Session W11: Optical Metamaterials

Ultrafast light dynamics in plasmonic metastructures

Coherent and incoherent nonlinear optical effects play important role in photonics, laser physics and quantum optics. However, nonlinear optical applications are limited by the available choice of naturally occurring materials and their generally weak nonlinear response. Weak nonlinearity of conventional materials can be enhanced by their nanostructuring or through metamaterial approach. Plasmonic and dielectric nanostructures provide numerous opportunities for designing optical response in both linear and nonlinear regimes. Combining dissimilar plasmonic and dielectric materials in one nanostructure offers additional prospects for devising optical properties and achieving functionalities not attainable otherwise. Here, we will discuss hetero-nanostructures for tailoring hot-electron dynamics, plasmonic nonlinearities, and ultrashort pulse manipulation. Going beyond traditional field enhancement effects, we show how the introduction of additional hot-electron relaxation pathways, anisotropy and nonlocality allows to accelerate of decelerate the temporal response of nonlinear optical effects in plasmonic nanostructures. The metamaterial designs for controlling ultrafast pulse propagation with metamaterials will also be discussed. Ultrafast optical and electronic processes in nanostructured materials may find applications in nonlinear photonics, photocatalysis and development of time-varying media.   

Low-frequency plasmon excitations in multicoaxial NIM cables

By using an elegant response function theory, which does not require matching of the messy boundary conditions,

we investigate the surface plasmon excitations in the multicoaxial cylindrical cables made up of

negative-index metamaterials. The multicoaxial cables with dispersive metamaterial components exhibit a

rather richer (and complex) plasmon spectrum with each interface supporting two modes: one TM and the

other TE for m0 (the integer order of the Bessel function). The cables with nondispersive metamaterial components

bear a different tale: they do not support simultaneously both TM and TE modes over the whole range

of propagation vector. The computed local and total density of states enable us to substantiate spatial positions

of the modes in the spectrum. Such quasi-one-dimensional systems as studied here should prove to be the milestones

of the emerging optoelectronics and telecommunications systems.   

Breaking the limitation of polarization multiplexing in optical metasurfaces with engineered noise

Noise is usually undesired yet inevitable in science and engineering. However, by introducing the engineered noise to the precise solution of Jones matrix elements, we break the fundamental limit of polarization multiplexing capacity of metasurfaces that roots from the dimension constraints of the Jones matrix. We experimentally demonstrate up to 11 independent holographic images using a single metasurface illuminated by visible light with different polarizations. To the best of our knowledge, it is the highest capacity reported for polarization multiplexing. Combining the position multiplexing scheme, the metasurface can generate 36 distinct images, forming a holographic keyboard pattern. This discovery implies a new paradigm for high-capacity optical display, information encryption, and data storage.

Reference:

Bo Xiong, Yu Liu, Yihao Xu, Lin Deng, Chao-Wei Chen, Jia-Nan Wang, Ruwen Peng, Yun Lai, Yongmin Liu, Mu Wang, “Breaking the limitation of polarization multiplexing in optical metasurfaces with engineered noise", Science 379, 294-299 (2023).   

Fabrication of Nanostructures for Diffractive Optical Elements on Fused Silica Glass

Diffractive optical lenses offer breakthrough features such as high-resolution, lightweight design, high-efficient performance and high-contrast focusing capabilities. These lenses can be employed in diverse fields including astronomy, free-space optical communications, spectroscopy, defense, and remote sensing. Traditionally, diffractive optics have exhibited a low transmission efficiency. In response, we have employed recent developments of photolithography techniques to fabricate diffractive nanostructures. In this study, we have fabricated multilevel Fresnel zone plates (FZP) and multilevel photon sieves (PS) on fused silica glass. Fused silica glass lenses offer large transparency range, low thermal expansion, and high resistance to optical damage, leading to great performance of these diffractive structures. As predicted from simulation data, the experimental results have exhibited 39% and 15.5% focusing efficiency for the 2-level FZP and 2-level PS, respectively, when compared with the amplitude-type FZP and PS of 10% and 5% focusing efficiencies, respectively. The outcome marks a significant advancement in the realm of high-resolution diffractive optics, enhancing the focusing efficiency that holds promise for various photonic applications.   

Refractory nanoscale plasmonic junctions of Titanium Nitride and Niobium.

Plasmonic tunnel junctions have great potential in the realization of nanoscale light-emitting devices and commonly used materials for these devices are metals such as gold and aluminum owing to their attractive optical properties in the visible range. A major drawback to their use is the unstable optical properties of their nanostructures at high current densities and elevated temperatures due to atomic motion, which hinders eventual device applications.  As such, it is imperative to consider refractory alternatives that guarantee the geometric stability of the light-emitting junctions at high temperatures and mimic the optical properties of noble metals in desired wavelength regimes. Here, we present preliminary results from our study of tunnel junctions composed of refractory materials; TiN and Nb that have demonstrated desirable plasmonic responses similar to gold in the red and near-infrared regime.