Tunable Nanophotonics Research Articles

Tunable and dynamic nanophotonics: introduction

In this introduction, we provide an overview of the papers that were accepted for publication in the feature issue “Tunable and dynamic nanophotonics” of the Journal of the Optical Society of America B. The feature issue contains 10 articles on cutting-edge topics in the field of tunable nanophotonic systems.

Tunable hyperbolic polaritons with plasmonic phase-change material In3SbTe2

Abstract Hyperbolic polaritons that originate from the extreme optical anisotropy in van der Waals (vdW) crystals have gained much attention for their potential in controlling nanolight. For practical use, there has been a strong interest to develop various manipulation strategies to customize the propagation of hyperbolic polaritons on a deeply sub-diffractional scale. In this regard, phase-change materials (PCMs) that possess two phases with different refractive indices offer suitably a tunable dielectric environment. Here, we report on the tuning of hyperbolic phonon polaritons in natural vdW crystals, hexagonal boron nitride (hBN), and alpha-phase molybdenum trioxide (α-MoO3), using the plasmonic phase-change material In3SbTe2 (IST). Unlike conventional PCMs whose both phases are dielectric, IST features a metallic crystalline phase that is stable at room temperature. The coupling between polaritons with their mirror charges in the underneath crystalline IST triggers an even stronger field confinement for polaritons. Moreover, benefited from the metallicity of laser-writable crystalline IST, we show an all-optical material platform in which crystalline IST boundaries efficiently excite and focus hyperbolic phonon polaritons in α-MoO3. Our experiments highlight the possibility to obtain new degrees of freedom in polariton engineering with plasmonic PCMs, thereby expanding the toolkit of tunable nanophotonics with flexible, on-demand fabrication and reconfiguration capabilities.

Editorial for the Special Issue on Tunable Nanophotonics and Reconfigurable Metadevices

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Tunable metasurfaces via the humidity responsive swelling of single-step imprinted polyvinyl alcohol nanostructures

The application of hydrogels in nanophotonics has been restricted due to their low fabrication feasibility and refractive index. Nevertheless, their elasticity and strength are attractive properties for use in flexible, wearable-devices, and their swelling characteristics in response to the relative humidity highlight their potential for use in tunable nanophotonics. We investigate the use of nanostructured polyvinyl alcohol (PVA) using a one-step nanoimprinting technique for tunable and erasable optical security metasurfaces with multiplexed structural coloration and metaholography. The resolution of the PVA nanoimprinting reaches sub-100 nm, with aspect ratios approaching 10. In response to changes in the relative humidity, the PVA nanostructures swell by up to ~35.5%, providing precise wavefront manipulation of visible light. Here, we demonstrate various highly-secure multiplexed optical encryption metasurfaces to display, hide, or destroy encrypted information based on the relative humidity both irreversibly and reversibly.

Photonic (computational) memories: tunable nanophotonics for data storage and computing

Abstract The exponential growth of information stored in data centers and computational power required for various data-intensive applications, such as deep learning and AI, call for new strategies to improve or move beyond the traditional von Neumann architecture. Recent achievements in information storage and computation in the optical domain, enabling energy-efficient, fast, and high-bandwidth data processing, show great potential for photonics to overcome the von Neumann bottleneck and reduce the energy wasted to Joule heating. Optically readable memories are fundamental in this process, and while light-based storage has traditionally (and commercially) employed free-space optics, recent developments in photonic integrated circuits (PICs) and optical nano-materials have opened the doors to new opportunities on-chip. Photonic memories have yet to rival their electronic digital counterparts in storage density; however, their inherent analog nature and ultrahigh bandwidth make them ideal for unconventional computing strategies. Here, we review emerging nanophotonic devices that possess memory capabilities by elaborating on their tunable mechanisms and evaluating them in terms of scalability and device performance. Moreover, we discuss the progress on large-scale architectures for photonic memory arrays and optical computing primarily based on memory performance.

High Q Resonant Sb2S3-Lithium Niobate Metasurface for Active Nanophotonics.

Phase change materials (PCMs) are attracting more and more attentions as enabling materials for tunable nanophotonics. They can be processed into functional photonic devices through customized laser writing, providing great flexibility for fabrication and reconfiguration. Lithium Niobate (LN) has excellent nonlinear and electro-optical properties, but is difficult to process, which limits its application in nanophotonic devices. In this paper, we combine the emerging low-loss phase change material with LN and propose a new type of high Q resonant metasurface. Simulation results show that the -LN metasurface has extremely narrow linewidth of 0.096 nm and high quality (Q) factor of 15,964. With LN as the waveguide layer, strong nonlinear properties are observed in the hybrid metasurface, which can be employed for optical switches and isolators. By adding a pair of Au electrodes on both sides of the LN, we can realize dynamic electro-optical control of the resonant metasurface. The ultra-low loss of , and its combination with LN, makes it possible to realize a new family of high Q resonant metasurfaces for actively tunable nanophotonic devices with widespread applications including optical switching, light modulation, dynamic beam steering, optical phased array and so on.

Two‐Photon Laser Writing of Soft Responsive Polymers via Temperature‐Controlled Polymerization

AbstractEnhancing the resolution of 3D patterning techniques in functional soft polymers enlarges the application areas of responsive shape‐changing materials, for tunable nanophotonics and nanorobotics. Thanks to the recent advances of polymer science, the palette of available materials for nanomanufacturing is becoming wider and wider—although the comprehension of their polymerization process by two‐photon polymerization is still incomplete. In this work, both shrinking of the minimal polymerizable unit and a significant improvement of the mechanical stability of microstructured soft polymers, in particular of liquid crystalline networks, are demonstrated. To this aim, temperature control enhances the resolution and reduces the swelling of the polymerized structures, thus avoiding deviations of the final structure from the intended design. This fine control on the nanoscale features enables the use of soft responsive materials not only for bulky microelements, but also for high‐resolution structures with more complex design.

Fabrication and dual-wavelength characterization of a binary mixture of light-responsive polymeric nanocapsules

Two different types of azo dye-doped liquid crystal mixtures were separately nano-confined and characterized and then dispersed in the same host matrix to enhance the wavelength tunability of the laser-induced transparency of the fabricated polymeric thin film nanocomposites. The obtained results indicated that the transmitted intensity can be controlled separately by applying dual-wavelength pump lasers irradiation based-on reorientation of liquid crystal mesogens followed by trans-cis photoisomerization of the different azo dye dopants inside the core of the polymeric nanocapsules. Since the fabricated thin films qualify the demand for improvement of laser-induced tunability, it is feasible to use the introduced nanocomposite as a smart light-responsive thin film layer that can be widely implemented in all-optical tunable nanophotonics.

Nanobenders as efficient piezoelectric actuators for widely tunable nanophotonics at CMOS-level voltages

Tuning and reconfiguring of nanophotonic components are needed to realize systems incorporating many components. The electrostatic force can deform a structure and tune its optical response. Despite the success of electrostatic actuators, they suffer from trade-offs between tuning voltage, tuning range, and on-chip area. Piezoelectric actuation could resolve these challenges, but only pm-per-volt scale wavelength tunability has been achieved. Here we propose and demonstrate compact piezoelectric actuators, called nanobenders, that transduce tens of nanometers per volt. By leveraging the non-uniform electric field from submicron electrodes, we generate bending of a piezoelectric nanobeam. Combined with a sliced photonic crystal cavity to sense displacement, we show tuning of an optical resonance by ~ 5 nm V−1 (0.6 THz V−1) and between 1520 ~ 1560 nm (~ 400 linewidths) within 4 V. Finally, we consider tunable nanophotonic components enabled by the nanobenders.

Active and Tunable Nanophotonics With Dielectric Nanoantennas

In recent years, high-index dielectric nanoantennas supporting Mie resonances have emerged as a promising platform to create low-loss nanophotonic devices. The multipolar resonances naturally supported by this kind of nanoantennas allow designing systems in which the out-coupling radiation, and in particular the directivity, can be tailored at will. Moreover, unlike plasmonic counterparts, local electromagnetic fields in resonant dielectric nanoparticles concentrate inside the structures rather than outside. This allows enhancing light–matter interactions in their volume and boosting their linear and nonlinear optical properties by choosing suitable semiconductors as the material platform to build them. In this article, we will discuss recent results on active and tunable nanophotonics based on resonant dielectric and semiconductor nanostructures. Specifically, we will focus on two main topics: active tuning of dielectric nanoantennas and enhancement and spectral shaping of light emission using dielectric nanoantennas, including lasing. Finally, future research directions and proposed practical applications will also be discussed.

Modelling of Electronically–Controlled Filters of Microwave (SHF), SubTHz and THz–Bands Based on Graphene Meta–Surfaces

Development of generating and receiving radiation methods and means by microwave, sub–Hz and THz ranges is connected with the creation of new high–speed elements of radioelectronics based on new nanomaterials. These includes graphene and nanotubes, in order to develop highly efficient tunable nanophotonics devices for signal processing using new principles, materials and structures. The creation of transmission lines, filters, parametric generators and amplifiers based on multilayer graphene structures is very perspective. However, for today, the physical phenomena and effects in graphene nanostructures are investigated poorly; there are no engineering methods of devices calculation, which is the main difficulty in the way of radioelectronic devices creating of new generation with new element base on the ground of graphene. For investigation of new nanoscale properties and functional possibilities of devices based on nanostructured materials and components – microresonators, transmission lines, antennas, etc. – in the microwave, sub–Hz and THz ranges, a unified approach to their mathematical modelling is required. To overcome the limitations associated with the calculation methods and design, the authors are grounding on the ideas of computational electrodynamics, successfully implemented in computer – aided modelling and design systems in the SHF technique.

Tunable Optical Nanocavity of Iron-garnet with a Buried Metal Layer

We report on the fabrication and characterization of a novel magnetophotonic structure designed as iron garnet based magneto-optical nanoresonator cavity constrained by two noble metal mirrors. Since the iron garnet layer requires annealing at high temperatures, the fabrication process can be rather challenging. Special approaches for the protection of metal layers against oxidation and morphological changes along with a special plasma-assisted polishing of the iron garnet layer surface were used to achieve a 10-fold enhancement of the Faraday rotation angle (up to 10.8°/µm) within a special resonance peak of 12 nm (FWHM) linewidth at a wavelength of 772 nm, in the case of a resonator with two silver mirrors. These structures are promising for tunable nanophotonics applications, in particular, they can be used as magneto-optical (MO) metal-insulator-metal waveguides and modulators.