There is no exact definition of what constitutes WDM coherent detection, but there is a common notion that it shall include (at least):

  • High-order amplitude/phase modulation
  • Polarization multiplexing
  • High-speed digital-to-analog converters (DAC) in the transmitter
  • Coherent detection using a local oscillator (LO) laser in the receiver
  • High-speed analog-to-digital converters (ADC) and sophisticated digital signal processing (DSP) in the receiver

The polar Diagram

  • The electromagnetic wave can be visualized in a polar diagram:

  • For practical reasons, Cartesian coordinates are used instead. The resulting diagram is called a constellation diagram:


QPSK modulation

  • Expand the modulation scheme to also include the phase, j, of the carrier wave (the frequency, fc, remains unchanged)


xQAM modulation

  • Expand the modulation scheme to also include the phase, j, and the amplitude of the carrier wave (but still without changing fc)



  • An electromagnetic wave propagating in the SM fibre can be considered as a superposition of two polarization states (s and p) perpendicular to each other, both of identical wavelength
  • These two states can be independently modulated and detected


Coherent Bits per Symbol Symbol Rate Bit Rate PDM
QPSK 2 25G 100G YES
8QAM 3 25G 150G YES
16QAM 4 25G 200G YES
64QAM 6 25G 300G YES



Difference between cfp2 and cfp2 dco

  • LAN-WDM (1295.56/1300.05/1304.58/1309.14nm)
  • 100GE or OTU4 (100G)
  • NRZ modulation
  • Direct detect Rx
  • Data transparent
  • Range 40km
  • MSA pinning (4 Tx data, 4 Rx data channels
  • Memory area: 8000h-8FFFh, 9000-9FFFh, A000-AFFFh
  • Power consumption 9W
  • C-band tunable (single wavelength)
  • 2x 100GE or 2x OTU4 or mix (200G)
  • Coherent Rx
  • DSP, framer, FEC and encryption
  • Range 1000+km
  • MSA pinning (8 Tx data, 8 Rx data plus some propriety pins not defined by the MSA
  • Memory area: 8000h-8FFFh, 9000-9FFFh, B000-BFFFh
  • Power consumption 16-20W

Coherent cfp -the dsp

  • Can compensate for almost any amount of chromatic dispersion found in commercially available fibre
  • Eliminates the need for DCM
  • CD is identical for both polarization states
  • Compensates for PMD and rotation of polarization along the fibre

What's new at Skylane Optics

See all news February January