Researchers from the State Key Laboratory of Luminescence and Applications, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, have successfully developed a wide-bandwidth, low-polarization semiconductor optical amplifier (SOA) based on tensile-strained quantum wells. The study, published in the journal Sensors, presents a significant advancement in optical communication technology, addressing the growing demand for higher bandwidth and lower polarization sensitivity. With the exponential growth of network traffic, optical communication systems are facing unprecedented challenges to expand their channel capacity. Traditional erbium-doped fiber amplifiers (EDFAs) struggle to meet these demands due to their narrow gain bandwidths, often limited to around 60nm. In contrast, SOAs offer compact dimensions, low power consumption, and the flexibility to tune their gain bandwidth through energy band engineering. The research team aimed to develop an SOA with a wider gain bandwidth, lower polarization sensitivity, and improved performance across the S+C+L bands.
The researchers designed a narrow-ridge tilted waveguide SOA with a length of 2.5mm and a width of 0.5mm. To reduce transmission losses and noise, they employed a tilted waveguide structure that deviates the active region from the cleavage plane center, theoretically reducing the facet reflectance by two orders of magnitude. Additionally, they incorporated strained quantum wells with a matching potential barrier structure in the active region to balance the TE and TM mode gains, resulting in a low polarization-dependent gain (PDG).
The epitaxial structure was grown using metal-organic chemical vapor deposition (MOCVD) on an InP substrate. The team optimized the waveguide width and tilt angle to maintain single-mode operation while minimizing facet reflectance. After extensive simulations and experiments, they settled on a waveguide width of 6µm and a tilt angle of 7°, achieving a facet reflectance below 0.01% under ideal conditions.
The developed SOA demonstrated outstanding performance at a wavelength of 1550nm and a drive current of 1.4A. It achieved an output power of 188mW, a small signal gain of 36.4dB, and a 3dB gain bandwidth of 128nm. Notably, the linewidth broadening was only 1.032 times, and the polarization-dependent gain was below 1.4dB, indicating excellent polarization insensitivity. Furthermore, the noise figure remained below 5.5dB, ensuring low noise operation.
This research represents a significant step forward in optical communication technology. The wide gain bandwidth, high gain, low polarization sensitivity, and low noise of the developed SOA make it an ideal candidate for applications across the S+C+L bands. It promises to enhance the transmission capacity and efficiency of optical communication systems, enabling the transmission of more data over longer distances with reduced signal degradation.
The simplicity of the fabrication process, using only I-line lithography technology, further underscores the practicality and cost-effectiveness of this approach. The researchers believe that their SOA has the potential to revolutionize the optical communication industry, enabling the development of more advanced and efficient communication networks.
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