Array Of Air Holes Research Articles

Low crosstalk 125 μm cladding heterogeneous six-core few-mode fiber with air-hole array and trench structure

In order to be compatible with the current optical fiber communication network, we propose a 125 μm diameter heterogeneous six-core two linear polarization modes fiber with air-hole array and trench (HAT) structure. The coupled power theory and finite element method (FEM) are used to investigate inter-core crosstalk (ICXT), bending loss, and other properties. The HAT structure can effectively suppress ICXT; and the maximum ICXT is less than −38 dB/100 km in C + L band. The effective refractive index difference (Δneff) between modes is greater than 3 × 10-3, inter-mode crosstalk (IMXT) can be ignored. The maximum intrinsic loss is 0.187 dB/km; relative core multiplicity factor reaches 32.21. The relative spatial efficiency is 18 times that of traditional single-mode fibers. This fiber can be produced by chemical vapor deposition and existing optical fiber manufacturing technology. The designed fiber can be directly connected to the communication network to reduce the cost of equipment renewal, and the communication capacity can be increased by 18 times.

Active control of mid-wavelength infrared non-linearity in silicon photonic crystal slab.

Natural materials' inherently weak nonlinear response demands the design of artificial substitutes to avoid optically large samples and complex phase-matching techniques. Silicon photonic crystals are promising artificial materials for this quest. Their nonlinear properties can be modulated optically, paving the way for applications ranging from ultrafast information processing to quantum technologies. A two-dimensional 15-μm-thick silicon photonic structure, comprising a hexagonal array of air holes traversing the slab's thickness, has been designed to support a guided resonance for the light with a wavelength of 4-μm. At the resonance conditions, a transverse mode of the light is strongly confined between the holes in the "veins" of the silicon component. Owing to the confinement, the structure exhibits a ratio of nonlinear to linear absorption coefficients threefold higher than the uniform silicon slab of the same thickness. A customised time-resolved Z-scan method with provisions to accommodate ultrafast pump-probe measurements was used to investigate and quantify the non-linear response. We show that optically pumping free charge carriers into the structure decouples the incoming light from the resonance and reduces the non-linear response. The time-resolved measurements suggest that the decoupling is a relatively long-lived effect on the scale comparable to the non-radiative recombination in the bulk material. Moreover, we demonstrate that the excited free carriers are not the source of the nonlinearity, as this property is determined by the structure design.

High-Q Quasi-Bound States in the Continuum in Terahertz All-Silicon Metasurfaces.

Bound states in the continuum (BIC)-based all-silicon metasurfaces have attracted widespread attention in recent years because of their high quality (Q) factors in terahertz (THz) frequencies. Here, we propose and experimentally demonstrate an all-silicon BIC metasurface consisting of an air-hole array on a Si substrate. BICs originated from low-order TE and TM guided mode resonances (GMRs) induced by (1,0) and (1,1) Rayleigh diffraction of metagratings, which were numerically investigated. The results indicate that the GMRs and their Q-factors are easily excited and manipulated by breaking the lattice symmetry through changes in the position or radius of the air-holes, while the resonance frequencies are less sensitive to these changes. The measured Q-factor of the GMRs is as high as 490. The high-Q metasurfaces have potential applications in THz modulators, biosensors, and other photonic devices.

High birefringence single-polarization composite structured anti-resonant fiber

We propose a highly birefringent, single-polarization composite structured anti-resonant fiber (CS-ARF). The proposed CS-ARF has an elliptical core, two symmetrically spaced arrays of elliptical air holes, and a six-tube anti-resonant structure. The birefringence and single-polarization characteristics of the proposed CS-ARF were analyzed in detail in the mid-infrared band using the finite element analysis method. The results show that the fiber can achieve birefringence up to the order of 10−2 and single-polarization transmission with a confinement loss (CL) below 10−5 dB/m in the mid-infrared band. When the refractive index of the elliptical core is set at na = 2.70, the designed CS-ARF maintains single polarization in the range of 2.5 μm to 3.197 μm with an extinction ratio of up to 1.08 × 107. In addition, we found that by setting the refractive index of the elliptical core, the CL in the y-polarization direction can be effectively adjusted.

Design and optimization of GI-PCF supporting the orbital angular momentum modes based on negative curvature structure.

Based on the negative curvature structure, we design a graded-index photonic crystal fiber (GI-PCF) supporting the orbital angular momentum (OAM) mode transmission and discuss its optimization strategy. The core of the designed GI-PCF is sandwiched by three-layer inner air-hole arrays with gradually decreasing air-hole radii and a single outer air-hole array, where the inner side of the annular core forms a graded refractive index distribution. All these structures are clad with negative-curvature tubes. By optimizing characteristic structural parameters, including the air-filling fraction of the outer array, the air-hole radii of the inner arrays, and the thickness of the tubes, the GI-PCF can support 42 OAM modes and most of them have a purity greater than 85%. Compared with conventional structures, the present design of GI-PCF has better properties on an overall level, which can stably transmit multiple OAM modes with high mode purity. These results inject new interest in the flexible design of PCF and have potential applications in various fields, including but not limited to the mode division multiplexing system and terabit data transmission.

High-Q resonances in terahertz all-silicon metasurface with imperforated air-hole array

High-Q resonances in terahertz all-silicon metasurface with imperforated air-hole array

An Asymptotic Energy Equation for Modelling Thermo Fluid Dynamics in the Optical Fibre Drawing Process

Microstructured optical fibres (MOFs) are fibres that contain an array of air holes that runs through the whole fibre length. The hole pattern of these fibres can be customized to manufacture optical devices for different applications ranging from high-power energy transmission equipment to telecommunications and optical sensors. During the drawing process, the size of the preform is greatly scaled down and the original hole pattern result might be modified, potentially leading to unwanted optical effects. Because only a few parameters can be controlled during the fabrication process, mathematical models that can accurately describe the fibre drawing process are highly desirable, being powerful predictive tools that are significantly cheaper than costly experiments. In this manuscript, we derive a new asymptotic energy equation for the drawing process of a single annular capillary and couple it with existing asymptotic mass, momentum, and evolution equations. The whole asymptotic model only exploits the small aspect ratio of a capillary and relies on neither a fitting procedure nor on any empirical adjustable parameters. The numerical results of the simplified model are in good accordance with experimental data available in the literature both without inner pressurization and when internal pressure is applied. Although valid only for annular capillaries, the present model can provide important insights towards understanding the MOF manufacturing process and improving less detailed approaches for more complicated geometries.

NONLINEAR CHARACTERISTICS OF SQUARE SOLID-CORE PHOTONIC CRYSTAL FIBERS WITH VARIOUS LATTICE PARAMETERS IN THE CLADDING

Nonlinear characteristics of fused silica, solid-core photonic crystal fibers (PCFs) with a square array of air holes are studied numerically. We present a novel design that emphasizes the difference in air hole diameters in the photonic cladding. These PCFs have the advantages of flat dispersion, high nonlinearity, and low attenuation. Based on simulation results, three optimal structures, denoted #F1, #F2, and #F3, having anomalous and all-normal dispersions in the near-infrared range are selected to investigate characteristic properties at the pump wavelength. Such PCFs open up many possibilities for nonlinear optical applications, especially supercontinuum generation.

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.

Photonic-crystals-based GAGG:Ce scintillator with high light output and fast decay time for soft X-ray detection

Gd2O2S:Tb (P43) powder was widely used in soft X-ray detection due to its high light yield. Compared with P43, GAGG:Ce scintillator has high light transmittance, fast decay time and strong radiation resistance. Photonic crystals (PhCs) can be used to enhance the light output of scintillator. In this paper, two-dimensional (2D) photonic crystals that consist of square arrays of air holes etched into TiO2 layer were fabricated on the exit surface of GAGG:Ce scintillator to enhance its light output. The luminescence spectra and the light output of GAGG:Ce scintillator with/without PhCs were measured at the BL08U1A beamline of Shanghai Synchrotron Radiation Facility. The results showed that the light output of GAGG:Ce scintillator with PhCs can be enhanced by a factor of 1.43 times compared with the reference GAGG:Ce scintillator, 2.35 times compared with YAG:Ce scintillator, 1.24 times compared with Gd2O2S:Tb scintillation ceramic and 0.76 times compared with P43 powder layer with the mass thickness of about 1.3mg/cm 2 with optical grease coupling. No significant change was observed in luminescence decay time between GAGG:Ce scintillator with and without PhCs. It makes GAGG:Ce scintillator with PhCs a promising material instead of P43 powder and YAG:Ce scintillator in soft X-ray detector.

Hybrid‐Piezoelectret Based Highly Efficient Ultrasonic Energy Harvester for Implantable Electronics

AbstractImplantable ultrasonic energy harvesters that scavenge wireless mechanic energy from ultrasound own remarkable potential in advanced medical protocols for neuroprosthetics, wireless power, biosensor, etc. The main challenge for this kind of device is to achieve high‐efficiency energy conversion in a weak ultrasonic pressure field. Here, a multilayered piezoelectret with strain enhanced piezoelectricity by introducing a parallel‐connected air hole array in an interdielectric layer sandwiched between a pair of electrets for an efficient ultrasonic energy harvester is presented. This device delivers a remarkable peak output power around 13.13 mW and short‐circuits current around 2.2 mA when implanted into tissues at 5~10 mm under an ultrasonic probe setup at 25 mW cm−2, which is higher than the required power threshold of bioelectronic devices and current threshold of nerve stimulation. Furthermore, the feasibility of supplying power to implantable bioelectronics and working as neuroproteins for peripheral nerve stimulation are both demonstrated. It is anticipated that this highly efficient, easily fabricated, and biocompatible device will potentially enable applications for multifunctional and advanced implantable bioelectronics in the next generation of diagnosis and therapy.

A porous core Zeonex THz fiber with low loss and small dispersion

A fabricated microstructured polymer optical fiber (MPOF), with porous core and porous cladding consisting of a hexagonal array of circular air-holes, is experimentally investigated via a terahertz (THz) time-domain spectroscopy (TDS) setup. The fiber features a low propagation loss ranged from 0.0180 to 0.0345 cm−1, in the frequency regime of 0.3–0.5 THz with diameter of 3 mm. Meanwhile, the dispersion and fabrication deformation are also discussed. Experimental results show there is a flat and near-zero dispersion band in the range of 0.39 to 0.45 THz with a value of −0.285 ± 0.02 ps/THz/cm The simulation and experimental results of transmission loss and dispersion are in good agreement within 0.3–0.5 THz. There are a few deviations regarding air porosity between theoretical and actual structure, and the absolute variation of air hole fraction in core and cladding is 0.485% and 1.657%, respectively. The proposed MPOF is potentially useful for efficient and convenient transmission of broadband THz radiation.

Design of pure silica-based photonic crystal fiber for supporting 114 OAM modes transmission

A novel photonic crystal fiber (PCF) based on pure silica is designed to transmit 114 orbital angular momentum (OAM) modes in the wavelength range of 1.2 μm–1.8 μm. The PCF composed of a central round air-hole, ring-shaped core, and air-hole array ensures effective refractive index differences of the constituent vector modes above 10−4 and stable transmission of the OAM modes. The finite element method is implemented to analyze the PCF. The confinement losses and nonlinear coefficients of all the eigenmodes at 1550 nm are less than 3.03 × 10−7 dB m−1 and 1.30 w−1 km−1, respectively. In addition, the PCF shows higher effective refractive index difference, lower confinement loss, and nonlinear coefficient thus holding large promise in high-performance fiber communication systems.

High Sensitivity Temperature Sensor Based on Two-Dimensional Photonic Crystal

In this work, a two-dimensional photonic crystal ring resonator based temperature sensor is investigated. The device consists of a hexagonal array of air holes surrounded by the base material of germanium (Ge). The sensing mechanism is based on the shifting of transmission peak with refractive index changes in Ge induced by variation of temperature. Simulation results are obtained using finite difference time domain method (FDTD). The photonic band gap is studied by plane wave expansion method (PWE). The sensor has high sensitivity of 270 pm/K and high quality factor of 2028.86 with` wide range of temperature detection between 300 K to 800 K. The size of the structure is 112.91 (µm)2 and appropriate for sensing applications in nanotechnology.

Phononic crystal locally-resonant cavity for detecting vinegar acidity

In this study, a highly sensitive and accurate phononic crystal-based sensing method was proposed. Our proposed idea has been studied numerically to identify the allowed and unallowable vinegar. The main difference between allowed and unallowable vinegar is the concentration of acetic acid dissolved in water. Therefore, the designed sensor must be able to accurately separate and sense the different percentages of water-soluble acetic acid. The proposed design consists of a periodic and regular array of air holes on the steel substrate, with the engineered defects idea for sound wave propagation and resonance to sense the different output waves in it. For different percentages of the acetic acid in the vinegar mixture, the resonance of propagating wave in the sensor part of the structure will cause a single frequency with a sharp peak corresponding to a certain amount of acetic acid concentration at the sensor output. Then, by changing even one percent concentration in the water-soluble acetic acid, the frequency peak will shift from the previous state. Finally, by studying the output frequency peaks, it is possible to determine the concentration of acetic acid in the vinegar. This method is very useful for detecting fraud in vinegar. The proposed design has the ability to separate 0% to 100% water-soluble acetic acid concentrations (vinegar mixture) in one percent steps with the high quality factor of 40000. Also, in this work, laboratory test challenges like fabrication tolerance and mixture losses effect are investigated which shows the high reliability.

Terahertz Hollow-Core Optical Fibers for Efficient Transmission of Orbital Angular Momentum Modes

Terahertz (THz) radiation has recently received a lot of interests in science and technology. The potential of orbital angular momentum (OAM) of light in the THz region is a novel idea for researchers with increasing applications in broadband communications. THz waveguides have rarely been reported to generate and guide OAM modes. In this paper, we propose for the first time hollow-core optical fibers consist of circular air-hole arrays for guiding THz OAM modes with the topological charge order up to l = 3. Using numerical simulations, two low-loss transmission windows over 0.47 - 0.65 THz (window1) and 0.95 - 1.20 THz (window2) are recognized to guide OAM modes. Results show that both windows of the THz fiber exhibit the flat near-zero dispersion as well as low confinement loss (~ 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> dB/cm) with simultaneously high purity of the OAM modes (higher than 90%). Finally, two designs of THz optical fibers consist of one and two rings of air-hole arrays in their cladding are examined and it is shown that difference of the confinement loss and the modal purity between two designs are negligible. This implies that hollow-core optical fibers consist of one ring of air-hole array in their cladding are very promising for efficient transmission of OAM modes in the THz region.

Wide-band self-collimation in a low-refractive-index hexagonal lattice.

Wide-angle, broadband self-collimation (SC) is demonstrated in a hexagonal photonic crystal (PhC) fabricated in a low-refractive-index photopolymer by multiphoton lithography. The PhC can be described as a hexagonal array of cylindrical air holes in a block of dielectric material having a low-refractive index. Optical characterization shows that the device strongly self-collimates light at near-infrared wavelengths that span 1360 to 1610 nm. SC forces light to flow along the extrusion direction of the lattice without diffractive spreading, even when light couples into the device at high oblique angles. Numerical simulations corroborate the experimental findings.

Low loss flat dispersive hexagonal porous core THz fiber

A low loss porous core hexagonal lattice photonic crystal fiber (PCF) is proposed. Design procedure and properties are investigated in terahertz (THz) band. We explore different important properties of the PCF to evaluate the merit of proposed design. Circular air hole at the center surrounded by rectangular air hole array in the fiber core is designed in such a way that maximizes the core porosity of the fiber. The structure of cladding, on the other hand, is designed with a large hexagonal air hole array with tiny isolation width, resulting in a minimum total loss. The bulk material loss is diminished by 85.8% using core porosity of 80%. Numerical result shows relatively low confinement loss at 1 THz with flattened dispersion. Withal, single-mode propagation is exhibited in the proposed PCF design. The novel approach of this proposed PCF is unique to ensure good confinement in the core with a reasonable amount of power fraction.

2D-Photonic crystal heterostructures for the realization of compact photonic devices

Herein, we presented a novel design of polarization beam splitter (PBS) based on the integration of heterostructure 2D- Photonic crystals (PhCs). Two PhC structures, namely PhC-type 1 and PhC-type 2, with different transmission characteristics are proposed. The first type of PhC is composed of a 2D-periodic array of circular air holes embedded in silicon substrate which facilitates the propagation of self-collimated TE and TM-polarized light. The second type of PhC consists of a 2D-periodic array of square-shaped air holes embedded in silicon substrate which carry a photonic bandgap (PBG) for TE-polarized light whereas TM-polarized light propagates unaffected by diffraction. When PhC-type 2 structure is arranged at 45° on both sides of the PhC-type 1 structure, this combination leads to the formation of PBS with a polarization extinction ratio (PER) as high as 30.7 dB. Furthermore, the same structure can be used to steer the TE-polarized light at 180° in a small footprint. Additionally, the heterostructure PhC can be used for TM-polarization maintain devices.

High symmetry nano-photonic quasi-crystals providing novel light management in silicon solar cells

Reduction of surface reflection loss is crucial for high efficiency next generation Si solar cells. Surface texturing provides a viable method to reduce loss over the full solar bandwidth. Previous studies have concentrated on simple moth-eye silicon pillar arrays protruding from the surface. Using FDTD simulation methods, we undertake a systematic investigation into performance benefits provided by complex semi-random photonic quasi-crystal surface patterning methodologies whereby arrays of air holes are etched deep into the solar cell surface. In contrast to other studies we carefully investigate the effect of lattice symmetry, systematically comparing performance of simple 6-fold symmetric triangular photonic crystal patterning to 12 fold symmetry photonic quasicrystal patterning and infinitely symmetric 2D Fibonacci patterning. We optimize key geometric parameters such as lattice pitch, hole size and etch depth to maximize optical performance for each lattice type. 12 fold photonic quasi crystal lattice is found to provide best overall anti-reflectance performance providing a solar-corrected average reflectance of 8.3% for a hole depth of 1.5 µm and 300 nm diameter, in comparison to 36.4% for a bare silicon solar cell surface. Practical feasibility of the optimal designs is demonstrated by fabrication of physical prototypes consisting of arrays of nm scale air-holes etched into the surface of a silicon slab fabricated Using e-beam lithography and ICP/RIE etching. FDTD Simulation methodology is validated by convergence studies as well as comparison to optical measurements on these fabricated devices. Furthermore, in contrast to previous studies we provide an in depth analysis of the physical mechanisms responsible for reduction in surface reflection, determining the parameter space where conventional Gaussian optical processes such as effective refractive index, refraction and Fresnel reflection dominate, vs parameter space where sub wavelength photonic crystal scattering effects play the main role. We finish up with an analysis of electrical performance for the optimal designs to further validate real world performance. Taking electrical performance into account we determine that infinite-symmetry 2D Fibonacci patterning far outperforms lower symmetry 12 fold and triangular arrangement. We believe that this is the first in depth investigation into 2D Fibonacci patterning in silicon solar cells.