda.'-3 are input to
the terminal 02 from the optical transmit/receive terminal station
50a and the RF signal is OFF and not input to the control port
30-7, the AOTF 30 outputs from the terminal 02' the optical signals
.lambda.-3, .lambda.'-3 toward the optical circulator 11 leading to
the optical fibers 8, 9. Further, when the AOTF 30 receives the
optical signals .lambda.-1, .lambda.'-1 at the terminal 01, from
the branch terminal station 60 via fiber 25, the AOTF 30 outputs
the optical signals .lambda.-1, .lambda.'-1 from the terminal
01'.
[0057] The optical signals in the parenthesis in FIG. 1 illustrate
these when the RF signal is not input to the control port 30-7, in
the state of the RF signal being OFF.
[0058] Further, the foregoing optical signals .lambda.-3,
.lambda.'-3, .lambda.-2, .lambda.'2, etc., each do not necessarily
represent an optical signal of one wavelength, but may represent an
optical signal containing a plurality of wavelengths.
[0059] When the RF signal is input to the AOTF 30, the wavelength
of an optical signal on which the acousto-optic effect by the SAW
exerts the influence is denoted by .lambda., on the other hand, the
wavelength of an optical signal on which it does not exert the
influence is denoted by .lambda.'. That is, if a prime symbol "'"
is used, the optical signal changes terminals depending on whether
the RF signal is present. The i of .lambda.-i indicates the
terminal port number to which the optical signal .lambda.-i is
input.
[0060] The RF signal input to the control port 30-7 is supplied
from an RF signal source (not illustrated), which is located inside
the wavelength demultiplexing/multiplexing device 1. However, the
RF signal source (not illustrated) alternatively may be provided in
one of the optical transmit/receive terminal stations 50a, 50b, or
in the branch terminal station 60. Hereunder, the embodiments will
be described referring to the RF signal source being provided
inside the wavelength demultiplexing/multiplexing device 1.
However, it should be recognized that the RF signal source may also
be installed outside the wavelength demultiplexing/multiplexing
device 1.
[0061] When the RF signal source is provided at a place remote from
the wavelength multiplexing/demultiplexing device 1, such as at the
optical transmit/receive terminal station 50b, the RF signal
generated at station 50b can be converted into an optical signal
and transmitted through one of the optical fibers 8, 9, 15 and 25.
The optical signal can then be converted back to an RF signal and
input to control port 30-7.
[0062] The first switching circuit 10 has an optical circulator
connected to one of the terminals (02') of the AOTF 30. The
switching unit 10 switches the input/output line from the AOTF 30
to the bi-directional optical transmission lines 8, 9. The optical
circulator shown in FIG. 1 has three terminals, and transmits
energy input from one terminal to an adjacent terminal, in a
direction shown by the arrow. (The optical circulator could have a
different number of terminals.) The optical circulator 11 has
terminals C1, C2 and C3. The terminal C1 is connected to the
optical fiber 9, the terminal C2 is connected to the terminal 02'
of the AOTF 30, and the terminal C3 is connected to the optical
fiber 8. When an optical signal is input from the terminal C1, the
circulator 11 guides the optical signal in the direction shown by
the arrow, and outputs the optical signal from terminal C2. That
is, terminal C2 is the adjacent terminal to terminal C1. Similarly,
optical signals input from terminal 02 of AOTF 30 enter the optical
circulator 11 through terminal C2 and exit the optical circulator
through terminal C3.
[0063] On the other hand, the second switching circuit 20 is
connected to the other input/output pair of the AOTF 30. That is,
switching circuit 20 is connected to terminals 01 and 02 of AOTF
30. The switching circuit 20 has an optical circulator 21 which
switches the input/output line from terminal 02 to the -optical
fibers 8 and 9. The optical circulator 21 has three terminals and
operates in the same manner as described above with regard to
optical circulator 11. That is, an optical signal enters the
optical circulator 21 at one terminal, is moved in the direction
shown by the arrow, and exits the optical circulator 21 at the next
adjacent terminal.
[0064] With the first switching unit 10, the second switching unit
20 and AOTF 30, the wavelength demultiplexing/multiplexing device 1
can add or drop optical signals having a desired wavelength.
According to the structure described with reference to FIG. 1,
optical signals .lambda.-4 and .lambda.'-4 propagate through
optical fiber 9 from the transmit/receive terminal station 50b, and
are input to terminal C1 of the optical circulator 11. Optical
signals .lambda.-4 and .lambda.'-4 are output to terminals 02' of
the AOTF via terminal C2 of the optical circulator 11. Similarly,
the optical circulator 11 receives optical signals .lambda.-1,
.lambda.'-3 (.lambda.-3, .lambda.'-3) from terminal 02' of the AOTF
30. These optical signals are applied to terminal C2 of the optical
circulator 11 and output to terminal C3 having optical fiber 8
connected thereto.
[0065] Similarly, the second switching unit 20 receives optical
signals .lambda.-3, .lambda.'-3 at terminal C1 of the optical
circulator 21. The optical signals, which originated from optical
transmit/receive terminal station 50a via optical fiber 8, are
output to terminal 02 of the AOTF 30. Likewise, optical signals
input to terminal C2 of optical circulator 21 are output from
terminal C3 of optical circulator 21.
[0066] The optical signals input to terminals 01, 02, 01' and 02'
are output from different terminals of the AOTF 30. Specifically,
the AOTF 30 receives an RF signal at control port 30-7 to generate
a surface acoustic wave (SAW) by a transducer in the AOTF 30. There
is an acousto optic effect between the SAW and the input light.
This allows the AOTF 30 to manipulate from where the optical
signals are output, thus enabling AOTF 30 to add or drop specific
wavelength components.
[0067] The AOTF 30 receives the optical signals .lambda.-3,
.lambda.'-3 from transmit/receive terminal station 50a via terminal
02. Optical signal .lambda.-3 is output from terminal 01' as a drop
signal (RF input present). On the other hand, AOTF 30 receives
optical signal .lambda.-2, .lambda.'-2 from the branch terminal
station 60 via terminal 01'. AOTF 30 outputs optical signal
.lambda.-2 from terminal 02 when the RF signal is present, thus
adding optical signal .lambda.-2.
[0068] With the device shown in FIG. 1, optical signals can be
switched with AOTF 30 and optical circulators 11, 21. Because the
AOTF 30 has a bi-directional operation, and because optical
circulators 11, 21 combine optical fibers, the number of AOTFs can
be reduced.
[0069] (a1) Modification of the First Embodiment
[0070] FIG. 2 is a block diagram illustrating a modification to the
WDM transmission system shown in FIG. 1. In the WDM transmission
system 110 transmit/receive terminal stations 50a and 50b
communicate through optical fiber 8-1. Optical fiber 8-1 is a
bi-directional optical fiber in which signals travel in both
directions. Like the device shown in FIG. 1, the
demultiplexing/multiplexing device 1-1 is positioned between the
optical transmit/receive terminal stations 50a and 50b.
[0071] The device 1-1 has first and second switching units 10-1,
20-1, each containing a three terminal optical circulator 11-1,
21-1. In this case, however, the lines leading from branch terminal
station 60 are one-way transmission lines, whereas in FIG. 1,
bi-directional transmission lines were used from terminal station
60. Drop lines 15-1b, 25-1b and add lines 15-1a, 25-1a are
provided. Optical circulator 21-1 connects lines 25-1a and 25-1b to
terminal 02 of AOTF 30. Similarly, optical circulator 11-1 connects
optical lines 15-1a and 15-1b to terminal 02' of AOTF 30. Both
optical circulator 21-1 and optical circulator 11-1 operate in the
same manner as described with regard to FIG. 1.
[0072] As can be seen in FIG. 2, optical signals .lambda.-4 and
.lambda.'-4 are supplied to terminal 02' of AOTF 30 via line 15-1a
and terminals C1 and C2 of optical circulator 11-1. Similarly,
optical signal .lambda.-1, .lambda.'-3 (.lambda.-3, .lambda.'-3)
are supplied to branch terminal station 60 from terminal 02' of
AOTF 30 via transmission line 15-1b, and terminal C3 and C2 of
optical circulator 11-1. The AOTF 30 switches signals in the same
manner shown in table 1 with regard to the first embodiment.
[0073] With regard to switching unit 20-1, optical signals
.lambda.-3, .lambda.'-3 are provided from terminal station 60 to
terminal 02 of AOTF 30 via transmission line 25-1a and terminals C1
and C2 of optical circulator 21-1. Optical signals .lambda.-2,
.lambda.'-2 (.lambda.-4, .lambda.'-4) are sent from terminal 02 of
AOTF 30 to branch terminal station 60 via terminals C2 and C3 of
optical circulator 21-1 and transmission line 25-1b. With the
switching units 10-1, 20-1 and the AOTF 30, the device 1-1 operates
substantially the same as the device shown in FIG. 1. With the
device shown in FIG. 2, fewer AOTFs are required, and thus, price
is reduced.
[0074] (b) Second Embodiment
[0075] FIG. 3 is a block diagram illustrating a WDM transmission
system employing a wavelength demultiplexing/multiplexing device of
the second embodiment. The WDM transmission system 120 shown in
FIG. 3 is substantially the same to the WDM transmission system 100
shown in FIG. 1 with the exception that in FIG. 3, all of the
components 50a, 50b, 60 are connected to the
demultiplexing/multiplexing device 120 via one way transmission
lines. To the contrary, in FIG. 1, bi-directional transmission
lines were used to connect branch terminal station 60.
[0076] The wavelength demultiplexing/multiplexing device 2 drops
selected optical signals from the WDM signals (.lambda.1,
.lambda.2, . . . , .lambda.n), which WDM signals are transmitted by
the transmit/receive terminal station 50a and propagated through
transmission fiber 8. The signals are dropped to branch terminal
station 60 via drop transmission fiber 15-2b. Device 2 adds optical
signals input from branch terminal station 60 via transmission
fiber 25-2a. The signals are added to the other optical signals and
output to transmit/receive terminal station 50b via transmission
fiber 8. Further, the wavelength demultiplexing/multiple- xing
device 2 drops selected optical signals from transmit/receive
terminal station 50b to drop transmission fiber 25-2b. Device 2
adds optical signals from add transmission fiber 15-2a to
transmission fiber 9, providing the added signals to
transmit/receive terminal station 50a.
[0077] Usually, the same wavelength is used as the dropped
wavelength and the added wavelength. The wavelength
demultiplexing/multiplexing device has first and second switching
units 10-2, 20-2. These switching units 10-2, 20-2 differ from the
switching units 10, 20 shown in FIG. 1 in that switching units 10-2
and 20-2 each have two optical circulators. With this
configuration, each of the trunk optical fibers 8, 9 is connected
to a separate optical circulator. The optical circulators 11-2a,
11-2b, 21-2a, 21-2b, each operate in the same manner as the optical
circulators described above.
[0078] The first switching unit 10-2 sends optical signals
.lambda.-4, .lambda.'-4 from branch terminal station 60 to terminal
01' of AOTF 30 via transmission line 15-2a and optical circulator
11-2a. The first switching unit 10-2 also send the optical signals
.lambda.'-1, .lambda.-3 (.lambda.-1, .lambda.'-1) from the terminal
01' of the AOTF 30 to the optical transmit/receive terminal station
50b via the optical circulator 11-2a and the optical fiber 8. The
first switching unit 10-2 further sends the optical signals
.lambda.-2, .lambda.'-2 from the optical transmit/receive terminal
station 50b to terminal 02' of AOTF 30 via optical fiber 9 and
optical circulator 11-2b. Yet further, first switching unit 10-2
sends optical signals 11-1, .lambda.'-3 (.lambda.-3, .lambda.'-3)
from terminal 02' of AOTF 30 to branch terminal station 60 via
optical circulator 11-2b and drop line 15-2b.
[0079] The second switching unit 20-2 sends optical signals
.lambda.-1, .lambda.'-1 from the optical transmit/receive terminal
station 50a to terminal 01 of the AOTF 30 via optical fiber 8 and
optical circulator 21-2a. Also, the second switching unit 20-2
sends optical signals .lambda.-2, .lambda.'-4 (.lambda.-4,
.lambda.'-4) from terminal 01 of AOTF 30 to branch terminal station
60 via optical circulator 21-2a and drop line 25-2b. The wavelength
demultiplexing/multiplexing device of the second embodiment drops
and adds desired optical signals with the functions of the first
switching unit 10-2, the second unit 20-2 and the AOTF 30. The
wavelength of the signal dropped or added depends on the RF signal
supplied to AOTF 30. More specifically, by varying the ON/OFF, the
number and frequency of the RF signals, the wavelength of the
optical signals is changed. The wavelength of the optical signals
dropped and added corresponds to the RF signal frequency, which RF
signal is input to control port 30-7 of AOTF 30. Of course, the
optical signals are dropped and added as described above only when
the RF signal is ON.
[0080] When the RF signal is ON and optical signals .lambda.-1,
.lambda.'-1 are input to terminal 01, optical signal .lambda.-1 is
output to terminal 02' as a drop signal and optical signal
.lambda.'-1 is output to terminal 01'. In this case, the drop
signal .lambda.-1 is transmitted to the branch terminal station 60
via the optical circulator 11-2b and the drop line 15-2b.
[0081] Further, when the RF signal supplied to control port 30-7 is
ON and optical signals .lambda.-4, .lambda.'-4 are supplied to
terminal 01' from branch terminal station 60, optical signal
.lambda.-4 is output from terminal 02 as an add signal and optical
signal .lambda.'-4 is output from terminal 01. Here, optical signal
.lambda.-4 (an add signal) is transmitted to transmit/receive
terminal station 50a through the optical circulator 21-2b and the
system optical fiber 9.
[0082] On the other hand, when no RF signal is supplied to AOTF 30,
namely RF signal is OFF, the wavelength demultiplexing/multiplexing
device 2 does not drop or add optical signals. That is, the signals
entering device 2 on lines 8 and 9 are the same signals exiting
device 2 on optical fibers 8, 9. For example, optical signals
.lambda.-1, .lambda.'-1 from optical transmit/receive terminal
station 50a are propagated on optical fiber 8 and input at terminal
C1 of the optical circulator 21-2a. These signals are transmitted
to terminal 01 of AOTF 30 and output back to optical fiber 8 via
terminal 01', and terminals C2 and C3 of optical circulator 11-2a.
In this manner, the wavelength demultiplexing/multiplex- ing device
of the second embodiment can switch optical signals with AOTF 30
and optical circulators 11-2a, 11-2b, 21-2a, 21-2b. The number of
AOTFs required is thus reduced, as is the cost.
[0083] (b1) First Modification of the Second Embodiment
[0084] FIG. 4 shows a WDM transmission system including a
wavelength demultiplexing/multiplexing device, which device is a
first modification of the second embodiment. The transmission
system shown in FIG. 4 differs from that shown in FIG. 3 in the
connections of optical circulators 21-2a and 21-2b. Otherwise, the
device is substantially similar to that shown in FIG. 3, and has
transmit/receive terminal stations 50a and 50b with wavelength
demultiplexing/multiplexing device 2-1 therebetween. In the first
switching unit 10-21, the optical fiber 9 is connected to terminal
01' of AOTF 30 via terminals C1 and C2 of optical circulator 11-2b.
Terminal 02' of AOTF 30 is connected to optical fiber 8 via
terminals C2 and C3 of optical circulator 11-2a.
[0085] On the other hand, in the second switching unit 20-21, both
optical fibers 8 and 9 are connected to optical circulator 21-2a.
Optical fiber 9 is connected to terminal C3 and optical fiber 8 is
connected to terminal C1, with terminal C2 connected to terminal 01
of AOTF 30. Therefore, optical signals from transmit/receive
terminal station 50 are transmitted to AOTF 30 via optical
circulator 21-2a. On the other hand, optical signals .lambda.'-2,
.lambda.-4 (.lambda.-2, .lambda.'-2) from the terminal 01 of AOTF
30 are transmitted to the transmit/receive terminal station 50 via
the optical circulator 21-2a and optical fiber 9.
[0086] Optical circulator 21-2b, on the other hand, is connected to
add line 25-2a, drop line 25-2b and terminal 02 of AOTF 30. Optical
signals .lambda.-3, .lambda.'-3 from branch terminal station 60 are
supplied to AOTF 30 via add line 25-2a and optical circulator
21-2b. Output signals from terminal 02 of AOTF 30, .lambda.'-4,
.lambda.-2 (.lambda.-4, .lambda.'-4), are transmitted to branch
terminal station 60 via terminals C2 and C3 of optical circulator
21-2b and drop line 25-2b.
[0087] The wavelength demultiplexing/multiplexing device 2-1 drops
optical signals having selected wavelength. The optical signals are
dropped from or added to the optical signals propagating through
optical fibers 8, 9. The signals are selected by varying the ON/OFF
state, the number and the frequency of the RF signal supplied to
AOTF 30.
[0088] For example, optical signals .lambda.-1, .lambda.'-1 from
the transmit/receive terminal station 50a are input to terminal 01
of AOTF 30 and output from terminal 01' or 02' of AOTF 30. When the
RF signal is ON, optical signal .lambda.-1 is output from terminal
02' and optical signal .lambda.'-1 is output from terminal 01'. On
the other hand, when an RF signal is not supplied to the AOTF 30,
that is, RF signal is OFF, optical signals .lambda.-1, .lambda.'-1
from optical transmit/receive terminal station 50a are directed to
branch terminal station 60 via optical fiber 8, terminal C1 and C2
of optical circulator 21-2a, terminals 01 and 01' of AOTF 30,
terminals C2 and C3 of optical circulator 11-2b and drop line
15-2b. Also, when an RF signal is not supplied to control port
30-7, optical signals .lambda.-3, .lambda.'-3 from branch terminal
station 60 are transmitted to the optical transmit/receive terminal
station 50b via the add fiber 25-2a, terminals C1 and C2 of optical
circulator 21-2, terminals 02 and 02' AOTF 30 and optical fiber 8.
Therefore, when an RF signal is not supplied to AOTF 30, the device
2-1 drops all optical signals (.lambda.-1, .lambda.'-1) from the
optical transmit/receive station 50a. Further, the device 2-1 sends
all optical signals (.lambda.-2, .lambda.'-2) from the optical
transmit/receive terminal station 50b to the optical
transmit/receive terminal station 50a without dropping any
signals.
[0089] (b2) Second Modification of the Second Embodiment
[0090] FIG. 5 is a block diagram illustrating a WDM transmission
system which includes a wavelength demultiplexing/multiplexing
device according to a second modification of the second embodiment.
In FIG. 5, both the first switching unit 10-21 and the second
switching unit 10-22 are configured like the second switching unit
20-21 in FIG. 4. That is, terminals 02 and 02' of AOTF 30 are
connected only to branch terminal station 60. The first switching
unit 10-22 in FIG. 5 is different from the first switching unit
10-21 in FIG. 4. The difference lies in the connections of the
optical circulators 11-2a', 11-2b'. For optical circulator 11-2b',
terminal C1 is connected to optical transmit/receive terminal
station 50b through optical fiber 9, terminal C2 is connected to
terminal 01' of AOTF 30 and terminal C3 is connected to
transmit/receive terminal station 50b through optical fiber 8.
[0091] In this manner, optical signals .lambda.-2, .lambda.'-2 from
the optical transmit/receive terminal station 50b are transmitted
to the AOTF 30 through the optical circulator 11-2b'. Also, optical
signals .lambda.'-1, .lambda.-3 (.lambda.-1, .lambda.'-1) from
terminal 01' of the AOTF 30 are transmitted to the optical
transmit/receive terminal station 50b through the optical
circulator 11-2b'.
[0092] For optical circulator 11-2a', terminal C1 is connected to
the branch terminal station 60 through add line 15-2a, terminal C2
is connected to the terminal 02' of AOTF 30 and, terminal C3 is
connected to the branch terminal station 60 through optical drop
line 15-2b. Therefore, add optical signals .lambda.-4, .lambda.'-4
from the branch terminal station 60 are transmitted to the AOTF 30
through the optical circulator 11-2a'. Optical signals .lambda.'-3,
.lambda.-1 (.lambda.-3, .lambda.'-3) from terminal 02' of AOTF 30
are transmitted to the branch terminal station 60 through the
optical circulator 11-2a'.
[0093] In operation, when an RF signal is ON and supplied to
control port 30-7 AOTF 30, device 2-2 drops from the optical
signals propagating in optical fibers 8, 9, which correspond to the
RF signal. Optical signals transmitted on add lines 25-2a, 15-2b
are added to the optical signals travelling on fibers 8, 9 if the
optical signals correspond to the RF signal.
[0094] For example, optical signals .lambda.-1, .lambda.'-1 from
the optical transmit/receive terminal station 50a are input to
terminal 01 of AOTF 30, and these optical signals .lambda.-1,
.lambda.'-1 can be output from a selected one of terminals 01', 02'
of AOTF 30. When the AOTF 30 is supplied with an RF signal at
control port 30-7, optical signal .lambda.-1 is output from
terminal 02' and sent to the branch terminal station 60 via
terminals C2 and C3 of optical circulator 11-2a' and drop line
15-2b. On the other hand, optical signal .lambda.'-1 is output from
terminal 01' and sent to the optical transmit/receive terminal
station 50b via terminals C2 and C3 of optical circulator 11-2b'
and optical fiber 8. The device 2-2 drops to branch terminal
station 60, an optical signal corresponding to the RF signal
(optical signal at which the acousto-optic effect is created with a
surface acoustic wave generated by a transducer in the AOTF
30).
[0095] Optical signal .lambda.-3, .lambda.'-3 from branch terminal
station 60 are input to terminal 02 of AOTF 30 and output from a
desired one of terminals 01' and 02' of AOTF 30. When an RF signal
is supplied to control port 30-7 optical signal .lambda.-3 is
output from terminal 01' of AOTF 30 and sent to the optical
transmit/receive station 50b via terminals C2 and C3 of optical
circulator 11-2b' and optical fiber 8. On the other hand, optical
signal .lambda.'-3 is output to terminal 02' and sent to the branch
terminal station 60 via terminal C2 and C3 of optical circulator
11-2a' and drop line 15-2b. That is, device 2-2 adds signals
supplied from add line 25-2a if the optical signal corresponds to
the RF signal. The added signals are transmitted to optical
transmit/receive terminal station 50b.
[0096] On the other hand, when no RF signal is supplied to control
port 30-7, device 2-2 does not drop or add optical signals. The
optical signals from optical transmit/receive terminal station 50a
are supplied to optical transmit/receive terminal station 50b and
vice versa.
[0097] (c) Third Embodiment
[0098] FIG. 6 is a block diagram illustrating a WDM transmission
system which includes a wavelength demultiplexing/multiplexing
device related to a third embodiment of the present invention.
[0099] As can be seen from FIG. 6, the second switching unit 20-21
is substantially the same as the second switching units 20-21 shown
in FIGS. 4 and 5. The first switching unit 10-3, however, is
different. The first switching unit 10-3 employs two optical
circulators 11-2a, 11-2b. The optical circulators 11-2a, 11-2b
switch between the optical fibers 8, 9, the drop line 15-2b and the
add line 15-2a. The first switching unit 10-3 is provided with a
switch (SW) 12, and the first switching unit 10-3 is different from
the first switching units 10-2, 10-21, 10-22 of the second
embodiment in this regard. Switch 12 acts as a forced switch
unit.
[0100] Switch 12 is activated by SW control terminal 12-1 to
forceably control switch 12. Switch 12 operates independently of
the RF frequency supplied to port 30-7 of AOTF 30 and switches all
wavelengths. However, a switching signal is generally supplied to
control terminal 12-1 to switch 12 when the RF signal is input to
control port 30-7. Although not limited, the switching signal will
be described as a signal to turn the switch ON.
[0101] FIGS. 7(a) and 7(b) are block diagrams illustrating the
operation of switch 12 related to the third embodiment. FIG. 7(a)
illustrates how the switch 12 operates when the switch is OFF, and
FIG. 7b illustrates how the switch 12 operates when the switch 12
is ON.
[0102] When the switch 12 is OFF, the switching signal is not
supplied thereto. In this case, optical signals .lambda.-1,
.lambda.'-1 from terminal C3 of the optical circulator 11-2b are
forceably switched into the optical fiber 8 for transmission to
optical transmit/receive terminal station 50b. On the other hand,
when switch 12 is ON with the switch signal supplied thereto,
optical signal .lambda.'-1 from terminal C3 of the optical
circulator 11-2b is switched to the optical drop line 15-2b. This
of course assumes that the RF signal corresponding to .lambda.-1 is
being supplied to control port 30-7 at the same time the switching
signal is being supplied to control terminal 12-1.
[0103] The wavelength demultiplexing/multiplexing device 3
selectively drops and adds signals. For example, as optical signals
.lambda.-1, .lambda.'-1 are transmitted from optical
transmit/receive terminal station 50a and input at terminal 01 of
AOTF 30, the optical signals .lambda.-1, .lambda.'-1 can be output
from a selected one of terminals 01', 02' of AOTF 30. When an RF
signal is supplied to control port 30-7 (RF signal is ON), optical
signal .lambda.-1 is output from terminal 02'. As mentioned above,
when the RF signal is supplied, the switching signal is generally
supplied concurrently. Accordingly, the optical signal .lambda.-1
from terminal 02' of AOTF 30 is output to optical transmit/receive
terminal station 50b through terminals C2 and C3 of optical
circulator 11-2a, switch 12 (see FIG. 7(b)) and optical fiber 8. On
the other hand, the optical signal .lambda.'-1 applied to terminal
01 is output to the branch terminal station 60 via terminal 01' of
AOTF 30, terminals C2 and C3 of optical circulator 11-2b, switch 12
(see FIG. 7(b)) and drop line 15-2b. That is, the wavelength
demultiplexing/multiplexing device 3 sends the optical signal
(.lambda.-1) corresponding to the RF signal to the optical
transmit/receive terminal station 50b. The wavelength
demultiplexing/multiplexing device 3 drops the optical signal
(.lambda.'-1) not corresponding to the RF signal.
[0104] When an RF signal is not supplied to control port 30-7, the
switch is generally OFF. In this case, the optical signals
.lambda.-1, .lambda.'-1 input at terminal 01 of the AOTF 30 are
output from terminal 01' of AOTF 30. Both optical signals
.lambda.-1, .lambda.'-1 are sent out to optical transmit/receive
terminal station 50b via terminals C2 and C3 of optical circulator
11-2b, switch 12 (see FIG. 7(a)) and optical fiber 8.
[0105] The device shown in FIG. 6 functions in a similar manner for
optical signals input from fiber 9. More specifically, when optical
signals .lambda.-2, .lambda.'-2 are input to terminal 01' of AOTF
30, the optical signals .lambda.-2, .lambda.'-2 are output from a
selected one terminals 01, 02 of the AOTF 30. When AOTF 30 is
supplied with the RF signal, switch 12 is generally ON. The optical
signal .lambda.-2 is sent from terminal 01' of AOTF 30 to terminal
02. From there, optical signal .lambda.-2 is sent to the branch
terminal station 60 via drop line 25-26. On the other hand, optical
signal .lambda.'-2 is output from the terminal 01 of AOTF 30, and
sent out to the optical transmit/receive terminal station 50a via
optical circulator 21-2a and optical fiber 9. Accordingly, the
optical signal corresponding to the RF signal is sent to the branch
terminal station 60, and the optical signal not corresponding to RF
signal is sent to the optical transmit/receive terminal station
50a.
[0106] When the control port 30-7 of the AOTF 30 is not supplied
with the RF signal, the wavelength demultiplexing/multiplexing
device 3 does not drop or add the optical signals propagating
through the optical fibers 8, 9. Optical switch 12 allows for the
direct control of which signals are sent to the branch terminal
station 60 and the optical transmit/receive terminal station 50b.
Optical switch 12 is provided outside of the AOTF 30, operates
independently, and allows for when an optical signal is not totally
added or totally dropped.
[0107] (d) Fourth Embodiment
[0108] FIG. 8 is a block diagram of a WDM transmission system,
which includes a wavelength demultiplexing/multiplexing device
related to a fourth embodiment of the invention is applied. The
fourth embodiment differs from the previous embodiments in that
only two single direction optical fibers 31, 32 may be necessary to
connect branch terminal station 60. A WDM transmission system 140
employs wavelength demultiplexing/multiplexing device 4 having a
wavelength multiplexer 35 to multiplex optical signals from the
first switching unit 10-3 and the second switching unit 20-21. A
wavelength demultiplexer 36 is provided to split the optical
signals from the branch terminal station 60 into the first
switching unit 10-3 and the second switching unit 20-21. The
optical signal transmitted from the first switching unit 10-3,
propagating through optical drop line 15-2b and the optical signal
transmitted from the second switching unit 20-21, propagating
through the optical drop line 25-2b are multiplexed together by
wavelength multiplexer 35 to be transmitted to branch terminal
station 60 via optical fiber 31. Optical signals from the branch
terminal station 60 travelling on optical fiber 32 are split by
wavelength demultiplexer 36 into the add line 15-2a leading to the
first switching unit 10-3 and the add line 25-2a leading to the
second switching unit 20-21.
[0109] When the wavelength demultiplexing/multiplexing device 4 is
provided with the wavelength demultiplexer 36 and the wavelength
multiplexer 35, it has to be taken into account that the wavelength
of the optical signal to propagate through the optical fiber 31
does not coincide with that of the optical signal to propagate
through the optical fiber 32. FIG. 9 is a chart illustrating a
wavelength arrangement of the WDM transmission system relating to
the fourth embodiment of the invention. According to the example of
the wavelength arrangement shown in FIG. 9, the band of optical
signals in the optical fiber 8 that connects the optical
transmit/receive terminal station 50a with the AOTF 30 is within
the wavelengths .lambda.-1, .lambda.'-1, and the wavelengths
.lambda.'-3, .lambda.'-4 cannot be used. On the other hand, the
band of optical signals in the optical fiber 9 that connects the
optical transmit/receive terminal station 50b with the AOTF 30 is
within the wavelengths .lambda.-2, .lambda.'-2, and the wavelengths
.lambda.-3, .lambda.-4 cannot be used. Thus, the wavelength
arrangement shown in FIG. 9 has a certain restriction for a usable
wavelength range.
[0110] According to the foregoing construction, the wavelength
demultiplexing/multiplexing device 4 relating to the fourth
embodiment of the invention drops and adds a desired optical
signal. For example, optical signals .lambda.-1, .lambda.'-1
transmitted from the optical transmit/receive terminal station 50a
are input to the terminal 01 of the AOTF 30 through the terminals
C1 and C2 of the optical circulator 21-2a. The optical signals
.lambda.-1, .lambda.'-1 can be output from a desired one of
terminals 01', 02' of the AOTF 30.
[0111] Here, when the control port 30-7 of the AOTF 30 is supplied
with an RF signal, namely, the RF signal is ON, the optical signal
.lambda.-1 is output from the terminal 02', and output to the
optical transmit/receive terminal station 50b through the optical
circulator 11-2a and the switch 12. On the other hand, the optical
signal .lambda.'-1 is output from the terminal 01', and output to
the wavelength multiplexer 35 through the optical circulator 11-2b,
the switch 12 and the optical drop line 15-2b. That is, the
wavelength demultiplexing/multiplexing device 4 sends the optical
signal corresponding to the RF signal to the optical
transmit/receive terminal station 50b. Further, the wavelength
demultiplexing/multiplexing device 4 drops the optical signals
which do not correspond to the RF signal.
[0112] On the other hand, when the control port 30-7 of the AOTF 30
is not supplied with the RF signal, namely, the RF signal is OFF,
the optical signals .lambda.-1, .lambda.'-1 from the optical
transmit/receive terminal station 50a are output from the terminal
01' of the AOTF 30. Thereafter, the optical signals .lambda.-1,
.lambda.'-1 are sent out to the switch 12 through the optical
circulator 11-2b. The switch 12 forcibly switches the optical
signals .lambda.-1, .lambda.'-1 into the trunk system optical fiber
8 to transmit the optical signals .lambda.-1, .lambda.'-1 to the
optical transmit/receive terminal station 50b.
[0113] Further, as the optical signals .lambda.-2, .lambda.'-2 from
the optical transmit/receive terminal station 50b are input to
terminal 01' of AOTF 30 through the terminals C1 and C2 of the
optical circulator 11-2b. The optical signals .lambda.-2,
.lambda.'-2 can be output from a selected one of terminals 01, 02
of the AOTF 30.
[0114] When the control port 30-7 of the AOTF 30 is supplied with
the RF signal, the optical signal .lambda.-2 is output from the
terminal 02, and sent out to the wavelength multiplexer 35 through
the optical circulator 21-2b and the drop line 25-2b. On the other
hand, when the control port 30-7 of the AOTF 30 is not supplied
with the RF signal, namely, the RF signal is OFF, the optical
signals .lambda.-2, .lambda.'-2 from the optical transmit/receive
terminal station 50b are output from the terminal 01 of the AOTF
30. Thereafter, the optical signals .lambda.-1, .lambda.'-1 are
sent out to the optical transmit/receive terminal station 50a
through optical circulator 21-2a.
[0115] Optical signals .lambda.'-1, etc., transmitted from the
first switching unit 10-3, propagating through the drop line 15-2b
and the optical signals .lambda.-2, etc., transmitted from the
second switching unit 20-21, propagating through the drop line
25-2b are multiplexed by the wavelength multiplexer 35 to be
transmitted into the optical fiber 31 to the branch terminal
station 60.
[0116] Optical signals .lambda.-4, .lambda.-3, .lambda.'-4,
.lambda.'-3 from the branch terminal station 60 are split by the
wavelength demultiplexer 36 into the add line 15-2a leading to the
first switching unit 10-3 and the add line 25-2a leading to the
second switching unit 20-21. For example, the optical signals
.lambda.-4, .lambda.-3, .lambda.'-4, .lambda.'-3 propagating
through the add line 15-2a are input to the terminal 02' through
the optical circulator 11-2a, and output from a desired one of
terminals 01, 02.
[0117] Here, when the control port 30-7 of the AOTF 30 is supplied
with the RF signal, the optical signals .lambda.-4, .lambda.-3 are
output from the terminal 01, and transmitted to the optical
transmit/receive terminal station 50a through the optical
circulator 21-2a and the optical fiber 9.
[0118] In this manner, according to the wavelength
demultiplexing/multiple- xing device 4, the number of the optical
fibers connecting between the wavelength
demultiplexing/multiplexing device 4 and the branch terminal
station 60 can be reduced, and the cost for making up the WDM
transmission system can also be reduced.
[0119] FIG. 10 is a block diagram illustrating a WDM transmission
system in which a wavelength demultiplexing/multiplexing device 4'
relating to an applied example of the fourth embodiment is
applied.
[0120] The wavelength demultiplexing/multiplexing device 4' of the
WDM transmission system 140' shown in FIG. 10 is different from
that shown in FIG. 8 in that the wavelength demultiplexer 36'
employs, an optical filter that splits the range of the wavelengths
from the branch terminal station 60. For example, the wavelengths
.lambda.-3 and .lambda.'-3 may be split from the wavelengths
.lambda.-4 and .lambda.'-4.
[0121] FIG. 11 is a chart to illustrate an example of the
wavelength arrangement of the WDM transmission system relating to
the applied example of the fourth embodiment of the invention. If
the wavelengths of the optical signals .lambda.-3, .lambda.'-4 in
the wavelength demultiplexing/multiplexing device 4 relating to the
foregoing fourth embodiment are used, the optical signals
.lambda.-3, .lambda.'-4 return back to the direction of incidence.
This condition will not be used in the operation of the WDM
transmission system, and it is not necessary to allocate a
wavelength range specially for the optical signals .lambda.-3,
.lambda.'-4. Therefore, the wavelength arrangement shown in FIG. 11
can effectively use the wavelength range.
[0122] The wavelength demultiplexer 36' is designed in advance in
consideration of the wavelengths .lambda., .lambda.' to be
split.
[0123] (d1) Modification of the Fourth Embodiment
[0124] FIG. 12 is a block diagram illustrating a WDM transmission
system which includes a wavelength demultiplexing/multiplexing
device 4-1 relating to a first modification of the fourth
embodiment of the invention is applied. The wavelength
demultiplexing/multiplexing device 4-1 is different from the device
shown in FIG. 8 in that the device shown in FIG. 12 is provided
with an AOTF 36-1 instead of a demultiplexer 36.
[0125] The AOTF 36-1 serves as a demultiplexer, splits the optical
signals from the branch terminal station 60, and sends out the
split optical signals into the add line 15-2a leading to the first
switching unit 10-3 and the add line 25-2a leading to the second
switching unit 20-21.
[0126] When the RF signal is supplied to the control port 30-7, the
AOTF 36-1 shown in FIG. 12 is able to split the wavelength range of
the optical signal .lambda.'-3 and the wavelength range of the
optical signal .lambda.-4. Under this condition, FIG. 13 is a chart
to illustrate an example of the wavelength arrangement of the WDM
transmission system 141 relating to the first modified example of
the fourth embodiment of the invention. In this wavelength
arrangement shown in FIG. 13, the wavelength allocation is
determined such that the wavelengths of the optical signals do not
coincide in one optical fiber.
[0127] The AOTF 36-1 and the AOTF 30 are supplied with the same RF
signal at the control ports 30-7 thereof. Therefore, the wavelength
selectivity of the AOTF 36-1 is interlocked to that of the AOTF
30.
[0128] According to the foregoing construction, the wavelength
demultiplexing/multiplexing device 4-1 relating to the first
modification example of the fourth embodiment sends out the optical
signals .lambda.'-3, .lambda.-4 from the branch terminal station 60
into the desired add lines 15-2a, 25-2a via the AOTF 36-1 as a
demultiplexer.
[0129] Concretely, when the control port 30-7 of the AOTF 36-1 is
supplied with the RF signal, the optical signal .lambda.'-3 is
output from the terminal 01' of the AOTF 36-1. Thereafter, the
signal .lambda.'-3 is input to the terminal 02 of AOTF 30 through
the optical circulator 21-2b, and then sent out from the terminal
02' to the optical transmit/receive terminal station 50b as the add
optical signal. Further, the optical signal .lambda.-4 is affected
by the acousto-optic effect and output from the terminal 02' of
AOTF 36-1. Thereafter, the signal .lambda.-4 is input to the
terminal 02' of the AOTF 30 through the optical circulator 11-2a,
and then sent out from the terminal 01 to the optical
transmit/receive terminal station 50a as the add optical
signal.
[0130] In this manner, according to the wavelength
demultiplexing/multiple- xing device 4-1 relating to the first
modification of the fourth embodiment, AOTF 36-1 is used as the
demultiplexer, and AOTF 36-1 can be interlocked with AOTF 30.
Further, in replacement of the AOTF 36-1, a variable optical filter
can also be employed, so that the optical signals propagating
through the trunk system optical fibers can be split in the same
manner. Further, an AOTF can be used in place of multiplexer 35,
thereby enhancing the flexibility of the wavelength
selectivity.
[0131] (e) Fifth Embodiment
[0132] FIG. 14 is a block diagram illustrating a WDM transmission
system which employs a a wavelength demultiplexing/multiplexing
device 5 relating to a fifth embodiment of the invention.
[0133] The wavelength demultiplexing/multiplexing device 5 differs
from that of the fourth embodiment in the interconnections and in
the provision of a wavelength demultiplexinglmultiplexing unit 40
in place of elements 35 and 36. The first and second switching
circuits 10-5, 20-5 are also configured somewhat differently.
[0134] The first switching unit 10-5 is provided with optical
circulators 11-5a, 11-5b. In optical circulator 11-5a, terminal C1
is connected to the optical fiber 9, terminal C2 is connected to
the terminal 02' of the AOTF 30, and terminal C3 is connected to
the optical fiber 8. On the other hand, in optical circulator
11-5b, terminal C1 is connected to the drop line 15-5b, terminal C2
is connected to terminal 01' of the AOTF 30, and terminal C3 is
connected to the add line 15-5a. The optical circulators of this
embodiment operate in the same manner as the optical circulators
described above.
[0135] The second switching unit 20-5 is provided with optical
circulators 21-5a and 21-5b. In the optical circulator 21-5a,
terminal C1 is connected to the optical fiber 8, terminal C2 is
connected to terminal 01 of the AOTF 30, and terminal C3 is
connected to the drop line 25-5b. On the other hand, in optical
circulator 21-5b, terminal C1 is connected to the optical fiber 9,
the terminal C2 is connected to the terminal 02 of the AOTF 30, and
terminal C3 is connected to the add line 25-5a.
[0136] The wavelength demultiplexing/multiplexing unit 40
multiplexes the optical signals transmitted from the first
switching unit 10-5 through the drop line 15-5b and the optical
signals transmitted from the second switching unit 20-5 through the
drop line 25-5b, and outputs the multiplexed optical signals toward
the branch terminal station 60. Also, the wavelength
demultiplexing/multiplexing unit 40 splits the optical signals from
the branch terminal station 60, and outputs the split optical
signals into the add line 15-5a leading to the first switching unit
10-5 and the add line 25-5a leading to the second switching unit
20-5.
[0137] In order to achieve the foregoing, the wavelength
demultiplexing/multiplexing unit 40 is provided with an AOTF 30-1
and optical circulators 41, 42. The AOTF 30-1 is designed to have
the same function and the same permeability as the foregoing AOTF
30. The RF signal supplied to the AOTF 30-1 is the same as that
supplied to the AOTF 30. Therefore, the ATOF 30-1 is interlocked
with the AOTF 30. The optical circulators 41, 42 each have the same
function as that of the previously described optical circulators
11-5.
[0138] Referring to the first switching unit 10-5, the optical
signal .lambda.'-1 output from the terminal 01' of the AOTF 30 is
sent out through the optical circulator 11-5b to the wavelength
demultiplexing/multiplexing unit 40. The optical signal .lambda.-4
from the wavelength demultiplexing/multiplexing unit 40 is sent out
to the terminal 01' of the AOTF 30 through the optical circulator
11-5b. Optical signals .lambda.-2, .lambda.'-2 from the optical
transmit/receive terminal station 50b are sent to terminal 02' of
the AOTF 30 through the optical circulator 11-5a, and the optical
signals .lambda.-1, .lambda.'-3 (.lambda.-4, .lambda.'-3) from the
terminal 02' of the AOTF 30 are sent to the optical
transmit/receive terminal station 50b through the optical
circulator 11-5a.
[0139] Referring to the second switching unit, the optical signal
.lambda.'-2 output from the terminal 01 of the AOTF 30 is sent out
through the optical circulator 21-5a of the second switching unit
20-5 to the wavelength demuitiplexing/multiplexing unit 40. The
optical signal .lambda.'-3 from the wavelength
demultiplexing/multiplexing unit 40 is sent to terminal 02 of the
AOTF 30 through the optical circulator 21-5b. Optical signals
.lambda.-1, .lambda.'-1 from the optical transmit/receive terminal
station 50a are sent out to the terminal 01 of the AOTF 30 through
the optical circulator 21-5a, and the optical signals .lambda.'-2,
.lambda.-4 from terminal 02 of AOTF 30 are sent to the optical
transmit/receive terminal station 50a through the optical
circulator 21-5b.
[0140] Referring to the wavelength demultiplexing/multiplexing unit
40, when the RF signal is supplied to the control port 30-7 of the
AOTF 30-1, the optical signal .lambda.-2 propagating through the
drop line 25-2b and the optical circulator 41 is input to the
terminal 01' of AOTF 30-1. And then, the output line of the optical
signal .lambda.-2 is switched by the acousto-optic effect by the
SAW, and output from terminal 02, along with the optical signal
.lambda.'-1, which does not correspond to the RF signal. Further,
the optical signals .lambda.-4, .lambda.'-3 from the branch
terminal station 60 are input to terminal 01, and the output line
of the optical signal .lambda.-4 (.lambda.-4 corresponds to the RF
signal) is switched to the terminal 02' from the terminal 01. Thus,
optical signal .lambda.-4 is output from the terminal 02'.
[0141] Therefore, the wavelength demultiplexing/multiplexing device
5 drops and adds a desired optical signal by the functions of the
first switching unit 10-5, the second switching unit 20-5, the AOTF
30, and the wavelength demultiplexing/multiplexing unit 40. In this
manner, the wavelength demultiplexing/multiplexing device 5
relating to the fifth embodiment is provided with AOTF 30-1 having
both the functions of the wavelength multiplexer and the wavelength
demultiplexer while being interlocked with the AOTF 30, thereby
reducing the number of the optical fibers, and further simplifying
the construction of the device.
[0142] FIG. 15 is a block diagram illustrating a WDM transmission
system which uses a wavelength demultiplexing/multiplexing device
5-1 relating to an applied example of the fifth embodiment. The
wavelength demultiplexinglmultiplexing device 5-1 of the WDM
transmission system 151 shown in FIG. 15 is provided with a switch
(SW) 22 as a forced switch unit in a second switching unit 20-5',
and this is different from the wavelength
demultiplexing/multiplexing device 5 related to the fifth
embodiment.
[0143] The switch 22 forcibly switches the transmission line of the
optical signal. When a switching signal is received at a SW control
terminal 22-1, the switch 22 switches the transmission line of the
optical signal. The switching signal used in this case is an
information to switch the switch 22 into the ON state, and this
switching signal is supplied when the RF signal is input to the
control port 30-7 of the AOTF 30.
[0144] FIGS. 16(a) and (b) are block diagrams to explain the
operation of the switch 22 relating to the applied example of the
fifth embodiment. FIG. 16(a) illustrates how switch 12 operates
when switch 22 is OFF, and FIG. 16(b) illustrates how switch 22
operates when switch 22 is ON.
[0145] When the switch 22 is OFF, the transmission line of optical
signals from the terminal C3 of the optical circulator 21-5a is
forcibly switched into the trunk system optical fiber 9 to be
transmitted to the optical transmit/receive terminal station 50a.
When the switch 22 is ON, it operates as shown in FIG. 16(b).
[0146] (f) Sixth Embodiment
[0147] FIG. 17 is a block diagram to illustrate a bi-directional
wavelength switching device 70 related to a sixth embodiment of the
invention. The bi-directional wavelength switching device 70 shown
in FIG. 17 switches a transmission line of an optical signal, and
is configured to switch the optical signals propagating through
bi-directional optical fibers 8-2, 8-3, 8-4, and 8-5 into desired
transmission lines.
[0148] The bi-directional wavelength switching device 70 is
provided with the AOTF 30 and a first switching unit 10-6.
[0149] The AOTF 30 is provided with two pairs of terminals,
including a first pair of terminals 01, 02, and a second pair
having a pair of terminals 01', 02'. If a plurality of optical
signals having different wavelengths are input to terminal 01, for
example, the AOTF 30 is able to output a part of the optical
signals from terminal 01' to which an optical signal is not input,
and to output the rest of the optical signals from the other
terminal 02'. Further, if optical signals are input to the other
terminals 02, 01', and 02', the AOTF 30 is designed to output the
optical signals from a desired terminal in the same manner as the
foregoing.
[0150] The first switching unit 10-6 is connected to the terminal
01' of the AOTF 30, and switches the input/output lines of the
optical signals between the AOTF 30 and the bi-directional optical
signal transmission line 8-4 and 8-5, by using an optical
circulator 11-6.
[0151] Optical circulator 11-6 operates in the same manner as the
previous optical circulators.
[0152] According to the foregoing construction, first the optical
circulator 11-6 switches the line of the optical signal input
through the optical fiber 8-5 to terminal 01' of the AOTF 30. When
the RF signal is supplied to control port 30-7, the AOTF 30 outputs
the optical signals corresponding to the frequency of the SAW from
terminal 02, and outputs the optical signals not corresponding from
the terminal 01. When the RF signal is not input, the AOTF 30
outputs the optical signals input at terminal 01' (from the
terminal C1 of the optical circulator 11-6) from the terminal
01.
[0153] Therefore, the bi-directional wavelength switching device 70
sends out an optical signal into a desired transmission line by
combining the functions of the AOTF 30 and the first switching unit
10-6. In this manner, according to the bi-directional wavelength
switching device relating to the sixth embodiment of the invention,
the optical signals can be switched by combining the
bi-directionally operational AOTF 30 with the first switching unit
10-6, and the number of AOTFs to be equipped can be reduced to
lower the production cost of the device, thus making a simplified
device.
[0154] Further, the bi-directional wavelength switching device 70
can be supplied as a component to achieve the basic function of
selecting the wavelength of an optical signal, and adding and
dropping optical signals in a wavelength
demultiplexing/multiplexing device (for example, OADM-BU or
OADM-NODE) used in the WDM transmission system. That is, any of the
optical fibers 8-2, 8-3, 8-4, and 8-5 can be used as an drop line
and an add line in the foregoing bi-directional wavelength
switching device 70. There are wide variations possible as to the
terminals where the optical circulator 11-6 is equipped.
[0155] FIG. 18 is a block diagram to illustrate a bi-directional
wavelength switching device 71 related to a modification of the
sixth embodiment of the invention. The bi-directional wavelength
switching device 71 shown in FIG. 18 is provided with a second
switching unit 20-6 on the side of the terminals 01, 02, opposite
to a first switching unit 10-6' and is different from the foregoing
bi-directional wavelength switching device 70.
[0156] The first switching unit 10-6' and the second switching unit
20-6 switch the input optical signals between the AOTF 30, and
optical fibers 9-0, 9-1, 9-2, 9-3, 9-4, and 9-5. In order to
achieve the foregoing, the first switching unit 10-6' and the
second switching unit 20-6 are provided with optical circulators
11-6' and 21-6, respectively. Further, the optical fibers 9-2 and
9-3, or the optical fibers 9-4 and 9-5 can be paired as an optical
fiber pair.
[0157] FIG. 19 is a block diagram to illustrate a bi-directional
wavelength switching device 72 relating to an applied example of
the sixth embodiment of the invention. The bi-directional
wavelength switching device 72 shown in FIG. 19 is provided with a
first switching unit 10-6a and a second switching unit 20-6a, each
of which has two optical circulators, and this is different from
the foregoing bi-directional wavelength switching device 71. The
first switching unit 10-6a and the second switching unit 20-6a
switch optical signals between the AOTF 30, and optical fibers
9'-1, 9'-2, 9'-3, 940 -4, 9'-5, 9'-6; 9'-7, 9'-8. Further, the
optical fibers 9'-1 and 9'-2, or the optical fibers 9'-3 and 9'-4,
etc., can be constructed by using an optical fiber pair.
[0158] (g) Others
[0159] The foregoing embodiments have focused mainly on an AOTF as
the optical device. However, a device having the same function as
an AOTF 30 can be used as the device to switch the input/output
lines of an optical signal, wherein such device has two pairs of
terminals and so that when a plurality of optical signals having
different wavelengths are input from one terminal a first terminal
pair, some optical signals are output from one terminal forming a
second terminal pair, and the rest of the optical signals are
output from the other terminal forming the second terminal
pair.
[0160] Further, even though the optical circulators have been
descried as having three terminals, optical circulators can have
four or more terminals, and the lines of the optical signals can be
switched in the same manner as mentioned above.
[0161] While the invention has been described in connection with
the preferred embodiments and examples, it will be understood that
modifications within the principle outlined above will be evident
to those skilled in the art without departing from the spirit and
scope of the invention. Thus, the invention is not limited to the
preferred embodiments and examples, but is intended to encompass
such modifications.
* * * * *