Enhanced resilience towards ROADM-induced optical filtering using subcarrier multiplexing and optimized bit and power...

Area of Science:

• Optical Networking
• Signal Processing
• Telecommunications

Background:

• Reconfigurable optical add-drop multiplexers (ROADMs) are crucial for flexible optical networks but introduce performance degradation due to cascading wavelength selective switches (WSSs).
• Traditional single-carrier systems suffer from uncompensated inter-symbol interference (ISI) penalties from WSS cascading, complicating real-time network control.
• Accurate evaluation of ROADM-induced penalties is essential for network controllers relying on physical layer quality of transmission.

Purpose of the Study:

• To develop an analytical framework for predicting and mitigating ROADM-induced penalties in 200G optical systems.
• To investigate the resilience of multi-subcarrier (MSC) modulation with hybrid formats to WSS cascading.
• To demonstrate the benefits of analytically-driven bit-loading for optimizing MSC signals against ROADM filtering.

Main Methods:

• Development of a fully analytical framework to predict ROADM penalties offline.
• Utilizing bit- and power-loading for transmitter-side mitigation of WSS cascading effects.
• Employing simulations and experimental validation of optimized MSC signals (8x4 Gbaud and 16x2 Gbaud) subjected to cascaded WSS filtering.

Main Results:

• The analytical framework accurately predicts ROADM-induced penalties, enabling offline estimation of mitigation settings.
• Optimized MSC signals exhibit increased resilience to ROADM filtering compared to standard single-carrier systems.
• Experimental results show approximately 2 dB gain in required SNR for optimized MSC signals versus a traditional 32 Gbaud single-carrier signal after passing through 8 cascaded WSSs.

Conclusions:

• Multi-subcarrier modulation with hybrid formats and analytical bit-loading offers a robust solution for mitigating ROADM filtering penalties.
• The proposed analytical approach facilitates efficient network control by enabling accurate penalty prediction and optimization.
• This research contributes to improving the performance and reliability of flexible optical networks facing WSS cascading challenges.