SOA-based optical burst power equalization for high-speed next generation passive optical networks

Abstract

Research on passive optical networks (PONs) capable of reaching speeds of 100 Gb/s per wavelength and beyond has become critical in recent years. One cost-effective solution is 4-level pulse amplitude modulation (PAM4), which utilizes affordable, low-bandwidth devices. The use of semiconductor optical amplifiers (SOAs) as receiver preamplifiers is being investigated to compensate the high PAM4 signal to noise ratio requirement and address PON loss budgets of up to 29 dB. The most recent ITU-T 50G standard specifies an expected loud-soft packet dynamic range of 20.5 dB, currently managed by burst mode trans-impedance amplifiers (BM-TIAs). However, conventional BM-TIAs face limitations in dynamic range and bandwidth when processing high-speed burst-mode upstream signals. To overcome these challenges, we propose burst power equalization in the optical domain to simplify the burst-mode receiver's design. This paper introduces two novel SOA-based equalization techniques referred to here as: (A) variable bias and (B) control light injection. These methods not only equalize the burst packets but mitigate nonlinear SOA patterning effects in high-power bursts. Our experimental results demonstrate that these SOA-based equalizers extend the dynamic range to 24 dB in a 100 Gb/s PAM4 system, maintaining bit error rates below the soft-decision forward error correction threshold. These findings show that SOA-based equalization reduces the need for high-gain BM-TIAs, thereby preventing any bandwidth limitations associated with the TIA. Furthermore, we show that complex digital signal processing is unnecessary to achieve high dynamic range using an SOA preamplifier, and linear equalization is sufficient to compensate low-cost 25G class receiver bandwidth limitations and relevant fiber dispersion effects. Our approach reduces system complexity while enhancing performance, and therefore represents a cost-effective and scalable solution, positioning SOA-based equalization as a critical innovation for future-proofing high-speed optical networks.