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Electronic Dispersion Compensation for optical communication systems

Electronic Dispersion Compensation for optical communication systems. NEC Labs America July 12 th , 2006. Techniques for EDC. FFE/DFE Single Side Band (SSB) with Microstripe MLSE Volterra Series Pre-distortion (including line-coding) Hybrids. FFE and DFE.

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Electronic Dispersion Compensation for optical communication systems

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  1. Electronic Dispersion Compensation for optical communication systems NEC Labs America July 12th, 2006

  2. Techniques for EDC • FFE/DFE • Single Side Band (SSB) with Microstripe • MLSE • Volterra Series • Pre-distortion (including line-coding) • Hybrids

  3. FFE and DFE • Standard techniques for equalization of linear channels • Easiest to implement, but worst performance compared to other techniques in linear systems • Performance further degraded with nonlinear systems such as the optical channel Experiments:

  4. SSB transmission • SSB preserves phase information, making the whole system linear • Compensation achieved by using Microstrip lines Experiments:

  5. MLSE • Theoretically optimal detector (with infinite states and continuous sampling). Practically, 2 Sa/b is good enough. Memory depends on amount of Dispersion • Need correct noise statistics, but usually use Gaussian approximation Experiments:

  6. Volterra Series • Taylor series approximation of nonlinear systems with memory • FFE/DFE with taps that are coefficients of nonlinear terms • Performance close to MLSE, but hard to optimize tap coefficients Experiments:

  7. Pre-distortion (1): Pulse Shaping • Modulation formats such as duobinary are line coding techniques that can be thought of as a kind of Pre-distortion Experiments: • Note: Dispersion values correspond to no power penalty compared to back-to-back • All Duobinary simulations/experiments show optimal system performance at certain values of dispersion, probably because duobinary spectrum partially cancel the dispersion effect • Simulations show more complicated line coding further enhance dispersion tolerance (Forestieri & Prati, JLT Nov. 2001)

  8. Predistortion (2): Inverting the dispersive Channel • EDC at transmitter to exactly cancel the channel effects (analogous to Pre-chirping). The non-linearity of photo-detector becomes a non-issue • Requires knowledge of the channel. Not a problem for CD since its relatively static. For PMD, might not be practical since it requires regular channel feedback Experiments:

  9. Hybrids: Pre-distortion and electronic processing at receiver • Most common form of hybrid investigated is Duobinary modulation with FFE/DFE/MLSE in IM/DD channels. With Duobinary modulation, FFE/DFE at receiver didn’t help while MLSE still provides benefits. Experiments: • In coherent systems with nonlinear effects, Savory (UCL, Elec. Lett. March 2006) showed through simulations that half pre-distortion – half receiver EDC optimizes performance

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