GROUP VELOCITY

1. The velocity of propagation of an envelope produced when an electromagnetic wave is modulated by, or mixed with, other waves of different frequencies. ( 188 ) Note: The group velocity is the velocity of information propagation and, loosely, of energy propagation. 2. In optical fiber transmission , for a particular mode , the reciprocal of the rate of change of the phase constant with respect to angular frequency . Note: The group velocity equals the phase velocity if the phase constant is a linear function of the angular frequency, = 2 f , where f is the frequency. 3. In optical-fiber transmission, the velocity of the modulated optical power .