Dynamic Plasma/Metal/Dielectric Crystals as mm-wave to Thz Communications and Sensing Devices, and Testing of Drude Model

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Future communications networks, such as those connecting cell phones and computers, must inexorably move to higher frequencies because of unrelenting demand for bandwidth. Several countries worldwide are presently developing communications systems operating above 100 GHz but few of the necessary components, such as beamsplitters, attenuators and phase shifters, exist at present. This proposal is motivated by the recent development at the University of Illinois of artificial 2D and 3D “crystals” comprising periodic arrays of microplasmas, dielectrics, and metal microcolumns. Because this new form of artificial (i.e., not found in nature), electromagnetically-active materials include microcolumns of low temperature plasma (similar to that in neon signs), the response of the crystal to an incoming electromagnetic field can be “tuned” at electronic speeds, in contrast to previous communications components whose properties are fixed. The research proposed for this NSF program will focus on the fundamental behavior of these dynamic crystals and their application to communications, sensing, and detection over the ~50 GHz – 2 THz spectral region. In addition to enabling new communications systems, it is anticipated that tunable plasma photonic crystals will yield new, sensitive detectors of environmental pollutants and will be capable of temporarily storing electromagnetic energy in the microwave, mm-wave, and sub-mm wave spectral regions. This NSF ECCS proposal, motivated by the recent development at the University of Illinois of artificial 2D and 3D crystals comprising periodic arrays of microplasmas, dielectrics, and metal microcolumns, focusses on the fundamental behavior of these dynamic crystals and their application to communications, sensing, and detection over the ~50 GHz – 2 THz spectral region. Because the microplasma electron density can be readily altered by orders of magnitude (and at electronic speeds), the electromagnetic response of such plasma photonic crystals (PPCs) can be manipulated so as to shift, strengthen, or eliminate transmission or attenuation modes (resonances) of the static (i.e., no plasma) crystal. It has been demonstrated, for example, that the Q of static crystal resonances in the 130-150 GHz region can be increased by a factor of 5 or more, and blue-shifted by 1 GHz, by generating low temperature plasma selectively within a metal/dielectric crystal. Furthermore, small cubic crystals having a simple, internal waveguide/coupled resonator structure exhibit (in preliminary data) mode-splitting and complete mode suppression near 139 GHz because the microplasma arrays control the degree of coupling between the waveguide and the resonator. This technology has not existed previously but it appears to have considerable promise for devices such as dynamic mm-wave and THz resonators, filters, mirrors, resonators, phase shifters, interferometers, and other devices in this spectral region. In particular, the dependence of the dielectric permittivity of low temperature plasma on electron density and background gas pressure allows one to manipulate the response of a PPC of a given structure. The time-dependent ability of such crystals to store (“trap”), reflect, and polarize radiation in the mm- and sub-mm wave regions will also be explored. Not only are these electromagnetically-active, artificial materials of interest for 100-500 GHz communications systems, but they are also of considerable value for fundamental science. Specifically, PPCs are ideally-suited as a testbed to rigorously test Drude’s formalism for the refractive index of low temperature plasma, particularly at the electron densities and atmospheric background pressures typical of microplasmas. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteriaThis award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.