Designing Photonic Functionalities with Metal-Dielectric Layered Media
In this doctoral research, we aimed to study light-matter interaction in resonant multilayer structures, to find new effective means of controlling this interaction, and to design and demonstrate novel photonic functionalities, which could result in new and more efficient photonic and microwave devices. As the strength of light-matter interaction depends on the intensity of the electric and magnetic field components of the electromagnetic wave, we used resonant multilayer structures to produce spatial field distributions with nodal and antinodal points, at which electric and magnetic field responses could be selectively enhanced or suppressed. We then introduced magnetic, nonlinear or phase-change materials in the resonant multilayers to enhance/suppress light-matter interaction and to achieve the desired photonic functionalities, such as efficient optical/microwave isolation and circulation, robust photonic limiting, modulation and switching, directional transmission and high-contrast polarization. The corresponding photonic devices were designed by using numerical methods and then realized and measured at microwave, millimeter-wave, and optical frequencies. The first group of photonic devices developed in this research are reflective photonic switches, modulators and limiters utilizing optical materials with nonlinear refraction (e.g., GaAs and ZnO) and phase-change materials (e.g., GST). At low incident intensity, the multilayer exhibits resonant transmittance, while at high incident intensity it becomes highly reflective in a broad spectral range due to induced changes in the refractive index of the nonlinear or phase-change material. We have achieved significant improvement in such important device characteristics as lower limiting threshold, higher damage threshold, and enhanced dynamic range. We have shown that the transition from resonant transmission to broadband reflection can also be triggered by a small change in the incident angle, thereby leading to the added functionality-reflective collimation. A reflective collimator with high sensitivity to the incident angle has been experimentally realized for the visible light. It was also utilized in optical/microwave isolators to provide omnidirectional isolation. A photonic limiter for the W-band with the phase-change component (VO2) has been designed and experimentally demonstrated. It is shown that a nanolayer of VO2 incorporated into a resonant multilayer cavity can undergo the transition from the insulating to the metallic state, induced by the high-power incident radiation and heating resulting from absorption. The second group of photonic devices developed in this research are layered-sheet Faraday isolators with virtually unlimited aperture and the possibility of a broadband, omnidirectional isolation. These involve a thin-sheet 45° Faraday rotator sandwiched between a pair of layered-sheet polarizers. A thin-sheet rotator including a magnetic Cobalt nanolayer incorporated in a resonant cavity at the position of the nodal plane of the E-filed and the antinodal plane of the H-field has been experimentally demonstrated in the Ka-band. The incorporation of dichroic nanolayers into the resonant multilayer cavity has provided a new generation of optical/quasi-optical polarizers. Highly reflective and totally absorbing polarizers, as well as asymmetric reflective/absorptive polarizers with significantly increased extinction ratios have been designed and realized in the W-band. The reflective polarizers are shown to have strongly reduced absorption of both wanted and unwanted polarizations and, therefore, enhanced high-power handling capabilities. The asymmetric layered-sheet polarizers perfectly transmit the wanted polarization, but completely reflect the unwanted polarization in forward propagation direction while exhibiting total resonant absorption of the unwanted polarization in the backward propagation direction. The asymmetric and absorbing layered-sheet polarizers can thus be utilized in constructing wide-aperture isolators. Finally, an integrated layered-sheet isolator has been developed. The integrated design still involves magnetic and dichroic layers incorporated in a resonant multilayer cavity, but the polarizers can no longer be identified as separate parts of the isolator. The integrated isolator can be simpler and more efficient than the traditional one with the distinct Faraday rotator and polarizers.