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100G/200G/400G相干光测试解决方案16 JULY 2018
High Speed Networks & Standards
Ethernet
40/100GbE
CFP
CEI VSR (25G)CAUI/XLAUI (10G)
Blade Servers
Router
Central Office
OIF CEI (19-28G)
Backplane, chip
10/40GbE
40/100GbE
100GbE
40GbE
To 40km
Roughly Speaking….
OIF: • Very long distances (100’s km)
• Very short distances (CEI, mm)
40/100G Ethernet:• Distances in between
coherent optical
lives here
OIF/ITULong Haul100G
City
100G Optical Long-Haul Block Diagram: Coherent Optical
3
Framer
+ HD
FEC
TX
FEC
DSP +
DAC
4x28 G
4x28 G
4x32G
Line Card Optical Transceiver
4x32G
QPSK or
QAM
x32G
QPSK or
QAM
x32G
QPSK/QAM
Coherent
Modulator
Coherent Rx 4:4
PHY
4:4
PHY4x32G
82 mm 41 mm 21 mm
CFP CFP2 CFP4
RX
ADC
DSP
FEC
Module content varies by implementation agreement
Metro and longhaul standard evolution
Speed per
CFP port
width
http://www.cfp-msa.org/
82 mm 41 mm 21 mm
CFP CFP2 CFP4
20 km 200 km 2000 km
Reach
QSFP28
100G SR4
100m
100
Gb/s
400
Gb/s
CFP2 ACO
PM QPSK
CFP2 ACO
PM 16QAM
200
Gb/sCFP2
100G ER4
127 mm (5x7”)
(Finisar)
5x7”
PM QPSK
IEEE
OIF PLL
CFP
PM QPSK
Italics = coming
soon
ACO = analog
coherent optics
CPAK
100G
ER4
Coherent Optical Networking
5
MARKET TRENDS
Coherent Optical Networking
6
KEY TECHNOLOGY TREND / INFLECTION POINT
200G module deployment
400G
400G systems available
400G/600G deployment
2017
2018
Late2018
Q4/2019
600G
Production shipment
Ciena, Acacia, Inphi, NTT Electronics
Inflection point
➢ Higher Baud rates➢ More symbols per Bit➢ Smaller footprint➢ Integration➢ Lower Power Consumption➢ Less Expensive Solutions
ModuleDeployment
ComponentProduction Equipment
Module R&DEquipment
Module ProductionEquipment
Module ProductionEquipment
Module ProductionEquipment
System ProductionEquipment
7
OVERVIEW – MODULATION FORMATS
10,000km
By encoding more bits into one analog symbol, higher order modulation formats increase capacity, but compromise on reach
Coherent Optical Networking
Mix and match with flexgrid
16 JULY 2018
Source: 400G White Paper; OIF contribution 2015.027
40 Gbaud8QAM
40 Gbaud8QAM
56 GbaudQPSK
56 GbaudQPSK
90 GHz (2 x 45)(100 GHz channel)
140 GHz (2 x 70)(150 GHz channel)
Also proposed:
Benefits of Coherent Signaling
9
•Higher Rx sensitivity
•Longer reach
•Lower power consumption
Local Oscillator
- signal amplification
•Optical link impairment correction in electrical DSP: PMD, CD, some nonlinear effects
Magnitude + Phase Detection
• Increase total data rate capacity over existing optical infrastructure
•Reduced electronic baseband bandwidth requirementsSpectral Efficiency
What is Coherent Optical Modulation?
Traditional 10G transmissions modulate the amplitude of the light,
a.k.a. or on-off keying (OOK). Direct detection is used in the receiver.
Coherent transmissions modulate the phase of the light, the
simplest case is phase shift keying.
OOK
On-Off Keying
1 bit/Baud (symbol)
By doubling the number of phase states, the bit/Baud rate is also doubled.
PSK
Phase Shift Keying
1 bit/Baud (symbol)
QPSK
Quadrature Phase Shift Keying
2 bits/Baud (symbol)
Optical Modulation Methods
0 1 0 1 1 0
0 1 0 1 1 0
Pure AM (OOK)
Pure PSK
11 5/12 52W-27502-2
Optical Modulation Methods continued
0 1 0 1 1 0
01 11 10 10 11 00
Typical BPSK
Typical QPSK
2-bits/ symbol
12 5/12 52W-27502-2
Optical Modulation Methods continued
01 11 10 10 11 00
011110101100
DP-QPSK
4-bits/symbol
QPSK
2-bits/ symbol
QPSK
2-bits/ symbol
13 5/12 52W-27502-2
What is Coherent Optical Modulation?
Rotating the polarization of one QPSK signal, and combining it with a second
QPSK signal, doubles the bits/Baud rate again.
DP-QPSK
Dual-Polarization QPSK
4 bits/Baud (symbol)π/2
Common Modulation Formats
Polarization Multiplexed QPSK Integrated Transmitter
16 3/2013 52W-27502-3
Intradyne + DSP Make It Work
17 3/2013 52W-27502-3
• Derr, 1992, PTL
Signal Spectra
LO
Without PLL, frequency and phase
error must be corrected in DSP
Integrated Dual Polarization IntradyneCoherent Receivers
18 3/2013 52W-27502-3
New OIF AgreementIA OIF2009.033.06
Replace input signals with reference signals
Replace ADC with real-time oscilloscope
Test overall:▪ Path gains▪ Cross talk▪ Phase anglesAt any frequency or wavelength
Coherent Detection
19 3/2013 52W-27502-3
Coherent System Building Blocks
16 JULY 2018
Data Source
Coherent Optical
Modulator
Coherent Receiver
A/Dlots of mathFiber optic cable
Electrical:4 data streams, “tributaries”, 1 each for X-I, X-Q, Y-I, and Y-Q
Original 4 tributaries finally recovered
Optical:All 4 tributaries into 2 polarizations of light on fiber cable
Electrical:4 waveforms
representing electric field on fiber cable
Not data!
Electrical:4 sampled
waveforms representing electric
field on fiber cableStill not data!
Because polarization of light is not fixed as it travels down the fiber optic cable, the signal that was originally the X-I tributary, may still be partially on X-I, but is likely also on X-Q, Y-I, and Y-Q!These 4 waveforms are not just the sampled original tributaries!
Imagine we replace the 4 AWGs with 4 APGs: Arbitrary Paint Generators, each generating a different color.
Each APG paints one quadrant of a ball.
As the ball travels down the hose it rotates arbitrarily.
Our “color detector” quadrants aren’t aligned
with the original colors or the ball. So each detector quadrant
receives some of each color.
Receiver signal processing
XIXQYQ YI
X0 X90 Y0 Y90
Front-End ImperfectionCompensation
Channel Impairment Equalization
Timing Recovery
Carrier Recovery
1. Deskew/NormalizationOrthogonality Compensation
3. Symbol Synchronization
2. CD Estimationand Compensation
4. PMD Compensationand Polarization Demux.
5. Carrier Frequency OffsetEstimation/Compensation
6. Carrier PhaseEstimation/Compensation
Structural Level Algorithmic Level
Source: 400G White Paper; OIF contribution OIF2015.204.03
Coherent System Building Blocks
16 JULY 2018
Data Source
Coherent Optical
Modulator
Coherent Receiver
A/Dlots of mathFiber optic cable
Electrical:4 data streams, “tributaries”, 1 each for X-I, X-Q, Y-I, and Y-Q
Original 4 tributaries finally recovered
Electrical:4 waveforms
representing electric field on fiber cable
Not data!
Electrical:4 sampled
waveforms representing electric
field on fiber cableStill not data!
Because polarization of light is not fixed as it travels down the fiber optic cable, the signal that was originally the X-I tributary, may still be partially on X-I, but is likely also on X-Q, Y-I, and Y-Q!These 4 waveforms are not just the sampled original tributaries!
This is why an O/E converter module in a sampling scope does not work with coherent signals and why a traditional BERT cannot be used for coherent optical BER testing.
Coherent System Building Blocks
16 JULY 2018
Data Source
Coherent Optical Transceiver
A/Dlots of math
Fiber optic cableTX
RXFiber optic cable
Refer to OIF
Intradyne + DSP Make It Work
25 3/2013 52W-27502-3
• Derr, 1992, PTL
Signal Spectra
LO
Without PLL, frequency and phase
error must be corrected in DSP
Understanding Electrical Bandwidth Requirements
• Square pulse (sin(fT)/(fT) shaped spectrum)
◦ “Capturing 5th harmonic” means >2.5 times baud rate
◦ Older NRZ standards required 0.75 times baud rate with specific roll-off shape
• Raised Cosine spectrum
◦ Bandwidth requirement is 0.5 times baud rate with specific roll-off or specified channel
◦ Total bandwidth requirement is (1+Alpha)*0.5*Baud_Rate
16 JULY 2018 26
Raised Cosine Square Pulsef0
Gbaud6-dB
BWTotal BW
α = 0.2Total BWα = 0.05
3-dB BW0.75*f0
5th Harmonic
32 16 19.2 16.8 24 80
64 32 38.4 33.6 48 160
80 40 48 42 60 200
Bandwidth Values in GHzTotal BW where spectrum goes to zero
Square
Pulse
f0 2f0 3f0
f0 2f0 3f0f0 = baud rate
Raised
Cosine
Measuring TX Constellation Imperfections: EVM
▪ Distance of a symbol point from the ideal location.
▪ Instantaneous or rms value
▪ Normalized to ideal symbol magnitude
▪ QAM EVM often normalized to largest symbol magnitude
EVMinst
m
xn
Re
Im
Key Differentiators of new Coherent System
1. Achieves the lowest EVM floor and lowest BER possible.
2. Future-proofed for 400G and beyond.
3. Minimizes the impact of test system connectivity on
coherent
measurements.
4. Customizable SW analysis and visualization for non-
standard
tests and applications.
Lowest EVM and BER
• EVM (Error Vector Magnitude) and BER are common coherent
optical quality measurements.
• Measurement systems inaccuracies in a coherent receiver system
can come from a number of different sources:
◦ OMA: IQ Phase Angle Errors
◦ OMA: IQ Gain Imbalance
◦ OMA: IQ Skew Errors
◦ OMA: XY Skew Errors
◦ Scope: cable length and quality
◦ Scope: sample rate and bandwidth
◦ Scope: noise floor
Lowest EVM and BER Measurement Floor
• EVM (Error Vector Magnitude) and BER are common coherent
optical quality measurements.
• Measurement systems inaccuracies in a coherent receiver system
can come from a number of different sources:
◦ OMA: IQ Phase Angle Errors
◦ OMA: IQ Gain Imbalance
◦ OMA: IQ Skew Errors
◦ OMA: XY Skew Errors
◦ Scope: cable length and quality
◦ Scope: sample rate and bandwidth
◦ Scope: noise floor
Can be removed with proper OMA calibration
Can be mitigated with proper test system connectivity.
For any given sample rate/BW, measurement accuracy boils down to scope noise floor.
Coherent Test System Building Blocks
PPG3204 32Gb/s Pattern Generator
AWG70001A Arbitrary
Waveform Generator
OM5110 Multi-format
Optical TransmitterOM4245 Optical Modulation
Analyzer
4
2
Fiber Optic 4– or –
DPS77004SX ATI Performance Oscilloscope
OM1106 Optical Modulation
Analysis Software
(Included with OM4245)
Coherent Signal
Generation
Coherent
Modulation/
Transmitter
Coherent
Receiver
Signal
Acquisition(scope)
Analysis
Software
Either the Transmitter or Receiver is typically replaced by the customer’s DUT.
Data Source
Coherent Optical Modulator (Tx)
Coherent Receiver
(Rx)A/D
lots of mathFiber optic cable
Signal Generation: PPG-Series
PPG benefits for coherent optical
• Up to 4 channels in a single instrument –
necessary for dual polarization for I and Q.
• Data rate up to 32Gb/s covers all 100G
test requirements.
• Very fast risetimes.
• Simple to set-up and use.
• Multi-level signals (such as 16QAM) can
be created using external devices
• $73k per channel in 4-channel instrument
(US list price).
32
PPG3204 Programmable Pattern
Generator
Sig GenTx Rx Scope SW
Signal Generation: AWG
AWG benefits for coherent optical
• Ability to customize waveform to
compensate for system losses.
• Ability to create impairments.
• Easier to create arbitrary multi-
level signals than PPG.
• Single-channel instrument
supports sample rate up to
50GS/s
33
Sig GenTx Rx Scope SW
AWG70001A Arbitrary Waveform
Generator
Tektronix Coherent Modulation Analysis Products
OM4245 45GHz Optical Modulation Analyzer$245,000
OM4225 25GHz Optical Modulation Analyzer $117,000
A.k.a. OMA (optical modulation analyzer), a.k.a. optical receiver
Optical-to-electrical converter for complex modulated signals
OM1106 Coherent Lightwave Signal Analyzer Software$51,800
Included with the OM4000-series products
OM2012 nLaser Tunable Laser Source $23,000Stand-alone laser source. Does not include SW orpolarization switch
OM2210 Coherent Receiver Calibration Source$26,900Stand-alone laser source w/software for generic receiver cal.
OM5110 46GBaud Multi-format Optical Transmitter$129,000
Coherent modulator with manual and automatic bias control
Oscilloscope Choices
• Real-time scope offers the
easiest system configuration,
but at a higher system cost
• Equivalent time scope offers
higher bandwidth and a lower
cost, but may not be practical
for all customers.
37
Sig GenTx Rx Scope SW
see Choosing an Oscilloscope
for Coherent Optical Modulation
Analysis for more information
Differences between ET systems and RT systems
38
Real-Time Systems Equivalent-Time Systems
Target Customers Often favored by Network Equipment Manufacturers and system integrators due to high RT sample rate and intradyne detection.
Often favored by optical component manufacturers due to very high vertical and time resolution. Homodyne detection is often fine.
Optical detection Intradyne – high sampling rate of RT scope allows frequency and phase tracking to be performed mathematically. No separate laser reference is required.
Homodyne – due to low sampling rate of ET scope a separate laser reference, split prior to the customer’s modulator, must be provided to allow proper frequency and phase tracking.
Vertical Resolution Determined by real-time scope vertical resolution. Determined by equivalent-time scope vertical resolution.
Maximum data rate With 33GHz RT scope: 60GbaudWith 20GHz RT scope: 40Gbaud
With 80E09: 60Gbaud (limited by OM4000)With 80E07: 60Gbaud (limited by 80E07)
Measurements available
All that are supported today. All supported today except for: PMD, laser freq. error, laser phase noise, true BER (equivalent BER may be supported)
System Price Largely affected by choice of real-time scope. Can be lower due to lower scope price.
Comparing Methods: Tek Advantage
39
Tektronix Architectural Innovation
Traditional Frequency Interleaving
✓ Improved SNR• Each ADC sees full
spectrum• Signal reconstruction
involves averaging improves SNR
✓ Signal-path symmetry
✓ Patented architecture
• Each ADC sees halfspectrum
• Signal reconstruction involves summation no improvement in SNR
Superior Noise Performance for High-Bandwidth Data Converters
LPF
Ou
tpu
t
DSP
Inp
ut
HF HF(mixed)
LF HFADC
ADC
(diplexer)
HF
LF
LF HF
(digitized)
LF LF
Superior Noise Performance
ADCLPF
LPF
LF
HF (out of phase)
LF
HF
LF HF
LF HF
LF HF
DSP
ADC
Ou
tpu
t
LF HF
Inp
ut
(sampled)
(sampled)
(digitized)
Sampler
Sampler
ATI Block
Future-Proofing Coherent Test
Many customers need to be able to test at 100G now, but can’t
afford to buy a completely new system in a few years for 400G.
100G(1 carriers of DP-QPSK)
400G (2 carriers of DP-16QAM)
400G (1 carrier of DP-16QAM)
Typical Baud Rate 28 – 32 GBaud 28 GBaud 56 GBaud
OMA & Scope BW required 23 GHz 44 GHz 44 GHz
Scope sample rate required 50 GS/s 100 GS/s 100 GS/s
Future-Proofing Coherent Test
The system can be
configured with a single
OMA + two 70kSX-series
scopes for 100G dual-
polarization R&D.
By switching scope inputs, the system can be used for single-polarization 400G signal.
Minimizing System Connectivity Impacts
Use case: 400G testing – 4x 70GHz scope channels
The DPO70000SX Series scopes have been designed to
be fully functional upside down permitting decreased
cable lengths.
Minimizing System Connectivity Impacts
Use case: 400G testing – 4x 70GHz scope channels
Tektronix arrangement of all ATI connectors in the center of the instrument allows the most compact connection possible to the receiver.
Quadrature gain and phase angles vs wavelength (old HRC)
17 JULY 2018
44
OM2210 Calilbration Source
Customizable SW Analysis and Visualization
The OM-Series User
Interface (OUI) provides a
complete coherent optical
software analysis suite.
The OUI is included with
all OM-series products.
It is also sold stand-alone
as OM1106.
Measuring TX Constellation Imperfections: Q-factor
Re
Im
▪ Counts errors as decision threshold is moved.
▪ Errors fitted to error function in “Q-space”
▪ → Plot, max-Q and optimum decision threshold
Measuring TX Constellation Imperfections: Phase Angle
Re
Im
Example: Modulator Bias Adjustment
Example: Adjusting Tributary Timing Skew
Measurements Available for QPSK Signals
Measurements Available for QAM Signals
20 G RZ DQPSK
One DC Module Being Compensated. CD = 900 ps/nm
2 CD Modules CD = 1700 ps/nm
55 3/2013 52W-27502-3
Full Automatically Measurements over 50+ items
• Optical Field◦ Wavelength range
◦ Polarization ER
◦ Laser phase noise
◦ PDL/ PMD/ CD
• Electrical Field
◦ Quadrature phase angle
◦ Constellation bias.
◦ Eye crossing points
◦ Std. dev. by quadrant
◦ I/Q skew
◦ Total skew
• System◦ Q-factor
56
Comprehensive Diagrams
57
Software Building Blocks
The OUI provides the user
interface and manages
interaction with scopes.
All signal analysis is executed in MATLAB.
Multiple Levels of Customization
Dynamic MATLAB
Integration
Through the
MATLAB Engine
Command
window, users
can dynamically
modify any
analysis
parameter or
function.
Multiple Levels of Customization
Custom
MATLAB Code
The high-level
“CoreProcessing”
analysis loop is
provided in
MATLAB source
code that users
can modify.
Multiple Levels of Customization
Custom MATLAB
Code
Many researchers,
both academic and
in R&D, want to
see the effects of
their own signal
processing
algorithms. The
OUI with it’s deep
customization
provides an
unprecedented
research platform.
Example Industry Approaches to 400G and Beyond
63
Sources: 1Beyond 100G, copyright 2012, Fujitsu Network Communications, Inc.2Dawn of the Terabit Age , copyright 2011, Infinera Corporation3Coherent Super-Channel Technologies, OSA Webinar , copyright 2011, Infinera Corporation4Super-Channels: DWDM Transmission at100Gb/s and Beyond, copyright 2012, Infinera Corporation51.5-Tb/s Guard-Banded Superchannel Transmission over 56× 100-km (5600-km) ULAF Using 30-Gbaud Pilot-Free OFDM-16QAM Signals with 5.75-b/s/Hz Net Spectral Efficiency, Alcatel-Lucent, Bell Labs
system rate# of
carriersmodulation
format
400 Gb/s1 2 DP-16QAM
500 Gb/s2 5 DP-QPSK
500 Gb/s3 10 DP-QPSK
1.0 Tb/s4 10 DP-QPSK
1.5 Tb/s5 8 DP-16QAM
87.5 GHz
400 Gb/s, 2 carriers
190 GHz 375 GHz
500 Gb/s, 10 carriers 1.0 Tb/s, 10 carriers1.5 Tb/s, 8 carriers
▪ No industry consensus on how to build super-channels – no one architecture fits all requirements.
▪ Vendors differ on characteristics as basic as carrier count and carrier spacing to what modulation format should be used.
Acquiring Super-Channels – Configuration
Example
• 4 Carrier Super-Channel
• Center frequencies
spaced at 35.5 GHz:
Channel 1: 193.9700 THz
Channel 2: 194.0055 THz
Channel 3: 194.0410 THz
Channel 4: 194.0765 THz
64
400G Multi-Carrier Super-Channel
Example: Spectrum of 4-Carrier Super-
Channel
65
Ch 1193.9700THz
Ch 2194.0055THz
Ch 3194.0410THz
Ch 4194.0765THz
Acquiring Super-Channels – Local Oscillator Tuning
• Coherent detection works
by combining the input
signal with a local
oscillator.
• The local oscillator
frequency determines the
center of the frequency
range that is detected.
• By sweeping the local
oscillator, different
frequency ranges can be
captured in sequence.
66
Acquiring Super-Channels – Local Oscillator Tuning
Example: Spectrum of 4-Carrier Super-Channel
Tune local oscillator to 1st carrier
capture 1st carrier with oscilloscope
Acquiring Super-Channels – Local Oscillator Tuning
Example: Spectrum of 4-Carrier Super-Channel
68
Re-tune local oscillator to 2nd carrier
capture 2nd carrierwith oscilloscope
Acquiring Super-Channels – Captured Spectrum
69
Acquiring Super-Channels – Digital Channel Filtering
70
Acquiring Super-Channels – Analyzing Results
Once channel filtering has
occurred, the traditional
coherent analysis on the
channel can occur
The results of all carriers can
be analyzed together:
• Numerical/Statistical
Measurements
• Constellation Diagrams
• Eye Diagrams
71
Acquiring Super-Channels – Analyzing Results
Once channel filtering has
occurred, the traditional
coherent analysis on the
channel can occur
The results of all carriers can
be analyzed together:
• Numerical/Statistical
Measurements
• Constellation Diagrams
• Eye Diagrams
72
Benefits of Multi-Carrier Scanning
• Achievable with current test and measurement technology
• Cost
• Inherently flexible
◦ No fixed grid
◦ No fixed modulation format
◦ No fixed number of channels
73
Channel equalization
• Existing OUI methodology is to measure any impairment and then
remove it if desired by applying an inverse filter
◦ Provides greatest physical insight since nothing is hidden
◦ Depends on measurement accuracy and system stability
◦ Often does not yield the lowest possible EVM
• New Feature
◦ A set of FIR filters are optimized to minimize EVM
◦ The filters may be updated for each data acquisition to accommodate
a changing system
◦ Decision Directed LMS
◦ Cascaded Multi-modulus Algorithm
◦ Can compensate for Polarization Mode Dispersion (PMD)
◦ Can compensate for most frequency domain effects including TX and
RX frequency response, limited by number of taps in filters.
17 JULY 2018
More Customized
TEKTRONIX CONFIDENTIAL 75