Single-mode fiber
termnetworkingISP & telecom
Stands for: Single-mode optical fiber (OS1/OS2)
The long-haul fiber: a core so narrow light travels one path - distance measured in tens of kilometers, not hundreds of meters.
Single-mode fiber's ~9-micron core admits a single propagation mode, eliminating the modal dispersion that limits multimode, so runs stretch from campus links to intercontinental cables. Standardized as OS1/OS2, usually yellow-jacketed, and driven by laser optics that historically cost more than multimode's - a gap that has narrowed enough that many new builds simply choose single-mode everywhere.
Also known as: single-mode, smf, os2, 9 micron