Technical Background

Refractive Index of Fibers

Host materials Optical telecommunication-grade fibers are made usually from silica glasses. The high purity glass is called the host material or substrate. Its bulk refractive index usually defines the refractive index of the fiber cladding. Adding dopant materials to the host material forms the fiber core. Dopant materials To change the refractive index of optical…

Fiber Propagation Modes

Scalar fiber modes The designation of Linearly Polarized (LP) Fiber modes is based on the assumption of weak guidance. Weakly guiding fibers have a small difference between core and cladding refractive index. Two numbers designate the LP (m, n) modes: m – azimuthal number n – orbital number where m = 0, 1, 2, ……

Group Delay and Dispersion Definitions

Material dispersion of the bulk glasses If the refractive index of the fiber material varies with wavelength, thus causing the group velocity to vary, it is classified as material dispersion. The group delay Tg is given by the product of the propagation distance z by the first frequency-derivative of the propagation constant: where n is…

Mode Field Diameter and Mode Area Definitions

Mode field diameter and area importance The Mode Field Diameter (MFD) is an important parameter related to the optical field distribution in the fiber. It has been shown that MFD provides useful information about the cabling performances, such as possible joint, macrobending, and microbending losses. The effective area of the fibers has a direct relation…

Cutoff Wavelengths

The cutoff wavelength for any mode is defined as the maximum wavelength at which that mode will propagate. The cutoff wavelength λc of LP11 is an important specification for a single-mode fiber. The operation wavelength must be greater than the cutoff wavelength of LP11 to operate the fiber in a single mode regime. λc can be determined analytically…

Fiber Loss Models

Fiber propagation loss definition The total fiber loss can be divided into material losses and fiber induced losses. Material losses include Rayleigh scattering, ultraviolet (UV), infrared (IR) absorption, and hydroxyl (OH) absorption losses. Material losses are the limiting losses in fibers. Fiber loss is defined as the ratio of the optical output power Pout from…

Fiber Birefringence Models

Fiber birefringence definition The birefringence is defined by the difference between the propagation constants of the polarization Eigenmodes, that is: The Differential Group Delay (DGD) per unit length is defined by: Intrinsic perturbations birefringence Intrinsic perturbations are accidentally introduced in the manufacturing process and are permanent feature of the fiber. These include a noncircular core…

Polarization Mode Dispersion Models

Polarization mode dispersion In ideal single-mode fibers, propagation constants of the two polarization Eigenmodes are degenerate. In real telecommunications fibers, perturbations act on the fiber in a way that it induces a birefringence, which splits this degeneracy. Consequently, when a pulse is launched in a fiber, it gives rise to a differential group delay between…

Technical References

[1] M. J. Adams, “An introduction to Optical Waveguides,” John Wiley & Sons, 1981. [2] M. Artiglia, “Mode field Diameter measurements in single-mode optical fibers,” J. Lightwave Tech. Vol. 7, no. 8, pp. 11391152, 1989. [3] F. Bruyère, “Effets de Polarisation dans les Systèmes à Amplification Optique de Longue Distance”, Ph.D dissertation, Univ. of Paris XI Orsay,…