Gigahertz All-Optical Modulation Using Reconfigurable Nanophotonic Metamolecules

Illuminating Recent Progress in Nanotransfer Printing: Core Principles, Emerging Applications, and Future Perspectives

As the demand for diverse nanostructures in physical/chemical devices continues to rise, the development of nanotransfer printing (nTP) technology is receiving significant attention due to its exceptional throughput and ease of use. Over the past decade, researchers have attempted to enhance the diversity of materials and substrates used in transfer processes as well as to improve the resolution, reliability, and scalability of nTP. Recent research on nTP has made continuous progress, particularly using the control of the interfacial adhesion force between the donor mold, target material, and receiver substrate, and numerous practical nTP methods with niche applications have been demonstrated. This review article offers a comprehensive analysis of the chronological advancements in nTP technology and categorizes recent strategies targeted for high-yield and versatile printing based on controlling the relative adhesion force depending on interfacial layers. In detail, the advantages and challenges of various nTP approaches are discussed based on their working mechanisms, and several promising solutions to improve morphological/material diversity are presented. Furthermore, this review provides a summary of potential applications of nanostructured devices, along with perspectives on the outlook and remaining challenges, which are expected to facilitate the continued progress of nTP technology and to inspire future innovations.

Gigahertz optoacoustic vibration in Sub-5 nm tip-supported nano-optomechanical metasurface

The gigahertz acoustic vibration of nano-optomechanical systems plays an indispensable role in all-optical manipulation of light, quantum control of mechanical modes, on-chip data processing, and optomechanical sensing. However, the high optical, thermal, and mechanical energy losses severely limit the development of nano-optomechanical metasurfaces. Here, we demonstrated a high-quality 5 GHz optoacoustic vibration and ultrafast optomechanical all-optical manipulation in a sub-5 nm tip-supported nano-optomechanical metasurface (TSNOMS). The physical rationale is that the design of the semi-suspended metasurface supported by nanotips of <5 nm enhances the optical energy input into the metasurface and closes the mechanical and thermal output loss channels, result in dramatically improvement of the optomechanical conversion efficiency and oscillation quality of the metasurface. The design strategy of a multichannel-loss-mitigating semi-suspended metasurface can be generalized to performance improvements of on-chip processed nano-optomechanical systems. Applications include all-optical operation of nanomechanical systems, reconfigurable nanophotonic devices, optomechanical sensing, and nonlinear and self-adaptive photonic functionalities.

A broadband and low-power light-control-light effect in a fiber-optic nano-optomechanical system

The coupling of the optical and mechanical degrees of freedom using optical force in nano-devices offers a novel mechanism to implement all-optical signal processing. However, the ultra-weak optical force requires a high pump optical power to realize all-optical processing. For such devices, it is still challenging to lower the pump power and simultaneously broaden the bandwidth of the signal light under processing. In this work, a simple and cost-effective optomechanical scheme was demonstrated that was capable of achieving a broadband (208 nm) and micro-Watt (∼624.13 μW) light-control-light effect driven by a relatively weak optical force (∼3 pN). In the scheme, a tapered nanofiber (TNF) was evanescently coupled with a substrate, allowing the pump light guided in the TNF to generate a strong transverse optical force for the light-control-light effect. Additionally, thanks to the low stiffness (5.44 fN nm^-1) of the TNF, the light-control-light scheme also provided a simple method to measure the static weak optical force with a minimum detectable optical force down to 380.8 fN. The results establish TNF as a cost-effective scheme to break the limitation of the modulation wavelength bandwidth (MWB) at a low pump power and show that the TNF-optic optomechanical system can be well described as a harmonic oscillator.

Spectrally broadband electro-optic modulation with nanoelectromechanical string resonators

In this paper, we present a shutter-based electro-optical modulator made of two parallel nanoelectromechanical silicon nitride string resonators. These strings are covered with electrically connected gold electrodes and actuated either by Lorentz or electrostatic forces. The in-plane string vibrations modulate the width of the gap between the strings. The gold electrodes on both sides of the gap act as a mobile mirror that modulate the laser light that is focused in the middle of this gap. These electro-optical modulators can achieve an optical modulation depth of almost 100% for a driving voltage lower than 1 mV at a frequency of 314 kHz. The frequency range is determined by the string resonance frequency, which can take values of the order of a few hundred kilohertz to several megahertz. The strings are driven in the strongly nonlinear regime, which allows a frequency tuning of several kilohertz without significant effect on the optical modulation depth.

Four-Mode Programmable Metamaterial Using Ternary Foldable Origami

Designing a multifunctional metamaterial with programmable feature has become a new trend in mechanical, acoustic, and electromagnetic research fields due to the controllability of their structural behaviors and functionalities. The codable or reconfigurable structures have shown more remarkable characteristics than the traditional and conventional metamaterials to implement functional programmability. However, structural complexity and hi-tech requirement are the biggest constraints to their practical applications. This paper numerically and experimentally investigates a programmable metamaterial based on ternary foldable origami in the gigahertz-frequency regime. The proposed metamaterial provides four transformable modes corresponding to four different functions of electromagnetic reflector and frequency-selectable absorbers by programming unique ternary foldable origami coded as "0", "1", and "2" for different folding levels. Interestingly, the proposed foldable origami consists of a simple dielectric paper and a bottom conductor, while there is no conductive pattern on the top. Therefore, the proposed programmable metamaterial is extremely robust and can be extended to a multiresonance mode and origami computing.

Printed optical metamaterials composed of embedded silver nanoparticles for flexible applications

For development of next-generation light control, a simple manufacturing technology to produce flexible metamaterials is a key component. Here, we report development of a printing method involving combination of a thermal nanoimprint method and a squeegeeing method, and demonstrate printed optical metamaterials made of commercially available ink consisting of silver nanoparticles. Optical evaluations of printed dipole resonators indicate dipole resonances corresponding to the structure lengths; these resonances are observed at wavelengths of 765-1346 nm. In particular, we report the important finding that, in metamaterials strongly affected by their constituent materials, a metamaterial structure made of the ink exhibits optical properties comparable to those produced by a vacuum deposition process.

Sub-diffraction spatial mapping of nanomechanical modes using a plasmomechanical system

Plasmomechanical systems - formed by introducing a mechanically compliant gap between metallic nanostructures - produce large optomechanical interactions that can be localized to deep subwavelength volumes. This unique ability opens a new path to study optomechanics in nanometer-scale regimes inaccessible by other methods. We show that the localized optomechanical interactions produced by plasmomechanics can be used to spatially map the displacement modes of a vibrating nanomechanical system with a resolution exceeding the diffraction limit. Furthermore, we use white light illumination for motion transduction instead of a monochromatic laser, and develop a semi-analytical model matching the changes in optomechanical coupling constant and motion signal strength observed in a broadband transduction experiment. Our results clearly demonstrate the key benefit of localized and broadband performance provided by plasmomechanical systems, which may enable future nano-scale sensing and wafer-scale metrology applications.

Electrically tunable plasmomechanical oscillators for localized modulation, transduction, and amplification

Plasmomechanical systems are an emerging class of device that hold great promise for manipulating light-matter interactions with high speed and sub-diffraction spatial resolution. However, realizing their potential requires developing active plasmomechanical systems that can localize their functionality to the level of an individual sub-wavelength plasmonic resonator. Here, we present an active, electrically tunable plasmomechanical system that uses a localized-gap plasmonic resonator to mediate optical, thermal, and mechanical interactions within a subwavelength footprint. Our device enables facile electromechanical modulation of localized plasmons, selective sub-diffraction transduction of nanomechanical motion, and functions as a plasmomechanical oscillator that can be injection locked to and thus amplify weak external stimuli. These functionalities benefit applications in nanomechanical sensing, spatial light modulators, and reconfigurable metasurfaces.

Gigahertz Optomechanical Modulation by Split-Ring-Resonator Nanophotonic Meta-Atom Arrays

Using polarization-resolved transient reflection spectroscopy, we investigate a metasurface consisting of coherently vibrating nanophotonic U-shaped split-ring meta-atoms that exhibit colocalized optical and mechanical resonances. With an array of these resonators formed of gold on glass, essentially miniature tuning forks, we monitor the visible-pump induced gigahertz oscillations in reflected infrared light intensity to probe the multimodal vibrational response. Numerical simulations of the associated transient deformations and strain fields elucidate the complex nanomechanical dynamics contributing to the ultrafast optical modulation and point to the role of acousto-plasmonic interactions through the opening and closing motion of the SRR gaps as the dominant effect. Applications include ultrafast acoustooptic modulator design and sensing.