Optical waveguides – With optical coupler – Switch
Reexamination Certificate
2000-11-30
2004-09-14
Bruce, David V. (Department: 2882)
Optical waveguides
With optical coupler
Switch
C385S015000, C385S016000, C385S011000, C359S490020
Reexamination Certificate
active
06792175
ABSTRACT:
This invention pertains to an all optical crossbar switch, in which each of multiple input sources is selectively connected optically to any of multiple output receivers.
In recent years increasingly large amounts of voice, video, and data have been carried by optical fibers. To minimize signal dispersion, these fibers generally support only a single optical mode each. To increase capacity large numbers of fibers are often bundled together.
Considerable effort has been made in improving methods for switching data or other signals. It is often necessary to switch data between optical fibers so that it travels correctly from its source to the proper destination. One way to switch data is to electronically detect the optical signals, and electronically switch those electronically-detected signals. New optical signals are then generated from the electronically switched signals, and are sent to appropriate output fibers. This hybrid optical-electrical-optical procedure is relatively complex, requires many optical and electronic components, and does not fully use the available optical bandwidth.
Alternatively, it is possible to switch signals solely in the optical domain, i.e., switching all of the optical signals in a fiber to the appropriate destination fiber with no intervening conversion to an electrical signal. All-optical switching should ideally be simpler, more reliable, and result in better use of bandwidth.
Prior optical crossbars, in which light propagates through integrated optical systems, are described for example in U.S. Pat. Nos. 4,013,000, 5,255,332, and 5,283,844. Prior optical crossbar switching systems have been rather complex, and have not yet fully proven themselves in practice. In the crossbar of the U.S. Pat. No. 4,013,000 patent, grating couplers selectively coupling inputs to outputs are mechanically moved between different positions by piezoelectric drivers; alternatives for mechanically moving the couplers were said to include inducing gratings by electro-optical, acousto-optical, or magneto-optical means. In the crossbar of the U.S. Pat. No. 5,255,332 patent, the reflectivity of grating couplers is altered by voltages applied to the gratings. In the crossbar of the U.S. Pat. No. 5,283,844 patent, redirection of optical signals along an optical waveguide is accomplished by means of total internal reflectance turning mirrors in which a portion of the waveguide, along with surrounding semiconductor layers, are etched to a point beneath a single quantum well and confinement layers, such that optical signals arriving at the etched facet are redirected.
U.S. Pat. No. 5,013,140 describes an N-to-1 optical switch using N deflection stages with polarization rotators and deflection means, e.g. a birefringent calcite crystal or a polarizing beam splitter, to determine which of 2
N
inputs is selected at the output.
U.S. Pat. No. 4,461,543 describes an optical switch in which a birefringent crystal followed by a polarization rotator is used to cause arbitrarily polarized light to form two beams of the same polarization, which are then deflected to selected parallel paths. A second polarization rotator reestablishes the initial polarization, and the beams are then recombined by a second birefringent crystal.
U.S. Pat. No. 6,031,658 discloses an optical scanner using a binary optical polarization sensitive cascaded architecture having binary switchable optical plates for scanning in one, two, or three dimensions. It was said that several such scanners could be combined on a three-dimensional surface to form an N×N fiber optic switch. Each scanner apparently uses a separate lens system for correct coupling to output fibers on another three-dimensional surface. Each scanner relies on an on-chip control birefringent mode nematic liquid crystal device or birefringent plate that can be programmed to generate “any desired optical wavefront.”
T. Nelson, Digital Light Deflection, Bell System Technical Journal, pp. 821-845 (May 1964) discloses a digital method of deflecting a light beam using n optical modulators and n birefringent crystals to provide 2
n
possible output beam positions. The thicknesses of successive birefringent crystals decreased by factors of 2 to allow addressing to binary output positions. Because each crystal can displace an input from one channel into a different channel, it would be cumbersome to adapt this device for use as a switch for multiple inputs, since it would be difficult to keep different beams separated from one another after they had entered a common intermediate channel. Thus this device is well-suited for use as a multiplexer or demultiplexer, switching N channels to 1 channel, or 1 channel to N channels. However, it would be awkward to use this device as a crossbar, which is a device that can arbitrarily, simultaneously, and independently switch each of several inputs to any one of several outputs, without interference between different channels.
“Small wonder: MEMS will power optical Internet,”
IEEE Computer
(July 2000) describes an all-optical switch based on mechanically controllable silicon microstructures and mirrors.
There is a continuing, unfilled need for an efficient, all-optical crossbar, suitable for switching from multiple inputs to multiple outputs, without interference between channels, and with little or no delay in the transmitted signals.
We have discovered an efficient, all-optical crossbar, in which multiple input sources are optically connected, in any desired combination (including one-to-one and many-to-one permutations), to multiple output receivers. The system is optically simple, has low insertion loss, and may be used to make connections between large numbers of inputs and outputs. It is well-adapted to switching signals on single and multiple mode optical fibers. The novel all-optical crossbar is well-suited to switching massive amounts of data between arrays of fiber optics. Such high-capacity switching will be useful, for example, in many Internet applications. The signal paths in the novel crossbar are all-optical. Electrical signals (control voltages) are used, but only for beam steering control. The signal is never converted to an electronic form during the switching. There is relatively little loss; the primary loss (at least in certain embodiments of the invention) will normally be the 3 db or so loss that results from a linear polarization of unpolarized input light.
The novel optical crossbar uses a series of deflecting elements, such as prisms or birefringent plates, to direct beams of light emitted from an input array of light sources. Each deflector deflects the light in a direction that is a function of the polarization of the light as it passes through the deflector. The deflectors deflect the light through a series of angles, so that after passing through n deflectors the light may be deflected into one of 2
n
different angles.
The particular output to which each particular input is directed is controlled by voltages applied to several deflection units, where each deflection unit comprises an array of polarization control elements and a polarization-sensitive angular deflector, such as a polarization-sensitive deflection prism. Depending on the output address selected for a given input, a polarization control element may leave the polarization of the light unchanged, or it may rotate the plane of polarization to select a different direction of deflection in the subsequent polarization-sensitive deflector. The various polarization-sensitive deflectors preferably differ in strength (e.g., have differing thicknesses) to allow switching that corresponds to arbitrary binary addressing. Also, the deflection units preferably can deflect light in either of two directions, for example either horizontally or vertically, so that the input and output arrays may be either one-dimensional or (preferred) two-dimensional.
As an example of the geometrical optics that may be used in embodiments of this invention, consider the arrangement illustrated in
FIG. 8
, in which light is emitted parallel to the
El-Amawy Ahmed
Feldman Martin
Vaidyanathan Ramachandran
Board of Supervisors of Louisiana State University and Agricultu
Bruce David V.
Kao Chih-Cheng Glen
Runnels John H.
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