Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1999-03-26
2002-09-03
Pascal, Leslie (Department: 2733)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200, C359S199200
Reexamination Certificate
active
06445473
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to an optical switching apparatus applied wavelength division multiplexing techniques thereto.
The optical switching apparatus switches optical signals without converting them into electrical signals. Recently, such optical switching apparatus might be expected to realize switching with a large amount of capacity which can not be realized by an electrical switching apparatus. In the art of optical switch, there are the following types: an optical space switching (or an optical space-division switching), an optical wavelength switching (or an optical wavelength-division switching), an optical time switching (or an optical time-division switching), and combinations thereof, such as an optical wavelength/space switching (an optical wavelength-division/space-division switching) and an optical wavelength/time switching (an optical wavelength-division/time-division switching).
In the optical space switching, channels are assigned only to spaces.
FIG. 1
shows an example of an optical space switching apparatus. In the example zeroth through third input channels are assigned to zeroth through third input ports
10
-
0
through
10
-
3
, respectively. On the other hand, zeroth through third output channels are assigned to zeroth through third output ports
11
-
0
through
11
-
3
, respectively. Such optical space switching apparatus
1
can connect between any input channel and any output channel.
The optical space switching apparatus which the present invention relates, comprises an existing optical space switch of splitter/combiner type where semiconductor laser amplifiers are used as optical gate switches. For example, such switch is disclosed in Yoshiharu Maeno et al “The Possibility of Optical Switching Technology for Parallel Processing Systems”, IEICE, SB-9-5, 1996.
FIG. 2
illustrates an optical switch of splitter/combiner type known to the inventors. The illustrated optical space switch comprises zeroth through third input waveguides
20
-
0
through
20
-
3
, zeroth through third beam splitters
21
-
0
through
21
-
3
, zeroth through fifteenth optical gate switches
22
-
0
through
22
-
15
, zeroth through third beam combiners
23
-
0
through
23
-
3
, and zeroth through third output waveguides
24
-
0
through
24
-
3
.
One kind of the existing optical gate switches is a semiconductor laser amplifier, which is turned Into a light-transmitting or an on state and a light absorbing or an off state when an electric current is fed thereto and is not fed thereto, respectively. For example, when the zeroth optical gate switch
22
-
0
turned into the on state, the zeroth input waveguide
20
-
0
is connected to the zeroth output waveguide
24
-
0
.
The splitter/combiner type optical switch is strictly nonblocking and serves as a so-called crossbar switch where every pairs of input and output ports have dedicated connection paths. And accordingly, the optical space switching apparatus comprising the above switch also serves as a crossbar network. On the other hand, the optical switch of splitter/combiner type requires optical gate switches, (the number of ports)
2
in number, and therefore, has a fault that it is difficult to be implemented, as the number of ports becomes large.
FIG. 3
shows another optical space switching apparatus known to the inventors. The apparatus is applied a wavelength division multiplexing (WDM) technology thereto, and achieves to reduce the number of the optical gate switches as compared with the apparatus illustrated in FIG.
2
. In this apparatus, zeroth through fifteenth input optical signal each having any one of zeroth through third wavelengths &lgr;
0
through &lgr;
3
are supplied from zeroth through fifteenth input ports
10
-
0
through
10
-
15
and combined by zeroth through third beam combiners
31
-
0
through
31
-
3
.
In detail, when the zeroth through third input optical signals having zeroth through third wavelengths &lgr;
0
through &lgr;
3
are input to the zeroth beam combiner
31
-
0
from the zeroth through third input ports, the zeroth beam combiner
31
-
0
combines the zeroth through third input optical signals to produce a zeroth WDM optical signal. Likewise, the first beam combiner
31
-
1
combines the fourth through seventh input optical signals having zeroth through third wavelengths &lgr;
0
through &lgr;
3
to produce a first WDM optical signal. The second beam combiner
31
-
2
are input the eighth through eleventh input optical signals having zeroth thereto from third wavelengths &lgr;
0
through &lgr;
3
from the eighth through eleventh input ports, and then, combines the eighth through eleventh input optical signals to produce a second WDM optical signal. The third beam combiner
31
-
3
combines the twelfth through fifteenth input optical signals having zeroth through third wavelengths &lgr;
0
through &lgr;
3
to produce a third WDM optical signal.
The optical space switch
32
illustrated in
FIG. 3
is of a 4×16 crossbar switch adapted to perform 1-to-4 multicasting at maximum. The illustrated switch
32
has zeroth through third input ports i
0
through i
3
to which the zeroth through third WDM optical signals are supplied and zeroth through fifteenth output ports o
0
through o
15
from which zeroth through fifteenth switched WDM optical signals are outputted. The zeroth through fifteenth output ports of the optical space switch
32
are connected to zeroth through fifteenth wavelength selectors
33
A-
0
through
33
A-
15
, respectively. The zeroth through fifteenth wavelength selectors
33
A-
0
through
33
A-
15
select the optical signal of the desired wavelengths from the zeroth through fifteenth switched WDM optical signals outputted from the optical space switch
32
and produce zeroth through fifteenth selected optical signals. The zeroth through fifteenth wavelength selectors
33
A-
0
through
33
A-
15
are connected to zeroth through fifteenth output ports
11
-
0
through
11
-
15
, respectively. The zeroth through fifteenth output ports
11
-
0
through
11
-
15
transmit the zeroth through fifteenth selected optical signals as zeroth through fifteenth output optical signals, respectively.
Thus, the optical space switching apparatus has a function of a 16×16 crossbar network. In the apparatus, the optical space switch
32
may be of splitter/combiner type described above, and may include sixty-four optical gate switches.
On the other hand, each of the existing wavelength selectors
33
A (suffixes omitted) comprises optical gate switches, the number of which is equal to the number of wavelengths transmitted into each selector. In the example described above with
FIG. 3
, the number of wavelengths multiplexed into the switched WDM optical signal is equal to four, and therefore, the number of optical gate switches is also equal to four. Specifically, in each selector, a wavelength demultiplexer demultiplexes switched WDM optical signal into individual optical signals with different wavelengths and transmits the individual optical signals into the optical gate switches, respectively. And then, one of the gate switches corresponding to desired wavelength turns on while the others turn off so that only the optical signal with desired wavelength is outputted from the selector.
As understood from the above, the optical switching apparatus of space division type illustrated in
FIG. 3
has 128 optical gate switches In total. On the other hand, another 16×16 apparatus consisting of a splitter/combiner type optical switch requires 256 optical gate switches. Thus, the number of optical gate switches which comprise the apparatus illustrated in
FIG. 3
is reduced to 1/2 as compared with another apparatus consisting splitter/combiner type optical switch.
As against the above optical space switching, optical wavelength/space switching assigns channels to both of wavelengths and spaces.
FIG. 4
shows another example of an optical wavelength/space switching apparatus. In the example, zeroth through third input channels are assigned to zerot
Henmi Naoya
Suemura Yoshihiko
Bello Augustin
Pascal Leslie
Sughrue & Mion, PLLC
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