Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1998-03-30
2001-09-04
Negash, Kinfe-Michael (Department: 2633)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200, C359S199200
Reexamination Certificate
active
06285479
ABSTRACT:
BACKGROUND OF THE INVENTION
1). Field of the Invention
The present invention relates to an optical cross connect unit, optical add-drop multiplexer, light source unit and adding unit suitably employed in the field of wavelength division multiplex transmission where a plurality of different wavelengths are multiplexed for transmission.
2). Description of the Related Art
A wavelength division multiplexing (which will be referred hereinafter to as a WDM) method has been known as a transmission technique which is capable of increasing the transmission capacity and of constructing a network having flexibility in adding and dropping of signals.
This WDM method relates to a technique for multiplexing and transmitting a plurality of different optical wavelength signals, and if multiplexing signals of the same transmission speed, permits the transmission of more information by a quantity corresponding to the number of wavelengths multiplexed as compared with a prior method in which light having one kind of wavelength is modulated and transmitted through one optical fiber. Further, even in the case of low-speed signals, the multiplexing based upon the WDM method can provide a transmission capacity similar to that in a method of sending signals with single wave at a high speed.
On the other hand, since the WDM method is made to make use of the band property of an optical fiber for the purpose of transmitting multiplexed signals (multiple signals), there is a need to set a large wavelength interval whereby the signals undergoes not influence from the adjacent wavelength signals.
Furthermore, on the basis of the above-mentioned WDM transmission system, there has been proposed an optical network in which a repeater, so-called node, is placed in a transmission path on the network. This node has an optical cross connect function to separate wavelength-multiplexed signals in accordance with every wavelength and to distribute the signals to desired transmission paths after conducting wavelength conversion when necessary, and further has an optical ADM function to freely perform the add/drop of desired optical wavelength signals including necessary information.
FIG. 14
is an illustration of a related art. As shown in
FIG. 14
, the optical cross connect unit
100
′ receives wavelength multiplexed signals each having a plurality of different wavelengths &lgr;
1
to &lgr;
8
coming through 16 optical fibers
0
′-
1
to
0
′-
16
, and performs the conversion of transmission light at every wavelength signal included in each of the wavelength multiplexed signals and the replacement of optical signals such as the interchange among the corresponding transmitting optical fibers
0
′-
1
to
0
′-
16
.
FIG. 15
is a block diagram showing the related art. As shown in
FIG. 15
, the optical cross connect unit
100
′ is made up of amplifiers
0
c
′-
1
to
0
c
′-
16
for amplifying powers of wavelength multiplexed signals, demultiplexers (branching filters)
10
a
′-
1
to
10
a
′-
16
for conducting demultplexing in accordance with every wavelength, ORs
21
a
′ for conducting the conversion of a given wavelength signal to an electric signal to transmit the conversion result, OSs
21
b
′ for newly producing transmission light, 8×16 DC switches
30
a
′-
1
to
30
a
′-
16
for taking the charge of control of destinations for 8 optical signals, 16×1 couplers
40
a
′-
1
to
40
a
′-
16
for multiplexing the optical signals from the 8×16 DC switches
30
a
′-
1
to
30
a
′-
16
, and amplifiers
0
d
′-
1
to
0
d
′-
16
for amplifying a power of combined light.
Furthermore,
FIGS. 16 and 17
are block diagrams each showing the related art. As shown in
FIG. 16
, each of the ORs
21
a
′ is composed of a photodiode (which will be referred hereinafter to as a PD)
21
a
′-
1
, while each of the OSs
21
b
′ is made up of 8 LD light sources
21
b
′-
1
, an optical switch
21
b
′-
2
for selecting one of lights (a plurality of light) from the 8 LD light sources
21
b
′-
1
, and a modulator
21
b
′-
3
for performing the modulation of light with a given wavelength on the basis of the information converted into an electric signal (photoelectric current) in the PD
21
a
′-
1
.
On the other hand, the OS
21
b
′ shown in
FIG. 17
comprises a wavelength variable LD
21
b
′-
4
for emitting 8 kinds of light having different wavelengths from each other, and a modulator
21
b
′-
3
for conducting modulation of light with a given wavelength from the wavelength variable LD
21
b
′-
4
on the basis of the information undergoing the electric conversion in the PD
21
a
′-
1
.
With this arrangement, the prior optical cross connect unit
100
′ is made to conduct the cross connect processing for each of the signals included in each of the wavelength multiplexed signals.
In such a mesh-like network, the optical cross connect unit receives N-wave multiplexed signals through M fibers, and separates them in accordance with every wavelength, and conducts a wavelength conversion if necessary, and further performs the optical-wavelength multiplexing for desired signals and transmits them through a desired fiber.
More specifically, an optical signal based upon each of lights wavelength-separated in the demultiplexers
10
a
′-
1
to
10
a
′-
16
is converted into an electric signal which in turn, is used for modulating light with a wavelength from a new light source, so that desired signals are forwarded toward desired fibers
0
′-
1
to
0
′-
16
in a manner that the switching among the paths is made through the switches
30
a
′-
1
to
30
a
′-
16
.
In addition to the aforesaid WDM method of conducting the transmission from point to point, there has been proposed a network based upon a WDM method having an ADM (Add-Drop Multiplexer) function in which a specific-wavelength signal light of the multiplexed signal lights is selectively allowed to pass through a repeating point, so-called node, placed in the middle of the transmission path while the signals with the other wavelengths are received by that node or a different signal light is added therein at this node to be transmitted toward a different node.
FIG. 18
is an illustration of a WDM based network
300
′ equipped with an ADM function. Further,
FIG. 19
is an illustration of a network
300
″ provided with an ADM function. In the illustrations, an ADM unit supplies, in relation to the wavelengths of 5 dropped lights, lights with wavelengths equal to the wavelengths of the 5 (or 4) dropped lights. Incidentally, in the case of actually conducting the branching of P waves to N waves (N: natural number) which is the maximum number in use, the number of wavelengths to be inserted does not always coincide with the P waves.
As shown in
FIG. 20
, the optical ADM unit
400
′-l includes switches
223
′ for selecting one light from
8
LD light sources, amplifiers
223
′-
1
for amplifying the powers of the lights from the switches
223
′, respectively, modulators
227
′ for conducting the modulation processing for lights from the switches
223
′, respectively, and a multiplexer
228
′ for wavelength-multiplexing optical signals from the 5 modulators
227
′.
With the above-mentioned arrangement, the optical ADM unit
400
′-
1
can freely achieve the drop/add of an optical signal.
On the other hand,
FIG. 21
illustrates an optical ADM unit
400
′-
2
equipped with a wavelength variable LD
221
′ which outputs 8 kinds of lights having wavelengths different from each other without having 8×5 LD light sources unlike the
FIG. 20
optical ADM unit
400
′-
1
. Even the optical ADM unit
400
′-
2
shown in
FIG. 21
is also capable of freely conducting the drop/add in a state where the signal is in an optical condition as well as the optical ADM unit
400
&p
Chikama Terumi
Kai Yutaka
Miyata Hideyuki
Okazaki Kazue
Onaka Hiroshi
Fujitsu Limited
Negash Kinfe-Michael
Staas & Halsey , LLP
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