OS2 Single-mode Duplex Fiber is a high-performance optical fiber cable designed for bidirectional, long-distance, and high-bandwidth data transmission, widely used in core networks requiring two-way communication. What is OS2 Single-mode Duplex Fiber? OS2 is an IEC (International Electrotechnical Commission) standard for single-mode fiber (SMF), featuring a 9/125 μm core/cladding diameter (9μm core for light transmission, 125μm cladding for total internal reflection). The “duplex” design integrates two independent fiber strands in one cable—one for transmitting data and the other for receiving—enabling direct bidirectional communication without pairing additional cables.