Enhanced gain in O-band quantum-dot semiconductor optical amplifier based on a dual-pass amplification scheme

Quantum dot (QD)-based semiconductor optical amplifiers (SOAs) are critical amplifying elements for future high-speed, cost-effective optical communication networks. In this work, we demonstrate a high-gain 1.3 µm QD SOA with a proposed dual-pass configuration, achieving a record small-signal gain of 44.5 dB and a saturation output power of 12 dBm. Compared to the single-pass configuration, the dual-pass design enhances output power by a factor of 8.5 and improves maximum gain by 11 dB at the same bias current of 300 mA. By employing the p-type modulation doping, the amplifier achieves a maximum double-pass gain of 21.1 dB with a 3-dB bandwidth of 20 nm at an elevated temperature of 80 °C. These results underscore the strong potential of QD-based amplifiers for ultra-high-gain operation, alleviating the power requirements of light source as well as eliminating the need for expensive cooling systems. This approach provides an attractive solution to enhance fiber-optic communication systems, enabling improved energy efficiency and expanded network capacity.