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Optical Modulation Analysis (OMA) Present and Future

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  • Define CMA and MMA: Constant Modulus Algorithm, Multi Modulus Algorithm
  • Transcript

    • 1. OMA: Present and Future May 29th, 2014 in collaboration with
    • 2. 2 III WTON 2014  Current State of OMA Solutions  How does an OMA work?  Detect, Measure or Characterize?  Future directions for the OMA  Summary and Conclusions Agenda 2
    • 3. 3 III WTON 2014 Current State of OMA Solutions
    • 4. 4 III WTON 2014 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? 4
    • 5. 5 III WTON 2014 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
    • 6. 6 III WTON 2014 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
    • 7. 7 III WTON 2014 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)
    • 8. 8 III WTON 2014 How Does an OMA work?
    • 9. 9 III WTON 2014 Optical Modulation Analyzer (OMA) 9 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.
    • 10. 10 III WTON 2014  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
    • 11. 11 III WTON 2014 IQScope - Coherent Optical Receiver 11  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)
    • 12. 12 III WTON 2014 Optical-LinQ OMA Analysis Software 12 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.
    • 13. 13 III WTON 2014 Optical-LinQ OMA Analysis Software Company Confidential 13 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
    • 14. 14 III WTON 2014 Polarization Demultiplexing: CMA Xpol Ypol xx yy yx xy
    • 15. 15 III WTON 2014 Polarization Demultiplexing: MMA Xpol Ypol xx yy yx xy
    • 16. 16 III WTON 2014 Phase Estimation
    • 17. 17 III WTON 2014 17 Detect? Measure? ….. Or Characterize?
    • 18. 18 III WTON 2014 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 18 MEASUREMENT – I can see something, 4mm wide. 4 CHARACTERIZATION – now I understand it!
    • 19. 19 III WTON 2014 A common performance metric for signals using complex modulation is the EVM (Error Vector Magnitude), defined as a percentage. A Simple Performance Metric 19 Q I |Pref| (11)(01) (00) (10) Constellation Diagram & EVM |Perror| 𝐸𝑉𝑀(%) = 𝑃𝑒𝑟𝑟𝑜𝑟 𝑃𝑟𝑒𝑓 ∗ 100
    • 20. 20 III WTON 2014 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 20 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
    • 21. 21 III WTON 2014 0 10 20 30 40 50 60 70 -5 -4 -6 -3 -2 -1 0 Frequency (GHz) Response(dB) LABMASTER10Zi(65GHz) IQSCOPE(40GHz) IQSCOPE (70GHz) LABMASTER10Zi(36GHz) COMPETITORS33GHzSCOPES LABMASTER10Zi(25GHz) LABMASTER10Zi(50GHz) AGILENTN4392AOMA OMA Bandwidths 21
    • 22. 22 III WTON 2014 0 10 20 30 40 50 60 70 -5 -4 -6 -3 -2 -1 0 Frequency (GHz) Response(dB) LABMASTER10Zi(65GHz) 3dB SIGNAL BANDWIDTH RANGE 32GBaud IQSCOPE(40GHz) IQSCOPE (70GHz) LABMASTER10Zi(36GHz) COMPETITORS33GHzSCOPES LABMASTER10Zi(25GHz) LABMASTER10Zi(50GHz) MINIMUMbandwidthforaccurateEVM(32GBaud) AGILENTN4392AOMA 22    Requirements for EVM Measurement of 32GBaud
    • 23. 23 III WTON 2014 0 10 20 30 40 50 60 70 -5 -4 -6 -3 -2 -1 0 Frequency (GHz) Response(dB) LABMASTER10Zi(65GHz) 3dB SIGNAL BANDWIDTH RANGE 56GBaud MINIMUMbandwidthforaccurateEVM(56GBaud) IQSCOPE(40GHz) IQSCOPE (70GHz) LABMASTER10Zi(36GHz) COMPETITORS33GHzSCOPES LABMASTER10Zi(25GHz) LABMASTER10Zi(50GHz) AGILENTN4392AOMA 23   Requirements for EVM Measurement of 56GBaud
    • 24. 25 III WTON 2014 The EVM is a widely used signal performance metric. However …….. EVM is only part of the picture! 25 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
    • 25. 26 III WTON 2014 Constellation plot @ 23GHz EVM = 5.5%EVM = 7.2% 32GBaud QPSK - IQSkew 26 Vector Diagram @ 23GHz Vector Diagram @ 36GHz DETECTION MEASUREMENT ? CHARACTERIZATION EVM = 7.2%
    • 26. 27 III WTON 2014 Constellation plot @ 23GHz EVM = 6.3%EVM = 8.3% 32GBaud QPSK – Modulator Chirp 27 Vector Diagram @ 23GHz Vector Diagram @ 36GHz DETECTION MEASUREMENT ? CHARACTERIZATION EVM = 8.3%
    • 27. 28 III WTON 2014 EVM 5.5% EVM 5.5% EVM 7.2% 56GBaud QPSK, Source with 40GHz Bandwidth 28 EVM = 23% 33GHz Measurement Bandwidth 65GHz Measurement Bandwidth EVM = 5.8% DETECTION or MEASUREMENT ? CHARACTERIZATION
    • 28. 29 III WTON 2014 29 Effects of Over/Under-Correcting our Optical Signals
    • 29. 30 III WTON 2014 FIR Filter (Under correction) 30 EVM =24.3% EVM =9.1% True signal from a low bandwidth source Same Signal with FIR Equalizer
    • 30. 31 III WTON 2014 Too much phase correction 31
    • 31. 32 III WTON 2014 Too little phase correction 32
    • 32. 33 III WTON 2014 33 The Future of OMAs
    • 33. 34 III WTON 2014 Custom Modulation Formats
    • 34. 35 III WTON 2014 Integrate your own Matlab DSP
    • 35. 36 III WTON 2014 BER with your Patterns
    • 36. 37 III WTON 2014 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?
    • 37. 38 III WTON 2014 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 38 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 +
    • 38. 39 III WTON 2014 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 39
    • 39. 40 III WTON 2014 40 Thank You! Questions? Fernando.gomez@teledynelecroy.com lduque@borealtec.com.br

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