Low-reflection photonic-crystal taper for efficient coupling between guide sections of arbitrary widths

We design and fabricate a new taper structure for adiabatic mode transformation in two-dimensional photonic-crystal waveguides patterned into a GaInAsP confining layer. The taper efficiency is validated by measurement of a reduction of the reflection between an access ridge and a photonic-crystal guide with one missing row from 6% to less than 1%. This taper is then incorporated into a 60 degrees bend; simulations demonstrate a 90% transmission between multimode ports.     

基于二维六方氮化硼材料的光子晶体非对称传输异质结构设计

二维六方氮化硼(hexagonal boron nitride,hBN)材料在产生光学稳定的超亮量子单光子光源领域有着潜在应用,有望用于量子计算和信息处理平台,已成为研究热点.而光学非对称传输设备是集成量子计算芯片中的关键器件之一.本文从理论上提出了一种基于hBN材料光子晶体异质结构的纳米光子学非对称光传输器件.运用平...     

Analysis and design of efficient coupling in photonic crystal circuits

A rigorous analysis and design of efficient coupling from photonic crystal (PhC) waveguides into conventional dielectric waveguides is reported. Closed-form expressions for the reflection and transmission matrices that completely characterize the scattering that occurs at the interface are derived based on an eigenmode expansion technique and a Bloch basis. Analytic expressions are used to analyze the reflection into PhC waveguides. We obtain that negligible reflection can be achieved by choosing a certain interface within a PhC unit cell. Furthermore, analytic expressions are used to design a novel and compact coupler structure in order to achieve high coupling efficiency when broad dielectric waveguides are considered. Thereby, transmission efficiencies near 100 from the fundamental guided Bloch mode into the fundamental waveguide mode are achieved.     

纤维光锥有效透过率的理论分析

光锥的有效透过率不仅影响光锥与CCD的耦合效率,而且会影响到耦合器件的信噪比.本文主要从理论上讨论了影响光锥有效透过率性能的因素,从纤维光学元件的实际内部结构推导出了其实际有效填充率,从光线在光锥中的传输特征推导出了光线在光锥中传播时产生的衰减损耗,最后提出了提高光锥有效透过率的方法和途径.     

High Efficiency One-Way Transmission by One-Dimensional Photonic Crystals with Gratings on One Side

We propose a scheme of optical one-way transmission by using one-dimensional photonic crystals （PhCs） with diffraction gratings on one side. The one-way transmission is realized by making the PhC opaque to the zeroth diffraction order and transparent to another propagating （in air） diffraction order. For such a structure with 10-period PhC, 93% of the incident energy passes through when an electromagnetic wave impinges from one side, and the transmittance decreases to the order of 0.001% as the electromagnetic wave illuminates from the other side.     

Tunable transmission and enhanced emission in ordered metallic nanostructures having varying channel shape

Extraordinary transmission spectra for one-dimensional (1D) gratings and two-dimensional (2D) metallic hole arrays change with the hole channel shape. In this paper, a converging-diverging channel (CDC) design was introduced. The transmission spectra corresponding to CDC-embedded nanostructures of 1D grating, circular and rectangular holes (2D hole arrays) are analyzed using three-dimensional (3D) finite-element method. Tuning of optical transmission by changing the CDC structure has been investigated. In addition, a cavity composed of a CDC metallic grating and a 1D photonic crystal (PhC) can lead to an enhanced emission. Large coherence length of the emission can be achieved by exploiting coherent properties of surface waves in grating and PhC.     

Metal wave-guide to dielectric image guide transition using exponential taper

A unique metal wave guide to dielectric image guide transition has been developed using exponential taper in dielectric wave guide. The propagation characteristics have been computed theoretically and taper impedance for the different cross-sections have been evaluated, so as to match it with the metal wave guide for efficient mode conversion. Transmission loss and return loss for triangular and exponentail taper with frequency for same dimensional parameters have been measured.     

Transmission of slow light through photonic crystal waveguide bends

The spectral dependence of the bending loss of cascaded 60 degrees bends in photonic crystal (PhC) waveguides is explored in a slab-type silicon-on-insulator system. An ultralow bending loss of (0.05 +/- 0.03) dB/bend is measured at wavelengths corresponding to the nearly dispersionless transmission regime. In contrast, the PhC bend is found to become completely opaque for wavelengths corresponding to the slow-light regime. A general strategy is presented and experimentally verified to optimize the bend design for improved slow-light transmission.     

电光聚合物波导中的锥形结构

提出并设计了一种基于电光聚合物的锥形波导,可用于单模光纤与电光聚合物波导器件之间的连接.锥形波导中采用了宽度锥形和折射率锥形结构.宽度锥形采用劈形形状,通过宽度和折射率的缓慢变化实现模场转换.劈形形状的宽度锥形具有较小的损耗且易于制作,折射率锥形可采用灰度掩膜光刻技术制作.研究了锥形波导的传输损耗与锥形波导的长度、波导宽度和厚度、材料吸收损耗等参数的关系及其优化,分析了锥形波导中的功率传输、模场分布与模式转换效率.结果显示锥形波导的传输损耗小于0.37 dB,光纤-波导-光纤的连接损耗优于1.62 dB,对插入损耗的改善达到8.78 dB,模场转换效率达到了83.7%.     

基于自准直效应的Fabry-Perot干涉仪的设计

报道了基于圆柱型光子晶体自准直效应的低功耗Fabry-Perot干涉仪。该干涉仪是在二维光子晶体中引入两排线缺陷构成的。引入的线缺陷具有高反射率和低透射率。在自准直频率范围0.187c/a~0.201c/a,线缺陷的透射率介于20.77%~40.65%。利用时域有限差分方法对FPI的透射谱进行研究,结果表明对两排缺陷的间距d即使进行微小的扩大也会引起透射峰向低频移动,透射谱的自由光谱范围和透射峰的频率随着d的增大而变小,透射谱的半高宽会随着线缺陷的反射率的提高而逐渐变小。     

Two-dimensional Si photonic crystals on oxide using SOI substrate

Two-dimensional photonic crystals (2D-PhCs) on oxide can be easily incorporated into photonic integrated circuits. Although an asymmetrical structure (air/PhC/oxide) is advantageous in terms of ease of fabrication, it has been pointed out that such a structure may have no photonic band gap (PBG). To clarify the characteristics of the asymmetrical structure, we calculated the band structure using the three-dimensional (3D) FDTD method and measured the transmission characteristics of a fabricated 2D Si-PhC on oxide. The calculations show that we can use a quasi-PBG even in an asymmetrical structure when the PhC thickness satisfies the single-mode condition. The measured transmission characteristics correspond to the calculated band structure and reveal the existence of a quasi-PBG. These results show that the asymmetrical 2D Si-PhC-on-oxide structure can be applied to various optical devices.     

Self-collimating photonic crystal polarization beam splitter

We present theoretical and experimental results of a polarization splitter device that consists of a photonic crystal (PhC) slab, which exhibits a large reflection coefficient for TE and a high transmission coefficient for TM polarization. The slab is embedded in a PhC tile operating in the self-collimation mode. Embedding the polarization-discriminating slab in a PhC with identical lattice symmetry suppresses the in-plane diffraction losses at the PhC-non-PhC interface. The optimization of the PhC-non-PhC interface is thereby decoupled from the optimization of the polarizing function. Transmissions as high as 35% for TM- and 30% for TE-polarized light are reported.     

Transmission characteristics simulation of an erbium-doped lithium niobate film photonic crystal slab

A photonic crystal slab (PhC slab) which was constructed as a 2D hexagonal lattice with a finite depth was etched into an Er:LiNbO₃ film waveguide. The band diagrams and transmission spectra were simulated by plane wave expansion (PWE) and the finite-difference time-domain (FDTD) method. A high refractive index contrast of 0.5 enables strong light confinement in the vertical direction and a broad band gap. The simulated transmittance spectra indicate that the stop band is determined by lattice constant. The transmission spectra along ΓM of the PhC slab with a lattice constant 500 nm show a 250-nm broad stop band in the wavelength range from 1.33 to 1.58 μm and sharp band edge.     

光纤锥探针传输特性的研究

本文采用局域模式耦合理论，对两类光纤锥探针－腐蚀锥和熔拉锥的传输特性进行了比较和分析，得出了光在探针锥中传输时耦合效率的分布情况，以及传输效率随锥长、针尖直径和光波长变化的特性。     

Fabrication and demonstration of square lattice two-dimensional rod-type photonic bandgap crystal optical intersections

This paper reports fabrication and demonstration of optical intersections in two-dimensional (2D) rod-type photonic crystal (PhC) structures. High resolution and aspect ratio 2D square lattice PhC waveguide intersections were designed and fabricated for application at the optical communication wavelengths centered at 1550 nm. In the silicon processing front, challenges resolved to overcome issues of drastically reduced process windows caused by the dense PhC rods arrays with critical dimensions (CDs) reduced to only a few hundred nanometers were addressed not only in terms of critical process flow design but also in the development of each processing module. In the lithographic process of deep ultraviolet laser system working at 248 nm, PhC rods of sub-lithographic wavelength CDs (115 nm in radii) were realized in high resolution, even near periphery regions where proximity errors were prone. In the deep etching module, stringent requirements on etch angle control and low sidewall scallops (undulations arising from time multiplexed etch and passivation actions) were satisfied, to prevent catastrophic etch failures, and enable optical quality facets. The successfully fabricated PhCs were also monolithically integrated with large scale optical testing fiber grooves that enabled macro optical fiber assisted coupling to the micro scale PhC devices. In the optical experiments, the transmission and crosstalk properties for the PhC intersection devices with different rod radii at the center of the PhC optical waveguides crossings were measured with repeatability. The properties of the PhC intersections were therefore optimized and verified to correspond well with first principle finite difference time domain simulations.     

Thermal properties and wavelength analysis of telecom oriented photonic-crystal VCSELs

Results of the self-consistent comprehensive analysis of a room-temperature operation of InP-based 1300-nm AlInGaAs photonic-crystal (PhC) VCSELs are presented. In particular, an influence of PhC parameters on thermal effects within VCSEL volume and its emission wavelength are analysed. The PhC has been found to introduce a number of opposite effects including a possible light leakage through PhC holes. From one side, PhC holes make more difficult heat-flux extraction from VCSEL volume leading to higher temperature increases within it. But, from the other side, a properly manufactured PhC creates an efficient radial confinement mechanism for VCSEL radiation field. It enhances an interaction between the field and the active-region carriers leading to a decrease in both the VCSEL lasing threshold and temperature increases. Seemingly both effects may similarly affect VCSEL operation, but our analysis revealed, that thermal properties of the PhC VCSEL are mainly dependent on an efficient confinement of its radiation field within the active region impeding a mode leakage through PhC holes, whereas an importance of deterioration of heat-flux extraction from VCSEL volume is much less essential. The wavelength shift induced by a change of PhC parameters has been found not to exceed 4×10⁻³ μm.     

Design and analysis of coherent OCDM en/decoder based on photonic crystal

The design and performance analysis of a new coherent optical en/decoder based on photonic crystal (PhC) for optical code -division -multiple (OCDM) are presented in this paper. In this scheme, the optical pulse phase and time delay can be flexibly controlled by photonic crystal phase shifter and time delayer by using the appropriate design of fabrication. According to the PhC transmission matrix theorem, combination calculation of the impurity and normal period layers is applied, and performances of the PhC-based optical en/decoder are also analyzed. The reflection, transmission, time delay characteristic and optical spectrum of pulse en/decoded are studied for the waves tuned in the photonic band-gap by numerical calculation. Theoretical analysis and numerical results indicate that the optical pulse is achieved to properly phase modulation and time delay, and an auto-correlation of about 8 dB ration and cross-correlation is gained, which demonstrates the applicability of true pulse phase modulation in a number of applications.     

Modelling of a two-dimensional photonic crystal as an antireflection coating for optoelectronic applications

In article a two-dimensional photonic crystal (PhC) is considered and modelled as a new generation antireflection coating for optoelectronic devices. Traditional antireflective coatings (ARCs) reduce the reflection of the radiation only – the new generation of antireflective coatings should affect the distribution of the radiation also. Such functionality can be provided by the two-dimensional PhC which reduce the reflection and scatter transmitted light. Prior to the fabrication, the PhCs should be designed and analysed. Results of the analysis should provide quantitative means for choice of materials and design solutions. In work, we analyse the electromagnetic field distribution as Poynting vectors inside the materials of optoelectronic devices, in order to investigate the possibility of improving the construction of future optoelectronic devices. Furthermore, we calculate the reflection and transmission of that ARC. It’s a complex optic analysis of new generation of ARC. The numerical analysis has been performed with the FDTD method in Lumerical Software. In work, we consider the two-dimensional photonic crystal on the top surface of optoelectronic structures. We compared the results with the traditional ARC from these same parameters as PhC: thickness and material. As an example, we presented the application of modelled, photonic crystal, thin-film, GaAs solar cells with PhC on top. The efficiency of this solar cell, using the photonic crystal, was improved by 6.3% over the efficiency of this same solar cell without PhC. Thus, our research strongly suggests that the unique properties of the photonic crystal could be used as a new generation of ARC.     

扫描近场光学显微镜中两类光纤探针传输特性的研究

采用局域模式耦合理论，对扫描近场光学显微镜中的两类光纤探针－腐蚀锥和熔拉锥的传输特性进行了比较和分析。给出了光在探针锥中传输时耦合效率的分布情况，以及传输效率随锥长，针尖直径和光波长变化的特性。     

塑料光纤双锥与半球腔的活动耦合效应

报道了用氮氖激光实现的塑料光纤双锥与介质半球(称半球腔)之间的活动耦合效应。测量了光纤双锥的发射效率，并测量了锥腔耦合效率与半球腔的表面积、锥腔距离之间的关系。根据这种效应，可以制成塑料光纤活动耦合器；如果再加上调谐滤波器，可制成适合塑料光纤通信网用的信号上下载装置。