Significantly Increased Electronic Compensation of Semiconductor Optical Amplifiers

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A system model diagram of an optical communication system including an embodiment of SOA impairment compensation logic
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Researchers
Guifang Li, Ph.D.
Xiaoxu Li, Ph.D.
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John Miner
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Patent Protection

Electronic compensation of nonlinear effects of semiconductor optical amplifiers

US Patent 8,452,191 B2
Publications
Complementary FIR filter pair for distributed impairment compensation of WDM fiber transmission
Photonics Technology Letters, Vol. 21, pgs. 292-294

In recent years, electrical dispersion compensation (EDC) and electrical nonlinearity compensation (ENLC) have received significant research activity as well as commercial interest. Specifically, EDC has the potential to decrease optical signal distortion in the electrical domain after detection in a photoreceiver. Optical channel impairments, caused by semiconductor optical amplifiers (SOA), can also result in signal degradation and limited carrying capacity.

UCF researchers have created a method involving post-compensation that can modify a received signal, compensate for the impairment, and can be implemented in either the optical domain or in the electrical/electronic domain. With the use of coherent detection and digital signal processing (DSP), post-compensation offers great flexibility when adaptive compensation is utilized within this scheme. It has also been proven to be very effective in chromatic dispersion compensation as well as intra-channel nonlinearity compensation.

Technical Details

The post-compensation method comprises receiving an optical signal distorted in the physical domain by an SOA and propagating the distorted optical signal backward in the electronic domain in a corresponding virtual SOA. The techniques of this post-compensation method involve the use of digital backward propagation in the electrical domain to convert a received optical signal into an estimated transmitted signal that then compensates for nonlinear impairments introduced by SOAs that reside along the transmission link(s).

With a simulated DSP speed of 25 GHz, the impairment compensation of a 1200-kilometer link requires 22.3M of multiply-accumulate (MAC) units. The computational efficiency is 464 kMAC/bit with latency of 10.2 microseconds, considerably smaller than the transmission latency of 6 milliseconds in the fiber. Based on simulation results, for a 12 × 100 Gb/s 16-QAM/WDM (quadrature amplitude modulation/wavelength-division-multiplexing) system using nonzero dispersion-shifted fiber (NZ-DSF), the computational load is halved by the complementary filter pair design. The transmission distance is increased from 500 to 1200 kilometers by ENLC while preserving the same Q-value.

Benefits

  • Significant increase in transmission distance
  • Stronger, less distorted signals
  • Greater flexibility of use

Applications

  • Long-haul networks
  • Ultra-long-haul networks