The single-mode 9/125 fiber (9125) is typically classified as OS1 or OS2, with OS2 being the standard for long-distance, low-attenuation applications.

Single-mode 9/125 fiber has a core diameter of 9 microns and a cladding diameter of 125 microns, allowing light to travel in a single mode, which minimizes dispersion and supports high-speed, long-distance transmission . The OS (Optical Specification) classification indicates the fiber's performance and intended environment: OS1 vs OS2:

• OS1: Designed for indoor, tight-buffered installations, typically in riser or plenum environments. It has slightly higher attenuation and is suitable for shorter distances within buildings .
• OS2: Designed for outdoor or long-haul applications, often in loose-tube constructions. It has lower attenuation, supports longer distances, and is ideal for data centers, campus backbones, and telecommunications networks . Performance Characteristics of OS2 9/125 Fiber:
• Typical attenuation: ~0.40 dB/km at 1310 nm and ~0.30 dB/km at 1550 nm .
• Supports high-speed data transmission: up to 1 Gbps over 80 km and 10 Gbps over 40 km .
• Durable and suitable for both indoor and outdoor environments, including aerial, buried, or plenum installations . In summary, the single-mode 9125 fiber can be either OS1 or OS2, but for modern high-performance and long-distance applications, OS2 is the preferred standard due to its lower attenuation and extended reach .