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Claims  |
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What is claimed is:
1. A free space optical interconnect system comprising:
a transmitter and a receiver, at least one of the transmitter and the
receiver comprising a plurality of elements whose number is redundant;
means for monitoring a misalignment between the transmitter and the
receiver, including means for determining a direction and an amplitude of
the misalignment; and
means for re-routing data from an element which is misaligned to a
redundant element selected along a direction associated with the direction
of the misalignment so as to provide data transmission through the system,
the re-routing being performed in response to a signal generated by the
monitoring means.
2. A system of claim 1, wherein the means for monitoring the misalignment
comprises means for monitoring a signal connection parameter between the
transmitter and the receiver.
3. A system of claim 2, wherein the means for monitoring the signal
connection parameter comprises means for monitoring a signal parameter at
the receiver.
4. A system of claim 2, wherein the means for monitoring the signal
connection parameter comprises means for monitoring a signal parameter at
the transmitter.
5. A system of claim 2, wherein the means for monitoring the signal
connection parameter comprises means for monitoring a signal parameter of
at least one element of at least one of the transmitter and the receiver.
6. A system of claim 2, wherein the signal connection parameter is an
intensity of the data signal.
7. A system of claim 1, wherein the means for monitoring the misalignment
comprises a dedicated alignment laser and a dedicated detector.
8. A system of claim 7, wherein the means for determining the direction and
the amplitude of the misalignment comprises means for measuring a position
of a laser spot of the dedicated alignment laser on the dedicated
detector.
9. A system of claim 1, wherein the means for monitoring the misalignment
comprises a detector selected from the group consisting of detectors for
monitoring lateral and vertical misalignments, and detectors for
monitoring tilt misalignments.
10. A system of claim 1, wherein the means for monitoring the misalignment
further comprises means for providing feedback between the transmitter and
the receiver regarding the misalignment.
11. A system of claim 10, wherein the means for providing the feedback
comprises means selected from the group consisting of optical fiber, LED,
electrical cable and electrical backplane.
12. A system of claim 3, wherein the means for determining the direction
and the amplitude of the misalignment comprises means for measuring an
intensity distribution at the receiver elements.
13. A system of claim 1, wherein the receiver only has redundant elements.
14. A system of claim 1, wherein the transmitter only has redundant
elements.
15. A system of claim 1, wherein the elements are arranged into a
one-dimensional array.
16. A system of claim 1, wherein the elements are arranged into a
two-dimensional array.
17. A system of claim 1, wherein the elements are arranged so as to form a
pre-determined pattern which provides a required optical transmission or
collection.
18. A system of claim 1, the system comprising one transmitter and one
receiver only for a uni-directional interconnection.
19. A system of claim 1, the system comprising a first module and a second
module, each module comprising one transmitter and one receiver for
corresponding bi-directional transmittance and receiving of data.
20. A system of claim 1, wherein the redundant elements are arranged into
clusters, the number of clusters being redundant and the number of
elements in each cluster being sufficient to accommodate the number of
data channels to be transmitted.
21. A system of claim 20, wherein the means for re-routing comprises means
for re-routing data from a cluster which is misaligned to a redundant
cluster which provides data transmission through the system.
22. A system of claim 21, wherein the elements are shared between different
clusters.
23. A system of claim 1, wherein the elements of the transmitter are
optical emitters.
24. A system of claim 23, wherein the emitters are selected from the group
consisting of VCSEL, SLD, LED, and edge emitting laser diodes.
25. A system of claim 1, wherein the elements of the transmitter are
optical modulators.
26. A system of claim 1, wherein the elements of the receiver are selected
from the group consisting of PIN detector, metal-semiconductor-metal
detector and avalanche photodiode.
27. A system of claim 1, the system being integrated within a package.
28. A module for free space optical interconnect system, comprising:
at least one of a transmitter and a receiver, at least one of the
transmitter and the receiver comprising a plurality of elements whose
number is redundant;
means for monitoring a misalignment of the module, including means for
determining a direction and an amplitude of the misalignment; and
means for re-routing data from an element which is misaligned to a
redundant element selected along a direction associated with the direction
of the misalignment so as to ensure data transmission through the system,
the re-routing being performed in response to a signal generated by the
monitoring means.
29. A module of claim 28, wherein the means for monitoring the misalignment
comprises means for monitoring a signal connection parameter at the
module.
30. A module of claim 29, wherein the signal connection parameter is an
intensity of the signal.
31. A module of claim 28, wherein the means for monitoring the misalignment
comprises detectors selected from the group consisting of detectors for
monitoring lateral and vertical misalignments, and detectors for
monitoring tilt misalignments.
32. A module of claim 28 wherein the means for determining the direction
and the amplitude of the misalignment comprises means for measuring a
position of a laser spot of a dedicated alignment laser on a dedicated
detector.
33. A module of claim 28, wherein the means for determining the direction
and the amplitude of the misalignment comprises means for measuring an
intensity distribution at the receiver elements.
34. A module of claim 28, wherein the module comprises one transmitter
only.
35. A module of claim 28, wherein the module comprises one receiver only.
36. A module of claim 28, wherein the module comprises one transmitter and
one receiver only for corresponding transmitting and receiving of data in
a bi-directional optical interconnect system.
37. A module of claim 28, wherein the elements are arranged into a
one-dimensional array.
38. A module of claim 28, wherein the elements are arranged into a
two-dimensional array.
39. A module of claim 28, wherein the elements are arranged so as to form a
pre-determined pattern which provides a required optical transmission or
collection.
40. A module of claim 28, wherein the redundant elements are arranged into
clusters, the number of clusters being redundant and the number of
elements in each cluster being sufficient to accommodate the number of
data channels to be transmitted.
41. A module of claim 40, wherein the means for re-routing comprises means
for re-routing data from a cluster which is misaligned to a redundant
cluster which provides data transmission through the system.
42. A module of claim 41, wherein the elements are shared between different
clusters.
43. A module of claim 28, wherein the elements of the transmitter are
optical emitters.
44. A module of claim 43, wherein the emitters are selected from the group
consisting of VCSEL, SLD, LED, and edge emitting laser diodes.
45. A module of claim 28, wherein the elements of the transmitter are
optical modulators.
46. A module of claim 28, wherein the elements of the receiver are selected
from the group consisting of PIN detector, metal-semiconductor-metal
detector and avalanche photodiode.
47. A module of claim 28, the module being integrated within a package.
48. A method of operating a free space optical interconnect system,
comprising a transmitter and a receiver, at least one of the transmitter
and the receiver having a plurality of elements whose number is redundant,
the method comprising the steps of:
(a) monitoring a misalignment between the transmitter and the receiver,
including determining a direction and an amplitude of the misalignment;
and
(b) when the amplitude of the misalignment is exceeding the threshold
value, re-routing data from an element which is misaligned to a redundant
element selected along a direction associated with the direction of the
misalignment so as to provide data transmission through the system.
49. A method of claim 48, wherein the step of monitoring the misalignment
comprises monitoring a signal connection parameter between the transmitter
and the receiver.
50. A method of claim 49, wherein the step of monitoring the signal
connection parameter comprises monitoring a signal parameter at the
receiver.
51. A method of claim 49, wherein the step of monitoring the signal
connection parameter comprises monitoring a signal parameter at the
transmitter.
52. A method of claim 49, the step of monitoring the signal connection
parameter comprises monitoring a signal parameter of at least one element
of at least one of the transmitter and the receiver.
53. A method of claims 49, the step of monitoring the signal connection
parameter comprises monitoring intensity of the data signal.
54. A method of claim 48, wherein the step of determining the direction and
the amplitude of the misalignment comprises measuring a position of a
laser spot of a dedicated alignment laser on a dedicated detector.
55. A method of claim 48, wherein the step of determining of the direction
and the amplitude of the misalignment comprises measuring an intensity
distribution at the receiver elements. |
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Claims |
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Description |
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FIELD OF THE INVENTION
The invention relates to a free space optical interconnect system and a
method of operation thereof, in particular to the system and method
providing tolerance to misalignments.
BACKGROUND OF THE INVENTION
Free space optical interconnect systems have long been proposed to deliver
fast, highly parallel data transfer. These systems have the potential to
obviate limitations of electrical interconnects, which are not capable of
supporting data throughputs beyond a capacity of several hundred Gb/s, and
to increase the capacity up to the Terabit/s range. Thus free space
interconnect systems are promising and attractive alternatives for various
telecommunication and computing applications.
However, the most important challenge preventing the current acceptance of
free space interconnect systems is alignment. Two issues are of concern:
the precision to which it is possible to align the system, and the
precision to which it is necessary to maintain this alignment during
operation. For practical applications it is necessary to establish and
maintain alignment of circuit boards carrying transmitters and receivers,
which may comprise an array of pixels, to within 10's of microns over a
distance of meters. Such a system requires extremely expensive highly
precision optomechanics, and to date has been implemented only in a
controlled laboratory environment. In real product usage, when vibrations,
temperature fluctuations and temperature gradients are encountered, the
optical links move out of alignment and data is not correctly transferred.
Therefore, the goal of providing some alignment tolerance for optical links
is to ensure the correct operation of all of the pixels on each array at
the highest possible speed. Correct operation is defined as the correct
reception of a logic 1 or logic 0 signal. Once the laser power, the
receiver sensitivity and the detector area have been defined, the
probability of correct reception of the logic bits is mainly a function of
optical beam misalignment. Misalignment mechanisms can be due solely to
mechanical movements, but in practice, optical effects can also
contribute. Six degrees of freedom of the mechanical movements:
translation in x, y, and z (.DELTA.x, .DELTA.y, .DELTA.z) and rotation
about the x, y, and z axes (.theta..sub.x, .theta..sub.y, .theta..sub.z),
where x and y axes define the plane of an optical module in its nominal
alignment position, with z axis being perpendicular to this plane, result
in a number of optical effects. These include an image shift (.DELTA.x,
.DELTA.y), image rotation (.theta..sub.z), defocus (.DELTA.z) and image
tilt (.theta..sub.x, .theta..sub.y). Image shift and rotation are
basically lateral translation effects, and defocus and image tilt
introduce defocus effects. Contributors to the overall lateral
misalignment effects include:
mechanical misalignment in x and y;
mechanical rotation about the z axis;
mismatches in focal lengths;
wavelength shifts and laser mode-hops caused by temperature fluctuations
and resulting in beam deflections introduced by diffractive elements;
distortions of the image of an array of sources by the interconnect lens
system, and
telecentricity, when defocus, in addition to increasing spot size,
introduces lateral misalignments in nontelecentric systems.
Contributors to the overall defocus effects include:
source array tilt;
image tilt;
curvature of the plane of best focus;
mechanical tilt about x and y axes;
misalignment along z axis.
Numerous attempts have been made to increase alignment tolerance for
optical interconnect systems which may be categorized as passive, active,
or dynamic strategies.
However, passive alignment of dense, high speed free space optical
interconnects for distances of more than 1 cm require mechanical support
structures that are too expensive, difficult to align, and insufficiently
stable for commercial applications, see, e.g., "Optoelectronic ATM switch
employing hybrid silicon (MOS/GaAs) FET-SEEDS", A. L. Lentine et al., SPIE
Proceeding, vol. 2692, pages 110-108, 1996; and "Optical bus
implementation system using Selfoc lenses", K. Namanaka, Optics Letters,
Vol. 16, No. 16, pp. 1222-1224, August 1991. Passive alignment is done
before any devices are powered up. This alignment technique is used in
almost all electrical connectors, and most optical fiber connectors are
passive. Recently, solder bump techniques have been applied to certain
free space optical interconnect components, and preliminary reports
indicate the potential for submicron alignment in all 6 degrees of freedom
over a scale of up to 1 cm, J. W. Parker "Optical Interconnection for
Advanced Processor Systems: A Review of the ESPRIT II OLIVES Program", L.
Lightwave Technology 9 (12), 1764-1773, 1991.
Active alignment requires some feedback about the quality of the alignment.
Usually the feedback is achieved by illuminating the system and monitoring
the alignment either visually or by measuring a photocurrent in the
detectors. Real-time active alignment is necessary if the alignment
tolerances are tight or the system stability is poor so that the system
will not remain aligned for a reasonable length of time. In this case, the
feedback and alignment actuators must be integrated into the system to
ensure permanent alignment. For example, CANON manufacturer uses image
recognition and active beam-steering using a liquid filled variable angle
prism in a single channel 155 Mb/s link product, which currently costs
$100K. The product uses built in viewing cameras and optical pattern
recognition techniques to define the system alignment, the complexity and
cost of such a system clearly limiting widespread application.
Alternatively, NTT has a system using actively controlled variable angle
liquid filled prisms for board to board parallel free space optical
interconnect, see. e.g. "Optical beam direction compensating system for
board-to-board free space optical interconnection in high-capacity ATM
switch", K. Hirabayashi et al., Journal of Lightwave Technology, Vol. 15,
No. 5, May 1997. Cost, size, environmental ruggedness and reliability of
these systems remain concerns.
Additionally, to develop both a marketable and reliable system, devices
have to be packaged in a useful and reliable manner. For large systems
including cumbersome and bulky mechanical parts providing alignment, this
could involve a significant amount of physical space just to house all the
individual components.
Recently, a proposal for avoiding high precision mechanics in free space
interconnect systems by use of redundant arrays of detectors has been put
forward by F. A. P. Tooley in IEEE Journal of Selected Topics in Quantum
Electronics April 1996, vol. 2, No. 1, pp. 3-13 and in Digest, IEEE Summer
Topical Meetings, Aug. 5-9 1996, p. 55-56. This system increases tolerance
to misalignment by providing an array of detectors in place of a single
detector and electrically re-routing the misaligned optical data to the
correct channel, or, alternatively, by replicating the signal a number of
times. The overhead associated with increasing the alignment tolerance
requires a control and router circuit, which adds electrical power
consumption.
In patent application Ser. No. 09/150,242 to Dominic Goodwill it has been
proposed to arrange redundant elements into redundant clusters, the number
of elements in each cluster being sufficient to accommodate the number of
data channels to be transmitted. The system also includes means for
identifying a misalignment between the transmitter and the receiver, and
means for re-routing data from the cluster which is misaligned to the
redundant cluster which thus re-directs data to/from the correct physical
location.
Unfortunately, there is a drawback associated with the use of redundant
elements in optical interconnect systems. Re-routing of data between the
redundant elements or clusters requires time for hunting for an
appropriate available element or cluster which would provide reliable data
transmission through the system. While hunting, some of the data
transmitted is inevitably lost. Accordingly, the faster the hunting and
re-routing, the more reliable the optical interconnect system is. If the
hunting process takes too long, it may result in losing the optical link
at all which is not acceptable in many circumstances. It also limits
general applications of free space optical interconnect systems.
Therefore there is a need for development of free space optical
interconnect systems tolerant to misalignments and methods of operation
thereof which would provide reliable data transmission through the system.
SUMMARY OF THE INVENTION
Thus, the present invention seeks to provide an optical interconnect system
and method which avoids or reduces the above-mentioned problems.
Therefore, according to one aspect of the present invention there is
provided a free space optical interconnect system comprising:
a transmitter and a receiver, at least one of the transmitter and the
receiver comprising a plurality of elements whose number is redundant;
means for monitoring a misalignment between the transmitter and the
receiver including means for determining a direction and an amplitude of
the misalignment; and
means for re-routing data from the element which is misaligned to a
redundant element selected along a direction associated with the direction
of the misalignment so as to provide data transmission through the system,
the re-routing being performed in response to a signal generated by the
monitoring means.
The means for monitoring the misalignment may include means for monitoring
a signal connection parameter between the transmitter and the receiver,
e.g. a signal parameter at the receiver or at the transmitter.
Alternatively the signal connection parameter may be a signal parameter of
at least one element of at least one of the transmitter and the receiver.
Conveniently, the signal connection parameter is an intensity of the data
signal.
In an embodiment of the invention, means for monitoring the misalignment
between the modules includes a dedicated alignment laser and a dedicated
detector, with the means for determining the direction and the amplitude
of the misalignment including a circuitry for measuring a position of the
laser spot of the alignment laser on the dedicated detector.
Alternatively, means for monitoring the misalignment may include a
detector selected from the group consisting of detectors for monitoring
lateral and vertical misalignments, and detectors for monitoring tilt
misalignments or other known suitable detectors. Optionally, the means for
monitoring the misalignment may further comprise means for providing
feedback between the transmitter and the receiver regarding the
misalignment, which can be conveniently selected from optical fiber, LED,
electrical cable, electrical backplane or other suitable means. As an
alternative to the embodiment described above, means for determining the
direction and the amplitude of the misalignment may include means for
measuring an intensity distribution at the receiver elements.
The elements of the transmitter and/or receiver may be arranged into a
one-dimensional or two-dimensional array, or any other pattern providing
the required optical transmission or collection. Alternatively, the
elements of the transmitter and/or receiver may be arranged into clusters,
the number of clusters being redundant and the number of elements in each
cluster being sufficient to accommodate the number of data channels to be
transmitted. If required, the elements may be shared by different
clusters. The system may comprise one transmitter and one receiver only to
provide a uni-directional interconnection. Alternatively, the system may
comprise two modules, each module having one transmitter and one receiver,
thus providing for a bi-directional transmission and receiving of data. It
may be arranged that the receiver only has redundant elements. If
required, the transmitter only may have redundant elements or redundant
clusters.
Preferably, the system is implemented with optical elements, such as bulk
optics (lenses, prisms, mirrors, splitters, et al.), binary optics (fanout
gratings, diffractive lenses, et al.), holographic elements, and
integrated optics.
Preferably, the elements of the transmitter are optical emitters or optical
modulators. The emitters may be vertical cavity surface emitting lasers
(VCSEL), light emitting diodes (LED) and edge emitting laser diodes or
other known devices. The modulators may be modulators based on
magneto-optic effect, modulators including liquid crystal devices,
ferroelectric modulators, e.g. lead lanthanum zirconate titanate (PLZT)
modulator, modulators including piezo-electric crystals, modulators
including deformable mirrors, electro-optical semiconductor
hetero-structure modulators, optical cavity modulators, or other known
modulators.
The receiver of the optical interconnect system comprises at least one
detector, preferably from PIN detector, metal-semiconductor-metal
detector, avalanche photodiode, or other known detectors.
Preferably, the transmitter and/or receiver, or the whole system described
above are integrated within a package or several packages, thus providing
compactness and efficient use of space.
According to another aspect of the invention there is provided a module for
free space optical interconnect system, comprising:
at least one of a transmitter and a receiver, at least one of the
transmitter and the receiver comprising a plurality of elements whose
number is redundant;
means for monitoring a misalignment of the module including means for
determining a direction and an amplitude of the misalignment; and
means for re-routing data from the element which is misaligned to a
redundant element selected along a direction associated with the direction
of the misalignment so as to provide data transmission through the system,
the re-routing being performed in response to a signal generated by the
monitoring means.
Beneficially, the means for monitoring the misalignment of the module
comprises means for monitoring a signal connection parameter at the
module, e.g. an intensity of the signal. Alternatively, the means for
monitoring the misalignment may comprise detectors for monitoring lateral
and vertical misalignments, detectors for monitoring tilt misalignments or
any other suitable known detectors. In an embodiment of the invention,
means for monitoring the misalignment of the module includes a dedicated
detector, with the means for determining the direction and the amplitude
of the misalignment including means for measuring a position of a laser
spot of a dedicated alignment laser on the dedicated detector.
Alternatively, it may include means for measuring an intensity
distribution, e.g. at the receiver elements. The module may include one
transmitter or one receiver only for a uni-directional link. If required,
it may include both the transmitter and receiver for corresponding
transmitting and receiving of data in a bi-directional optical
interconnect system. Preferably, the elements of the module are arranged
into a one-dimensional array or two-dimensional array. Alternatively, they
may be arranged so as to form a pre-determined pattern providing the
required optical transmission or collection. Optionally, the redundant
elements may be arranged into clusters, the number of clusters being
redundant and the number of elements in each cluster being sufficient to
accommodate the number of data channels to be transmitted. Accordingly,
the means for re-routing comprises means for re-routing data from a
cluster which is misaligned to a redundant cluster which provides data
transmission through the system. If required, the elements may be shared
between different clusters. Beneficially, the elements of the transmitter
are optical emitters, e.g. VCSEL, SLD, LED, edge emitting laser diodes or
other known emitters. Alternatively the elements of the transmitter may be
optical modulators. The elements of the receiver may be selected from PIN
detector, metal-semiconductor-metal detector, avalanche photodiode or
other known suitable detectors. Beneficially, the module is integrated
within a package.
According to yet another aspect of the invention there is provided a method
of operating a free space optical interconnect system, comprising a
transmitter and a receiver, at least one of the transmitter and the
receiver having a plurality of elements whose number is redundant, the
method comprising the steps of:
(a) monitoring a misalignment between the transmitter and the receiver,
including determining a direction and an amplitude of the misalignment;
and
(b) when the amplitude of the misalignment is exceeding a pre-determined
threshold value, re-routing data from the element which is misaligned to a
redundant element selected along a direction associated with the direction
of the misalignment so as to provide data transmission through the system.
Conveniently, the step of monitoring the misalignment comprises monitoring
a signal connection parameter between the transmitter and the receiver,
e.g. a signal parameter at the receiver or at the transmitter. Optionally,
the step of monitoring the signal connection parameter comprises
monitoring a signal parameter of at least one element of at least one of
the transmitter and the receiver, e.g. monitoring intensity of the data
signal. In the embodiment of the invention, the step of determining the
direction and the amplitude of the misalignment comprises measuring a
position of a laser spot of a dedicated alignment laser on a dedicated
detector. Alternatively, this step may include measuring an intensity
distribution, e.g. at the receiver elements.
Free space optical interconnect systems formed using the techniques
described above are more reliable compared to other existing free space
interconnect systems having redundant elements. Monitoring of the
misalignment between the transmitter and the receiver, determining the
direction and the amplitude of the misalignment and comparing the
amplitude with the threshold value allows re-routing of data to available
redundant elements well in advance before the quality of data transmission
deteriorates substantially and before the link is dropped or data is lost.
The use of redundant elements also obviates the need of packaging which
requires precise alignment and which is often expensive and bulky. The
interconnect systems based on the present invention have simpler
mechanical design, have no moving parts and may be implemented with lower
cost mechanics. As a result, they can be manufactured more readily and at
much lower cost, and providing higher reliability at the same time.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described in greater detail with references to
the attached drawings wherein:
FIG. 1 illustrates a schematic view of a free space optical interconnect
system for a uni-directional link according to an embodiment of the
invention;
FIG. 2a illustrates an arrangement of the transmitter and receiver elements
into one-dimensional array in the embodiment of FIG. 1;
FIG. 2b illustrates a system of FIG. 2a experiencing a vertical shift
misalignment of the receiver module;
FIG. 2c illustrates a system of FIG. 2a experiencing a vertical shift
misalignment of the transmitter module; and
FIG. 2d illustrates a definition of a direction associated with the
direction of the misalignment.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
A schematic view of a free space optical interconnect system 10 according
to the embodiment of the present invention is shown in FIG. 1. The system
10 comprises a first module 12, the module being a transmitter module, and
a second module 14, the module being a receiver module, and provides a
uni-directional link between the modules. The transmitter module 12
carries a transmitter 16 having a plurality of transmitter elements for
transmission of data, the receiver module carrying the corresponding
receiver 20 having a plurality of receiver elements 22 for receiving the
data. The number of elements of the receiver 20 is redundant, i.e. more
than necessary compared to the number sufficient to accommodate the data
channels to be transmitted. Each of the transmitter elements is a vertical
cavity surface emitting laser (VCSEL), emitting a beam normal to the plane
of the module 12 through the lens 32 of the transmitter package 16, and
the receiver elements are detectors, forming a one-dimensional array.
An arrangement of transmitter and receiver elements is shown in more detail
in FIG. 2. As a way of example, the transmitter 16 carries three lasers
26, 28 and 30 which are arranged into a one-dimensional array, the
distance between the adjacent lasers being 0.25 mm to 1.25 mm. The
receiver 20 includes seven detectors 22 designated a1 to a7, three of them
being used at any given moment for receiving data and the rest four of
them being redundant and used for receiving data when the system is
misaligned.
Lasers 26, 28, 30 are housed together with driver circuits 50 in a package
on the transmitter module 12. Laser beams from lasers are emitted through
the lens 32 collimating or nearly collimating the light and received at
the detector array 22 being focused on the array through the lens 34. The
detectors 22 are housed together with receiver circuits 23 in a package on
the receiver module 14.
Means for monitoring a misalignment between the transmitter 16 and the
receiver 20 is implemented by use of a dedicated alignment laser 36 and a
large slow position sensing alignment detector 40 at the receiver module
14 (FIG. 1). The laser 36 is packaged with a lens 38 so as to emit a
narrow beam perpendicular to the transmitter module 12. The beam is
received by the detector 40 which monitors the mutual alignment of modules
12 and 14, and as a result, the alignment of the transmitter 16 and the
receiver 20. Means for determining the direction and amplitude of the
misalignment between the modules is implemented by use of control
circuitry 44 at receiver module. The circuitry 44 monitors the current
position of the alignment laser 36 on the detector 40 and compares it to
the stored position of the alignment laser, the position being
characterized by reliable data transmission between the modules. The
receiver 20 also includes means for re-routing data between the detectors
implemented by use of drive circuitry 23.
The system 10 is packaged in the following manner. The transmitter module
12 and receiver module 14 comprise part of printed circuit boards. The
printed circuit boards are mounted in shelves, racks and frames made of
plastic and metal. The printed circuit boards, shelves, racks and frames
have holes and windows as necessary to allow the data, alignment and
feedback light to pass. The lasers 26, 28, 30, the drive circuit 50 and
the lens 32 are mounted using adhesives within a metal and ceramic
multi-chip package, and the package is soldered onto the substrate of the
transmitter module 12. Likewise, the detectors 22, the receiver circuit 23
and the lens 34 are similarly packaged and mounted.
The system 10 operates in the following manner. First, the data to be
transmitted is routed to the lasers 26, 28, 30 which emit light collimated
by lens 32 and sent to the receiver 20. The focusing lens 34 collects the
light from the lasers and directs it on the detectors 22, e.g. producing
spots on detectors a3, a4 and a5 from lasers 26, 28 and 30 respectively as
shown in FIG. 2a which illustrates the situation when the system is
initially aligned. Simultaneously, the alignment laser 36 sends a
reference beam through the lens 38, and the beam is received by a position
sensing alignment detector 40. The position of the reference beam on the
detector 40, and consequently the position of the module 14, is read out
by a control circuitry 44 and compared with a stored position (e.g. an
aligned position of the system) which characterizes reliable data
transmission between the modules. When the modules 12 and 14 are
misaligned, the circuitry 44 detects a difference between the current and
stored position of the reference beam and compares the difference with a
pre-determined threshold value. The circuitry 44 also identifies a
direction of the misalignment as a direction in which the reference beam
of the alignment laser moves from the stored position to its current
position. When the difference between the positions exceeds the threshold
value, the circuitry 44 sends a signal to the receiver circuit 23 to
re-route the data to redundant detectors, the new detectors in use being
chosen in a direction associated with the direction of the misalignment as
will be described below.
As a way of example, let's assume that the receiver module 14 experiences a
vertical shift misalignment in a direction designated by vector AB as
shown in FIG. 2b. Accordingly the direction and amplitude of this
misalignment is measured by circuitry 44 as described above. When the
amplitude of the misalignment exceeds the threshold, a signal is sent to
drive circuitry 23 to re-route the data to another set of detectors. The
new detectors are selected in a direction opposite to the direction of the
misalignment, i.e. in the direction opposite to the vector AB so as to
compensate for the occurred misalignment. As illustrated in FIG. 2b, the
new set of detectors may include, e.g., detectors a2, a3 and a4. The new
detectors now receive data from the correct physical location and ensure
reliable data transmission through the system. A new position of the
alignment laser 36 on the detector 40 which corresponds to the use of the
new set of detectors is now stored, thus replacing the previous stored
position of the alignment laser. Accordingly, all new measurements of the
misalignment between the modules are referred to the new stored position.
If required, a new threshold value identifying maximal deviations from the
stored position may be introduced.
Alternatively, it may happen that the transmitter module 12 experiences a
misalignment similar to that of the receiver module described above, i.e.
a vertical shift misalignment in a direction designated AB as shown in
FIG. 2c. Then, assuming that the re-routing is supposed to be done between
the receiver elements 22, it means that it should be done in a direction
coinciding with the direction of the misalignment to provide reliable data
transmission, i.e. in the direction AB. New detectors in use may be, e.g.,
detectors a4, a5 and a6 correspondingly as illustrated in FIG. 2c.
In other situations, more complex types of misalignments may occur and/or
the light generated by the transmitter elements may be projected onto
receiver elements with the use of optical elements, e.g. mirrors, prisms
etc., which change the initial direction of the laser beams generated by
the transmitter elements. In such situations, the new detectors for
receiving data will be selected in a direction associated with the
direction of the misalignment, the direction of re-routing being dependent
on how an image plane of the transmitter module is projected onto the
receiver module. As a way of example, FIG. 2d illustrates a scheme where
light generated by the transmitter module 12 is re-directed onto the
receiver module 20 at an angle of 90 degrees by using a plane mirror 35.
In this arrangement, when the misalignment of the transmitter module
occurs in a direction designated by vector AB, the direction associated
with the direction of the misalignment will be identified as a direction
CD shown in FIG. 2d. Accordingly, the re-routing between the receiver
elements will be made along the direction CD.
The optical interconnect system 10 described above has the following
dimensions: separation between modules 12 and 14 is about .about.10
inches, focal lengths of the lenses 32 and 34 are about 10 mm, an angle
between the laser beams generated by adjacent lasers, designated by
numeral 19 in FIG. 1, is about 1 degree. These dimensions provide an
alignment tolerance of about 4 mm over 10 inches of interconnect distance.
Other dimensions of the system may be also used to provide alignment of
the system for larger distances, e.g. up to meters.
An initial set-up of the system 10 may be done by using one of the methods
providing cycling through the redundant elements, e.g. a method similar to
that described in a patent application Ser. No. 09/150,242 to Goodwill
which is incorporated herein by reference.
The system and method of its operation described above are suitable for
compensation of relatively slow misalignments, i.e. the misalignments
which have a typical time interval between changes much greater than time
intervals between re-routing of data.
Instead of the system described above which has redundant elements of the
receiver only, it is contemplated that the system may include redundant
elements of the transmitter only, or both of the receiver and the
transmitter. The number of redundant elements may be arbitrary, depending
on the system requirements.
The elements of the transmitter and/or receiver may be arranged into a
one-dimensional or two-dimensional array, or any other pattern providing
the required optical transmission or collection.
Instead of the system described above providing one-directional link, an
alternative embodiment of the system may provide a bi-directional link,
having one transmitter and one receiver at each module for corresponding
transmittance and reception of data.
In another embodiment it is contemplated that the elements of the receiver
20 and/or the transmitter 16 may be arranged into clusters. Conveniently,
the number of clusters is redundant and the number of elements in each
cluster is sufficient for the transmission of the required number of data
channels. If required, the elements may be shared between different
clusters. Correspondingly, re-routing of data is performed between
redundant clusters of the receiver 20 and/or the transmitter 16, depending
on the direction and the amplitude of the misalignment.
The means for monitoring the misalignment may include means for monitoring
a signal connection parameter between the transmitter and the receiver,
e.g. a signal parameter at the receiver or at the transmitter.
Alternatively the signal connection parameter may be a signal parameter of
at least one element of at least one of the transmitter and the receiver.
Conveniently, the | | |
