nondispersive

Nondispersive refers to a property of waves or signals in which all frequency components propagate with the same phase and group velocity, so a waveform or pulse maintains its shape during propagation, apart from overall attenuation and constant delay. In a nondispersive medium, the refractive index or phase velocity is effectively independent of frequency across the relevant band.

In optics and electromagnetism, a medium is nondispersive if its refractive index n(λ) is constant over the wavelengths of interest. Then all spectral components travel at the same speed v = c/n, so there is no chromatic dispersion. Vacuum is the canonical nondispersive medium for electromagnetic waves; many real materials are approximately nondispersive only over a limited spectral range.

In communications and signal processing, a nondispersive channel or transmission line has a constant time delay for all frequency components, so a signal’s shape is preserved. Dispersive channels cause different frequencies to travel at different speeds, producing pulse broadening and distortion.

In practice, true nondispersiveness is an idealization; most media exhibit some dispersion. Designers often use material systems or narrowband signals to approximate nondispersive behavior, or employ dispersion compensation in systems such as optical fibers.

In acoustics, the propagation speed of sound is roughly independent of frequency in many media for audible ranges, making those media effectively nondispersive at those frequencies, though exceptions exist due to material properties or environmental conditions.