Chromatic dispersion and PMD mitigation at 10 Gb/s using Viterbi equalization for DPSK and DQPSK modulation formats

Area of Science:

• Optical Communications
• Digital Signal Processing

Background:

• Chromatic dispersion and polarization-mode dispersion (PMD) significantly degrade signal quality in high-speed optical fiber systems.
• Nonreturn-to-zero differential phase-shift keying (NRZ-DPSK) and differential quadrature phase-shift keying (NRZ-DQPSK) are advanced modulation formats used in modern optical networks.

Purpose of the Study:

• To investigate the effectiveness of Viterbi equalization for mitigating chromatic dispersion and PMD.
• To evaluate the performance improvements in 10 Gb/s NRZ-DPSK and NRZ-DQPSK systems utilizing Viterbi equalization.

Main Methods:

• Monte Carlo simulations were employed to analyze system performance.
• Viterbi equalization was applied to receivers for nonreturn-to-zero on-off keying (NRZ-OOK), NRZ-DPSK, and NRZ-DQPSK.

Main Results:

• Viterbi equalization demonstrably improved the performance of NRZ-OOK, NRZ-DPSK, and NRZ-DQPSK receivers.
• A NRZ-DQPSK receiver equipped with a Viterbi equalizer exhibited a chromatic dispersion tolerance of approximately 5000 ps/nm.
• The same receiver showed a first-order PMD tolerance of around 160 ps at a 3 dB optical signal-to-noise ratio (OSNR) penalty.

Conclusions:

• Viterbi equalization is a viable technique for enhancing the robustness of optical communication systems against chromatic dispersion and PMD.
• The study quantifies significant performance gains, particularly for NRZ-DQPSK systems, enabling higher data rates over longer distances.