Optical Measurements in 100 and 400 Gb/s Networks: Will Coherent Receivers Take Over? Fred Heismann Chief Scientist Fiberoptic Test & Measurement Key Trends in DWDM and Impact on Test & Measurement Complex Modulation Formats with Polarization Multiplexing Coherent Receivers with Phase- and PolarizationDiversity + DSP Flexible Grid, Superchannels and Nyquist WDM More sensitive to ASE noise How do I measure in-band OSNR? Large tolerance to CD & PMD Do I still need to measure fiber dispersion? Optical Constellation Analyzer Do I ever need another optical test instrument? High-Resolution OSA Where are my standards for center frequencies? © 2012 JDS Uniphase Corporation | JDSU CONFIDENTIAL AND PROPRIETARY INFORMATION 2 Coherent Receiver with High-Speed Digital Signal Processing LO Laser PBS 0º / 90º Mixer ADC ADC Data PD Signal Decoding ADC Phase Recovery PBS ADC 0º / 90º Mixer CD Compensation 100 Gb/s PM-QPSK PMD Compensation Digital Signal Processor  Unprecedented tolerance to fiber dispersion • More than 30,000 ps/nm GVD and at least 25 ps mean DGD • Do I still need to measure fiber CD and/or PMD?  Additional measurement capabilities • CD, PMD, PDL and even OSNR • Do I still need to measure in-band OSNR? © 2012 JDS Uniphase Corporation | JDSU CONFIDENTIAL AND PROPRIETARY INFORMATION 3 Do I Still Need to Measure CD, PMD and / or OSNR? Do I still need to measure fiber link CD and PMD?  NO – if I want to upgrade my system from 10 Gb/s to 100 Gb/s • Dispersion tolerance of coherent receiver is large enough  YES – if I am going to use “new” fiber • PMD tolerance of coherent receivers is limited Do I still need independent OSNR measurements?  YES – if my coherent receiver does not measure OSNR • Not all coherent receivers have this capability  YES – for performance verification of newly installed systems • Need to establish accurate baseline  YES – for trouble-shooting of failing systems • If receiver does not work  no OSNR measurement How else can I measure in-band OSNR of polarizationmultiplexed signals? © 2012 JDS Uniphase Corporation | JDSU CONFIDENTIAL AND PROPRIETARY INFORMATION 4 Coherent Optical Constellation / Modulation Analyzer ADC PD LO Laser PBS 0º / 90º Mixer ADC SoftwareBased Digital Signal Processor Results PBS ADC 0º / 90º Mixer Digital Storage Optical Signal ADC  Unprecedented capabilities to analyze optical signals • • • • • Constellation analysis: EVM, amplitude & phase distortions / offsets, … Eye analysis: shape, noise, jitter, Q-factor, crosstalk, OSNR, … Polarization analysis: SOP, PMD, PDL, DOP, skew , … Bit-pattern analysis: BER, Q-factor, … Frequency analysis: Optical spectrum © 2012 JDS Uniphase Corporation | JDSU CONFIDENTIAL AND PROPRIETARY INFORMATION 5 Commercial Optical Constellation / Modulation Analyzers High-quality coherent receiver + real-time digitizing oscilloscope + software-based digital signal processing = bulky instrument Not quite field deployable © 2012 JDS Uniphase Corporation | JDSU CONFIDENTIAL AND PROPRIETARY INFORMATION 6 Will Measurement Capabilities Migrate to Transponders? Software-based DSP • More versatile • More capabilities • Relatively slow • Relatively bulky ASIC-based DSP • Less versatile • Fewer capabilities • Real time processing • Small footprint Coherent Transponder ? DSP with increased measurement capabilities In-situ analysis of signal quality and fiber properties Why would I ever need another optical test instrument? © 2012 JDS Uniphase Corporation | JDSU CONFIDENTIAL AND PROPRIETARY INFORMATION 7 Why Would I Need Other Optical Test Instruments?  Fiber loss is still very important • Propagation and splice losses, reflections, … • Especially important for systems with distributed Raman amplification • Still need optical power and OTDR measurements  Trouble-shooting of failing systems • Constellation analyzer requires decoding of received signal • If signal cannot be decoded  no measurements • Need independent instruments for OSNR, PMD, spectrum, …  Installation and verification of new systems • Full fiber link characterization: loss, CD, PMD, OTDR measurements • Initial performance evaluation: power levels, center frequencies, OSNR  Introduction of optical superchannels and Nyquist WDM • Spectral analysis of entire superchannel (>100 GHz BW) • High-resolution OSA with wider wavelength range than OMA © 2012 JDS Uniphase Corporation | JDSU CONFIDENTIAL AND PROPRIETARY INFORMATION 8 Other Optical Instruments Employing Coherent Detection  Coherent optical sampling scope • Modulation analyzer with short-pulse LO laser • Waveform analysis with much higher bandwidth  Coherent OTDR • Higher sensitivity  longer distances - Submarine cables > 10 000 km • Higher resolution (< 10 m)  Coherent OFDR • Very high-resolution (component testing)  High-resolution coherent OSA • High spectral resolution ( 5 … 300 MHz) • Leveraging telecommunication components  Coherent PMD analyzer • In-service PMD measurement (single-polarized signals only) © 2012 JDS Uniphase Corporation | JDSU CONFIDENTIAL AND PROPRIETARY INFORMATION 9 Coherent High-Resolution Optical Spectrum Analyzer WDM Input Signals Coherent Receiver with Polarization Diversity LPF PBS Scanning Local Oscillator Laser Pp(ν) 3 dB Coherent Mixers with Balanced Detection 3 dB RF Power Detectors Laboratory instrument Ps(ν) 3 dB LPF  5 MHz … 300 MHz spectral resolution • Determined by electrical bandwidth of receiver  >70 dB dynamic range  > 1000 GHz/s tuning speed  Sub-GHz accuracy over entire C-band © 2012 JDS Uniphase Corporation Field instrument | JDSU CONFIDENTIAL AND PROPRIETARY INFORMATION 10 High-Resolution Spectra of Modulated Optical Signals -10 Optical Power [dB] -20 Measured with Coherent OSA (300 MHz Resolution) -30 -40 -50 -60 -70 195.17 10 Gb/s NRZ-OOK 2.5 Gb/s NRZ-OOK 43 Gb/s PM-QPSK 195.22 195.27 Optical Frequency [THz] © 2012 JDS Uniphase Corporation | 195.32 JDSU CONFIDENTIAL AND PROPRIETARY INFORMATION 11 Output Spectrum of Faulty 128 Gb/s PM-QPSK Transmitter -20 Optical Power [dB] 128 Gb/s PM-QPSK -30 -40 Gratingbased OSA -50 High-Resolution OSA -60 -80 -40 0 40 Relative Frequency [GHz] © 2012 JDS Uniphase Corporation | 80 JDSU CONFIDENTIAL AND PROPRIETARY INFORMATION 12 Ultra-Densely-Spaced “Nyquist WDM” Signals for 400 Gb/s  25 … 33% higher spectral efficiency than conventional signals  Signals are no longer centered on 12.5 GHz ITU grid 5 Relative Optical Power [dB] 150 GHz 4 x 100 Gb/s or 4 x 200 Gb/s 0 -5 -10 -15 200 GHz -20 -25 -150 -100 -50 0 50 100 150 Relative Optical Frequency [GHz] © 2012 JDS Uniphase Corporation | JDSU CONFIDENTIAL AND PROPRIETARY INFORMATION 13 High-Resolution Spectral Analysis of Nyquist WDM Signals Densely Spaced Nyquist Signals Signals shall not overlap Precise adjustment of center frequencies is critical 50-GHz Spaced Nyquist Signals  How accurately can I measure the center frequencies? •  What reference frequencies shall I use? •  Determine from 3 or 10 dB bandwidth? Optical subcarriers may not be centered on 12.5 GHz ITU grid Are absolute center frequencies the right metric? • Or should it be the relative spacing of center frequencies? © 2012 JDS Uniphase Corporation | JDSU CONFIDENTIAL AND PROPRIETARY INFORMATION 14 What Comes Next?  In-service OSNR measurements on 100 / 400 Gb/s signals • How can we measure in-band noise of polarization-multiplexed signals? - All physical parameters of light are used for data encoding - Polarization extinction method doesn’t work • Can coherent receivers help us to distinguish signal from noise? - Without decoding of the digital information - When signals are distorted by large CD / PMD and optical filters  Compact coherent wavemeters? • Hand-held devices for CWDM and DWDM systems • When will the technology become cheap enough?  Measurement of non-linear noise and crosstalk? • Is it possible to distinguish nonlinear effects from ASE noise? - SPM, XPM, XPolM, FWM © 2012 JDS Uniphase Corporation | JDSU CONFIDENTIAL AND PROPRIETARY INFORMATION 15 Will Coherent Receivers Take Over? I certainly believe so!  Enhanced measurement capabilities in coherent transponders • In-situ analysis of signal quality and fiber link properties  More T&M instruments using coherent detectors • Fault location • Trouble shooting • Installation and verification tests © 2012 JDS Uniphase Corporation | JDSU CONFIDENTIAL AND PROPRIETARY INFORMATION 16 Thank You!