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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

CEI VSR (25G)CAUI/XLAUI (10G)

Blade Servers

Router

Central Office

OIF CEI (19-28G)

Backplane, chip

10/40GbE

40/100GbE

100GbE

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

100G Optical Long-Haul Block Diagram: Coherent Optical

Framer

4x28 G

Line Card Optical Transceiver

QPSK or

QPSK/QAM

Coherent

Modulator

Coherent Rx 4:4

PHY4x32G

82 mm 41 mm 21 mm

CFP CFP2 CFP4

Module content varies by implementation agreement

Metro and longhaul standard evolution

Speed per

CFP port

http://www.cfp-msa.org/

82 mm 41 mm 21 mm

CFP CFP2 CFP4

20 km 200 km 2000 km

QSFP28

100G SR4

CFP2 ACO

PM QPSK

CFP2 ACO

PM 16QAM

Gb/sCFP2

100G ER4

127 mm (5x7”)

(Finisar)

5x7”

PM QPSK

OIF PLL

PM QPSK

Italics = coming

ACO = analog

coherent optics

Coherent Optical Networking

MARKET TRENDS

KEY TECHNOLOGY TREND / INFLECTION POINT

200G module deployment

400G systems available

400G/600G deployment

Late2018

Q4/2019

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

System ProductionEquipment

OVERVIEW – MODULATION FORMATS

10,000km

By encoding more bits into one analog symbol, higher order modulation formats increase capacity, but compromise on reach

Mix and match with flexgrid

16 JULY 2018

Source: 400G White Paper; OIF contribution 2015.027

40 Gbaud8QAM

56 GbaudQPSK

90 GHz (2 x 45)(100 GHz channel)

140 GHz (2 x 70)(150 GHz channel)

Also proposed:

Benefits of Coherent Signaling

•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.

On-Off Keying

1 bit/Baud (symbol)

By doubling the number of phase states, the bit/Baud rate is also doubled.

Phase Shift Keying

1 bit/Baud (symbol)

Quadrature Phase Shift Keying

2 bits/Baud (symbol)

Optical Modulation Methods

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

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

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

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.

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

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

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

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

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).

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

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.

see Choosing an Oscilloscope

for Coherent Optical Modulation

Analysis for more information

Differences between ET systems and RT systems

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

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

HF HF(mixed)

LF HFADC

(diplexer)

(digitized)

Superior Noise Performance

ADCLPF

HF (out of phase)

(sampled)

(digitized)

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

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

▪ 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

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

Comprehensive Diagrams

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.

Custom

MATLAB Code

The high-level

“CoreProcessing”

analysis loop is

provided in

MATLAB source

code that users

can modify.

Custom MATLAB

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

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

400G Multi-Carrier Super-Channel

Example: Spectrum of 4-Carrier Super-

Channel

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.

Example: Spectrum of 4-Carrier Super-Channel

Tune local oscillator to 1st carrier

capture 1st carrier with oscilloscope

Example: Spectrum of 4-Carrier Super-Channel

Re-tune local oscillator to 2nd carrier

capture 2nd carrierwith oscilloscope

Acquiring Super-Channels – Captured Spectrum

Acquiring Super-Channels – Digital Channel Filtering

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

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

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

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

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