Fiber Impairment Compensation Using Coherent Detection and Digital Signal Processing
- ISSN: 0733-8724
- DOI: 10.1109/JLT.2009.2028245
Next-generation optical fiber systems will employ coherent detection\nto improve power and spectral efficiency, and to facilitate flexible\nimpairment compensation using digital signal processors (DSPs). In\na fully digital coherent system, the electric fields at the input\nand output of the channel are available to DSPs at the transmitter\nand receiver, enabling the use of arbitrary impairment pre-compensation\nand post-compensation algorithms. Linear time-invariant (LTI) impairments\nsuch as chromatic dispersion and polarization-mode dispersion can\nbe compensated by adaptive linear equalizers. Non-LTI impairments,\nsuch as laser phase noise and Kerr nonlinearity, can be compensated\nby channel inversion. All existing impairment compensation techniques\nultimately approximate channel inversion for a subset of the channel\neffects. We provide a unified multi-block nonlinear model for the\njoint compensation of the impairments in fiber transmission. We show\nthat commonly used techniques for overcoming different impairments,\ndespite their different appearance, are often based on the same principles\nsuch as feedback and feedforward control, and time- versus frequency-domain\nrepresentations. We highlight equivalences between techniques, and\nshow that the choice of algorithm depends on making tradeoffs.