Signal interconnect incorporating multiple modular units

Details Signal interconnect incorporating multiple modular units Signal interconnect incorporating multiple modular units

2001-03-14

2004-10-05

Font, Frank G (Department: 2877)

Optical waveguides

With optical coupler

Switch

Reexamination Certificate

active

06801680

ABSTRACT:

FIELD OF THE INVENTION
The invention pertains to optical cross-connect switches. More particularly, the invention pertains to such switches which incorporate modular interconnect fabrics.
BACKGROUND OF THE INVENTION
Optical switches are known and are useful in implementing optical communications networks using fiberoptic transmission lines. In such networks, it is at times necessary to switch the optical signals between optical transmission paths.
One known type of optical switch is an optical cross-connect switch. In such switches, in a general case, any one of N input lines can be coupled to any one of N output lines.
One known type of cross-connect switch
10
is implementable using the Spanke architecture illustrated in FIG.
1
. In a Spanke architecture with N inputs and N outputs, N1×N switches
12
a, b, c, . . . n
are connected by an interconnect fabric
16
to N1×N output switches
18
a, b . . . n.
The interconnect fabric
16
has N2 total static connections. One connection is between each input-output pair of switches. Therefore, an N×N fabric has a total of N
2
fibers with N
2
inputs and N
2
outputs.
Insertion loss is a major concern in optical cross-connect switches. Although a single stage Spanke design can achieve small insertion loss, this solution creates yet another problem: namely, the difficulty of creating the large interconnecting fabric because the fabric contains N
2
connections.
Methods are known to implement small interconnect fabrics. For example, pre-routed fibers can be sandwiched between flexible plastic sheets sometimes called optical flypapers. They are however very difficult to create for N>32. Alternately, the interconnections can be made from N
2
individual fibers. However, this solution is time consuming to build and difficult to maintain.
There thus continues to be a need to be able to cost effectively design and implement larger cross connect switches of various sizes. It would be especially advantageous if it would not be necessary to custom create a different interconnect networks for each switch. Preferably, a known interconnect design can be reliably and cost effectively manufactured and could be used to implement a variety of switches.
SUMMARY OF THE INVENTION
A recursive process for creating large signal interconnects from a plurality of smaller, standardized, interconnect modules, which could incorporate individual optical fibers or electrical conductors, produces interconnect systems for specific applications using only standard modular building blocks. In accordance with the method, a first modular K×K interconnect network having K
2
signal carriers is defined and implemented. For L inputs,
L
K
input groups are formed. For M outputs,
M
K
output groups are defined.
A plurality of
(
L
K
×
M
K
)
of the first modular interconnects can be used to form an L×M passive interconnect network having L×M signal carriers.
A plurality of the L×M, modular interconnects, all of which are substantially identical, and all of which are based upon multiples of the basic K×K modular interconnect can be combined to form a larger N×N interconnect. For example, where L=M, and where N is an integer multiple of M,
N
M
input groups and
N
M
output groups result in
(
N
M
)
2
M×M modules being needed to implement the N×N connectivity. This type of network is especially desirable in that economies of scale in manufacturing, reliability and inventory can be achieved since N×N networks for various values of N can be implemented using multiple, identical K×K basic building blocks which in turn form the larger M×M assemblies which are combined to make the N×N networks.
In one embodiment, an N×N cross-connect switch incorporates a plurality of substantially identical interconnect modules. A plurality of input switches is coupled to N
2
inputs to the modules. A plurality of output switches is coupled to N
2
output sides of the modules.
In one aspect, the switches can be divided into groups with one set of groups associated with the input sides of some of the modules and another set of groups associated with the output sides.
In another aspect, a switch requiring N inputs and N outputs can be implemented with multiple identical modules that have K
2
inputs and K
2
outputs. The number of required modules is (N/K)
2
. In such configurations, the connectivity between the interconnect, a plurality of 1×N input switches and a plurality of N×1 output switches can be implemented using optical ribbon cables. The pluralities of switches each contain N switches.
Interconnect modules can be implemented with optical transmitting fibers. Alternately, they could be implemented with electrical conductors.
A method of implementing an N×N cross-connect switch includes establishing a K×K modular interconnect where K<N. Providing
(
N
K
)
2
interconnect modules. Coupling N
2
inputs to and receiving N
2
outputs from the modules.
In yet another aspect, interconnects, implemented from pluralities of smaller interconnect modules can in turn become modular building blocks for even larger interconnect fabrics. In accordance herewith M×M fabrics can be implemented with smaller N×N building blocks. In one embodiment, M is an integer multiple of N.
Non-symmetrical switches with N1 inputs and N2 outputs can be implemented using K×K interconnect modules where K<N1 and K<N2. With
N1
K
input groups and
N2
K
output groups,
(
N1
K
×
N2
K
)
interconnect modules will be required.
Numerous other advantages and features of the present invention will become readily apparent from the following detailed description of the invention and the embodiments thereof, from the claims and from the accompanying drawings.


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patent: 5703707 (1997-12-01), Dieudonne et al.
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patent: 6330102 (2001-12-01), Daneman et al.
Philip J. Lin, Wide Area Optical Backbone Networks. Doctoral Dissertation, © Massachusetts institute of Technology Feb. 1996; Cambridge, Massachusetts, USA.

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