Optical switch

Details Optical switch Optical switch

2001-09-24

2004-04-06

Nasri, Javaid H. (Department: 2839)

Optical waveguides

With optical coupler

Switch

Reexamination Certificate

active

06718081

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical switch, and in particular to an optical switch comprising a plurality of input ports and output ports, and performing a path establishment between the input ports and the output ports.
With a recent traffic growth, an increase in network capacity has been demanded. Therefore, construction of an optical network based on Wavelength Division Multiplexing (WDM) technology has been required in a backbone network.
The WDM technology increases a point-to-point transmission capacity by transmitting a plurality of optical signals having different wavelengths on a single optical transmission line. Also, for applications of the WDM technology, there are cited an optical switch apparatus such as an add-drop multiplexer adding/dropping information of a specified wavelength, and an optical cross-connect switching over a transmission line per optical wavelength.
In such an optical switch apparatus, an optical switch to perform a path switchover of an optical signal per wavelength plays an important part.
2. Description of the Related Art
FIG. 13
shows an arrangement (
1
) of an optical switch apparatus (optical cross-connect)
100
including a general optical switch (routing portion)
20
. The optical switch apparatus
100
accommodates a plurality of input optical transmission lines
1
_
1
-
1
_m (hereinafter, occasionally represented by a reference numeral
1
) and output optical transmission lines
2
_
1
-
2
_m (hereinafter, occasionally represented by a reference numeral
2
), and routes wavelength-multiplexed optical signals coming from the input optical transmission lines
1
to the desired output optical transmission lines
2
per wavelength. Also, an operation system
41
shown in
FIG. 13
monitors/controls the optical switch apparatus
100
to perform a path establishment and a path switchover.
The optical switch apparatus
100
is composed of branching portions
10
_
1
-
10
_m (hereinafter, occasionally represented by a reference numeral
10
) branching the wavelength-multiplexed optical signals (wavelengths: &lgr;
1
, &lgr;
2
, . . . , &lgr;n) coming from the input optical transmission lines
1
_
1
-
1
_m, the optical switch (routing portion)
20
routing the optical signals inputted from the input ports to the desired output ports, wavelength converters
31
_
11
-
31
_
1
n
, . . . ,
31
_m
1
-
31
_mn (hereinafter, occasionally represented by a reference numeral
31
) converting the wavelengths of the inputted optical signals into desired wavelengths, and couplers
30
_
1
-
30
_m (hereinafter, occasionally represented by a reference numeral
30
) coupling the optical signals whose wavelengths are converted.
For examples of the wavelength converter
31
, there are cited a method of converting a wavelength in the state of light by making use of a Semiconductor Optical Amplifier (SOA), a method of converting a wavelength by making use of a light-electricity converter and an electricity-light converter, and the like. Also, the branching portion
10
and the coupler
30
can be composed of elements using an Arrayed Waveguide Grating (AWG) and a dielectric multilayer film.
FIG. 14
shows an arrangement (
2
) of the optical switch apparatus (optical cross-connect)
100
including the optical switch. In this arrangement (
2
), light reproducers
11
_
11
-
11
_
1
n
, . . . ,
11
_m
1
-
11
_mn are inserted at the preceding stage of the optical switch
20
in the optical switch apparatus
100
shown in
FIG. 13
, and light reproducers
32
_
11
-
32
_
1
n
, . . . ,
32
_m
1
-
32
_mn, which also serve as wavelength converters, are arranged instead of the wavelength converters
31
at the subsequent stage.
The light reproducers
11
_
11
-
11
_
1
n
, . . . ,
11
_m
1
-
11
_mn are thus provided because the optical cross-connect
100
is generally deployed in a long-distance network in many cases and an optical signal waveform inputted to the optical cross-connect
100
deteriorates to the extent that the signal with the original quality can not be reproduced only with an amplification of an optical amplifier.
Also, for example of the optical switch
20
shown in
FIGS. 13 and 14
, there are cited a waveguide-type switch utilizing a thermal optical effect, a mechanical-type switch utilizing a motor, and the like.
FIGS. 15A and 15B
show an arrangement of the optical switch
20
using switch elements
21
_
1
-
21
_
16
(hereinafter, occasionally represented by a reference numeral
21
) of a Mach-Zehnder interference-type which is the waveguide-type switch.
The optical switch element
21
is a two-input-two-output-type switch having input terminals
5
_
1
and
5
_
2
, and output terminals
6
_
1
and
6
_
2
. When the element
21
is on, the input terminal
5
_
1
and the output terminal
6
_
1
are connected, and the input terminal
5
_
2
and the output terminal
6
_
2
are connected respectively. When the element
21
is off, the input terminal
5
_
1
and the output terminal
6
_
2
are connected, and the input terminal
5
_
2
and the output terminal
6
_
1
are connected respectively.
Although the optical switch
20
in
FIG. 15A
is different from that in
FIG. 15B
for the connection method of the optical switch elements
21
, both switches comprise a four-input-four-output optical switch
20
which connect input ports
3
_
1
-
3
_
4
to output ports
4
_
1
-
4
_
4
in a one-to-one relationship.
In case a path is established between the input port
3
_
1
and the output port
4
_
2
for example, the optical switch
20
in
FIG. 15A
sets the optical switch elements
21
_
4
,
21
_
3
,
21
_
6
,
21
_
10
, and
21
_
14
off, and sets only the optical switch element
21
_
2
on. In the optical switch
20
, the numbers of the optical switch elements through which the paths pass are not equal.
On the other hand, the optical switch
20
in
FIG. 15B
sets the optical switch elements
21
_
1
,
21
_
6
, and
21
_
14
off, and sets only the optical switch element
21
_
11
on. This optical switch
20
is called PI-LOSS composition, where the number of the optical switch elements
21
through which each path passes is 4, so that optical losses on the paths are basically equal.
These optical switches
20
have problems as follows:
(1) Crosstalk occurs in the optical switches
20
, so that a crosstalk signal has a bad influence on an optical signal;
(2) Since the number of the optical switch elements required by the optical switches
20
increases in proportion to the square of the number of the input/output ports and the insertion loss increases, it is difficult to enlarge the scale.
The problem (1) will be first described.
FIG.16
illustrates crosstalks which occur in the above-mentioned four-input-four-output optical switch
20
. When the path is established between the input port
3
_
1
and the output port
4
_
2
and an optical signal S is transmitted through this path as shown, the optical signal S simultaneously leaks to the output ports
4
_
1
,
4
_
3
, and
4
_
4
, so that crosstalks C
1
, C
2
, and C
3
occur.
Crosstalks caused by the optical signals of other paths, which are similar to these crosstalks C
1
-C
3
, also occur at the output ports
4
_
1
-
4
_
4
. All of the crosstalks are overlapped per output port, which forms the crosstalk of each output port.
For a solution of the problem (1), a crosstalk shutdown apparatus mentioned in the Japanese Patent Application Laid-open No.11-41636 is composed so that a crosstalk which propagates through the input port and the output port, and a crosstalk within the optical signal are detected at the input port and/or output port, are intercepted, thereby passing only the optical signal.
The problem (2) will be described.
For the solution of the problem (2), N input×N output optical switch
20
using
2
N (N=16 in
FIG. 17
) movable mirrors as shown in
FIG. 17
has been proposed. In this optical switch
20
, the number of the mirrors increases in proportion to the number of the input/output ports. Accordingly, since neither the numbe

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