Triangular Lattice Photonic Crystal Research Articles

A Terahertz Circulator Based on Magneto Photonic Crystal Slab

In this paper, a terahertz circulator based on a magneto photonic crystal slab is envisaged. The triangular lattice photonic crystals with a line defect waveguide were constructed on an Al2O3 ceramic slab. Two cylindrical ferrites and two copper-clad plates in the junction of the Y-shaped wave-guide worked as a magneto-optical cavity resonator to approve the nonreciprocal function. In the working frequency range, 0.212–0.238 THz, the isolation of the circulator was better than 20 dB, and the insertion loss was better than 1 dB. The designed circulator based on the magneto photonic crystal slab experienced low loss and a wide bandwidth that satisfied its use in the THz application.

Ray tracing and wave optics behavior of the Eaton lens and invisible sphere triangular lattice photonic crystal

The Eaton lens and invisible sphere are known as devices that create fixed deflection angles in the ray trajectories striking them. The wave optics behavior of these tools, however, can be different. Two triangular lattice photonic crystals (TLPCs) composed of the Eaton lens and invisible sphere are studied in this paper. The differences between ray and wave optics behaviors in the TLPCs are explained. We investigate the ray trajectories in the two TLPCs, separately. Then, for studying wave behavior in TLPCs, the band structures of the two photonic crystals are extracted numerically. Transmission diagrams for six-layer TLPCs are also plotted to approve the band calculations. It is observed that, in some particular frequency ranges, the wave behavior in the TLPCs composed of the Eaton lens and invisible sphere can be quite opposite to the expected behavior of the rays.

Dual-polarization two-dimensional valley photonic crystals

<p indent="0mm">The introduction of topology in photonic systems has attracted considerable attention not only for the elaborate molding of light but also for its practical applications in novel photonic devices. Recently, Xiao-Dong Chen, Jian-Wen Dong, et al. from Sun Yat-sen University proposed the polarization-valley Hall effect of light in a 2D triangular-lattice photonic crystal (PC). This work proposed an approach to apply the polarization degree of freedom (DoF) in 2D valley Hall PCs.

A Millimeter-Wave Y-Shaped Circulator Based on Magneto Photonic Crystals

In this paper, a millimeter-wave Y-shaped circulator based on magneto photonic crystals is demonstrated. The triangular lattice photonic crystal with Y-shaped line defect waveguide is constructed by Al2O3 ceramic posts. The magneto-optical cavity resonator in the junction of Y-shaped waveguide consists of two cylindrical ferrites and two triangular metal pedestals. The transmission characteristics of the circulator experimented under the external magnetic bias H0 = 300 Gs. In working frequency range 24∼28 GHz the isolation of circulator is better than 20 dB, and the best insertion loss is as low as 0.2 dB. The experimented results are well agreed with the simulation results.

Band gap properties and self-collimation in a tenfold quasicrystal structure photonic crystals applying multicircular ring scatterers

In this paper, a kind of tenfold photonic quasicrystals based on the Penrose puzzle theory with the application of multicircular ring scatterers (MCRSs) is presented. It is divided into four kinds of square supercells and employed in a square lattice to constitute the first-order (1st), second-order (2nd), third-order (3rd), and fourth-order (4th) tenfold quasicrystal structure photonic crystals (TFQCSPCs) accordingly. In an attempt to evaluate the dispersion maps and equifrequency contour (EFC) profiles of such long-range ordered but not really periodic TFQCSPCs, an enhanced plane wave expansion (PWE) method is adopted. The photonic crystals (PCs) discussed in this paper are first classified into two major categories, air hole and dielectric column types which will be referred to as type 1, type 2 respectively in the following. The varying features of photonic band gaps (PBGs) of TFQCSPCs are inquired about by changing the refractive index (n) of the relevant medium and the number of rings (H) of MCRSs under two broad prerequisites of type 1 and type 2 PCs. The results are also compared with the associated properties of PBGs of traditional square lattice PCs (TSLPCs) and traditional triangular lattice PCs (TTLPCs) which employ MCRSs. Then, the 1st and 2nd TFQCSPCs and TSLPCs are fabricated in the form of hollow air holes dug in the silicon plate, and the transformation of their PBGs and EFCs is researched when the width (W) and H of the ring are adjusted. The possibility of implementing the phenomenon of polarization-insensitive self-collimation (PISC) in TFQCSPCs and TSLPCs is explored by examining the smoothest EFCs in EFC mappings. Eventually, our work actualizes the PISC phenomenon at seven normalized frequency (NF) values of 0.074, 0.168, 0.170, 0.172, 0.265, 0.270, and 0.297, which fills the gap of the PISC phenomenon in the low-frequency domain.

Multiport Routing of Topologically Optical Transport Based on Merging of Valley-Dependent Edge States and Second-Order Corner States

Topological photonics provide a novel platform to robustly manipulate the flow of light and design high-performance nanophotonic devices. To do this, a fundamental mechanism is the flexible control of optical transport based on topological boundary states on edges or corners. In this work, we design a multiport device to route the topologically optical transport by using both valley-dependent edge states (VDESs) and second-order corner states (SOCSs). The VDESs are derived from sublattice symmetry breaking in a honeycomb lattice, while SOCSs are induced by the lattice deformation of Kagome lattice. In terms of unit cell, we find that both configurations can be reconsidered as the same triangular-lattice photonic crystal, which consists of a hexagon-profile air hole array in silicon background. Therefore, a four-port device is designed based on the two configurations. In simulation, we observe the frequency-dependent routing effect of the topologically optical transport by merging of VDESs and SOCSs. This work not only shows a novel platform to explore various topological phases in the photonic system but also provides guidance in the development of topological photonic integrated circuits with mode division multiplexing.

All-optical half adder based on triangular lattice photonic crystals with uniform structural parameters

All-optical half adder based on triangular lattice photonic crystals with uniform structural parameters

Evolution of topological edge modes from honeycomb photonic crystals to triangular-lattice photonic crystals

The authors demonstrate that edge modes can exist at triangular photonic crystal slabs where Berry curvature vanishes, and they experience no reflection at 120 degrees bending as in quantum valley Hall photonic crystals.

Design of compact polarization-insensitive multimode interference triplexer

A compact polarization-insensitive multimode interference (MMI) triplexer is proposed. The triplexer can process signals among three wavelengths of 1310, 1490 and 1550 nm in the fibre-to-the-home (FTTH) systems. The polarization insensitivity is obtained by adjusting the refractive index of SiN x in the Si/SiN x /Si sandwiched structure. A triangular lattice array air-hole photonic crystal embedded in the MMI waveguide can transmit and reflect downstream and upstream signals, respectively. Furthermore, a cascaded MMI structure is used to separate two downstream signals. The performance parameters of the triplexer are analysed by three-dimensional finite-difference time-domain method. The results show that the size of the triplexer is only 5.5 × 234.5 µm2, the insertion loss and crosstalk are as low as 0.45 dB and −27.2 dB respectively. Besides, the triplexer has a large 3 dB bandwidth up to 105 nm, and it has potential application value in the FTTH systems.

All‐optical half adder based on non‐linear triangular lattice photonic crystals with improved contrast ratio

All‐optical half adder based on non‐linear triangular lattice photonic crystals with improved contrast ratio

Efficient absorption enhancement approaches for AlInAsSb avalanche photodiodes for 2-μm applications.

Recently, advances in imaging and LIDAR applications have stimulated the development of high-sensitivity receivers that operate at wavelengths of ≥ 2 µm, which has driven research on avalanche photodiodes (APDs) that operate in that spectral region. High quantum efficiency is a key performance parameter for these photodetectors. Increasing the thickness of the absorption region is a straightforward approach to increase the quantum efficiency. However, the primary source of dark current is the narrow-bandgap material used for 2-µm detection. Increasing its thickness results in higher noise. In this paper, we describe two approaches to enhance the quantum efficiency, both of which are superior to a conventional anti-reflection (AR) coating. For normal incidence at 2 µm, finite-difference time-domain (FDTD) simulations show the absorption can be enhanced by more than 100% with a triangular-lattice photonic crystal, and nearly 400% by applying a metal grating. This is achieved by coupling normal incidence light into the laterally propagating modes in the device. Moreover, the significantly higher absorption of the metal grating compared to the photonic crystal is due to the high coupling efficiency provided by the metal grating. This work provides promising methods and physical understanding for enhancing the quantum efficiency for 2-µm detection without increasing absorber thickness, which also enables low dark current and high bandwidth.

Dual Ring Resonator Based 3D-Photonic Crystal For Add Drop Filter Using FDTD-Least Square Technique

The structure of an optical add-drop filter (ADF) which depends on a very-compact ring resonator made from a photonic crystal has been presented in the paper. An adequate structure of a three channel wavelength de-multiplexer along with a finite difference time domain is demonstrated in the visibility area. A 3D triangular lattice photonic crystal with 1.735 nm air pores in a silicon nitride planar waveguide provides a constraint for the light which can be detected. The double resonator has been simulated on a three-dimension photonic crystal and for the simulation of results, MATLAB has been used. The resultant structure consisting of three drops wavelengths at λ1 = 1555 nm, λ2 = 1579 nm, and λ3 = 1595 nm approximately. The average spacing between the adjacent channels is around 20 nm and the FSR obtained from numerical simulation is about 179 GHz. The output wavelength carries normalized transmissions of 0.97 having an inner rod radius for inner core 800. In addition to this, the Alternating Least Square—Add-Drop Filter (ADF)—Finite Difference Time Domain method has been used to achieve three various outputs such as transmitted intensity, reflectivity fineness, and constant factor. In future aspects, the simulation results can be further used in the fields of networks to design more accurate and efficient photonic crystals based on de-multiplexing devices.

A high-performance refractive index sensor based on a triangular-lattice photonic crystal with defect and surface modes

The refractive index sensing capabilities of a 2D triangular-lattice photonic crystal (PhC) with defective and surface modes are studied. These are composed of silicon columns arranged in a liquid environment. Through changing the rods’ shape on the PhC’s surface from a circle to an ellipse and optimizing the sizes of two adjacent ellipses, the surface localized mode can be generated. Combining the central defective mode with surface modes, an ultra-small three-working-wavelength PhC refractive index sensor is proposed. The shift of the resonant wavelengths influenced by the slight alteration of the protein’s thickness attached by the special rods is studied, and it is found that a minimum alteration of the protein’s thickness of about 4 nm can be distinguished, and a maximum refractive index sensitivity of 0.516 is obtained. Three kinds of analytes can be detected in real-time and at the same time, which are bounded around the input/output surfaces and the central rods through biological specific binding.

Numerical optimization design for waveguide bends with low-loss and wide-bandwidth in two-dimensional photonic crystal slabs

In this paper, we demonstrate some optimization designs for waveguide bends in two-dimensional photonic crystal slabs based on the effective index approximation. Four different types of waveguide bends with low-loss and wide-bandwidth are designed, which involve 60°, Z-shaped, Y-shaped and 120° waveguide bends in the two-dimensional triangular lattice photonic crystals. In all numerical experiments, the electromagnetic fields in the photonic crystal slab waveguides are solved by the finite element method in COMSOL software. Several strategies are applied to design slab waveguide bends with low-loss and wide-bandwidth, for example, adding some elliptical air-holes near the corner or adjusting the radii of some air-holes. For four optimized structures, the transmission efficiencies at 1550 nm are all more than 92%. As we show, this is achieved over a −0.915 dB bandwidth of more than 65 nm in all waveguide bends. The numerical results indicate that the design scheme we applied to optimize waveguide bends in photonic crystal slabs is simple and efficient, which can provide some useful guidance for further three-dimensional design.

Magnetic photonic crystal circulator based on gradient changing width waveguide

In this paper, a novel Y-shaped photonic crystal circulator based on a photonic crystal gradient changing width waveguide is proposed. The gradient changing width waveguide is constructed by triangular lattice photonic crystals with dielectric cylindrical posts. Simulation results show that the waveguide has well transmission characteristics with low ripple and high efficiency. The Y-shaped photonic crystal circulator is envisaged based on the waveguide with three ferrite posts in waveguide junction. Insertion loss and isolation of the circulator are 0.0028 dB and 53.36 dB respectively, which were theoretically analyzed through FEM method.

Polarization-independent and super broadband flat lens composed of graded index annular photonic crystals

Abstract In this paper, we propose two types of all-dielectric polarization-independent graded index annular flat lens with a wide operating frequency range. The lenses are composed of two-dimensional triangular and square lattice photonic crystals with circular silica ( S i O 2 ) rods in the air. We assume in both square and triangular structures, the lenses are obtained by making air holes within each dielectric rod and we consider that the outer radius of the created annular rods is maintained constant while the size of the inner air holes varies along the transverse direction whose the air holes variation follow two types of linear and parabolic function. The graded structures are made in such a way that the modulus of the refractive index is biggest at the centre and decreases towards the edges. The optical properties and the physical background of the polarization-independent focusing mechanism are studied in frequency and spatial domains, using plane wave expansion and finite-difference time-domain methods. Our numerical results show that, through an appropriate set of design, the designed lenses are able to focus the light regardless of polarization for a wide frequency range into approximately same focal length in which difference between the focal distance of TE and TM polarization modes stays below λ 4 . Compared to previously polarization-independent designed photonic crystal based lenses, our proposed structures work under much wider frequency range. Also, in contrast with most of the graded structures, our graded lens are made without altering the lattice constant along the optical axis or transverse to the optical axis. Moreover, the design approach is restricted to the use of silica and non-use of more complicate materials such as liquid crystals, plasma, and the like. Thus, the designed systems can be constructed easier relative to the previously designed lenses.

Integrated Single Frequency, High Power Laser Sources Based on Monolithic and Hybrid Coherent Beam Combining

Monolithic and hybrid integration platforms are both important for photonic integrated circuits. It is desirable for the laser sources integrated in both platforms to provide high power and single frequency operation for many emerging applications. However, it is difficult to realize simultaneous high power and single frequency operation by using conventional semiconductor distributed feedback lasers. Integrated coherent beam combining (CBC) is a promising solution to overcome this challenge. In this paper, coherently combined, integrated diode laser systems are experimentally demonstrated through both monolithic and hybrid CBC. For monolithic CBC of broad-area lasers in the InP platform, two single triangular-lattice photonic crystal (PC) Bragg lasers are combined. The measurement results show that the output power of the combined PC Bragg lasers is increased and the single frequency operation is maintained. As for the hybrid CBC, a chipscale coherently combined laser system is experimentally demonstrated in the InP-Si3 N4 platform through the manipulation of optical feedback at different output ports of the coupled laser cavities. Coherent combining of two InP-based reflective semiconductor amplifiers are obtained by use of the cross-coupling provided by an adiabatic 3-dB coupler in silicon nitride, with a combining efficiency of ∼92%.

Slow Light Propagation in Photonic Crystal-Based Meandering Delay Lines Using the PTS Material

In this paper, rectangular and triangular photonic crystal (PC) delay lines are designed using PTS (p-toluene sulfonate) at 1550 nm. PTS possesses a high nonlinear refractive index; consequently, when it interacts with an incident light, it provides slow light propagation in a PTS-based device due to the Kerr effect. First, a PC waveguide (PCW) is designed by introducing a line defect made of PTS bars. Such a defect, by using PTS, provides two significant advantages; these include slow group velocity and extremely high optical confinement for a propagating wave through the PCW. Then, two similar PCWs are placed next to each other to investigate the crosstalk phenomenon between them. By choosing an appropriate distance between them, the rectangular and triangular PC reflective meandering delay lines are realized. The rectangular lattice PC reflective meandering delay line exhibits lower propagation losses because this lattice shows a higher transmission coefficient at the corners in comparison with the triangular one. On the other hand, the triangular lattice PC reflective meandering delay line provides very low group velocity for a propagating light wave at the wavelength of 1550 nm; as a consequence, a higher slowing factor is achieved for the triangular lattice PC reflective meandering delay line due to the stronger light–PTS interactions. Simulations are performed using LUMERICAL FDTD SOLUTION v8.15.

Numerical analysis of light extraction enhancement of GaN-based thin-film flip-chip light-emitting diodes with high-refractive-index buckling nanostructures

Abstract In this work, the light extraction efficiency enhancement of GaN-based thin-film flip-chip (TFFC) light-emitting diodes (LEDs) with high-refractive-index (TiO2) buckling nanostructures was studied using the three-dimensional finite difference time domain method. Compared with 2-D photonic crystals, the buckling structures have the advantages of a random directionality and a broad distribution in periodicity, which can effectively extract the guided light propagating in all azimuthal directions over a wide spectrum. Numerical studies revealed that the light extraction efficiency of buckling-structured LEDs reaches 1.1 times that of triangular lattice photonic crystals. The effects of the buckling structure feature sizes and the thickness of the N-GaN layer on the light extraction efficiency for TFFC LEDs were also investigated systematically. With optimized structural parameters, a significant light extraction enhancement of about 2.6 times was achieved for TiO2 buckling-structured TFFC LEDs compared with planar LEDs.

Anomalous transparency in photonic crystals and its application to point-by-point grating inscription in photonic crystal fibers

It is common belief that photonic crystals behave similarly to isotropic and transparent media only when their feature sizes are much smaller than the wavelength of light. Here, we counter that belief and we report on photonic crystals that are transparent for anomalously high normalized frequencies up to 0.9, where the crystal’s feature sizes are comparable with the free space wavelength. Using traditional photonic band theory, we demonstrate that the isofrequency curves can be circular in the region above the first stop band for triangular lattice photonic crystals. In addition, by simulating how efficiently a tightly focused Gaussian beam propagates through the photonic crystal slab, we judge on the photonic crystal’s transparency rather than on isotropy only. Using this approach, we identified a wide range of photonic crystal parameters that provide anomalous transparency. Our findings indicate the possibility to scale up the features of photonic crystals and to extend their operational wavelength range for applications including optical cloaking and graded index guiding. We applied our result in the domain of femtosecond laser micromachining, by demonstrating what we believe to be the first point-by-point grating inscribed in a multi-ring photonic crystal fiber.