Quarter-wave design criteria for omnidirectional structural colors

Structural colors are caused by light interference from periodic multi-layer dielectric stacks and exhibit rich, highly-chromatic colors. However, avoiding a color shift due to angular variation remains a challenge. The design criteria for angle-independent structural colors have been studied by treating a quarter-wave stack of alternating dielectric material layers as a one-dimensional photonic crystal. A refractive index zone has been identified that exhibits narrowband omnidirectionality for structural colors in the visible wavelength range. It was found that a quarter-wave stack of high refractive index (RI) paired-layers (n _H = 2.85 and n _L = 2.5), which have low RI contrast (n _H /n _L = 1.14), is key in fabricating omnidirectional structural color materials. The theoretical predictions discussed here are verified experimentally using a titania/halfnia (TiO₂/HfO₂) multilayer stack.     

Optical diodes and omnidirectional reflectors based on one-dimensional quasiperiodic photonic crystals

The optical properties of one-dimensional quasiperiodic photonic crystals with linear profiles of modulation parameters are considered. It is shown that such systems possess a wider photonic band gap as compared to the ideal periodic system and can be used as omnidirectional reflectors. The asymmetric profiles of parameters in these systems results in the appearance of nonreciprocity of a new type that makes possible their use as the ideal, purely optical diodes.     

Multi-parameters measurement based on cascaded Bragg gratings in magnetic fluid-infiltrated photonic crystal fibre

Simultaneous measurement of multi-parameters is demonstrated quantitatively using two fibre Bragg gratings inscribed on a high birefringence photonic crystal fibre (PCF) and common PCF, respectively. The birefringence coefficient and the Bragg wavelengths corresponding to the fast-axis mode and slow-axis can be magnetic-controlled by filling magnetic fluid (MF) into several cladding air-holes. Based on the dependence of the MF refractive index on temperature and magnetic field, the sensitivity of the spectral response of the device to longitudinal strain, magnetic field and temperature are characterized, and the results of its application as a multi-parameter sensor are also presented.     

Infrared spectrally selective low emissivity from Ge/ZnS one-dimensional heterostructure photonic crystal

Ge/ZnS one-dimensional heterostructure photonic crystal (1DHPC) was successfully prepared by alternating thin films of Ge and ZnS on the quartz substrate by using the optical coating technology. The microstructure and spectral emissivity of as-prepared 1DHPC were characterized by using scanning electron microscopy (SEM) and fourier transform infrared spectrometer (FTIR), respectively. The test result of spectral emissivity shows that the average emissivities of as-prepared Ge/ZnS 1DHPC in the atmospheric windows of 3–5 μm and 8–14 μm can be as low as 0.046 and 0.190, respectively, but the average emissivity in the non-atmospheric window of 5–8 μm can be as high as 0.579. The results indicate that the as-prepared Ge/ZnS 1DHPC has obviously infrared spectrally selective low emissivity characteristic, basically meets the requirements of our design. The as-prepared 1DHPC with infrared spectrally selective low emissivity is promising for use as a material to unify the infrared stealth and effective cooling of the aircraft.     

A compact optical wavelength splitter in one-dimensional photonic crystal waveguides

A fundamental T-branch in one-dimensional photonic crystal waveguides based on the omnidirectional reflection is constructed. Numerical simulations of this T-branch indicate that without any structural optimization, four high reflectance peaks and three high transmittance peaks appear alternately within a wide enough frequency band. The T-branch with the unique transmission characteristics can be used as a wavelength splitter. Combining the fundamental T-branch with flexible bends of one-dimensional photonic crystal waveguides, we construct simple and compact wavelength splitters with arbitrary branching angles. Those wavelength splitters are expected to be applied to high density photonic integrated circuits.     

光子晶体在Si基发光器件中的应用

在Si基集成光电子学的发展中,实现高效的Si基光源始终是人们期待的目标.但是Si材料的间接带隙特性导致其发光效率低.目前,已经探索了多种Si基材料体系以提高Si材料的发光效率,但是尚未取得突破性的进展.近年来,光子晶体以其独特的控光能力而备受人们的关注,将光子晶体引入到Si基材料体系中可以显著提高Si基材料的发光效率,这无疑对Si基光电子学的发展起到了重要的贡献.本文简述了利用光子晶体提高Si基材料发光效率的机制,介绍了光子晶体在几种Si基材料中的应用,探索了Si基光子晶体发光器件的潜在应用前景.     

用遗传算法搜索一维光子晶体带隙

利用遗传算法和传输矩阵法计算一维光子晶体能带结构,将一维光子晶体用像素填充法进行二进制编码模拟,结果找到全方位相对禁带宽度达42.54%的4层结构和43.75%的2层结构;给出了一维光子晶体4层最佳结构的能带图、20个原胞的反射率透射率频谱图.发现一维2层光子晶体的全方位禁带宽度对每层厚度的变化是不敏感的,但是随着两种介质折射率差的增大而增大.     

Linear and nonlinear optical properties of hollow core photonic crystal fiber

We review the optical guidance properties of hollow-core photonic crystal fibers. We follow a historical perspective to introduce the two major optical guidance mechanisms that were identified as operating in these fibers: photonic bandgap guidance and inhibited coupling guidance. We then review the modal properties of these fibers and assess the transmission loss mechanisms in photonic bandgap guiding hollow-core photonic crystal fiber. We dedicate a section to a review of the technical basics of hollow-core photonic crystal fiber fabrication and photonic microcell assembly. We review some of the early results on the use of hollow-core photonic crystal fiber for laser guiding micro-sized particles, as well as the generation of stimulated Raman scattering, electromagnetically induced transparency and laser frequency stabilization when the fiber core is filled with a gas-phase material. We conclude this review with a non-exhaustive list of prospects where hollow-core photonic crystal fiber could play a central role.     

Terahertz narrow-band filter based on rectangle photonic crystal

A terahertz filter with a channel drop cavity and a resonant reflection cavity in a two-dimensional photonic crystal is theoretically proposed. The channel drop cavity is used to trap photons at resonant frequency from the bus waveguide through coupling and emit them to a drop waveguide, while the resonant reflection cavity is used to realize wavelength selective reflection feedback in the bus waveguide. The transmission properties of the terahertz filter are simulated using the finite element method. It is found that a peak with the central frequency of 1.12 THz is existed in the transmission spectrum. The full width at half maximum of the passband is only 5 GHz, and the peak drop efficiency is up to 94.8%.     

Ultrashort pulse compression by using one-dimensional inhomogeneous photonic crystal

Ultrashort pulse compression by propagation in one-dimensional inhomogeneous photonic crystals with symmetric and asymmetric refractive index profiles are studied by using the transfer matrix method and Fourier analysis. The effect of different parameters, like chirp value of the incident pulse, angle of incidence, and number of unit cells on the compress factors, are investigated and temporal evolution of the reflected pulse is calculated. Compress factors as low as 32% for a sinusoidal profile are obtained using this structure.     

Optical modulator based on coupled photonic crystal cavities

Abstract

We propose and numerically investigate an optical signal modulator based on two-photonic crystal nanobeam cavities coupled through a waveguide. The suggested modulator shifts the resonant frequency over a scalable range. We design a compact optical modulator based on photonic crystal nanobeams cavities that exhibits high stability to manufacturing. Photonic crystal waveguide tuning in the low-intensity region of the resonant mode is demonstrated. The advantages of the suggested approach over the single-resonator optical modulator approaches include the possibilities to shift the modulator frequency over a scalable range that depends on switching energy level and to effectively electrically tune the device in the low-intensity region of the resonant mode.     

Polarization-dependent angle filters based on one-dimensional photonic crystals using mu-negative materials

We study transmission properties of one-dimensional photonic crystals consisting of mu-negative and positive index materials by using transfer matrix methods. The results show that transmission properties of the transverse electric waves depend on permittivity (?), while transmission properties of the transverse magnetic waves depend on permeability (μ); there exists a transmission band inside the single-negative gap in this periodic structure without defects, and the transmission band is insensitive to the incident angle for the transverse electric waves but sensitive for the transverse magnetic waves. This property can be used to make polarization-dependent angle filters.     

Extension of bandgap and switching effect of hetero-structure consisting of one-dimensional anisotropic photonic crystal

This paper presents an approach to control overlapping of band structure using a hetero-structure made of two one-dimensional photonic crystals (PCs) with anisotropic media. Some unique features, such as the extension of band structure and band edge resonance, have been discussed using a 4 × 4 transfix matrix method. The results show that by altering the relative orientation of the optical axes of the adjacent layers, it is possible to tailor the band structure of the PCs and control overlapping of the band structure of the hetero-structure. We also found that resonance modes operating near the band edge can be switched by altering the relative orientation of the optical axes of adjacent layers. These properties can be applied to tunable optical filters or optical switches.     

可见光区一维光子晶体纳米膜偏振带通滤波器的设计

应用一维时域有限差分方法研究各种条件下一维二元光子晶体的偏振带通滤波特性,具体数值分析了掺杂层位置、厚度、电磁参数、入射角度四种因素对偏振滤波特性的影响.数值结果表明传统意义上的光学多层膜是一维二元光子晶体在光学厚度满足四分之一波长时的特例;可见光区的偏振滤波器的窄带滤波特性与掺杂层的位置有关,掺杂层在整个膜中间位置时偏振分离效果好,掺杂层的厚度与周期层厚度相差越大则分离效果越好,两组元折射率相差越大越易形成禁带,入射角越大禁带越窄,偏振的分离度越好.特别是P偏振局域模更多;在线度参数相同的情况下介质电磁参数对禁带有较大影响,禁带只有在两组元折射率相差越大才能形成,介质损耗同样是不可忽略的因素;光源的入射角对禁带有重大影响.本文的研究对光子器件的设计有一定的指导作用.     

基于p型多孔硅的一维光子晶体的微结构分析

经由阳极氧化实现了p型硅基的60周期(120层)反射结构,并在此基础上成功制作了基于一维光子晶体的全反射镜,其中心反射波长位于1.6μm左右,反射率几乎为100%的禁带带宽约为0.25μm.     

Nonlinear analysis of a photonic crystal laser

An approximate nonlinear analysis of light generation in two-dimensional square- and triangular-lattice photonic crystal lasers including gain saturation effects is presented for the TE modes. This model extends earlier studies which took into account only TM modes. Our approach is based on coupled mode theory. With the help of an energy theorem and a threshold field approximation an approximate formula relating the small signal gain required to obtain a given output power to the structure parameters has been obtained. It has been used to calculate laser characteristics revealing an optimum coupling strength for which laser structure achieves maximum power efficiency.     

一维杆状声子晶体的带隙特性

用有限元方法计算了一维杆状声子晶体的振动传输特性及其振动模态,从振形角度分析了一维杆状声子晶体相关参数(物理参数、尺寸参数)对带隙起始频率及带隙宽度的影响,发现带隙的形成与其模态振形密切相关,各参数对声子晶体带隙的影响主要是影响了个模态所在的频率,从而改变了其带隙的起始位置及宽度。     

Ultra-bandwidth polarization splitter based on soft glass dual-core photonic crystal fiber

A novel ultra-bandwidth polarization splitter based on soft glass dual-core photonic crystal fiber (DC-PCF) is designed in this paper, which is analyzed through the finite element method (FEM). The coupling characteristics of the designed DC-PCF can be enhanced by a high refractive index As₂S₃ core. Numerical results show the ultra-bandwidths of the x- and y-polarization modes can reach to 86 nm and 60 nm as the extinction ratios better than −20 dB and −30 dB at the vicinity of the wavelength of 1.31 μm. The length of the designed soft glass DC-PCF is 52.29 mm and the extinction ratios of the x- and y-polarization modes are −85.57 dB and −56.81 dB at the wavelength of 1.31 μm, respectively. In addition, the designed splitter has a tolerance of ±10 nm in its all structure parameters, which make the design not sensitive to the perturbation during the fabrication process.     

A 2*4 all optical decoder switch based on photonic crystal ring resonators

Based on photonic crystal ring resonators and nonlinear Kerr effect in this paper, we proposed a 2*4 all optical decoder switch. Our proposed structure has two logic input ports and one bias input port. This decoder switch has four output ports. Via these two logic input ports, we control the bias signal to transfer toward which output port. We employed numerical methods such as plane wave expansion and finite difference time domain methods for analyzing the proposed structure.     

Pulsed optical parametric amplification based on photonic crystal fibres

In this paper, we simulate pulsed one-pump fibre optical parametric amplifiers (1-P FOPAs) based on photonic crystal fibres in telecommunication region. At first, a PCF is designed such that its zero-dispersion wavelength is located at 1535 nm in order to fulfil the phase-matching condition for the parametric amplification in the telecommunication region. Then, the dispersion coefficients of the PCF including β₂, β₃, β₄ and β₅ as well as the nonlinear parameters are calculated at the pump, signal and idler wavelengths. Finally, the coupled nonlinear Schrödinger equations are numerically solved and the impacts of pump power and the pulse shape on the evolution of each pulse along the 1-P FOPA are investigated. The results show that the peak powers of the pump, signal and idler are periodically varied and each pulse is distorted and broadened as it propagates down the fibre optical parametric amplifiers. Also, the pulse distortion and broadening increase with the increase in both propagation distance and the input peak power.