Frequency-domain detection of superluminal group velocity in a distributed Bragg reflector

Using a free-space configuration and a frequency-domain detection setup, group velocities of electromagnetic waves in a distributed Bragg reflector are investigated. Experimental data indicate that, near the regions of minimal transmission in our configuration, the group velocity is 2.1 times faster than the speed of light in vacuum. A transmission model based on diagonalization of the transfer matrix is used to compare the experimental data and the theoretical calculations, and good agreement is obtained. An overview of the experimental uncertainties and their effects on the measured quantities is provided.