All-optical phase-preserving multilevel amplitude regeneration.

Area of Science:

• Optical communications
• Nonlinear optics
• Signal processing

Background:

• High-order modulation formats like star-8QAM are crucial for increasing data rates.
• Amplitude noise and nonlinear phase noise are significant impairments in optical transmission systems.
• Existing regeneration techniques often struggle with phase preservation or simultaneous noise reduction.

Purpose of the Study:

• To demonstrate all-optical phase-preserving amplitude regeneration for star-8QAM signals.
• To investigate the reduction of amplitude noise under different distortion types.
• To evaluate the enhanced robustness against nonlinear phase noise in fiber transmission.

Main Methods:

• Utilizing a modified nonlinear optical loop mirror (NOLM) for amplitude regeneration.
• Experimentally applying the NOLM to star-8QAM signals with deterministic amplitude modulation and broadband noise.
• Conducting numerical simulations to validate experimental findings and explore operational regimes.

Main Results:

• Simultaneous reduction of amplitude noise on both high and low power states of star-8QAM.
• Increased robustness against nonlinear phase noise originating from fiber nonlinearity.
• Suppression of amplitude noise conversion into nonlinear phase noise.
• Demonstrated benefit for single-level operation at higher power states.

Conclusions:

• All-optical phase-preserving amplitude regeneration is feasible for star-8QAM using a modified NOLM.
• The proposed scheme effectively mitigates amplitude noise and enhances system resilience to nonlinear phase noise.
• This technique offers a promising solution for improving performance in high-speed optical communication systems.