Photonic Crystal Structure Research Articles

A compact high-performance decoder using the resonant cavities in photonic crystal structure

A compact high-performance decoder using the resonant cavities in photonic crystal structure

Topology Optimization-Based Design of Topological Edge-State Wavelength Division Multiplexer

Previous research processes on topological insulators were mainly based on the manual adjustment of a large number of fine parameters to achieve the desired properties. Here, we propose to treat the design process of photonic crystals as an objective function through topological optimization theory, allowing the desired properties to arise spontaneously with the optimization. Through topology optimization, we have designed and implemented three topological photonic crystals with different topological characteristics and dual-band protection common bandgap. The results show that functional edge modes with desired propagation properties can be generated within these two bandgaps by constructing domain walls between photonic crystal structures with different topological phases. The unidirectional transmission characteristics of the wave can also be observed, which provides an easy way to implement a wavelength division multiplexer.

Photonic Crystal Based Ultrafast and Highly Sensitive Refractive Index Sensor

In this paper, a novel approach is proposed to detect the concentration of virus with different refractive indices in saliva using two-dimensional photonic crystal (PC) structures. The proposed 18×17 hexagonal PC structure consists of air holes in a silicon slab with silicon-on-insulator (SOI) techniques. The plane wave expansion (PWE) method is used to find the photonic band gap (PBG). The mid-gap wavelength of PBG increases linearly with a refractive index of infiltrated samples in air holes. The change in PBG size increases linearly by an average slope of 4.45 with respect to the change in refractive index concentration. The proposed sensor exhibits a maximum sensitivity of 1206.4 nm/RIU for 100% concentration of virus and minimum sensitivity of 950.4 nm/RIU for 0% concentration of virus with an ultra-fast average response time of 10.6 fs to test the samples. The present work can be useful for sensing variation in bio-molecular RI and other infection’s presence in various biological targets at an early stage.

Experimental probe of twist angle-dependent band structure of on-chip optical bilayer photonic crystal.

Recently, twisted bilayer photonic materials have been extensively used for creating and studying photonic tunability through interlayer couplings. While twisted bilayer photonic materials have been experimentally demonstrated in microwave regimes, a robust platform for experimentally measuring optical frequencies has been elusive. Here, we demonstrate the first on-chip optical twisted bilayer photonic crystal with twist angle-tunable dispersion and great simulation-experiment agreement. Our results reveal a highly tunable band structure of twisted bilayer photonic crystals due to moiré scattering. This work opens the door to realizing unconventional twisted bilayer properties and novel applications in optical frequency regimes.

Multi-mode strong coupling in Fabry-Pérot cavity-WS2 photonic crystal hybrid structures.

Optical microcavities embedded with transition metal dichalcogenide (TMDC) membranes have been demonstrated as excellent platforms to explore strong light-matter interactions. Most of the previous studies focus on strong coupling between excitons of unpatterned TMDC membranes and optical resonances of various microcavities. It is recently found that TMDC membranes patterned into photonic crystal (PhC) slabs can sustain guided-mode resonances that can be excited and probed by far-fields. Here, we present a comprehensive theoretical and numerical study on optical responses of Fabry-Pérot (F-P) cavity-WS2 PhC hybrid structures to investigate the multi-mode coupling effects between excitons, guided-mode resonances and F-P modes. We show that both the exciton resonance and the guide-mode resonance of the WS2 PhC can strongly interact with F-P modes of the cavity to reach strong coupling regime. Moreover, a Rabi splitting as large as 63 meV is observed for the strong coupling between the guided-mode resonance and the F-P mode, which is much larger than their average dissipation rate. We further demonstrate that it is even possible to realize a triple mode strong coupling by tuning the guide-mode resonances spectrally overlapped with the exciton resonance and the F-P modes. The hybrid polariton states generated from the triple mode coupling exhibit a Rabi splitting of 120 meV that greatly exceeds the criterion of a triple mode strong coupling (∼29.3 meV). Our results provide that optical microcavities embedded with TMDC PhCs can serve as promising candidates for polariton devices based on multi-mode strong coupling.

Photonic Crystal Films Based on Polymer Particles with a Core/Shell Structure Responding to Ethanol.

Responsive photonic crystals assembled from colloidal particles have been increasingly utilized in detection and sensing devices owing to their attractive ability to change color in response to external conditions. Methods of semi-batch emulsifier-free emulsion and seed copolymerization are successfully applied for the synthesis of monodisperse submicron particles with a core/shell structure, a core being formed by polystyrene or poly(styrene-co-methyl methacrylate) and a shell being formed by poly(methyl methacrylate-co-butyl acrylate). The particle shape and diameter are analyzed by the dynamic light scattering method and scanning electron microscopy, and the composition is investigated by ATR-FTIR spectroscopy. As shown by scanning electron microscopy and optical spectroscopy, the thin-film 3D-ordered structures based on poly(styrene-co-methyl methacrylate)@poly(methyl methacrylate-co-butyl acrylate) particles exhibited the properties of photonic crystals with minimum number of defects. For polymeric photonic crystal structures based on core/shell particles, a pronounced solvatochromism with respect to ethanol vapor (less than 10 vol %) is observed. Moreover, the nature of the crosslinking agent has a significant effect on the solvatochromic properties of 3D-ordered films.

Second Harmonic Generation in 1D Nonlinear Plasma Photonic Crystals

AbstractIn this paper, a 1D nonlinear plasma photonic crystal (NPPC) structure composed of polarized ferroelectric crystals and nonlinear plasma periodic alternation is proposed. The transfer matrix method is employed to analyze the second harmonic generation (SHG) problem of this structure. In the designed NPPCs, the fundamental wave (FW) operates in the gigahertz (GHz) band and the nonlinear plasma is controlled by an external high‐intensity control wave (CW). Numerical simulations are performed to investigate the effects of different incident angles and external CW intensities on the total conversion efficiency (T‐con) of the second harmonic wave (SHW). Additionally, the internal electric field distribution and incident light intensity within the nonlinear structure are analyzed. The importance of the relationship between the FW frequency and photonic band gap (PBG) in enhancing SHG is summarized. The results demonstrate that the optimal structure can be obtained by changing the structural parameters, such that the FW and SHW are tuned to the edge of the PBG. At this point, the electromagnetic field density is large, the group velocity is small, the local field is enhanced, and the nonlinear optical interaction is increased, resulting in a significant increase in the T‐con of the SHW.

Compact all-optical decoder design for optical integrated circuits.

This paper constructs and discusses a 1×2 decoder based on two-dimensional photonic crystals. The designed decoder is a priority decoder with one main input and one enabled input. This logic circuit's structure is very simple and compact, and it employs a photonic crystal structure with dimensions of 11×11 rods built of GaAs. The calculation results reveal that the output power values for logical mode 1 are extremely close to the power of the light source, whereas the power is very low and close to zero in logical mode 0. As a result, the difference between logical values 0 and 1 in the output will be adequate, and the circuit's accuracy will be good. The finite difference-time domain (FDTD) approach is used for time computations and light propagation in waveguides.

Programmable Shaping of Femtosecond Pulses Using a One-Dimensional Photonic Crystal with Continuous Spatial Modulation of the Refractive Index

An algorithm for constructing the structure of a one-dimensional photonic crystal, which forms a femtosecond pulse of an arbitrary given shape when reflecting a Gaussian pulse, is developed theoretically. The method is illustrated by the example of a rectangular pulse. Examples for simple pulse shapes are given, the influence of optical absorption is evaluated, and a method for its compensation is proposed.

Performance analysis of photonic crystal fiber structure based on different highly nonlinear materials

Generally, fiber with a large mode area is desired for fiber laser and beam delivery applications. But the use of these fiber types is restricted to linear optical applications due to the lower value of the nonlinear coefficient. This paper investigates a single material-based photonic crystal fiber (PCF) with improved optical characteristics, applicable for linear and nonlinear optics. The light propagation in the structure is explored by applying finite element solver-based COMSOL multiphysics software. Five nonlinear optical materials are utilized as background material to get the optimized material with high performance PCF. Using this PCF, the improved optical properties of PCF such as moderate effective mode area of 115.85 [Formula: see text], chromatic dispersion, confinement loss of 10[Formula: see text] dB/m, the nonlinear coefficient of 543W[Formula: see text]Km[Formula: see text], splicing loss of 2.013 dB, and numerical aperture are numerically analyzed. This single-mode PCF also shows the low bending loss for the bending radius of 7[Formula: see text]mm. The amended PCF structure is found to be suitable for high-power fiber laser, supercontinuum generation, wavelength conversion, and slow-light generation.

A D-Shaped SPR-Based PCF Sensor with an Extremely High-Amplitude Sensitivity for Measuring the Refractive Index.

In this work, a new D-shaped photonic crystal fibre sensor structure based on surface plasmon resonance (SPR) is purposed for measurement of analyte refractive index (RI). In this design, a silica cylinder is polished into a D-shaped silica material structure with a flattened surface where two Au nanowires are coated. Some air holes are omitted to form the core mode region. With the implementation of gold nanowires and a core region for the exciting SPR effect with variate physical values, analyte RI can be measured with a wavelength coverage from 850 to 1350nm. The numerical simulation shows the maximum wavelength sensitivity of the purposed design achieves 19,600nm/RIU with an RI coverage from 1.37 to 1.42. Moreover, the sensor has a tremendous amplitude sensitivity and the maximum absolute value is about 2300RIU-1. Benefiting from these outstanding performance, the purposed structure can be given priority when it is applied in biomedical detecting and environmental assessment science.

A Dual-Core Surface Plasmon Resonance-Based Photonic Crystal Fiber Sensor for Simultaneously Measuring the Refractive Index and Temperature

In this correspondence, a new photonic crystal fiber biosensor structure on the basis of surface plasmon resonance is proposed for the measurement of the refractive index (RI) and TSM temperature simultaneously. In this design, the central and external surface of the biosensor structure are coated with thin gold film. A hole adjacent to the inner gold film is filled with temperature-sensitive material (TSM). With the implementation of internal and external gold coatings along with TSM, the biosensor achieves the measurement of the RI and temperature with two disjoint wavelength coverage. Numerical simulations and calculation results illustrate that the average wavelength sensitivity of the biosensor structure, respectively, achieves 7080 nm/RIU and 3.36 nm/°C with RI coverage from 1.36 to 1.41 and temperature coverage from 0 to 60 °C. Moreover, benefiting from realization of different wavelength regions in RI and temperature sensing, it is believed that the proposed biosensor structure for the measurement of the RI and temperature will have range applications in the fields of medical diagnostics and environmental assessments.

Photo‐Responsive Azobenzene‐Containing Inverse Opal Films for Information Security

AbstractStimuli‐responsive photonic crystals (PCs) have attracted increasing attentions owing to the unique optical feature in regulating the propagation of light and tunable structural colors in response to external stimuli, emerging application potential on diverse fields. However, the development of stimuli‐responsive PCs with wide visible light range, broad shift of bandgaps, and adjustable responsive rates for counterfeiting remains challenging. Herein, a simple strategy for the preparation of photo‐responsive azobenzene‐containing inverse opal (AzoIO) films is reported. First, azobenzene‐containing composites are generated by filling functional monomers into voids of silica colloids crystals. Followed by the thermal polymerization and subsequent etching, a series of AzoIO films are successfully fabricated with adjustable structural colors in wide visible wavelength. Upon irradiation with linearly polarized visible light (LPVL), a slowly broad blueshift of bandgaps (≈138 nm, 3200 s) is observed due to the anisotropic shrinkage of the periodic PC structures. However, UV light irradiation contributed to a fast broad blueshift of bandgaps (≈131 nm, 10 s), owing to the photoisomerization merit of azobenzene moiety. The proof‐of‐concept study on the applications in light‐modulated multicolored writable paper, encryption films, and fast writing/erasing demonstrated the potential for information security. This work paves an avenue for developing promising optical anti‐counterfeiting materials.

Optical and Electrical Modulation Strategies of Photoelectrodes for Photoelectrochemical Water Splitting.

When constructing efficient, cost-effective, and stable photoelectrodes for photoelectrochemical (PEC) systems, the solar-driven photo-to-chemical conversion efficiency of semiconductors is limited by several factors, including the surface catalytic activity, light absorption range, carrier separation, and transfer efficiency. Accordingly, various modulation strategies, such as modifying the light propagation behavior and regulating the absorption range of incident light based on optics and constructing and regulating the built-in electric field of semiconductors based on carrier behaviors in semiconductors, are implemented to improve the PEC performance. Herein, the mechanism and research advancements of optical and electrical modulation strategies for photoelectrodes are reviewed. First, parameters and methods for characterizing the performance and mechanism of photoelectrodes are introduced to reveal the principle and significance of modulation strategies. Then, plasmon and photonic crystal structures and mechanisms are summarized from the perspective of controlling the propagation behavior of incident light. Subsequently, the design of an electrical polarization material, polar surface, and heterojunction structure is elaborated to construct an internal electric field, which serves as the driving force to facilitate the separation and transfer of photogenerated electron-hole pairs. Finally, the challenges and opportunities for developing optical and electrical modulation strategies for photoelectrodes are discussed.

Highly hydrostable and flexible opal photonic crystal film for enhanced up-conversion fluorescence sensor of COVID-19 antibody

Efficient detection of related markers is significant for the early screening of COVID-19. Near infrared (NIR) light excited up-conversion fluorescence probes are ideal for biosensing but limited by the low luminescence efficiency. In this work, a novel highly stable opal photonic crystal (OPC) structure was designed to provide an OPC effect for up-conversion fluorescence enhancement, and sensitive Novel Coronavirus IgG up-conversion FRET-based sensor was further constructed. For the problems of water stability and mechanical stability of polymer OPC which cannot be solved for a long time, polymer spray combined with a flipped OPC film strategy is presented. Fragmented size OPC film was firmly fixed by polymer modification layer, which gave large size OPC film great water stability, mechanical stability and bending performance without affecting the fluorescence enhancement property. On this basis, the up-conversion emission intensity was enhanced significantly, and fluorescence resonant energy transfer (FRET) based Novel Coronavirus IgG antibody sensor was constructed. Monolayer up-conversion nanoparticles (UCNPs) on the surface of the polydopamine (PDA)/OPC film can make the fluorescent signal more sensitive, and effectively reduce the detection limit. The test device integrating NIR excitation and mobile phone realized the visual fast detection, showing remarkable sensing performance for COVID-19 antibodies with the limit of detection (LOD) of 0.1 ng mL−1. This detection platform will provide a more effective tool for early detection of the novel coronavirus.

Designing the Structure of a One-Dimensional Photonic Crystal with a Given Spectrum of the Reflection Coefficient

A method for solving the inverse problem of designing the structure of a one-dimensional photonic crystal is proposed and experimentally implemented. It is known that a one-dimensional photonic crystal with a spatial sinusoidal modulation of the refractive index, has a narrow photonic bandgap at a frequency related to the spatial frequency of this sinusoid. A reverse engineering method is proposed for one-dimensional photonic crystals with an arbitrary given reflection spectrum by expanding this spectrum into elementary photonic band gaps and then summing them. The application of this method to fabricate examples of photonic crystals with simple shapes of spectral reflection curves is demonstrated.

Biomimetic thermally responsive photonic crystals film with highly robust by introducing thermochromic dyes

Thermally responsive photonic crystals (TRPCs) are intelligent responsive materials that can dynamically coordinate electromagnetic wave transmission, translating thermal stimuli into optical signals and structural color changes. However, it remains a big challenge to develop a robust TRPC, because of the thermochromic mechanism of unstable dramatic volume change that collapses photonic crystal (PC) structure. We demonstrate a highly robust and flexible TRPC film inspired by the chameleon, combining thermochromic dyes (TDs) with PC for a synergistic response. There is only negligible color fluctuation even after 2000 color-change cycles, attributing to no lattice parameter change during the thermal stimulus. Moreover, both positive (transparency to opaque color) and negative (opaque color to transparency) TDs are introduced into TRPC, implementing a full-color RGB thermally-responsive system. The response of the positive-TRPC and negative-TRPC temperatures were 32.0 and 50.5 °C, respectively. A TRPC film with environmental adaptability was designed, which offers a promising route to anti-counterfeiting, steganography and smart window.

Inverse designed photonic crystals for spatial filtering

Zero incidence angle spatial filters of a compact design can be very useful, among others, for intracavity spatial filtering in high-power micro-lasers. Typically, micro-lasers, especially in high-power operation regimes, emit beams of low spatial quality due to the large aspect ratio of the laser resonator. A promising proposal for compact spatial filtering is the integration of the Photonic Crystals structures into the micro-resonator of the laser. Here, we report efficient spatial filters with desired filtering properties engineered by the inverse design. Such filters can be designed not only separately for both polarizations of the incident radiation but also simultaneously for both S and P polarizations. Moreover, we fabricate the inverse-designed structure by physical vapor deposition and highlight good correspondence of the angle-wavelength transmission map to the target one.

Design and analysis of 1:2 line optical decoder based on linear optics

In this paper, a simple design of all-optical photonic crystal (PhC) based 1:2 line decoder has been proposed and its operating principle is based on light beam interference. The designed structure has a hexagonal arrangement of air holes in Si substrate with a finite slab height. In our proposed structure, different path lengths have been made so that the light beams should interact out of phase. Effective refractive index method has been adopted to reduce the simulation time. The Finite Difference Time Domain (FDTD) and Plane Wave Expansion (PWE) methods have been applied to evaluate the proposed structures. The required footprint area for proposed device is reported as 215 µm2. Minimum contrast ratio between the logic states of “1” and “0” is obtained as 10 dB. This device is designed based on solely linear optical phenomena in a holes-in-slab PhC structure. Therefore, mechanically stabled, ultra-compact design and simple working mechanism of the proposed optical decoder can be a potential candidate for future generation Photonic Integrated Circuits (PICs).

Smith–Purcell radiation controlled by the transmission characteristics and quality factor of a layer

Photonic crystal structures have attracted significant attention because of their ability to confine light, especially outgoing waves in a bandgap. In this study, we investigate a layer that can control the Smith–Purcell radiation. The results show that transmission characteristics and quality factor of a 1D photonic crystal can narrow the radiation spectrum and enhance the radiation intensity. From another perspective, the entire structure can be treated as a composite grating, the radiation spectra of which are obtained by theoretical calculations and agree with that from the analysis based on the role of the 1D photonic crystal. Therefore, it can be concluded that the radiation from a composited structure can be simplified by the radiation controlled by the 1D metal photonic crystal, and it provides a fast way to reshape the radiation spectra by designing the transmission characteristic and quality factor of the photonic crystal. Furthermore, a layer with special transmission characteristics and quality factor above a reflection grating can be used to achieve coherent and tunable Smith–Purcell radiation, which is significant for the development of band-controllable light or terahertz radiation sources.