waveguidedispersion

Waveguide dispersion is the wavelength dependence of the propagation characteristics of light in a guided structure due to the geometry and boundary conditions of the waveguide. It arises when the confinement of light within a core with finite dimensions alters the effective optical path and the phase velocity for different wavelengths, even if the material itself is non-dispersive. In optical systems, the group velocity and phase velocity of a guided mode vary with wavelength because the mode’s effective index changes with wavelength as a result of the waveguide’s cross-section, refractive-index contrast, and mode profile.

In practical terms, waveguide dispersion contributes to the total chromatic dispersion observed in a guided system. For an optical fiber, total dispersion is commonly described as the sum of material dispersion, due to the intrinsic wavelength dependence of the glass, and waveguide dispersion, due to the fiber’s geometry and mode structure. The combined effect determines how different spectral components of a pulse travel, influencing pulse broadening and timing in communication links.

Waveguide dispersion can be engineered by adjusting waveguide dimensions and index contrast. In planar, strip, slot, and photonic crystal waveguides, changing core thickness or width, cladding properties, or the surrounding medium shifts the effective index spectrum and can tailor dispersion to be normal or anomalous at a given wavelength. Applications include dispersion engineering for ultrafast optics, slow-light devices, and dispersion compensation in fiber-optic systems.

Note that in multimode waveguides, modal dispersion arises from differences between modes; waveguide dispersion refers to the wavelength dependence within a guided mode.