Tunable and broadband negative group delays in a birefringent waveguide

We report the observation of negative group delay in a simple anisotropic cylindrical waveguide in the millimeter-wave region. With a 45° linearly polarized input, a relatively broad band of negative group delay was observed with 3.57% bandwidth, where the maximum group advancement achieved was about 24 times greater than the luminal delay, implying a fractional advancement of 13.32%. The peak advancement can be precisely controlled by tuning the incident field polarization azimuth, which should benefit the applications in wave-packet switching and signal processing.