Survey of Short-ReachOptical 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 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

• 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 ConcentricityEnables V-groove Alignment

1985 VINTAGE FIBER

0

5

10

15

0

0.08

0.16

0.24

0.32 0.4

0.48

0.56

0.64

0.72 0.8

Splice Loss (dB)

Fre

qu

ency

1995 VINTAGE FIBER

0

10

20

30

0

0.08

0.16

0.24

0.32 0.4

0.48

0.56

0.64

0.72 0.8

Splice Loss (dB)

Fre

qu

ency

1985 VINTAGE FIBER

02468

0

0.08

0.16

0.24

0.32 0.4

0.48

0.56

0.64

0.72 0.8

Splice Loss (dB)

Fre

qu

ency

1995 VINTAGE FIBER

0

5

10

15

0

0.08

0.16

0.24

0.32 0.4

0.48

0.56

0.64

0.72 0.8

Splice Loss (dB)

Fre

qu

ency

Active Core Alignment V-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 of12-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

FC SMA

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 stepsThermal cycling is problematic for electronic devices

Detector Technologies

MSM(Metal Semiconductor Metal)

PIN

APD

Waveguide

Contact InP p 1x1018

Multiplication InP n 5x1016

Transition InGaAsP n 1x1016

Absorption InGaAs n 5x1014

Contact InP n 1x1018

Substrate InP Semi insulating

Semiinsulating GaAs

Contact InGaAsP p 5x1018

Absorption InGaAs n- 5x1014

Contact InP n 1x1019

Absorption Layer

Guide Layers

Simple, Planar, Low CapacitanceLow Quantum Efficiency

Trade-off Between Quantum efficiency and Speed

High efficiencyHigh speedDifficult to couple into

Gain-Bandwidth: 120GHzLow NoiseDifficult to makeComplex

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 5-6.5 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-192 10 Gbps VSR Standards (OIF)

Desig-nation

Max

Reach

Fiber

Type

Number

of fibers

(Half-Duplex)

Data Rate

Laser

Type

Wavelength

VSR-1 300 m MMF 12 1.25 gbps

VCSEL

array

850 nm

VSR-2 600 m SMF 1 10 Gbps FP 1310 nm

VSR-3 300 m MMF 4 2.5 Gbps

VCSEL

array

850 nm

VSR-4 300 m MMF 1 10 Gbps VCSEL 850 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-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.

http://www.xenpak.org/http://www.xfpmsa.org/http://www.x2msa.org/

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

• 3.125 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 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

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