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A Network Architecture for Bidirectional Data Transfer in HighEnergy Physics Experiments Using Electroabsorption Modulators PAPADOPOULOS, S. 1 ,2 , DARWAZEH, I. 2, DETRAZ, S. 1, PAPAKONSTANTINOU, I. 2, SIGAUD, C. 1, SOOS, C. 1, STEJSKAL, P. 1, STOREY, S. 1, TROSKA, J. 1, VASEY, F. 1 1 European Organisation for Nuclear Research – CERN, 2 University College London Presentation Overview Introduction/Motivation The network architecture The electroabsorption modulator – Principle of operation Results - Static Measurements Results - Dynamic Measurements Conclusion 29/09/2011 Topical Workshop on Electronics for Particle Physics 2011 2 Introduction/Motivation LHC upgrade: 29/09/2011 Higher data rate required Provides framework to explore new technologies and increase infrastructure efficiency Use of low mass, low power consumption, radiation resistant components as frontend devices very important Topical Workshop on Electronics for Particle Physics 2011 3 Link Requirements A bidirectional link, transferring information to and from the detector over the same fiber would offer a more efficient infrastructure Information transferred over current TTC and data readout links could be transferred over single, unified infrastructure Unconventional requirements (highly asymmetric, upstream-intensive) compared to commercial networks (e.g. PONs) Requirements for the upgraded optical links Upstream Rate/link Detector) Data 10Gbps (From Downstream Data 1Gbps -broadcast Rate (To Detector) Link Length Target Ratio 29/09/2011 <1km Splitting ≥1:16 Topical Workshop on Electronics for Particle Physics 2011 4 Upstream Transmission Use of Reflective Electroabsorption Modulators (REAMs) to transmit data upstream (from detector to counting room) REAMs probably radiation hard – as indicated by the results of RD-23 REAMs potentially consume less power (intrinsic device power consumption <1mW Vs. 10s of mW for VCSELs) Upstream unknown component and system issues Investigate feasibility 29/09/2011 Topical Workshop on Electronics for Particle Physics 2011 5 Downstream Transmission Use of different wavelengths for upstream and downstream to achieve bidirectionality over single fiber Simultaneous transmission of data and information currently transferred over TTC network 29/09/2011 Topical Workshop on Electronics for Particle Physics 2011 6 Network Architecture Downstream simple and similar to current TTC broadcast system Bidirectional architecture, using single fiber for US and DS transmission meeting data rate requirements 29/09/2011 Topical Workshop on Electronics for Particle Physics 2011 7 Electroabsorption Modulator – Principle of Operation Electroabsorption Modulators absorb light according to the electric field across the device Static Response: the ratio of the output light intensity over the input light intensity expressed as a function of the externally applied bias voltage The static response can be used to determine the maximum achievable extinction ratio – Extinction Ratio: P(“0”)/P(“1”) – which can have a significant effect on system performance The static response depends on input light wavelength and device temperature 29/09/2011 -3 -4 -5 Static Response (T(V)) (dB) -6 -7 -8 -9 -10 -11 -12 0 0.5 1 1.5 2 2.5 Reverse Bias (V) Topical Workshop on Electronics for Particle Physics 2011 3 3.5 4 8 Static Response and Wavelength Reverse Bias Voltage (V) Maximum achievable extinction ratio shows a maximum at ~1545 nm: Insertion loss decreases Static response minimum moves to higher voltage Hence proper laser can be selected Required voltage swing to achieve maximum extinction ratio is ~2V at 1545nm 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8 3 3.2 3.4 3.6 3.8 1520nm -6 1530nm -8 1540nm 1550nm -10 1560nm -12 1570nm -14 1580nm -16 1640nm -18 9 5 8 4 7 3 6 2 5 1 4 0 3 -1 2 -2 1 -3 0 1500 29/09/2011 1510nm -4 1520 1540 1560 Topical Workshop on Electronics for Particle Physics 2011 1580 1600 1620 1640 Required Voltage Swing (V) -2 Static Response T(V) (dB) Important trends with increasing wavelength: Extinction Ratio (dB) 0 -4 9 Static Response and Temperature • Increasing temperature leads to: – Increase of insertion loss – Decrease of the reverse bias voltage level at which the static response minimum occurs – Slight increase of the maximum extinction ratio Measurement at 1550 nm • Device is temperaturesensitive • In commercial applications use of TEC is an appropriate solution • Not in our application – mass and power increase 29/09/2011 Topical Workshop on Electronics for Particle Physics 2011 10 Extinction Ratio Power Penalty Vs. Temperature The extinction ratio power penalty was calculated for two cases: When optimum modulation voltage levels are used at different temperatures (i.e. there is a voltage adaptation mechanism) When fixed modulation voltage levels are used at different temperatures (i.e. no adaptation mechanism) There is a significant increase in the extinction ratio power penalty for high temperature variation Temperature variations of the order of ~5oC can be easily accommodated 29/09/2011 Topical Workshop on Electronics for Particle Physics 2011 11 Dynamic Measurements at 1545nm – Eye Diagrams at 10Gbps Q=(I1 –I0 )/(σ1+σ0) Optical eye diagram, Q=7 (received power=-9.3dBm, equivalent BER=10-12) Optical eye diagram, Q=9 (received power=-7.9dBm, equivalent BER=10-20) 29/09/2011 Topical Workshop on Electronics for Particle Physics 2011 12 Dynamic Measurements at 1545nm – Eye Diagrams at 10Gbps Electrical eye diagram, Q=7 (received power=-16.4dBm, equivalent BER=10-12) Electrical eye diagram, Q=9 (received power=-13.5dBm, equivalent BER=10-20) 29/09/2011 Topical Workshop on Electronics for Particle Physics 2011 13 Dynamic Measurements at 1545 nm – Estimated BER Vs Average Power The required average power to achieve BER=10-12 is Prec=16.4dBm (launched power: -6.6dBm) Using a 10dBm DFB laser would allow us achieving a 1:16 splitting ratio (possibly even 1:32, depending on Rx) 6.5 10 10 7 10 10 -10 -11 -12 -13 Q Value 8 10 -16 8.5 10 9 9.5 10 -19 Estimated BER 7.5 -22 10 10.5 -17 29/09/2011 -16 -15 -14 -13 -12 -11 -10 Average Received Power (dBm) -9 10 -8 Topical Workshop on Electronics for Particle Physics 2011 -25 14 Conclusion A new architecture for bidirectional data transfer in the HL-LHC has been presented Use of Reflective Electroabsorption Modulators – possible advantages in terms of radiation hardness and power consumption – at the front-end Efficient use of resources 10Gbps transmission has been experimentally verified Radiation hardness tests to be carried out in the near future (order for samples has been already placed) Simultaneous operation of REAM as a Tx and Rx to be investigated 29/09/2011 Topical Workshop on Electronics for Particle Physics 2011 15 Backup slide - Main theme of presentation We would like to have maximum “distance” between “0” and “1”, affected by => received power, extinction ratio We would also like to minimize noise standard deviation, affected by => thermal noise, relative intensity noise, reflection-induced noise 29/09/2011 Topical Workshop on Electronics for Particle Physics 2011 16 Backup slide - Sources of power penalty Discussed in this presentation: Extinction Ratio Reflections Relative Intensity Noise Not discussed in this presentation: 29/09/2011 Dispersion (not source of major power penalty) Chirping (not source of major power penalty) Modal Noise (irrelevant) Mode partition noise (irrelevant) Topical Workshop on Electronics for Particle Physics 2011 17 Backup slide - Link budget calculations Upstream Link Budget Calculations Quantity Seeding Power Value Source 7 dBm Downstream Calculations Link Quantity Value Transmitter Power 0 dBm Receiver Sensitivity -19 dBm Overall Fiber Loss 0.4 dB Receiver Sensitivity Connector Loss 2 dB Overall Fiber Loss 0.2 dBm Splitting Loss 1+10log(N) Connector Loss 2 dB Filter Loss 1.5 dB Splitting Loss 1+10log(N) Circulator Losses 1.5 dB Filter Loss 0.75 dB Circulator Losses 0.75 dB REAM Loss Insertion 3.5 dB dB<αREAM,ins<5 Power Margin -25 dBm Power Penalties – αPen,DS Downstream Power Penalties – αPen,US Upstream 29/09/2011 Budget 19.6 – 10log(N) – αREAM,ins – αPen,US Power Margin Topical Workshop on Electronics for Particle Physics 2011 20.3 – 10log(N) – αPen,US 18 Backup Slide: Extinction ratio power penalty and choice of optimum wavelength There is a relatively wide wavelength region where the overall power penalty caused by the imperfect extinction ratio and the insertion loss is stable 1545 nm has been judged to be a good compromise between low required voltage swing and optimum overall power penalty 29/09/2011 Topical Workshop on Electronics for Particle Physics 2011 19 Backup slide - Static response and polarization • Polarization sensitivity at 1545 nm has been measured • Maximum extinction ratio difference 1 dB (ignored in the rest of the document) 29/09/2011 Topical Workshop on Electronics for Particle Physics 2011 20 Backup slide - Saturation/Optical input power and maximum absorption • Maximum absorption variation <1dB • Input optical power dynamic range (>10dB) much higher than the required 29/09/2011 Topical Workshop on Electronics for Particle Physics 2011 21 Backup slide - Noise Measurements Optical head thermal noise (BW=30GHz): 10.50uW Electrical head thermal noise (BW=20GHz): 260uV Electrical head + 10G PIN Diode: 780.5uV PIN diode induced thermal noise: 735.8uV Equivalent optical thermal noise:2.9uW Overall “Conversion efficiency” (measured by comparing optical and electrical noise): ~265V/W Implied receiver sensitivity (Q=7): -14dBm Tunable laser relative intensity noise: ~ -146dB/Hz Insertion of REAM between tunable laser and scope did not lead to noise increase (no shot noise added+no reflection-induced performance degradation) 29/09/2011 Topical Workshop on Electronics for Particle Physics 2011 22 Backup slide - Impact of Relative Intensity Noise For Q=9, RIN=145dB/Hz, RIN power penaly ~0.1dB (negligible) 29/09/2011 Topical Workshop on Electronics for Particle Physics 2011 23 23 Backup slide - Impact of reflections Can affect system performance through the following mechanisms: 29/09/2011 Beating of signal and reflections at the receiver Cavity formation Disturbance of laser diode operation Topical Workshop on Electronics for Particle Physics 2011 24 Backup slide - Impact of reflections Bragg grating reflectivity vs wavelength Reflectivity Vs Wavelength 15 15 53 53 15 .1 53 15 .2 53 15 .3 53 15 .4 53 15 .5 53 15 .6 53 15 .7 53 15 .8 53 .9 15 15 54 54 15 .1 54 15 .2 54 15 .3 54 15 .4 54 15 .5 54 15 .6 54 15 .7 54 15 .8 54 .9 15 55 0 Fraction of power reflected (dB) -5 -10 -15 -20 -25 -30 -35 -40 Wavelength (nm) 29/09/2011 Topical Workshop on Electronics for Particle Physics 2011 25 25 Backup slide - Impact of Reflections Q-Penalty Vs Reflectivity 9 8 Q-Value Difference 7 6 5 4 3 2 1 -0 .1 5 -8 .7 -1 5 0. 6 -1 3 1. 0 -1 5 3. 0 -1 5 5. 5 -1 5 8. 8 -2 5 0. 0 -2 5 3. 3 -2 5 3. 4 -2 5 5. 7 -2 5 7. 2 -2 5 7. 4 -2 5 9. 1 -2 5 9. 9 -3 5 0. 4 -3 5 0. 5 -3 5 1. 9 -3 5 3. 9 -3 5 6. 25 0 Reflectivity (dB) 29/09/2011 Topical Workshop on Electronics for Particle Physics 2011 26 26 Backup slide - Possible implementation – Front- and back-end Laser diode depicted: 3cm(length)x1.5cm(wid th) Circulator depicted: 5.5mm(diameter)x80m m(length) 29/09/2011 Topical Workshop on Electronics for Particle Physics 2011 27 9 5 8 4 7 3 6 2 5 1 4 0 3 -1 2 -2 1 -3 0 -4 1510 1520 1530 1540 1545 1550 1555 1560 1570 1580 1640 Wavelength (nm) Required Voltage Swing (V) Extinction Ratio (dB) Graphs