What are the specifications of single-mode optical fiber

Single-mode optical fiber typically has a 9 µm core, 125 µm cladding, operates at 1310 nm or 1550 nm, and supports long-distance, low-attenuation transmission.

Core and Cladding

Single-mode fibers have a small core diameter of about 8–10 µm, usually standardized at 9 µm, which allows only a single transverse mode of light to propagate, minimizing modal dispersion . The cladding diameter is typically 125 µm, providing total internal reflection and mechanical protection for the core . The core-to-cladding ratio is therefore approximately 9/125.

Operating Wavelengths

Single-mode fibers are designed to operate primarily in the O-band (1310 nm) and C-band (1550 nm), which are optimal for low attenuation and long-distance transmission . Some fibers also support the L-band (1625 nm) for dense wavelength division multiplexing (DWDM) applications.

Numerical Aperture and V-Number

The numerical aperture (NA) of single-mode fibers is small, typically around 0.10–0.14, which limits the acceptance angle of light and ensures single-mode propagation . The V-number (normalized frequency) must be below approximately 2.405 to maintain single-mode operation, calculated using the core radius, wavelength, and NA.

Attenuation and Dispersion

Single-mode fibers exhibit low attenuation, typically around 0.2–0.35 dB/km at 1550 nm, allowing transmission over tens of kilometers without repeaters . They also have minimal chromatic dispersion, which is critical for high-speed, long-distance communication.

Standards and Classifications

The most widely used standards are ITU-T G.652 (standard single-mode fiber) and G.657 (bend-insensitive fiber). Performance classifications include OS1 (indoor, up to 2 km) and OS2 (outdoor, long-haul, up to 100 km) based on attenuation and installation environment . G.652.D is considered a “future-proof” variant supporting DWDM systems.

Summary

Key parameters of single-mode optical fiber include:

• Core diameter: ~9 µm
• Cladding diameter: 125 µm
• Operating wavelengths: 1310 nm, 1550 nm
• Numerical aperture: ~0.10–0.14
• V-number: <2.405 for single-mode operation
• Attenuation: 0.2–0.35 dB/km
• Standards: ITU-T G.652/G.657, OS1/OS2 classifications These parameters make single-mode fiber ideal for long-distance, high-bandwidth telecommunications, data center interconnects, and FTTH deployments .