How do single-mode and multi-mode optical fibers differ in structural design, operational mechanisms, and practical deployment scenarios?

Q: How do single-mode and multi-mode optical fibers differ in structural design, operational mechanisms, and practical deployment scenarios?   A: Single-mode optical fibers feature an ultra-thin core diameter (less than 10 micrometers) that constrains light propagation to a direct, linear pathway, enabling data transmission across distances exceeding 100 kilometers with minimal signal degradation. In contrast, multi-mode variants utilize a broader core structure that permits multiple light reflection trajectories, resulting in greater modal dispersion and limiting effective transmission ranges to approximately 2 kilometers.   Both fiber types leverage total internal reflection within glass or plastic strands to transmit binary-coded light pulses, outperforming metallic conductors by supporting bandwidths up to 400 Gbps—far exceeding the 1 Gbps capacity of traditional copper Ethernet cables—while maintaining electromagnetic interference immunity. Single-mode fibers dominate long-haul telecommunications infrastructure requiring extended reach, whereas multi-mode configurations offer cost advantages for short-range applications like data center interconnects, where their wider core simplifies light source alignment and reduces hardware expenses despite distance limitations.