Properly structuring materials at subwavelength scale allows for strong light-matter interaction, thereby enhancing near-field effects and engineering far-field scattering through intermodal interference. A majority of such effects are associated with plasmonics where electromagnetic waves created in the vicinity of metallic nanostructures is able to give rise to a variety of novel phenomena and fascinating applications. In the recent years, dielectric nanoparticles with high refractive index based on optically induced electric and magnetic Mie resonances attract a plethora of attention. In this rapidly developing field, dissipative loss in optical materials is considered one of the major challenges. Here, in this dissertation, we show that, counter-intuitively, it contributes positively to sub-wavelength scale light enhancement and confinement, and also improves scattering efficiency in the far field.
In the first part of this dissertation, near field enhancement in dissipative dielectric antennas is demonstrated to be orders of magnitude higher than their lossless dielectric counterparts, which is particularly favorable in deep UV applications where metals are plasmonically inactive and transparent dielectrics always have low index. The loss facilitated field enhancement is the result of large material permittivity contrast and electric field discontinuity. These dissipative dielectric nanostructures can be easily achieved with a great variety of dielectrics at their Lorentz oscillation frequencies, thus having the potential to build a completely new material platform boosting light-matter interaction over broader frequency ranges, with advantages such as bio-compatibility, CMOS compatibility and harsh environment endurance.
Additionally, manipulation of ultra-violet light through metasurface in the far field utilizing the silicon loss is then presented. We experimentally demonstrate Si metasurfaces working effectively over a broad band down to 290nm, with efficiencies comparable to plasmonic metasurface performance in the infrared regime. And for the first time, we show photolithography enabled by metasurface-generated ultraviolet holograms. We attribute such performance enhancement to the large scattering cross-sections of Si antennas in the ultraviolet range, which is adequately modeled via a circuit model. Our new platform will deepen our understanding of the role of material dissipation and introduce even more material options to broadband metaphotonic applications, including those in integrated photonics and holographic lithography technologies.
Dynamically tunable far field with subwavlength nanostructures is always desired for practical applications. In the last section of this dissertation, we introduce a lithography free and field-programmable photonic metacanvas. Previous attempts of realizing such idea used micro-mechanical metamaterials or amorphous-crystalline phase transition materials, which are limited in terms of the functionalities, efficiency, cost, and high working temperature (> 600oC). It is much desired to reconfigure photonic devices in a fast, large-scale, cost-effective, reliable, and free-style way at or near room temperature. Here, we present a completely rewritable meta-canvas on which arbitrary photonic devices can be rapidly written, erased and rewritten. The writing is with a low-power (1 mW) continuous laser and the entire process stays below ~ 90oC. Using these devices we demonstrate dynamical manipulation of optical waves for light propagation, reconstruction and polarization. Such meta-canvas supports physical (re)compilation of photonic operators akin to that of FPGA, opening up possibilities where a single photonic element can be field-programmed to deliver complex, system-level functionalities.