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Description  |
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FIELD OF THE INVENTION
This invention relates to optoelectronic apparatus and more particularly to
such apparatus for use in information handling systems.
BACKGROUND OF THE INVENTION
As information handling systems become more complex, and require more
information to be handled at greater speeds, they need components of more
compact size, greater capacity, and faster speeds. It is widely believed
that optoelectronic components are particularly promising for use in such
systems because optics offers considerable advantages over pure
electronics as a communication medium, as data rates move into the gigabit
range. For example, it now appears that free space optics offers
considerable advantages over wire leads for the interconnection of
processing elements in computer systems that use closely spaced
semiconductive chips as the processing elements, as in computers that
involve massively parallel computation.
Such optical interconnection networks depend importantly on optical
components that are compact, rugged, efficient and sealable for use in
large systems. The present invention is directed at providing such
apparatus.
The present invention is its preferred embodiments focuses particularly on
devices adapted to function in a parallel computation system of the kind
described in our copending application Ser. No. 07/994,220, filed Dec. 18,
1992 having the same assignee as this application. However, such devices
should also be useful in various other forms of high speed information
handling systems.
In that application, there is described a parallel processing system that
divides the processing elements into clusters and includes an interconnect
network that is of a three-stage modified-clos type. It uses electronic
switches in the first and third stages for switching between processing
elements in a common cluster and optoelectronic switches to switch between
clusters in the second stage that use free-space light beams for use as
the transmission medium between clusters. This system is designed so that
generally only two routing decisions need to be made in interconnecting
any two processing elements. The present invention provides components
that are particularly well adapted for use in the second stage of such a
system. Reference can be made to such copending application for a more
detailed description.
In such a system, the second stage comprises a plurality of lasers that
serve as transmitters and a plurality of photodetectors that serve as
receivers, the communications therebetween being by light beams that
originate from the lasers and terminate at the photodetectors, the routing
therebetween being done by various optical elements.
For such communication, an optoelectronic switch is advantageously employed
by means of which one laser is an array of lasers is selectively energized
by a transmitting processing element, the selection being dependent on the
cluster to which belongs the photodetector of the processing element
intended as the destination of the information being transmitted.
In one aspect, the present invention is a device that serves as a suitable
optoelectronic switch that permits such selection.
Advantageously, each processing element includes both an information
processor and a routing portion and all the routing portions in a cluster
are interconnected by way of a local switch that permits each processing
element to communicate with all other processing elements in a cluster.
Additionally, information that is generated in the information processor of
a processing element and intended for transfer to a different cluster may
be transferred by way of its routing portion to the routing portion of a
different processing element in the same cluster for transfer by the
optical interconnection network.
As a consequence, each routing portion has available to it, for transfer by
the optical interconnection network, information from the information
processor of each of the processing elements in the cluster.
By use of the routing portions, it becomes possible to couple the
information from any processing element of the cluster to any
optoelectronic switch in the same cluster.
In a similar fashion, advantageously each photodetector in a cluster is
coupled to a routing portion of a processing element, and so can couple to
the routing portion of any processing element in the cluster, whereby the
information received by the photodetector in the cluster can be
transferred to any processing element in the cluster for use by it.
Moreover, a light beam, in its routing from the laser associated with the
cluster of the transmitting processing element to the photodetector
associated with the cluster of the receiving processing element, may
experience considerable attenuation since such routing may involve passage
through a number of microlenses and reflection from a number of partially
transmissive mirrors.
Accordingly, in another aspect, the present invention is a regenerator that
can be inserted in the path of a weak light beam and then used to
intercept the light beam, amplify or regenerate it, and send it along on a
path that is collinear with the path from which the beam was initially
intercepted.
SUMMARY OF THE INVENTION
As mentioned above, in one aspect the invention is a novel optoelectronic
switch. This switch is designed to be supplied by an input signal intended
for a particular destination, which destination is used to determine which
laser of an array of lasers is to be intended by the input signal. In a
particular embodiment, the lasers are arranged in a two-dimensional array
in a first semiconductive chip and the input signal is applied to a second
semiconductive chip in which there has been formed a switch,
advantageously of a binary H-tree configuration, whose leaves form a
two-dimensional pattern that matches the two-dimensional pattern of the
laser anodes of the first chip. Accordingly, the first chip can be butted
against the second chip and there bonded to form electrical contacts
between the pads at the ends of the leaves of the H-tree switch in the
second chip and the anode electrodes of the lasers of the first chip. The
address information associated with the input signal is used by the switch
to select the laser appropriate to the intended destination of the signal
information. Both chips typically might be of gallium arsenide. However,
it is anticipated that soon it will be feasible to integrate the two chips
into a monolithic chip. Such an optoelectronic chip should have
application in various systems other than that described in the copending
application. Additionally, each laser may be of the same wavelength or
many different wavelengths may be involved.
In accordance with another aspect of the invention, a light regenerator for
insertion in the path of the light beams is formed by a hybrid
detector/transmitter that is provided with correction for the
detector/transmitter physical position offset. Such correction may be
provided in a variety of ways including either the use of v-groove mirrors
to compensate for the original detector/laser offset or the addition of a
second detector/transmitter that provides a second compensating offset, or
the use of controlled polarizations and a birefringent element to provide
a compensating offset.
In another aspect, the invention is an arrangement for coupling light beams
of different wavelengths into and out of optical channels for use in a
wavelength division multiplexing arrangement.
BRIEF DESCRIPTION OF THE DRAWING
The invention will be better understood from the following more detailed
description taken in conjunction with the accompanying drawing in which:
FIG. 1 shows schematically the basic elements of a free space optical
interconnection network of the kind to which the invention is primarily
applicable.
FIG. 2 is a three dimensional exploded view of an optoelectronic switch in
accordance with one aspect of the invention.
FIGS. 3, 4 and 5 are cross sectional view of three different embodiments of
regenerators in accordance with the second aspect of the invention.
FIG. 6 shows an arrangement for cooling a plurality of beams of different
wavelengths into and out of free space optical channels in accordance with
another aspect of the invention.
DETAILED DESCRIPTION OF THE INVENTION
With reference now to the drawing, the parallel computation system 10
contains a number of columns 11, each column including a plurality of
circuit boards 12, each circuit board including a cluster of processing
elements 13. The processing elements are advantageously divided among the
various boards such that during computations the processing elements
between which the communication is expected to be appreciable are located
as a cluster on a common board and the communication between processing
elements on a common board is controlled by electronic circuitry on the
common board. However, communication between clusters on different circuit
boards is done optically to avoid the complexity of providing wire leads
between the boards, which could be complex when hundreds of circuit
boards, each with tens of processing elements are involved, and the
destination of signals between processing elements might need to be
changed rapidly.
To provide optical communication between the boards each circuit board is
provided with a number of optoelectronic switches 15. In accordance with
the invention, each optoelectronic switch in a monochromatic system is
designed to include a two-dimensional array of lasers in which, each emits
light of the same wavelength, but each is positioned to route its beam to
a different photodetector associated with a distant circuit boards. The
output of a processing element which is to be directed to the input of a
processing element not on the common circuit board is applied to the input
of the optoelectronic device and switched to the laser aimed at a distant
photodetector on the appropriate circuit board for accessing the desired
processing element. Then at the receiving end, the output of the receiving
photodetector can be routed electronically to the desired processing
element. To this end, each circuit board is associated with both a
plurality of optoelectronic switches 15 to serve its transmitting
processing elements and an array of photodetectors 16 to serve its
receiving processing elements. Appropriate deflecting elements 17 are used
to deflect the beams emitted by the optoelectronic switches into
appropriate paths for travel to their intended destinations and to deflect
the beams from their travel paths into the appropriate photodetectors.
Additional deflecting elements 18 are located at the ends of each column
for routing the beams appropriately through the various columns.
Microlenses (not shown) are also typically included along the beam paths.
Also included at various points along the beam paths are repeaters 40 to
be described more fully below.
In FIG. 2 there is shown a three-dimensional exploded view of an
optoelectronic switch 15 in accordance with the invention for use at the
transmitting end as the source of data streams for routing in a particular
channel.
As seen, the switch 15 includes two principal components, a chip 20 which
houses the electronic circuitry that provides the routing of the input
data to a particular diode laser and a chip 30 which includes an array of
lasers of which one is to be selected for emitting a beam of light aimed
at a photodetector associated with the cluster of the processing element
with which the transmitting processing element is to communicate.
To this end, the 20 chip houses a binary tree switch, preferably of the
known H-type configuration, whose input terminal 21, corresponding to the
root of the tree is supplied with the signal information to be transmitted
by the sending processing element. The tree includes various branches 23
arranged in a common plane so that no branch crosses over another so that
pads 26 at the leaf ends form a two-dimensional array, advantageously a
square array, as shown. Each of the leaf pads 26 is provided with a solder
bump that serves as a connection pad to the tree. The chip 20 further
includes a plurality of individual switches 27 that can be set to a high
or low resistance state by control signals. The switches can be
field-effect transistors connected between branch points of the tree. The
switches are appropriately set by the address of the intended destination
to route the signal information to the desired leaf of the tree. The
signal information is then used to modulate the light beam emitted by the
laser to which the chosen leaf is coupled. The chip 20 may also house the
driver circuits for proper bias and modulation of the emitting laser.
The second component 30 of the switch 10 comprises a chip in which there
has been formed a two-dimensional array of diode injection lasers that are
surface emitting to emit a beam substantially circular in cross-section to
simplify the optics for the routing of the beams. The anode electrodes 31
of the lasers form a two-dimensional square pattern that closely matches
the two-dimensional square pattern of the solder bumps at leaf pads 26 so
that when chip 20 is bonded to chip 30 low-loss electrical connections are
formed between the binary tree leaf pads and the laser array anode
electrodes. A common cathode can be used for all the lasers in the chip.
At some future date, it may become feasible to make the switch 15
essentially all in a monolithic chip, such as a chip essentially of
gallium arsenide or other suitable semiconductor. In such a case by
appropriate positioning of the various elements in the chip, there may be
reduced the need for electrode connections in the chip. Of course, for
some applications, it may be feasible to use other materials, such as
silicon, for chip 20.
With reference back to FIG. 1, it will be important to include various
optical elements, such as microlenses for optically relaying the various
laser beams and deflecting elements for routing the various beams between
the lasers and the photodetectors. It can be appreciated that some of
these paths may be relatively long during which their beams can suffer
considerable attenuation.
To compensate for such possible attenuation, it is important to amplify or
regenerate some of the beams. It is also important, if the optics is to
avoid becoming too complex, to provide such amplification or regeneration
in a manner that permits the regenerated beam to maintain essentially the
same path it had before amplification or regeneration.
Unfortunately at the present state of technology, there is not available a
practical form of colinear optical amplifier so that it is necessary to
use hybrid forms of regenerators, usually known as repeaters, that involve
optic-to-electronic conversion followed by electronic-to-optic
reconversion. Because such operations consume power, it is preferably to
regenerate selectively only the weakest signals in a given repeater array
and to include multiple repeater arrays in the network.
In FIG. 1, there are also shown included repeaters 40 at various points,
advantageously either at the ends of selected columns, or in the paths
between columns. The repeaters may take various forms, each of which
however is designed to produce an output beam which is not only an
amplified version of the input beam but also is colinear with the input
beam.
One embodiment of such a repeater is shown in FIG. 3. The repeater 50
includes a mirror assembly comprising the pair of right angle isoceles
prisms 51, 52 positioned to form a plane interface 53 which is provided
with at least one localized reflecting facet 54 where the weak beam A to
be regenerated would otherwise pass through the interface. As shown, at
the facet this beam is reflected vertically to be incident on a
photoreceiver 55 that converts the beam into an electrical signal that is
amplified and then used to modulate a laser 56. This laser is positioned
to emit a beam that is displaced horizontally from the reflecting facet 54
and that passes largely unaffected through the mirror assembly to be
incident on a second photoreceiver 57 that converts the incident beam into
an electrical signal. This signal in turn is used to excite laser 58 that
generates a new beam designed to pass partially through the mirror
assembly but is redirected as it reaches the interface 53 the localized
reflecting facet 54 that redirects the incident beam along a path that
forms a continuation of the path the beam would have taken through the
mirror assembly had it not suffered the initial redirection. As a
consequence, the beam now regenerated passes along a collinear extension
of its original path. Moreover, a beam not needing regeneration, such as
beam B, passes through the interface 53 at a point free of any reflecting
facet and so is little affected by passage through the mirror assembly.
It is, of course, possible to include several reflecting facets at
interface 53 to deflect additional beams for regeneration in similar
fashion to form a repeater array for a number of beams.
An alternative assembly is shown in FIG. 4. The repeater 50 differs from
that of FIG. 3 in that in place of the second photoreceiver-laser pair, it
employs a polarizing micromirror facet 61 at the interface 62 of mirror
assembly 63, a birefringent element, such as a calcite plate 64, a quarter
wave plate 65 and mirror 66, for displacing the regenerated beam A
provided by the photoreceiver-laser pair 67 sufficiently that it is
redirected along its original path.
Similarly, as still another embodiment, that may prove to be preferred FIG.
5 shows a repeater 70 that utilizes a V-groove reflecting mirror 71 to
displace the regenerated beam A provided by the photoreceiver-laser pair
72 sufficiently that it is redirected along it original path after
reflection in reflecting facet 73 at the mirror assembly interface 74.
Wavelength division multiplexing can be accomplished in various ways. In
one form, each laser in a given laser array can be of the same wavelength
to facilitate the manufacturer of such arrays, but the lasers in different
arrays would be of different wavelengths.
Alternatively, a single laser array can include many lasers operating at
different wavelength. At the present state of the art this would
complicate the manufacture of such an array. However, it is likely that
advances in the state of the art will some day make such an array readily
available.
In some instances, it may be desirable to have a laser array that includes
a plurality of groups of lasers, all the lasers in the group emitting the
same wavelength, but different groups emitting different wavelengths.
In a wavelength division multiplexing system, a number of light beams of
different wavelengths would share a common light path for part of their
travel through the network but ultimately they would be separated to
target different photoreceivers.
To route the beams of different wavelengths on a common light path
appropriately, the optical elements used to deflect the beams should be
made wavelength selective as would be apparent to a worker in the art. In
particular, the repeaters shown in FIGS. 3, 4 and 5 can be made wavelength
selective by choice of the reflecting facets and the wavelength of the
regenerating laser.
In a monochromatic system in which all the light beams are of the same
wavelength, a large number of beam paths is needed. The number of beam
paths needed can be reduced by using wavelength division multiplexing in
which each optical path accommodates a plurality of beams each of a
different wavelength.
FIG. 6 illustrates one possible arrangement 80 for coupling into an out of
a free space optical network that uses three wavelengths. Three diode
laser arrays 81A, 81B and 81C each of a different wavelength are coupled
to the optical path by way of a separate mirror assembly 82A, 82B and 82C
basically of the kind previously described except that at the interface
between the two prisms of the assembly the reflecting facets are replaced
by a coating 84 that acts as a narrow band reflection interference filter
that deflects the intended wavelength by 90 degrees and transmits all
other wavelengths. In this way the beams emitted by the three laser arrays
are combined and then deflected by the mirror assembly 85 which does
include at the prism interface facets 87 for deflecting the various beams
vertically into the main optical channels appropriately.
Conversely, optical beams of the three different wavelengths traveling
vertically in the optical channels are deflected horizontally by such
reflecting facets for travel horizontally for passage through mirror
assemblies 86A, 86B and 86C, which resemble mirror assemblies 82A, 82B and
82C in that each is adapted to deflect selectively different ones of the
beams of different wavelengths being used but to transmit all others. In
this way beams of particular wavelength may be directed at the appropriate
photodetectors 89 in the manner previously described.
These embodiments similarly may be modified to provide for regeneration of
multiple beams as previously described.
It should be evident that various other modifications may be made either in
the optical interconnection network or the components which have been
described without departing from the spirit and proper scope of the
invention.
In particular, various design considerations will determine the optimum
position of the repeaters in the network, the number of beams to be
amplified at a particular repeater and the amount of amplification
provided at a given repeater.
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