Nonlinearity mitigation for high-speed optical OFDM transmitters using digital pre-distortion.

Area of Science:

• Optical communications
• Signal processing

Background:

• Optical orthogonal frequency-division multiplexing (OOFDM) signals are susceptible to nonlinear distortions from optical modulators.
• These distortions degrade the performance of high-speed optical communication systems.

Purpose of the Study:

• To propose and experimentally validate a digital pre-distortion (DPD) algorithm for linearizing optical modulators.
• To improve the performance of high-speed OOFDM transmitters by compensating for modulator nonlinearities.

Main Methods:

• An adaptive DPD algorithm with a learning structure was employed to determine the inverse transfer function of modulators.
• Polynomial modeling was used to represent the modulator's transfer function.
• Experiments were conducted using electro-absorption modulated lasers (EMLs) and Mach-Zehnder modulators (MZMs) with OOFDM signals up to 30-Gb/s.

Main Results:

• The DPD algorithm successfully compensated for nonlinear distortions introduced by optical modulators.
• Performance improvements were demonstrated, with and without considering the memory effects in the DPD model.
• A substantial improvement in the optical modulation index was achieved.

Conclusions:

• Digital pre-distortion is an effective technique for linearizing optical modulators in high-speed OOFDM systems.
• The proposed DPD algorithm can significantly enhance the quality and performance of optical communication signals.
• Considering memory effects in the DPD model further optimizes distortion compensation.