10GB-100GB Parallel Optical Interconnect Challenges

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10GB-100GB Parallel Optical Interconnect
Challenges
XLoom Communications
Dr. Hanan Yinnon Consultant, Former CSO XLoom
Communications, Ltd., Tel Aviv, Israel March
10th, 2011
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Outline

• The need for optical interconnect solutions
• Current solutions
• XLoom iFlame optical engine
• 4 parallel lane 5 Gbps transceiver based on XLoom
  iFlame - Avdat
• Future development

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• The need for optical interconnect solutions
• Current solutions
• XLoom iFlame optical engine
• 4 parallel lane 5 Gbps transceiver based on XLoom
  iFlame - Avdat
• Future development

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The need for optical interconnects
Computing power and storage needs grow.
Interconnects need to become smaller, consume
less power, and provide higher bandwidth Server
farms grow link distances increase 
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Copper and fiber link data rates and ranges
Chip-Chip Card-Card Datacenter
Campus Metro
Multimode Optical
Singlemode Optical
Clearly, copper needs to be replaced with optics
to get reach and ease of use at higher bit rates
line rate Gbps
Electrical
100 m
10 m
1 km
1 m
10 km
0.1 m
Length of a single-channel link km
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Advantahes of optics over copper
Volume of a 10 m cable
Weight of a 10 m cable
Bending radius
Link length
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Additional advantages of optical fibers

• Immunity to EMI/RFI
• Potential immunity to EMP
• Potential immunity to nuclear radiation

Index profile of a RadHard fiber
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Optical transmission options

• Electronics
• Current electronic technology limits bit rate to
  around 40 Gbps per single transmitter
• Optics
• Multimode fibers can be used at low wavelength
  (850 nm) where inexpensive lasers are available
  (VCSEL)
• However, Multimode fibers have limited bandwidth
  max effective 5GHzkm
• Lasers are also approaching the bandwidth
  limitation
• Solutions
• Wavelength Division Multiplexing (WDM)
  expensive, used for SM system only
• Parallel multi-lane interconnects viable
  solution for short lengths

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Still in 2011, many links use copper

• The main problem is cost
• Optics and analog electronics cost does not scale
  like digital electronics
• Due to
• The need for manual or semi-automatic processes
  mostly alignment issues
• Sensitivity of diode lasers to operating
  conditions need for optimization
• Integration of optics and electronics requires
  combination of a variety of technologies besides
  semiconductor design and fabrication.
• Commonly used Figure-of-Merit for interconnects
  is given in /Gbps
• Today it is common to pay 2/Gbps/end for
  optical interconnect, but Xlooms target is
  lt0.1/Gbps/end

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How to lower cost of optics?

• Design
• Multi-lane interconnects 4, 10, 12 or even more
• Multimode fiber more tolerant to misalignment
  in light coupling
• Vertical cavity laser diodes (VCSEL) lower
  component cost and lower power consumption for
  same speed, mounting ease
• Manufacturing
• Large-scale optical coupling alignment wafer
  scale and passive alignment should lend itself to
  full automation
• Controllable, repeatable process, not rocket
  science

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InfiniBand (HPC) links

• Designed for data centers, grid computers, server
  farms mostly short distance
• Copper solutions limited to 3 15 m (depending
  on bit rate). Optical solutions reach more than
  100 m (10 Gbps)
• Links aggregation 4X (server/switch) or 12X
  (clusters and supercomputer inter-switch
  connections).

SDR 2.5 Gbps DDR 5.0 Gbps QDR 10.0 Gbps
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40 and 100 Gbps Ethernet

• IEEE 802.3ba intended mostly for data centers
• Various link definitions backplane, data cables,
  multi-mode fibers, single-mode fibers
• Largest market share expected to be multi-mode
  links
• Two MMF options
• 40GBASE-SR4 2 x 4 parallel lanes (duplex)
• 100GBASE-SR10 2 x 10 parallel lanes (duplex)
• Two MM fiber types
• OM3 max link length 100 m
• OM4 max link length 150 m

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Servers by Ethernet Connection Speed
Source Intel Broadcom (April 2007)
millions server units
millions server units
10 year transition for 1G Ethernet
5 years for 10GBE
5 years for 40GBE
10 year transition for 1G Ethernet
5 years for 10GBE
5 years for 40GBE
Source Intel Broadcom (April 2007)
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• The need for optical interconnect solutions
• Current solutions
• XLoom iFlame optical engine
• 4 parallel lane 5 Gbps transceiver based on XLoom
  iFlame - Avdat
• Future development

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Intel Emcore Active Cable Manufacturing process

• Assembly of VCSELs on sub mount
• Attach sub mount to PCB under a hole in the PCB
• Active alignment of the coupling prism to the
  VCSEL
• Repeat the whole process for the Photodiode array

Prism Optics
Fiber
Sub-mount
VCSEL
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Intel Emcore processMain observations

• Optical subassembly includes
• Double active alignment of Fiber lens prism to
  VCSEL array and PD array and adhesive curing
  cycles
• Estimated process time 15 min per transmitter -
  Labor intensive manual process
• No optical connector
• Applicable only for active cables

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Reflex PhotonicsManufacturing process

• Assembly of VCSEL / Photodiode array on substrate
• Placement of spacer plate on the substrate

• Cover VCSEL / Photo Diode array with clear Epoxy

• Flat polish transparent epoxy

• Active align to fiber array module Similar to
  the Infineon process

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Outline

• The need for optical interconnect solutions
• Current solutions
• XLoom iFlame optical engine
• 4 parallel lane 5 Gbps transceiver based on XLoom
  iFlame - Avdat
• Future development

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XLoom chip scale optical technologysolves
density, power, and reach

• iFlame technology
• Optical-to-electronic conversion on a miniature
  scale
• Commercially-available lasers/photodiodes and
  circuits
• Glass substrate allows for easy light coupling
• Aligned and assembled on the wafer level (6 in
  process)
• Standard semiconductor micromachining processes

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iFlame light-coupling scheme
protective cap
reflectors
reflector bar
epoxy
fiber
substrate
VCSEL/PD
metal traces
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iFlame Lens Optical Design
Ray-tracing optical design (sequential analysis,
using ZEMAX)
Focus on flat mirror
Near-field pattern at detector Example of offset
z-focus
Imaging 11
Acceptance angle lt NA of fiber/ VCSELs
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iFlame Manufacturing process

• structure is repeated in 2D on a 6 wafer
• grooves created at the same time on all devices
• simultaneous alignment of all devices
• Lead free (ROHS)

polyimide
silicon/glass
grooves
MT pins
fibers
Patterned device wafer ready for saw
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Reflector bars
Reflectors bars are manufactured separately in a
wafer form, cut, and attached to device wafer
using an automated machine (passive alignment)
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Standard Semiconductor EquipmentUsed in Assembly
Flip-chip machine mounts the lasers and detectors
Fibers inserted into the alleys
Saw cuts the groves
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iFlame optical turn technology

• Wafer-level assembly simultaneous alignment of
  many module optics
• Passive alignment visual, automation possible
• Array optics multiple channels assembled
  simultaneously
• Low profile multiple environments/applications

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iFlame optical chip (without the cap)
reflector bar
Mounted VCSELs seen from optical side
VCSEL array
PD array
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• The need for optical interconnect solutions
• Current solutions
• XLoom iFlame optical engine
• 4 parallel lane 5 Gbps transceiver based on XLoom
  iFlame - Avdat
• Future development

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Avdat - 4X Infiniband DDR transceiver

• Infiniband 4X DDR optical transceiver
• Plug-compatible with CX4 connector
• 20 Gbps bandwidth in each direction
• Room-temperature field replaceable
• Infiniband, PCI-E, 10GFC, XAUI-ext.
• Switch and host-channel adapters (HCA)

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InfiniBand Electrical VS. Optical cablesand
Avdat
Electrical cable connector
CX4 Connector
Avdat
Active Electrical Cable
Quellan
Media Converter
Active Optical Cable
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InfiniBand Optical Host-Channel Adapter
(w/iFlame technology (Mellanox PCB)
electrical
Choose electrical or optical connector at a later
stage in manufacturing
optical
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Parallel Optics Design and Manufacturing
Challenges

• Signal integrity
• Microwave reflections ? output waveform, receiver
  waveform
• Crosstalk ? receiver sensitivity
• VCSEL performance adjustment
• Drive currents ? output waveform
• Over-temperature performance ? output waveform
• Thermal management ? output waveform, reliability
  (lifetime)
• Optical coupling
• Optical loss ? receiver sensitivity
• Coupled power ratio ? to suit fiber laser
  bandwidth
• Qualification
• Laser safety ? Must meet Class 1M
• EMI ? meet spec

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Thermal management

• Most heat generated in the receiver IC and the
  laser driver IC
• Lasers are very sensitive to heat (performance
  and reliability suffer)

• Design features
• Low thermal resistance lt15 ºC/W
• Resistance to thermal shock and thermal cycle
• Total power dissipation lt 1 W

wire-bonds
RF absorber
optical chip
Heat-conducting block
Laser driver / Receiver chip
Printed Circuit Board
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Laser performance challenges
Laser dynamic nonlinearity AND long bond-wires
(microwave mismatch) increase ringing in the
light output. The hump moves with current and
bond-wire length
6-layer PCB
Short bond-wire (0.5 mm)
Long bond-wire (1.5 mm)
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iFlame performance at 5Gbpsper channel
TX
Ch 1
Ch 2
Ch 3
Ch 4
RX
Compliance with InfiniBand specifications at SDR
and DDR Models applicable in PCI-E, and
InfiniBand environments. Qualified IEC/EN
60825-1/A22001 Class 1M, Laser safety FCC
Part 15 Class B
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Xloom R_at_D lab
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• The need for optical interconnect solutions
• Current solutions
• XLoom iFlame optical engine
• 4 parallel lane 5 Gbps transceiver based on XLoom
  iFlame - Avdat
• Future development

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Leveraging the iFlame technology

• InfiniFlame 12X
• Front panel pluggable transmitter/receiver set
• Low-profile XFP form-factor 30-pin connector
• MPO/MTP optical interface
• Enables 36-ports in a ½ height box
• InfiniBand, Fibre-Channel, Ethernet

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Optical engines for active cables

• When producing optical engines for standard
  products (such as QSFP MSA) alignment pins must
  be included production must be on a strip level
• Optics for active cables and other noon-standard
  applications, not needing alignment pins, can be
  done on a wafer level a major cost advantage

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24 parallel channels on a single MPO
Initial designs have already been prepared
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• Thank You

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