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Key Features & Specifications

  • 4x 33 GHz system bandwidth, 4 x 40 GHz optical receiver bandwidth
  • Specified typical system noise floor 1.8% rms EVM
  • 66 Gbaud symbol rate
  • 264 Gbit/s for QPSK, 512 Gbit/s for QAM 16
  • Analysis span 66 GHz
  • Optical wavelength range 1528 nm to 1630 nm
  • Absolute wavelength accuracy +/- 5 pm typical
  • Factory specials up to 4x 63 GHz system bandwidth are now available. Ask your local Keysight representative for details


N4391A Best in Test Image

The N4391A is a high end turn-key optical modulation analyzer for advanced research in single and multi-carrier 400 Gbit/s and 1Tbit/s complex modulated transmission systems. It is based on the latest Z-Series Keysight oscilloscopes, a 40 GHz dual polarization coherent receiver and optical modulation vector signal analysis software offering most flexible analysis tools and smart setup for easiest instrument setup.


  • Highest confidence in test results through full calibrated turn-key solution
  • Widest range of modulation format offering
  • Based on world class Z-Series 4 channel Keysight oscilloscope


  • Fully integrated in Vector Signal Analysis software with smart setup
  • Analysis software also available as PC stand-alone version
  • User configurable APSK and OFDM demodulator
  • Modulation-format transparent polarization alignment
  • Clearly structured measurement resultsaward_logo
  • Optical characterization results for each polarization plane separately
  • Optical summary results for complete signal
  • BER and Q factor separated for each polarization plane and overall signal
  • Freely configurable screen layout
  • Internal PMF switch to select internal or external local oscillator laser for best long term test results
  • Free selection and sequence of DSP algorithms
  • Various CD and PMD compensation and measurement algorithms
  • Integration of user DSP algorithm with the same freedom as Keysight algorithms


 Default screen with smart set up dialog