Maximum likelihood sequence detection in laser phase noise-impaired coherent optical systems.

Area of Science:

• Optical communications
• Signal processing
• Photonics

Background:

• Laser phase noise (LPN) significantly degrades performance in coherent optical systems.
• Existing methods like DAML and Mth power approaches have limitations in mitigating LPN.
• Accurate phase estimation is often complex and computationally intensive.

Purpose of the Study:

• To introduce and evaluate a Maximum Likelihood Sequence Detection (MLSD) receiver for coherent optical systems.
• To demonstrate the effectiveness of MLSD in overcoming laser phase noise impairments.
• To compare MLSD performance against established methods like DAML and Mth power approaches.

Main Methods:

• Utilizing a Maximum Likelihood Sequence Detection (MLSD) receiver architecture.
• Implementing MLSD with linear operations and no explicit phase estimation.
• Evaluating performance based on Optical Signal-to-Noise Ratio (OSNR) penalty and laser linewidth tolerance.

Main Results:

• MLSD consistently reduces the OSNR penalty, showing a 1.1 dB improvement at a Bit Error Rate (BER) of 10⁻⁴ with a memory length L=3.
• MLSD offers significantly improved laser linewidth tolerance, approximately four times better than DAML at a 1dB OSNR penalty and BER of 10⁻⁴ (L=3).
• The receiver demonstrates robust performance in LPN-impaired systems.

Conclusions:

• MLSD provides a superior solution for mitigating laser phase noise in coherent optical systems.
• The proposed receiver offers enhanced OSNR penalty and linewidth tolerance compared to existing techniques.
• MLSD's reliance on linear operations and lack of explicit phase estimation simplifies implementation while improving performance.