SOA enhanced optical line terminal for future optical access network
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Full Text E-thesis
Date
2026-02-28
Authors
Jamali, Fariba
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Publisher
University College Cork
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Abstract
Future passive optical networks (PONs) aim to deliver data rates of 100 Gb/s per wavelength using intensity-modulation direct detection (IM/DD) and up to 400 Gb/s per wavelength using coherent technology. Achieving these targets requires overcoming the large dynamic range of burst-mode upstream packets, typically around 20.5 dB, caused by differential loss between optical network units (ONUs). Conventional burst-mode receivers rely on transimpedance amplifiers (BM-TIAs) that adjust electrical gain for each burst, but their limited linearity and bandwidth restrict scalability to higher speeds. As IM/DD systems approach and exceed 100 Gb/s per wavelength, they also struggle to meet the 29 dB optical power budget defined by the International Telecommunication Union (ITU-T) G.9804 standard. Coherent transmission is therefore seen as a promising solution for extending PON capacity, offering superior receiver sensitivity, higher spectral efficiency, and inherent chromatic dispersion tolerance.
This thesis investigates Semiconductor Optical Amplifier (SOA)-based optical burst power equalisation as a promising approach to dynamic range management across both IM/DD and coherent PON architectures. By regulating optical gain before photodetection, SOA-based equalisation mitigates gain saturation effects, suppresses nonlinear distortions, and reduces the need for complex digital signal processing. Two novel techniques are developed and experimentally demonstrated: (A) variable bias and (B) control light injection. Both methods achieve a 24 dB dynamic range in 100 Gb/s 4-level pulse amplitude modulation (PAM4) burst-mode transmission with bit error rates below the soft-decision forward error correction threshold using a simplified low-gain receiver.
The optical-domain equalisation concept is further extended to coherent PONs employing dual-polarisation 16-quadrature amplitude modulation (DP-16QAM). In this case, a low-power local oscillator (LO) configuration is implemented to demonstrate compatibility with potential comb-source-based architectures. This design relaxes the wavelength alignment requirement between the ONU and the LO, addressing one of the main challenges in coherent PONs where ONU wavelengths can drift by a few nanometers. SOA gain control enhances linearity and enables high-fidelity burst detection without requiring fast BM-TIAs.
These findings show that SOA-based equalisation eliminates the need for high-gain BM-TIAs, thereby preventing bandwidth, gain, and dynamic range limitations associated with the TIA in both coherent and IM/DD systems. Furthermore, the results demonstrate that complex digital signal processing is unnecessary to achieve high dynamic range using an SOA preamplifier, and that simple linear equalisation is sufficient to compensate for low-cost 25G-class receiver bandwidth limitations and moderate fibre dispersion in IM/DD systems.
To explore manufacturable integration, a transfer-printed SOA preamplifier is demonstrated for the first time in a 100 Gb/s PON context, confirming its potential for scalable, and low-cost receiver designs. Overall, this work establishes SOA-based optical power equalisation as a key enabler for next-generation high-speed PONs. It provides a pathway to support 100 Gb/s IM/DD and 400 Gb/s coherent operation while maintaining high dynamic range, receiver sensitivity, and system simplicity, enabling fully integrated, energy-efficient, and cost-effective optical access networks.
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Keywords
PON , SOA , Optical equalisation , Next generation , Burst-mode , CPON , Integrated SOA
Citation
Jamali, F. 2026. SOA enhanced optical line terminal for future optical access network. PhD Thesis, University College Cork.