Optical waveguides – With optical coupler – Switch
Reexamination Certificate
2001-10-26
2003-09-09
Kim, Robert H. (Department: 2882)
Optical waveguides
With optical coupler
Switch
C385S018000
Reexamination Certificate
active
06618517
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based on, and claims priority of, Canadian Patent Applications Nos. 2,326,362 filed Nov. 20, 2000, and 2,327,862 filed Dec. 6, 2000.
MICROFICHE APPENDIX
Not Applicable.
TECHNICAL FIELD
The present application relates to the field of optical cross-connects, and in particular to a cascadable optical cross-connect.
BACKGROUND OF THE INVENTION
Optical matrix cross-connects (or switches) are commonly used in communications systems for transmitting voice, video and data signals. Generally, optical matrix cross-connects include multiple input and/or output ports and have the ability to connect, for purposes of signal transfer, any input port/output port combination, and preferably, for N×M switching applications, to allow for multiple connections at one time. At each port, optical signals are transmitted and/or received via an end of an optical waveguide. The waveguide ends of the input and output ports are optically connected across a switch core. In this regard, for example, the input and output waveguide ends can be physically located on opposite sides of a switch core for direct or folded optical pathway communication therebetween, in side-by-side matrices on the same physical side of a switch core facing a mirror, or they may be interspersed in a single matrix arrangement facing a mirror.
Establishing a connection between any input port and a selected output port involves configuring an optical pathway across the switch core. One known way to configure the optical pathway is by moving or bending optical fibers using, for example, piezoelectric actuators. The actuators operate to displace the fiber ends so that signals from the fibers are targeted at one another so as to form the desired optical connection across the switch core. The amount of movement is controlled based on the electrical signal applied to the benders. By appropriate arrangement of actuators, two-dimensional targeting control can be effected.
Another way of configuring the optical path between an input port and an output port involves the use of one or more movable mirrors interposed between the input and output ports. In this case, the waveguide ends remain stationary and the mirrors are used to deflect a light beam propagating through the switch core from the input port to effect the desired switching. Micro-electro-mechanical mirrors known in the art can allow for two-dimensional targeting to optically connect any input port to any output port. For example, U.S. Pat. No. 5,914,801, entitled MICROELECTROMECHANICAL DEVICES INCLUDING ROTATING PLATES AND RELATED METHODS, which issued to Dhuler et al on Jun. 22, 1999; U.S. Pat. No. 6,087,747, entitled MICROELECTROMECHANICAL BEAM FOR ALLOWING A PLATE TO ROTATE IN RELATION TO A FRAME IN A MICROELECTROMECHANICAL DEVICE, which issued to Dhuler et al on Jul. 11, 2000; and U.S. Pat. No. 6,134,042, entitled REFLECTIVE MEMS ACTUATOR WITH A LASER, which issued to Dhuler et al on Oct. 17, 2000, disclose micro-electro-mechanical mirrors that can be controllably moved in two dimensions to effect optical switching. U.S. Pat. No. 6,097,858, entitled SENSING CONFIGURATION FOR FIBER OPTIC SWITCH CONTROL SYSTEM, and U.S. Pat. No. 6,097,860, entitled COMPACT OPTICAL MATRIX SWITCH WITH FIXED LOCATION FIBERS, both of which issued to Laor on Aug. 1, 2000, disclose switch control systems for controlling the position of two-dimensionally movable mirrors in an optical switch.
An important consideration in cross-connect design is minimizing physical size for a given number of input and output ports that are serviced, i.e., increasing the packing density of ports and beam directing units. It has been recognized that greater packing density can be achieved, particularly in the case of a movable mirror-based beam directing unit, by folding the optical path between the ports and the movable mirror and/or between the movable mirror and the switch interface. Such a compact optical matrix switch is disclosed in U.S. Pat. No. 6,097,860. In addition, further compactness advantages are achieved therein by positioning control signal sources outside of the fiber array and, preferably, at positions within the folded optical path selected to reduce the required size of the optics path.
Another technique of minimizing cross-connect size is to minimize the number of mirrors within the switch core. For example, a typical two-dimensional (2D) switch core employs a matrix of N
2
independently movable mirrors, which enable N×N switching using a single reflection of a light beam propagating between an input port and a selected output port. However, since each of the N
2
mirrors must be independently controlled, increases in the size of the switch core (that is, increasing N) implies an exponential increase in the number of mirrors, and a corresponding increase in the size of the switch control circuitry. These factors combine to impose practical limits on the size of the cross-connect. One way of overcoming this problem, and thereby enabling the construction of high capacity cross-connects, is to employ a three-dimensional (3D) switch core, in which 2N independently movable mirrors are used to enable N×N switching. Within a 3D switch core, optical switching is performed using two reflections of the light beam propagating between an input port and a selected output port. The reduced number of mirrors required by a 3D switching core (2N as compared to N
2
required by a 2D switching core) is beneficial in that it permits the construction of a physically smaller switch core. Additionally, it permits a corresponding reduction in the size of the switch control system, and therefore enables construction of higher capacity cross-connects.
While it is desirable to minimize the physical size of the cross-connect, a competing demand is to maximize the number of fibers (or waveguides) between which signals can be switched. In electronic switching technologies, this is commonly accomplished by connecting a plurality of cross-connect blocks together to form a network having a larger capacity. As is known in the art, a fully non-blocking M×M cross-connect can be created using a plurality of smaller (that is, lower capacity) N×N cross-connect blocks interconnected to define a 3-layer Clos network.
Implementation of Clos network architectures in the optical domain requires that cross-connect blocks be cascaded. This, in turn, requires that each block be capable of N×2N switching. As is well known in the art, N×2N optical switching can be accomplished using a conventional 2D N×2N switch core, in which 2N mirrors are positioned within a propagation path of an input light beam to selectively switch the light beam to a respective one of 2N output ports. An analogous technique uses a switch core composed of a MEMS array having N independently positionable mirrors, each of which is designed to switch a respective incident light beam to a selected one of 2N output ports. Both of these approaches suffer from scalability limitations, as even small increases in the value of N result in sizable increases in either the number of mirrors (and thus the size of the switch core) or the number of positions to which each mirror must be positioned (and thus the complexity of the control system).
An alternative technique of implementing N×2N switching is to provide the switch core with express paths that couple inbound optical signals directly to an express output port (typically connected to an input port of an adjacent switch block) effectively bypassing the switch core. Such express paths can readily be implemented in a conventional 2D N×N switch core, by positioning a respective express output port on the opposite side of the switch core from each input port. With this arrangement, when all of the N mirrors associated with any one input port are positioned out of the propagation path, the light beam from the input port will transit the switch core to the respective express output port unhindered. However, in a 3D switch
Ducellier Thomas
MacDonald Robert Ian
Artman Thomas R
JDS Uniphase Inc.
Kim Robert H.
Teitelbaum Neil
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