Group velocity dispersion (GVD) is the second order effect of dispersion, expressed as the derivative of group velocity with respect to angular frequency in s²/m. Light of different frequencies has different refractive indices in a medium, and therefore different phase velocities, leading to the phenomenon of dispersion. Understand the concept of group velocity must first understand the wave packet, the wave packet consists of different frequencies of light, its maximum amplitude at the propagation speed that is the group velocity.

In the medium, the phase velocity of different frequency light is not consistent, resulting in changes in the shape of the wave packet, which is the group velocity dispersion or group velocity dispersion. Only when the group velocity dispersion effect is small, the group velocity is meaningful. If the group velocity dispersion effect is significant, the wave packet will be rapidly disintegrated, at this time the group velocity loses its practical significance. To minimize the group velocity dispersion effect, the wave packet bandwidth needs to be small enough.

Phase velocity dispersion is a first-order effect, linearly related to the frequency of light in the medium. And group velocity dispersion is a second-order effect, and the frequency of light in the medium square correlation. The two together determine the propagation characteristics of light in a medium. Group velocity dispersion affects the shape and stability of light pulses and is a key parameter in fiber optic communication, laser technology and optical system design.

In fiber optic communication systems, group velocity dispersion is the main factor leading to optical pulse broadening, signal distortion and communication quality degradation. By reasonably designing system parameters, such as introducing negative group velocity dispersion fibers or using dispersion-shifted fibers, the group velocity dispersion effect can be effectively reduced to achieve high-speed and large-capacity optical communications. In addition, group velocity dispersion is also important for laser pulse compression, optical imaging and spectral analysis.

To summarize, group velocity dispersion, as a second-order effect of dispersion, has a significant impact on the propagation of light in a medium. By understanding its definition, properties and its role in practical applications, group velocity dispersion can be effectively utilized or reduced to meet the needs of optical transmission performance in different fields.