Signal interconnect incorporating multiple modular units

An interconnect element incorporates a plurality of smaller, substantially identical, interconnect modules. Multiple identical elements can in turn be combined to form larger interconnect networks. Signal paths in the elements can be implemented with optical fibers or electrical conductors.

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 switch10is implementable using the Spanke architecture illustrated inFIG. 1. In a Spanke architecture with N inputs and N outputs, N 1×N switches12a, b, c, . . . n are connected by an interconnect fabric16to N 1×N output switches18a, b. . . n.

The interconnect fabric16has N2total static connections. One connection is between each input-output pair of switches. Therefore, an N×N fabric has a total of N2fibers with N2inputs and N2outputs.

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 N2connections.

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 N2individual 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 K2signal carriers is defined and implemented. For L inputs,

LK
input groups are formed. For M outputs,

MK
output groups are defined.

A plurality of

(LK×MK)
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,

NM
input groups and

NM
output groups result in

(NM)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 N2inputs to the modules. A plurality of output switches is coupled to N2output 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 K2inputs and K2outputs. 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

(NK)2
interconnect modules. Coupling N2inputs to and receiving N2outputs 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 N1inputs and N2outputs can be implemented using K×K interconnect modules where K<N1and K<N2. With

N1K
input groups and

(N1K×N2K)
interconnect modules will be required.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 2illustrates a 12×12 cross-connect switch30in accordance with the present invention. It will be understood that while switch30has been illustrated for exemplary purposes as a 12×12 cross-connect switch, the number of inputs and the number of outputs is not limited to 12 and could be N>12. It will be also understood that the inputs to and outputs from the switch30could be light beams or could be electrical signals without departing from the spirit and scope of the present invention.

Switch30includes N input switches32a. . .32n. In the illustrated embodiment, N=12, there would be 12 input switches each of which would be a 1×N type of switch, such as a 1×12 switch. The switch30also includes N, N×1 output switches34a. . .34n. In the illustrated example inFIG. 2, there would be 12 such output switches which would have 12 inputs and one output at each switch.

The input switches and the output switches are coupled together by a plurality30′ of substantially identical, static, modular K×K interconnect elements36a. . .36l, K<N. The number of elements is,

(NK)2.
Where N=12 and K=4, then nine 4×4 interconnect elements are required.

Each modular K×K, interconnect element has K2inputs and K2outputs. A representative 4×4 modular interconnect element, such as element36i, having 16 inputs that are coupled to 16 outputs is illustrated inFIG. 2A. Such modules include a plurality of pre-routed signal carriers36i-1optical fibers or electrical conductors. Sixteen signal carriers, for the illustrated 4×4 module, are sandwiched between a pair of plastic sheets, or attached to a single sheet,36i-2.

A first plurality of four, 4-way connectors36i-3and a second plurality of four, 4-way connectors36i-4complete the module the connectors can be individual or multi-path connectors.

The switch30, as noted previously has,

(NK)
groups, each K×K interconnect module connects a single input group to a single output group with

(NK)2
group pairs, the number of K×K interconnect modules.

Each group of K fibers such as40a,42acan be formed of individual fibers, or, of K-wide fiber ribbon cables having K-wide multi-fiber optical connectors.

Each group includes, for K=4, four 1×12 input switches such as32a,32b,32c,32d. Groups of K fibers, such as fiber groups40a,40b,40care coupled to K respective inputs each of interconnect elements36a,36band36c. With respect to input switch32n, 3 groups of K fibers,40l,40m,40n, where K=4, are coupled to respective inputs of K×K fabric interconnect modules36j,36k,36l.FIG. 3illustrates in more detail connections for a portion of the exemplary switch30.

Output switches34a,34b,34c,34dreceive groups of fibers,42a,42b,42c, and42d, where K=4, from K×K interconnect module36a. In the same way, K×K interconnect module36lis coupled via groups of K fibers, such as42k,42l,42mand42nto 1×N, illustrated as 1×12, output switches34k,34l,34m,34n.

The architecture of switches such as switch30inFIG. 2is expandable and variable depending on the value of N and the value of K. As an alternate, if N=128 and K=32, the number of interconnect modules

(NK)2
is 16. In this instance, each interconnect module would have K2or 322inputs and the same number of outputs.

The use of multiple, smaller, modular interconnect elements, as illustrated inFIG. 2, makes it possible to build interconnects where N is a large number, such as for example 128 or larger, using only a plurality of K×K modular interconnect units to form an interconnecting sheet. All of the units can be manufactured so as to be substantially identical.

While the K×K modules36a. . .36las disclosed inFIG. 2can incorporate a plurality of optical fiber lines, similar interconnects could be implemented using, modular electrical conductors. The above described signal carrier management process produces interconnects quite unlike the prior art of either a single pre-routed fabric of N2fibers or N2individual fibers.

The ability to implement increasingly larger switches using pluralities of a common interconnect module, to form interconnecting sheets, has important manufacturing, inventory control and quality control consequences. Only one, or at most a few, standard fiber or wire interconnect modules need be manufactured. Hence, the manufacturing process can be optimized to produce a few different types of modules. Since manufacturing turn around time can be minimized, less inventory needs to be maintained. Finally, quality control can be improved, and enhanced since fewer configurations are being created.

Common interconnect modules are also advantageous from a maintenance point of view. In case of a cut or failed fiber or wire only that respective modular interconnect element need be replaced.

The K×K interconnect modules ofFIG. 2can be used to implement non-symmetrical switches. For example, with N1inputs and N2outputs,

N1K
input groups and

N2K
output groups can be defined. These result in

(N1K×N2K)
input/output group pairs and interconnect modules to implement the required network. Input switches and output switches can be coupled to the network.

FIG. 4illustrates an even larger M×M interconnect50. Where M is an integer multiple of N, the interconnect50can be implemented using a plurality of N×N interconnect modules, such as the module30′-iwhich corresponds to interconnect30′ ofFIG. 2. The recursive application of the modules30′, which in turn are based upon the smaller K×K submodules ofFIG. 2, makes the construction of even larger interconnects practical as they are all ultimately based on two modular interconnect elements

One modular building block is the basic k×k modular fabric element, such as the element36aor361illustrated inFIGS. 2 and 3. A second modular building block is the N×N composite fabric element30′ provided that M is an integer multiple of N. If desired, multiple modular M×M interconnects an be combined into yet a larger network.

As illustrated inFIG. 4, in the network50, groups of N signal carriers, such as the groups52a,52b. . .52ncoupled to interconnect module30′-1are combined with groups of N carriers coupled to other modules such as30′-2. . .30′kto form the composite M×M interconnecting sheet50. With N carriers in a group, there will be

MN
groups resulting in

(MN)2
interconnect modules, such as the module30′-1being required. Each N×N interconnect module connects a single input group of N to a single output group with

(MN)2
group pairs. Those of skill will understand that the interconnect50could be combined with appropriate types of input/output switches as discussed previously with respect toFIG. 2.

It will also be understood that the M×M interconnect modules50can be similarly combined, as discussed above to create larger interconnect networks, again from a plurality of substantially identical M×M modules.