Modulator-Based, High Bandwidth
Optical Links for HEP Experiments
G. Drake, W. S. Fernando , R. W. Stanek ,D. G. Underwood
High Energy Physics Division, Argonne National Lab, Argonne,
Il, United States
Log(BER)
Noise (mV)
Jitter (ps) Nice open eye at BER=10 -18
For a link at 10 Gb/s - 10 -18 BER =1 error in ~1000 days !
10 -12 BER = ~ 900 errors per day !

• Two methods for optical data transmission
– Direct modulation of light: common in short distance, short wave length communication, all current LHC experiments use this technology
Elec. Tx Current driver
Laser
(VCSEL)
Optical Tx
Optical Rx
Elec. Rx Receiver PIN diodes
– Indirect modulation of light: long distance, long wave length communication. ATLAS
TileCal will test this technology in 2013 (demonstrator) for use in Phase 2 upgrade
Laser (CW)
Elec. Tx
Voltage driver
Modulator
Optical Tx
Elec. Rx
Receiver
PIN diodes
Optical Rx
Monolithically integrated Silicon photonic device

– Mach–Zehnder interferometer based
ΔVoltage  Δrefractive index  phase  amplitude
Pockels effect, Kerr effect, free carrier dispersion effect
Materials: LiNbO3, Si, InP
– Absorption based
ΔVoltage  Δoptical absorption
Franz-Keldysh (FK) effect in bulk semiconductors
Input Output and quantum-confined Stark effect (QCSE) in quantum-well (QW) structures.
Materials: InP, SiGe, Graphene

• L iNbO3 - based on the crystal property
– High bandwidth, tested rad-hard, very long (~5 cm), expensive, high drive voltages
• InP - based on the crystal property
– Very High bandwidths, should be rad-hard, small (~2 mm), low drive voltages, expensive at present, special-purpose technology
• Si - based on the free carrier dispersion effect
– High bandwidth, rad-hard (?) , small (~1 mm), inexpensive, could monolithically integrate, commercially available, use existing Si
Technology

• Modulators are very simple and reliable. No known failure mechanisms
– e.g. Luxtera transceiver MTBF > 2.3 x 10 9 hrs (300 million device hours accumulated without a single intrinsic failure)
• E.g. 1 device failure in TileCal >34 years (9 months running, 1024 transceivers)
VCSEL Photonic Si modulator

•
•
•
6

•
– Availability: COTS devices 1 st choice
– Reliability: Proven in the field
– Radiation tolerance: ~100 krad TID, ~10 12 p/cm 2 (and rad-hard SM fibers are cheaper than doped MM)
– Cost: Cost Savings over SNAP12 Baseline
– Implementation: Ease over Baseline
– Bandwidth : 56 Gb/s per readout board
– BER : minimal correction needed
9.8 mm
We propose to implement optical links to be used in the TileCal
Phase 2 upgrade based on Luxtera’s silicon photonic transceiver. This comes in a standard QSFP package which can be easily plugged into a motherboard. We are doing a Demonstrator.
4 x 10Gb/s transceiver from Luxtera, 130nm Silicon on Insulator (SOI)

Commercial Integrated
Optics Chips are a
Promising Form of
Modulators.
1 cm
1 cm on one integrated optics silicon chip
 10Gb/s each fiber
 Use of modulators and CW laser
 Low power, small size
Speed
10 + Gb/fiber commercial integrated optics
40 Gb/fiber with other commercial units
Laser reliability
Either CW laser onboard
Or displace laser outside detector.
(DFL has Different junction structure than VCSELs)
Low Bit Error Rate
10 -18 vs typical 10 -12 for current systems
Simplified error correction schemes
Low power
One CW laser - split many ways
Modulators are very efficient
Short electrical paths – no cable drivers
Low voltage drivers – not current
Rad hard optical parts
We have tested silicon integrated optics for >64 krad application
Modulator parts should work at much higher levels
Optical part expected to work at multi-Mrad
8

ANL Bench Tests of Quality and BER of the Complete Link
(Modulator & Receiver with 200m SM fiber)
FPGA board generate
PRBS7 bit stream
@10.3125 Gb/s
4 SMA cables to Tx
4 SMA cables from Rx
QSFP Interface board
Luxtera
Mod
Rx
Tx
Use FPGA to generate random bit stream
4 input ports, 4 output ports.
SMA
8 SM fiber bundle
DSA8200
Communication
Analyzer
100 m
Scope to monitor Quality (eye diagram) and calculate Bit Error
Rate (BER)
Feedback
9 9

Mask 140% of 10GBASE-R
The quality of the link is measured and compared with IEEE 802.3ae and the performance exceeds the requirements by 40% more

-18
Per link @ 10 Gb/s
10 -18 BER =1 error in ~1000 days !
10 -12 BER = ~ 900 errors per day
Log(BER)
ANL test
Luxtera / Molex
Test
Noise (mV)
Jitter (ps)
Nice open eye at
BER=10 -18
Why is Low BER important ?
• High BER requires Forward Error Correction (FEC) which consumes 30% of the bandwidth and requires error correction which consumes power and introduce susceptibility to radiation
• BER < 10 -18 ~ ~ no need for FEC -> save money and bandwidth and more rad-hard!
Achieved:
• Per Link 10Gb/s (faster by x2 the upgrade target)
• BER < 10 -18 (better by x10 6 over upgrade performance)
• Lower power consumption (factor of x6 the upgrade target)

Technology
Bandwidth (Gb/s)
Bit Error Rate (BER)
Fiber Type
Reach (m)
Power (mW/Gb/s)
Reliability
Versatile Links (target)
Per fiber
Directly modulated laser based ( eg. VCSEL)
5
(10 -12 )
Multi Mode
100
100
VCSELS have many failure mechanisms, complex
* Estimate
Luxtera
40 G
InP
Modulators
Modulator based
80
LiNbO3
Modulator
40 14
10 -18
4000
8
Single Mode
10000
<50*
10000
<50*
No known failure mechanisms, very simple

Overall Plan for Demo of Luxtera / Molex QSFP Modulator based Devices
On-Detector Counting House
200 M
13

6
TO USA15
Note Extra I2C and monitor links through QSFP connector to emulate non-rad-hard PIC uC
QSFP connector
PM
T
12 tubes shaper
Integrator charge injection
PM
T shaper
Integrator charge injection
ADC low gain
ADC hi gain
12 bit ADCs
6 differential serial links
(4 Tx, 2 Rx)
Stockholm and Valencia are now designing the mainboard and ROD to accommodate the Luxtera
QSFP package.
ADC low gain
ADC hi gain
Integrator multiplexer
Integrator
ADC
Luxtera QSFP has 4 x 14 Gb/s transceivers
QSFP: Quad Small Form Factor Pluggable
Includes duplicate backup links
Inside ATLAS Tilecal Iron Girder

First Steps of ANL Radiation Test Program
Links run continuously at 10 Gb/s during irradiation
3 technologies
Integrated Silicon – CMOS (4-channel)
InP single channel
LiNO3 single channel
Proton Beam Electron Beam
NO SEE @ 10 12 protons/cm and 3.5 x min ionizing
2 & 64 krad TID OK after ~100 krad TID
15

•
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•
•
•
•
Only issue so far
•
16

In this Luxtera / Molex device uC is used for startup reads and sets parameters for operation also allows readout of temperature, current, etc
After startup, the device will continue to operate until power down
(or perhaps some large change in device)
We can use external I2C, etc through spare pins on
QSFP connector to eliminate uC
17

USB
FPGA board
8 SMA 8 SMA
QSFP board
PC
USB
I2C Main
+ Power
Receivers
8 Fiber
~100 m
12 V
Shielded from radiation
I2C
2 x Differential I2C
QSFP
I2C
QSFP connect
SMA
CW Lasers
PM Fiber
Fiber SM
Fiber SM
2 Fibers SM
Radiation Exposure Region
LiNbO3
InP
QSFP
Electrical feedback
Monitoring optical power,
Voltages, currents
4 x 10Gb/s
BER testing
18

• Modulators are a robust replacement for VCSEL-based optical readout:
– High Speed: >10 Gb/s. No speed limits
– Reliable: Rad hard, BER ~10 -18 . MTBF ~2.3 x 10 9 hrs
• We have proposed an optical link be used in TileCal and have built a prototype link based on Luxtera transceiver
– Characterized it for use @ 10 Gb/s with < 10 -18 BER
– Tested radiation hardness up to 8 x 10 11 p/cm 2
• No SEU at this level
• Need some changes to the controller ----
• Investigating other COTS modulator devices made of other materials.
• Investigating options to use modulators in very high radiation environments such as tracker upgrades

•
– Low latency (no velocity factor)
– Work over distances from few mm (internal triggers) to ~Km (counting house) or far ( to satellite orbit)
– Low mass
– No fiber routing
– Communicate between ID layers for trigger decisions.

A trigger concept using modulators and prisms
Data path for on-board tracking trigger which could couple 2 planes of 3D doublets.
21

A commercially available MEMS mirror
(Developed at ARI, Berkeley)
April 10, 2020
Argonne Center for Nan-scale Materials (CNM) developed novel MEMS mirrors that should solve the problems of commercial mirrors. The mirror is supported laterally and it can be actuated using
4 torsional actuators.
22

A nice demonstration
1 Gb/s to a target moving ~1 cm at > 100 Hz
Reflective lens
Reflection
850 nm LASER
For alignment
This Assembly moves
X
ADC
Y
TIA
Si Detectors
Rigid Coupling optical  electric
SFP
SPI
Lookup table
FPGA
Digital filter
Small
Prism
1550 LASER Beam
GRIN lens to wires
Capture
FPGA
Bit Error Tester
DAC
SPI
Amp
X
Y
MEMS Mirror to steer
Asphere Lens to launch wires
Modulator
No Bit errors overnight
CW LASER
1550 nm
23

1 Gb/s over 80 Meters
24

• Radiation Test Luxtera Molex without the microcontroller
Protons 3.5 x min ioni.
Gammas total dose up to 3 MR
Neutrons
• Radiation test components of Luxtera/Molex
Voltage Regulator
Laser
ATLAS Tilecal Demonstrator Tests
Kintex 7 FPGA
Radiation test Other Devices and other materials
For higher radiation environments
Develop other Optical Communication capabilities
25

• Modulators are simple, reliable, fast
• Silicon Integrated Technology exists for some HEP applications
• For ATLAS Tilecal demonstrator we expect: factor 10 6 lower BER, factor ~ 3 cost savings factor ~ 6 power savings simplification
• We are continuing to test commercial and other modulators
• Have demonstrated precise beam steering with
MEMS mirrors

27

[1] KK. Gan, F. Vasay, T Weidberg, “Lessons Learned and to be Learned from LHC”, Joint ATLAS-CMS Working Group on Opto-
Electronics for SLHC, ATL-COM-ELEC-2007-001 CMS-IN-2007/066
[2] Philippe Farthouat’s 2011 ATLAS upgrade talk
[3] T. Weidberg “VCSEL Reliability Studies and Development of Robust VCSEL Arrays” TWIPP 2011
[4] W. Fernando, “Overview and status of ATLAS pixel detector”, Nucl.Instrum.Meth., A596, 58-62 (2008)
[5] D. Giugni, S. Michal, R. Boyd, ATLAS PIXEL nSQP Project, ATL-IP-ES-0150
[6] Papotti et. al ,“An Error-Correcting Line Code for a HEP Rad-Hard Multi-GigaBit Optical Link”, 12th Workshop on
Electronics For LHC and Future Experiments, Valencia, Spain, 25 - 29, pp.258-262 (2006)
[7] Molex specifications
(http://www.molex.com/molex/products/family?key=fourteen_data_rate_fdr__active_optical_cable_aoc&channel=products&chanName=fa mily&pageTitle=Introduction&parentKey=fiber_optic_product_families)
[8] J. Gilmore, TMB Mezzanine SEU Testing - Preliminary Results (www.physics.ohiostate.edu%2F~gilmore%2Fcms%2Fregulators%2Fcyclotron_report_v2.ppt)
[9] W. Pascher et al., “Modelling and design of a travelling-wave electro-optic modulator on InP”, Opt. Quant. Electron., vol.
35(4), 453-464 (2003)
[10] R. A. Soref and B.R. Bennett , “Electrooptical Effects In Silicon”, J. Quantum Electron., 23, 123 (1987)
[11] M. Bruzzi, "Radiation damage in silicon detectors for high-energy physics experiments," Nuclear Science, IEEE
Transactions on , vol.48, no.4, pp.960-971, Aug 2001
[12] S.T. Liu et al., "Total dose radiation hard 0.35 μm SOI CMOS technology," Nuclear Science, IEEE Transactions on , 45(6),
2442-2449 (1998)
[13] F Vasey et al, “The Versatile Link common project: feasibility report”, JINST 7 C01075 (2012) doi:10.1088/1748-
0221/7/01/C01075
[14] HHI specifications (http://www.hhi.fraunhofer.de/en/departments/photonic-components/inp-modulators/)
[15] T. Pinguet et al. , "Monolithically integrated high-speed CMOS photonic transceivers," Group IV Photonics, 2008 5th
IEEE International Conference on , vol., no., pp.362-364, 17-19 Sept. 2008
[16] C. Gunn, et al., “A 40Gbps CMOS Photonics Transceiver”, Proceedings of SPIE 6477, 64770N (2007).
[17] BT Huffman et al.The Radiation Hardness of Certain Optical Fibres for the LHC Upgrades at -25C. JINST 2010 5 C11023.

References
RD23 Collaboration, “Optoelectronic Analog Signal Transfer for LHC Detectors”.
CERN/DRDC/91-41/DRDC/P31. CERN, Geneva 1991.
[PIXEL]W. Fernando, “Overview and status of ATLAS pixel detector”,. Nucl.
Instrum.Meth 2008; 58-62: A596.
[KK] K.K.Gan, W. Fernando, H. Kagan, R. Kass, A. Law et al, “Radiation-Hard
Optical Link for SLHC”. Nucl.Instrum.Meth,2008:88, 2008:88-92:A596.
L.S. Yan, Q.Yu, A.E.Willner (UCLA), "Simple Measurement of the Chirp Parameter of Optical Modulators Using Partial Optical Filtering", Optoelectronics and semiconductor integrated Devices, P2.28, IEEE.
[CHIRP] "Simple Measurement of the Chirp Parameter of Optical Modulators Using
Partial Optical Filtering", L.S. Yan, Q.Yu,
A.E.Willner (UCLA) Optoelectronics and semiconductor integrated Devices
P2.28 IEEE.
[LITHIUM] E.L. Wooton, et. al. (JDS Uniphase), ‘ “« A Review of Lithium Niobate
Modulators for Fiber-Optic Communications Systems ”, » ) IEEE Journal of
Selected Topics in Quantum Electronics, Vol.6 No1,(, (2000) S 1077-260X(260X
(00)01136-9.
[TIPP2011] W. Fernando, D. Underwood, R. Stanek, “Optical Data Links –
Technology for Reliability and Free Space Links”, Physics Procedia, TIPP11-D-
11-00045, (2012) to be published.

[DPF] W. Fernando, D. Underwood, R. Stanek “New Optical Link Technologies for
HEP Experiments”, Meeting of the Division of Particles and Fields of the American
Physical Society, Brown University, August, 2011 arXiv:1109.6842v1.
[IEEE] D. Underwood, P. DeLurgio, G. Drake, W. Fernando, D. Lopez, G. Drake, B.
SalvachuaFerrando, R. Stanek, “Development of Low Mass Optical Readout for High
Data Bandwidth Systems” IEEE Nuclear Science Symposium Conference Record
(NSS/MIC), 624-629, 2010.
[IBM]W. Green, M. Rooks, L. Sekaric, and Y. Vlasov “Ultra-compact, low RF power, 10
Gb/s silicon MachZehnder modulator”, Opt. Express 2007; 17106-17113:15.
[JINST] D. Underwood, B. Salvachua-Ferrando, R. Stanek, D. Lopez, J. Liu, J. Michel,
L. C. Kimerling, “New Optical Technology for low mass intelligent trigger and readout”,.
JINST 5:C07011,2010.
[InP] 40Gb/s InP Modulator ……………………………………… http://www.hhi.fraunhofer.de/fileadmin/hhi/downloads/PC/flyer/40_Gbits_InP_Web.pdf.
[PIC] I.Galysh, K.Doherty, J. McGuire, H.Heidt, D.Niemi,G.Dutchover, (The StenSat
Group) "CubeSat: Developing a Standard Bus for Picosatellites" http://www.stensat.org/Publications/SPIE.PDF
.
[FPGA] Z.K.Baker, M.E.Dunham, K.Morgan, M.Pigue, M.Stettler, P.Graham,
E.N.Schmierer, J.Power (Los Alamos) “Space Based FPGA Radio receiver Design,
Debug, and Development of a Radiation Tolerant Computing System”.International
Journal of reconfigurable Computing, Volume 2010,Article ID 546217, doi:10.1155/2010/546217.
30

The Future of Optical Links - Light Modulators
Commercial integrated optics chips are a promising form of modulators
Features -
Speed- 10 Gb/fiber commercial integrated optics
40 Gb/fiber with some commercial units
Laser reliability-
Either CW laser onboard (different junction structure than VCSELs)
Or displace laser outside detector.
Low Error Rate
10 -18 vs typical 10 -12 for current systems
Simplified error correction schemes
Low power
One CW laser - split many ways
Modulators are very efficient
Short electrical paths – no cable drivers
Low voltage drivers – not current drivers
Rad hard optical parts
We have thoroughly tested silicon integrated optics for 64 K rad application
Modulator parts should work at much higher levels
Optical part expected to work at multi-Mrad levels
31

 The commercial MEMS mirrors have ~40 dB resonance peaks at 1 and 3 KHz.
 To use the direct feedback, developed an inverse Chebyshev filter which has a notch at
1 kHz, and appropriate phase characteristics (Left Figure)
 With the filter we were able to make the beam follow a reflecting lens target within about 10 μm when the target moved about 1 mm (Right Figure).
 Still has some fundamental issues at large excursion (~1 cm)
 A separate feedback link solves this issue
The amplitude-frequency map of our analog feedback loop, demonstrating phase stability at
100 Hz.
April 10, 2020
32
A test setup used to demonstrate MEMS mirror steering with an analog control loop which compensates for the mirror resonances at 1 and 3 KHz.

Due to diffraction, there is an optimum diameter for a beam for a given distance in order to reduce 1/r 2 losses
 The Rayleigh distance acts much like Beta-Star in accelerators
– Relates waist size and divergence
– Depends on wavelength
 If we start with a diameter too small for the distance of interest, the beam will diverge, and will become 1/r 2 at the receiver, and we will have large losses (We can still focus what we get to a small device like an APD or PIN diode ). This is typical of space, Satellite, etc. applications.
 If we start with an optimum diameter, the waist can be near the receiver, and we can capture almost all the light and focus it to a small spot
 Examples, ~ 1 mm for 1 m, ~ 50 mm for 1 Km
33
April 10, 2020 33

 A system has been developed to test in a
Voltaire switch (model 4036) with continuous data flow
 Switch is fully populated (36 ports) and data is injected in each port at 40Gbps.
 Infiniband port counters are used to monitor the actual data flow and presence of errors
 Test is run at room temperature.
 Proven with a long term BER test on a random cable samples
 Tests proved that there is no noise floor