Influence of Stimulated Brillouin Scattering (SBS) in Fiber Transmission and Its Threshold Optimization
SBS stands for Stimulated Brillouin Scattering. When the optical power injected into fiber exceeds the SBS threshold, a considerable portion of useful optical power is converted into backward-propagating scattered light. Apparently, SBS caps the launch optical power of fiber and triggers back-reflection once beyond the threshold. As an inherent nonlinear property of fiber medium rather than of light itself, SBS represents the primary nonlinear impairment in fiber optics and degrades the system Carrier-to-Noise Ratio (CNR) by limiting the maximum allowable fiber launch power. For long-haul transmission, sufficient input optical power is required to deliver signals over extended distances. Simply put, excessive incident light excites lattice vibration within the silica fiber core and shifts the refractive index, which in turn induces SBS.
To elevate the SBS threshold, manufacturers integrate dedicated SBS suppression circuitry inside 1550 nm optical transmitters. Top-tier international 1550 nm transmitters feature an SBS threshold of ≥19 dBm, representing state-of-the-art performance in this field. During optical link design, the actual fiber launch power must be kept below the transmitter’s rated SBS threshold. Nevertheless, an excessively high SBS threshold is not always desirable: threshold broadening technology widens the optical source spectrum, aggravating fiber dispersion and shortening achievable transmission reach. Moreover, SBS threshold extension circuits inevitably worsen transmitter noise and nonlinear distortion performance. For practical engineering deployment, an SBS threshold of 16 dBm serves as an optimal compromise for 1550 nm long-distance transmission systems.
The above is merely qualitative analysis; quantitative configuration in field implementation needs to adapt to on-site practical conditions. Generally speaking, a lower SBS threshold improves transmission quality yet restricts transmission span, and vice versa.
