Optical waveguides – With optical coupler – Switch
Reexamination Certificate
2002-07-08
2004-09-28
Sanghavi, Hemang (Department: 2874)
Optical waveguides
With optical coupler
Switch
C385S017000, C385S024000, C398S050000, C398S083000
Reexamination Certificate
active
06798936
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical switching system and an optical switching method used in the field of an optical communication system, and particularly relates to an optical switching system and an optical switching method wherein a wavelength division type technique and a space division type technique are effectively combined.
2. Related Art
In the recent years, optical switches for switching an optical signal as it is without converting it to an electric signal have been gaining attention in the field of an optical communication system, as a technique for realizing a large capacity switch which is hard to realize with an electric switch. Optical switches include a space division type, a wavelength division type, a time division type, etc. Further, there are techniques in which those types are combined, such as a wavelength/space division type, a wavelength/time division type, etc. Some of those combined types will now be explained.
FIG. 10
is a block diagram of an ordinarily conceivable wavelength division type optical switching system. This wavelength division type optical switching system comprises optical wave dividers
51
, optical wave multiplexers
52
, and space division type optical switches
53
. The optical wave dividers
51
are provided to input light transmission paths Input
1
to Input k respectively, and divide an optical signal in accordance with frequencies. One space division type optical switch
53
includes (k×k) number of space division type optical switches prepared for n number of lights &lgr;
1
to &lgr;n obtained by division and each having its own wavelength. The optical wave multiplexers
52
are provided to output light transmission paths Output
1
to Output k respectively, and multiplex optical signals each having its own wavelength. With this structure, the wavelength division type optical switch needs to comprise an optical wave divider
51
and optical wave multiplexer
52
for every input or output optical fiber, and further to comprise a space division type optical switch for every wavelength. Therefore, a lot of optical fibers are necessary, and this is not suitable for miniaturizing the device.
On the other hand, Unexamined Japanese Patent Application KOKAI Publication NO. H11-243564 discloses an optical switch having intermediate function and structure between a space division type optical switching system for switching light paths on an optical fiber by optical fiber basis, and a wavelength division type optical switching system for switching light paths on a wavelength by wavelength basis. This optical switch will be explained with reference to FIG.
11
.
As illustrated in
FIG. 11
, this optical switch comprises a plurality of branching units
54
, insertion units
55
, a first space division type optical switch
56
, a second space division type optical switch
57
, and a third space division type optical switch
58
. The branching units
54
are provided to input light transmission paths Input
1
to Input k
1
, respectively. The branching units
54
select a signal having a predetermined wavelength from an input wavelength-multiplexed optical signal, output the selected signal to the second space division type optical switch
57
, and output the remaining optical signal to the first space division type optical switch
56
. The second space division type optical switch
57
routes the branched optical signal to a predetermined output light transmission path in order to output the branched optical signal. On the other hand, the insertion units
55
multiplex an optical signal input by the third space division type optical switch
58
with the optical signal input by the first space division type optical switch
56
, and after this, transmit the resultant optical signal to output light transmission paths Output
1
to Output k
1
.
The optical switching system disclosed in Unexamined Japanese Patent Application KOKAI Publication No. H11-243564 is simply structured, and has an advantage that light transmission paths can be shared. However, since a wavelength-multiplexed signal needs to pass through the branching units
54
and/or insertion units
55
, there is a problem that the loss of the optical signal is large. Further, in order to compensate for the loss of an optical signal, it is necessary to provide an optical amplifier, or to perform optical/electric/optical (hereinafter, referred to as O/E/O) conversion. However, there has been a problem that using such methods makes a device large-sized.
An example of an optical switching system employing a wavelength/space division type optical switch is disclosed in Unexamined Japanese Patent Application KOKAI Publication No. H11-275614.
FIG. 12
is a schematic block diagram of this device. This optical switching system comprises optical multiplexers
61
, an optical wavelength router
62
, a space division optical switch
63
, and optical wavelength selectors
64
. The optical multiplexers
61
multiplex optical signals having different frequencies. The optical wavelength router
62
divides the optical signal multiplexed by the optical multiplexers
61
in accordance with wavelength, and outputs the divided signals to the space division optical switch
63
. The space division optical switch
63
routes each optical signal in accordance with wavelength. Further, the optical wavelength selectors
64
each select an optical signal having a desired wavelength and output the selected optical signal. This optical switching system can increase or decrease the number of wavelengths to be multiplexed. This enables the number of wavelengths to be multiplexed to be optimized. Accordingly, effects that (1) the amount of hardware such as optical gate switches, etc. necessary for an optical switching system can be minimized, and that (2) in a case where the number of wavelengths to be multiplexed is reduced, optical amplifiers used as optical gate switches, etc. do not reach saturation, can be obtained.
However, the optical switching system disclosed in Unexamined Japanese Patent Application KOKAI Publication No. H11-275614 requires all data which will pass through this optical switching system to pass through the gate switches so as to be switched inside tile device. Accordingly, there is a problem that the device becomes large-sized.
On the other hand, as a large-sized optical switching system, one employing an MEMS (Micro-electromechanical System), etc. is developed (NIKKEI ELECTRONICS Jan. 29, 2001 issue (NO. 788) pp. 146-167). With this optical switching system employing the MEMS, a small-sized optical switching system can be structured, even though there are a relatively large number of switch ports. However, since insertion loss of light caused in the large-sized optical switch is large, it is required to use an optical amplifier conversion device, etc. Therefore, there is a problem that the optical switching system as a whole becomes large-sized.
The above optical switching system can serve well under certain usage conditions, or with some restrictions. However, various problems might be caused, when considering increase in the traffic and demand for miniaturization of the optical switching device which might be expected in the future. That is, even in a case where conducting optical switching operation where large amount of data are processed, it will be inevitable in the future to miniaturize the optical switching system, increase the number of switch ports, and reduce the insertion loss of an optical signal. Especially, miniaturizing the device and increasing the number of switch ports are contradictory to each other. With regard to this, an efficient method which minimizes the need for performing O/E/O conversion now performed in the existing devices is demanded.
Further, as the amount of information handled in a network increases, the size of processing sections of an electronic circuit is enlarged, and this increases the cost of node devices.
SUMMARY OF THE INVENTION
It is an object of the present invention to sol
NEC Corporation
Sanghavi Hemang
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