Fiber optic cables are classified by core size, mode type, wavelength, and international standards such as IEC, ITU-T, and TIA.

Core Classification by Mode and Diameter

Fiber optic cables are primarily classified into single-mode (SMF) and multimode (MMF) fibers:

• Single-Mode Fiber (SMF): Has a small core diameter, typically 8–10 microns, allowing only one light mode to propagate. Common standards include ITU-T G.652 (low-loss, zero-dispersion at 1310 nm), G.655 (non-zero dispersion-shifted for DWDM), and G.657 (bend-insensitive fibers) for long-haul, metro, and access networks .
• Multimode Fiber (MMF): Has a larger core diameter, typically 50 or 62.5 microns, supporting multiple light modes. MMF is classified by OM (Optical Multimode) ratings:
  • OM1: 62.5 µm core, 200 MHz·km bandwidth at 850 nm, max 3.5 dB/km attenuation .
  • OM2: 50 µm core, 500 MHz·km bandwidth at 850 nm, max 3.0 dB/km attenuation.
  • OM3: 50 µm core, 2000 MHz·km bandwidth at 850 nm, optimized for 10–40 Gbps.
  • OM4: 50 µm core, supports 40–100 Gbps over shorter distances, 850 nm wavelength .

Standards Governing Fiber Classification

Fiber optic core classification is defined and regulated by several international standards:

• IEC 60793: Specifies optical fiber characteristics, including core/cladding dimensions, numerical aperture, and attenuation.
• IEC 60794: Covers fiber optic cable construction and mechanical performance.
• ITU-T Recommendations: G.652, G.655, G.657 define single-mode fiber types, dispersion, and wavelength performance.
• TIA-568.3-E: Defines performance, transmission, and testing requirements for premises optical fiber cabling, including polarity and connectivity methods for duplex and array systems .
• ISO/IEC 11801: Provides international guidance for structured cabling in commercial buildings.
• Telcordia GR-20: Addresses reliability and environmental performance for outside plant fiber cables .

Key Considerations

• Bandwidth and Attenuation: Core classification affects maximum transmission distance and data rate.
• Wavelength Compatibility: Single-mode fibers are optimized for 1310 nm and 1550 nm, while multimode fibers typically operate at 850 nm and 1300 nm.
• Application: OM1/OM2 are suitable for legacy networks, OM3/OM4 for high-speed data centers, and single-mode fibers for long-haul and metro networks.
• Polarity and Connectivity: Standards like TIA-568.3-E define fiber polarity methods (Methods A, B, C, U1, U2) to ensure proper transmitter-receiver alignment . In summary, fiber optic core classification combines physical core size, mode type, and standardized optical performance, guided by IEC, ITU-T, TIA, and ISO/IEC standards to ensure interoperability, reliability, and optimal network performance.