Experimental Implementation Of Achromatic Multiresonant Metasurface For Broadband Pulse Delay

By implementing multiple sharp resonances on a single metasurface, one can combine the strong delay of constituent resonances along with the broad aggregate bandwidth of the resonance ensemble, "tricking" the delay-bandwidth limit. Ensuring that the group delay is spectrally constant across the aggregate bandwidth, we can delay arbitrarily broadband pulses without distortion. Here, we demonstrate a concrete experimental implementation of an achromatic time delay metasurface in reflection by fitting five resonant meta-atoms in a subwavelength unit cell to provide five spectrally interleaved sharp resonances (three electric and two magnetic). The proposed metasurface exploits a solely resonant phase delay, instead of propagating phase accumulation, leading to an ultrathin (lambda(0)/19) realization. We successfully design a group delay metasurface in the 10 GHz regime that can delay broadband, 700 MHz Gaussian pulses by 2 ns (20 times the carrier cycle). Subsequent microwave measurements verify the large (>4 pi) phase span over a wide high-reflection band, highlighting the practical potential of metasurfaces for dispersion control applications that rely on large and broadband phase delays.