NEGATIVE GROUP DELAY TIMES IN FRUSTRATED GIRES-TOURNOIS AND FABRY-PEROT INTERFEROMETERS

It is demonstrated in this paper that a Gires-Tournois interferometer illuminated with an angle of incidence greater than the critical angle for total internal reflection introduces a negative group delay time, whatever the orientation of the electric field vector of the wave wit h respect to the plane of incidence, when the evanescent wave in the d ielectric layer is reflected by a dielectric substrate whose refractiv e index is between those of the incident medium and of the dielectric layer, When the evanescent wave in the dielectric layer is reflected b y a nonabsorbing metal, the group delay time is negative when the elec tric field vector is in the plane of incidence and positive when the e lectric field vector is perpendicular to the plane of incidence, Simil arly, a frustrated Fabry-Perot interferometer shows negative group del ay times for angles of incidence greater than specific p-wave and s-wa ve critical angles.