OS2 Single-mode Simplex Fiber is a high-performance single-mode optical fiber cable designed for long-distance, high-bandwidth data transmission, widely used in telecom backbones and enterprise core networks. What is OS2 Single-mode Simplex Fiber? OS2 is a standard for single-mode fiber (SMF) defined by the International Electrotechnical Commission (IEC). It features a 9/125 μm core/cladding diameter (9μm core for light transmission, 125μm cladding for total internal reflection). The “simplex” design means it has one fiber strand, used for one-way data transmission (paired with another simplex cable for bidirectional communication if needed).