Controlled Access. Restriction lift date: 2026-09-30
Enabling high baud rate terabit superchannels
Loading...
Files
Date
2025
Authors
Canas Estrada, Natalia
Journal Title
Journal ISSN
Volume Title
Publisher
University College Cork
Published Version
Abstract
Internet service providers rely on optical systems to transmit and receive data through the optical fibre network, supporting applications ranging from video streaming to autonomous driving. To meet growing user demands, optical communication systems have evolved to maximize spectral efficiency and aggregated data rates by transmitting multiple closely-spaced optical carriers within a single fiber. However, opto-electronic components are reaching their performance limits in terms of electro-optic conversion, bandwidth, and frequency response. Innovative solutions are necessary. Superchannel systems offer a promising approach, utilizing off-the-shelf components to achieve high spectral efficiency by transmitting closely-spaced optical carriers that overlap. The optical carriers are treated as a single entity that collectively deliver multiple terabits per second. These systems, if designed for compact architectures, could be well-suited for integration into photonic integrated chips.
A critical component in superchannel systems is the Mach-Zehnder modulator (MZM), used to generate the optical carriers and encode data onto optical carriers through amplitude and phase modulation. However, MZMs are prone to bias drifts, requiring an effective DC bias control for stable operation. This work addresses the challenge of MZM bias drift by first characterizing the behavior of single and nested MZMs to understand their transfer functions. Based on the analysis and results, a simple DC bias monitoring method based on asymmetric dithering signals is proposed. The proposed method allows slope identification when the MZM is biased at quadrature. Time-interleaving is proposed to extend this approach to multiple devices using low-frequency dither signals of varying frequencies to monitor each MZM. This method successfully identifies bias point drifts by analyzing the peak-to-peak and mean power of the low-frequency components of the modulated signal.
The proposed technique was experimentally validated in an NRZ-OOK system transmitting at 10, 12.5, and 20 Gbit/s, demonstrating negligible impact on the bit error rate (BER) performance. Additionally, a DC bias control method based on the perturb-and-observe approach was developed and tested in simulations, effectively correcting bias drifts. These findings demonstrate a simple and feasible solution for stabilizing MZMs, ensuring reliable integration into advanced optical communication systems such as superchannels.
Description
Controlled Access
Keywords
Superchannels , DC bias control , Optical communications , Mach-Zehnder modulator
Citation
Canas Estrada, N. 2025. Enabling high baud rate terabit superchannels. PhD Thesis, University College Cork.