Nanophotonic Technologies Research Articles

Scalable Fabrication of Integrated Nanophotonic Circuits on Arrays of Thin Single Crystal Diamond Membrane Windows.

Diamond has emerged as a promising platform for nanophotonic, optical, and quantum technologies. High-quality, single crystalline substrates of acceptable size are a prerequisite to meet the demanding requirements on low-level impurities and low absorption loss when targeting large photonic circuits. Here, we describe a scalable fabrication method for single crystal diamond membrane windows that achieves three major goals with one fabrication method: providing high quality diamond, as confirmed by Raman spectroscopy; achieving homogeneously thin membranes, enabled by ion implantation; and providing compatibility with established planar fabrication via lithography and vertical etching. On such suspended diamond membranes we demonstrate a suite of photonic components as building blocks for nanophotonic circuits. Monolithic grating couplers are used to efficiently couple light between photonic circuits and optical fibers. In waveguide coupled optical ring resonators, we find loaded quality factors up to 66 000 at a wavelength of 1560 nm, corresponding to propagation loss below 7.2 dB/cm. Our approach holds promise for the scalable implementation of future diamond quantum photonic technologies and all-diamond photonic metrology tools.

Performance of Planar, Rib, and Photonic Crystal Silicon Waveguides in Tailoring Group-Velocity Dispersion and Mode Loss

Nanophotonic technologies have attracted a lot of attention to co-develop optical and electronic devices on silicon (Si) that further miniaturize modern optical communication systems. Optical properties of these miniaturized devices are highly dependent on waveguide geometry and can be tailored for various applications with minor changes in cross-sectional areas. This paper investigates the performance of widely discussed planar, rib, and photonic crystal Si waveguides by manipulating the dimensions of Si core designed for single mode operation across the 1.2 to 1.6 μm telecommunication bands. Each of the waveguide is studied and compared for a set of properties, including effective refractive index, group index, group-velocity dispersion, and mode loss, with and without narrow bends, which can be instrumental in selecting the correct type and geometry of the waveguide required for any specific application.

Photonic Approach to Optimize Energy Consumption for On-chip Clos Network

To meet energy-efficient performance needs, the computation has positioned to parallel computer architectures, such as chip multiprocessors (CMPs), internally interconnected via networks-on-Chip (NoC) to achieve increasing communication needs. To accomplish scaling execution as center include increment to the hundreds future CMPs, all things considered, will require elite, yet vitality productive interconnects. Silicon Nano photonics is a promising swap for electronic on-chip interconnect for its high data transfer capacity and low inactivity, by the by, earlier methods have required high static force for the laser and warm ring tuning. We propose novel Nano photonic NoC (PNoC) design, upgraded for elite and force effectiveness. This paper makes three essential elements: a novel, Nano photonic engineering which isolates the system into subnets for better productivity; an exclusively photonic, inband, appropriated discretion plan; and a channel sharing schematic are using the same waveguides and wavelengths for intervention as information transmission. As a result the interconnection can be reduced latency with increased throughput.

Nanoengineered Surfaces for Thermal Energy Conversion

We provide an overview of the impact of using nanostructured surfaces to improve the performance of solar thermophotovoltaic (STPV) energy conversion and condensation systems. We demonstrated STPV system efficiencies of up to 3.2%, compared to ≤1% reported in the literature, made possible by nanophotonic engineering of the absorber and emitter. For condensation systems, we showed enhanced performance by using scalable superhydrophobic nanostructures via jumping-droplet condensation. Furthermore, we observed that these jumping droplets carry a residual charge which causes the droplets to repel each other mid-flight. Based on this finding of droplet residual charge, we demonstrated electric-field-enhanced condensation and jumping-droplet electrostatic energy harvesting.

Graded metascreens to enable a new degree of nanoscale light management.

Optical metasurfaces, typically referred to as two-dimensional metamaterials, are arrays of engineered subwavelength inclusions suitably designed to tailor the light properties, including amplitude, phase and polarization state, over deeply subwavelength scales. By exploiting anomalous localized interactions of surface elements with optical waves, metasurfaces can go beyond the functionalities offered by conventional diffractive optical gratings. The innate simplicity of implementation and the distinct underlying physics of their wave-matter interaction distinguish metasurfaces from three-dimensional metamaterials and provide a valuable means of moulding optical waves in the desired manner. Here, we introduce a general approach based on the electromagnetic equivalence principle to develop and synthesize graded, non-periodic metasurfaces to generate arbitrarily prescribed distributions of electromagnetic waves. Graded metasurfaces are realized with a single layer of spatially modulated, electrically polarizable nanoparticles, tailoring the scattering response of the surface with nanoscale resolutions. We discuss promising applications based on the proposed local wave management technique, including the design of ultrathin optical carpet cloaks, alignment-free polarization beam splitters and a novel approach to enable broadband light absorption enhancement in thin-film solar cells. This concept opens up a practical route towards efficient planarized optical structures with potential impact on the integrated nanophotonic technology.

Numerical and experimental investigation of light trapping effect of nanostructured diatom frustules

Recent advances in nanophotonic light-trapping technologies offer promising solutions in developing high-efficiency thin-film solar cells. However, the cost-effective scalable manufacturing of those rationally designed nanophotonic structures remains a critical challenge. In contrast, diatoms, the most common type of phytoplankton found in nature, may offer a very attractive solution. Diatoms exhibit high solar energy harvesting efficiency due to their frustules (i.e., hard porous cell wall made of silica) possessing remarkable hierarchical micro-/nano-scaled features optimized for the photosynthetic process through millions of years of evolution. Here we report numerical and experimental studies to investigate the light-trapping characteristic of diatom frustule. Rigorous coupled wave analysis (RCWA) and finite-difference time-domain (FDTD) methods are employed to investigate the light-trapping characteristics of the diatom frustules. In simulation, placing the diatom frustules on the surface of the light-absorption materials is found to strongly enhance the optical absorption over the visible spectrum. The absorption spectra are also measured experimentally and the results are in good agreement with numerical simulations.

Applied physics. Obtaining optical properties on demand.

Reconfigurable metamaterials provide a flexible platform for nanophotonic technology

Plasmon Enhanced Internal Photoemission in Antenna-Spacer-Mirror Based Au/TiO₂ Nanostructures.

Emission of photoexcited hot electrons from plasmonic metal nanostructures to semiconductors is key to a number of proposed nanophotonics technologies for solar harvesting, water splitting, photocatalysis, and a variety of optical sensing and photodetector applications. Favorable materials and catalytic properties make systems based on gold and TiO2 particularly interesting, but the internal photoemission efficiency for visible light is low because of the wide bandgap of the semiconductor. We investigated the incident photon-to-electron conversion efficiency of thin TiO2 films decorated with Au nanodisk antennas in an electrochemical circuit and found that incorporation of a Au mirror beneath the semiconductor amplified the photoresponse for light with wavelength λ = 500-950 nm by a factor 2-10 compared to identical structures lacking the mirror component. Classical electrodynamics simulations showed that the enhancement effect is caused by a favorable interplay between localized surface plasmon excitations and cavity modes that together amplify the light absorption in the Au/TiO2 interface. The experimentally determined internal quantum efficiency for hot electron transfer decreases monotonically with wavelength, similar to the probability for interband excitations with energy higher than the Schottky barrier obtained from a density functional theory band structure simulation of a thin Au/TiO2 slab.

Photophysics of Point Defects in ZnO Nanoparticles

Zinc oxide (ZnO) nanoparticles have recently been identified as a promising candidate for advanced nanophotonics applications and quantum technologies. This work reports the formation of luminescent point defects and describes their photophysical properties. In particular, it is shown using correlative photoluminescence, cathodoluminescence, electron paramagnetic resonance (EPR), and X‐ray absorption near‐edge spectroscopy that green luminescence at 2.48 eV and an EPR line at g = 2.00 belong to a surface oxygen vacancy () center, while a second green emission at 2.28 eV is associated with zinc vacancy (VZn) centers. It is established that radiative point defects can be excited in the visible that exhibits nanosecond lifetimes using both above bandgap and sub‐bandgap 405 and 532 nm excitation. This work provides important knowledge towards employment of point defects in ZnO in nanophotonics technologies.

Plasmonics on the slope of enlightenment: the role of transition metal nitrides.

The key problem currently faced by plasmonics is related to material limitations. After almost two decades of extreme excitement and research largely based on the use of noble metals, scientists have come to a consensus on the importance of exploring alternative plasmonic materials to address application-specific challenges to enable the development of new functional devices. Such a change in motivation will undoubtedly lead to significant advancements in plasmonics technology transfer and could have a revolutionary impact on nanophotonic technologies in general. Here, we report on one of the approaches that, together with other new material platforms, mark an insightful technology-driven era for plasmonics. Our study focuses on transition metal nitrides as refractory plasmonic materials that exhibit appealing optical properties in the visible and near infrared regions, along with high temperature durability. We take heat-assisted magnetic recording as a case study for plasmonic technology and show that a titanium nitride antenna satisfies the requirements for an optically efficient, durable near field transducer paving the way to the next-generation data recording systems.

The simulation study of the plasmonic coupling effect for the Ag nanoparticle-nanowire structure

This paper presents a simulation study of the photon-to-plasmon coupling effect for the silver (Ag) nanoparticle-nanowire structure. The calculated results show that the in-coupling light efficiency depends on many factors, involving the gap between the nanoparticle and the nanowire, the size of the nanoparticle, the wavelength of the incident light and the dielectric environment. Under certain conditions, the in-coupling light efficiency of such a structure can be increased as compared with that of a single nanowire, suggesting that this nanoparticle-nanowire system can be used as an interesting structure for subwavelength waveguides, optical sensors and many other applications in the field of nanophotonics technology.

Examining nanophotonics for integrated hybrid systems: a review of plasmonic interconnects and modulators using traditional and alternative materials [Invited

The scaling that has governed the continual increase in density, performance, and efficiency of electronic devices is rapidly reaching its inevitable limitations. In order to sustain the trend of ever-increasing bandwidth and performance, new technologies are being considered. Among the many competitors, nanophotonic technologies are especially poised to have an impact on the field of integrated devices. Here, we examine the available technologies, both traditional photonics and plasmonics, with emphasis on the latter. A summary of the previous advances in the field of nanophotonics (interconnects and modulators), along with more recent works investigating novel and CMOS-compatible materials, are presented with a graphical comparison of their performance. We suggest that nanophotonic technologies offer key advantages for future hybrid electrophotonic devices, where the movement toward new material platforms is a precursor to high-performance, industry-ready devices.

Two-dimensional material nanophotonics

The emerging two-dimensional (2D) materials exhibit a wide range of electronic properties, ranging from insulating hexagonal boron nitride, semiconducting transition metal dichalcogenides such as molybdenum disulfide, to semi-metallic graphene. Here, we first review the optical properties and applications of a variety of 2D materials, followed by two different approaches to enhance their interactions with light: through their integration with external photonic structures and through their intrinsic polaritonic resonances. Finally, we cover a narrow bandgap layered material, black phosphorus, which serendipitously bridges the zero gap graphene and the relatively large-bandgap TMDCs. The plethora of 2D materials and their heterostructures, together with the approaches for enhancing light-matter interaction offers the promise of scientific discoveries and nanophotonics technologies across a wide range of electromagnetic spectrum.

UNION: A Unified Inter/Intrachip Optical Network for Chip Multiprocessors

As modern computing systems become increasingly complex, communication efficiency among and inside chips has become as important as the computation speeds of individual processing cores. Traditionally, to maximize design flexibility, interchip and intrachip communication architectures are separately designed under different constraints. Jointly designing communication architectures for both interchip and intrachip communication could, however, potentially yield better solutions. In this paper, we present a unified inter/intrachip optical network, called UNION, for chip multiprocessors (CMPs). UNION is based on recent progresses in nanophotonic technologies. It connects not only cores on a single CMP, but also multiple CMPs in a system. UNION employs a hierarchical optical network to separate interchip communication traffic from intrachip communication traffic. It fully utilizes a single optical network to transmit both payload and control packets. The network controller on each CMP not only manages intrachip communications, but also collaborates with each other to facilitate interchip communications. We compared UNION with a matched electrical counterpart in 45-nm process. Simulation results for eight real CMP applications show that on average UNION improves CMP performance by 3× while reducing 88% of network energy consumption.

(Invited) Transport and Electroluminescence Properties of Size-Controlled Silicon Nanocrystals Embedded in SiO2 Matrix Following the Superlattice Approach

In this invited talk, we will report our latest advances in the field of nanostructured silicon-based light emitters with special emphasis in those that are rare earth doped. We have recently shown that it is possible to push external quantum efficiencies over the 10% by fine tuning the material composition and by using a new device concept that we have called hot electron engineering.Most of the rare earth amount introduced in the host material must be optically active. This can be accomplished by using a deposition method that introduces the rare earth during film growth and by a suitable passivating annealing procedure that: i) does not promote rare earth precipitation and clustering; ii) brings the rare earth to the 3+ oxidation state and iii) reduces non radiative defects. Additionally, for electroluminescent devices the matrix composition must be engineered so that it allows conduction-band transport in contrast with defective systems in which transport is hopping-like.The hot electron engineering concept relies on the fact that the rare earth excitation process in Si-based dielectric matrices proceeds mainly via impact excitation by hot electrons. Thus, devising suitable structures for which electrons can be accelerated to average energies that are resonant to the rare earth excitation energies, will improve both efficiency and maximum power emission. Additionally, driving the device with pulsed polarization and short duty cycle will improve device efficiency and lifetime. Finally, the structures must allow at the same time significant light extraction efficiency. This can be accomplished by improving the antireflective properties of the whole stack and/or by nanostructuring the ITO or polysilicon electrode.We will be show silicon oxides, nitrides and oxynitrides as hosts for the rare-earth species and, additionally, we will display the advantages and drawbacks of introducing small percentages of carbon and aluminum. The rare-earth species incorporated in those matrices are Er, Ce, Tb, Eu and Nd and their light emission efficiency depend in a complex way on matrix composition, material processing, device structure and device polarization. The simplest hot electron engineering structures are bilayers and trilayers with silicon oxide as accelerator. More complex structures like multilayers and superlattices will be also introduced and optimal designs will be proposed. Some reliability issues and potential solutions for them will be also presented.We acknowledge existing collaborations in this field with teams of the McMaster University at Hamilton (Canada), Institut de Microelectrònica de Barcelona (Spain), Nanophotonics Technology Center of Valencia (Spain), Instituto de Óptica of Madrid (Spain), Ion Beam Institute at Rossendorf (Germany), IMTEK at the University of Freiburg (Germany) and CIMAP-CNRS at Caen (France).

Design of a Bufferless Photonic Clos Network-on-Chip Architecture

On-chip photonic waveguides have been proposed as a feasible replacement for the long interconnects that cause speed and power bottlenecks. Along with recent advancements in nanophotonic technologies, we believe that combining on-chip waveguides with high-radix Network on Chip (NoC) topologies is a promising way to improve NoC performance. In this paper, we propose the BufferLess phOtonic ClOs Network (BLOCON) to exploit silicon photonics. We propose a scheduling algorithm named Sustained and Informed Dual Round-Robin Matching (SIDRRM) to solve the output contention problem, a path allocation scheme named Distributed and Informed Path Allocation (DIPA) to solve the Clos network routing problem, and a methodology to achieve an optimal off-chip laser-power budget. In the simulation results, we show that with SIDRRM and DIPA, BLOCON improves the delay and on-chip power performance of the compared electrical and photonic NoC architectures over synthetic traffic patterns and SPLASH-2 traces.

Monolithic Silicon Integration of Scaled Photonic Switch Fabrics, CMOS Logic, and Device Driver Circuits

We demonstrate 4 × 4 and 8 × 8 switch fabrics in multistage topologies based on 2 × 2 Mach–Zehnder interferometer switching elements. These fabrics are integrated onto a single chip with digital CMOS logic, device drivers, thermo-optic phase tuners, and electro-optic phase modulators using IBM's 90 nm silicon integrated nanophotonics technology. We show that the various switch-and-driver systems are capable of delivering nanosecond-scale reconfiguration times, low crosstalk, compact footprints, low power dissipations, and broad spectral bandwidths. Moreover, we validate the dynamic reconfigurability of the switch fabric changing the state of the fabric using time slots with sub-100-ns durations. We further verify the integrity of high-speed data transfers under such dynamic operation. This chip-scale switching system technology may provide a compelling solution to replace some routing functionality currently implemented as bandwidth- and power-limited electronic switch chips in high-performance computing systems.

Extending the Performance and Energy-Efficiency of Shared Memory Multicores with Nanophotonic Technology

As the number of cores increases exponentially on a single chip, the design and integration of both the on-chip network facilitating intercore communication, and the cache coherence protocol for enabling shared memory programming have become critical for improved energy-efficiency and overall chip performance. With traditional metal interconnects facing stringent energy constraints, researchers are currently pursuing disruptive solutions such as nanophotonics for improved energy-efficiency. Cache coherence in multicores can be enforced effectively by snoopy protocols; however, broadcasting every cache miss can limit the scalability while consuming excess energy. In this paper, we propose PULSE, a nanophotonic broadcast tree-based network for snoopy cache coherent multicores. To limit the energy-penalty from broadcasting (and thereby splitting) optical signals, we direct the optical signal from the external laser such that only the subset of requesters can receive the optical signal. Furthermore, as cache blocks are shared by a few cores, we propose a multicast version of PULSE called multi-PULSE that predicts the sharers' for each L2 miss and morphing the broadcast to a multicast network. We evaluate the energy and performance using CACTI and SIMICS on 16-core and 64-core versions of PULSE and multi-PULSE for Splash-2, PARSEC, and SPEC CPU2006 benchmarks and compare to electrical networks, optical networks, and another cache filtering techniques. Our results indicate that PULSE outperforms competitive electrical/optical networks by 60 percent in terms of execution time, and multi-PULSE reduces average energy from 10 to 80 percent even with a few mispredictions.

Eleven Nanometer Alignment Precision of a Plasmonic Nanoantenna with a Self-Assembled GaAs Quantum Dot

Plasmonics offers the opportunity of tailoring the interaction of light with single quantum emitters. However, the strong field localization of plasmons requires spatial fabrication accuracy far beyond what is required for other nanophotonic technologies. Furthermore, this accuracy has to be achieved across different fabrication processes to combine quantum emitters and plasmonics. We demonstrate a solution to this critical problem by controlled positioning of plasmonic nanoantennas with an accuracy of 11 nm next to single self-assembled GaAs semiconductor quantum dots, whose position can be determined with nanometer precision. These dots do not suffer from blinking or bleaching or from random orientation of the transition dipole moment as colloidal nanocrystals do. Our method introduces flexible fabrication of arbitrary nanostructures coupled to single-photon sources in a controllable and scalable fashion.

Quantum-dot supercrystals for future nanophotonics

The study of supercrystals made of periodically arranged semiconductor quantum dots is essential for the advancement of emerging nanophotonics technologies. By combining the strong spatial confinement of elementary excitations inside quantum dots and exceptional design flexibility, quantum-dot supercrystals provide broad opportunities for engineering desired optical responses and developing superior light manipulation techniques on the nanoscale. Here we suggest tailoring the energy spectrum and wave functions of the supercrystals' collective excitations through the variation of different structural and material parameters. In particular, by calculating the excitonic spectra of quantum dots assembled in two-dimensional Bravais lattices we demonstrate a wide variety of spectrum transformation scenarios upon alterations in the quantum dot arrangement. This feature offers unprecedented control over the supercrystal's electromagnetic properties and enables the development of new nanophotonics materials and devices.