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Description  |
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TECHNICAL FIELD OF THE INVENTION
The present invention is related to optical communication systems and, more particularly, to optical backplanes associated with communicating information between components of a computer system and communicating multiple optical signals in
telecommunication networks.
BACKGROUND OF THE INVENTION
The current generation of computers is often limited by the speed at which information can be transmitted between electronic components such as processors and memory chips. For example, a typical personal computer bus or motherboard operates at
a frequency of only 100 MHz, whereas processors are often able to reach speeds of 1 GHz. Similarly, logic circuits frequently outpace inter-board interconnect speeds within subsystems which depend on communications between cards within a computer.
Development of technologies for communications within computer systems to replace conventional passive backplanes and motherboards is a long standing goal to achieve higher data throughputs. Under current conditions, bus traffic generally increases as
computing power of a processor increases. Therefore, limited bus bandwidth associated with many computer systems represents a major bottleneck to efficient communications between board-to-board data interfaces.
There are two major types of optical backplanes: free space and guided wave. Free space optical backplane bus system generally has free space channels and diffractive optical elements to direct associated signal beams. Guided wave optical
backplanes generally include optical beams traveling through total internal reflection within an associated waveguiding plate. DOEs such as holographic gratings are frequently used as beamsplitter/deflectors in guided wave optical backplanes.
Difficulties have been noted in both types of optical backplane with obtaining uniform optical signal power levels at the respective outputs. Uniform intensity of output optical signal power levels is difficult to obtain even when diffraction
efficiencies of associated DOE's has been optimized in a prior guided wave optical backplanes.
Optical backplanes typically include one or more optical signal input ports and one or more optical signal output ports. Incoming optical signals are monitored at each input port. The optical signal is generally directly coupled to an optical
backplane which routes the signal to another unit or component associated with the optical communication system. One example of such components includes optical cross connect fabric, optical switches, wavelength division multiplexers and/or
demultiplexers. Optical backplanes often provide a cost effective and compact solution for many optical communication systems.
SUMMARY OF THE INVENTION
In accordance with teachings of the present invention a method and apparatus are disclosed for broadcasting and rebroadcasting optical signals to multiple components of a computer system. One aspect of the present invention includes an optical
backplane assembly for communicating optical signals with multiple components based on guided wave interconnects. The invention may be implemented with holograms and active optical elements providing interfaces between a conventional electrical
backplane with attached components such as circuit boards and an optical backplane. One embodiment includes a distributor installed as a center component having a receiver, a doubly multiplexed hologram, and a transmitter. Any signals coming from one
of the components may be collected by the receiver of the distributor and rebroadcast from the transmitter of the distributor to all of the other components.
A further aspect of the present invention includes an optical bus assembly with very high data throughput capability as compared with conventional passive busses and backplanes. The optical bus assembly preferably includes bidirectional signal
paths to both receive and transmit optical signals between a plurality of components such as circuit boards. Active couplers formed in accordance with teachings of the present invention may both receive and transmit optical signals. Each active coupler
may include active optical elements such as an optical signal transmitter and an optical signal receiver. Each active coupler may also include a hologram or holographic optical element which functions as an optical signal beam splitter and an optical
signal deflector.
Technical advantages of the present invention include increased bandwidth capacity, increased speed, reduced cross talk and reduced interference during communication of optical signals between various components of a computer system or a
communication system. Additional components may be added to an optical backplane assembly formed in accordance with teachings of the present invention without substantially decreasing associated bandwidth capacity or speed of data communication between
components and without a significant increase in cross talk or interference during communication of optical signals between the components. The number of slots or electrical connections associated with the optical backplane assembly may be substantially
increased without reducing overall performance characteristics of the optical backplane assembly and attached components.
An optical backplane assembly formed in accordance with teachings of the present invention may use existing slots or electrical connections associated with presently available electrical backplanes and existing electrical circuit cards or any
other component. Both initial assembly and later modification of the optical backplane assembly may be easily accomplished by directly connecting components with the conventional electrical backplane. Any component coupled with an optical backplane
assembly formed in accordance with teachings of the present invention may transmit and receive data or information from all other components coupled with the optical backplane assembly. Also, components may be inserted or removed from the optical
backplane assembly without limiting or restricting communication between other components coupled with the optical backplane assembly.
Another aspect of the present invention includes an optical backplane assembly with a distributor operable to switch optical signals in large optical communication or telecommunication networks. The distributor is preferably located adjacent to
a midpoint in the optical backplane assembly. The distributor may receive optical signals from other components attached to the optical backplane assembly, switch the optical signals, and rebroadcast the optical signals to the other components.
An optical backplane assembly with a central distributor formed in accordance with teachings of the present invention provides substantial advantages as compared to prior guided wave and free space optical backplane systems used for broadcasting
signals. These advantages include equalized fan-out power or output power, increased interconnect distance, and simpler fabrication. The distributor with active optical elements allows doubling associated interconnect distances as compared to many
prior optical backplanes. The present invention reduces the total number of diffractive optical elements such as single holograms and doubly multiplexed holograms required to produce an optical backplane assembly. The number of fabrication and assembly
steps is also reduced.
BRIEF DESCRIPTION OF THE DRAWINGS
A more complete understanding of the present invention and advantages thereof may be acquired by referring to the following description taken in conjunction with the accompanying drawings, in which the reference numbers may indicate like
features, and wherein;
FIG. 1 is a schematic drawing showing an exploded, isometric view with portions broken away of an optical bus assembly formed in accordance with teachings of the present invention;
FIG. 2a is a schematic drawing showing respective optical signals transmitted from components coupled with the optical bus assembly of FIG. 1 to an associated distributor;
FIG. 2b is a schematic drawing showing the distributor of FIG. 2a transmitting or rebroadcasting optical signals to all other components coupled with the optical bus assembly of FIG. 1;
FIG. 3 is a schematic drawing showing portions of a prior art optical backplane assembly formed with three doubly multiplex hologram and two single holograms to provide five board interconnects;
FIG. 4 is a schematic drawing showing one example of a prior art optical backplane assembly communicating optical signals in free space between attached components;
FIG. 5a is a schematic drawing showing optical signal power distribution between multiple components coupled with an optical backplane formed in accordance with teachings of the present invention;
FIG. 5b is a schematic drawing which demonstrates that substantially the same amount of optical signal power will be delivered to the distributor of an optical backplane assembly formed in accordance with teachings of the present invention;
FIG. 6 is a graphical representation of optical power distribution associated with multiple components coupled to an optical backplane formed in accordance with teachings of the present invention;
FIG. 7a is a schematic drawing showing another embodiment of an optical backplane formed in accordance with teachings of the present invention;
FIG. 7b is a schematic drawing showing an alternative embodiment of an optical signal coupler satisfactorily for use with an optical backplane assembly formed in accordance with teachings of the present invention;
FIG. 8a is a schematic drawing showing an exploded isometric view with portions broken away of an optical bus assembly formed in accordance with teachings of the present invention to switch a large number of multiplexed optical signals associated
with telecommunication systems and networks; and
FIG. 8b is a schematic drawing with portions broken away showing a comparison between the distributor of FIG. 8a and a plurality of conventional optical switches used in telecommunication systems and networks.
DETAILED DESCRIPTION OF THE
INVENTION
Preferred embodiments of the present invention and its advantages are best understood by reference to FIGS. 1 through 8b, wherein like reference numbers may be used to indicate like and corresponding parts.
The terms "optical signal or signals" and "lightwave signal or signals" are used in this application to include the full range of all electromagnetic radiation which may be satisfactorily used to communicate information through a waveguide,
waveguiding plate and/or fiber optic cables. An optical backplane assembly incorporating teachings of the present invention may be satisfactorily used to communicate optical signals in the infrared, visible and ultraviolet spectrum.
The terms "polymer" and "polymers" are used in this application to include any macromolecule combinations formed by the chemical union of multiple, substantially identical combining units or monomers and have satisfactory characteristics for use
as diffractive optical elements such as holograms or for use as a waveguiding plate. Combinations of two, three or four monomers are often referred to respectively as dimmers, trimmers, and tetromers. These combinations may be further classified as
inorganic, organic, natural, synthetic or semisynthetic. For purposes of this application, the term "polymers or other combinations of monomers" means any combination of two or more monomers or other combining units which may be satisfactorily used to
form a waveguide in accordance with teachings of the present invention including, but not limited to, inorganic, organic, natural, synthetic and semisynthetic combinations.
The terms "active optical element" and "active optical elements" are used in this application to include various types of transmitters and receivers satisfactory for communicating optical signals between multiple components such as electrical
circuit boards using an optical backplane formed in accordance with teachings of the present invention. Examples of such active optical elements include, but are not limited to, lasers, light emitting diodes (LEDs), PIN photodiodes and other
photodetectors. PIN refers to p-type intrinsic n-type junction. For some applications vertical cavity surface emitting lasers (VCSELs) may be used as active optical elements in accordance with teachings of the present invention.
The term "backplane" often means a circuit board containing sockets or slots into which other circuit boards or components may be plugged. For personal computers, the terms "backplane" and "motherboard" generally mean a large circuit board that
contains multiple slots for expansion cards. Backplanes may be described as either active or passive. Active backplanes, in addition to slots, contain logic circuits that perform computing functions. Passive backplanes typically contain no logic
circuits. The terms motherboard and backplane are often used synonymously when describing components of a computer system.
The term "bus" for computer systems often means a collection of wires which transmit data from one portion of the computer system to another portion. For example, many personal computers include an internal bus that connects all internal
components with the associated central processing unit (CPU) and the associated main memory. All or portions of a computer system bus may be mounted on an associated backplane or motherboard. An optical backplane assembly formed in accordance with
teachings of the present invention may include a waveguiding plate or other types of waveguides which function as an optical signal bus to transmit data and information in the form of optical signals between multiple components coupled with the optical
backplane assembly.
The term "latency" is often used to describe the time that one component in a system is waiting for information or data from another component in the system. Latency is generally waiting time. In a network or bus, latency is the amount of time
required for a packet of information or data to travel from a source to a destination. Latency and bandwidth define the speed and capacity of a network or bus.
Portions of optical backplane assembly 20 incorporating teachings of the present invention are shown in FIG. 1. Optical backplane assembly 20 may also sometimes be referred to as "an optical bus assembly." For the embodiment of the present
invention as shown in FIG. 1, optical backplane assembly 20 includes optical backplane 30 and electrical backplane 80. Optical backplane 30 may sometimes be referred to as optical bus 30. Multiple slots 82 are preferably provided on electrical
backplane 80 for operably coupling various components 84 thereto. Components 84 may be part of a computer system (not expressly shown) and/or part of a communication network (not expressly shown).
One of the main functions of optical backplane assembly 20 includes providing bidirectional signal paths for communicating or broadcasting and rebroadcasting optical signals between components 84 attached thereto. The present invention allows
each component 84 to both send and receive optical signals from all of the other components 84 attached to optical backplane assembly 20.
For the embodiment of the present invention as shown in FIG. 1, electrical backplane 80 includes five (5) slots 82. Each component 84 may be respectively coupled with electrical backplane 80 using slots 82. Various types of electrical
connections and sockets may be satisfactorily used as slots 82. Each slot 82 may be operable to receive various components such as electrical circuit boards and a distributor. For purposes of describing various features of the present invention, slots
82 have been designated 82a, 82b, 82c, 82d and 82e. Respective components 84 coupled with slots 82 have been designated 84a, 84b, 84c, 84d and 84e. Although only five slots 82 and five associated components 84 are shown in FIG. 1, important technical
advantages of the present invention include the ability to add additional slots and components to an optical backplane assembly without substantially decreasing or limiting the power level of optical signals communicated there between and without
reducing or limiting operational characteristics of the associated optical backplane assembly.
Optical backplane 30 preferably includes waveguiding plate 32 and supporting structure 34. As discussed later in more detail, waveguiding plate 32 may be formed from various types of materials including, but not limited to, polymers satisfactory
for use in communicating optical signals therethrough. Various types of supporting structures may also be used to form an optical backplane in accordance with teachings of the present invention. The present invention is not limited to supporting
structure 34.
Waveguiding plate 32 may have a generally elongated configuration with a generally square or rectangular cross section such as shown in FIG. 1. The dimensions, particularly thickness 44, of waveguiding plate 32 are greater than a typical
waveguide used to communicate optical signals. The length of waveguiding plate 32, spacing between diffractive optical elements 110 disposed thereon and thickness 44 are selected such that optical signals may be communicated from one component 84
through waveguiding plate 32 to an immediately adjacent component 84 using total internal reflection (TIR).
Supporting structure 34 includes respective ends 36 and 38 which cooperate with each other to partially define opening 40 disposed therebetween. The configuration and dimensions of opening 40 are preferably selected to be compatible with the
desired configuration and dimensions of waveguiding plate 32. For the embodiment of the present invention as shown in FIG. 1 electrical backplane 80 and ends 36 and 38 of supporting structure 34 contain respective holes or openings 42 which may be
aligned with each other during fabrication of optical backplane assembly 20. Various types of mechanical fasteners (not expressly shown) may be used with holes 42 to maintain desired alignment between respective active couplers 100 and diffractive
optical elements 110. An optical backplane assembly may be formed in accordance with teachings of the present invention with a waveguiding plate and a supporting structure having various configurations other than the configurations shown in FIG. 1.
Respective active couplers 100 are preferably disposed between each slot 82 and optical waveguiding plate 32. Active couplers 100 and associated diffractive optical elements 110 function as interfaces between electrical signals associated with
components 84 and optical signals transmitted or communicated through waveguiding plate 32. For the embodiment of the present invention as shown in FIGS. 1 through 2b, each active coupler 100 may include two active optical elements such as optical
receiver 102 and optical transmitter 104. For some applications each optical receiver 102 may include a preamplifier, a detector and a postamplifier. Each optical transmitter 104 may include a VCSEL and associated driver.
Each active coupler 100 may also include an associated diffractive optical element 110. For embodiments such as shown in FIGS. 1-2b and 5a-8b, diffractive optical elements 110 may be holograms or holographic optical elements formed from various
types of polymers. For some applications, diffractive optical elements 110 may be described as relatively thick, multiplexed holograms or holographic optical elements with functions and operating characteristics similar to conventional Bragg gratings.
The holograms may also be described as "phase holograms" which do not absorb optical signal power. Diffractive optical elements 110 may also be described as "volume holograms" which deflect optical signals at a selected angle as the optical signals pass
through the hologram. The term "hologram" as used in this application may also include a holographic optical element (HOE).
For purposes of describing various features of the present invention, respective active couplers 100, optical receivers 102, optical transmitters 104 and holograms or diffractive optical elements 110 have been designated as a, b, c, d and e. As
previously noted, any number of components 84 may be coupled with an optical bus assembly formed in accordance with teachings of the present invention. Therefore, the present invention is not limited to use with only five active couplers 100 as shown in
FIG. 1.
Active couplers 100 are preferably attached to and operably connected with respective slots 82 and disposed immediately adjacent to waveguiding plate 32. This configuration allows insertion and/or removal of components 84 from their respective
slots 82 without affecting the ability of active couplers 100 to communicate or broadcast optical signals through waveguiding plate 32. Also, inservion and/or removal of one component 84 does not affect alignment of the respective active coupler 100 and
diffractive optical element 110 relative to waveguiding plate 32 and other active couplers 100.
For some applications slots 82a, 82b, 82d and 82e and associated active couplers 100a, 100b, 100d and 100e may be symmetrically arranged with respect to component 84c and its associated slot 82c and active coupler 100c. Components 84, slots 82
and respective active couplers 100 may also be symmetrically arranged with respect to each other along an optical axis (not expressly shown) associated with optical waveguiding plate 32. The operational characteristics associated with active couplers
100 may be approximately the same.
For the embodiment of the present invention as shown in FIG. 1, optical transmitters 104a and 104b, optical receiver 102c and optical transmitters 104d and 104e are generally aligned with each other along a first optical signal channel provided
by waveguiding plate 32. The first optical signal channel is represented by arrows 111. Optical receivers 102a and 102b, optical transmitter 104c and optical receivers 102d and 102e are generally aligned with each other along a second optical signal
channel provided by waveguiding plate 32. The second optical signal channel is represented by arrows 112.
Respective diffractive optical elements such as holograms 110a, 110b, 110c, 110d and 110e are preferably disposed on waveguiding plate 32 adjacent to respective slots 82 and attached active couplers 100. Optical signals will communicate through
a relatively small air gap or free space between each active coupler 100 and its associated hologram 110. As previously noted holograms 110 may be described as "volume holograms" which deflect an optical signal at a selected angle as the optical signal
passes therethrough. For the embodiment as shown in FIG. 1, each hologram 110 preferably deflects optical signals at an angle of approximately forty-five degrees 45.degree. relative to the longitudinal axis or the optical axis (not expressly shown)
associated with waveguiding plate 32.
Total internal reflection of optical signals will occur within waveguiding plate 32 when optical signals propagate within waveguiding plate 32 at an angle greater than a critical angle associated with the dimensions and the type of material used
to form waveguiding plate 32. For the embodiment of the present invention as shown in FIG. 1, thickness dimension 44 of waveguiding plate 32, the longitudinal spacing between adjacent holograms 110 and associated active couplers 100 is selected so that
optical signals communicated between components 84 will experience total internal refraction.
For some applications slot 82c and its associated active coupler 100c are preferably located proximate a midpoint of waveguiding plate 32. Component 84c may function as a "distributor" to receive respective optical signals transmitted from
components 84a, 84b, 84d and 84e and to rebroadcast such optical signals to the other components 84a, 84b, 84d and 84e. For some applications, distributor 84c may modify one or more of the received optical signals depending upon the type of electrical
circuits and software associated with distributor 84c. Distributor 84c may also generate optical signals which are transmitted or communicated to other components 84a, 84b, 84d and 84e. A central distributor such as distributor 84c may perform
functions similar to a regenerator in a fiber optic communication system. The distributor may be used to amplify weak optical signals, reshape optical signals, and rebroadcast clean optical signals to all other components coupled with the associated
optical backplane assembly.
Optical backplane assembly 20 may be described as a centralized system for communicating optical signals when distributor 84c is located approximately over the center of waveguiding plate 32 between components 84a and 84b and components 84d and
84e. One of the functions of component 84c or distributor 84c is to collect data or information transmitted from one or more components 84 and to rebroadcast such data or information to all other components 84.
Active couplers 100 in cooperation with diffractive optical elements 110 and waveguiding plate 32 function as board-to-board or component-to-component interconnectors. Distributor 84c may be compared with an active 2.times.3 optical coupler,
with two inputs from associated components 84, one output to distributor 84c, and two outputs to other components 84 disposed on opposite sides of distributor 84c. Interconnect distance is often a major performance parameter for many optical bus
assemblies associated with computer systems and telecommunication systems. Due to optical cross talk in many optical systems, only a limited number of components may be attached to each bus. Interconnect distances associated with optical bus assembly
20 can be doubled by use of central distributor 84c.
Hologram 110c associated with active coupler 100c may be described as a doubly multiplexed hologram (DH) which functions as a beam splitter and a deflector. Holograms 110a, 110b, 110d and 11 | | |
