Silicon-based Photonic Crystals Research Articles

Two-dimensional silicon-based dielectric column photonic crystal point defect microcavity Neural network modelling

In order to solve the problem that it is difficult to predict the microcavity photonic energy bands of point defects in two-dimensional silicon-based dielectric column photonic crystals, this paper proposes a method to predict the microcavity photonic energy bands of point defects in two-dimensional silicon-based photonic crystals by using an artificial neural network model. In this paper, the energy band structure of triangular lattice point defects at different radii is calculated using MPB, and a neural network model is established based on this data and the accuracy of the established model is verified.

High Field Confinement Enhancement in Silicon-based Photonic Crystal with Different Point Defects

Two-dimensional silicon-based photonic crystals as optical analogs to electronic semiconductors are presented in this paper, emphasizing the design and analysis of two-dimensional structures. Employing the Lumerical FDTD solver, we initially crafted defect-free photonic crystals within a hexagonal lattice of air holes on a silicon slab (6.57 μm along x, 6.57 μm along y, 0.75 μm along z). The lattice parameters (a = 0.365 μm, r = 0.1095 μm, with r = 0.3a) established a target resonant wavelength of 1.5 μm. Utilizing Finite Difference Time-Domain (FDTD), we evaluated electric field decay, resonant modes, and the Q factor. The defect-free structure exhibited a peak Q factor of 736.004 at a resonant wavelength of 1262.87 nm. Removal of a central hole enhanced the Q factor to 1286.96 at 1391.07 nm. Introducing various line defects, the structure with three holes removed from vertical positions emerged as the optimal candidate for silicon-based photonic crystal cavity resonators, displaying the highest Q factor near the target resonant wavelength. Additionally, the structure with seven holes removed showed stable linear decays at both resonant wavelengths, suggesting its potential as a cavity resonator design candidate.

Enhancing photoelectrochemical CO2 reduction with silicon photonic crystals.

The effectiveness of silicon (Si) and silicon-based materials in catalyzing photoelectrochemistry (PEC) CO2 reduction is limited by poor visible light absorption. In this study, we prepared two-dimensional (2D) silicon-based photonic crystals (SiPCs) with circular dielectric pillars arranged in a square array to amplify the absorption of light within the wavelength of approximately 450nm. By investigating five sets of n + p SiPCs with varying dielectric pillar sizes and periodicity while maintaining consistent filling ratios, our findings showed improved photocurrent densities and a notable shift in product selectivity towards CH4 (around 25% Faradaic Efficiency). Additionally, we integrated platinum nanoparticles, which further enhanced the photocurrent without impacting the enhanced light absorption effect of SiPCs. These results not only validate the crucial role of SiPCs in enhancing light absorption and improving PEC performance but also suggest a promising approach towards efficient and selective PEC CO2 reduction.

Topological phonon-polariton funneling in midinfrared metasurfaces.

Topological photonics offers enhanced control over electromagnetic fields by providing a platform for robust trapping and guiding of topological states of light. By combining the strong coupling between topological photons with phonons in hexagonal boron nitride (hBN), we demonstrate a platform to control and guide hybrid states of light and lattice vibrations. The observed topological edge states of phonon-polaritons are found to carry nonzero angular momentum locked to their propagation direction, which enables their robust transport. Thus, these topological quasiparticles enable the funneling of infrared phonons mediated by helical infrared photons along arbitrary pathways and across sharp bends, thereby offering opportunities for applications ranging from Raman and vibrational spectroscopy with structured phonon-polaritons to directional heat dissipation.

Near-Field Excited Archimedean-like Tiling Patterns in Phonon-Polaritonic Crystals

Phonon-polaritons (PhPs) arise from the strong coupling of photons to optical phonons. They offer light confinement and harnessing below the diffraction limit for applications including sensing, imaging, superlensing, and photonics-based communications. However, structures consisting of both suspended and supported hyperbolic materials on periodic dielectric substrates are yet to be explored. Here we investigate phonon-polaritonic crystals (PPCs) that incorporate hyperbolic hexagonal boron nitride (hBN) to a silicon-based photonic crystal. By using the near-field excitation in scattering-type scanning near-field optical microscopy (s-SNOM), we resolved two types of repetitive local field distribution patterns resembling the Archimedean-like tiling on hBN-based PPCs, i.e., dipolar-like field distributions and highly dispersive PhP interference patterns. We demonstrate the tunability of PPC band structures by varying the thickness of hyperbolic materials, supported by numerical simulations. Lastly, we conducted scattering-type nanoIR spectroscopy to confirm the interaction of hBN with photonic crystals. The introduced PPCs will provide the base for fabricating essential subdiffraction components of advanced optical systems in the mid-IR range.

Optically tunable topological photonic crystal

Topological photonic insulators can enable the development of efficient integrated photonic devices with minimized scattering losses. The optical properties of the majority of topological structures proposed to date are fixed by designs such that no changes to their performance can be made once the device has been fabricated. However, tunability is important for many applications, including modulators, switches, and optical buffers. We therefore propose a straightforward way to dynamically control transmission in a silicon-based topological photonic crystal using all-optical free-carrier excitation that allows for fast refractive index modulation. The changes in both the real and imaginary parts of the refractive index cause a blue shift of the transmission spectrum by up to 20 nm and a reduction in transmission by approximately 85% . With the control mechanism used here, we can achieve switching times of the order of nanoseconds. The structures proposed here are compatible with the standard semiconductor industry fabrication process and operate at telecommunication wavelengths.

Nonlinear dynamics and chaos in an optomechanical beam

Optical nonlinearities, such as thermo-optic mechanisms and free-carrier dispersion, are often considered unwelcome effects in silicon-based resonators and, more specifically, optomechanical cavities, since they affect, for instance, the relative detuning between an optical resonance and the excitation laser. Here, we exploit these nonlinearities and their intercoupling with the mechanical degrees of freedom of a silicon optomechanical nanobeam to unveil a rich set of fundamentally different complex dynamics. By smoothly changing the parameters of the excitation laser we demonstrate accurate control to activate two- and four-dimensional limit cycles, a period-doubling route and a six-dimensional chaos. In addition, by scanning the laser parameters in opposite senses we demonstrate bistability and hysteresis between two- and four-dimensional limit cycles, between different coherent mechanical states and between four-dimensional limit cycles and chaos. Our findings open new routes towards exploiting silicon-based optomechanical photonic crystals as a versatile building block to be used in neurocomputational networks and for chaos-based applications.

Engineering the Properties of Polymer Photonic Crystals with Mesoporous Silicon Templates

The effect of molecular weight on the rate and extent of melt-infiltration of polystyrene into mesoporous silicon-based photonic crystals is investigated as a function of polymer molecular weight. Polymer viscosity and chain end-to-end (Ree) distance correlate with the rate and extent of infiltration. High molecular weight (Mw) polystyrene (200 or 400 kDa) infiltrates the mesoporous material in two distinct phases: a rapid phase where the larger pores of the template are filled, followed by a slower phase during which the smaller pores fill. Low molecular weight polystyrene (20 and 35 kDa) fills the pores more uniformly, progressing into the film as a single, relatively distinct front of liquid polymer. Scanning electron microscope (SEM) analyses of cross sections of the films are consistent with the optical measurements, showing a lower extent of infiltration for the higher molecular weight polymers. Removal of the porous Si templates by soaking in a chemical etchant generates free-standing films of nanostructured polymer. The low molecular weight samples display better replication. Partial removal of the template enables tuning of the hydrophobicity of the free-standing polymer films, which is demonstrated with a flexible and chemically stable polyvinylidene fluoride polymer.

Fabrication and stabilization of silicon-based photonic crystals with tuned morphology for multi-band optical filtering

One-dimensional silicon-based photonic crystals are formed by the electrochemical anodization of silicon substrates in hydrofluoric acid-based solution using an appropriate current density profile. In order to create a multi-band optical filter, two fabrication approaches are compared and discussed. The first approach utilizes a current profile composed of a linear combination of sinusoidal current waveforms having different frequencies. The individual frequency of the waveform maps to a characteristic stop band in the reflectance spectrum. The stopbands of the optical filter created by the second approach, on the other hand, are controlled by stacking multiple porous silicon rugate multilayers having different fabrication conditions. The morphology of the resulting optical filters is tuned by controlling the electrolyte composition and the type of the silicon substrate. The reduction of sidelobes arising from the interference in the multilayers is observed by applying an index matching current profile to the anodizing current waveform. In order to stabilize the resulting optical filters against natural oxidation, atomic layer deposition of silicon dioxide on the pore wall is employed.

Proposal for achieving in-plane magnetic mirrors by silicon photonic crystals

Magnetic mirrors exhibit predominant physical characteristics such as high surface impedance and strong near-field enhancement. However, there is no way to implement these materials on a silicon lab chip. Here, we propose a scheme for an in-plane magnetic mirror in a silicon-based photonic crystal with a high-impedance surface, in contrast to the previous electric mirrors with low surface impedance. A tortuous bending waveguide with zero-index core and magnetic mirror walls is designed that exhibits high transmission and zero phase change at the waveguide exit. This type of magnetic mirror opens the door to exploring the physics of high-impedance surfaces and applications in integrated photonics.

Dynamical Bragg Diffraction in the Laue Geometry in 1D Porous Silicon-Based Photonic Crystals

We consider optical effects accompanying the dynamical Bragg diffraction in the Laue geometry in one-dimensional photonic crystals (PhC). We predict theoretically, and observe in the experiment, the diffraction-induced pulse splitting of femtosecond light pulse, the optical switching due to the optical pendular effect, and the effects of selective compression and focusing. These effects originate from the interaction of two spatial eigenmodes of the photonic crystal: Borrmann and anti-Borrmann, which are spatially localized within a PhC in the layers with low and high dielectric constants, respectively.

A physical model for band gap of silicon-based photonic crystal of air hole at telecom wavelengths

Band structures of silicon photonic crystal (PC) with different lattices and shapes of air holes at telecom wavelengths were investigated by plane-wave expansion method, and the related physical models were proposed. Calculated results demonstrate that photonic band gap (PBG) can be effectively manipulated by photon confinement effect and lattice symmetry effect. With the increase of filling fraction, the ability with which photons are confined by PC is enhanced, PBG is opened and the central frequency undergoes a blue-shift. PBG is enlarged as the lattice symmetry increases. Shape and rotation of lattice element are also studied. Band gap with the rotation angle which follows periodicity and symmetry indicates its anisotropy. The optimal cavity structures for different lattices are also found.

Real-time 1D hyperspectral imaging of porous silicon-based photonic crystals with one-dimensional chemical composition gradients undergoing pore-filling-induced spectral shifts

A line-scan hyperspectral imager can provide real-time spectral information at many points along a transect of a gradient-modified material. This is demonstrated by monitoring the optical reflectance spectrum of a porous silicon photonic crystal with a hydrophobic/hydrophilic pore-wall surface composition gradient while it is immersed in water to which ethanol is added. The combination of the hyperspectral imager and the pore-wall composition gradient allows a detailed study of the pore filling process. It is observed that even the most hydrophobic pores fill to a small extent when only a small amount of ethanol has been added. This gradient of filling is in contrast to visible observation of the porous silicon samples, which can suggest a step change in pore filling. The pore-filling process can take many minutes when the solution composition allows pores at a given position along the gradient to be about 50% filled. These observations demonstrate the utility of aligning a line-scan hyperspectral imager with a gradient material.

Polarization-insensitive self-collimation and beam splitter based on triangular-lattice annular photonic crystals

This paper systematically investigates the self-collimation behavior in silicon-based triangular-lattice annular photonic crystals (PCs). It is found that, in comparison with normal air-hole PCs, annular PCs more easily suppress the separation between TE-2 and TM-2 bands along the Γ-M direction by increasing the inner radius of annular air rings. Such a feature is quite beneficial in the formation of a flat equi-frequency contour for both polarizations at the same frequency, which means a polarization-insensitive self-collimation (PISC) effect. Further analysis has shown that, to support PISC, the minimum ratio between the inner and outer radii of annular air rings will gradually increase as the outer radius changes from 0.25a to 0.49a. When the ratio is fixed, the annular air rings with larger outer radius will provide wider common frequency area to realize PISC. We have also investigated the transmission feature for different annular PCs and chosen an optimal structure to illustrate the PISC effect. Finally, a polarization beam splitter has been proposed and demonstrated based on the unique PISC and band-gap feature in triangular-lattice annular PCs.

Sensitive detection of protein and miRNA cancer biomarkers using silicon-based photonic crystals and a resonance coupling laser scanning platform.

Enhancement of the fluorescent output of surface-based fluorescence assays by performing them upon nanostructured photonic crystal (PC) surfaces has been demonstrated to increase signal intensities by >8000×. Using the multiplicative effects of optical resonant coupling to the PC in increasing the electric field intensity experienced by fluorescent labels ("enhanced excitation") and the spatially biased funneling of fluorophore emissions through coupling to PC resonances ("enhanced extraction"), PC enhanced fluorescence (PCEF) can be adapted to reduce the limits of detection of disease biomarker assays, and to reduce the size and cost of high sensitivity detection instrumentation. In this work, we demonstrate the first silicon-based PCEF detection platform for multiplexed biomarker assay. The sensor in this platform is a silicon-based PC structure, comprised of a SiO2 grating that is overcoated with a thin film of high refractive index TiO2 and is produced in a semiconductor foundry for low cost, uniform, and reproducible manufacturing. The compact detection instrument that completes this platform was designed to efficiently couple fluorescence excitation from a semiconductor laser to the resonant optical modes of the PC, resulting in elevated electric field strength that is highly concentrated within the region <100 nm from the PC surface. This instrument utilizes a cylindrically focused line to scan a microarray in <1 min. To demonstrate the capabilities of this sensor-detector platform, microspot fluorescent sandwich immunoassays using secondary antibodies labeled with Cy5 for two cancer biomarkers (TNF-α and IL-3) were performed. Biomarkers were detected at concentrations as low as 0.1 pM. In a fluorescent microarray for detection of a breast cancer miRNA biomarker miR-21, the miRNA was detectable at a concentration of 0.6 pM.

Controlling the filtering characteristics of the two-dimensional silicon-based photonic crystal with elliptic air holes

Light propagation characteristics of the channel filters based on the two-dimensional photonic crystals with elliptic defects are studied by the finite-difference time-domain method. The two-dimensional photonic crystal consists of a triangular array of air holes immersed in the silicon background. Shape alteration of the air hole from a circle to an ellipse offers a powerful approach to engineer the resonant frequency of channel filters. And the resonant frequency can be flexibly adjusted only by changing the orientation angle of the elliptic holes. A six-channel drop filters based on the elliptic holes with different obliquities is designed. Connected with the active optical device, above structure can be employed as a kind of frequency division and direction separation device, which is suitable in the complicated optical circuits.

Bragg reflection of light from silicon-based two-dimensional photonic crystals under multiwave-diffraction conditions

Mechanisms of the formation of the Bragg reflection spectra of light from two-dimensional photonic crystals have been studied in terms of an approach based on dynamic diffraction theory. The spectra have been calculated for a structure with a hexagonal silicon-based lattice. The calculated reflection contours are compared with the energy spectra of the eigenmodes of a spatially limited photonic crystal. It is demonstrated for the first time that it is possible to observe multiwave diffraction effects in the optical spectra of two-dimensional photonic-crystal structures.

Observation of the temporal Bragg-diffraction-induced laser-pulse splitting in a linear photonic crystal

Temporal Bragg-diffraction-induced laser-pulse splitting into two pulses propagating with different group velocities is observed in multilayered linear photonic crystals (PCs). This phenomenon originates from spatially inhomogeneous light localization within the PCs at the Laue scheme of the dynamical Bragg diffraction. In a homogeneous medium at the PC output each pulse is spatially separated into two pulses, propagating in the transmission and diffraction directions, respectively. The experiments are carried out for a one-dimensional porous silicon-based PC consisting of 375 spatial periods of 800 nm thickness using a femtosecond Ti:sapphire laser as a probe. A linear dependence of the time splitting of each pair of transmitted and diffractively reflected pulses on the crystal thickness is demonstrated and is supported by theoretical estimations.

Silicon-based photonic crystals fabricated using proton beam writing combined with electrochemical etching method

A method for fabrication of three-dimensional (3D) silicon nanostructures based on selective formation of porous silicon using ion beam irradiation of bulk p-type silicon followed by electrochemical etching is shown. It opens a route towards the fabrication of two-dimensional (2D) and 3D silicon-based photonic crystals with high flexibility and industrial compatibility. In this work, we present the fabrication of 2D photonic lattice and photonic slab structures and propose a process for the fabrication of 3D woodpile photonic crystals based on this approach. Simulated results of photonic band structures for the fabricated 2D photonic crystals show the presence of TE or TM gap in mid-infrared range.

Mesoporous silicon photonic structures with thousands of periods

In this work, we present the results on the fabrication and characterization of the structural and optical properties of thick mesoporous silicon-based 1D photonic crystals (PC) containing up to 2500 periods (400 μm thick) made by electrochemical etching in the hydrofluoric acid solution. The composition of multilayered structures with good spatial periodicity up to thousands of layers and with good reproducibility of porosity of alternate layers is demonstrated that is proven by SEM measurements. Comparative studies of the reflectivity spectra from the front and back sides of a thick free-standing PC also testify a good periodicity of the multilayer structure which manifests itself by the appearance of the photonic band gaps. We demonstrate that the main mechanism that restricts the fabrication of thick porous silicon-based photonic crystals is the local decreasing of the HF concentration in pores.