1. 10GB-100GB Parallel Optical Interconnect Challenges
XLoom Communications
10GB-100GB Parallel Optical Interconnect Challenges
Dr. Hanan Yinnon
Consultant, Former CSO
XLoom Communications, Ltd., Tel Aviv, Israel
March 10th, 2011
XLoom Proprietary and Confidential 1

2. 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 2

3. 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 3

4. 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  4

5. 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
0.1 m
1 m
10 m
100 m
1 km
10 km
Length of a single-channel link [km] 5

6. Advantahes of optics over copper
Weight of a 10 m cable
Volume of a 10 m cable
Bending radius
Link length
XLoom Proprietary and Confidential

7. Additional advantages of optical fibers
Immunity to EMI/RFI
Potential immunity to EMP
Potential immunity to nuclear radiation
Index profile of a RadHard fiber
XLoom Proprietary and Confidential

8. 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 ~ 5GHz*km
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
XLoom Proprietary and Confidential

9. 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 Xloom’s target is <$0.1/Gbps/end 9

10. 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” 10

11. 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 11

12. 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

13. Servers by Ethernet Connection Speed
Source: Intel & Broadcom (April 2007)
millions server units
millions server units
10 year transition for 1G Ethernet
10 year transition for 1G Ethernet
5 years for 10GBE
5 years for 10GBE
5 years for 40GBE
5 years for 40GBE
Source: Intel & Broadcom (April 2007) 13

14. 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 14

15. 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
VCSEL
Sub-mount
XLoom Proprietary and Confidential

16. Intel – Emcore process Main 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
XLoom Proprietary and Confidential

17. Reflex Photonics Manufacturing 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
XLoom Proprietary and Confidential

18. 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 18

19. XLoom chip scale optical technology solves 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 19

20. iFlame light-coupling scheme
protective cap
reflectors
reflector bar
epoxy
fiber
substrate
VCSEL/PD
metal traces 20

21. 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 1:1
Acceptance angle < NA of fiber/ VCSELs 21

22. 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 22

23. Reflector bars
Reflectors bars are manufactured separately in a wafer form, cut, and attached to device wafer using an automated machine (passive alignment)

24. Standard Semiconductor Equipment Used in Assembly
Flip-chip machine mounts the lasers and detectors
Fibers inserted into the alleys
Saw cuts the groves 24

25. 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 25

26. iFlame optical chip (without the cap)
reflector bar
Mounted VCSELs
seen from optical side
VCSEL array
PD array 26

27. 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 27

28. 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) 28

29. InfiniBand™ Electrical VS. Optical cables and Avdat
Electrical cable connector
CX4 Connector
Avdat
Active Electrical Cable
Media
Converter
Quellan
Active Optical Cable 29

30. InfiniBand™ Optical Host-Channel Adapter (w/iFlame technology (Mellanox PCB)
electrical
Choose electrical or optical connector at a later stage in manufacturing
optical 30

31. 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 31

32. 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 <15 ºC/W
Resistance to thermal shock and thermal cycle
Total power dissipation < 1 W
wire-bonds
RF absorber
optical chip
Heat-conducting
block
Laser driver / Receiver chip
Printed Circuit Board 32

33. 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) 33

34. iFlame performance at 5Gbps per channelTX
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 /A2:2001 Class 1M, Laser safety
FCC Part 15 Class B 34

35. Xloom lab

36. 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 36

37. 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 37

38. 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
XLoom Proprietary and Confidential

39. 24 parallel channels on a single MPO
Initial designs have already been prepared
XLoom Proprietary and Confidential

40. XLoom Proprietary and Confidential
Thank You
XLoom Proprietary and Confidential 40