Phase Transition Driven and Angle Multiplexed Broad/Narrowband THz Absorber

An absorber containing a vanadium dioxide (VO
$_{2}$
) resonator is designed and numerically studied to provide the thermally switchable response between the broad and narrow absorption spectrum. In the insulating phase, VO
$_{2}$
resonator supports the dielectric resonance through the creation of standing waves to provide the narrow absorption spectrum with a high quality factor of more than
$300$
. In the metallic phase, the surface charge distribution on the resonator remains responsible to excite the fundamental and higher order magnetic dipoles with the nearby and merged spectrum hence a broad absorption band covering
$2.19\text{--}5.56$
THz is achieved. The absorber response can be thermally switchable. The geometry of the absorber can excite the multiple narrow resonances based on Brewster’s effect. Also, the scanning of incident angle can provide a tunable narrow spectrum over a broad spectral range. The absorber operation is validated through the theory of multiple reflections.