Troubleshooting Coherent Optical Communication Systems

1. Troubleshooting Coherent Optical
Communication Systems
Created by:
Michael Koenigsmann
Application Specialist
Digital & Photonic Test Division
May 18th 2015
© 2015 Keysight Technologies
Presented by:
Rodrigo Vicentini
Applications Engineering Manager
Latin America Region

2. Agenda
• Market and Technology Trends
• Coherent Measurement Challenges
• Typical Tests in Coherent Transmission Systems
• Typical Impairment Emulation in the electrical Domain
• Tools to generate signals for Coherent Optical Applications
• References

3. Market and Technology Trends
Drivers for higher Datarates

4. Page 4
Troubleshooting
Coherent Optical
Comms Systems
Market and Technology Trends
Big Data Demand drives Technology Changes
Challenges:
• Transmission demand exceeds system capacity
• Cost-effective increase of capacity
• Pressure to release new technology on time
To maximize transmission within Phy layer, combine & optimize
all dimensions for efficiency, cost, power, reach, reliabiliy etc.
• Mobile apps and services,
• high resolution devices,
• Internet of Things
drive
high speed I/O, network and data center traffic
Modulation
SymbolRate
Multi level signaling
in digital links,
e.g. C-Phy, PAMx
Parallel lines, subcarrier density
Polarization Mux, OFDM, DMT
Amplitude & Phase
modulation in optical links
e.g. QPSK, QAMx
Maximize Bits per Symbol
Increase Symbol Rate
32 GBd and beyond
Nyquist fs > 2 x fmax
Rule of thumb:
sampling rate = 2.5x Signal BW
Maximize # of carriers
By 2020 there will be around 20 Billion
devices connected to the Internet
© 2015 Keysight Technologies

5. Page
Maximize Transmission within Physical Layer
Troubleshooting
Coherent Optical
Comms Systems
Different techniques…
Motivation
Higher Order Modulation Formats  OFDM
From OOK to Coherent Detection
Time-Domain Pulse Shaping
Polarization Division Multiplex
4
© 2015 Keysight Technologies

6. Page
Application Requirements
Troubleshooting
Coherent Optical
Comms Systems 6
Coherent Optical Communication
• Requirements for a test instrument:
• Flexibilty to address different modulation schemes
• Clean signal to test your device and not your instrument
• Bandwidth at least 20 GHz
• 4 sychronized channels to support dual polarization (= 2 pairs of I/Q signal)
QPSK QAM128 OFDM
Need higher data throughput: 100 G  400 G  1 Tbit/s
© 2015 Keysight Technologies

7. Page
Emulate Optical Distortions in the Electrical Space
7
Pattern
Gen
RefTx or
golden
Line Card
Error
Detector
Network or
Test Bed
DUT
(100/400G
Rx)
AWG
DUT
(DSP)
ADC
ADC
ADC
ADC
Digital Coherent Receiver DSP Test
Error
Detector
DUT
(100/400G
Tx)
AWG
- or -
Traditional setup
Test setup with AWG
Deterministic and precise testing with complex impairments
e.g. Phase Noise, OSNR, Polarization, PMD
Troubleshooting
Coherent Optical
Comms Systems
OSNR
Gen.
DUT
(100/400G
Rx)
AWG
Error
Detector
E/O
- or -
© 2015 Keysight Technologies

8. Page
AWG’s in Coherent Optical Applications
– Endless modulation formats for higher data throughput
– Generates clean signals at 32 GBd and beyond
– Provides 4 independent analog outputs for dual-polarization
optical applications
• Uses out of the box and in-situ calibration to achieve a clean signal at
the device under test
• Emulate optical distortions in the electrical space
8
Cost-effective increase in capacity
16 QAM at 32 GBd with < 4% EVM
QPSK Signal
with added
phase noise;
emulating a
2 MHz laser
line width
Troubleshooting
Coherent Optical
Comms Systems
Optical
Modulation
Generator TooI
© 2015 Keysight Technologies

9. Coherent Measurement Challenges
• Clean Signal generation (electrical & optical)
• Clean Signal at defined test points
• High datarates 32 GBd and beyond
• Accurate and Repeatable Test Signals
• Distortion Emulation
• Flexible Modulation Formats

10. Page
Accurate and Repeatable Test Results
Out-of-the-box calibration ensures clean signal at the frontpanel connector
In-situ calibration – extend clean signal to the receiver test point
• S-Parameters of channel are embedded or de-embedded
• Frequency/Phase response is measured in-system and
then de-embedded
11
QPSK, 32 GBd PRBS 6 Gbit/s
Without correction With correction Without correction With correction
Troubleshooting
Coherent Optical
Comms Systems
© 2015 Keysight Technologies

11. Page
Out-of-the Box Calibration & In-situ calibration
Pre-distortion techniques for frequency and phase response compensation
12
AWG
Optionally: optimize the
second I/Q pair at the same time Troubleshooting
Coherent Optical
Comms Systems
or
iqtools
Optical
Modulation SW
phase and
frequency response
data
I/Q I/Q
Vector Signal Analysis (VSA) software
to determine frequency and phase response
Infiniium Series
Oscilloscope
© 2015 Keysight Technologies

12. Page
In-situ-calibration
13
End-to-end equalization
Measure frequency/phase response as determined by the coherent receiver
 End-to-end calibration of the whole transmission system
 This includes the characteristic of the receiver as well !
Troubleshooting
Coherent Optical
Comms Systems
M8195A
I
Y-Polarization
Q
I
Q
X-Polarization
π/2
π/2
Tunable Laser
N4391A or N4392A
AWG
MZMAmplifiers
Coherent
Receiver
Optional Fiber &
Optical Amplifiers
Optical Modulation
Generator Tool phase and
frequency response
data
© 2015 Keysight Technologies

13. Typical Tests in
Coherent Transmissions
© 2015 Keysight Technologies

14. Page 15
Test application: system and link stress test
TX
electronic
IQ
Mod.
Carrier
Laser
ROADM
WSS
Optical
Coherent
IQ det.
RX
Signal
Processing
LO
Laser
Typical test requirements:
 BER (EVM) vs. Power or OSNR
 Spectral behavior over 1-2 neighbor channels
 Signal integrity along the link (time domain modulation analysis)
 Nonlinear characteristics (PMD, PDL, CD,…)
N4391A or N4392A
Troubleshooting
Coherent Optical
Comms Systems
15
ROADM – Reconfigurable Optical Add-Drop Multiplexer
WSS - Wavelength Selective Switching
© 2015 Keysight Technologies

15. Page 16
Test application: Rx stress test (optical)
Multi-format Reference Transmitter or
optical AWG with or without stress generation
M8195A + OMFT + Tunable Laser
+ Optical Modulation Gen. Tool
Optical
Coherent
IQ det.
RX
Signal
Processing
LO
Laser
Stress generation
on Optical Signal
- Loss
- Polarization
- PMD
- OSNR
- Non-Linearities
Troubleshooting
Coherent Optical
Comms Systems
16
© 2015 Keysight Technologies
Typical requirements:
 Availability of numerous modulation formats for research and development
 High quality PAMx, (D)QPSK and QAMx signal for manufacturing
 Arbitrary constellations for advanced research required (arbitrary stress)
 BER vs various stress parameters
 Some customers need RZ DQPSK
 Support of up to 56 GBd rates for >> 100G research
 PRBS test pattern, Pre-defined or User-defined
 Test of receiver algorithm robustness with distorted signals

16. Page 17
Test application: Rx stress test (electrical)
Typical requirements:
 Availability of numerous modulation formats for research and development
 High quality PAMx, (D)QPSK and QAMx signal for manufacturing
 Arbitrary constellations for advanced research required (arbitrary stress)
 BER vs various stress parameters
 Some customers need RZ DQPSK
 Support of up to 56 GBd rates for >> 100G research
 PRBS test pattern, Pre-defined or User-defined
 Test of receiver algorithm robustness with distorted signals
Multi-format Reference Transmitter or
optical AWG with or without stress generation
M8195A + OMFT + Tunable Laser
+ Optical Modulation Gen. Tool
Optical
Coherent
IQ det.
RX
Signal
Processing
LO
Laser
Stress generation
on Optical Signal
- Loss
- Polarization
- PMD
- OSNR
- Non-Linearities
Stress generation
on Electrical Signal
- Loss
- Polarization
- PMD
- OSNR
- Non-Linearities
Troubleshooting
Coherent Optical
Comms Systems
17
M8195A +
Optical Modulation Gen. Tool
© 2015 Keysight Technologies

17. Page 18
Test application: IQ modulator
Typical test requirements:
 Cut-off frequency for each path
 In-application test to specify best EVM and other measures
 Polarization behavior
 Phase Response, Skew
 Modulator Bias Control
Multiformat TX
DAC electrical output !
Analysis of
modulation quality and
polarization behaviour
Frequency response
of modulator
TX
electronic
IQ
Mod.
Carrier
Laser
I
Y-Polarization
Q
I
Q
X-Polarization
π/2
π/2
Tunable
Laser
M8195A + Tunable Laser
+ Optical Modulation Gen. Tool
LCA
N4391A or N4392A
Troubleshooting
Coherent Optical
Comms Systems
18
© 2015 Keysight Technologies

18. Page
Troubleshooting
Coherent Optical
Comms Systems 19
Typical Measures Indication
EVM & Q-Factor General figure of merit for Signal Quality
EVM percentile
Signal Quality w/o the effect of IQ Gain Imbalance
and Quadrature Error
IQ Gain Imbalance Different amplitudes for I- and Q-Signal
IQ Skew Timing skews between I- & Q-Signal
IQ Offset Wrong bias setting or DC offset at modulator
Quadrature Error
IQ phase shifter, wrong bias point of 90 º phase
shifter
Frequency Error Carrier Frequency Offset between Tx & Rx, EVM
Symbol Rate Error, V-shape in ErrorVector vs Time Mismatch in Symbol Rate between Tx and Rx
Dual Pol: IQ Skews, X-Y Skew & X-Y Imbalance Skew & Gain differences between Polarizations
Bit Error Results
Indentify Bit Errors per Polarization or across
Polarization
Missing Transitions in Constellation De-correlation issue between I- & Q-Signal
Coherent testing
Typical Measures
© 2015 Keysight Technologies

19. Page
EVM & Q-Factor
20
Troubleshooting
Coherent Optical
Comms Systems
Error Vector
connects the measured
Vector and the expected
vector, Error Vector
Magnitude or EVM is
magnitude of this vector
EVM Q-factor
1% ~ 100
2% ~ 50
5% ~ 20
10% ~ 10
The Q-Factor describes the signal-to-noise ratio at the
decision points. It is calculated from the EVM. The
formula is proportional to 1/EVMa and the result is
converted into dB. It is calculated from the Eye-Diagram
aEVM
1
Q 
© 2015 Keysight Technologies

20. Page
EVM percentile
21
Troubleshooting
Coherent Optical
Comms Systems
EVM_pctl
EVM_pctl defines the radius of a
circle around a group of measured
constellation points centered at
the reference constellation point.
In contrast to EVM_pctl, the
classical EVM value from the VSA
software includes I-Q Imbalance
and Quadrature Error and is a
RMS averaged value.
The “Hit Ratio” multiplied with the
number of points is equal to the
number of points outside the
circle.
For Gaussian Noise dominated
impairments, the classical EVM
and the EVM_pctl are equal if a
“Hit Ratio” of 0.3173 is selected.
The "Hit Ratio" can be set in the
EVM_percentile algorithm of the
OMA Software.
© 2015 Keysight Technologies
Constellation
Reference
EVM_pctl

21. Page
IQ Gain Imbalance
22
Troubleshooting
Coherent Optical
Comms Systems
IQ Gain Imbalance
compares the amplitude
of the I signal with the
amplitude of the Q signal
and shows the difference
in dB.
The effects of IQ gain
imbalance are best viewed
in constellation diagrams
where the width of the
constellation diagram is
different than its height.
 Rectangular shape of
constellation, different
amplitudes in I- and Q-Eye
© 2015 Keysight Technologies

22. Page
IQ Skew
23
Troubleshooting
Coherent Optical
Comms Systems
IQ Skew
Timing skew between
I- and Q-signals
 distorted IQ Plot, Eye-
Diagrams are shifted
with respect to each
other
 45° transitions open up
 Increased EVM
© 2015 Keysight Technologies

23. Page
IQ Offset
24
Troubleshooting
Coherent Optical
Comms Systems
IQ Offset
DC offsets at the I- or the
Q-Signals cause I/Q or
origin offsets as shown.
I/Q offsets can also result
in carrier feedthrough.
It is a measure for the shift
between the origin of the
measured constellation
with regard to the origin of
the reference constellation
(yellow).
Without DC offsets, the
carrier feed through as well
as the IQ offset becomes
zero (-infinity dB).
 Vertically shifted Eye-
Diagram traces
 Carrier Feedthrough
 EVM
carrier feed through
Individual
I- and Q-
Imbalance
available
© 2015 Keysight Technologies

24. Page
Quadrature Error
25
Troubleshooting
Coherent Optical
Comms Systems
Quadrature Error
indicates the orthogonal
error between the I and Q
Quadrature-Phase.
Ideally, I and Q should be
orthogonal (90 degrees
apart). In the screenshot to
the right a quadrature error
of 22.91 degrees means I
and Q are 67,09
degrees apart instead of 90
degrees.
This could result from
wrong bias point setting for
the 90° phase shifter in the
Mach-Zehnder-Modulator
 distorted IQ Plot,
distorted Eye-diagrams
 EVM
π/2
I
Q
© 2015 Keysight Technologies

25. Page
Frequency Error
26
Troubleshooting
Coherent Optical
Comms Systems
Frequency Error
shows the carrier's frequency error
relative to the VSA's center
frequency displayed in Hertz. It is
the amount of frequency shift from
the VSA's center frequency that the
VSA must perform to achieve carrier
lock. The maximum allowable
Frequency Error depends on the
Modulation Format used. Here’s a
list of formats:
2 GHz
Modulation Format Maximum frequency offset
QPSK 9.6% symbol rate
16-QAM 4.8% symbol rate
32-QAM 3.15% symbol rate
64-QAM 4.65% symbol rate
128-QAM 0.3% symbol rate
256-QAM 0.3% symbol rate
512-QAM 0.15% symbol rate
1024-QAM 0.15% symbol rate
2048-QAM 0.1% symbol rate*
4096-QAM 0.1% symbol rate*
© 2015 Keysight Technologies

26. Page
Symbol Rate Error
27
Troubleshooting
Coherent Optical
Comms Systems
Symbol Rate Error
If the Digital Demodulator
is only able to recover the
clock phase but not the
clock rate, a wrong
symbol rate shows up as
typical „V“ shape when
looking at EVM vs time
plot.
 Symbols start to spread
all over the constellation
 High EVM
Measured SymbolRate ≠
SymbolRate setting
© 2015 Keysight Technologies

27. Page
Dual Pol: IQ Skews, XY Skew and XY Imbalance
28
Troubleshooting
Coherent Optical
Comms Systems
Optical Signal
Summary Screen
Display of
- Timing skew between
I- and Q-Signals for X-
and Y-Polarization
- Timing skew between
X- and Y-Polarization.
- Gain Imbalance
between X and Y
Polarization
- Symbol Rate Display
- Frequency Error
between Tx and Rx (in
this case OMA)
- EVM and Q-Factor
© 2015 Keysight Technologies

28. Page
Bit Error Results
29
Troubleshooting
Coherent Optical
Comms Systems
Bit Error Result Screen
- Actual BER
- Cumulated BER
- BER (EVM)
- Bit & Error Counts
- Delay between X & Y
- PRBS generation details
© 2015 Keysight Technologies

29. Page
PRBS Pattern Sources
30
Troubleshooting
Coherent Optical
Comms Systems
Effects of IQ PRBS Delay in bit (PRBS length 215-1)
0 bit
2 bit
4 bit
1 bit
3 bit
5 bit
Effects of Delay issues between I- & Q-Data Source
Effect of PRBS delay
Using the same PRBS
sequence for I and Q and
decorrelating it with a too
small delay might lead to
missing transitions and
asymetric spectral
content !
Screenshots were taken
based on a PRBS 215-1
with different delays
between I and Q showing
result in the corresponding
constellation and
spectrum.
© 2015 Keysight Technologies

30. Typical Impairment Emulation in the
electrical Domain

31. Page
Example Impairment
Troubleshooting
Coherent Optical
Comms Systems 32
Phase Noise in Optical Modulation Generator Tool
© 2015 Keysight Technologies

32. Page
Carrier Phase Noise
33
Troubleshooting
Coherent Optical
Comms Systems
Analysis of Carrier
PhaseNoise
PhaseNoise Analysis of
modulated signals.
Display of Carrier Phase,
Lorentzian Linewidth,
Flicker & Random Noise.
Graphical result of Phase
Spectrum and
corresponding Phase
Spectrum Model
Upper Constellation
shows performance
without PhaseTracker.
Lower Constellation
shows result after
PhaseTracking Algorithm
using Kalman Filters.
500kHz Linewidth
2MHz Linewidth
5MHz Linewidth
© 2015 Keysight Technologies

33. Page
Emulation of PolController
34
Troubleshooting
Coherent Optical
Comms Systems
Polarization Pattern: Great Circle
© 2015 Keysight Technologies

34. Page
Emulation of PolController
35
Troubleshooting
Coherent Optical
Comms Systems
Polarization Pattern: Slicer
© 2015 Keysight Technologies

35. Page
Stokes Space Analysis in OMA: Great Circle & Slicer
36
Troubleshooting
Coherent Optical
Comms Systems
Analysis of Stokes Space
Trajectory
The OMA allows to analyze
polarization changes. Two patterns
„Great Circle“ and „Slicer“ are
generated with the AWG electrically.
This electrical signal can be used for
receiver stress testing.
Here the electrical signal is directly
connected to the OMA inputs.
Great Circle Slicer
© 2015 Keysight Technologies

36. Page 37
35ps PMD,
991ps^2 SOPMD
Troubleshooting
Coherent Optical
Comms Systems
Example Impairment: PMD (1st and 2nd order)
PMD in Optical Modulation Generator Tool
© 2015 Keysight Technologies

37. Page
Example Impairment: PMD (1st and 2nd order)
38
Troubleshooting
Coherent Optical
Comms Systems
PMD Analysis in OMA
The OMA allows to
compensate and
analyze the PMD.
An electrical signal is
generated with the
AWG and analyzed by
the OMA.
This signal could be
used for receiver stress
testing.
© 2015 Keysight Technologies

38. Tools to generate signals for
Coherent Optical Applications
© 2015 Keysight Technologies

39. Page
Go Where you Have Never Been Able to Test Before
– Sample rate up to 65 GSa/s
per channel
– 20 GHz analog bandwidth
– 1, 2 or 4 differential channels
per 1-slot AXIe module
– In Speed, in Bandwidth and in Channel Density
Explore your possibilities
New M8195A 65 GSa/s AWG
– Up to 16 GSa of waveform memory per
module (*)
– Amplitude up to 1 Vpp(se) (2 Vpp(diff.)),
voltage window -1.0 … +3.3V
– Ultra low intrinsic jitter
(RJrms < 200 fs @ 32 Gb/s PRBS 211-1)
– 16-tap FIR filter in hardware for
frequency response compensation (*)
– Multi-module synchronization up to 16
channels per 5-slot AXIe chassis (*)
(*) rev 2
40
Troubleshooting
Coherent Optical
Comms Systems
© 2015 Keysight Technologies

40. How about Optical IQ Modulator ?
I
Y-polarization
Q
I
Q
X-polarization
π/2
π/2
© 2015 Keysight Technologies

41. Page
Optical IQ Modulator:
Troubleshooting
Coherent Optical
Comms Systems 42
Optical Multiformat Transmitter: OMFT by IDPhotonics / HHI
• Symbol rate
 46 GBd for binary formats such as
BPSK, QPSK
 34 GBd: for multi-level formats
such as 16QAM
• typically >23 GHz BW
 Dual polarization I-Q modulator
with typically 28 GHz bandwidth
 40 GHz linear RF amplifiers
• C+L band
• Manual as well as automatic bias
setting (automatic for QPSK and 16-
QAM only)
• In combination with DAC/AWG:
pre-distortion to compensate for
nonlinearities of amplifiers and
modulator
• 19“ form factor
OMFT frequency response (S-parameters)
and RF cables de-embedded in AWG
In combination with M8195A AWG
© 2015 Keysight Technologies
OMFT performance verified in combination
with M8195A AWG

42. Page
Optical Modulation Generator Tool with E/O
Troubleshooting
Coherent Optical
Comms Systems 43
E/O Modulator pre-distortion
E/O converter in Optical Mod. Gen Tool
• Apply pre-distortion to compensate
modulator non-linearities
• Includes settings to compensate for amplifier
gain and Vp
• Provides compensation of E/O modulator
frequency response (S-parameters)
© 2015 Keysight Technologies

43. Page
AWG software tools for optical applications
44
Troubleshooting
Coherent Optical
Comms Systems
Optical Modulation Generator Tool *
• Dedicated for optical applications
• Generates 2 x I/Q simultaneously
• Optical impairments in electrical domain
• Signal Path De-Embedding using S-
Parameters, VSA Equalizer and factory cal
* based on MATLAB
Optical Modulation Generator Tool (1)
© 2015 Keysight Technologies
Waveform
Input page
Basic Setup
Amplitude
Pulse
Shaping

44. Page
AWG software tools for optical applications
45
Troubleshooting
Coherent Optical
Comms Systems
Optical Modulation Generator Tool *
• Dedicated for optical applications
• Generates 2 x I/Q simultaneously
• Optical impairments in electrical domain
• Signal Path De-Embedding using S-
Parameters, VSA Equalizer and factory cal
* based on MATLAB
Optical Modulation Generator Tool (1)
Compensation of Cable
Skews & S-Parameters
© 2015 Keysight Technologies

45. Page
AWG software tools for optical applications
46
Troubleshooting
Coherent Optical
Comms Systems
* based on MATLAB
Optical Modulation Generator Tool (2) Optical Modulation Generator Tool *
Electrical Emulation of Optical Signal
Properties in Real Time (1):
- Phase Noise & Laser Linewidth
- Polarization Rotation
- 1st & 2nd order PMD
(1) with Rev 2 of AWG
in Oct 2015
© 2015 Keysight Technologies
Polarization
Phase
Noise
PMD

46. Tools for Coherent Signal Analysis

47. Page
N439xA Optical Modulation Analyzer Family
N4391A Optical Modulation Analyzer
• 4 x 33 GHz in a single scope
• 4 x 63 GHz as dual instrument
setup special (call factory)
• 4 x 80 GSa/s sampling rate (160 Gsa/s for 63 GHz)
• Up to 2 GSa/Ch memory
• Lowest noise floor (typ. 1.5% EVMrms)
Troubleshooting
Coherent Optical
Comms Systems 48
For coherent transmission research & Mfg
N4392A integrated Optical Mod. Analyzer
• Compact, fully integrated, no external cabling
• 4 x 23 GHz in a single instrument for dual
polarization optical analysis
• 4 x 23 GHz electrical inputs for dual polarization
ICR testing
• 4 x 63 GSa/s sampling rate
• 16 kSa/Ch memory
• Noise floor (typ. 2 % EVMrms)
© 2015 Keysight Technologies

48. Page
Smart Setup in OMA Software
Troubleshooting
Coherent Optical
Comms Systems 49
„Smart setup“ - the easiest way to setup an OMA
0 Enter carrier wavelength or frequency
Enter symbol rate
Check modulation format
Select between back to back and link measurement
-> done
1
2
3
4
1
2
3
4
© 2015 Keysight Technologies

49. Page
Tabular Measurement results, well structured
Troubleshooting
Coherent Optical
Comms Systems 50
Per Polarization results Cross Channel results
X-Polarization
Y-Polarization
© 2015 Keysight Technologies

50. Page
Widest Selection of Modulation Formats
Troubleshooting
Coherent Optical
Comms Systems 51
No limits … Custom APSK & OFDM
It‘s your choice:
• 39 pre-defined modulation formats
or
• Custom APSK demodulation
o Up to 8 amplitude levels
o In up to 256 constellation points
o More to come, stay tuned ...
• Custom OFDM demodulation
For now and the future !
© 2015 Keysight Technologies
Custom
APSK
Custom
OFDM

51. Page
Summary Optical Communication Solutions
52
Keysight’s Offering
Wideband AWG
Tools for Coherent Signal Generation
Accurate and Repeatable Impairments
Tools for Coherent Signal Analysis
Troubleshooting
Coherent Optical
Comms Systems
N4391A
OMA
M8195A
AWG
Opt.
Mod.
Gen.
Tool
© 2015 Keysight Technologies

52. Page
Further References
53
Troubleshooting
Coherent Optical
Comms Systems
Publication title Publication No.
N4391A Optical Modulation Analyzer – Data Sheet 5990-3509EN
N4392A Integrated Optical Modulation Analyzer – Data Sheet 5990-9863EN
Infiniium Z-Series Oscilloscopes - Data Sheet 5991-3868EN
M8195A 65 GSa/s Arbitrary Waveform Generator 5992-0014EN
Metrology of Advanced Optical Modulation Formats - White Paper 5990-3748EN
Kalman Filter Based Estimation and Demodulation of Complex Signals – White paper 5990-6409EN
Vector Signal Analysis Basics - Application Note 5989-1121EN
Digital Modulation in Communications Systems - An Introduction – Application Note 5965-7160E
Essentials of Coherent Optical Data Transmission - Application Note 5991-1809EN
Contact: michael_koenigsmann@keysight.com
More Information is available from these Jumpstations:
Arbitrary Waveform Generator M8195A and
Optical Modulation Generator Software: www.keysight.com/find/M8195A
Optical Modulation Analyzer: www.keysight.com/find/OMA
Lightwave Component Analyzer: www.keysight.com/find/LCA
© 2015 Keysight Technologies

53. Questions?
Comments?
54
Troubleshooting
Coherent Optical
Comms Systems

54. Page
Troubleshooting
Coherent Optical
Comms Systems 55

55. Backup

56. Page
Overview: AWG Software tools for coherent
optical applications
Soft Front Panel
Optical
Modulation
Software
IQTools
Availability
Comes with
M8195A Firmware
Purchased
separately
Available free of
charge
Requires - MATLAB runtime
Modulation
Formats
QPSK, QAMx and
many more
QPSK, QAMx
QPSK, QAMx,
OFDM
Dual I/Q Yes Yes No
Built-in Cal Yes Yes Yes
In-system Cal Manual Automatic 1, 2
Automatic 1, 2, 3
I/Q Skew Manual Manual Automatic
Optical
impairments
(incl. support for real-
time DSP)
No Yes No
1
Keysight Infiniium Series Scope needed
2
using VSA Equalizer
3
using own cal routine
MATLAB
Troubleshooting
Coherent Optical
Comms Systems 57
© 2015 Keysight Technologies

57. Page
N4391A & N4392A core specification comparison
Troubleshooting
Coherent Optical
Comms Systems 58
Parameter N4391A N4392A
Analog Bandwidth 4x 33 GHz 4x 23 GHz
EVM noise floor typ. 1) < 1.5 % rms < 2 % rms
Sample rate 4x 80 GSa/s 4x 63 GSa/s
Max. BaudRate 63 GBd 46 GBd
Sensitivity -20 dBm -22 dBm
Sample Memory Up to 4x 2 GSa 4x 16 kSa
Software platform VSA/OMA 4.x
Wavelength accuracy +/- 5 pm +/- 2 pm
Weight ~ 48 kg (106 lbs) 13 kg (28.7 lbs)
Portability no yes
1) @ reference conditions
© 2015 Keysight Technologies

58. Page
 Debug your Tx by identifiying
the path of each data stream
 Full flexibility to setup the link
from pattern source to tributary
 Select Pre-defined or
User PRBS files
 Easy intuitive setup
Individual BER Test on each Tributary
Troubleshooting
Coherent Optical
Comms Systems 59
Debug your transmitter faster
© 2015 Keysight Technologies

59. Page
New Measurements and Result Tables
Troubleshooting
Coherent Optical
Comms Systems 60
 7 new measurement traces and
tables related to each
polarization plane
 4 new measurement traces and
tables for cross-channel
measurement results
 Get new measurement results
in the same way as you are
used to.
© 2015 Keysight Technologies

60. Page
Improved Training Tools
Troubleshooting
Coherent Optical
Comms Systems 61
12 Demo traces in VSA demo
environment for self paced learning
 32 GBd demo files measured at
5 power levels
 Selection of 5 generic files with
various modulation formats
 Selection of PAM 4 recordings
 New help system
 Dynamic Help
 Demo Video
© 2015 Keysight Technologies

61. Page
OMA Software 4.1 (1)
Get deeper insight
 to behavior of your carrier laser
relative to used local oscillator
 by seeing IQ offset resolved
in I and Q part to speed up
transmitter alignment
 by analyzing X-Y imbalance
to see imbalances in power
between polarization planes
Carrier phase display
– Residual carrier phase
calculated from Kalman
phase tracking
Troubleshooting
Coherent Optical
Comms Systems 62
I - Q resolved IQ offset
– Offset of I component of
the modulator
– Offset of Q component of
the modulator
X - Y Imbalance
– Basic test for PDL
analysis by analyzing
X-Y imbalance over time
© 2015 Keysight Technologies

62. Page
OMA Software 4.1 (2)
Get deeper insight
 In long term signal distribution
by percentile EVM analysis
 By requesting more analysis
points for your own algorithm
 Adding software Brick Wall Filter
 Plotting a scalar value over
number of screen updates to
analyze long term effects
EVM percentile
– Calculate the percentile of
a selectable hit ratio
– Resolved to polarization
plane or full signal
Troubleshooting
Coherent Optical
Comms Systems 63
More Algorithms
– Brick Wall Filter
– Request more points
Value over time
– Plot any scalar measured
value over selectable
number of frames
© 2015 Keysight Technologies

63. Page 64
Optical
Coherent
Rx
RX
Signal
Processing
LO
Laser
Typical Tests in
Complex Transmissions
Loss, PDL
CD, PMD
TX
electronic
IQ
Mod.
Carrier
Laser
Carrier Laser
 Line-width
 Phase Noise
Transmitter
 Signal Quality (EVM,
Skews…)
Received Signal
 Signal Quality (EVM, BER,…)
 Distortion caused by link impairments
Carrier Laser
 Line-width
 Phase Noise
Coherent Rx assembly
 Phase Angle vs l
 Skew
 Relative gain
 Polarization
 S-parameter
 CMRR
Modulator
 S-parameter
 S21, Bandwidth
 El. ReturnLoss
 Skews, Crosstalk
Substitute TX Electronic
 Multiformat AWG M8195A
 Optical Impairment Emulation
 Clean Signal
 Wide Bandwidth
Substitute Tx with “Golden Tx” based on
AWG M8195A and Reference Modulator
N4391A / N4392A
N4391A / N4392A
N4391A / N4392A
N4392A
M8195A + OMFT
M8195A
LCA
LCA
64
© 2015 Keysight Technologies

64. Page 65
Typical AWG requirement (electrical)
65
Company Confidential
Troubleshooting
Coherent Optical
Comms Systems
© 2015 Keysight Technologies
32 GBd, 16QAM  EVM ~ 3%rms
32 GBd, 16QAM  EVM ~ 3%rms

65. Page 66
… up to the high end you can achieve
Troubleshooting
Coherent Optical
Comms Systems
66
32 GBd, 64 QAM = 192 Gb/s
56 GBd, QPSK = 112 Gb/s
© 2015 Keysight Technologies