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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
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Introduction/Motivation
The network architecture
The electroabsorption modulator – Principle
of operation
Results - Static Measurements
Results - Dynamic Measurements
Conclusion
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Introduction/Motivation
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LHC upgrade:
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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
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Link Requirements
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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
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<1km
Splitting ≥1:16
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Upstream Transmission
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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
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Downstream Transmission
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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
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Network Architecture
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Downstream simple and
similar to current TTC
broadcast system
Bidirectional architecture,
using single fiber for US
and
DS
transmission
meeting
data
rate
requirements
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Electroabsorption Modulator – Principle of
Operation
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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
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-3
-4
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Static Response (T(V)) (dB)
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-6
-7
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-9
-10
-11
-12
0
0.5
1
1.5
2
2.5
Reverse Bias (V)
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3.5
4
8
Static Response and Wavelength
Reverse Bias Voltage (V)
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Maximum
achievable
extinction ratio shows a
maximum at ~1545 nm:
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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
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1510nm
-4
1520
1540
1560
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1580
1600
1620
1640
Required Voltage Swing (V)
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-2
Static Response T(V) (dB)
Important trends with
increasing wavelength:
Extinction Ratio (dB)
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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
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Extinction Ratio Power Penalty Vs.
Temperature
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The extinction ratio power penalty was
calculated for two cases:
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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
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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)
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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)
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Dynamic Measurements at 1545 nm –
Estimated BER Vs Average Power
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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
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Q Value
8
10
-16
8.5
10
9
9.5
10
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Estimated BER
7.5
-22
10
10.5
-17
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-12
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Average Received Power (dBm)
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10
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Conclusion
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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
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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
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Backup slide - Sources of power
penalty
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Discussed in this presentation:
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Extinction Ratio
Reflections
Relative Intensity Noise
Not discussed in this presentation:
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Dispersion (not source of major power penalty)
Chirping (not source of major power penalty)
Modal Noise (irrelevant)
Mode partition noise (irrelevant)
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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
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Budget
19.6 – 10log(N) –
αREAM,ins – αPen,US
Power Margin
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20.3 – 10log(N) –
αPen,US
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Backup Slide: Extinction ratio power penalty
and choice of optimum wavelength
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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
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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)
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Backup slide - Saturation/Optical input power
and maximum absorption
• Maximum absorption variation <1dB
• Input optical power dynamic range (>10dB)
much higher than the required
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Backup slide - Noise Measurements
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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)
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Backup slide - Impact of Relative Intensity
Noise
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For Q=9, RIN=145dB/Hz, RIN power penaly
~0.1dB (negligible)
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Backup slide - Impact of reflections
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Can affect system performance through the
following mechanisms:
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Beating of signal and reflections at the receiver
Cavity formation
Disturbance of laser diode operation
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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
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Wavelength (nm)
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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
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-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)
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Backup slide - Possible implementation –
Front- and back-end
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Laser diode depicted:
3cm(length)x1.5cm(wid
th)
Circulator
depicted:
5.5mm(diameter)x80m
m(length)
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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