Question

In Acoustic-Optics, What is the difference between a dispersive and non-dispersive medium?

Answer 1

Dissipative" media absorb electromagnetic energy, if only partially. In principle, all media are dissipative to some degree, even superconductors above DC. I believe both dielectric losses (as in a lossy substrate) and ohmic losses (as in a poor metal conductor) would both count as dissipative.

"Dispersive" media propagate different waves at different velocities. "Chromatic Dispersion" is when the velocity depends on wavelength, as in the glass of fiber optics. There are other kinds of dispersion, though, such as modal dispersion (e.g. in a waveguide where different modes, even at the same frequency, propagate at different velocities) or polarization dispersion, where different polarizations travel at different velocities. Although dispersion doesn't cause absorption of energy pe se, it can still account for "loss" in communication links as the modulated waveform will smear out and cause adjacent "bits" to overlap and interfere with each other (i.e. distortion or inter-symbol interference).