Fiber optic cable dispersion coefficient requirements

The standard chromatic dispersion coefficient for ITU-T G.652 single-mode fiber is typically 17 ps/(nm·km) at 1550 nm, with zero-dispersion near 1310 nm.

Overview of Chromatic Dispersion

Chromatic dispersion (CD) in optical fibers refers to the wavelength-dependent variation in group velocity, causing pulse broadening as different spectral components travel at different speeds. It is a critical parameter for high-speed and long-distance optical communication systems, affecting signal integrity and limiting transmission distance without compensation . CD is often expressed in ps/(nm·km), representing the time delay per unit wavelength per kilometer of fiber.

ITU-T G.652 Standard

The ITU-T G.652 Recommendation defines the characteristics of standard single-mode fibers (SSMF) optimized around the 1310 nm zero-dispersion wavelength but also suitable for 1550 nm operation . Key points include:

• Zero-dispersion wavelength (ZDW): Approximately 1310 nm
• Chromatic dispersion coefficient at 1550 nm: Typically 17 ps/(nm·km)
• Dispersion slope: Specifies the rate of change of dispersion with wavelength, important for DWDM systems
• Fiber categories: G.652.A/B/C/D, with G.652.D being the most common low-water-peak fiber for wideband operation (1260–1625 nm) The standard provides maximum and minimum boundary lines for CD across the 1270–1625 nm range, ensuring compatibility with both analog and digital transmission systems .

Measurement and Compliance

Chromatic dispersion is measured using interferometric or phase-shift methods, and the results are used to verify compliance with ITU-T G.652 specifications . For system design, worst-case dispersion values are often considered, especially in DWDM or high-speed Ethernet applications, to ensure reliable transmission . The standard also defines polarization mode dispersion (PMD) and attenuation limits, which are related but distinct parameters.

Practical Implications

• At 1310 nm: CD is near zero, minimizing pulse broadening for short-haul systems
• At 1550 nm: CD is positive (~17 ps/(nm·km)), requiring dispersion compensation for long-haul or high-speed links
• Low-water-peak fibers (G.652.D): Allow operation across 1260–1625 nm, supporting CWDM and DWDM systems without excessive attenuation In summary, the dispersion coefficient standard for single-mode fiber is defined by ITU-T G.652, with 17 ps/(nm·km) at 1550 nm and near-zero dispersion at 1310 nm, providing a baseline for fiber selection, system design, and compliance testing .