Negative group delay through subwavelength hole arrays

It is demonstrated that superluminal transmission with a negative group delay can be obtained through a periodic grating supporting resonant and Rayleigh-Wood anomalies. Theoretical, numerical, and experimental results are given for (sub)millimeter wave fields transmitted through an array of subwavelength holes and sandwiched between dielectric slabs. The underlying physics is the coupling of resonant anomalies and Rayleigh-Wood anomalies. The resonant anomalies appear due to the periodic array-induced coupling of the incident field to the dielectric slab TM or TE guided modes while the Rayleigh-Wood anomalies are related to the redistribution of power between propagating and evanescent diffraction orders. The conclusions reached apply to general periodic gratings operating in the regime of coupled resonant and Rayleigh-Wood anomalies.