Two-dimensional Photonic Crystals Research Articles

Two-dimensional photonic crystal based optical CNOT gate

Two-dimensional photonic crystal based optical CNOT gate

Robust Topological Edge States in C6 Photonic Crystals

The study of photonic crystals has emerged as an attractive area of research in nanoscience in the last years. In this work, we study the properties of a two-dimensional photonic crystal composed of dielectric rods. The unit cell of the system is composed of six rods organized on the sites of a C6 triangular lattice. We induce a topological phase by introducing an angular perturbation ϕ in the pristine system. The topology of the system is then determined by using the so-called k.p perturbed model. Our results show that the system presents a topological and a trivial phase, depending on the sign of the angular perturbation ϕ. The topological character of the system is probed by evaluating the electromagnetic energy density and analyzing its distribution in the real space, in particular on the maximal Wyckoff points. We also find two edge modes at the interface between the trivial and topological photonic crystals, which present a pseudospin topological behavior. By applying the bulk-edge correspondence, we study the pseudospin edge modes and conclude that they are robust against defects, disorder and reflection. Moreover, the localization of the edge modes leads to the confinement of light and the interface behaves as a waveguide for the propagation of electromagnetic waves. Finally, we show that the two edge modes present energy flux propagating in opposite directions, which is the photonic analogue of the quantum spin Hall effect.

Dual-Band Laser Stealth Based on Quasi Photonic Crystals

A quasi photonic crystal (QPC) dual-band absorber for laser stealth is designed and numerically studied. It consists of a defective two-dimensional photonic crystal on a thick Ni film. The defective photonic crystal is a continuous Ge layer with air holes, but some of the holes are periodically removed. Under a normal incidence that is perpendicular to the plane of the defects, the absorptivity can achieve 92.8% at the 1.064 μm wavelength and 93.2% at the 1.55 μm wavelength. Within large incident angles (<45 degrees), the dual-band absorptivity is still >80%. Additionally, the emissivity is as low as 5.8%~20.0% and 2.8%~5.8% in the 3–5 μm and 8–14 μm atmospheric windows. It is found that the introduced defects can couple the incidence into the structure and lead to spectral peaks (electromagnetic resonances) even without the bottom Ni film. With the help of the high-loss Ni film, the resonances are transformed into magnetic or/and electric modes of different orders. As a result, the QPC generates four absorption peaks. They are superimposed in pairs, resulting in enhanced absorption of the two laser wavelengths.

Manifestation of “Slow” Light in the Photocurrent Spectra of Ge/Si Quantum Dot Layers Combined with a Photonic Crystal

The spectral characteristics of the photocurrent in the near-infrared range in vertical Ge/Si p–i–n photodiodes with Ge quantum dots embedded in a two-dimensional photonic crystal are investigated. The interaction of the quantum dots with photonic Bloch modes leads to the resonant enhancement of the sensitivity of photodiodes. The dependences of the photocurrent on the angle of incidence of light are used to determine the dispersion relations of the Bloch modes. Regions in the dispersion characteristics where the group velocity of photons is close to zero are revealed. It is established that the maximum enhancement of the photocurrent relative to a photodiode without photonic crystal, which can be up to a factor of ~60, results from the interaction of quantum dots with “slow” Bloch modes.

Topological photonic crystal fiber with honeycomb structure.

We analyze a new type of photonic crystal fiber which consists of the core and cladding that distinct in topology by tuning the position of air holes in each hexagonal unit cell where the C6v symmetry is respected. The p-d band inversion between the core and cladding leads to topological interface modes inside the band gap, which can propagate along the fiber with a nonzero momentum in perpendicular to the corss section of a fiber. The helical topological interface modes possess the pseudospin-momentum locking effect inherited from the corresonding two-dimensional photonic crystal characterized by the Z2 topology. The wave functions for the topological interface modes are analytically studied and compared successfully to the numerical results, enlighting a novel way to use photonic crystal fiber to transfer information.

Selective activation of topological valley corner states in C3-symmetric photonic crystals

Higher-order topological insulators have drawn great research attention in nanophotonics due to their ability to both support robust edge states and lower dimensional corner states. In this work, we present a theoretical proposal for achieving topologically switchable and valley-selective corner states based on two-dimensional C3-symmetric photonic crystals (PCs), with breaking of inversion symmetry. Through the concatenation of two valley PCs with contrasting topological indices, we demonstrate the emergence of two types of valley-locked chiral topological edge states resulting from the valley–valley interaction. More importantly, we find that the system exhibits two distinct types of corner states, characterized by strong robustness and high localization, when the PCs are spliced at a 60° angle. However, the corner states are absent when the splicing angle is set as 120°. According to the theoretical analysis, the selective activation of topological valley corner states is related to the sign flip of valley Chern number at the corner. Based on this feature, we further propose a topological photonic switching device, in which the corner can be lighted up or off selectively. By combining the benefits of higher-order topology and valley degree of freedom, our work provides an efficient and flexible method for light manipulation.

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.

Design and analysis of a two-dimensional photonic crystal plus-shaped resonator for the detection of different cancerous cells and urine glucose

In this paper, a simple two-dimensional (2D) photonic crystal (PhC) plus-shaped resonator is suggested to detect different cancer cells as well as urine glucose. A novel biosensor design is presented that features a plus-shaped PhC resonator capable of detecting cancerous cells in human skin, cervix, blood, adrenal glands and breast, as well as detecting glucose levels in human urine to diagnose the likelihood of diabetes. Our biosensor boasts of an impressive quality factor of 307 for cancerous skin cells and 670.6 for glucose concentration in the blood. In addition, the device offers a maximum sensitivity of 750[Formula: see text]nm/RIU for detecting various cancerous cells and 2420[Formula: see text]nm/RIU for glucose in human urine. By positioning the resonator and the waveguide in a way that enables light to resonate in the middle of the structure and pass to the output terminal, we were able to focus on the absorption rate rather than the transmission. As a result, the maximum glucose and cancerous cell absorption rates reach 87.1% and 89.8%, respectively. Our unique yet simple sensor structure offers exciting new possibilities for detecting different cancerous cells and glucose concentrations, while the impressive sensitivity and quality factor make it an exceptional candidate for a wide range of biosensing applications.

Coexistence of Fano and electromagnetically induced transparency resonance line shapes in photonic topological insulators

Due to the bending resistance and defect immunity of the topological optical structure, topological photonics is extended to researching Fano line shapes or electromagnetically induced transparency-like (EIT-like) line shapes. In this paper, two-dimensional photonic crystal with Kekule´ distortion is designed to realize quantum spin Hall effect and quantum valley Hall effect simultaneously. The stable topological corner states and edge states are obtained. Corner states as dark modes interfere with edge states as bright mode to induce Fano or EIT-like line shapes. As far as we know, we first realize the coexistence of Fano and EIT-like line shapes based on the coexistence of quantum spin Hall effect and quantum valley Hall effect. Our results provide a new way to realize multi-channel sensing technology.

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.

Design of unidirectional and tunable channels in two-dimensional photonic crystal composed of local PT symmetric structure

Design of unidirectional and tunable channels in two-dimensional photonic crystal composed of local PT symmetric structure

Optical non-volatile correction of SERS wavelength using optical pumping

In this paper, we propose a reconfigurable two-dimensional photonic crystal (PC) made from a new ultralow loss phase change material for detecting and imaging applications of surface-enhanced Raman scattering (SERS). The proposed all-dielectric structure is composed of identical holes periodically distributed on Sb2S3 as a substrate, tuned by optical pumping. The proposed PC is investigated using full-wave simulation of the CST with the finite-difference frequency domain method over a wide bandwidth of optical wavelengths. In this study, compensation for the error of the Fano resonance wavelength due to the fabrication process is realized through tuning optical pumping applied to the configuration. Also, the numerical results show the designed PC supports two high-quality Fano resonance modes, leading to uniform and high field enhancement with a SERS enhancement factor of 1.23 × 1012, which is significant for the application of SERS enhancement.

Tunable Photonic Band Gaps in Two-Dimensional Bravais–Moiré Photonic Crystal Composed of High-Tc Superconductors

In this study, we perform a theoretical study of light propagation properties in two-dimensional square photonic crystals (PCs) following Bravais–Moiré (BM) patterns composed of copper oxide high-temperature superconductors (HTSCs). The BM PCs are made of cylindrical cores formed from the combination of two square Bravais lattices. The Moiré pattern forms due to a commensurable rotation of one of these lattices with respect to the other. The dielectric function of the superconducting material is modeled by the two-fluid Gorter–Casimir theory. We report on the corresponding gap, the mapping as a function of the radius of dielectric cores, as well as the dispersion relations of TM modes for BM PCs and for the waveguide system built of defect lines within such a crystal. The BM PCs were composed of copper oxide HTSCs, which exhibit large tunability in terms of temperature.

Polarization-insensitive epsilon-mu-near-zero effect in two-dimensional annular photonic crystals

We report polarization-insensitive epsilon-mu-near-zero (EMNZ) effect for both transverse-electric (TE) and transverse-magnetic (TM) polarizations in two types of two-dimensional (2D) annular PCs (APCs). The square-lattice air-ring (or dielectric-ring) type 2D APC can support non-accidental Dirac-like degeneracy for three low-energy TE (or TM) bands and accidental Dirac-like degeneracy for three higher-energy TM (or TE) bands at the same frequency. We rigorously demonstrate the polarization-insensitive EMNZ effect in 2D APCs based on the S-parameters inversion technique.

Effects of orientational and positional randomness of particles on photonic band gap

A recent work [PRL, 126, 208002 (2021)] has explored how thermal noise-induced randomness in a self-assembled photonic crystal affects photonic band gaps (PBGs). For the system of a two-dimensional photonic crystal composed of a self-assembled array of rods with square cross sections, it was found that its PBGs can exist over an extensive range of packing densities. Counterintuitively, at intermediate packing densities, the transverse magnetic (TM) band gap of the self-assembled system can be larger than that of its corresponding perfect system (rods arranged in a perfect square lattice and having identical orientations). Due to shape anisotropicity, the randomness in the self-assembled system contains two kinds of randomness, i.e., positional and orientational randomness of the particles. In this work, we further investigate how PBGs are influenced solely by positional or orientational randomness. We find that compared to the perfect situation, the introduction of only orientational randomness decreases the transverse electric (TE) band gap while having no obvious effects on the transverse magnetic (TM) band gap. In contrast, the introduction of only positional randomness decreases the TE band gap significantly, while it can widen or narrow the TM band gap, depending on the parameter range. We also discuss the thermal (i.e., self-assembled) system where two kinds of randomness are present. Our study contributes to a better understanding of the role orientational randomness and positional randomness play on PBGs, and may benefit the PBG engineering of photonic crystals through self-assembly approaches.

Metamaterials for light extraction and shaping of micro-scale light-emitting diodes: from the perspective of one-dimensional and two-dimensional photonic crystals.

Metamaterials have attracted broad attention owing to their unique versatile micro- and nano-structures. As a kind of typical metamaterial, photonic crystals (PhCs) are capable of controlling light propagation and constraining spatial light distribution from the chip level. However, introducing metamaterial into micro-scale light-emitting diodes (µLED) still exists many unknowns to explore. This paper, from the perspective of one-dimensional and two-dimensional PhCs, studies the influence of metamaterials on the light extraction and shaping of µLEDs. The µLEDs with six different kinds of PhCs and the sidewall treatment are analyzed based on finite difference time domain (FDTD) method, in which the optimal match between the PhCs type and the sidewall profile is recommended respectively. The simulation results show that the light extraction efficiency (LEE) of the µLEDs with 1D PhCs increases to 85.3% after optimizing the PhCs, and is further improved to reach 99.8% by the sidewall treatment, which is the highest design record so far. It is also found that the 2D air ring PhCs, as a kind of left-handed metamaterials, can highly concentrate the light distribution into 30° with the LEE of 65.4%, without help of any light shaping device. The surprising light extraction and shaping capability of metamaterials provides a new direction and strategy for the future design and application of µLED devices.

Design of All-Optical Logic Half-Adder Based on Photonic Crystal Multi-Ring Resonator

In this paper, a novel design of an all-optical half-adder (HA) based on two two-ring resonators in a two-dimensional square-lattice photonic crystal (PC) structure without nonlinear materials is proposed. The all-optical HA comprises AND and XOR gates where each gate is composed of cross-shaped waveguides and two-ring resonators in a 2D square-lattice PC that are filled with silicon (Si) rods in silica (SiO2). The AND and XOR gates are analyzed and simulated using plane-wave expansion (PWE) and finite-difference time-domain (FDTD) methods. Simulation results show that light guiding inside the device functions as AND and XOR gates. Thus, the proposed device has the potential for use in optical arithmetic logic units for digital computing circuits. The structure comprises an optical AND gate and an optical XOR gate that were designed to work at the C-band spectrum. Results show that there is a clear distinction between logic states 1 and 0 with a narrow power range that leads to a better robust decision on the receiver side for minimized logic errors in the photonic decision circuit. Thus, the proposed HA can be a key component for designing a photonic arithmetic logic unit.

Graded-Index Active Layer for Efficiency Enhancement in Polymer Solar Cell

In this paper, narrow-bandgap polymer acceptors combining a benzotriazole (BTz)-core fused-ring segment, named the PZT series, were used with a high-absorption-efficiency polymer (PBDB) compound with branched 2-butyl octyl, linear n-octyl, and methyl to be utilized as a graded-index (GI) active layer of the polymer solar cells (PSCs) to increase the photocurrent and enhance solar efficiency compared to the existing PBDB-T:PZT and PBDB-T:PZT-γ. In addition, a two-dimensional photonic crystal (2D-PhC) structure was utilized as a light-trapping anti-reflection coating (ARC) thin film based on indium tin oxide (ITO) to reduce incident light reflection and enhance its absorption. The dimensions of the cell layers were optimized to achieve the maximum power-conversion efficiency (PCE). Furthermore, the design and simulations were conducted from a 300 nm to 1200 nm wavelength range using a finite difference time-domain (FDTD) analysis. One of the most important results expected from the study was the design of a nano solar cell at (64 µm)2 with a PCE of 25.1%, a short-circuit current density (JSC) of 27.74 mA/cm2, and an open-circuit voltage (VOC) of 0.986 V.

Retraction Note to: Self-collimated beams in two-dimensional photonic crystals: properties and applications

Retraction Note to: Self-collimated beams in two-dimensional photonic crystals: properties and applications

Realization of an all-optical 2*4 decoder based on a two-dimensional photonic crystal

Realization of an all-optical 2*4 decoder based on a two-dimensional photonic crystal