Optical waveguides – With optical coupler – Switch
Reexamination Certificate
1998-12-28
2001-11-13
Font, Frank G. (Department: 2877)
Optical waveguides
With optical coupler
Switch
C385S018000, C359S212100, C359S850000, C359S855000, C359S856000, C359S857000, C359S862000
Reexamination Certificate
active
06317530
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to cross-connect switches for use in optical networks and more particularly to such switches that use micromirrors as a switching element to permit the switching of optical signals directly without the need to convert them to electrical signals.
BACKGROUND OF THE INVENTION
The growing interest in optical networks for use in communication systems has led to growing interest in switching apparatus, such as cross-connect switches, that switch optical signals directly using micromirrors as the switching element. Generally these systems use flip-mirror chips arranged in a two-dimensional grid connected in crossbar style. An input collimated beam supplied to an input port by an optical fiber is guided along an optical path, typically either in free space or over a plane of silicon, until it is intercepted and reflected by a flip-chip micromirror that has been electronically activated to make a 45° angle with the input beam, after which the beam travels in a path at a 90° angle to its earlier path to an output port where it is collected by an output fiber. Such a system, for example, is described in a paper entitled “Free Space Micromachined Optical Switches with Submillisecond Switching Time for Large Scale Optical Crossconnects,”
IEEE Photonics Technology Letters,
V10, 4, 1998, pp. 525-527.
The problem with this approach is that a small diameter collimated beam can travel only a limited distance before broadening. Accordingly unless the beam is relay-imaged by one or more intervening lenses, this problem limits the number of input and output ports feasible. Moreover placing a relay lens between each of the N×N flip-mirrors needed in an N×N switch introduces too much loss for large values of N, such as for the 1024×1024 switch typically required in state-of-the-art switches. Another problem is that there is considerable variation in the lengths of the various paths between the input and output ports and this complicates keeping all beams focused by interposed lenses.
SUMMARY OF THE INVENTION
The present invention is a scalable multistage interconnection switch for optical signals that uses a novel layout of switches that are micromechanical mirrors that are movable by an actuator and are designed to reflect on both surfaces, in combination with stationary mirrors that are sided on only one surface for redirecting the paths of the beams. Advantageously, there may also be included along the beam paths lenses for keeping the beams well focused. By making both surfaces reflective, as by coating, each mirror can act as a 2×2 switch as previously described in a paper entitled “High Density Connecting-Symmetric Free-Space Micromachined Polygon Optical Crossconnects with Low Loss for WDM Networks,” Postdeadline Paper PD-24,
Optical Fiber Communications,
1998, San Jose, Calif., whose teaching is incorporated herein by reference.
It is a characteristic of the novel layout that all paths between an input port and an output port are essentially of equal length, which permits the lenses to be used readily for relay imaging. Also this facilitates the location of lenses along the beam paths so that they can form beam waists where the switches are located. As a result small movements of a switch are needed to properly redirect the incident beam. Also this fact permits the lenses to be readily used for relay imaging when this is desired.
As used herein, a multistage switching network is one that includes successive layers or sets of switches such that at each layer a light beam can be switched to a new path and that generally includes log
2
N layers for an N×N switch. Such layers generally use fewer switches than do the older cross-bar switches, which reduces the total switch complexity, and also facilitates the location of lenses to keep the beam well defined.
The principles of multistage networks are described in a paper entitled “Growth, Complexity and Performance of Telephone Connecting Networks” by V. E. Benes, published in
The Bell System Technical Journal,
Vol. 62, No. 3, February 1963, pp. 499-539 and its teaching is incorporated herein by reference.
REFERENCES:
patent: 5841917 (1998-11-01), Jungerman et al.
patent: 5872878 (1999-02-01), Bergmann
patent: 6144781 (2000-11-01), Goldstein et al.
Font Frank G.
Lucent Technologies
Mooney Michael P.
LandOfFree
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