Dynamic plasma/metal/dielectric photonic crystals in the mm-wave region: Electromagnetically-active artificial material for wireless communications and sensors

Inexorable demand for increasing bandwidth is driving future wireless communications systems into the 100 GHz-1 THz region, thereby fueling demand for new sources and modulators but also complementary devices such as resonators, phase shifters, and filters. Few such devices exist at present, and the electromagnetic properties of those available at millimeter-wavelengths are generally fixed and characterized by broad (i.e., low Q) resonances. We introduce a class of 3D plasma/metal/dielectric photonic crystals (PPCs), operating in the 120-170 GHz spectral range, that are dynamic (tunable and reconfigurable at electronic speeds) and possess attenuation and transmission resonances with bandwidths below 50 MHz. Interference between sublattices of the crystal, which controls the resonance line shapes, is manipulated through the crystal structure. Incorporating Bragg arrays of low-temperature plasma microcolumns into a dielectric/metal scaffold that is itself a static crystal forms two interwoven and electromagnetically coupled crystals. Plasma-scaffold lattices produce multiple, narrowband attenuation resonances that shift monotonically to higher frequencies by as much as 1.6 GHz with increasing plasma electron density. Controlling the longitudinal geometry of the PPC through electronic activation of successive Bragg planes of plasma columns reveals an unexpected double-crystal symmetry interaction at 138.4 GHz and resonance Q values above 5100. The introduction of point or line defects into plasma column/polymer/metal crystals increases transparency at resonances of the scaffold (Borrmann effect) and yields Fano line shapes characteristic of coupled resonators. The experimental results suggest the suitability of PPC-based metamaterials for applications including multichannel communications, millimeter-wave spectroscopy, and fundamental studies of multiple, coupled resonators. (C) 2019 Author(s).