Optical waveguides – With optical coupler – Switch
Reexamination Certificate
2001-06-01
2004-01-13
Kim, Robert H. (Department: 2882)
Optical waveguides
With optical coupler
Switch
Reexamination Certificate
active
06678436
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to telecommunications networks, and more particularly, to pure optical switches which direct light pulses from one optical fiber to another without electrical conversion.
BACKGROUND OF THE INVENTION
Telecommunications service providers continue to seek ever greater bandwidth at ever lower prices. Their data networks must be flexible to allow for continual upgrades, also referred to as “provisioning”. They must also designed for rapid fault recovery to avoid service degradation and even outages. High speed optical data networks now carry most of the long haul, and much of the metropolitan area data traffic in developed countries. Along such networks microprocessor controlled routers perform so-called “OEO” transcriptions, converting optically encoded data received from input optical fibers to electrical signals, reading destination code, and then reconverting the electrical signals back to optically encoded data and sending it along output optical fibers. As transmission speeds pass 2.488 Gbits/sec (OC-48 level), this conversion step becomes more difficult to perform and the cost of conventional high throughput electrical switches becomes unacceptable.
Pure optical switches direct light pulses directly from one optical fiber to another without electrical conversion and therefore offer the promise of eliminating much of the OEO transcriptions in high bandwidth fiber optic data transmission networks. Electrical routing intelligence would still be needed to direct traffic. However, currently about eighty percent of the traffic handled by a conventional router passes straight through and reading the destination header in most cases is a waste of time and system resources. By separating the control information from the transmitted data, pure optical switching would bring substantial increases in the throughput rate of optical data networks.
A variety of miniature electromechanical devices have been developed for changing the path of light in free space to direct light pulses from one optical fiber to another optical fiber. One promising approach utilizes three dimensional (3D) microelectromechanical systems (MEMS). Generally speaking, MEMS fabrication technology involves shaping a multi-layer monolithic structure by sequentially depositing and configuring layers of a multi-layer wafer. The wafer typically includes a plurality of polysilicon layers that are separated by layers of silicon dioxide and silicon nitride. The shaping of individual layers is done by etching that is controlled by masks patterned by photolithographic techniques. MEMS fabrication technology also entails etching intermediate sacrificial layers of the wafer to release overlying layers for use as thin elements that can be easily deformed and moved. Further details of MEMS fabrication technology may be found in a paper entitled “MEMS The Word for Optical Beam Manipulation” published in
Circuits and Devices,
July 1997, pp. 11-18. See also “Multiuser MEMS Processes (MUMPS) Introduction and Design Rules” Rev. 4, Jul. 15, 1996 MCNC Mems Technology Applications Center, Research Triangle Park, N.C. 27709 by D. Keoster, R. Majedevan, A. Shishkoff and K. Marcus.
FIG. 1
is a diagrammatic illustration of a conventional 3D MEMS optical switch
10
. A first array
12
of micro-machined mirrors is aligned with an input optical fiber bundle
14
, and juxtaposed opposite a second array
16
of micro-machined mirrors. Electrical command signals from a switch controller (not illustrated) cause individual mirrors in the arrays
12
and
16
to tilt. Input light pulses transmitted through a selected fiber in the input bundle
14
that strike an individual mirror in the first array
12
can be directed to another specific mirror in the second array
16
and from that mirror to a selected fiber in an output optical fiber bundle
18
aligned with the second array
16
. The individual light beams travel along Z-shaped paths
19
in free space. There is usually a lens (not illustrated) between the first and second mirror arrays
12
and
14
. The purpose of this lens is to image the facets of the fibers in the input bundle
14
onto the facets of the fibers in the output bundle
18
. Because the light beams coming out of the fibers in the input bundle
14
diverge, the lens is necessary to focus the light onto the fibers in the output bundle
18
. In some cases, there are two lenses between the two arrays
12
and
14
to form a sort of telescope in order to accomplish this imaging. The optical switch
10
has distinct advantages over electrical switches in that the former operates completely independent of changes in the bit rate, wavelength and polarization.
3D MEMS optical switches are targeted for use in network cores and nodes in both long haul and metropolitan area data networks. 2D MEMS optical switches simply raise or lower pop-up mirrors at fixed angles to switch to a given data port. See for example U.S. Pat. No. 5,994,159 of Aksyuk et al. assigned to Lucent Technologies, Inc. and U.S. Pat. No. 6,097,859 of Sogarard et al. assigned to the Regents of the University of California. In the 3D MEMS optical switch of
FIG. 1
, optical signals are reflected by the first and second arrays
12
and
16
each made of micro-machined mirrors that can each be tilted variable amounts in two axes, bouncing an incoming optical signal from a selected optical fiber in the input bundle
14
to a selected optical fiber in the output bundle
18
in a manner that results in less signal loss than in 2D MEMS optical switches.
The 3D MEMS optical switch of
FIG. 1
accommodates any data rate or transmission protocol and its architecture is more readily scalable than 2D MEMS optical switch designs. Larger switching capacities are achieved simply by doubling, rather than squaring, the number of mirrors needed for the desired channel count. 2D MEMS optical switches are really not practical beyond a 32×32 matrix. 3D MEMS optical switches have been commercially announced that offer a 64×64 input/output capacity in a relatively small form factor. They have high cross-talk rejection and flat passband response and are well suited for use in wavelength-division multiplexed (WDM) optical data networks.
While 3D MEMS optical switches show great promise, it would be desirable to provide an alternate architecture for a large capacity pure optical switch that does not rely on arrays of two-axis tilting micro-machined mirrors. Precise angular alignment of these miniature mirrors can be difficult to achieve. Such a switch would need to exhibit similar high cross-talk rejection and flat passband response.
SUMMARY OF THE INVENTION
It is therefore the primary object of the present invention to provide a large capacity pure optical switch which does not rely on twin arrays of two-axis tilting micro-machined mirrors.
In accordance with a first embodiment of the present invention, an optical switch includes an array of optical fibers having a plurality of facets lying in a first plane. An array of lenses is formed in a second plane spaced from, and generally parallel to, the first plane. There is one lens corresponding to each fiber for receiving and focusing light beams emanating from the array of optical fibers. A plurality of actuators are provided for each independently translating a corresponding lens a predetermined amount within the second plane along an X axis and a Y axis. A mirror is spaced from, and generally parallel to, the second plane. The lenses are configured and translatable by their actuators such that a light beam emanating from the facet of a first selected optical fiber in the array of optical fibers can be deflected in a first predetermined manner by a first one of the lenses, reflected off of the mirror back to the array of lenses, and deflected in a second predetermined manner by a second one of the lenses and focused on the facet of a selected second optical fiber.
In accordance with a second embodiment of the present invention an optical switch includes a first array of optical f
Agilent Technologie,s Inc.
Kim Richard
Kim Robert H.
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