2D Photonic Crystals Research Articles

Nano-Photonic Crystal D-Shaped Fiber Devices for Label-Free Biosensing at the Attomolar Limit of Detection.

Maintaining both high sensitivity and large figure of merit (FoM) is crucial in regard to the performance of optical devices, particularly when they are intended for use as biosensors with extremely low limit of detection (LoD). Here, a stack of nano-assembled layers in the form of 1D photonic crystal, deposited on D-shaped single-mode fibers, is created to meet these criteria, resulting in the generation of Bloch surface wave resonances. The increase in the contrast between high and low refractive index (RI) nano-layers, along with the reduction of losses, enables not only to achieve high sensitivity, but also a narrowed resonance bandwidth, leading to a significant enhancement in the FoM. Preliminary testing for bulk RI sensitivity is carried out, and the effect of an additional nano-layer that mimics a biological layer where binding interactions occur is also considered. Finally, the biosensing capability is assessed by detecting immunoglobulin G in serum at very low concentrations, and a record LoD of 70 aM is achieved. An optical fiber biosensor that is capable of attaining extraordinarily low LoD in the attomolar range is not only a remarkable technical outcome, but can also be envisaged as a powerful tool for early diagnosis of diseases.

A comparative simulation study of light–matter coupling in 1D photonic crystals with 2D perovskite active layer

Light–matter interaction operating in the strong coupling regime offers wide prospects of applications going from nano-photonics to quantum communications. The most practical implementations are to embed the active matter into Fabry–Perot microcavities or photonic crystals. In this work we focus on the strong coupling of two-dimensional (2D) perovskite in 1D grating waveguide. We use rigorous coupled wave analysis to simulate electromagnetic wave confinement in the 1D waveguide. Various sets of waveguide geometrical parameters are examined to achieve the strong coupling regime for three different configurations of the active layer in the waveguide. To extract quantitatively the relevant physical parameters, such as strength of light–matter interaction, we develop a Hamiltonian formalism to reproduce results obtained by simulation. It is shown that the strongest interaction is to have the active layer inserted in the main slab of the waveguide. It is, however, still weaker by about 20% as compared to the use of Fabry–Perot microcavities.

Photonic-crystal-based hybrid wavelength-mode division multiplexer for SOI platforms

This paper presents a 12-channel hybrid wavelength-mode division multiplexer (WDM-MDM) based on 2D photonic crystals. The proposed device consists of microring resonators (MRRs) and asymmetric directional couplers (ADCs) to perform three-channel wavelength division multiplexing and four-channel mode division multiplexing operations, respectively. Each MRR can work bi-directionally, providing the same wavelength channels separately in two drop ports. The bus waveguides in the cascaded ADCs are optimized to convert the fundamental modes to the corresponding higher-order modes and are connected through taper regions for the smooth transition of modes. The designed device is simulated using the finite-difference time-domain solver, achieving a maximum channel spacing and insertion loss of 5.05 nm and 0.97 dB, respectively. The device size of the proposed WDM-MDM is 74.98µm×32.82µm. The fabrication tolerance study is performed for uniform over-etch and under-etch conditions. The temperature tolerance study on the resonant wavelength is performed, and the temperature coefficient shift of <0.0254nm/K is achieved. The proposed device can potentially increase the channel capacity for on-chip high-density optical interconnects.

Versatile design of tunable Faraday rotator for terahertz band using graphene-InSb-graphene and 1D photonic crystal

A Faraday rotator, composed of graphene-InSb-graphene as magnetic floor and Si- SiO2 materials as the non-magnetic floor is designed to operate at 10 THz frequency, promising for realizing future communication devices. The height of the dielectric layers significantly influences the selection of the resonance frequency. Additionally, the structure can be tuned to operate at a desired frequency thanks to the adjustable surface conductivity of graphene. The findings reveal that variations in the strength of the applied magnetic field intricately modulate the Faraday rotation (FR) and subsequently alter the transmission spectrum. Specifically, values exceeding 40 degrees of FR and a transmission rate of 50% were attainedwhen the magnetic field strength (B) was set at 2 Tesla. Finally, we have proposed a design process for a Faraday rotator that can operate at any arbitrary frequency in the THz band. This innovative design has the potential to introduce a novel approach in ultrathin magneto-optical nanophotonic devices, enabling the realization of polarization rotators characterized by elevated transmittance and reduced reliance on applied static magnetic fields within the THz band.

Optimization of Optical Biosensor Based on 1D Photonic Crystals with Metaheuristic Algorithms for Measuring Glucose Concentration

We aim to simulate an optimal optical biosensor based on one-dimensional crystal photonics, for measuring blood and urine glucose concentration. By optimizing the sensor structure through metaheuristic optimization algorithms, sensitivity was increased. To measure blood and urine glucose concentration, these materials are used as a defect layer in one-dimensional crystal photonics, consisting of three materials: magnesium fluoride (MgF2), borosilicate glass (BK7), and orphan iodide (LiI) with refractive indices of 37/1, 1/5, and 1/99. By changing the concentration of glucose, the refractive index of the defect layer changes, changing the optical properties of the defect layer in the photonic crystal and the spectrum of transmitted and reflected light. According to the amount of light absorption by glucose, a wavelength range of 900–2200 nm (near infrared) was used as the input light. The transfer matrix method was used to calculate multi-layer systems. This method is based on the definition of two matrices, the boundary matrix and the diffusion matrix, which can be used to directly apply the boundary conditions. By plotting the spectrum passing through the crystal using the transfer matrix method and determining the location of the peak in the spectrum, the sensitivity of the sensor was calculated for different concentrations of glucose in blood and urine. The sensitivity obtained before optimization was 530 nm RIU−1, while after optimization it reached 842 nm RIU−1.

Ultrahigh reflectivity photonic crystal membranes with optimal geometry

Photonic crystal (PhC) structures with subwavelength periods are widely used for diffractive optics, including high reflectivity membranes with nanoscale thickness. Here, we report on a design procedure for 2D PhC silicon nitride membrane mirrors providing optimal crystal geometry using simulation results obtained with rigorous coupled-wave analysis. The Downhill Simplex algorithm, a robust numerical approach to finding local extrema of a function of multiple variables, is used to optimize the period and hole radius of PhCs with both hexagonal and square lattices, as the membrane thickness is varied. Following these design principles, nanofabricated PhC membranes made from silicon nitride have been used as input couplers for an optical cavity, resulting in a maximum cavity finesse of 33 000, corresponding to a reflectivity of 0.999 82. The role played by the spot size of the cavity mode on the PhC was investigated, demonstrating the existence of an optimal spot size that agrees well with predictions. We find that, compared to the square lattice, the hexagonal lattice exhibits a spectrally wider reflective range, less sensitivity to fabrication tolerances, and higher reflectivity for membranes thinner than 200 nm, which may be advantageous in cavity optomechanical experiments. Finally, we find that all of the cavities that we have constructed exhibit well-resolved polarization mode splitting, which we expect is due primarily to a small amount of anisotropic stress in the silicon nitride and PhC asymmetry arising during fabrication.

2D Photonic Colloidal Liquid Crystals Composed of Self-Assembled Rod-Shaped Particles.

Photonic crystals, characterized by their periodic structures, have been extensively studied for their ability to manipulate light. Typically, the development of 2D photonic crystals requires either sophisticated equipment or precise orientation of spherical nanoparticles. However, liquid-crystalline (LC) materials offer a promising alternative, facilitating the formation of periodic structures without the need for complex manipulation. Despite this advantage, the development of 2D photonic periodic structures using LC materials is limited to a few colloidal nanodisk liquid crystals. Herein, 2D photonic colloidal liquid crystals composed of biomineral-based nanorods and water is reported. The soft photonic materials with 2D structure by self-assembled LC colloidal nanorods are unique and a new class of photonic materials different from conventional solid 2D photonic materials. These colloids exhibit bright structural colors with high reflectance (>50%) and significant angular dependency. The structural colors are adjusted by controlling the concentration and size of the LC colloidal nanorods. Furthermore, mechanochromic hydrogel thin films with 2D photonic structure are developed. The hydrogels exhibit reversible mechanochromic properties with angular dependency, which can be used for an advanced stimuli responsible sensor.

Circularly polarized beam-scanning antenna with eliminated open-stopband

In the paper, a circularly polarized (CP) frequency beam-scanning antenna based on photonic crystal (PC) is proposed, which possesses the characteristics of eliminating open-stopband (OSB). In the microwave field, the PC is typically constructed by embedding the air or metal column into the material. However, it is difficult for the PC with perfect magnetic conductor walls to accomplish the degeneracy of eigenmodes at the Γ point. Additionally, antennas based on the PC with perfect electric conductor walls exhibit a narrow scanning angle. The proposed unit based on 1D PC possesses perfect electric and magnetic conductor walls. The unit can not only eliminate OSB but also has a wide scanning range. In addition, the unit breaks into the original symmetrical field distributions of 1D PC. Based on the perturbation theory, leaky-wave slots can be designed to generate electromagnetic waves with the CP characteristics. And a CP antenna based on the unit is designed. The antenna can achieve a 70° beam-scanning within the entire operating band (7.6–9.2 GHz), and the variation of the realized gains is below 1.0 dBi around the broadside frequency. Simultaneously, the antenna is fabricated and measured. The measured results are in accordance with the simulation, which validates the success of the design.

Design and Comparative Analysis of an Ultra-Fast, Low-Power All-Optical 4 × 2 Encoder Using a Silicon Y-Shaped 2D Photonic Crystal

Design and Comparative Analysis of an Ultra-Fast, Low-Power All-Optical 4 × 2 Encoder Using a Silicon Y-Shaped 2D Photonic Crystal

Influence of One-Dimensional Photonic Crystal on Raman Signal Enhancement: A Detailed Experimental Study

The enhancement of Raman signals using photonic crystal structures has been the subject of numerous experimental and theoretical studies, leading to a variety of issues and inconsistencies. This paper presents a comprehensive experimental investigation into the impact of alignment between the laser excitation wavelength and the specific position of the photonic band gap on signal enhancement in Raman spectroscopy. By employing one-dimensional (1D) porous silicon photonic crystals, a systematic analysis across a large number of spectra was conducted. The study focused on examining the signal enhancement of both the Raman ∼520 cm–1 silicon band, representing the constituent material of photonic crystal, and the most prominent Raman bands of crystal violet, used as a probe molecule. The probe molecules were both infiltrated into and adsorbed on top of the photonic crystal structure. The obtained experimental results for the contribution of 1D photonic crystals to Raman signal enhancement are much smaller compared to most predictions. The Raman signal of silicon and the signal from the probe molecule are enhanced ≤2.5 times when the laser excitation aligns with the edge of the photonic band gap, strictly defined as the position at the very bottom of the reflectance peak. The results have been discussed within the context of theoretical explanations.

Prediction of Electric Load Neural Network Prediction Model for Big Data

In this study, the two-dimensional hexagonal Photonic crystal energy band structure was simulated using COMSOL Multiphysics field simulation software. The 2D hexagonal Photonic crystal structure was constructed by setting parameters such as periodic boundary conditions and air hole radius. Using the frequency domain solver of COMSOL software, the transmission and reflection spectra of the structure were calculated, and the energy band structure diagram was obtained. The effects of different parameters on the energy band structure were analyzed by adjusting the structure parameters. The results show that the fine tuning of the energy band structure of 2D hexagonal Photonic crystals can be realized by adjusting the radius of air holes and the periodic boundary conditions. This study provides a useful reference for further research on the properties and applications of 2D photonic crystals.

Back-focal plane scanning spectroscopy for investigating the optical dispersion of large-area two-dimensional photonic crystal fabricated by capillary force lithography

In this article, we introduce our custom-built back-focal plane (BFP) scanning spectroscopy to explore an angle-resolved optical dispersion in two-dimensional (2D) photonic crystal (PhC) constructed with hexagonal lattice of nano-scaled dielectric rods. We fabricated a uniformly large-area photonic crystal measuring 1 cm by 0.5 cm, featuring a polymer-based hexagonal lattice on a gold layer, using capillary force lithography. This precision enables the effective confinement of photonic modes, leading to enhanced optical interactions. We successfully map out the angle-resolved reflectance spectra by directly scanning BFP, revealing the structure's angle dependent optical response and providing insights into its iso-frequency contours. Our approach simplifies the exploration of advanced optical materials, highlighting the role of precise fabrication and measurement techniques in understanding and utilizing the optical properties of structured materials for various technological applications.

Three-dimensional photonic crystal optical gas sensor for trace detection and ultrafast response of chemical warfare agent in atmospheric humidity

Chemical warfare agents (CWAs) are toxic that pose a threat to the environment and human health, even trace amounts of CWAs can be fatal. In view of this, there is an urgent need to develop gas sensors for trace detection and ultrafast response of CWAs. Herein, an optical gas sensor has been proposed based on metal−organic frameworks (MOFs) three−dimensional (3D) photonic crystal to detect trace CWAs’ simulant (dimethyl methylphosphonate, DMMP) in different atmospheric humidity (RH 20 %, RH 40 %, RH 60 %, RH 80 %). At relative humidity (RH) of 20 %, the sensor shows excellent selectivity of DMMP due to the specific interactions of van der Waals force between UiO−67 and phosphoryl oxygen (OP) group of DMMP (C3H9O3P), the ultrahigh sensitivity (42.7 ppb), ultrafast response (0.5 s) are profit from the ordered superstructure of 3D photonic crystal and its complete photonic bandgap. At higher humidity (RH 40%–80 %), the sensor shows excellent stability, long–term repeatability, and it still keeps ultrahigh sensitivity (12.1 ppb), ultrafast response (0.49 s) for DMMP at RH 80 %. Moreover, an optical gas sensor array has been prepared to solve the problem of cross−sensitive between DMMP and other CWAs at highest humidity (RH ≥ 80 %), the average classification accuracy can reach 98.6 %.

Enhancement of Light Efficiency of Deep-Ultraviolet Light-Emitting Diodes by Encapsulation with a 3D Photonic Crystal Reflecting Layer.

Recently, UVC LEDs, which emit deep ultraviolet light, have found extensive applications across various fields. This study demonstrates the design and implementation of thin films of three-dimensional photonic crystals (3D PhCs) as reflectors to enhance the light output power (LOP) of UVC LEDs. The 3D PhC reflectors were prepared using the self-assembly of silica nanospheres on a UVC LED lead frame substrate via the evaporation-induced method (side) and the gravitational sedimentation method (bottom), respectively. These PhCs with the (111) crystallographic plane were deposited on the side wall and bottom of the UVC LED lead frame, acting as functional materials to reflect UVC light. The LOP of UVC LEDs with 3D PhC reflectors at a driving current of 100 mA reached 19.6 mW. This represented a 30% enhancement compared to commercial UVC LEDs with Au-plated reflectors, due to the UVC light reflection by the photonic band gaps of 3D PhCs in the (111) crystallographic plane. Furthermore, after aging tests at 60 °C and 60% relative humidity for 1000 h, the relative LOP of UVC LEDs with 3D PhC reflectors decreased by 7%, which is better than that of commercial UVC LEDs. Thus, this study offers potential methods for enhancing the light output efficiency of commercial UVC light-emitting devices.

Resonator embedded photonic crystal surface emitting lasers

The finite size of 2D photonic crystals results in them being a lossy resonator, with the normally emitting modes of conventional photonic crystal surface emitting lasers (PCSELs) differing in photon lifetime via their different radiative rates, and the different in-plane losses of higher order spatial modes. As a consequence, the fundamental spatial mode (lowest in-plane loss) with lowest out-of-plane scattering is the primary lasing mode. For electrically driven PCSELs, as current is increased, incomplete gain clamping results in additional spatial (and spectral) modes leading to a reduction in beam quality. A number of approaches have been discussed to enhance the area (power) scalability of epitaxy regrown PCSELs through careful design of the photonic crystal atom1–3. None of these approaches tackle the inflexibility in being unable to independently modify the photon lifetime of the different modes at the Γ2 point. As a method to introduce design flexibility, resonator embedded photonic crystal surface emitting lasers (REPCSELs) are introduced. This device, combining comparatively low coupling strength photonic crystal structures along with perimeter mirrors, allow a Fabry–Pérot resonance effect to be realised that provides wavelength selective modification of the photon lifetime. We show that surface emission of different surface emitting modes may be selectively enhanced, effectively changing the character of the modes at the Γ2 point. This is a consequence of the selective modification of in-plane loss for particular modes, and is dependent upon the alignment of the photonic crystal (PhC) band-structure and distributed Bragg reflectors’ (DBRs) reflectance spectrum. These findings offer new avenues in surface emitting laser diode engineering. The use of DBRs to reduce the lateral size of a PCSEL opens the route to small, low threshold current (Ith), high output efficiency epitaxy regrown PCSELs for high-speed communication and power sensitive sensing applications.

Three-periodic 1D photonic crystals based on dielectric oxides SiO2, Al2O3, TiO2, ZrO2: an emerging class of structures with wide possibilities for applied photonics

One-dimensional three-periodic photonic-crystal (PC) structures based on dielectric nonmagnetic materials (SiO2, Al2O3, TiO2, ZrO2) that form [(ab)N(cd)M]K supercells including “internal” subcells of the (ab)N and (cd)M types are considered. The classification of this class of structures makes it possible to distinguish three large groups of subcells that differ in optical contrast values (low-, medium-, and high-contrast). Using the transfer matrix method, frequency-angle spectra and energy characteristics of the PC structures are studied and optimal combinations of layers (and contrast) are found, enabling obtaining controllable photonic band gaps (PBGs). A generalization of the obtained results shows that in the transparent region, the optical and energy properties of structures with high and medium optical contrast are of the greatest practical interest. It is found that the group of medium-contrast structures has a greater flexibility in the formation and rearrangement of the PBG due to a practically equivalent effect of the optical properties of both cells on the transmission spectrum. An analysis of the spatial-angular distribution of the transverse component of the Umov-Poynting vector and variation in the number of subcells (internal periods) shows that the structure of this group can provide a controlled radiation pattern (at a telecommunication wavelength of 1.55 μm) on the lateral surface of the PC. The findings may give a competitive advantage in the development of polarization-sensitive couplers, highly sensitive angle sensors for fiber-optic systems, and optical filters operating in the infrared range.

Large‐Scale Bottom‐Up Fabricated 3D Nonlinear Photonic Crystals

Nonlinear optical effects are used to generate coherent light at wavelengths difficult to reach with lasers. Materials periodically poled or nanostructured in the nonlinear susceptibility in three spatial directions are called 3D nonlinear photonic crystals (NPhCs). They enable enhanced nonlinear optical conversion efficiencies, emission control, and simultaneous generation of nonlinear wavelengths. The chemical inertness of efficient second‐order nonlinear materials () prohibits their nanofabrication until 2018. The current methods are restricted to top‐down laser‐based techniques limiting the periodicity along the z‐axis to . The first bottom‐up fabricated 3D NPhC is demonstrated in sol–gel‐derived barium titanate by soft‐nanoimprint lithography: a woodpile with eight layers and periodicities of (‐plane) and (z‐plane). The surface areas exceed , which is two orders of magnitude larger than the state‐of‐the‐art. This study is expected to initiate bottom‐up fabrication of 3D NPhCs with a supremely strong and versatile nonlinear response.

Au nanodisks-based 2D photonic crystals fabricated by single-beam laser interference lithography: A simple and reliable alternative for highly efficient large-scale SERS molecular sensors

Noble metal-based Photonic Crystals (PCs) have emerged as outstanding candidates for precise light management, projecting applications in strategic areas for society like high-sensitivity and fast molecular (inorganic/organic/bio) sensing by Surface-Enhanced Raman Spectroscopy (SERS). In this work, we report an exhaustive study on the potential of large-scale (active area >1 [cm2]) Au nanodisks-based 2D PCs fabricated by single-beam Laser Interference Lithography (LIL) for high-performance SERS molecular sensing. This technique was used to fabricate periodic nanoarrays (period of 470 [nm]) of Au nanodisks with thicknesses from 50 up to 125 [nm]. The period was chosen following Finite-Difference Time-Domain (FDTD) simulations that suggested the best electric-near field enhancement for this condition. Confocal Raman microscopy and Methylene Blue (MB) as active Raman marker, were used to assess the samples' performance for molecular sensing. SERS studies have shown that the nanodisks' thickness can be a considerable size parameter for the Raman signal amplification, observing higher signal enhancements for higher thicknesses. The observed thickness effects on the Raman signal enhancement were consistent with FDTD simulations, which predicted higher electric-near field amplifications for higher thickness within the red/near-infrared range. Results show that our PCs enable to measure the characteristic Raman footprint of the analyte with good spectral resolution using relatively low powers (0.04–1 [mW]) and short acquisition times (1–30 [s]), considering an MB surface mass density as low as 2.6 [ng/cm2]. SERS enhancement factors as high as 2 x 107 were achieved for PCs with the highest thickness, representing a competitive performance concerning typically reported values (104–107) for current noble metal-based PCs technologies and a new record concerning PCs fabricated by LIL (104–105). This research demonstrates the high competitivity of these simple Au nanodisks-based 2D PCs, fabricated using an efficient large-scale and low-cost lithography technique, for fast, high spectral resolution and highly reproducible SERS-based molecular sensing.

Angle-Multiplexed 3D Photonic Superstructures with Multi-Directional Switchable Structural Color for Information Transformation, Storage, and Encryption.

Creating photonic crystals that can integrate and switch between multiple structural color images will greatly advance their utility in dynamic information transformation, high-capacity storage, and advanced encryption, but has proven to be highly challenging. Here, it is reported that by programmably integrating newly developed 1D quasi-periodic folding structures into a 3D photonic crystal, the generated photonic superstructure exhibits distinctive optical effects that combine independently manipulatable specular and anisotropic diffuse reflections within a versatile protein-based platform, thus creating different optical channels for structural color imaging. The polymorphic transition of the protein format allows for the facile modulation of both folding patterns and photonic lattices and, therefore, the superstructure's spectral response within each channel. The capacity to manipulate the structural assembly of the superstructure enables the programmable encoding of multiple independent patterns into a single system, which can be decoded by the simple adjustment of lighting directions. The multifunctional utility of the photonic platform is demonstrated in information processing, showcasing its ability to achieve multimode transformation of information codes, multi-code high-capacity storage, and high-level numerical information encryption. The present strategy opens new pathways for achieving multichannel transformable imaging, thereby facilitating the development of emerging information conversion, storage, and encryption media using photonic crystals.

Theoretical Study of Symmetrical 1D Photonic Crystal as a Blood Cancer Sensor

Theoretical Study of Symmetrical 1D Photonic Crystal as a Blood Cancer Sensor