Download Optical Links

Experience with Parallel Optical Link
for the CDF Silicon Detector
S. Hou for the DOIM group
Academia Sinica, Taiwan
VERTEX 2002
Introduction
DOIM: Dense Optical Interface Module
Byte-wide parallel optical link
8-bits + clock
53 Mbyte/sec, BER10-12
Transmitter :
Laser-diode array
ASIC driver chip
Receiver :
PIN-diode array
ASIC receiver chip
Multi-mode fiber ribbon
Laser, Electrical characteristics
Bit-error rate test
Aging test
Radiation Hardness
Implementation in CDF
VERTEX 2002
Transmitter: Laser diode
InGaAs/InP Edge-emitting laser diode :
1550 nm wavelength
12-ch diode array (9 used)
250 m pitch
20 mA/channel
Cleaved mirrors
Facet coating
Bare laser power:
1 mW/ch @20mA
Insertion to fiber:
200 ~ 800 W/ch
Fabrication by
Chunghwa Telecom
Telecommunication Laboratories
VERTEX 2002
Transmitter: driver ASIC
Custom design, biCMOS 0.8 m,AMS
bipolar transistors only
Inputs :
Diff. ECL or LVDS signals compatible
differential 100 mV
Enable by TTL low
Nine channels :
Vcc-VLD across
output transistor, 50 , laser
control current consumption
At 3V, 20mA/ch nominal
~2mA/0.1V adjustable slope
VERTEX 2002
Transmitter assembly
Die-bond / Wire bond
laser-diode array on BeO submount
driver chip on substrate
fibers on V-groove
Alignment
fibers to laser emitting facets
VERTEX 2002
Receiver : PIN & ASIC
InGaAs/InP PIN diode :
12-ch array, matching laser diode wavelength
by TL, Chunghwa Telecom.
Operation condition :
50 ~ 800 W on, 10 W off
1.1 W/module
Outputs :
differential ECL, nine independent channels
VERTEX 2002
Receiver assembly
Die-bond / Wire bond
PIN-diode array on Al2O3 submount
driver chip on substrate
fibers on V-groove
Alignment, fibers to PIN-diodes
VERTEX 2002
Assembly procedure
VERTEX 2002
Transmitter characteristics
Transmitter tests :
L-I-V and temperature
50 MHz diff. Inputs, 2.5V common mode 100 mV, 50% +Dcyc
Laser light MT-12ST fanout & Tek O/E probe
VERTEX 2002
Laser diode: L-I-V
Laser light at 20, 30, 40oC
water-bath chiller precision ~0.1oC
measured at substrate
I-V
little temperature dependence
approximately linear
L-V
Drop with temperature
Duty cycle
diff. Input 50%
stable, little offset to 50%
VERTEX 2002
Laser diode: temperature
Light power vs. Temperature
Measured in stable
cooling/heating process
Temperature at substrate
precision ~0.1oC
Approximately linear drop
to temperature
VERTEX 2002
Receiver response
Receiver connected to a Transmitter
Light power chosen for
wide distribution
Light pulse width are consistent
Receiver ECL outputs
by a Tektronix diff. probe
Consistent duty cycles in favored
operation range (2.8~3.2V)
Saturates for high light level
VERTEX 2002
Transmitter uniformity : light outputs
Production transmitters
light from pigtail at 30oC
wide deviation channel-by-channel
mainly due to insertion efficiency
Span within ~400 W
 ~72 W to the mean/module
Effect operation dynamic range in
threshold, saturation limit
VERTEX 2002
Transmitter uniformity : light pulse widths
Ch-Ch Light power deviation
Is approximately a const. scaling factor
L-V linear fit, normalized slope to L(3V) indep. of light power
Light pulse width is uniform, ~1%, indep. of light power
VERTEX 2002
Receiver uniformity : ECL duty cycles
Two production batches
monitored at 550 W & 970 W
light pulse width 45%
ECL duty cycle is uniform
48.1% at 550 W, (2nd batch)
=0.7%
4% wider in 1st batch
due to chip tuning
Wide light input range
Saturation monitored at 970 W
VERTEX 2002
Receiver uniformity : duty cycle deviation
Input lights
~950 W, width 45%
for all channels
ECL outputs of a module
deviation to the mean
~1.5%
for both batches
VERTEX 2002
Bit-Error Rate test
BERT by Fermilab
PC ISA boards TTL to
Tbert, Rbert boards
At 63 MHz,
minimum BER 10 –12
Burn-in
3-days on ASICs, diodes
1-day BERT
 reject devices infant mortality
bad components fail quickly
VERTEX 2002
Accelerated Aging test
4 transmitters at 60oC, 330 days
Wear-out degradation
0.15 0.08 W/day at 60oC
no failure
Accelerating factor
F=exp(Ea/ kb) (1/T1 –1/T2)
F=29 for T= – 5oC
Failure due to light degradation
Min transmitter spec 200 W
down below receiver threshold 50 W
~100 days at 60oC, or 8 years at – 5oC
90% C.L. for 0 failure, P=0.064
upper limit = 40 ch. In 3 years
VERTEX 2002
INER 30 MeV proton Irradiation
CDF requirement : 200 kRad tolerance
INER test beam : transmitter in DC mode.
fiber connection out of beam area, measuring L, T versus dose.
VERTEX 2002
Bulk damage, annealing
Bulk damage dominant, linear dep. to dose
Ratio of light drop is consistent for a module, indep. of light power
Degradation 10% for 200 kRad
VERTEX 2002
UC Davis 63.3 MeV proton
UC Davis test beam : 10 transmitters on two Port Cards
Examined after 200, 400 kRad, for L I, V measurements
Light degradation ~10% for 200 kRad
Similar I-V, L-V characteristics after irradiation,
slope for L vs. V degrades similarly.
VERTEX 2002
DOIM implementation : transmitters
Transmitters on Port Cards
Total 570 transmitters
128 Port Cards,
5 transmitter each board
VERTEX 2002
DOIM implementation : receivers
Receivers on FTM
10 receivers on each board, reading 2 Port Cards
VERTEX 2002
Status
570 pairs implemented
~10 % bit-error flagged
excess light at -5oC
optical reflection, contact
electrical pin contact
2% has fatal damage
is improving
VERTEX 2002
Summary
DOIM, a byte-wide optical link is implemented in CDF
Edge-emitting laser light  linear to I-V and T
Laser-diode array coupling to pigtail fibers
large deviation  a major disadvantage
Radiation tolerance is high
bulk-damage dominant  linear degradation to dose
VERTEX 2002