Dielectric Photonic Structures Research Articles

New Nanophotonics Approaches for Enhancing the Efficiency and Stability of Perovskite Solar Cells.

Over the past decade, the power conversion efficiency (PCE) of perovskite solar cells (PSCs) has experienced a remarkable ascent, soaring from 3.8% in 2009 to a remarkable record of 26.1% in 2023. Many recent approaches for improving PSC performance employ nanophotonic technologies, from light harvesting and thermal management to the manipulation of charge carrier dynamics. Plasmonic nanoparticles and arrayed dielectric nanostructures have been applied to tailor the light absorption, scattering, and conversion, as well as the heat dissipation within PSCs to improve their PCE and operational stability. In this review, it is begin with a concise introduction to define the realm of nanophotonics by focusing on the nanoscale interactions between light and surface plasmons or dielectric photonic structures. Prevailing strategies that utilize resonance-enhanced light-matter interactions for boosting the PCE and stability of PSCs from light trapping, carrier transportation, and thermal management perspectives are then elaborated, and the resultant practical applications, such as semitransparent photovoltaics, colored PSCs, and smart perovskite windows are discussed. Finally, the state-of-the-art nanophotonic paradigms in PSCs are reviewed, and the benefits of these approaches in improving the aesthetic effects and energy-saving character of PSC-integrated buildings are highlighted.

Simultaneous solar rejection and infrared emission switching using an integrated dielectrics-on-VO2 metasurface

Passive infrared emittance switching can be achieved with a metal-to-insulating phase transition material vanadium dioxide (VO2), but its non-transitioning bandgap results in high absorptance in the visible wavelength range. To achieve a half-order reduction of absorptance in the visible to near-infrared region, we design integrated dielectric photonic metasurface structures on monolithic VO2 coatings. This combination of nano/micro-patterned dielectric diffractive and resonant gratings with a multilayer VO2 structure preserves the terrestrial thermal wavelength emission switching capabilities. We demonstrate a periodic microscale diffractive prism array, comparing the reflectance provided by either infrared-transparent germanium (Ge) or silicon (Si). Despite the advantage of total internal reflection in the broad near-infrared region, some bandgap absorption limits the performance in the visible wavelengths. A better theoretical means to reflect broadband light via waveguide-like Fabry–Pérot resonance are near-wavelength 1D and 2D High Contrast Grating (HCG) high-index metasurface structures surrounded by a low-index host medium. This HCG metasurface allows broadband high-quality reflection within the dual-mode (or tri-mode) region from 1.0 to 2.2 µm wavelengths for HCG with a refractive index of 4.0, which corresponds to Ge. This study investigates the advantages and disadvantages along with the thermal performance of these metasurface augments aimed to enable thermally switchable passive radiative cooling—thermal emission exceeding solar absorption—of solar cells, terrestrial buildings, and energy storage devices.

Integrated Photonic Structure Enhanced Infrared Photodetectors

The application fields of infrared photodetectors are quite extensive. Compared with traditional infrared photodetection materials such as IV and III–V semiconductors, newly emerging low‐dimensional materials and quantum materials (e.g., 2D materials and quantum wells) have many advantages in different aspects, such as wide spectral range, low dark current, room temperature operation, and high processing compatibility. However, the performance of photodetectors based on low‐dimensional materials is limited by the ultra small thicknesses, polarization selectivity, and the poor absorption efficiency. Therefore, improving the performance of infrared photodetectors based on low‐dimensional materials has been a focus research task in recent years. The integration of photonic structures can improve the performance of infrared photodetectors, such as enhancing absorption efficiency, reducing the volume of active materials, and increasing polarization selectivity. Herein, different kinds of photonic structure integrated infrared photodetectors, roughly divided into two categories, namely, dielectric photonic structure integrated ones and metallic photonic structure integrated ones, are reviewed. The active materials include 2D materials, quantum wells, quantum dots, and carbon nanotubes.

Fourier-plane investigation of plasmonic bound states in the continuum and molecular emission coupling

Abstract Bound states in the continuum (BICs) or trapped modes can provide an important new avenue for strong light confinement via destructive interference. Dielectric photonic structures have been extensively studied for optical BICs. However, BICs in plasmonic nanostructures have not been explored much yet. Herein, we present a thorough experimental study of plasmonic BICs via Fourier-plane spectroscopy and imaging. Optical mode dispersion in a metal grating covered by a dielectric layer is directly measured in an angle-resolved white light reflection spectrum. Two dielectric layer thicknesses are considered. Both plasmonic and photonics modes are supported in the visible range using a thicker dielectric film; hence, either hybrid or purely plasmonic BICs can be formed. With a thinner dielectric layer, only plasmonic modes are strongly excited and purely plasmonic BICs appear. Our measurements exhibit all features expected for BICs, including a substantial increase in the Q factor. We also demonstrate that the BIC position can be switched from one optical mode branch to the other by tuning a metal grating parameter. Moreover, by mixing luminescent dyes in a dielectric layer, light emission coupling into BICs is investigated. We find that the photoluminescence peak disappears at the BIC condition, which is attributed to the trapping of molecular emission at plasmonic BICs. Therefore, both white light reflection and dye emission measurements in the Fourier plane clearly indicate the formation of trapped modes in plasmonic nanostructures. Our observation implies that plasmonic BICs can enable a highly effective light trapping device despite the simple structure of the device geometry. Plasmonic supercavity design based on the BIC concept may provide many interesting future opportunities for nanolasers, optical sensing, and nonlinear enhancement.

Perfect absorption for monolayer transition-metal dichalcogenides by critical coupling

Due to the inherent atomical size, transition-metal dichalcogenides (TMDCs) have a weak coupling with free-space light and exhibit poor optical absorption, which restricts some practical applications. Exploring an effective way to boost their absorption is important and highly desired. In this work, based on the temporal coupled-mode theory, a generic guide to approach 100% absorption of an absorber is presented. From such a theory, the perfect absorption of TMDCs integrated with dielectric photonic structure is both theoretically and numerically demonstrated. This proposed structure has advantageous tunability at the wavelengths of interest by adjusting structure parameters. Moreover, the angular dependence of the light absorption of such a structure for different polarizations is also investigated. The present work of boosting light absorption would be particularly favorable for applications in advanced photodetectors and modulators.

Subwavelength optical trapping and transporting using a Bloch mode.

Multi-functional optical manipulations, including optical trapping and transporting of subwavelength particles, are proposed using the Bloch modes in a dielectric photonic structure. We show that the Bloch modes in a periodic structure can generate a series of subwavelength trapping wells that are addressable by tuning the incident wavelength. This feature enables efficient optical trapping and transportation in a peristaltic way. Since we are using the guiding Bloch mode in a dielectric structure, rather than using plasmonic or dielectric resonant cavities, these operations are wide band and free from joule loss. The Bloch mode in a simple periodic dielectric structure provides a new platform for multi-functional optical operations and may find potential applications in nanophotonics and biomedicine.

Manipulating bandwidth of light absorption at critical coupling: An example of graphene integrated with dielectric photonic structure

For an optical absorber, its efficiency and bandwidth determine ultimately its light-collection performance. A general way to realize the high-efficiency absorption and manipulate the absorption bandwidth is certainly important and highly desired. In this paper, based on the coupled-mode theory, a general strategy for tailoring the bandwidth of an absorber (to broaden or narrow it) is presented. A graphene-based absorber integrated with a lossless resonator is designed, and it is shown that by increasing the layer number of graphene and adjusting structure parameters, the broadband absorber at critical coupling could be realized. Meanwhile, by adjusting the location of graphene in the structure, an ultra-narrow-band absorber could also be realized. Present work of controlling both efficiency and bandwidth of an absorber would be particularly favorable for applications in light harvesting, light emitting devices, and optical modulators.

Nonradiating photonics with resonant dielectric nanostructures

AbstractNonradiating sources of energy have traditionally been studied in quantum mechanics and astrophysics but have received very little attention in the photonics community. This situation has changed recently due to a number of pioneering theoretical studies and remarkable experimental demonstrations of the exotic states of light in dielectric resonant photonic structures and metasurfaces, with the possibility to localize efficiently the electromagnetic fields of high intensities within small volumes of matter. These recent advances underpin novel concepts in nanophotonics and provide a promising pathway to overcome the problem of losses usually associated with metals and plasmonic materials for the efficient control of light-matter interaction at the nanoscale. This review paper provides a general background and several snapshots of the recent results in this young yet prominent research field, focusing on two types of nonradiating states of light that both have been recently at the center of many studies in all-dielectric resonant meta-optics and metasurfaces: opticalanapolesand photonicbound states in the continuum. We discuss a brief history of these states in optics, as well as their underlying physics and manifestations, and also emphasize their differences and similarities. We also review some applications of such novel photonic states in both linear and nonlinear optics for the nanoscale field enhancement, a design of novel dielectric structures with high-Qresonances, nonlinear wave mixing, and enhanced harmonic generation, as well as advanced concepts for lasing and optical neural networks.

Elastic dependence of defect modes in one-dimensional photonic crystals with a cholesteric elastomer slab

We studied the transmission spectra in a one-dimensional dielectric multilayer photonic structure containing a cholesteric liquid crystal elastomer layer as a defect. For circularly polarized incident electromagnetic waves, we analyzed the optical defect modes induced in the band gap spectrum as a function of the incident angle and the axial strain applied along the same axis as the periodic medium. The physical parameters of the structure were chosen in such a way the photonic band gap of the cholesteric elastomer lies inside that of the multilayer. We found that, in addition to the defect modes associated with the thickness of the defect layer and the anisotropy of the elastic polymer, two new defect modes appear at both band edges of the cholesteric structure, whose amplitudes and spectral positions can be elastically tuned. Particularly, we showed that, at normal incidence, the defect modes shift toward the long-wavelength region with the strain; whereas, for constant elongation, such defects move toward larger frequencies with the incidence angle.

One-dimensional dielectric bi-periodic photonic structures based on ternary photonic crystals

We investigate the transmittivity spectra, fields, and energy distribution of the electromagnetic eigenwaves propagating in a one-dimensional (1D) dielectric photonic crystal [(TiO2/SiO2)NAl2O3]M with two periods formed by unit cells TiO2/SiO2 and (TiO2/SiO2)NAl2O3. Spectra of TE- and TM-modes depend on the geometric parameters of the structure and undergo modifications with the change in the period numbers, layer thicknesses, and incidence angle. Special attention is paid to the applicability of the hybrid effective medium approximation comprising the long-wave approximation and two-dimensional (2 × 2) transfer matrix method. We demonstrate spectral peculiarities of the bi-periodic structure and also show the differences between the band gap spectra of the bi-periodic and ternary 1D dielectric photonic crystals. The presented photonic crystal structure can find its applications in optoelectronics and nanophotonics areas as omnidirectional reflectors, optical ultra-narrow bandpass filters, and antireflection coatings.

Light‐Induced Tuning and Reconfiguration of Nanophotonic Structures

AbstractInteraction of light pulses of various durations and intensities with nanoscale photonic structures plays an important role in many applications of nanophotonics for high‐density data storage, ultra‐fast data processing, surface coloring and sensing. A design of optically tunable and reconfigurable structures made from different materials is based on many important physical effects and advances in material science, and it employs the resonant character of light interaction with nanostructures and strong field confinement at the nanoscale. Here we review the recent progress in physics of tunable and reconfigurable nanophotonic structures of different types. We start from low laser intensities that produce weak reversible changes in nanostructures, and then move to the discussion of non‐reversible changes in photonic structures. We focus on three platforms based on metallic, dielectric and hybrid resonant photonic structures such as nanoantennas, nanoparticle oligomers and nanostructured metasurfaces. Main challenges and key advantages of each of the approaches focusing on applications in advanced photonic technologies are also discussed.

Bloch Surface Wave-Coupled Emission at Ultra-Violet Wavelengths.

The interaction of fluorophores with nearby metallic structures is now an active area of research. Dielectric photonic structures offer some advantages over plasmonic structures, namely small energy losses and less quenching. We describe a dielectric one-dimensional photonic crystal (1DPC), which supports Bloch surface waves (BSWs) from 280 to 440 nm. This BSW structure is a quartz slide coated with alternating layers of SiO2 and Si3N4. We show that this structure displays BSWs and that the near-UV fluorophore, 2-aminopurine (2-AP), on the top surface of the structure couples with the BSWs. Fluorophores do not have to be inside the structure for coupling and show a narrow angular distribution, with an angular separation of wavelengths. The Bloch wave-coupled emission (BWCE) radiates through the dielectric layer. These BSW structures, with useful wavelength range for detection of intrinsic protein and cofactor fluorescence, provide opportunities for novel optical configurations for bioassays with surface-localized biomolecules and for optical imaging using the coupled emission.

Parametric generation of energetic short mid-infrared pulses for dielectric laser acceleration

Laser-driven high-gradient electron acceleration in dielectric photonic structures is an enabling technology for compact and robust sources of tunable monochromatic x-rays. Such advanced x-ray sources are sought in medical imaging, security, industrial, and scientific applications. The use of long-wavelength pulses can mitigate the problem of laser-induced breakdown in dielectric structures at high optical intensities, relax the structure fabrication requirements, and allow greater pulse energy to be injected into the structure. We report on the design and construction of a simple and robust, short-pulse parametric source operating at a center wavelength 5 μm, to be used as a pump for a dielectric photonic structure for laser-driven acceleration. The source is based on a two-stage parametric downconversion design, consisting of a β-BaB2O4-based 2.05 μm optical parametric amplifier (OPA) and a ZnGeP2-based 5 μm OPA. The 2.05 μm OPA is presently pumped by a standard Ti:sapphire chirped-pulse amplified laser, which will be replaced with direct laser pumping at wavelengths in the future. The design and performance of the constructed short-pulse mid-infrared source are described. The demonstrated architecture is also of interest for use in other applications, such as high harmonic generation and attosecond pulse production.

Nanophotonics of optical fibers

AbstractThis review is concerned with nanoscale effects in highly transparent dielectric photonic structures fabricated from optical fibers. In contrast to those in plasmonics, these structures do not contain metal particles, wires, or films with nanoscale dimensions. Nevertheless, a nanoscale perturbation of the fiber radius can significantly alter their performance. This paper consists of three parts. The first part considers propagation of light in thin optical fibers (microfibers) having the radius of the order of 100 nanometers to 1 micron. The fundamental mode propagating along a microfiber has an evanescent field which may be strongly expanded into the external area. Then, the cross-sectional dimensions of the mode and transmission losses are very sensitive to small variations of the microfiber radius. Under certain conditions, a change of just a few nanometers in the microfiber radius can significantly affect its transmission characteristics and, in particular, lead to the transition from the waveguiding to non-waveguiding regime. The second part of the review considers slow propagation of whispering gallery modes in fibers having the radius of the order of 10–100 microns. The propagation of these modes along the fiber axis is so slow that they can be governed by extremely small nanoscale changes of the optical fiber radius. This phenomenon is exploited in SNAP (surface nanoscale axial photonics), a new platform for fabrication of miniature super-low-loss photonic integrated circuits with unprecedented sub-angstrom precision. The SNAP theory and applications are overviewed. The third part of this review describes methods of characterization of the radius variation of microfibers and regular optical fibers with sub-nanometer precision.

Enhanced method for determining the optical response of highly complex biological photonic structures

We present a set of techniques that enhances a previously developed time domain simulation of wave propagation and allows the study of the optical response of a broad range of dielectric photonic structures. This method is particularly suitable for dealing with complex biological structures, especially due to the simple and intuitive way of defining the setup and the photonic structure to be simulated, which can be done via a digital image of the structure. The presented techniques include a direction filter that permits the decoupling of waves traveling simultaneously in different directions, a dynamic differential absorber to cancel the waves reflected at the edges of the simulation space, and a multifrequency excitation scheme. We also show how the simulation can be adapted to apply a near to far field method in order to evaluate the resulting wavefield outside the simulation domain. We validate these techniques, and, as an example, we apply the method to the complex structure of a microorganism called Diachea leucopoda, which exhibits a multicolor iridescent appearance.

Enhanced transmission and giant Faraday effect in magnetic metal–dielectric photonic structures

Due to their large electrical conductivity, stand-alone metallic films are highly reflective at microwave (MW) frequencies. For this reason, it is nearly impossible to observe Faraday rotation in ferromagnetic metal layers, even in films just tens of nanometres thick. Here, we show using numerical simulations that a stack of cobalt nano-layers interlaced between dielectric layers can become highly transmissive and display a large Faraday rotation in a finite frequency band. A 45° Faraday rotation commonly used in MW isolators can be achieved with ferromagnetic metallic layers as thin as tens of nanometres.

Diamond nanophotonics.

We demonstrate the coupling of single color centers in diamond to plasmonic and dielectric photonic structures to realize novel nanophotonic devices. Nanometer spatial control in the creation of single color centers in diamond is achieved by implantation of nitrogen atoms through high-aspect-ratio channels in a mica mask. Enhanced broadband single-photon emission is demonstrated by coupling nitrogen–vacancy centers to plasmonic resonators, such as metallic nanoantennas. Improved photon-collection efficiency and directed emission is demonstrated by solid immersion lenses and micropillar cavities. Thereafter, the coupling of diamond nanocrystals to the guided modes of micropillar resonators is discussed along with experimental results. Finally, we present a gas-phase-doping approach to incorporate color centers based on nickel and tungsten, in situ into diamond using microwave-plasma-enhanced chemical vapor deposition. The fabrication of silicon–vacancy centers in nanodiamonds by microwave-plasma-enhanced chemical vapor deposition is discussed in addition.

Study of the omnidirectional photonic bandgap for dielectric mirrors based on porous silicon: effect of optical and physical thickness

We report the theoretical comparison of the omnidirectional photonic bandgap (OPBG) of one-dimensional dielectric photonic structures, using three different refractive index profiles: sinusoidal, Gaussian, and Bragg. For different values of physical thickness (PT) and optical thickness (OT), the tunability of the OPBG of each profile is shown to depend on the maximum/minimum refractive indices. With an increase in the value of the maximum refractive index, the structures with the same PT showed a linear increment of the OPBG, in contrast to the structures with the same OT, showing an optimal combination of refractive indices for each structure to generate the maximum OPBG. An experimental verification was carried out with a multilayered dielectric porous silicon structure for all the three profiles.

OVERLAPPING TE AND TM BAND GAPS IN SQUARE LATTICE PHOTONIC CRYSTAL OF HOLLOW DIELECTRIC RODS

A numerical study is performed on photonic band gap of 2D square lattice photonic crystal with varied layered dielectric rods by using the plane wave expansion method for the purpose of investigating the effects of geometrical and permittivity variations. The results show that in general the TE and TM band gaps do not coexist in the band structure of this layered rods system. However, for a specific choice of the system parameters leading to a photonic crystals of hollow dielectric rods, both TE and TM photonic band structures feature perceptible band gaps with significant overlap, yielding effective complete photonic band gaps (CPBG). The study further shows that the CPBG can be enlarged by varying both radii of the hollow rods. It is found that a large CPBG can be attained which is comparable in size with those found in hexagonal lattice photonic crystal of air holes as well as square lattice photonic crystal rods incorporating dielectric veins.

Omnidirectional photonic bangap in dielectric mirrors: a comparative study

We report the theoretical comparison of the omnidirectional photonic band gap (OPBG) of one-dimensional dielectric photonic structures, using three different refractive index profiles: sinusoidal, Gaussian and Bragg. For different values of optical thickness, the tunability of the OPBG of each profile is shown to depend on the maximum, minimum and the difference of the refractive indices. An experimental verification was carried out with a multilayered dielectric porous silicon structure for all the three profiles. The optimal combination of refractive indices for each structure which generates the maximum OPBG has also been calculated. Such study can be useful to design the required OPBG structures for photonic applications.