Understanding how light interacts with matter at the nanometre scale is a fundamental issue in optoelectronics and nanophotonics. In particular, many applications (such as bio-sensing, cancer therapy and all-optical signal processing) rely on surface-bound optical excitations in metallic nanoparticles. However, so far no experimental technique has been capable of imaging localized optical excitations with sufficient resolution to reveal their dramatic spatial variation over one single nanoparticle. Here, we present a novel method applied on silver nanotriangles, achieving such resolution by recording maps of plasmons in the near-infrared/visible/ultraviolet domain using electron beams instead of photons. This method relies on the detection of plasmons as resonance peaks in the energy-loss spectra of subnanometre electron beams rastered on nanoparticles of well-defined geometrical parameters. This represents a significant improvement in the spatial resolution with which plasmonic modes can be imaged, and provides a powerful tool in the development of nanometre-level optics.

Mapping surface plasmons on a single metallic nanoparticle

Real-time capability is a key factor which affects the practicality of an indoor positioning system significantly. While visible light positioning (VLP) is widely studied since it can provide indoor positioning functionality with LED illumination, the existing VLP systems still suffer from the high positioning latency and are not practical for mobile units with high moving speed. In this paper, a real-time VLP system with low positioning latency and high positioning accuracy is proposed. With the lightweight image processing algorithm, the proposed system can be implemented on low-cost embedded system and support real-time accurate indoor positioning for mobile units with a fast moving speed. Experimental results show that the proposed system implemented on a Raspberry Pi can achieve a positioning accuracy of 3.93 cm and support the moving speed up to 38.5 km/h.

Real-time visible light positioning supporting fast moving speed.

LED based high accuracy indoor visible light positioning algorithm

Advances in plasmonic materials and devices have given rise to a variety of applications in photocatalysis, microscopy, nanophotonics, and metastructures. With the advent of computing power and artificial neural networks, the characterization and design process of plasmonic nanostructures can be significantly accelerated using machine learning as opposed to conventional FDTD simulations. The machine learning (ML) based methods can not only perform with high accuracy and return optical spectra and optimal design parameters, but also maintain a stable high computing efficiency without being affected by the structural complexity. This work reviews the prominent ML methods involved in forward simulation and inverse design of plasmonic nanomaterials, such as Convolutional Neural Networks, Generative Adversarial Networks, Genetic Algorithms and Encoder–Decoder Networks. Moreover, we acknowledge the current limitations of ML methods in the context of plasmonics and provide perspectives on future research directions.

/pdf/instantaneous-property-prediction-and-inverse-design-of-3cqrwwpo.pdf

Instantaneous Property Prediction and Inverse Design of Plasmonic Nanostructures Using Machine Learning: Current Applications and Future Directions

A CMOS-compatible plasmonic waveguide with a metal or metal-like strip sandwiched in-between dielectrics has been proposed for intra-chip communication in the more-than-Moore era. A sequence of numerical models has been presented to evaluate the plasmonic waveguide performance. For device-level consideration, we demonstrated through simulations that Cu (1450 nm pitch) and PLD-TiN (900 nm pitch) plasmonic waveguides symmetrically sandwiched by SiO2 with much smaller and hence denser interconnects, are promising candidates for use in global wires for the asynchronous communication. This design of plasmonic waveguide can bridge the CMOS circuitry and high-speed communication at optical frequencies within chip. For a system-level assessment, both of them have the same bandwidth throughput of ∼19.8 Gbps. The other performance parameters of Cu and PLD-TiN plasmonic waveguides are respectively, signal latency of ∼ $0.18\text{ ps}\ $ and $0.19\text{ ps},$ energy dissipation per computing bit of ∼ $2.5 \times {10^{ - 3}}{\rm{\ fJ}}/{\rm{bit}}$ and $3.8 \times {10^{ - 3}}{\rm{\ fJ}}/{\rm{bit}}$ , and 25% crosstalk coupling length of $155{\rm{\ \mu m}}$ and $125{\rm{\ \mu}} \text{m}$ . These findings suggest that plasmonic waveguide for intra-chip communication surpass those of existing electronic interconnects for all the categories of performance parameters.

The Design of CMOS-Compatible Plasmonic Waveguides for Intra-Chip Communication

Electro-optic modulators are among the most important building blocks in optical communication networks. Lithium niobate, for example, has traditionally been widely used to fabricate high-speed optical modulators due to its large Pockels effect. Another material, barium titanate, nominally has a 50 times stronger r-parameter and would ordinarily be a more attractive material choice for such modulators or other applications. In practice, barium titanate thin films for optical waveguide devices are usually grown on magnesium oxide due to its low refractive index, allowing vertical mode confinement. However, the crystal quality is normally degraded. Here, a group of scandate-based substrates with small lattice mismatch and low refractive index compared to that of barium titanate is identified, thus concurrently satisfying high crystal quality and vertical optical mode confinement. This work provides a platform for nonlinear on-chip optoelectronics and can be promising for waveguide-based optical devices such as Mach-Zehnder modulators, wavelength division multiplexing, and quantum optics-on-chip.

A Barium Titanate-on-Oxide Insulator Optoelectronics Platform.

Silicon-Based Quantum Mechanical Tunnel Junction for Plasmon Excitation from Low-Energy Electron Tunneling

Ultrafast electro-optical conversion at nanoscale is of fundamental interest for information transfer and optical interconnects. Light emission from a quantum tunnel junction provides an opportunity owing to its unique capability of ultrafast response and small footprint. However, the main challenge to the wide adoption of the tunnel junction is its low emission efficiency caused by the low inelastic electron tunneling proportion and radiation efficiency. In this Letter, an electrically driven silicon light source with its efficiency enhanced by using a nano-antenna in a metal-insulator-semiconductor junction is proposed. Strong plasmon confinement in the nano-antenna provides large local density of optical states and bridges the wave vector mismatch between nanoscale volume field confinement and far-field radiation. Two orders of magnitude of emission enhancement are achieved over typical planar MIS junctions.

Nano-antenna enhanced waveguide integrated light source based on an MIS tunnel junction.

To develop methods to generate, manipulate, and detect plasmonic signals by electrical means with complementary metal-oxide-semiconductor (CMOS)-compatible materials is essential to realize on-chip electronic-plasmonic transduction. Here, electrically driven, CMOS-compatible electronic-plasmonic transducers with Al-AlOX -Cu tunnel junctions as the excitation source of surface plasmon polaritons (SPPs) and Si-Cu Schottky diodes as the detector of SPPs, connected via plasmonic strip waveguides of Cu, are demonstrated. Remarkably, the electronic-plasmonic transducers exhibit overall transduction efficiency of 1.85 ± 0.03%, five times higher than previously reported transducers with two tunnel junctions (metal-insulator-metal (MIM)-MIM transducers) where SPPs are detected based on optical rectification. The result establishes a new platform to convert electronic signals to plasmonic signals via electrical means, paving the way toward CMOS-compatible plasmonic components.

Yan Liu

Papers

A Barium Titanate-on-Oxide Insulator Optoelectronics Platform.

Silicon-Based Quantum Mechanical Tunnel Junction for Plasmon Excitation from Low-Energy Electron Tunneling

Nano-antenna enhanced waveguide integrated light source based on an MIS tunnel junction.

The Design of CMOS-Compatible Plasmonic Waveguides for Intra-Chip Communication

CMOS-Compatible Electronic–Plasmonic Transducers Based on Plasmonic Tunnel Junctions and Schottky Diodes