Optical network

Details Optical network Optical network

1998-12-22

2002-08-06

Pascal, Leslie (Department: 2633)

Optical: systems and elements

Deflection using a moving element

Using a periodically moving element

C359S199200, C359S199200

Reexamination Certificate

active

06429955

ABSTRACT:

FIELD OF THE INVENTION
This inventions relates to an optical network that is available for communication networks, such as public communications network, local area network, interconnection network of computers etc.
BACKGROUND OF THE INVENTION
Optical networks where optical signal is exchanged among multiple nodes using an optical switch etc. are expected as means to realize such a large capacity of network that cannot have been realized in conventional electrical networks. In a communication network, not applying only in optical network, it is typical that, to a transmit node, a destination address, i.e., the number of a receive node is given and the routing control is carried out based on the destination address. In an electrical network, the destination address is written in the header of packet at the transmit node, switches in the network can read this destination address and perform the routing control by itself.
However, in the case of optical network, it is not easy to perform the routing control by an optical switch itself because the logical operation of optical signal is difficult to conduct. So, in optical networks, it is typical that a controlled objective, such as an optical switch, is connected through a dedicated control line with a transmit node and the routing control is performed using it.
FIG. 1
shows an example of a conventional broadcast and select type of 4×4 optical network that uses wavelength division multiplexing (e.g., Biswanath Mukherjee, “WDM-Based Local Lightwave Networks Part I: Single-Hop Systems”, IEEE Network, May 1992, pp. 12-27). Optical transmitters
5
at transmit nodes t
0
to t
3
transmit optical signals with different wavelengths &lgr;
0
to &lgr;
3
, and these optical signals are wavelength-multiplexed by a star coupler
6
and distributed to four wavelength selectors
7
. Each of the wavelength selectors
7
selects only optical signal with desired one wavelength from the four wavelengths and outputs it, and an optical receiver
4
at receive nodes r
0
to r
3
receives it. For the routing control, the respective transmit nodes t
0
to t
3
are connected through control lines (not shown) with all the wavelength selectors
7
.
When, like this optical network, there are many controlled objectives for the respective transmit nodes and they are located on the receive node side, it is necessary to provide so long control lines. Therefore, in optical networks, it is desired that the controlled objectives be concentrated near the transmit nodes as close as possible.
Two examples of conventional optical networks where controlled objectives are concentrated close to transmit nodes are explained below.
The first example is a wavelength routing type of optical network shown in FIG.
2
. Each node is provided with a wavelength tunable optical transmitter
1
that can output an optical signal with an arbitrary wavelength of wavelengths &lgr;
0
to &lgr;
3
. A star coupler
6
couples the transmitted optical signal and distributes it. Each of optical filters
8
-
0
to
8
-
3
transmits only optical signal with wavelength &lgr;
0
to &lgr;
3
proper thereto, and an optical receiver
4
to each receive node r
0
to r
3
receives it. In this optical network, the wavelength of optical signal corresponds to a destination address by one—one relation. Therefore, the controlled objective of each transmit node is only its own wavelength tunable optical transmitter
1
.
The second example is an optical network using optical switch shown in FIG.
3
. An optical switch
9
switches and outputs an optical signal, thereby conducting the communication between an arbitrary transmit node and an arbitrary receive node. The optical switch
9
is a splitter/combiner type optical switch that has mesh interconnections between 1×4 optical switches
10
and optical combiners
11
(e.g., Maeno et al., IEICE 1996 General Meeting, SB-9-5). The 1×4 optical switch
10
is composed of an optical splitter
20
and optical gate switches
21
which are of semiconductor optical amplifiers. By turning on arbitrary one of the four optical gate switches and turning off the others, an optical signal input can be output from an arbitrary output port. In this optical network, the controlled objective of each transmit node is only one 1×4 optical switch
10
. For example, a transmit node
5
-
0
can transmit a packet to an arbitrary receive node by controlling the optical gate switches
21
-
0
to
21
-
3
.
The problems of the above conventional examples are described below.
Although, in the optical network of the first conventional example, wavelengths with the same number as the number of receive nodes are necessary, the number of wavelengths available is restricted by various factors. For example, when a wavelength tunable semiconductor laser is used as the wavelength tunable optical transmitter
1
, the number of wavelengths available is restricted since the tuning range of the wavelength tunable semiconductor laser is limited. Also, when an optical amplifier is used in the optical network, the number of wavelengths available is restricted by the bandwidth of the optical amplifier. Therefore, in the optical network of the first conventional example, there is the problem that the number of nodes cannot be increased so much.
Also, in the optical network of the first conventional example, there is the problem that simultaneously transmitting a packet from one transmit node to multiple receive nodes, so called “multicast”, cannot be conducted. When a broadcast type of services are performed on the network, it becomes necessary for a same packet to be sent from one transmit node to multiple receive nodes. For the network with no multicast function, a same packet needs to be one by one sequentially sent to multiple receive nodes, the transmit node is occupied during that period, therefore the transmit node cannot send out the next packet until the transmission of the same packet to all the receive nodes is completed. On the other hand, in the optical network of second conventional example, the multicast is available. For example, turning on the optical gate switches
21
-
0
to
21
-
2
, the multicast from the transmit node t
0
to the receive nodes r
0
, r
1
and r
3
can be performed. Since the transmit node can simultaneously send a same packet to multiple receive nodes, it can quickly make the transition to the next packet transferring. Thus, to enable the multicast is a key matter in building an optical network.
In the second example, the number of optical gate switches
21
needed to compose the optical switch
9
is the number of input and output ports to the second power. Therefore, when the number of input and output ports is increased, the scale of switch is increased, therefore causing serious problems that the cost is abruptly increased and that the implementation is very difficult to conduct. For example, 16 optical gate switches only are required for the optical switch
9
of 4×4, however 256 optical gate switches are required for 16×16 and 4096 optical gate switches are required for 64×64. Hence, to reduce the number of gate switches required is also a key matter.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the invention to provide an optical network where the control objectives are concentrated close to transmit node and, furthermore, the routing control is very easy to conduct.
It is a further object of the invention to provide an optical network where similar scale to that of the conventional optical network can be provided by using reduced number of components.
It is a further object of the invention to provide an optical network with excellent modularity so called.
According to the invention, an optical network, comprises:
wavelength tunable optical transmitters of number MN, where N is an integer of two or more, each of which outputs an optical signal with arbitrary one of M wavelengths &lgr;
1
, &lgr;
2
, . . . , &lgr;
M
, where M is an integer of two or more, that are different from one another;
a MN×N

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