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? Questions and discussion

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 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

Lesson from the Aircraft Industry

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

What Convergence Means for 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 Four, twelve, or sixteen fibers Usually spaced at 250  m pitch Connectors, splicing more complex Cost per splice about 2 ~ 2.5x Lower cost per fiber

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 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 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 Active Core AlignmentV-groove Alignment

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 Images courtesy AFL Telecommunications

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 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 ST Biconic FCSMA ESCON “old” FDDI Images used with permission of Alcoa-Fujikura, Ltd.

Images used with permission of US Conec, Ltd. Ribbon Fiber Connectors: MT Ferrule Technology

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 MT-RJ Images used with permission of Alcoa-Fujikura, Ltd. Duplex-LC LC MU

Laser Diode Structures Most require multiple growth steps Thermal cycling is problematic for electronic devices

Detector Technologies MSM (Metal Semiconductor Metal) PIN APD Waveguide Contact InP p 1x10 18 Multiplication InP n 5x10 16 Transition InGaAsP n 1x10 16 Absorption InGaAs n 5x10 14 Contact InP n 1x10 18 Substrate InP Semi insulating Semiinsulating GaAs Contact InGaAsP p 5x10 18 Absorption InGaAs n- 5x10 14 Contact InP n 1x10 19 Absorption Layer Guide Layers Simple, Planar, Low Capacitance Low Quantum Efficiency Trade-off Between Quantum efficiency and Speed High efficiency High speed Difficult to couple into Gain-Bandwidth: 120GHz Low Noise Difficult to make Complex Key: Absorption Layer Contact layers Layer Structure Features

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 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 coding gain Chips appearing designed for RZ rather than NRZ applications

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 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 Gbps VSR Standards (OIF) Desig- nation Max Reach Fiber Type Number of fibers (Half- Duplex) Data Rate Laser Type Wavelen gth VSR-1300 mMMF gbps VCSEL array 850 nm VSR-2600 mSMF110 GbpsFP1310 nm VSR-3300 mMMF42.5 Gbps VCSEL array 850 nm VSR-4300 mMMF110 GbpsVCSEL850 nm

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 XFP Applications: OC192/STM Gb/s 10 Gigabit FC 10.5 Gb/s G 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 X2 10 Gigabit Small Form Factor Pluggable MSA

SFF Transceiver Showing Duplex-LC Receptacle Image courtesy Picolight, Inc.

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 Gbps per lane XAUI chips resets jitter accumulation XAUI chips establish lane order XAUI chips eliminates lane-to-lane skew

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 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

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