Optical waveguides – With optical coupler – Switch
Reexamination Certificate
2000-07-31
2002-12-10
Healy, Brian (Department: 2874)
Optical waveguides
With optical coupler
Switch
C385S016000, C385S018000
Reexamination Certificate
active
06493480
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to optical switches for telecommunications and related applications, and particularly to multi-stage optical cross-connects.
2. Technical Background
A cross-connect is generally a big, complex switch, or, more specifically, a device for connecting any one of N signal inputs to any one of M signal outputs. Large cross-connects in practical use today employ complex electronic switching. But because optical signals can carry data for much greater distances at much greater rates than electronic signals, development of optical cross-connects is proceeding in response to ever increasing demand for higher capacity, more efficient telecommunications.
The basic logical structure of a cross-connect is shown schematically in FIG.
1
. Any one of the input lines
20
may be selectively connected to any one of the output lines
30
. This may be achieved, for example, by a plurality of switching devices positioned at respective cross-points
40
between the input and output lines, where each switching device allows a connection to be selectively established between the associated input and output lines.
In an optical cross-connect, the input lines
20
of
FIG. 1
may take the form of waveguides of various forms including those formed on or in a substrate, or optical signal beam paths for unconfined beams propagating in free space or in another medium, or the like. Optical signals entering such a cross-connect along the input lines
20
in the direction A, for example, may be redirected at selected ones of the cross-points
40
so as to exit the switch along desired ones of the output lines
30
in direction B, for example.
Depending on the particular switching devices employed and other factors, the geometry of a typical optical cross-connect may vary from that shown in FIG.
1
. For example, the intersection of waveguides or beam paths may be at angles other than right angles, and inputs may arrive in more than one direction A, and outputs may leave in more than one direction B, as shown in
FIG. 2
, for example. Inputs and outputs may also be interchangeable and/or physically indistinguishable in an optical switch, so one line may function as either or both. Accordingly, while “input” and “output” will be used for convenient reference herein, it is to be understood that these are equivalent terms in the context of the optical switches as described and claimed herein, and are understood not to limit the structure and functionality of the inventive devices thus described.
Devices employing frustrated total internal reflection are also known to those of ordinary skill in the art. All these and such other switching devices as known to those of skill in the art may be used in optical switches of the type shown schematically in
FIGS. 1 and 2
.
One example of such switching devices are small mechanical mirrors known as “MEMS” (Micro-Electro-Mechanical Systems) mirrors. MEMS mirrors can be used with either a beam-based or a wave-guide based switch. In either case, the mirrors are positioned at or near the cross-points
40
and are controllably moveable so as to be selectively inserted at the respective cross-points. With a mirror inserted at a selected cross-point, a beam or a guided wave arriving at that cross-point is redirected from direction A to direction B at that cross-point. In a switch employing inputs from two directions A as in
FIG. 2
, double-surfaced mirrors can be used. An example wave-guide and MEMS-mirror switch is disclosed in U.S. patent application Ser. No. 99/24,591, filed Oct. 20, 1999, assigned in common with the present application and incorporated herein by reference. An example free-space beam and MEMS mirror optical switch is disclosed in U.S. Pat. No. 5,960,132 also incorporated herein by reference.
Another example switching device suggested for use in optical switches of the type shown schematically in
FIG. 1
is a fluid injection device. By injecting a fluid into (or removing a fluid from) a cross-point of a waveguide structure, the index of refraction can be varied at the cross-point so as to reflect an incoming guided wave arriving at the crosspoint into the associated output waveguide. The construction and use of such a switching device is disclosed, for example, in U.S. Pat. No. 5,978,527 incorporated herein by reference.
Another example switching device suggested for use in optical switches of the type shown schematically in
FIG. 1
uses liquid crystals formed within the waveguides at the respective cross-points. The construction and use of such devices is disclosed in U.S. patent application Ser. No. 09/604,039 and U.S. patent application Ser. No. 09/431,430, commonly assigned with the present application and incorporated herein by reference.
Devices employing techniques such as photonic crystals or frustrated total internal reflection are also known to those of ordinary skill in the art. All these and such other switching devices as known to those of skill in the art may be used in optical switches of the type shown schematically in
FIGS. 1 and 2
.
Where waveguides are used (rather than beams) for light propagation within the switch, the crossing pattern of the input and output lines shown in
FIGS. 1 and 2
may be folded back on itself, such as is as shown schematically in FIG.
3
. An example of a switch of this design using MEMS mirrors is disclosed in U.S. Pat. No. 5,148,506, incorporated herein by reference.
While all of the above-described switching devices may be useful in switch designs such as those of
FIGS. 1-3
, as the scale of the switch increases, these switch designs are less practical. The number of cross-points typically increases as the number of inputs times the number of outputs, making large-scale switches, such as 1024×1024 for example, difficult to implement.
It is well known that larger cross-connects can be formed from several smaller cross-connects linked together. One way of linking non-blocking cross-connects together to produce a larger non-blocking cross-connect is illustrated in FIG.
4
.
FIG. 4
shows an example layout for an arrangement known as a three-stage Clos network. The network shown, as a whole, provides an N×N non-blocking cross-connect. Stage
1
includes multiple cross-connects, each with n inputs and 2n−1 outputs, as illustrated for cross-connect number
1
of Stage
1
. The N inputs to the network are received by a total of N
of these cross-connects in Stage
1
. For each of the N
cross-connects of Stage
1
, each of the 2n−1 outputs are routed to a respective Stage
2
cross-connect, as illustrated for cross-connect
2
of stage
1
. Stage
2
includes 2n−1 cross-connects, one for each output of the Stage
1
cross-connects. Each cross-connect of stage
2
has N
inputs and outputs. For each of the 2n−1 cross-connects of stage
2
, each of the N
outputs are routed to a respective Stage
3
cross-connect, as illustrated for cross-connect
2
of Stage
2
. Stage
3
includes N
cross-connects, one for each output of the Stage
2
cross-connects. Each of Stage
3
cross-connects has 2n−1 inputs and n outputs. The n outputs of all of the Stage
3
cross-connects together provide the N outputs of the network. As may be appreciated from
FIG. 4
, the interconnections between the stages in such a multi-stage switch can be complex.
SUMMARY OF THE INVENTION
The present invention includes, in one aspect, a multi-stage optical cross-connect including a first stage having a plurality of first stage sub-switches each structured and positioned so as to receive inputs along a plurality of first stage input directions and to send outputs along a plurality of first stage output directions, and a second stage including a plurality of second stage sub-switches each structured and positioned so as to receive inputs along a plurality of second stage input directions and to send outputs along a plurality of second stage output directions, and a third stage including a plurality of third-s
Corning Incorporated
Pappas Joanne N.
Wood Kevin S
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