Beam splitter and beam bends based on self-collimation effect in two-dimensional photonic crystals

Basing on the self-collimation effect of photonic crystals, one-to-two beam splitter, beam bend and one-to-three beam splitter are, respectively, designed by introducing a different line defect along the same direction. From the equal-frequency contour plot which is calculated by the plane wave expansion method, we obtain the frequency and the propagate direction of the self-collimated beam. The self-collimated beam propagation in photonic crystals with different line defects is simulated by the two-dimensional finite-difference time-domain method with perfectly matched layer absorbing boundary conditions. The simulation results show that one-to-two beam splitter, beam bend and one-to-three beam splitter can be realized by appropriately arranging the line defect along the proper direction. Such devices can greatly enhance photonic crystals for use in high-density optical integrated circuits.     

二维旋转直柱光子晶体的频率带隙结构分析

设计了一种二维方形旋转正四边形直柱光子晶体,利用平面波展开方法计算了其光子频率带结构,发现在低频和高频区域,该类光子晶体的光子频率禁带明显增大.计算了空气中Al材料的旋转四边形直柱光子晶体的带结构和态密度,当填充比等于0.5时存在绝对带隙,旋转角度为45°时绝对带隙最大,旋转角度为0时,光子频率禁带位于高频区域.利用FDTD方法检验了计算结果,并分析了旋转角度为45°时,正四边形直柱光子晶体的波导特性以及TM模的电场分布.     

Numerical study of two-dimensional metamaterial composites: the existence of a stop band

Two-dimensional metamaterial photonic crystals composed of dispersive left-handed materials and a right-handed medium were investigated. The existence of a stop band was studied by finite-difference time-domain calculations incorporated into an auxiliary differential equation (FDTD-ADE) method. The existence of a stop band was studied in the case of Drude-type dispersion responses for the dielectric permittivity and magnetic permeability of the metamaterial. A distinct stop band appears when the dispersive left-handed metamaterials are embedded in a positive-refractive-index medium and spatially isolated from each other. In contrast, the stop band is absent when the metamaterials span the entire photonic crystal.     

Thermal properties and two-dimensional photonic band gaps

The effect of temperature on a two-dimensional square lattice photonic crystal composed of Si rods arranged in an air background was investigated theoretically using the plane-wave expansion method. Both the thermal expansion effect and thermo-optical effect are considered simultaneously. We have discussed the role of temperature in creating the complete photonic band gap as a function of temperature. Two different shapes of rods, i.e. square and circular, are considered in the presence of the two polarization states, i.e. TE and TM waves. The numerical results show that the photonic band gap can be significantly enlarged compared to the photonic band gap at room temperature. The effect of temperature on the complete photonic band width in the cylindrical rods case is more significant. Cylindrical and square Si rods may work as a temperature sensor or filter, among many other potential applications.     

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.     

带隙可调光子晶体的研究进展

介绍了近几年带隙可调光子晶体的研究进展。带隙调节的机制主要有改变晶体材料的平均折射率和改变晶体的结构参数两种。综述了通过电场调制、磁场调制、压力调制、光照调制、温度调制和复合调制等实现带隙实时可调的研究进展,提出了目前存在的问题及研究方向。     

Genetic optimization of two-dimensional photonic crystals for large absolute band gaps under light line

A binary genetic algorithm with floating crossover and mutation probabilities is used to design two-dimensional photonic crystals for large absolute band gaps under a light line. The unit cell is composed of a small number of round rods and is arranged in a square lattice. The photonic band structure of each chromosome is calculated by the plane-wave expansion method. Starting from randomly generated photonic crystals, the genetic algorithm finally yielded a photonic crystal with an absolute common band gap of 0.0618(2πc/a) at the mid-frequency of 0.4084(2πc/a).     

一种双通道窄带滤光片的设计与制备

对光子晶体技术在滤光片设计中的应用进行了可行性研究。利用一维光子晶体进行了双通道窄带滤光片的设计,并利用离子束辅助沉积方法进行了滤光片的镀制。同时研究了膜层的误差对滤光片光谱性能的影响,表明其敏感层主要是缺陷层。实验结果表明,运用光子晶体概念进行双通道窄带滤光片设计是可行的。     

Ultra-high Q one-dimensional hybrid PhC-SPP waveguide microcavity with large structure tolerance

Abstract

A photonic crystal – surface plasmon-polaritons hybrid transverse magnetic mode waveguide based on a one-dimensional optical microcavity is designed to work in the communication band. A Gaussian field distribution in a stepping heterojunction taper is designed by band engineering, and a silica layer compresses the mode field to the subwavelength scale. The designed microcavity possesses a resonant mode with a quality factor of 1609 and a modal volume of 0.01 cubic wavelength. The constant period and the large structure tolerance make it realizable by current processing techniques.     

Low-power optical switching with Kerr nonlinear material in two-dimensional photonic crystal nanocavity

We investigate numerically optical bistability in direct-coupled cavity–waveguide photonic crystal system using the finite-difference time-domain method. The quality factor of the cavity is optimized by engineering the geometrical parameters. Numerical results indicate that the threshold power of optical bistability can be reduced greatly due to the increased quality factor.     

A 1 × 4 optical splitter for TE modes based on a silicon photonic crystal self-collimation ring resonator

A 1?×?4 optical splitter (OS) is proposed for TE modes based on a self-collimation (SC) effect ring resonator (SCRR) in an air-hole type silicon photonic crystal. A 1?×?4 OS consists of four beam splitters formed by varying the radii of the air holes. Utilizing multiple-beam interference theory, the theoretical transmission spectra at each port in the OS were analyzed. By forming four splitters in a SCRR properly, self-collimation light can come out from four ports with the light-intensity ratio we set. OSs were investigated using the two-dimensional finite-difference time-domain (FDTD) simulation technique. The simulation results have good agreement with the theoretical prediction. Because of its small dimensions, whole silicon material, and air-hole type, this structure may have an important role in photonic integrated circuits.     

All-optical controllable channel-drop filters in two-dimensional square-lattice photonic crystals

A novel all-optical controllable channel-drop filter in photonic crystals (PC) of square lattice is presented. We show that using a resonant-cavity-based add-drop filter with a wavelength-selective reflection feedback and a single-control switching module which is based on nonlinear PC microcavities, the dropped channel can be routed to the drop port or returned to the bus waveguide. Using the temporal coupled-mode theory and two-dimensional nonlinear finite-difference time-domain method, the performance of the proposed device is investigated and the simulation results show the validity of the proposed design.     

Evolution of two-dimensional crystal morphologies by surface diffusion with anisotropic surface free energies

The Wulff shape of a crystal surface in equilibrium under anisotropic surface free energy has been widely reported and a typical differentiable anisotropic free energy functional form has been used in illustrations. Here we study the evolution of an arbitrary initial two-dimensional crystal shape to equilibrium and we classify the anisotropy in three cases. We find that when the typical surface free energy is critically anisotropic, multiple equilibrium states exist and the evolved equilibrium shape depends on the initial crystal configuration. Numerical simulations show that corners and planar facets develop on the surface in evolution. In cases of severe anisotropy, small surface facets and coarsening can occur. In contrast, when the typical surface free energy is mildly anisotropic, the evolving surface is smooth and the equilibrium shape is unique for a variety of the initial crystal shapes.     

Terahertz pulse generation using one-dimensional photonic crystals via optical rectification effect

Generation in one-dimensional photonic crystals of a single-cycle terahertz (THz) pulse via the optical rectification effect was studied by using the Green's function method. The bandwidth and the carrier frequency of the generated THz pulse are, respectively, in the range 2–8?THz and 2–18?THz. By decreasing the duration of the input pulses these ranges can be enlarged, but pulse shape is also deformed. The results show that by setting the carrier frequency of the input pulse on the edges of the gap, the amplitude of the generated THz pulse is maximized and its bandwidth is narrowed, but for carrier frequencies located inside the gap the situation is reversed. Moreover, by adjusting the carrier frequency of the input pulse on upper gaps few-cycles THz pulses are generated.     

Ge/ZnS一维光子晶体的设计、制备及低红外发射率性能

通过从理论上分析介质层厚度、不同介质材料的折射率差及周期数对一维光子晶体红外发射率的影响规律,设计得到了可实现8~14μm波段低红外发射率性能的Ge/ZnS一维光子晶体。随后采用光学镀膜技术在石英基片上通过交替沉积Ge层和ZnS层的方法制得所设计的一维光子晶体,并采用扫描电镜(SEM)及傅里叶变换红外光谱(FTIR)分别对其微结构及光谱发射率进行了系统研究。结果表明,所制备一维光子晶体在8~14μm波段具有低红外发射率性能,其平均发射率可低至0.195。采用Ge、ZnS等无机半导体材料,通过合理的一维光子晶体设计同样可以获得低至0.2以下的红外发射率。     

Theoretical modelling of one dimensional photonic crystal based optical demultiplexer

An optical demultiplexer through one-dimensional Si–SiO₂ photonic crystal structure in the presence of air cavity with a single crystal PMN-0.38PT material is presented. The transmittance of this structure is obtained using the transfer matrix method. The transmittance of this structure shows a sharp passband in the band gap region. It is observed that by introducing PMN-0.38PT layer in both sides of the air cavity, the existing band gap region of Si–SiO₂ structure is slightly increased. Here, PMN-0.38PT material is working as a tunable element for passband. By applying some external potential on PMN-0.38PT crystal, the thickness of cavity layer can be tuned and the passband can be placed at any desired wavelength in the band gap region. Since the photonic band gap region contains a range of wavelengths which are not allowed to pass through the structure can be considered as a multiplex signal for the proposed demultiplexer. Therefore, any optical signal that lies in the band gap region of the structure can be separated into its components as a pass band. Hence, the proposed structure will work as an optical demultiplexer.     

Non-reciprocity and topology in optics: one-way road for light via surface magnon polariton

Abstract

We show how non-reciprocity and topology are used to construct an optical one-way waveguide in the Voigt geometry. First, we present a traditional approach of the one-way waveguide of light using surface polaritons under a static magnetic field. Second, we explain a recent discovery of a topological approach using photonic crystals with the magneto-optical coupling. Third, we present a combination of the two approaches, toward a broadband one-way waveguide in the microwave range.