What Is Coherent Optics ? Part1

What Is Coherent Optics ? Part1

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)

HIGHER MODULATION SCHEMES - PDM

• 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)
• DP-QPSK, DP-8QAM, DP-16QAM
• 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