Radius Of Air Holes Research Articles

Optomechanical crystal nanobeam cavity with high optomechanical coupling rate

An optomechanical crystal nanobeam cavity, only by increasing the radius of air holes in the defect region, is proposed and optimized for a high optomechanical coupling rate. In our proposed cavity, the photonic and phononic defect modes are simultaneously confined by each corresponding bandgap, and the overlap of the optical and mechanical modes can be improved simply by adjusting the radius of the air holes. Accordingly, an optomechanical coupling rate (g) as high as 1.16 MHz is obtained, which is the highest coupling rate among the reported optomechanical crystal cavities. What’s more, the proposed cavity also exhibits a high mechanical frequency of 4.01 GHz and a small effective mass of 85 fg for the fundamental mechanical mode.

The micro-cavity of the two dimensional plasmonic photonic crystal

In this manuscript, we proposed a novel and effective two dimensional hybrid plasmonic photonic crystal micro-cavity structure to confine the surface plasmon to a sub-wavelength scale mode volume and obtain a relatively high quality factor. By introducing a single-cell defect at the two dimensional triangular lattice photonic crystal layer, the defect cavity has been established to provide sub-wavelength scale plasmonic mode localization within the hybrid plasmonic photonic crystal structure TM band gap. Comprehensive analysis methods of three-dimensional finite difference time domain method (3D-FDTD) have been used to analyze the characteristics of the micro-cavity of this hybrid structure, including the effects of the radius of the nearest neighbor air holes around the defect, the cavity length of the defect and the thickness of the gain medium on the features of the micro-cavity. By using a quantum dots (QDs)-polymer as a gain medium for the low index thin layer, a gain threshold as low as g t h = 534 cm −1 can be achieved with such structures, and deep sub-wavelength mode volume of 0.00201 (λ/ n ) 3 is also obtained.

Optimization of Microstructure Optical Fiber using PWE Method for Investigation of Glucose in Intralipid

Investigation of glucose in intralipid using microstructure optical fiber is reported in this paper. The optical fiber is realized by 5 × 5 air holes on square lattice silicon substrate. The principle of measurement of glucose in intralipid is based on the variation of electric field with respect to percentage of glucose. The simulation for electric field distribution is done using plane wave expansion method, where optimization is realized by varying radius of air holes and lattice spacing of crystal structure. With varying both radius and lattice spacing and employing PWE method, simulation result revealed that both peak electric field and output power emerging from microstructure fiber increases with the increase of glucose concentration for certain radii and lattice spacing. Aside this present result divulged that microstructure fiber with lattice spacing of 1 μm and radius of air holes of 300 nm is suitable to investigate glucose in an intralipid. Finally an experimental setup is proposed to measure the glucose concentration.

High extraction efficiency inGaN-based light-emitting diodes with air-hole photonic crystal slab

In this paper, extraction efficiency in simplified and layered light-emitting diodes (LEDs) of GaN photonic crystal with periodic air holes is studied by three-dimensional finite-difference time-domain method. Photonic band structures of the photonic crystal are obtained by plane-wave expansion method. The results about simplified GaN -LED show that extraction efficiency is very sensitive to the structure parameters tuning, and increases considerably inside the transverse-electric-like gap region. A maximum extraction efficiency above 90% can be achieved. The effects of the PC thickness and air-hole radius on relative extraction efficiency of layered GaN -LED are analyzed. They show optimal values to obtain high relative extraction efficiency.

Near-infrared gallium nitride two-dimensional photonic crystal platform on silicon

We demonstrate a two-dimensional free-standing gallium nitride photonic crystal platform operating around 1550 nm and fabricated on a silicon substrate. Width-modulated waveguide cavities are integrated and exhibit loaded quality factors up to 34 000 at 1575 nm. We show the resonance tunability by varying the ratio of air hole radius to periodicity, and cavity hole displacement. We deduce a ∼7.9 dB/cm linear absorption loss for the suspended nitride structure from the power dependence of the cavity in-plane transmission.

New Design of Integrated 2D Photonic Crystal Narrow Band Filters Using the FDTD-2D Method

AbstractIn this paper, integrated 2D photonic crystal narrow band filter design is achieved based on transmission spectra shift. The presented effective technique for the design of narrow band resonant filters obtained by one-missing-row and by choosing proper radii of air holes of the waveguide is proposed. The 2D photonic crystals are designed by utilizing cascaded waveguides with different radii of air holes. The results are presented for normal incident wave with TE polarizations with a narrow spectral bandwidth centered at λ = 1.55 μm. We also discuss the filtering process and its necessary modifications to achieve efficient filtering. A final synthesized filter topology is presented and a band from 1.53 μm to 1.57 μm around 1.55 μm is transmitted with a maximum transmission of about 77% with better performances is achieved.

Design of Photonic Crystals Waveguide Using Microfluidic Infiltration

The use of photonic crystals (PCS) in biosensor applications has lead to the development of highly sensitive and selective microfluidic sensor elements. Two main advantages of these devices for sensing applications are their high sensitivity and their reduced size, which makes it possible, in one hand, to detect very small analytes without the need of markers (label-free detection), and to integrate many of these devices on a single chip to perform a multi-parameter detection on the other hand. In the present paper, we analyze the design of a highly sensitive microfluidic sensors based on 2D photonic crystal slab waveguide formed by increasing the radii of air holes localized at each side of the line defect and filling with homogenous de-ionized water (nc =1.33). The transmission spectrum of the sensor has been obtained with the use of Finite Difference Time Domain (FDTD) method and it has been observed that a 306 nm wavelength position of the lower band edge shift was observed corresponding to a sensitivity of more than 927 nm per refractive index unit (RIU). Development of microfluidic sensor designs that enhance sensitivity is especially important because it allows detection of lower concentrations of analytes.

3~5μm宽带超低色散平坦硫系光子晶体光纤

Using the dispersion controlled feature of chalcogenide photonic crystal fiber,the broadband ultralow dispersion-flattened chalcogenide photonic crystal fibers was designed,and the multipole method was used to research the effects of the hole pitch and the aperture ratio on the dispersion curves.By optimizing the diameter of the air holes of different layers in cladding,the structure with 0.7μm air hole radius of inside two layers,0.8μm air hole radius of outer two layers and 5μm hole pitch were obtained.The simulation results show that this structure is broadband flattened dispersion in 3~5μm,and the absolute value of dispersion is less than 3.8ps·nm-1·km-1.

Photonic Bandgap Tuning of Photonic Crystals by Air Filling Fraction

In this paper, the type of photonic crystals (PCs) which consists of air holes surrounded by silica as a background with square lattice arrangement in two dimension (2D) has been assumed. A plane wave expansion method (PWEM) is implemented to calculate the photonic band structure of this kind of PC, then the effect of changing air filling fraction is studied on the photonic band structure diagram, by changing the air hole radius and lattice constant (a). As a result, a tuning and shifting of the photonic bandgaps (PBGs) has been obtained.

Single Mode Operation of Substrate Integrated Non-Radiative Dielectric Waveguide and an Excitation Scheme of ${\rm LSE}_{11}$ Mode

It is shown that a substrate integrated non-radiative dielectric (SINRD) waveguide supports only the fundamental longitudinal-section-electric mode (LSE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> ) over a frequency band determined by the radius of air holes. The single mode operation eliminates the need of a mode suppressor which is a potential advantage of using LSE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> mode compared to the use of the other fundamental mode, namely the longitudinal-section-magnetic mode (LSM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> ). The conditions for obtaining the maximum single mode operation bandwidth are investigated. An excitation scheme of the LSE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> mode using a rectangular waveguide is presented and the measurement results of a fabricated back-to-back transition at 94 GHz are provided.

Integration of bandpass guided-mode resonance filters with mid-wavelength infrared photodetectors

Guided-mode resonances have been exploited to filter the normal-incidence transmission of mid-infrared wavelengths through a photonic crystal slab. A two-dimensionally periodic structure has been integrated with a quantum dot infrared photodetector to narrow its mid-wavelength infrared photoresponse spectrum. Finite-difference time-domain simulations were employed to extract the filter transmittance, which is dominated by a peak near 6 µm. The simulated resonance is linearly tunable with the air-hole radius but it is insensitive to small changes in the incidence angle. To realize this filter, a patterned Ge slab was fabricated on a CaF2 cladding layer, on the InGaAs/GaAs photodetector. Filters fabricated on a plain GaAs substrate were also characterized by Fourier-transform infrared spectroscopy. This transmittance was consistent with the corresponding simulation, however the resonance peak was degraded in comparison to the filtered photodetector and its associated simulations.

Modeling and experimental investigations of Fano resonances in free-standing LiNbO_3 photonic crystal slabs

In this paper the Fano resonance in a free-standing LiNbO(3) photonic crystal slab is demonstrated. We present a numerical analysis and experimental measurements with free space illumination where the dependence of slab thickness, radius of air holes and lattice types are investigated. The unique property of polarization dependence for LiNbO(3) photonic crystal slabs is also analyzed, and we show that the transmission spectra exhibit significant sensitivity (~25nm) to polarization. A monolithic free-standing LiNbO(3) photonic crystal slab was fabricated using ion beam enhanced etching (IBEE) technology. Measurement results of the reflection spectra agree with the numerical analysis.

Design and Analysis of Taper Structure for Light Coupling into Photonic Crystal Waveguides Fabricated by Si-Ion Implantation

In this paper, we designed and analyzed an efficient taper structure to couple light into and out of photonic crystal waveguides (PhCWs) fabricated by Si-ion implantation and electron beam lithography. The coupling structure employs the gentle refractive-index distribution produced in the SiO2layer by Si-ion implantation. A taper structure is designed for effective coupling of transverse electric (TE) polarized light (λ = 1.55 μm) into a submicron size PhCW consisting of triangular lattice of air holes (lattice constant,a= 0.666 μm, radius of air holes,r= 0.232 μm, waveguide width, W1 ~ 0.7 μm). The influence of the taper length on the transmission characteristics is investigated. Efficiency in excess of 95% is demonstrated using the finite-difference time-domain and beam propagation methods. This is important for their practical applications in photonic integrated circuits.

Improvement of light extraction efficiency of GaN-based blue light-emitting diode by disorder photonic crystal

Sub-wavelength photonic crystal can effectively improve the light extraction efficiency (LEE) of the light emitting diode (LED). However, it is inevitable to have defects, (namely disorder structures) during its fabrication. In this study, the LED model with ideal quadrate photonic crystal is optimized by using the finite-different time domain method. Three different LED structures with various disordered photonic crystals are further simulated. We investigate the influences of several stochastic variables (including position, radius, and depth of an air hole) of the photonic crystal on the LEE of GaN based blue LEDs. It can be found that regarding photonic crystal LED whose air hole radius is optimized to 80 nm, the stochastic variables of the position and radius will reduce its LEE. However, an opposite trend is found when this radius is replaced by 60 nm, which is not optimized. Furhermore, the LEE fluctuates inside to an extent of 53.8% as two stochastic variables (including the randomized position and the randomized radius) change from 0 nm to ±20 nm. The influence of the stochastic variables of the depth of air hole can be neglected since this variation is very small. The results in this paper have an important reference value for designing and fabricating high-performance blue light photonic crystal LED.

Air-Holes Radius Change Effects and Structure Transitions in the Linear Photonic Crystal Nanocavities

The strong localization of electromagnetic modes in high-Q/Vm (quality factor/modal volume) photonic crystal (PhC) nanocavities (NCs) makes them strong candidates for enhanced optical nonlinear effects, such as cavity quantum electrodynamics (QED) phenomena. These applications require precise control of cavity resonances mode. The cavity resonance is strongly depending on the lattice constant, a, and the air-hole radius, r, of photonic crystals. Slight modifications in the geometries of the photonic crystals will result in large differences in the dispersion characteristics. In this paper, by using BandSOLVE and FullWAVE software of RSoft Photonics CAD package, at first L1, L3 and L5 NCs in a semiconductor slab have been simulated in a hexagonal lattice of air-holes (radius r) with lattice constant a=270 nm and constant fill factor (r/a=0.29). Then, with radius reduction of the two ends air-holes (TEA-H), different confinement characteristics of photonic modes such as: numbers of confined modes, wavelengths, quality factors and two dimensional field profiles have been investigated. Calculations have shown that when radius of (TEA-H) in the linear NCs with n missing air-holes in a line, Ln, reaches to nearly zero value, transition in the structure to the L(n+2) NCs, with roughly different qualities has been observed. Also, improvement in the quality factors of higher-order modes will be achieved. Understanding of the higher-order modes and two dimensional field profiles of the confined photonic modes are useful for the design of more efficient nano-lasers and observation of the cavity QED effects.

高品质因子和高传输效率的二维光子晶体耦合腔波导研究

We present a design of 2D photonic crystal coupled-cavity waveguide with a high transmission efficiency and a quality factor simultaneously.By optimizing the structural parameters such as amount and radius of air holes between microcavities and waveguide,a 90% transmission efficiency is obtained with a Q factor of 8.20×104.In order to increase Q factor without sacrificing too much efficiency,a new kind of coupled-cavity waveguide is formed by introducing microcavity chains.Photons hop in adjacent microcavies.For this new kind of waveguide,Q factor is improved one order higher and transmission efficiency only decrease by 40%.The result has a practical gui-ding significance for application of photonic crystal in various different fields such as slow light,light trap,optical transmission.

The Heterostructure Photonic Crystal Waveguide Splitter

We propose a two-dimensional heterostructure photonic crystal (PhC) waveguide splitter composed of different air-hole radii in the core and claddings. Two PhCs in the core and claddings are treated as two effective homogeneous media in the first photonic band. By using a triangular coupler in the input port, light can be efficiently coupled from the conventional waveguide into the PhC waveguide splitter. Total internal reflections take place at outer interfaces and confine light in the PhC waveguide very well. Finally, incident light is divided into three parts, and each of them couples to output waveguides with total transmission more than 90%.

Geometrical study of a hexagonal lattice photonic crystal fiber for efficient femtosecond laser grating inscription

We have studied transverse propagation of femtosecond pulse duration laser light through the microstructure of hexagonal lattice photonic crystal fibers. Our results provide insight in the role of the microstructure on the amount of optical power that reaches the core of the PCF, which is of particular importance for grating inscription applications. We developed a dedicated approach based on commercial FDTD software and defined a figure of merit, the transverse coupling efficiency, to evaluate the coupling process. We analyzed the propagation of femtosecond laser pulses to the core of a wide range of PCFs and studied the influence of the PCF orientation angle, the air hole pitch and air hole radius on the energy reaching the core. We have found that the transverse coupling efficiency can benefit from a dedicated design of the microstructured cladding and an accurate fiber orientation. We designed a dedicated PCF microstructure that enhances transverse coupling to the core at a wavelength of 800 nm.

The Effect of Hole Radius on The Properties of Large Pitch Photonic Crystal Fiber

Three proposals of large pitch (Λ=5µm) photonic crystal fibers (PCFs) are studied. The effect of air hole radius on the properties of the fundamental mode of these fibers are considered. All the parameters of the proposed structured were kept constant except the hole radius were varied 0.5, 0.8, and 1.0μm for the PCF1, PCF2 and PCF3 respectively.

Analysis of coupling characteristics of midinfrared high polarization chalcogenide glass dual-core photonic crystal fiber

A kind of chalcogenide glass midinfrared dual-core photonic crystal fiber has been proposed in this paper. The coupling characteristic of this fiber has been studied by multipole method using the basic theory of coupling. It is found that the birefringence of dual-core PCF with pitch 5.4 μm, air-hole radius 1.35 μm and air-filling fraction 0.5 is 0.551×10-2 at normalized frequency λ/Λ = 2.04 μm. At normalized frequency λ/Λ = 0.93 μm, coupling lengths are 145.32 μm and 154.68 μm for x-polarized mode and y-polarized mode, respectively. The band extended to midinfrared. This dual-core photonic crystal fiber with coupling length and high polarization is useful for manufacturing midinfrared band optical fiber coupler.