Optical Interconnect Technology

1
Optical Interconnect Technology

• Ray Chen, Ph.D.
• Dept. of Electrical and Computer Engineering
• The University of Texas at Austin

2
Introductionprojection of bandwidth
3
Potential markets for UTs IP portfolio

• Optical backplane
• Optical PC board
• Passive waveguide components
• Active optical components
• Optical biosensor

Source IBM
4
Global optical communications revenue and
projection
5
Fully embedded board-level optical
interconnection

• Unique architecture for optical PWB (Printed
  Writing Board) all the optical components are
  interposed inside the PCB
• Solves the package problem/reduces cost effects

1x12 VCSEL
1x12 PIN photodiode
12-channel polymer waveguide 109 cm
6
Lamination of optical waveguide film and
integration of thin film VCSEL

• 12-channel polymer waveguide and 45 micro-mirror

• Cross-section of laminated optical layer
  

• Cu transmission lines for VCSEL (or PD)
  integration

PCB Sub
PSA film
Optical layer
Top emitting VCSEL
via
PCB Sub
2 mm

• PSA (pressure-sensitive adhesive) film 100/200
  mm
• Optical waveguide film layer 170 mm

Cu trans. lines (thickness 10 mm)
Bottom emitting VCSEL
7
Backplane interconnects point-to-point

• Point-to-point
• Data rate 6.25G10Gbps
• Differential pairs to a central switching fabric
• Signal density gt50 layers, 104 nets
• Wiring congestion!
• Switching delay
• Speed limit
• Via
• Dielectric absorption of FR4

8
Why high-speed optical networks

• Example A music CD contains 660 Mbytes of data.
  How long would it take to send this from Austin
  to Dallas?
• What use is all that bandwidth?

Speed Method Transfer Time
56 Kilobits/sec PC modem 26.2 hours
500 Kb/sec Cable modem 2.93 hours
1.5 Mb/sec DSL 59 minutes
10 Mb/sec Commercial T1 service 8.8 minutes
100 Mb/sec Fiber to the home 53 seconds
9
Fully embedded board-level optical
interconnection
45? micro-mirror
Copper trace
Micro-via
Optical PCB
Waveguide
Photodiode
VCSEL array
Cross-section view of optical PCB
R. T. Chen, et al., Proc. IEEE, 88, 780-793
(2000).
10
Polyimide-based 1-to-48 fanout H-tree optical
waveguide on Si-substrate
(c)
(d)
11
Optical signal distribution in a network card
12
Substrate-removed 1 X 12 GaAs VCSEL array

• Flatten optical layer to facilitate embedded
  structure
• 10 mm thickness VCSEL formation
• Mechanical lapping 50 mm
• Chemical wet-etching (citric acid H2O2 ) 10 mm

Original VCSEL on GaAs substrate
Substrate-removed VCSEL (10 mm)
13
Integration of VCSEL and PIN photodiode with
optical waveguide film

• Photolithography UV-aligner
• UV-curable adhesive

112 VCSEL
112 PIN photodiode
12-channel polymer waveguide 109 cm
14
Speed measurement of substrate-removed 850nm
wavelength VCSEL

• BER/Q-factor/Jitter RMS
• Vbias 2.0 V / Ibias 5.0 mA

Eye-diagram
Vbias 2.0 V Ibias 5.0 mA Ampl 0.5 V Offs
0 V Freq. 10 Gb
NRZ mode PRBS 231-1 Jitter RMS 4.6
ps Q-factor 5.18 Eye width 71.7 ps
15
Speed measurement of substrate-removed VCSEL and
PIN photodiode
Frequency response of 850 nm VCSEL
Frequency response of 850 nm PIN photodiode