Survey of ShortReach Optical Interconnect

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Survey of Short-ReachOptical Interconnect

• Ken Pedrotti
• Robert Dahlgren

Presented 10 November 2005
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Outline

• Introduction
• Pure silica fiber trends
• Splicing trends
• Connector trends
• Active component trends
• Transceiver module trends
• What to expect in the year 2010?
• Questions and discussion

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Short Reach Links

Optical Internetworking Forum (OIF)

VSR-1 through VSR-4 classifications

Gigabit Ethernet

Multimode 850 nm

10 Gigabit Ethernet

Singlemode or parallel multimode

Fibre Channel

Serial HIPPI

Proprietary links

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Main Commercial Trends

• Fiber to the home/curb/pedestal deployment is
  moving forward
• Common form factors
• Smaller form factors
• Standards-based specifications
• Short Reach and VSR standards
• Convergence of specs at 1 and 10 Gbps
• WDM begat DWDM and CWDM
• Pure silica core fiber less of a niche
• Ribbon fiber and mass splicing/termination

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Lesson from the Aircraft Industry
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Convergence

• Telecom and datacom PHYs have less distinction
• Traditional datacom companies like Cisco are
  making more carrier-class equipment
• Common medium (often SMF)
• Data rates moving towards convergence
• OC-192, 10G Ethernet, 10G Fibre Channel
• Possible to unify component markets to take
  advantage of economies of scale

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What Convergence Meansfor VSR Links

• 1 and 10 Gbps may be the sweet spot for short
  links up to 300 m for some time
• 850 nm VCSEL and MMF
• Single and multi-fiber arrangements
• Broad support from industry in volume
• Common electrical interface
• 40 Gbps and 100 Gbps serial technology too
  expensive for VSR
• WDM approaches not suitable for VSR

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Ribbon Optical Fiber

• Four, twelve, or sixteen fibers
• Usually spaced at 250 mm pitch
• Connectors, splicing more complex
• Cost per splice about 2 2.5x
• Lower cost per fiber

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Pure-Silica Core Fiber Trends

• Several manufacturers now make optical fiber for
  high radiation environments.
• Singlemode, step-index multimode, graded index
  multimode
• Cost premium TBD compared to standard (e.g.
  Ge-doped core) fiber of the same type
• Improved polymer coatings

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Pure-Silica Core Fiber Vendors

• Fujikura Ltd.
• Oxford Electronics
• Mitsubishi International
• Verrillion Inc.
• OFS (formerly Lucent)
• CorActive On custom basis
• Sumitomo Electric
• 3M dropped production
• Corning MMF in development

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Evolution of Arc Fusion Splicing

• Active alignment with optical source and detector
  at the fiber endfaces
• Local injection into core and detection
• Imaging-based alignment
• Ribbon fiber splicers (mass splicing)
• V-groove (passive) splicers
• Enabled by tighter fiber concentricity specs
• Smaller, lighter, better ergonomics
• Compensation schemes, loss estimation

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Improvement of Fiber ConcentricityEnables
V-groove Alignment
Active Core Alignment
V-groove Alignment
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Splicing trends

• Continued acceptance of v-groove based splicers
  in non RD applications
• Continuing acceptance of mass fusion splicing for
  ribbon fiber
• Continued development of custom splice
  programming, e.g. thermal diffusion core
  expansion for specialty fiber
• Laser-based fiber stripping and cleaving needs
  cost reduction

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Mass Fusion Splice of12-fiber Ribbonized SMF
Images courtesy AFL Telecommunications
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Splice Economics

• Splicing cost roughly 2040 not including costs
  associated with access and packaging. Can be
  much higher.
• Mass splices cost roughly 2 2.5x for a 12-fiber
  ribbon
• Spliceless ATLAS design tradeoff
• Need lower cost fiber recoating systems and
  proof-testers for High-Rel applications
• Splicer manufacturers Fitel, Fujikura, 3sae

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Connector Market Landscape

• Simplex-SC is de-facto standard for telecom.
• Duplex-SC is de-facto standard for datacom.

• Newer Small Form Factor connectors vying for
  market dominance.
• Several incompatible connectors for ribbon fiber
  applications.

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Legacy Connectors
ST
Biconic
FC
SMA
ESCON
old FDDI
Images used with permission of Alcoa-Fujikura,
Ltd.
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Ribbon Fiber ConnectorsMT Ferrule Technology
Images used with permission of US Conec, Ltd.
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Small Form Factor Connectors

• Driven by smaller front-panel opening, like the
  ubiquitous R-45 telephone/ethernet jack.
• Driven by low-cost 100 Mbps and 1 Gbps ethernet
  system and cable companies
• High front panel density low cost/port
• Telcos are looking to replace SC connector
• High front panel density CO and closet space
• Incorporate cost-saving features
• Incorporate ergonomic features
• Some allow field termination

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Some SFF Connectors
MT-RJ
LC
Duplex-LC
MU
Images used with permission of Alcoa-Fujikura,
Ltd.
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Laser Diode Structures
Most require multiple growth steps Thermal
cycling is problematic for electronic devices
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Detector Technologies
Features
Layer Structure
Simple, Planar, Low Capacitance Low Quantum
Efficiency
MSM (Metal Semiconductor Metal) PIN APD Wav
eguide
Semiinsulating GaAs
Contact InGaAsP p 5x1018 Absorption
InGaAs n- 5x1014 Contact InP
n 1x1019
Trade-off Between Quantum efficiency and Speed
Gain-Bandwidth 120GHz Low Noise Difficult to
make Complex
Contact InP p
1x1018 Multiplication InP n
5x1016 Transition InGaAsP n
1x1016 Absorption InGaAs n
5x1014 Contact InP n
1x1018 Substrate InP Semi
insulating
High efficiency High speed Difficult to couple
into
Absorption Layer
Guide Layers
Absorption Layer Contact layers
Key
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VCSEL status and trends

• VCSELs dominate where DFB laser or high power is
  not needed
• Many suppliers at the 1 Gbps level
• Reliability established at 850 nm
• 1300 nm devices have been slow to reach
  commercialization
• Low cost visible VCSELs becoming available at 635
  and 650 nm
• TBD 3 Gbps and 10Gbps

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Semiconductor Trends

• CMOS and SiGe-BiCMOS has taken over the chip
  market up to 10Gb/s rates
• 40 Gb/s OC-768 is waiting, with components ready
  but deployments few
• As long haul market has softened component
  manufacturers have targeted current new
  developments at gigabit and 10G Ethernet
  applications
• Addition of Forward error correction (FEC) drives
  maximum bit rate up eg. SONET 9.952Gb/s to 12.5
  Gb/s with a 5-6.5 coding gain
• Chips appearing designed for RZ rather than NRZ
  applications

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Semiconductor Trends

• Transceivers are including more monitoring and
  feedback control elements in chips to reduce part
  counts and size
• With CMOS implementations practical at 10Gb/s
  more multirate-multiprotocol solutions appearing
  thus increasing volumes and lowering product
  costs
• More network protocol processing in highly
  integrated chips
• Transmitters with low speed supervisory tone
  modulation inputs
• Equalization and compensation of analog links
• Smaller packaging
• TBD rad-hard electronics

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Transceivers conform to standards

• Under the auspices of IEEE, ANSI, ITU
• Highly technical, dry, and can be political.
• Strict rules of operation, balloting to approve.
• Communication protocol and Physical Layer
• SONET, Fibre Channel, ATM, Gigabit Ethernet
• Optical connector intermatability standard
• Duplex-SC, duplex-LC, MT-RJ, SG
• Environmental
• Telecordia, Product Safety, Military, EMC

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Example OC-192 10 Gbps VSR Standards (OIF)
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Transceivers conform to MSAs

• Standards bodies only define the minimum
  necessary requirements for interoperability.
• Multi-source Agreements (MSAs) between
  manufacturers describe common features outside of
  the standard, e.g. module pinout
• Generates consensus and critical mass without
  violating anti-trust guidelines.
• Electrical connector/formfactor standards
• 1x9, GBIC, GLM, 2x5, 2x10, SFP
• 200pin, 300pin, XFP, Xenpak

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Example MSA Form Factors
10 Gigabit Small Form Factor Pluggable MSA

• XFP Applications
• OC192/STM-64 9.95 Gb/s
• 10 Gigabit FC 10.5 Gb/s
• G.709 10.7 Gb/s
• 10 Gigabit Ethernet 10.3 Gb/s
• Smaller space and lower cost alternative to
  parallel-optics VSR.
• XFP Value Propositions
• Protocol Agnostic - "any application, any rate".
• Allows 16 XCVRs on a typical 19" rack with 23mm
  pitch density.
• Single footprint for all links.
• Less than 1/3 the power and size of an MSA with
  parallel interface.
• Hot plugable.
• XFI (10 Gigabit Serial Electrical Interface)
  Electrical Signaling
• Supports 12" of FR4 with one connector
• Low EMI and power due to nominal 500 mV
  differential drive.
• Slew control for improved Signal Integirty and
  lower EMI.
• TX and RX signals each are a 100 Ohm differential
  pair, AC coupled for simplicity.

Xenpak

Xpak
http//www.xenpak.org/ http//www.xfpmsa.org/ http
//www.x2msa.org/
X2
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SFF Transceiver Showing Duplex-LC Receptacle
Image courtesy Picolight, Inc.
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XAUI Electrical Interface

• Defined in IEEE 802.3ae, section 42
• Extends the Media Independent Interface
• Fewer pins than full parallel I/O
• Quartet of differential pair per direction
• 3.125 Gbps per lane
• XAUI chips resets jitter accumulation
• XAUI chips establish lane order
• XAUI chips eliminates lane-to-lane skew

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Transceiver Trends

• More intelligence and RAM in modules
• Price erosion of 10 Gbps modules
• Garden variety 1 Gbps modules at near-commodity
  pricing
• Equalization of optical dispersion
• Vcc of 3.3V (and lower) rather than 5V
• Better EMI and ESD margins
• Gbps modules for polymer optical fiber
• Special BiDi modules for FTTx

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What to expect in 2010for VSR Data Links

• Fiber used in shorter and shorter links
• 1300 nm VCSELs
• Silicon Photonics
• Resonant microcavity devices
• Few new connectors
• Electronic dispersion compensation
• More intelligence in transceivers
• Inexpensive mini fusion splicers

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Questions

• Is one gigabit/second technology adequate for the
  lifetime of the detector?
• Radiation hardness of VCSELs and
  commercially-available transceivers
• Can we use 1310/850 BiDi module to aid with
  photobleaching?
• Is it economically feasible for spliceless design
  made completely of pure silica fiber
• Suitability of photonic crystal fiber