U.S. patent application number 14/868578 was filed with the patent office on 2017-06-01 for optical interconnection methods and systems exploiting mode multiplexing.
The applicant listed for this patent is THE ROYAL INSTITUTION FOR THE ADVANCEMENT OF LEARNING / MCGILL UNIVERSITY, SCUOLA SUPERIORE SANT'ANNA. Invention is credited to Nicola Andriolli, Isabella Cerutti, Odile Liboiron-Ladouceur, Philippe Velha.
Application Number | 20170155465 14/868578 |
Document ID | / |
Family ID | 55585597 |
Filed Date | 2017-06-01 |
United States Patent
Application |
20170155465 |
Kind Code |
A9 |
Liboiron-Ladouceur; Odile ;
et al. |
June 1, 2017 |
OPTICAL INTERCONNECTION METHODS AND SYSTEMS EXPLOITING MODE
MULTIPLEXING
Abstract
Optical solutions to address and overcome the issues of
superseding/replacing electrical interconnection networks have
generally exploited some form of optical space switching. Such
optical space switching architectures required multiple switching
elements, leading to increased power consumption and footprint
issues. Accordingly, it would be beneficial for new optical, e.g.
fiber optic or integrated optical, interconnection architectures to
address the traditional hierarchal time-division multiplexed (TDM)
space based routing and interconnection to provide reduced latency,
increased flexibility, lower cost, and lower power consumption.
Accordingly, it would be beneficial to exploit networks operating
in multiple domains by overlaying mode division multiplexing to
provide increased throughput in bus, point-to-point networks, and
multi-cast networks, for example, discretely or in combination with
wavelength division multiplexing.
Inventors: |
Liboiron-Ladouceur; Odile;
(Montreal, CA) ; Andriolli; Nicola; (Pisa, IT)
; Cerutti; Isabella; (Pisa, IT) ; Velha;
Philippe; (San Giuliano Terme, IT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
THE ROYAL INSTITUTION FOR THE ADVANCEMENT OF LEARNING / MCGILL
UNIVERSITY
SCUOLA SUPERIORE SANT'ANNA |
MONTREAL
PISA |
|
CA
IT |
|
|
Prior
Publication: |
|
Document Identifier |
Publication Date |
|
US 20160094308 A1 |
March 31, 2016 |
|
|
Family ID: |
55585597 |
Appl. No.: |
14/868578 |
Filed: |
September 29, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62056650 |
Sep 29, 2014 |
|
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|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04J 14/02 20130101;
H04J 14/028 20130101; H04B 10/2581 20130101; G02B 6/2938 20130101;
H04J 14/04 20130101; H04Q 2011/0016 20130101; H04Q 11/0005
20130101; H04Q 2011/0024 20130101; G02B 6/12004 20130101 |
International
Class: |
H04J 14/04 20060101
H04J014/04; H04B 10/2581 20060101 H04B010/2581; H04J 14/02 20060101
H04J014/02; H04Q 11/00 20060101 H04Q011/00; G02B 6/293 20060101
G02B006/293; G02B 6/12 20060101 G02B006/12 |
Claims
1. An optical node comprising: an input port coupled to a first
optical link supporting a plurality of wavelengths and plurality of
transverse modes; an output port coupled to a second optical link
supporting a plurality of wavelengths and a plurality of transverse
modes; a third optical link coupled to the input port and the
output port supporting the plurality of wavelengths and the
plurality of transverse modes; at least one of: an optical
transmitter block coupled to the third optical link for launching
at the output port a generated optical signal at a predetermined
wavelength of the plurality of wavelengths and a predetermined
transverse mode of the plurality of transverse modes for
transmission; and an optical receiver block coupled to the third
optical link for extracting a received optical signal from the
input port at a predetermined wavelength of the plurality of
wavelengths and a predetermined transverse mode of the plurality of
transverse modes.
2. The optical node according to claim 1, wherein when the at least
one of is an optical transmitter block it comprises: a
multi-wavelength optical source emitting on M predetermined
wavelengths; a 1:N optical splitter coupled to the multi-wavelength
optical source to generate N parallel multi-wavelength channels; N
optical wavelength selectors, each coupled to one of the N parallel
multi-wavelength channels and selecting a predetermined wavelength
of the M predetermined wavelengths; and N optical mode selectors,
each coupled to the output of an optical wavelength selector and
converting the received predetermined wavelength from the optical
wavelength selector to a predetermined transverse mode of the
plurality of transverse modes and coupling it to the third optical
link.
3. The optical node according to claim 1, wherein when the at least
one of is an optical receiver block it comprises: a plurality of
optical mode selectors, each for coupling a predetermined optical
signal from the third optical link to a photodetector, wherein the
predetermined optical wavelength is a predetermined wavelength of
the plurality of wavelengths and a predetermined transverse mode of
the plurality of transverse modes.
4. The optical node according to claim 1, wherein the optical
transmitter block, the optical receiver block, and the third
optical link are all predetermined portions of a photonic
integrated circuit.
5. The optical node according to claim 1, wherein the optical node
is an optical node of a plurality of optical nodes; and the first
optical links and second optical links and the third optical links
are predetermined portions of a closed loop shared waveguide
forming a predetermined portion of a photonic integrated
circuit.
6. The optical node according to claim 1, wherein the optical node
is an optical node of a plurality of optical nodes; and the first
optical links and second optical links and the third optical links
are each formed from a pair of shared waveguides, wherein the
optical transmitter blocks of the plurality of optical nodes are
associated with a first shared waveguide of the pair of shared
waveguides and the optical receiver blocks of the plurality of
optical nodes are associated with a second shared waveguide of the
pair of shared waveguides.
7. The optical node according to claim 1, wherein the shared
waveguide comprises either: a plurality of closely spaced
singlemode optical waveguides wherein the resulting array of
optical waveguides support a plurality of modes, wherein each mode
is a predetermined transverse mode of the plurality of transverse
modes; and a single optical waveguide supporting a plurality of
modes, wherein each mode is a predetermined transverse mode of the
plurality of transverse modes.
8. The optical node according to claim 1, wherein the optical mode
converter comprises either: a first converter comprising an input
section comprising at least one of a plurality of R closely spaced
singlemode optical waveguides with first predetermined spacings
that separate or a multimode waveguide and an output comprising R
singlemode optical waveguides with second predetermined spacings; a
phase modulation section comprising R singlemode optical waveguides
with predetermined second spacings coupled to the output of the
input section; an output section comprising a coupler coupled to
the other end of the phase modulation section and tapering to a
central portion comprising the R closely spaced singlemode optical
waveguides with first predetermined spacings and an output section
wherein the R closely spaced singlemode optical waveguides separate
to R singlemode optical waveguides with third predetermined
spacings; and a plurality of electrodes associated with a
predetermined subset of the R singlemode optical waveguides with
predetermined second spacings, wherein inducing predetermined phase
shifts within a predetermined subset of the R singlemode optical
waveguides with predetermined second spacings results in an optical
transverse mode of the plurality of optical transverse modes
supported by the plurality of R closely spaced singlemode optical
waveguides received at the input being converted to another optical
transverse mode of the plurality of optical transverse modes at the
output; and a second converter comprising: a multimode optical
waveguide supporting a plurality of modes, wherein each mode is a
predetermined transverse mode of the plurality of transverse modes;
a launch singlemode optical waveguide; and a coupler for coupling
the single mode of the launch waveguide to a predetermined mode of
the multimode optical waveguide.
9. The optical node according to claim 1, wherein the predetermined
transverse mode of the plurality of transverse modes for the at
least one of the received optical signal and the generated optical
signal is either fixed in dependence upon an aspect of the optical
node or tunable.
10. The optical node according to claim 1, wherein when the at
least one of is an optical transmitter block it comprises: a remote
multi-wavelength laser and a wavelength demultiplexer; a wavelength
selector comprising a plurality of wavelength selective elements;
and a mode selector comprising a plurality of mode selective
elements, wherein each mode selective element is coupled to a
predetermined wavelength selective element and converts the
received predetermined wavelength from the optical wavelength
selector to a predetermined transverse mode of the plurality of
transverse modes and coupling it to the third optical link
11. The optical node according to claim 1, wherein when the at
least one of is an optical transmitter block it comprises: a
plurality of wavelength tunable optical sources; and a mode
selector comprising a plurality of mode selective elements, wherein
each mode selective element is coupled to a predetermined
wavelength selective element and converts the received
predetermined wavelength from the optical wavelength selector to a
predetermined transverse mode of the plurality of transverse modes
and coupling it to the third optical link.
12. The optical node according to claim 1, wherein when the at
least one of is an optical transmitter block it comprises: a remote
multi-wavelength laser; a wavelength selector comprising a
plurality of wavelength selective elements, each wavelength
selective element for removing a predetermined portion of the
optical signals received from the remote multi-wavelength laser;
and a mode selector comprising a plurality of mode selective
elements, wherein each mode selective element is coupled to a
predetermined wavelength selective element and converts the
received predetermined wavelength from the optical wavelength
selector to a predetermined transverse mode of the plurality of
transverse modes and coupling it to the third optical link
13. The optical node according to claim 1, wherein when the at
least one of is an optical transmitter block it comprises: a
plurality of fixed wavelength optical sources; a mode selector
comprising a plurality of mode selective elements, wherein each
mode selective element is coupled to a predetermined fixed
wavelength optical source of the plurality of fixed wavelength
optical sources and converts the received predetermined wavelength
to a predetermined transverse mode of the plurality of transverse
modes and coupling it to the third optical link
14. The optical node according to claim 1, wherein when the at
least one of is an optical transmitter block it comprises: a fixed
wavelength optical source; a splitter coupled to the fixed
wavelength optical source and generating a plurality of outputs a
mode selector comprising a plurality of mode selective elements,
wherein each mode selective element is coupled to an output of the
splitter and converts the received optical signal to a
predetermined transverse mode of the plurality of transverse modes
and coupling it to the third optical link.
15. The optical node according to claim 1, wherein when the at
least one of is an optical receiver block it comprises: a mode
selector comprising a plurality of mode selective elements, wherein
each mode selective element is coupled to the third optical link
and converts a received predetermined transverse mode of the
plurality of transverse modes to an output mode; and a wavelength
selector block comprising a plurality of wavelength selective
elements, wherein each wavelength selective element is coupled to a
mode selective element and filters the output mode to a
predetermined wavelength range.
16. The optical node according to claim 1, wherein when the at
least one of is an optical receiver block it comprises: a mode
selector comprising a plurality of mode selective elements, wherein
each mode selective element is coupled to the third optical link
and couples a predetermined transverse mode of the plurality of
transverse modes at a predetermined wavelength to an output
mode.
17. The optical node according to claim 1, wherein when the at
least one of is an optical receiver block it comprises: a mode
selector comprising a plurality of mode selective elements, wherein
each mode selective element is coupled to the third optical link
and converts a received predetermined transverse mode of the
plurality of transverse modes to an output mode; and a wavelength
demultiplexer for generating a plurality of outputs from the output
mode, each output having a predetermined wavelength range.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This patent application also claims the benefit of U.S.
Provisional Patent Applications 62/056,650 filed Sep. 29, 2014
entitled "Mode Multiplexing Optical Interconnection Methods and
Systems", the entire contents of which are incorporated herein by
reference.
FIELD OF THE INVENTION
[0002] This invention relates to optical interconnection networks
and more particularly to circuit board level, interchip, and
intrachip optical interconnections and networks.
BACKGROUND OF THE INVENTION
[0003] Optical fiber communications is seen as one of the most
reliable telecommunication technologies to achieve consumers' needs
for present and future applications. It is reliable in handling and
transmitting data through hundreds of kilometers with an acceptable
bit error rate and today, optical fiber communication dominates as
the physical medium for medium and long distance data transmission
systems and telecommunications networks. At the same time optical
fiber solutions now appear in short-haul applications, local area
networks, fiber-to-the-home/curb/cabinet, and digital cable
systems. Over the same 30 year time period (1984-2014) as optical
networks have evolved from initial 140 Mb/s links to wavelength
division multiplexed Tb/s links microprocessors have evolved from
single core 20 MHz processors to 4 and 6 core 2-4 GHz desktop and
server processors and 60 core 1 GHz server processors. Meanwhile
Internet evolved from a few million users on desktop computers to
nearly three billion users representing approximately 40% of the
global population on a range of devices from laptops through smart
televisions to gaming consoles and smart phones.
[0004] Data centres are facilities that store and distribute the
data on the Internet. With an estimated 14 trillion web pages on
over 750 million websites, data centres contain a lot of data.
Further, with almost three billion Internet users accessing these
websites, including a growing amount of high bandwidth video, there
is a massive amount of data being uploaded and downloaded every
second on the Internet. At present the compound annual growth rate
(CAGR) for global IP traffic between users is between 40% based
upon Cisco's analysis (see
http://www.cisco.com/en/US/solutions/collateral/ns341/ns525/ns537/ns705/n-
s827/white_paper
c11-481360_ns827_Networking_Solutions_White_Paper.html) and 50%
based upon the University of Minnesota's Minnesota Internet Traffic
Studies (MINTS) analysis. By 2016 this user traffic is expected to
exceed 100 exabytes per month, or over 42,000 gigabytes per second.
However, peak demand will be considerably higher with projections
of over 600 million users streaming Internet high-definition video
simultaneously at peak times. All of this data flowing into and out
of these data centres will generally be the result of data
transfers between data centres and within data centres so that
these overall IP traffic flows must, in reality, be multiplied many
times to establish the total IP traffic flows.
[0005] Data centres are filled with tall racks of electronics
surrounded by cable racks where data is typically stored on big,
fast hard drives. Servers are computers that take requests and move
the data using fast switches to access the right hard drives and
either write or read the data to the hard drives. In mid-2013
Microsoft stated it had itself over 1 million servers. Connected to
these servers are routers that connect the servers to the Internet
and therein the user and/or other data centres.
[0006] According to Facebook.TM., see for example Farrington et al.
in "Facebook's Data Centre Network Architecture" (IEEE Optical
Interconnects Conference, 2013 available at
http://nathanfarrington.com/presentations/facebook-optics-oida13-slides.p-
ptx), there can be as high as a 1000:1 ratio between intra-data
centre traffic to external traffic over the Internet based on a
single simple request. Within data centre's 90% of the traffic
inside data centres is intra-cluster.
[0007] At the same time as requiring an effective yet scalable way
of interconnecting data centres and warehouse scale computers
(WSCs), both internally and to each other, operators must provide a
significant portion of data centre and WSC applications free of
charge to users and consumers, e.g. Internet browsing, searching,
etc. Accordingly, data centre operators must meet exponentially
increasing demands for bandwidth without dramatically increasing
the cost and power of the infrastructure. At the same time
consumers' expectations of download/upload speeds and latency in
accessing content provide additional pressure.
[0008] Historically microprocessor improvements from 1984-2004 were
driven through increasing clock speeds as processor speeds
increased from 20 MHz to 3 GHz. Subsequently processor speeds have
typically maintained in the 2.5-4 GHz range and many microprocessor
manufacturers have stated that circuit speeds are unlikely to
exceed 5 GHz as both static and dynamic power dissipation
considerably increase for deep sub-100 nm CMOS. Already, an
Intel.TM. Core.TM. i7-5960X desktop processor with 8 cores
operating up to 3.5 GHz with 20 MB cache consumes up to 140 W and
an Intel.TM. Xeon Phi.TM. 7120X server coprocessor with 61 cores
operating up to 1.2 GHz with 16 GB cache memory consumes 300 W.
Such multi-core processors have therefore driven performance
enhancements of the period 2004-2104. However, in many-core
architectures, the overall performance of the computing system
depends not only on the capabilities of the processing nodes but
also the electrical interconnection networks carrying the
communications between processors and between processors and
memories.
[0009] Already optical interconnection solutions play critical
roles in data centre operations for the interconnection of servers,
hard drives, routers etc., where the goal is to move data as fast
as possible with the lowest latency, the lowest cost and the
smallest space consumption on the server blade. Gigabit Ethernet is
too slow and 10 Gb/s solutions such as 10G Ethernet and Fibre
Channel are deployed whilst 10/20 Gb/s Fibre Channel and 40G/100G
Ethernet are emerging based upon multiple 10 Gb/s channels run over
parallel multimode optical fiber cables or wavelength division
multiplexed (WDM) onto a singlemode fiber. Intra-rack and local
inter-server communications typically exploit 100GBASE-SR10 links
with OM3/OM4 multimode optical fibers providing 100 m/150 m reach.
General inter-server communications within a data centre that can
be a few thousand meters and hence 100GBASE-LR4 singlemode optical
fiber links with reach up to 10 km may be employed. Today, in
addition to addressing such link speed enhancements, focus is being
made to the architectures employed within the data centre in order
to reduce latency and ease physical implementation where tens of
thousands of fiber optic cables may be run within the data centre.
Today the largest data centres comprise 50,000 to 100,000
servers.
[0010] However, within the server the electrical interconnection
networks also suffer issues when scaling to a large number of
processors due to the server level interconnections albeit
differing in several aspects. Simple topologies, such as a
chip-global bus, exhibit high latency, require power-hungry
repeaters, and occupy large footprint. More complex topologies can
be exploited, such as direct networks for example, which connect
neighbouring processing nodes within a predetermined topology
through point-to-point dedicated links. Still, these networks just
like the spline-leaf networks connecting servers require the signal
to cross multiple hops for connecting distant cores and are prone
to contention between concurrent message transmissions, both
leading to increased latency and power consumption. Accordingly,
providing additional bandwidth for inter-circuit, intra-board, and
inter-board applications just as with server connections will
require the adoption of optical communication solutions.
Accordingly, these will require the provisioning of low cost, small
footprint, and low power solutions in order to meet the
requirements of the applications and ongoing market drivers.
Accordingly integrated optoelectronic solutions offer a technology
option addressing these requirements.
[0011] Within the prior art, optical solutions to address and
overcome the issues of superseding/replacing electrical
interconnection networks have generally exploited some form of
optical space switching. Such optical space switching architectures
required multiple switching elements, leading to increased power
consumption and footprint issues. Accordingly, it would be
beneficial for new optical, e.g. fiber optic or integrated optical,
interconnection architectures to address the traditional hierarchal
time-division multiplexed (TDM) space based routing and
interconnection to provide reduced latency, increased flexibility,
lower cost, and lower power consumption.
[0012] In order to address this, the inventors exploit multiple
domains by overlaying mode division multiplexing to provide
increased throughput in bus, point-to-point networks, and
multi-cast networks, for example, discretely or in combination with
wavelength division multiplexing. Further, routing within networks
according to embodiments of the invention may be based upon space
switching, wavelength domain switching, and mode division switching
or combinations thereof. In this manner the inventors provide
interconnections exploiting N.times.W.times.M.times.D Gb/s photonic
interconnects wherein N channels are provided each carrying W
wavelength division signals with M modes each at D Gb/s.
[0013] Other aspects and features of the present invention will
become apparent to those ordinarily skilled in the art upon review
of the following description of specific embodiments of the
invention in conjunction with the accompanying figures.
SUMMARY OF THE INVENTION
[0014] It is an object of the present invention to address
limitations within the prior art relating to optical
interconnection networks and more particularly to circuit board
level, interchip, and intrachip optical interconnections and
networks.
[0015] In accordance with an embodiment of the invention there is
provided an optical node comprising: [0016] an input port coupled
to a first optical link supporting a plurality of wavelengths and
plurality of transverse modes; [0017] an output port coupled to a
second optical link supporting a plurality of wavelengths and a
plurality of transverse modes; [0018] a third optical link coupled
to the input port and the output port supporting the plurality of
wavelengths and the plurality of transverse modes; [0019] at least
one of: [0020] an optical transmitter block coupled to the third
optical link for launching at the output port a generated optical
signal at a predetermined wavelength of the plurality of
wavelengths and a predetermined transverse mode of the plurality of
transverse modes for transmission; and [0021] an optical receiver
block coupled to the third optical link for extracting a received
optical signal from the input port at a predetermined wavelength of
the plurality of wavelengths and a predetermined transverse mode of
the plurality of transverse modes.
[0022] In accordance with an embodiment of the invention there is
provided a method of transmitting data encoded onto an optical
signal by selectively exciting a predetermined mode of a plurality
of modes within an optical waveguide.
[0023] In accordance with an embodiment of the invention there is
provided a method of transmitting data encoded onto an optical
signal by selectively coupling the transmitter to an optical
waveguide in order to excite a predetermined mode of a plurality of
modes within an optical waveguide.
[0024] In accordance with an embodiment of the invention there is
provided a method of receiving data encoded onto an optical signal
by selectively at least one of filtering and coupling a
predetermined mode to a photodetector, the predetermined mode being
one of a plurality of modes supported by the optical waveguide.
[0025] In accordance with an embodiment of the invention there is
provided a system comprising: [0026] a plurality of transmitters,
each transmitter generating an encoded optical signal; [0027] an
optical waveguide based network comprising optical waveguide
supporting a plurality of optical modes; [0028] a plurality of
first mode filters, each first mode filter of the plurality of
first mode filters for coupling the output of a predetermined
transmitter of the plurality of transmitters to a predetermined
optical mode of the plurality of optical modes supported by the
optical waveguide; [0029] a plurality of second mode filters, each
second mode filter of the plurality of second mode filters for
coupling a predetermined optical mode of the plurality of optical
modes supported by the optical waveguide to an optical
photodetector.
[0030] In accordance with an embodiment of the invention there is
provided a method of transmitting data by encoding parallel data
onto a plurality of optical signals generated from a single optical
emitter and then coupling each optical signal of the plurality of
optical signals to a predetermined mode of a plurality of modes
supported by an optical waveguide.
[0031] In accordance with an embodiment of the invention there is
provided a method of receiving parallel data by filtering parallel
data encoded onto a plurality of modes supported by an optical
waveguide to a plurality of photodetectors, each photodetector
receiving the data encoded onto a predetermined mode of the
plurality of modes.
[0032] Other aspects and features of the present invention will
become apparent to those ordinarily skilled in the art upon review
of the following description of specific embodiments of the
invention in conjunction with the accompanying figures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0033] Embodiments of the present invention will now be described,
by way of example only, with reference to the attached Figures,
wherein:
[0034] FIG. 1A depicts the deployment of optical networking and
optical interconnections within the global telecommunications
architecture;
[0035] FIG. 1B depicts a typical prior art leaf-spine architecture
for interconnecting servers within a data centre and data centres
to each other;
[0036] FIG. 1C depicts a typical prior art server blade
architecture;
[0037] FIG. 2 depicts a bus/ring based architecture, according to
an embodiment of the invention, exploiting wavelength and mode dual
domain division multiplexing via tunable wavelength fixed mode
transmitters;
[0038] FIG. 3 depicts a bus/ring based architecture, according to
an embodiment of the invention, exploiting wavelength and mode dual
domain division multiplexing via wavelength selective fixed mode
transmitters;
[0039] FIG. 4 depicts a bus/ring based architecture, according to
an embodiment of the invention, exploiting wavelength and mode dual
domain division multiplexing via tunable wavelength tunable mode
transmitters;
[0040] FIG. 5 depicts a bus/ring based architecture, according to
an embodiment of the invention, exploiting mode and wavelength dual
domain division multiplexing via fixed wavelength tunable mode
transmitters;
[0041] FIG. 6 depicts a bus/ring based architecture, according to
an embodiment of the invention, exploiting mode and wavelength dual
domain division multiplexing via fixed wavelength tunable mode
transmitters and limited mode count receivers;
[0042] FIG. 7 depicts a bus/ring based architecture, according to
an embodiment of the invention, exploiting mode domain division
multiplexing via wavelength tunable mode transmitters;
[0043] FIG. 8 depicts a matrix architecture according to an
embodiment of the invention exploiting mode and wavelength dual
domain division multiplexing via fixed wavelength tunable mode
transmitters with wavelength selective receivers;
[0044] FIG. 9 depicts a matrix architecture, according to an
embodiment of the invention, exploiting mode and wavelength dual
domain division multiplexing via arrayed fixed wavelength tunable
mode transmitters;
[0045] FIG. 10 depicts a bus/ring based architecture, according to
an embodiment of the invention, exploiting mode and wavelength dual
domain division multiplexing via tunable wavelength tunable mode
transmitters;
[0046] FIG. 11 depicts a matrix architecture, according to an
embodiment of the invention, exploiting mode and wavelength dual
domain division multiplexing via tunable wavelength tunable mode
transmitters with wavelength specific receivers;
[0047] FIG. 12 depicts a matrix architecture, according to an
embodiment of the invention, exploiting mode and wavelength dual
domain division multiplexing via fixed wavelength fixed wavelength
tunable mode transmitters with wavelength demultiplexed
receivers;
[0048] FIG. 13 depicts a mode and wavelength switched
Interconnection Network (Net) implemented as a single
monolithically integrated circuit;
[0049] FIG. 14 depicts a coupled singlemode waveguide array and its
resulting optical modes;
[0050] FIG. 15 depicts the coupling matrix between launch and
output waveguides for an optimized waveguide structure supporting
embodiments of the invention for mode selective filtering and
launching;
[0051] FIG. 16 depicts a multi-waveguide mode filter according to
an embodiment of the invention for mode selective filtering and
launching within mode selective receivers and transmitters
according to embodiments of the invention.
DETAILED DESCRIPTION
[0052] The present invention is directed to optical interconnection
networks and more particularly to circuit board level, interchip,
and intrachip optical interconnections and networks.
[0053] The ensuing description provides exemplary embodiment(s)
only, and is not intended to limit the scope, applicability or
configuration of the disclosure. Rather, the ensuing description of
the exemplary embodiment(s) will provide those skilled in the art
with an enabling description for implementing an exemplary
embodiment. It being understood that various changes may be made in
the function and arrangement of elements without departing from the
spirit and scope as set forth in the appended claims.
[0054] A "tunable laser" as used herein, and throughout this
disclosure, refers to a laser whose wavelength of operation can be
altered in a controlled manner. This includes, but is not limited
to, lasers where the optical length of the cavity can be modified
and thus continuously tuned over a wavelength range. Such lasers
include distributed feedback (DFB) semiconductor lasers, vertical
cavity surface emitting lasers (VCSELs), temperature tuned lasers,
MEMS based external cavity lasers (ECLs), multiple prism grating
ECLs, tunable VSCELs, and DFB laser arrays.
[0055] An "external modulator" as used herein, and throughout this
disclosure, refers to a device employed to modulate an optical
signal, typically within an optical waveguide. This includes, but
is not limited to, external modulators that exploit absorption by
varying a materials absorption coefficient or refraction by varying
the refractive index of a material. Absorption based external
modulators may exploit, for example, the Franz-Keldysh effect,
quantum confined Stark effect, excitonic excitation, Fermi level
changes, or changes in the free carrier concentration. Refractive
modulators typically exploit the electro-optic effect within a
Mach-Zehnder interferometer.
[0056] A "mode" as used herein and throughout this disclosure,
refers to the configuration of the electromagnetic radiation
supported by a medium which has been structure such that the
section is invariant by translation along the direction of
propagation of the said "mode". This includes, but is not limited
to, modes of electromagnetic radiation within the visible to
near-infrared regions of the electromagnetic spectrum confined to a
waveguide.
[0057] A "wavelength filter" as used herein, and throughout this
disclosure refers to a flexible, optical device that selectively
transmits optical signals over a predetermined wavelength range.
This includes, but is not limited to, fixed dichroic filters,
tunable Fabry-Perot resonator filters, liquid crystal tunable
filter, MEMS based tunable filters, and tilting grating tunable
filters.
[0058] A "mode filter" as used herein, and throughout this
disclosure, refers to an optical device which selectively filters a
mode from the plurality of modes within an optical waveguide or
optical fiber. This includes, but is not limited to, mode filters
that couple through free space optics to a subsequent optical
device, fixed mode filters that couple from a multimode optical
waveguide to a singlemode optical waveguide, tunable mode filters
that couple a selected mode from the plurality of modes within a
multimode optical waveguide to a singlemode optical waveguide,
fixed mode filters that couple from a singlemode optical waveguide
to a multimode optical waveguide, tunable mode filters that couple
a singlemode optical waveguide to a selected mode from the
plurality of modes within a multimode optical waveguide, a ring
resonator filter, coupled rings resonator filter, a directional
coupler, a tunable directional coupler, a multimode interference
filter, a tunable multimode interference filter, a photonic crystal
filter, and nanostructure based filters. Such mode filters may
include mode filters for selectively coupling modes laterally
and/or vertically to different modes of an optical waveguide.
[0059] An "optical waveguide" as used herein, and throughout this
disclosure refers to a dielectric medium or combination of medium
invariant per translation along the direction of propagation,
supporting the propagation of optical signals within a
predetermined wavelength range formed. An optical waveguide may be
an isolated structure comprising at least a core and a cladding,
e.g. an optical fiber, or it may be formed as part of a carrier, or
formed within a substrate, e.g. a planar lightwave circuits, an
integrated optical devices, or an optical waveguide. This includes,
but is not limited to, flexible optical waveguides formed from
extruded glass, extruded doped silica, extruded chalcogenide
glasses, and polymer. This includes, but is not limited to, optical
waveguides formed within AlGaAs--GaAs material systems,
InGaAsP--InP material systems, ion-exchanged glass, ion-exchanged
ferroelectric materials (e.g. proton exchanged LiNbO3), doped
ferroelectric materials (e.g. titanium doped lithium niobate),
silica-on-insulator, silica-on-silicon, doped silicon, ion
implanted silicon, polymer on silicon, silicon oxynitride on
silicon, polymer on silicon, Silicon-On-Isolator (SOI) and polymer
on polymer.
[0060] An "optical fiber" as used herein, and throughout this
disclosure refers to a flexible optical waveguide which due to its
transparency over a predetermined wavelength range transmits
optical signals. This includes, but is not limited to, step-index
optical fibers, graded-index optical fibers, silica optical fibers,
chalcogenide glass optical fibers, and polymer optical fibers. Such
optical fibers may be multimode supporting multiple modes. Such
optical fibers may be circular thereby supporting multiple modes
that are laterally/vertically/radially symmetric modes, rectangular
supporting multiple modes laterally but singlemode in vertically,
rectangular supporting multiple modes laterally with limited modes
vertically (e.g. 2-5), as well as waveguides with similar or other
cross-sections. Such optical fibers may be discrete, in ribbon
format assembled from discrete optical fibers with discrete
claddings per optical fiber, in ribbon format with common cladding
between optical fibers, optical fibers embedded in a polymer
flexible film, and optical fibers attached to a polymer flexible
film.
[0061] A "receiver" as used herein, and throughout this disclosure,
refers to a device that converts received optical signals to
electrical signals. This includes, but is not limited to, discrete
photodetectors, photodetectors with electrical amplification,
photodetectors with electrical gain and logic generation circuits,
p-n photodiodes, p-i-n photodiodes, avalanche photodiodes, and
metal-semiconductor-metal photo detectors.
[0062] Referring to FIG. 1, there is depicted the deployment of
optical networking and optical interconnections within the global
telecommunications architecture. According at the highest layer
there are SONET/SDH/DWDM long-haul and ultra-long-haul transport
networks exploiting 40/80 or more channels of dense wavelength
division multiplexed (DWDM) transmission at 2.5 Gbs/10 Gbs or more
per fiber. Coupled to the transport layer within the carrier core
are high speed, high port count, high reliability elements
supporting the carrier backbone (e.g. time sensitive telephony),
data, and Internet traffic together with core routers and
asynchronous transfer mode (ATM) core switches which groom traffic
for the transport networks and route data/telephony/Internet
traffic etc. down/up from the carrier edge. At the same time the
carrier core exploits optical fiber based interconnections for the
central offices distributed across the carrier's territory.
[0063] Within the carrier edge a range of devices are connected via
edge routers to the carrier core and to the metropolitan area
networks (MAN) serving communities, business districts etc. Such
elements include media gateways, voice gateways, central offices,
managed switches (MS), broadband (BB) remote access servers (RAS),
ATM frame relay (FR) switches, RAS, etc. Such elements groom data
for the MAN from the carrier core and similarly route data from the
MAN to the carrier core and transport. Below the MAN are layers of
Internet service provider (ISP) access and then Enterprise/small
office-home office (SOHO)/Residential access. The former is
achieved through a variety of functional blocks coupled to the MAN
via optical fiber links including digital loop carrier (DLC),
digital subscriber line access multiplexers (DSLAM), cable TV
(CATV) head-ends, add-drop multiplexers (ADM), and Internet Message
Access Protocol (IMAP). Within the Enterprise/SOHO/Residential
access optical fiber typically penetrates through dedicated leased
lines although a variety of Fiber-to-the Home/Curb/Box
architectures bring optical fiber into the so-called "last mile" to
the consumer.
[0064] Disposed at different levels within this architecture the
servers supporting the provisioning of Internet data are
distributed together with the data centres. These are typically
connected to the transport layer directly and service national data
distribution as well as connecting multiple
regional/provincial/state data centres together to support more
localized traffic management, content storage, data replication
etc. Accordingly, as noted supra a single request from a user on a
residential CATV network is routed, typically, optically from the
cable head end to the MAN and therein via routers and switches with
optical interconnections to local servers and therein through the
carrier core networks to the data centres wherein the appropriate
transfer of data back to the user occurs. With optical
interconnection within the data centre the optical interface is on
the server and may as noted previously trigger hundreds of other
server-server requests and data transfers including long haul and
ultra-long haul links.
[0065] Now referring to FIG. 1B there is depicted a typical prior
art leaf-spine architecture for interconnecting servers within a
data centre according to the prior art. As depicted first data
centre 100A is connected directly to SONET/SDH/DWDM Transport 150
whilst second and third data centres 100B and 100C are each
connected to Metropolitan Area Network 160 and therein to
SONET/SDH/DWDM Transport 160. Within each data centre, for example
first to third data centre 100A to 100C, a router 110 that connects
the spine switches 120 to the network, e.g. SONET/SDH/DWDM
Transport 150 in the instance of first data centre 100A and
Metropolitan Area Network 160 in the instance of the second and
third data centres 100B and 100C. Each spine switch 120 is
connected to a plurality of leaf switches 130 and therein to a
server rack or server racks 140. Within a typical exemplary
embodiment each shelf within rack is a two rack unit (2RU) bay
supporting a server or servers with a pair of 10 Gb/s Ethernet
connections to the leaf switch 130. With typically 10 shelves per
rack then each leaf switch receives and transmits 20.times.10
Gb/s=200 Gb/s of data to/from the server rack 140. Each leaf switch
130 is connected within the embodiment depicted to a number of
spine switches 120 wherein typically the links from each leaf
switch 130 to each spine switch 120 are partitioned either
according to the number of spine switches 120 to which the leaf
switch is connected and their interconnections or asymmetrically
according to predetermined rules and storage rules associating like
data to closely associated servers, for example.
[0066] For example, as depicted in FIG. 1B 8 server racks 140 with
160 server nodes overall supporting 10 Gb/s Ethernet each may be
connected to 4 leaf switches 130. Accordingly, the server rack
140-leaf switch 120 connection is 200 Gb/s upstream/downstream, as
noted above implemented through 20.times.10 Gb/s, which are then
connected to the 4 spine switches 120 wherein each leaf switch
130-spine switch 120 may be implemented to support 4.times.50
Gb/s=200 Gb/s for example such that each spine switch 120 is
connected to each spine switch 120 with a 50 Gb/s link.
Alternatively, a leaf switch 130 may be connected to asymmetrically
to the spline switches 130 such that a "nearest neighbour" spline
switch 120 is coupled at 80 Gb/s and the remaining 3 spline
switches 120 connected with 40 Gb/s. Alternatively, a "nearest
neighbour" may be connected at 100 Gb/s, a pair of "next nearest
neighbours" at 40 Gb/s and the fourth spline switch 120 at 20
Gb/s.
[0067] FIG. 1B depicts a full Clos network interconnection between
the spline switches 120 and the leaf switches 130 implemented such
that every spine switch 120 is connected to every leaf switch.
Historically, partial Clos networks were implemented due to the
costs and complexity of the cabling interconnections but have
increased latency and hence a tradeoff made within data centres of
cost/complexity and latency. However, it would be evident that
server to server connectivity within a server rack 140 is still
through a leaf switch 130 and between server racks 140 through a
pair of leaf switches 130 and spine switch 120. However, as noted
above, absent increased data processing/handling capacity from the
servers, increased data handling is today achieved through
multi-server parallel processing and data centres continuously
increasing in physical dimensions.
[0068] Now referring to FIG. 1C, there is depicted a server blade
architecture within the prior art in first and second schematics
170A and 170B. Accordingly, the server blade comprises a first and
a second microprocessors 150A and 150B which are directly coupled
together as well as being coupled to I/O Controller 180. The first
microprocessor 170A is coupled to twenty four Double Data Rate
(DDR) synchronous Dynamic Random-Access Memory (DRAM) Dual In-Line
Memory Modules (DIMM) 160 whereas the second microprocessor 150B is
coupled to a pair of I/O mezzanine connectors 185 and an expansion
node connector 190 wherein the mezzanine connectors are coupled to
10 Gb/s Ethernet interfaces (not shown for clarity) and the
expansion coupler allows the server blade to an expansion node,
which may for example, host twelve 2.5'' hard disk drives (HDD)
providing, for example, 14.4 TB. The twenty four DDR DRAM DIMM 160
modules may for example provide 384 GB of on-blade memory which may
be increased to 768 GB with a load reduced DDR DRAM DIMM.
Accordingly, it would be evident that as discussed supra replacing
the 10 Gb/s Ethernet interface for the server blade with a 20 Gb/s
or 40 Gb/s interface does not increase the capacity of the server
blade as it is internally limited by the data buses internally such
as those between the first microprocessor 150A and the 24 DDR DRAM
DIMM 160 modules and second microprocessor 150B and expansion node
controller 190 and the external HDD drives. Similarly, the other
data buses of interest to increase the server blade performance
include those from the first and the second microprocessors 150A
and 150B respectively to the I/O Controller 180 and other Solid
State Drives (SSDs) within the Front Panel I/O 195 block of the
server blade.
[0069] As discussed above, multi-core processors are widespread and
many core processors common within server applications. However, as
noted before, the overall performance of a discrete computing
system not only depends on the capabilities of the processing
nodes, but relies more and more on the electrical interconnection
network carrying the communication among processors and between
processors and memories. Considering FIG. 1C, then such electrical
interconnection "bottlenecks" included between the first and the
second microprocessors 150A and 150B respectively, between first
and second microprocessors 150A and 150B and I/O Controller 180,
first and second microprocessors 150A and 150B and first to twenty
four DDR DRAM 160, first and second microprocessors 150A and 150B
and I/O Controller 180 to the expansion node 190 and the
associated, for example, 12 2.5'' HDD. Simple electrical
topologies, such as a chip-global bus, exhibit high latency,
require power-hungry repeaters, and occupy large footprint. More
complex topologies can be then exploited, such as the direct
networks, which connect neighbouring processing nodes in some fixed
topology through point-to-point dedicated links Still, these
networks require the signal to cross multiple hops for connecting
distant cores and are prone to contention between concurrent
message transmissions, both leading to increased latency and power
consumption.
[0070] Accordingly, these elements may, according to embodiments of
the invention, rather than being multiple discrete electrical
interconnections connecting electrical components be part of a
single optical network eliminating multiple hops between
interconnect/device and allowing interconnection of elements
directly through the optical network. Beneficially, such an optical
interconnection network offers significant additional bandwidth and
latency reduction within the requirement for high speed electrical
switching and/or routing devices. Architecturally the same
transmitter and receiver devices, as will be evident from
embodiments of the invention below, may be exploited in linear bus,
bus/ring, and cross-connect/matrix architectures as well as designs
allowing partitioning such that, for example, memories are accessed
with single channels but microprocessors can be dynamically
addressed with 2, 4, 8, or more channels according to processor
requirements. Similarly, the more recent server leaf-spine
architectures such as that depicted in FIG. 1B, can be replaced
with a fully connected architecture such that a group of servers
form nodes on an extended optical bus allowing direct server to
server interconnection within a server rack or across a number of
server racks whilst another node or nodes on the optical bus
couples the optical bus to a higher network, e.g. replacing the
spine switches, etc.
[0071] Embodiments of the invention exploit the propagation of
optical signal through modes in an optical guiding medium, e.g. an
optical fiber or an optical waveguide, as an additional domain to
carry, route, and switch data in addition to the prior art networks
exploiting time domain multiplexing for a single data stream and
wavelength division multiplexing to information. These modes
supported by an optical waveguide have the interesting property of
being orthogonal, meaning that the information carried by a mode is
not affected by another one even if the data is carried at the same
wavelength. Accordingly, multiple modes at the same wavelength can
be exploited to add transmission capacity and/or routing and/or
network flexibility.
[0072] In one embodiment of the invention, a single-domain
mode-based interconnection network, may be devised and implemented
with multiple input ports and multiple output ports allowing the
routing/distribution/switching of data from any input port to any
output port by exploiting the propagation modes of the optical
guiding medium rather than wavelength division multiplexing (WDM)
techniques. Accordingly, an output port may be assigned a unique
propagation mode, distinct from the other ports, and hence
establishing an input with the same propagation mode and/or
converting an established input allows the data to be routed to
that output port. Within an exemplary implementation data packets
to be routed are electronically stored in an ingress buffer at each
input port with a scheduler controlling which data packets are to
be transmitted to which output port and when. Once selected, a
packet is optically transmitted to the output ports using the
optical guiding medium along the mode corresponding to its
destination port. Multiple packets can be multiplexed together
(mode multiplexing) on the same transmission medium specifically
designed to supports the transmitted modes, e.g. an optical fiber
or an optical waveguide. Within this simple embodiment the number
of output ports and accordingly the throughput of this
single-domain mode-based interconnection network are limited by the
number of propagation modes that can be supported by the multimode
waveguide. In some guiding media, the number of modes can be a
small number, e.g. 5-10, whilst in others the number of modes can
be tens or hundreds to thousands.
[0073] In this case, the transmission medium can be conceived as a
bus where all input ports transmit, and where each output port
reads the related packets. An alternative solution requires to
close the bus in a ring configuration, enabling all-to-all
communication on both ring directions. Another embodiment of the
invention is upon the joint exploitation of mode multiplexing and
wavelength multiplexing leading to what the inventors refer to as a
dual-domain interconnection network. The architecture may therefore
consist of a plurality of cards (or tiles as referred to within
this patent specification), each with multiple electrical input
ports and multiple optical output ports although optionally the
number of electrical input ports may provide a number of output
ports through an electrical connection matrix such that there are
more optical output ports than electrical input ports, more
electrical input ports than optical output ports, or these may be
equal and the electrical connection matrix allows reconfiguration
of the association of an electrical input port to an optical output
port. Implementations of this dual-domain interconnection network
may therefore include bus, ring, space switched, and passive
distributive networks: For example, where R=(N/2) each electrical
input may be coupled to two optical outputs such that transmission
to two other nodes is always performed to address latency/likely
routing or typical data patterns for example. Optionally a single
electrical input signal could be broadcast on all N outputs.
[0074] Wavelength-mode interconnection networks, according to
embodiments of the invention, may be configured such that a tile
(card) is assigned a unique wavelength distinct from the other
tiles (cards). In each tile, each output port is assigned a unique
mode, distinct from the other ports of the same tile. Switching of
packets from any input port on any tile to any output port on any
tile occurs by optically transmitting the packet data with the
wavelength and the mode assigned to the packet' destination tile
and port. For this purpose, a tunable transmitter is required at
each input port. Also each input port requires a tunable mode
selector or, in an alternative embodiment, a device (e.g., an
electronic crosspoint) able to flexibly connect any transmitter
with fixed mode generators. Based upon the uniqueness of each
combination of wavelengths and modes, it is possible to multiplex
the different packets' transmission (wavelength and mode
multiplexing) on the same optical guiding medium (e.g., optical
fiber or optical waveguide).
[0075] Mode-wavelength interconnection networks, according to
embodiments of the invention, may be configured such that each tile
is assigned a unique mode distinct from the other tiles. In each
tile, each output port is assigned a unique wavelength, distinct
from the other ports of the same tile. Switching of packets from
any input port on any tile to any output port on any tile occurs by
optical transmitting the packet data with the mode and the
wavelength assigned to the packet` destination tile and port.
Optionally, each input port enters an electronic cross-point switch
able to flexibly connect them to the fixed-wavelength transmitters
either discretely implemented or through a multi-wavelength laser.
Alternatively, the driver circuit 250 may be removed and a
multi-wavelength laser source and wavelength switches, such as
multi-wavelength laser source 320 and wavelength switches 330A to
330N in FIG. 3 employed. Also, a tunable mode selector is required
at each input port. Based upon the uniqueness of each combination
of wavelengths and modes, it is possible to multiplex the different
packets' transmission (wavelength and mode multiplexing) on the
same optical guiding medium (e.g., optical fiber or optical
waveguide).
[0076] Space-mode interconnection networks, according to
embodiments of the invention, exploit an architecture wherein each
port on a tile is addressed through a unique mode, and each tile is
connected to a proper port of an optical space switch. Switching of
packets from any input port on any tile to any output port on any
tile occurs by optically transmitting the packet data with the mode
assigned to the packet' destination port and properly steering each
packet to the destination tile with an optical space switch. Each
input port requires a tunable mode selector or, in an alternative
embodiment, a device (e.g., an electronic cross-point) able to
flexibly connect any transmitter with fixed mode generators. Based
upon the uniqueness of each combination of paths and modes, it is
possible to multiplex the different packets' transmission.
[0077] An even more scalable architecture is based on the joint
exploitation of mode multiplexing, wavelength multiplexing and
space multiplexing (or time multiplexing) leading to what the
inventors refer to as triple-domain interconnection networks. Such
an architecture, may for example, consist of C clusters of M tiles,
each tile having R input ports and N output ports. Addressing to
the proper cluster, tile, and port is achieved by exploiting (in
possibly different order) mode, wavelength and space (or time)
domains. While mode can be exploited to address a port and/or a
tile, mode can also be exploited to make use of what the inventors
refer to as a quad-domain interconnection network. In this, rather
than serializing the data from an electronic circuit, parallel data
is encoded in parallel onto multiple modes of a wavelength such
that data is generated, transmitted, and received in parallel. By
assigning time slots to ports such an approach may reduce the
number of required lasers whilst maintaining high throughput.
[0078] Considering a multimode fiber then the number of supported
modes is proportional to the square of the diameter core of the
optical fiber, proportional to the numerical aperture (and therein
the refractive index difference and cladding index), and inversely
proportional to the wavelength. Accordingly, a silica graded index
optical fiber with a refractive index of 1.452, with an index
difference of 1%, operating at 1550 nm with a diameter of 50 .mu.m
supports several hundred modes in contrast to a silica graded index
optical fiber with index difference <0.4% and a diameter of 8
.mu.m which is single mode. Accordingly, adjusting the diameter and
index contrast allows for fibers with a 10, 20, 40 modes to be
implemented, for example.
[0079] Accordingly, referring to FIG. 2 there is depicted a
bus/ring based architecture 200, according to an embodiment of the
invention, exploiting wavelength and mode dual domain division
multiplexing via tunable wavelength fixed mode transmitter tiles
210. As depicted, M transmitter tiles 210 are coupled to an optical
bus 270 and therein to M receiver tiles 220. Each transmitter tile
210 comprises an array of N tunable lasers 230A to 230N which are
each coupled to an external modulator 240. Each tunable laser 230
being tunable to one of M wavelengths, .lamda..sub.1, . . . ,
.lamda..sub.M. Each of the N external modulators 240 is coupled to
a driver circuit 250 which receives N input signals for
transmission.
[0080] Driver circuit 250 may, for example, simply be an array of
drivers to convert the digital data input to the appropriate
voltages and/or currents to drive the external modulator 240.
Alternatively, driver circuit 250 may include an electrical
switching circuit to couple any input data port to any external
modulator 240 or optionally may couple a single electrical input to
a programmable number of modulators 240. The output of each
external modulator 240 is coupled to the optical bus 270 to launch
a different mode, Mode.sub.1 . . . Mode.sub.N onto the optical bus
270.
[0081] Subsequently coupled to the optical bus 270 are receiver
tiles 220 wherein each receiver tile 220 comprises N mode filters
intended to filter one of the modes Mode.sub.1 . . . Mode.sub.N at
a predetermined wavelengths .lamda..sub.1, . . . , .lamda..sub.M
that are supported by the optical bus 270 and transmitter tiles
210. Accordingly, receiver tile 1 Rx comprises N mode filters 280A
to 280N intended to filter one of the modes
(Mode.sub.1:.lamda..sub.1); (Mode.sub.2:.lamda..sub.1); . . . ;
(Mode.sub.N:.lamda..sub.1) from the optical bus 270 wherein in
generalized form receiver tile K Rx filters
(Mode.sub.1:.lamda..sub.1); (Mode.sub.2:.lamda..sub.1); . . . ;
(Mode.sub.N:.lamda..sub.1). Each of the N mode filters 280A to 280N
is coupled to a receiver 260 wherein the optical signal is
reconverted to the electrical domain.
[0082] Accordingly, a signal coupled to a transmitter tile
1.ltoreq.J.ltoreq.M may be routed to a receiver tile K by setting
one of the tunable lasers 240A . . . 240N to the K.sup.th
wavelength .lamda..sub.K. The externally modulated optical signal
is then mode converted to the L.sup.th mode based upon the selected
tunable laser 240A to 240N, 1.ltoreq.L.ltoreq.N, for launch onto
the optical bus 270 wherein it is subsequently filtered by the
L.sup.th mode filter 280 on the K.sup.th receiver tile 220.
Additional capacity between the J.sup.th transmitter tile 210 and
the K.sup.th receiver tile 220 may be provided by also setting one
or more other tunable lasers within the J.sup.th transmitter tile
210 to the K.sup.th wavelength .lamda..sub.K wherein these one or
more other tunable lasers are coupled to other modes than the
L.sup.th and hence may be simultaneously filtered from the signals
on the optical bus 270 by the appropriate one or more mode filters
280.
[0083] In this manner, the architecture depicted in FIG. 2 allows
for M transmitter tiles 210 to programmably, under external
control, provide communications over optical bus 270 to M receiver
tiles 220 in singlecast (one-to-one) as well as multicast
(one-to-many) format. Further, the capacity for each link is
programmable as multiple tunable lasers may be set to the same
wavelength of a receiver tile. Accordingly, with M transmitter
tiles 210 using N wavelengths to couple to N receiver tiles 220 and
each external modulator supporting modulation at R Gb/s then the
capacity of the bus and network is N.times.M.times.R Gb/s. It would
be evident that the optical bus 270 may be closed to form a ring
network as known in the art. Transmitter tiles 210 and receiver
tiles 220 may be located together as with other prior art
transceiver designs.
[0084] Now referring to FIG. 3, there is depicted a bus/ring based
architecture 300, according to an embodiment of the invention,
exploiting wavelength and mode dual domain division multiplexing
wavelength selective tunable mode transmitter tiles 310 in
combination with an optical bus 270 and a plurality M receiver
tiles 220 such as described above in respect of FIG. 2. In contrast
to the transmitter tiles 210 in FIG. 2 the array of N external
modulators 240 within the transmitter tiles 310 are coupled to an
array of wavelength selective switches 330A to 330N which are
themselves coupled to a multi-wavelength laser 320. Accordingly, as
each external modulator 240 within an array is associated with a
predetermined mode Mode.sub..alpha. where
1.ltoreq..alpha..ltoreq.N, its associated wavelength switch 330A
allows the Mode.sub..alpha., from the transmitter tile 310, to be
varied to one of the wavelength set .lamda..sub.1, . . . ,
.lamda..sub.M provided by the multi-wavelength laser 320 which has
multiple outputs for the multiple transmitter tiles 310.
Accordingly, whilst each transmitter tile 310 can select a receiver
tile 220, through the appropriate selection of wavelength
associated with the receiver tile 220, by a wavelength switch 330
within that transmitter tile 310, each receiver tile 220 can only
be addressed with a single channel from that transmitter tile 310.
Accordingly, the architecture depicted in FIG. 3 allows singlecast
and multicast transmission from each transmitter tile 310 to each
receiver tile 220 but with fixed link capacity as multiple external
modulators 240 cannot access the same wavelength unlike the
transmitter tiles 210 in FIG. 2.
[0085] However, if the wavelength switch 330 allowed for wavelength
filtering without 100% routing then multiple wavelength switches
330 and external modulators 240 may be set to the same wavelength
allowing multiple channels to be coupled to the same receiver tile
220. Such a wavelength switch 330 may, for example, be a tap
coupler in combination with an optical amplifier and a tunable
wavelength filter.
[0086] Now referring to FIG. 4, there is depicted a bus/ring based
architecture 400, according to an embodiment of the invention,
exploiting wavelength and mode dual domain division multiplexing
via tunable wavelength tunable mode transmitters tiles 410.
Overall, the architecture 400 is similar to architectures 200 and
300 in FIGS. 2 and 3 except that the transmitter tiles 410 of
architecture 400 now employ tunable mode converters 420 coupled to
the outputs of the external modulators 240 that are themselves
coupled to the outputs of tunable lasers 230. Accordingly, an
optical path within a transmitter tile 410 comprising tunable laser
230, external modulator 240, and tunable mode filter 420 allows for
each channel to be set both in mode and wavelength. In this manner
the multicast and singlecast modes of transmission from each
transmitter tile 410 are maintained but the routing constraints of
the architecture 400 are more relaxed than that of architectures
200 and 300.
[0087] Referring to FIG. 5, there is depicted a bus/ring based
architecture 500, according to an embodiment of the invention,
exploiting mode and wavelength dual domain division multiplexing
via fixed wavelength tunable mode transmitter tiles 510.
Accordingly, this architecture can be considered the dual of
architectures 200 to 400. In this embodiment a plurality of M
transmitter tiles 510 each with N wavelength channels communicate
via an optical bus 270 to a plurality of M receiver tiles 540 each
operating at a predetermined Mode.sub.X where 1.ltoreq.X.ltoreq.M
and supporting N different wavelength channels, each addressing a
different output port in each receiver tile 540. Accordingly, mode
filters 280A to 280N in architectures 200 to 400 are exploited
arranged in a dual set-up, wherein each mode filter in a given
receiver tile 540 is tailored to a specific mode. Modes are
supported through the optical bus 270 and transmitted from the
transmitter tiles 510. Each transmitter tile 510 is again coupled
to a multi-wavelength laser 320 but, rather than an array of
wavelength selective switches 330 as in architecture 300, the input
from the wavelength laser 320, which is split by splitter 520 to
all transmitter tiles 510, is coupled to a wavelength demultiplexer
(DMUX) 530 such that each external modulator 240 is operating at a
predetermined wavelength but its output is now switchable in output
mode through the tunable mode converters 420 coupled to the output
of each external modulator 240. Accordingly the selection of an
external modulator 240 determines the receiver element in the
receiver tile 220 to which the signal will be coupled.
[0088] Now referring to FIG. 6, there is depicted a bus/ring based
architecture 600, according to an embodiment of the invention,
exploiting mode and wavelength dual domain division multiplexing
via fixed wavelength tunable mode transmitters tiles 510 and
limited mode count receivers tiles 610. Accordingly, as with
architecture 500 each of the M transmitter tiles 510 can launch up
to N wavelengths each adjustable in mode over M modes. However, now
each receiver tile 610 comprises a broadband mode filter 630
filtering a single mode over a wide wavelength range, as opposed to
mode filters 280A to 280N in architectures 200 to 500 wherein each
mode filter of mode filters 280A to 280N is tailored to a specific
mode at a specific wavelength, wherein each receiver tile 220 is
wavelength specific or is tailored to a specific mode over a wide
wavelength range to allow a generic receiver tile 220. It would be
evident that other combinations may be provided such as splitting
the wavelength range over 2 or more tiles according to the
waveguide and mode filter characteristics such that 2 or more
receiver tiles are employed. As such, the output of the mode filter
630 tailored to a specific mode Mode.sub.X where
1.ltoreq.X.ltoreq.M is coupled to a wavelength DMUX 620 wherein
each demultiplexed wavelength is then coupled to a receiver.
Accordingly, a transmitter tile 510 can increase capacity to a
receiver tile 610 by adding additional wavelengths through the
setting of their tunable mode converters 420 to the Mode.sub.X of
that receiver tile 610.
[0089] Referring to FIG. 7, there is depicted a bus/ring based
architecture 700, according to an embodiment of the invention,
exploiting tunable mode transmitter tiles 710 and fixed mode
receiver tiles 750 exploiting broadband single mode filter coupled
to a receiver. The plurality of transmitter tiles 710 comprise a
laser diode 720, external modulator 240, and tunable mode converter
420 such that the transmitter tile 710 is established transmitting
a specific mode Mode.sub.X where 1.ltoreq.X.ltoreq.N. The outputs
from the transmitter tiles 710 are coupled bus 270, which may form
part of a ring, such that the output of each transmitter tile 710
is coupled to the intended receiver tiles 730. Accordingly, with
all transmitter tiles 710 operating on different modes each
transmitter tile 710 communicate to a receiver tile 730.
[0090] Now referring to FIG. 8, there is depicted a matrix
architecture 800, according to an embodiment of the invention,
exploiting space and mode dual domain division multiplexing via
fixed wavelength tunable mode transmitter tiles 810 are employed in
conjunction with receiver tiles 220 such as described above, in
respect of FIG. 2, and comprises a plurality of N mode filters each
coupling a specific mode X=1.ltoreq.Mode.sub.X.ltoreq.X=N to a
receiver. Each fixed wavelength tunable mode transmitter tile 810
comprises a laser 720 coupled to a plurality of external modulators
240 via splitter 820 wherein the output of each external modulator
240 is coupled to a tunable mode coupler 420 to couple the output
of the external modulator 240 to a predetermined mode
X=1.ltoreq.Mode.sub.X.ltoreq.X=N. The multiple modes from the
tunable mode couplers 420A to 420N are coupled to the matrix
interconnection 840 via a mode MUX 830. The matrix interconnection
840 provides wavelength independent distribution of each input
packet coming from a mode-multiplexed matrix input to the mode
multiplexed matrix outputs. Accordingly, the singlecast and
multicast routing from the transmitter tile 810 is accommodated
whilst dynamic channel bandwidth is supported by the number of
parallel wavelength channels transmitted. Optionally, the tunable
mode converters 820A to 820N may be replaced with fixed mode
couplers provided that a driver circuit 250 is added to
electrically cross-connect the N input ports and the N modulators
240.
[0091] Referring to FIG. 9, there is depicted a matrix architecture
900 according to an embodiment of the invention exploiting mode and
wavelength dual domain division multiplexing via arrayed fixed
wavelength multiple mode transmitter tiles 910 coupled via a matrix
950 to a plurality of receiver tiles 930. Each transmitter tile 910
has an architecture similar to receiver times 810 in FIG. 8 except
that rather than being single wavelength the transmitter tile 910
incorporates a multi-wavelength source 320 coupled to a wavelength
demultiplexer (DMUX) wherein each wavelength is coupled to an
external modulator 240 and therein mode converter 420 before being
coupled through a wavelength multiplexer (MUX) 940 to the matrix
950. As matrix 950 provides distribution of each input port to all
output ports each receiver tile 930 receives all wavelengths and
all modes from the plurality of transmitter tiles 910. Within the
receiver tile 910 there are a plurality of tunable mode filters
920A to 920N each providing a broadband mode filter for a
predetermined mode X=1.ltoreq.Mode.sub.X.ltoreq.X=N. The output of
each of the plurality of mode filters 920A to 920N is coupled to a
receiver via a programmable wavelength filter 940. Accordingly,
each receiver tile 930 can receive data from one or more
transmitter tiles 910 simultaneously, whilst each transmitter tile
910 may similarly transmit to multiple receiver tiles 930.
[0092] Now referring to FIG. 10, there is depicted a bus/ring based
architecture 1000, according to an embodiment of the invention,
exploiting mode and wavelength dual domain division multiplexing
via tunable wavelength tunable mode transmitter tiles 1010 in
conjunction with single mode wavelength specific receiver tiles
1020. Each transmitter tile 1010 of the plurality W of transmitter
tiles 1010 comprises a tunable laser 230 in conjunction with
external modulator 240 and tunable mode converter 420, such that it
transmits on a single wavelength in a single mode but the
wavelength and mode are tunable by the transmitter tile 1010 under
control signals. Each of the plurality S of receiver tiles 1020
comprises a narrowband single mode filter 1020A to 1020S coupled to
the optical bus 270 and a receiver within its receiver tile 1020.
Accordingly, with each tunable laser 230 operating
.lamda..sub..alpha. (1.ltoreq..alpha..ltoreq.M) and Mode.sub..beta.
(1.ltoreq..beta..ltoreq.N) and similarly each receiver tile 1020
implemented for single wavelength operation and single mode
operation then it would be evident that W=S=M.times.N. Accordingly,
a relatively large number of nodes, each with a transmitter tile
1010 and receiver tile 1020, may be supported on the optical bus
270 for modest {M, N}. The capacity of a node upon the optical bus
270 is then determined by the number of transmitter tiles 1010
and/or receiver tiles 1020, respectively associated with the node.
In this manner, a node may be modular and incrementally increased
in capacity as well as each transmitter tile 1010 and/or receiver
tile 1020, respectively being according to some embodiments of the
invention
[0093] Referring to FIG. 11, there is depicted a matrix
architecture 1100, according to an embodiment of the invention,
exploiting space and mode and wavelength triple domain division
multiplexing via tunable wavelength tunable mode transmitter tile
arrays 1120 with wavelength specific receiver tile arrays 1130. As
depicted each transmitter tile array 1130 comprises a plurality K
of transmitter tiles 1110 which are essentially the same
architecture as transmitter tiles 410 as described above, in
respect of FIG. 4, wherein a plurality of N channels are
implemented comprising tunable laser 230, external modulator 240,
and tunable mode converter 420 but rather than each output being
coupled separately to the optical bus 270 the plurality of N
channels are multiplexed via a mode-wavelength MUX 1140. The
outputs of the plurality K of transmitter tiles 1110 are then
combined through a K:1 coupler 1130 to form the output from each
transmitter tile array 1120 before being routed to matrix 1150.
[0094] The outputs from matrix 1150 are coupled to each receiver
tile array 1130 wherein they are wavelength demultiplexed by K:1
wavelength demultiplexer (DMUX) 1160 to the plurality K receiver
tiles 220 wherein each receiver tile 220 allows optical signals at
the wavelength
.lamda..sub.1.ltoreq..lamda..sub.RX.ltoreq..lamda..sub.K to be
separated by the plurality of mode filters and converted back to
electrical signals by the receivers. Accordingly, with a M.times.M
matrix 1150, M transmitter tile arrays 1120 are coupled to M
receiver tile arrays 1130.
[0095] Accordingly, the M.times.M matrix 1150 should be able to
accept, on each input port, multiple packets simultaneously
arriving on different optical modes and wavelengths, and should be
able to independently route each packet destined for an output port
independent of the mode and wavelength.
[0096] Alternatively, as depicted in FIG. 12 the optical mode is
employed to address a specific receiver tile 1240 within a receiver
tile array 1250 and the wavelength employed to address a port
within that receiver tile 1240. Accordingly, transmitter tiles 1210
are employed exploiting a multi-wavelength laser source 320 and a
wavelength DMUX 1230 within a transmitter tile array 1220 and their
outputs coupled to the K:1 coupler 1130 before being coupled to the
M.times.M matrix 1150. Each output from the M.times.M matrix 1150
is then coupled to a mode demultiplexer 1270 upon each receiver
tile array 1250 such that each mode Mode.sub..beta.
(1.ltoreq..beta..ltoreq.N) is coupled to a receiver tile 1240. Each
receiver tile 1240 being a wavelength DMUX 1230 and an array of
optical receivers.
[0097] FIG. 13 depicts a Mode and Wavelength switched
Interconnection Network (MWIN) 1300 implemented as a single
monolithically integrated circuit according to an embodiment of the
invention. In common with preceding architectures described and
depicted in respect of FIGS. 2 to 12 a high degree of
parallelization is achieved with the generic architecture of the
MWIN is organized using M tiles 1310, each one connected to a
compute tile supporting, for example, a processor core, its memory
cache (L1 and L2) and directory. The transmission side of the MWIN
tiles 1310 supports N input ports, each one equipped with a
transmitter (Tx). The N Tx's are connected (e.g. via wire bonding)
to the electronic buffers, storing the messages to be switched
between compute tiles. The receiver side of each tile 1310 supports
N output ports, each one equipped with a receivers (Rx) connected
(e.g. via wire bonding) to the compute tile. To enable switching of
electrically-stored messages between any compute tiles 1310, the
optical signals generated by the Tx's are sent through a wavelength
selector 1320 and a mode selector 1330, which flexibly tune the
proper wavelength and mode of the optical signals. The signals of
all the tiles 1310 are then multiplexed on a single shared
waveguide 1340, depicted with a ring topology in FIG. 13 although
other geometries may be employed supporting all modes and
wavelengths.
[0098] The MWIN may be employed in different configurations
including two basic configurations, wavelength-mode and
mode-wavelength, which are defined depending on how the destination
tiles and ports are being identified. In the wavelength-mode
configuration, see tile 1350 in FIG. 13, destination tile is
uniquely identified by a specific wavelength (.lamda..sub.i, i=1, .
. . , M) and each output port of a tile is uniquely identified by a
specific mode (.mu..sub.j, j=1, . . . , N). In the mode-wavelength
configuration (not illustrated), each destination tiles is
identified by a specific mode (.mu..sub.i, i=1, . . . , M) and each
output port of a tile is identified by a unique wavelength
(.lamda..sub.j, j=1, . . . , N).
[0099] Accordingly, a building block (BB) of a tile 1350 for the
wavelength-mode configuration of MWIN 1300 can be implemented as a
silicon (Si) Photonic Integrated Circuit (PIC) comprising a
multi-wavelength laser source 1360, followed by a power splitter
with N branches 1370. Each branch is associated to a specific mode
addressing a unique port of a tile. By controlling the micro-ring
resonators 1380 on each branch, a wavelength is selected and
modulated according to the scheduler decisions. Each modulated
signal is then coupled to the shared waveguide 1340 through a mode
coupler 1395 which selects a specific mode. The shared waveguide
1340 can be realized with a novel design consisting in an array of
narrow waveguides designed to support orthogonal bound states
referred as "supermodes". These supermodes can be exploited as the
propagation modes of a conventional multi-mode waveguide with the
advantage of lower inter-modal crosstalk.
[0100] Whilst the shared waveguide 1340 is depicted in MWIN 1300 as
a ring it would be evident that other designs of the shared
waveguide, the MWIN architecture, and the BBs may be employed
without departing from the scope of the invention. For instance,
the ring waveguide can be replaced by an open bus with potentially
lower in-channel crosstalk while enabling all-to-all communications
by properly placing the transmitting and receiving side of each
tile. Some BBs can be dedicated or shared by different inputs,
leading to different physical layer performance. Also, other PIC
designs trading flexibility for complexity and energy efficiency,
e.g. the number of laser sources, are possible for the wavelength
and mode selectors. It would be evident that that different levels
of complexity and performance exist between different possible
implementations providing designer of MWINs with a design space for
implementing embodiments of the invention rather than a single
design.
[0101] Now referring to FIG. 14 there is depicted a coupled
singlemode waveguide array (SMWA) 1420 and its resulting
"supermode" optical modes, first to fifth mode profiles 1430 to
1470 respectively, such as may be employed for the shared
waveguide/optical bus of embodiments of the invention. As depicted
in optical micrograph 1410 the SMWA 1420 is a compact array of
singlemode waveguides which are spaced such that optical coupling
occurs between the waveguides wherein the resulting supermodes are
defined by the properties of the multiple singlemode waveguides,
their optical coupling, and the relative phases between them. A
benefit of a SMWA is that the waveguide array can be designed to
generate a set of orthogonal bound eigen-states, the supermodes,
which are different from the set of modes propagating in standard
multi-mode waveguides. Such a technique offers the advantage of
lower inter-modal crosstalk, <-25 dB, with respect to the
propagation in multimode waveguides. Moreover, an SMWA as evident
from FIG. 16 allows an easier integration of electrical controls
(e.g., each waveguide can be individually tuned) and has a
footprint hardly larger than the size of a standard multi-mode
waveguide. FIG. 14 depicts a set of five orthogonal supermodes,
obtained on an array of five coupled Si waveguides with widths
[430, 440, 450, 440, 430] nm and gaps of [550, 500, 500, 550] nm.
Now referring to FIG. 15 there is depicted a coupling matrix
between launch and output waveguides for an optimized waveguide
structure supporting embodiments of the invention for supermode
selective filtering and launching.
[0102] Now referring to FIG. 16 there is depicted a multi-waveguide
mode filter (MW-MF) according to an embodiment of the invention for
supermode selective filterings and launching within mode selective
receivers and transmitters according to embodiments of the
invention. The MW-MF provides one possible PIC implementation of a
mode selector according to an embodiment of the invention and
exploits an array of coupled single-mode waveguides that are
tapered to realize a structure where the optical power can be
transferred from one supermode to another. An interferometer
configuration is implemented with a phase shifter capable of
inducing a generic shift on each arm to enable the generation of
any mode .mu..sub.i (1.ltoreq.i.ltoreq.N). The mode selector has
been simulated with a commercial-grade eigenmode solver and
propagator, assuming that the injected optical signal is at mode 1
at the input as depicted in schematic 1610. Simulation results of
the working principle are shown in first and second simulation
results 1620 and 1630 respectively. When the phase shift of the two
rightmost arms is .phi.=0, the mode of the output signal remains
the same, i.e., mode 1 in which only the central waveguide is
excited, see first simulation result 1620. When .phi.=.pi., the
mode of the output signal is changed to mode 3 as evident from
second simulation result 1630 and where a clear mode switching
between the two settings is visible.
[0103] The foregoing disclosure of the exemplary embodiments of the
present invention has been presented for purposes of illustration
and description. It is not intended to be exhaustive or to limit
the invention to the precise forms disclosed. Many variations and
modifications of the embodiments described herein will be apparent
to one of ordinary skill in the art, in light of the above
disclosure. The scope of the invention is to be defined only by the
claims appended hereto, and by their equivalents. Whilst the
embodiments of the invention described above in respect of FIGS. 2
through 16 employ amplitude modulation it would be evident that
other modulation techniques may be employed including, but not
limited to, phase modulation and coherent detection, frequency
modulation, and polarization modulation.
[0104] Within the preceding descriptions with respect to
embodiments of the invention optical signals are transmitted and
received based upon exploiting mode division multiplexing
discretely or in combination with wavelength division multiplexing.
Whilst the preceding descriptions are primarily depicted and
described with so-called "supermode" optical waveguides formed from
an array of singlemode optical waveguides or dielectric structures
(as each structure may not support optical waveguiding in isolation
or themselves be multimode) it would be understood by one of skill
in the art that these represent one class of multimode optical
waveguide that may be employed within the embodiments of the
invention. For example, the "supermode" optical waveguide may be
replaced by a single multimode optical waveguide (multiple
transverse modes) or a combination of one or more multimode optical
waveguides alone or in combination with other dielectric structures
and/or optical waveguides. For example, a photonic crystal
supporting multiple transverse modes formed from sub-wavelength
structures may be employed or multiple dielectric structures with
narrow gaps etc.
[0105] Further, in describing representative embodiments of the
present invention, the specification may have presented the method
and/or process of the present invention as a particular sequence of
steps. However, to the extent that the method or process does not
rely on the particular order of steps set forth herein, the method
or process should not be limited to the particular sequence of
steps described. As one of ordinary skill in the art would
appreciate, other sequences of steps may be possible. Therefore,
the particular order of the steps set forth in the specification
should not be construed as limitations on the claims. In addition,
the claims directed to the method and/or process of the present
invention should not be limited to the performance of their steps
in the order written, and one skilled in the art can readily
appreciate that the sequences may be varied and still remain within
the spirit and scope of the present invention.
* * * * *
References