optical modulation analysis (oma) present and future
TRANSCRIPT
OMA: Present and
FutureMay 29th, 2014
in collaboration with
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Current State of OMA Solutions How does an OMA work? Detect, Measure or Characterize? Future directions for the OMA Summary and Conclusions
Agenda
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Current State of OMA Solutions
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Optical Modulation Analyzers (OMAs) started as instruments that analyze the quality of polarization multiplexed modulated optical signals.
- M-PSK
- M-QAM
Moving towards full characterization of optical Electric field:
- Amplitude
- phase
- polarization
What is an OMA?
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Advantages
Heterodyne configuration, can use an independent laser for reference LO input
Versatile: can be used to measure Tx signals back-to-back or Rx side signals after transmission
through fiber
DSP algorithms are compatible with Commercial Transceiver designs
Best Solution for system Measurements
Only Solution that can give a BER
Can support non-repeating patterns
Real-time OMA Systems
Agilent N4391A
Coherent Solutions & Teledyne LeCroy
IQScope-RT + LabMaster
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Performance Considerations Performance is very tightly coupled with the system bandwidth and the sample rate
Bandwidth must be significantly higher than the Heterodyne signal (source under test spectrum + carrier offset). Otherwise:
the rise/fall time may be inaccurate, your transitions between symbols may be inaccurate
Sample Rate must be above Nyquist of the Heterodyne signal
DSP algorithms can “Over Correct” the signal under test Carrier Recovery needs phase estimation algorithms, such as Viterbi & Viterbi. May over-
correct and make the signal appear better than it actually is. If not careful, the polarization demultiplexing can correct impairments that are present on the
source under test, such as XYSkew, XYPowerBalance, Cross-talk
Real-time OMA Systems
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Advantages Highest bandwidth (70GHz +): most accurate transition measurement Number of points/symbol is not dependent on the scope’s sampling rate = Finer granularity of
measurement Higher vertical bit resolution of equivalent-time oscilloscope = lower quantization noise and the
ability to measure higher order modulation formats
Disadvantages Can only provide BER estimates Can only support repeating patterns Poor phase recovery for system experiments
Transmitter characterization is its strength
Equivalent-time OMA systems
Tektronix OM4000
EXFO PSO-200
(Optical Sampling)
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How Does an OMA work?
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Optical Modulation Analyzer (OMA)
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The IQScope is not an “ICR” in a box. We use carefully selected discrete components to ensure the highest performance available.
Within the LabMaster, the Optical LinQ software provides access to the OMA tools from within the DSO software.
At start-up, the software runs a calibration routine to ensure repeatable & accurate measurements.
The DSP uses market-recognized (but highly optimized) algorithms for extracting the signals from the incoming data-streams.
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An OMA must show you the impairments, should not correct or hide any impairments DSP must be designed from the ground up with impairments in mind
OMA cannot make the same assumptions as DSP transceivers No Frames or training sequences are available Data May not be orthogonally Polarized Some hardware may be defective (drivers, modulators, etc) May have large IQPhase error May have large bias errors
OMA has the luxury of offline processing
OMA is not a Transceiver
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IQScope - Coherent Optical Receiver
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The IQScope Coherent Optical Receiver is available with up to 70GHz true analog bandwidth.
Proprietary IP enabling connection to equivalent time oscilloscopes for high resolution homodyne transmitter characterization.
Built using state-of-art components, matched and assembled to give highest possible performance and reliability.
Bandwidth options: • 37GHzmin, 42GHztyp
• 65GHzmin, 70GHztyp
Full operation across C & L-Bands
Internal oscillator• C Band (<100kHz LW)• L Band (<100kHz LW)
• (C+L) Band (<100kHz LW)
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Optical-LinQ OMA Analysis Software
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1. Seamless integration within the LabMaster software.
2. Full functionality – no additional charges for specific features.
3. Updated quarterly with new algorithms and analysis tools.
4. Software support & quarterly updates are free-of-charge for 3 years.
5. Custom features can be accommodated.
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Optical-LinQ OMA Analysis Software
Company Confidential
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Analysis Views Parametric Measurements
IQ Trajectory and Constellation EVM (%)
I & Q Eye Diagrams Fast BER Estimation
EVM% Eye Diagram True BER Measurement
Intensity and Phase Eye Diagrams Constellation Phase Error
Spectrum of I & Q IQ Quadrature Error
Spectrum of E-field Q Factor
Time charts: PDL (Polarization Dependant Loss)
• Phase PMD (Polarization Mode Dispersion)
• Phase Error IQ Imbalance
• I and Q I and Q Bias Error
• EVM IQ Offset
• Carrier Phase IQ Skew
• Polarization XY Skew
Frequency Offset
Magnitude Error
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Polarization Demultiplexing: CMA
Xpol
Ypol
xx
yy
yx
xy
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Polarization Demultiplexing: MMA
Xpol
Ypol
xx
yy
yx
xy
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Phase Estimation
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Detect? Measure?
….. Or Characterize?
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DETECTION – I can see something….
If you can detect something, it doesn’t mean you can measure it!If you can measure one parameter, it doesn’t mean you have characterized it!
Subtlety of Definitions
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MEASUREMENT – I can see something, 4mm wide.4
CHARACTERIZATION – now I understand it!
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A common performance metric for signals using complex modulation is the EVM (Error Vector Magnitude), defined as a percentage.
A Simple Performance Metric
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Q
I
|P ref|
(11)(01)
(00) (10)
Constellation Diagram & EVM
|Perror|
𝐸𝑉𝑀 (% )=√|𝑃𝑒𝑟𝑟𝑜𝑟||𝑃𝑟𝑒𝑓|
∗100
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To obtain a meaningful EVM measurement, the scope bandwidth must be equal to or greater than the 3dB point.
A 32GBaud signal will have a 3dB point containing frequency components between16GHz and 32GHz. However, there is still significant frequency content above the 3dB point that is critical to characterizing the signal.
EVM Measurements – Bandwidth Requirements
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In a transceiver, the electrical signals are spectrally shaped using a DSP filter to reduce the bandwidth requirement of the transmitter. This is commonly a Root Raised Cosine (RRC) filter. The 3dB bandwidth of this signal is 1/2 of the original signal, ~70%
For a 32GBaud signal this is 23GHz For a 56GBaud signal this is 40GHz
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-4
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-3
-2
-1
0
Frequency (GHz)
Res
pon
se (
dB) L
AB
MA
ST
ER
10Zi (65G
Hz)
IQS
CO
PE
(40GH
z)
IQSCOPE (70GHz)
LA
BM
AS
TE
R 10Z
i (36GH
z)
CO
MP
ET
ITO
RS
33GH
z SC
OP
ES
LA
BM
AS
TE
R 10Z
i (25GH
z)
LA
BM
AS
TE
R 10Z
i (50GH
z)
AG
ILE
NT
N4392A
OM
A
OMA Bandwidths
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Frequency (GHz)
Res
pon
se (
dB) L
AB
MA
ST
ER
10Zi (65G
Hz)
3dB SIGNAL BANDWIDTH RANGE32GBaud
IQS
CO
PE
(40GH
z)
IQSCOPE (70GHz)
LA
BM
AS
TE
R 10Z
i (36GH
z)
CO
MP
ET
ITO
RS
33GH
z SC
OP
ES
LA
BM
AS
TE
R 10Z
i (25GH
z)
LA
BM
AS
TE
R 10Z
i (50GH
z)
MIN
IMU
M bandw
idth for accurate E
VM
(32G
Baud)
AG
ILE
NT
N4392A
OM
A
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Requirements for EVM Measurement of 32GBaud
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-2
-1
0
Frequency (GHz)
Res
pon
se (
dB) L
AB
MA
ST
ER
10Zi (65G
Hz)
3dB SIGNAL BANDWIDTH RANGE56GBaud
MIN
IMU
M bandw
idth for accurate E
VM
(56G
Baud)
IQS
CO
PE
(40GH
z)
IQSCOPE (70GHz)
LA
BM
AS
TE
R 10Z
i (36GH
z)
CO
MP
ET
ITO
RS
33GH
z SC
OP
ES
LA
BM
AS
TE
R 10Z
i (25GH
z)
LA
BM
AS
TE
R 10Z
i (50GH
z)
AG
ILE
NT
N4392A
OM
A
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Requirements for EVM Measurement of 56GBaud
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The EVM is a widely used signal performance metric. However ……..
EVM is only part of the picture!
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1. The EVM is just a number. It tells you if you have a problem, but gives you no information about the cause.
2. There are many system impairments which are not captured by an EVM measurement until they are very severe, limiting it’s use as a system optimization metric.
For example ……IQ Skew, Modulator Chirp
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Constellation plot @ 23GHz
EVM = 5.5%EVM = 7.2%
32GBaud QPSK - IQSkew
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Vector Diagram @ 23GHz Vector Diagram @ 36GHz
DETECTION MEASUREMENT ? CHARACTERIZATION
EVM = 7.2%
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Constellation plot @ 23GHz
EVM = 6.3%EVM = 8.3%
32GBaud QPSK – Modulator Chirp
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Vector Diagram @ 23GHz Vector Diagram @ 36GHz
DETECTION MEASUREMENT ? CHARACTERIZATION
EVM = 8.3%
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EVM 5.5%
EVM 5.5%
EVM 7.2%
56GBaud QPSK, Source with 40GHz Bandwidth
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EVM = 23%
33GHz Measurement Bandwidth 65GHz Measurement Bandwidth
EVM = 5.8%
DETECTION or MEASUREMENT ? CHARACTERIZATION
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Effects of Over/Under-Correcting
our Optical Signals
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FIR Filter (Under correction)
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EVM =24.3%
EVM =9.1%
True signal from a low bandwidth source
Same Signal with FIR Equalizer
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Too much phase correction
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Too little phase correction
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The Future of OMAs
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Custom Modulation Formats
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Integrate your own Matlab DSP
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BER with your Patterns
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Hardware: Fully Automated Calibrations
Skew, IQPhase error, Frequency Response Mag/Phase Very low linewidth Local-Oscillators
DSP: Data independent Polarization demultiplexing Data independent Phase estimation
Where do we go from here?
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There are a variety of Real and Equivalent Time Optical Modulation Analyzer solutions in the marketplace. They can all DETECT the presence of a complex optical modulated signal.
Summary
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However...Sufficient OMA bandwidth is essential to MEASURE & CHARACTERIZE today & tomorrow’s optical communication systems.
The LabMaster 10Zi is the ONLY modular, bandwidth scalable real-time oscilloscope on the market. The LabMaster/IQScope OMA Solution has the highest bandwidth available, by X2 !
BANDWIDTH + SCALABILITY =
BEST PERFORMANCE
BEST VALUE-FOR-MONEY+
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By working in close collaboration Teledyne LeCroy and Coherent Solutions have developed the highest performance OMA solution available.
We will also show you that the unparalleled bandwidth, scalability, and analysis tools provided by this system offer you:
1. The best technology to enable you to CHARACTERIZE your coherent optical communication systems and components.
2. The unique ability to upscale your bandwidth and channels – future-proofing your investment.
Providing World-Leading OMA Solutions
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Thank You!
Questions?