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Survey of Short-Reach Optical Interconnect. Ken Pedrotti Robert Dahlgren. Presented 10 November 2005. Outline. Introduction Pure silica fiber trends Splicing trends Connector trends Active component trends Transceiver module trends What to expect in the year 2010?

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Survey of short reach optical interconnect

Survey of Short-ReachOptical Interconnect

Ken Pedrotti

Robert Dahlgren

Presented 10 November 2005


  • 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

Short reach links 300m
Short Reach Links < 300m

  • 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

Main commercial trends
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


  • 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

What convergence means for vsr links
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

Ribbon optical fiber
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

Pure silica core fiber trends
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

Pure silica core fiber vendors
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

Evolution of arc fusion splicing
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

  • Improvement of fiber concentricity enables v groove alignment
    Improvement of Fiber ConcentricityEnables V-groove Alignment

    Active Core Alignment

    V-groove Alignment

    Splicing trends
    Splicing trends

    • Continued acceptance of v-groove based splicers in non R&D 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

    Mass fusion splice of 12 fiber ribbonized smf
    Mass Fusion Splice of12-fiber Ribbonized SMF

    Images courtesy AFL Telecommunications

    Splice economics
    Splice Economics

    • Splicing cost roughly 20~40 € 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

    Connector market landscape
    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.

    Legacy connectors
    Legacy Connectors






    “old” FDDI

    Images used with permission of Alcoa-Fujikura, Ltd.

    Ribbon fiber connectors mt ferrule technology
    Ribbon Fiber Connectors:MT Ferrule Technology

    Images used with permission of US Conec, Ltd.

    Small form factor connectors
    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

    Some sff connectors
    Some SFF Connectors





    Images used with permission of Alcoa-Fujikura, Ltd.

    Laser diode structures
    Laser Diode Structures

    Most require multiple growth steps

    Thermal cycling is problematic for electronic devices

    Detector technologies
    Detector Technologies


    Layer Structure

    Simple, Planar,

    Low Capacitance

    Low Quantum Efficiency


    (Metal Semiconductor Metal)




    Semiinsulating GaAs

    Contact InGaAsP p 5x1018

    Absorption InGaAs n- 5x1014

    Contact InP n 1x1019

    Trade-off Between

    Quantum efficiency

    and Speed



    Low Noise

    Difficult to make


    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


    Vcsel status and trends
    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

    Semiconductor trends
    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

    Semiconductor trends1
    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

    Transceivers conform to standards
    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…

    Example oc 192 10 gbps vsr standards oif
    Example OC-192 10 Gbps VSR Standards (OIF)

    Transceivers conform to msas
    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…

    Example msa form factors
    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.




    Sff transceiver showing duplex lc receptacle
    SFF Transceiver Showing Duplex-LC Receptacle

    Image courtesy Picolight, Inc.

    Xaui electrical interface
    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

    Transceiver trends
    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

    What to expect in 2010 for vsr data links
    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


    • 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