Waveguide modulated non-local optical interaction of semiconductor microdisks

The non-local optical interaction of two semiconductor microdisks with a waveguide bridged at radial direction is proposed and studied by three dimensional finite-difference time-domain （FDTD） electromagnetic simulations. The strong and weak optical interactions between two microdisks are observed and ascribed to the internal coupled modes with different coupling ratios. The vertical radiation losses and the related mode quality factors are modulated by waveguide length and present oscillation characteristics for the resonant modes. In addition, the optical leakage of coupling system is affected by the etching depth of disks due to tile emission of minor components of electric field.     

Modelling of photonic crystals for the design of photonic device based on SOI substrate

In this paper, we report a photonic integrated circuit (PIC), which consisting of a photonic crystal (PC) coupled by a dielectric waveguide to an optical fibre. The PC consists of a sequence of dielectric rods based on a silicon (Si) strip on a silicon dioxide (SiO₂) layer. The finite-difference time-domain (FDTD) method is reviewed and then used to model and predict the optical and the geometrical parameters used to design the fundamental elements of the PIC. The air gap width and the etching depth of the grooves are characterised. The coupling between the PC, and traditional dielectric waveguides is studied and coupling efficiency is evaluated. Diffractive losses are shown to affect strongly the performances of the proposed PIC. In addition, the effect of the air gap width on the diffractive losses and the coupling efficiency between successive neighbouring silicon sections is analysed. The field profile distribution in the structure is calculated and performed. The effects of an incorporated defect are studied, showing a high quality factor.     

Directly laser-written integrated photonics devices including diffractive optical elements

Femtosecond laser-written integrated devices involving Fresnel Zone Plates (FZPs) and waveguide arrays are demonstrated as built-in optical couplers. These structures were fabricated in borosilicate glass using a direct laser writing technique. The optical properties of these integrated photonic structures were investigated using CW lasers and high-resolution CCDs. For a single FZP coupled to a single waveguide, the overall coupling efficiency was 9%. A multiplexed optical coupler composed of three FZP layers was demonstrated to couple three waveguides simultaneously in a waveguide array. Structures of this type can be used as platforms for multichannel waveguide coupling elements or as microfluidic sensors that require higher light collecting efficiency.     

Analysis of an ultra-compact wavelength filter based on hybrid plasmonic waveguide structure

In this letter, we propose and analyze an ultra-compact wavelength filter on silicon-based hybrid plasmonic waveguides, which confines light in a nanometeric silica dioxide layer between the silicon substrate and metal cap. The filter consists of a stub structure coupled to a straight waveguide. The three-dimensional finite-difference time-domain (FDTD) method is applied to calculate the spectral responses of such devices. Similar resonant behaviors are obtained since those devices are based on two-dimensional Metal-Insulator-Metal waveguide structure. Results also show that by adding stubs and tuning the distance between stubs can further improve the device's performance and shape the spectral response to some extent.     

Integrated optical proximity microsensor

This paper presents the design, simulation and experimental results of an integrated proximity sensor manufactured on silicon substrate. The sensor was designed for microrobotic applications like integration into a microgripper arm or detection of the position of gripper arms relative to an object. The structure is based on an SU8 polymeric optical waveguide splitted into three arms, integrated with a multielement photodetector on silicon substrate. Each element of the photodetector is a metal-semiconductor-metal (MSM) photodiode with Ti/Al Schottky interdigitated electrodes.The operation principle of this sensor consists in the light coupling in the central arm of the optical waveguide, interaction with the object (reflection) of the radiation which exits from this principal arm, the coupling of the “affected” radiation which comes back through the end of the waveguide and its splitting into three arms of the optical waveguide. From the optical waveguide, the light is coupled in photodiode and the photogenerated carriers are collected to the electrodes giving the electrical signal which is read and processed in real time.The optimal parameters of the waveguide (width, thicknesses of the core and the claddings) of the photodetector and the coupling between them were defined by simulation, using FDTD and BeamProp method (Opti FDTD software). Our microsensor can detect the position of an object in the range of 0-300 μm, as position sensor and with high precision in the range of zero to twice the wavelength, as proximity sensor.     

基于波导、金和氧化锌的随机激光器的研究

通过将金属金嵌入到上下两层波导结构中,与ZnO随机粒子相结合,设计出一种新型结构的随机激光器。采用时域有限差分法(FDTD),数值模拟了该随机激光器系统的光场分布和模式频谱图,并针对金粒子和金薄膜两种情况进行对比分析。结果显示,采用金粒子作夹层时,出射激光模式数量减少,单色性较好;采用金薄膜作夹层时,出射激光光强较大。     

Polarization mode conversion in an optical microdisk resonator vertically coupled to a waveguide bus

Due to the existence of non-zero, and asymmetrics cross-polarization coupling coefficients between a microdisk and a waveguide bus, high Q (∼10,000) overcoupled microdisks with minimal internal losses and sharp bending curvature (small radii) vertically coupled to a narrow-width ridge waveguide can be engineered as a proper candidate for a narrow-band polarization rotator. A semi-analytical calculation method is presented to realize microdisk-waveguide system as a polarization rotator.     

Irreversible coupling by use of dissipative optics

The time reversibility of optical propagation impedes the definite performance of many optical devices, such as couplers, polarization converters, etc. We suggest a novel concept in which we use media with loss and gain, thus breaking the time-reversal characteristics, to achieve a unidirectional optical mode interference and coupling, which is a desirable feature for light-wave circuits. Using a matched periodic modulation of both the index of refraction and loss (gain) of the medium, we implement a spatially single sideband perturbation, which breaks the symmetry to allow only a unidirectional energy transfer from mode m to mode n of the optical structure. We elaborate on this phenomenon in coupling between two modes of a multimode optical waveguide.     

Optical switch effect of metal–dielectric–metal plasmonic waveguide coupled with stub structure

The transmission line theory (TLT) and the finite difference time domain (FDTD) method are applied to investigate the optical transmission characteristics of the metal–dielectric–metal (MDM) plasmonic waveguide coupled with a stub structure. The transmission rate of the FDTD simulation results demonstrates periodically variation from less than 1% to more than 92% as a function of the length of the stub, which fits well with the results of TLT. Furthermore, the transmission also performs a periodically switch distribution with the change of the refractive index of the stub from 1.0 to 2.0 gradually. Both methods are adopted for modulating the superposition phase of the interference between the reflected surface plasmon polaritons (SPPs) wave from the end of the stub and the passing SPPs wave in the waveguide, which can be interpreted as the principle mechanism for the optical switch effect of the MDM waveguide with a stub structure.     

基于一种易于制作的混合型表面等离激元波导结构的超紧凑截线滤波器

提出并分析了一种结构紧凑的截线型滤波器。该滤波器建立在一种硅基混合型表面等离激元波导结构上。与通常的混合等离激元结构相比,该波导结构在制作时只需对顶部的一层硅材料进行刻蚀,不需在光刻步骤进行对准和套刻,工艺简单易行。该截线滤波器由一截突柱波导与直波导耦合组成,并采用三维时域有限差分方法对其频谱响应进行模拟计算。计算结果表明该滤波器与现有文献中的二维金属-绝缘体-金属波导截线滤波器具有类似的频谱特性。另外,还进一步分析了截线部分及波导自身尺寸对器件输出频谱的影响。     

Laser-assisted magnetic recording light-delivery system with a coupling element and a laterally tapered vertically multistepped waveguide

In a light-delivery system for laser-assisted magnetic recording, which provides high-areal-density storage by heating the storage medium during the writing process, a laser diode light source and a near-field transducer must be efficiently coupled using inexpensive optical devices. We describe a light-delivery system using an element for end-fire coupling and a spot-size converter. To couple the light emitted from the end of an optical fiber to a spot-size converter inexpensively, a couple element requiring no other lens elements between the fiber and converter was developed. A vertically multistepped and laterally tapered waveguide suitable for fabrication by planar processing was also developed. These devices are well suited for practical use.     

DNA implementation for optical waveguide as a switchable transmission line and memristor

In this paper, an optical waveguide has been developed based on the (Deoxyribonucleic acid) DNA core as a multi-slab structure by switching characteristic at 300 THz. We show that how the DNA with various electrical characteristics can be considered as a reconfigurable material which is placed between two optical metal layers. Therefore, we can control the current and voltage density values based on the divergence of the DNA types as an optical switch. Moreover, we can select the Au and Ag for the metal coat. In this research, we demonstrate that the Ag/DNA/Ag and Au/DNA/Ag have better performance in switching qualification than Au/DNA/Au model as a conventional structure. This DNA core waveguide has a switchable feature which cannot be found at any conventional plasmonic waveguide. The FDTD time domain is used for simulating the waveguide and the current density is considered as an ON/OFF switch. We carry out parametric studies for the physical dimensions of the waveguide and illustrate that how we can improve the switching characteristic. Moreover, we have checked the coupling effect between the transmission lines and defined the figure of merit for switching quality. This structure can be considered as an optical memristor and optical “YES” gate which couldn’t be obtained by other graphene waveguide while it became feasible based on DNA switching feature.     

Coupled metallic ring gap waveguide

Employing the surface plasmon polaritons (SPPs), a kind of coupled metallic squareness ring waveguide structure is presented. Its properties has been analyzed with the finite different time domain method and the coupling length has been derived from the coupled mode theory. It is demonstrated that the SPPs excited by the light with different wavelength will come out from different output port due to different coupling length. By appropriately designing the structure, it can be utilized to realize some optics devices such as multiple-wavelength sorter and beam splitter. This will break through the diffraction limit of traditional optical devices.     

Coupled-resonator optical waveguide: a proposal and analysis

We propose a new type of optical waveguide that consists of a sequence of coupled high-Q resonators. Unlike other types of optical waveguide, waveguiding in the coupled-resonator optical waveguide (CROW) is achieved through weak coupling between otherwise localized high-Q optical cavities. Employing a formalism similar to the tight-binding method in solid-state physics, we obtain the relations for the dispersion and the group velocity of the photonic band of the CROW's and find that they are solely characterized by coupling factor k(1) . We also demonstrate the possibility of highly efficient nonlinear optical frequency conversion and perfect transmission through bends in CROW's.     

T型缝隙结构表面等离子波导的基本特性研究

An air channel inside a silver metal film is usually used as a typical Channel Plasmon Polariton （CPP） waveguide. This paper presents research on the basic properties of this waveguide using the Finite Difference Time Domain（FDTD） method. The relationship between transmission power and structure of the waveguide is investigated. The simulation results show that the subwavelength trapezoidal CPP waveguide is superior to the rectangle CPP waveguide for controlling SPP radiation loss and enhancing the transmitted power. As a result, if the rectangle CPP waveguide is replaced by a trapezoidal CPP waveguide in certain integrated optical devices, their performance may be improved.     

基于倏逝场耦合的石墨烯波导光传输相位特性仿真与实验研究

石墨烯材料应用到各种光波导器件中正成为新一代光子器件的重要发展方向之一,目前基于石墨烯的光纤和集成光子器件研究越来越受到国内外的重视. 本文建立了一种由微纳光纤耦合光倏逝场,并在石墨烯薄膜中传输的模型. 通过有限元分析法,研究了光在这种石墨烯波导中传输光场的强度分布和相位特性,并通过实验进行了验证. 结果表明,沿着微纳光纤-石墨烯光波导传播的倏逝场的强度分布和相位均受石墨烯材料作用,石墨烯材料能有效聚集和导行波导中传输的高阶模,在单位传输长度上具有更密集的等相位面. 本文提出了一种利用微纳光纤耦合光倏逝场研究石墨烯相位响应特性的新方法,对基于石墨烯波导的新型调制器、滤波器、激光器和传感器等光子器件的设计和应用具有一定的参考意义. 关键词： 石墨烯平面光波导 倏逝波 光场强度 相位     

Highly efficient optical coupling and transport phenomena in chains of dielectric microspheres

Using the generalized multiparticle Mie theory, we investigate optical coupling and transport through chains of dielectric microspheres. We identify two distinct coupling mechanisms of optical transport in terms of the coupling efficiency between neighboring microspheres, namely, evanescent coupling and nanojet coupling. We demonstrate that perfect whispering gallery mode propagation through a chain of evanescently coupled microspheres can be achieved. However, optical coupling and transport through a chain of nanojet-inducing microspheres is less efficient due to the radiative nature of photonic nanojets. Understanding these two optical coupling mechanisms is critical for selecting appropriate microspheres to build coupled resonator optical waveguides and other photon-manipulation devices for effective and low-loss guiding of photons.     

基于表面等等离波子的新型Y分支波导

新型高效的纳米光波导器件的研制纳米集成光学的核心技术之一。Y分支波导作为最基本的分光和光路连接元件是纳米光学器件设计与制备的基础。运用时域有限差分(FDTD)法,模拟计算了基于表面等等离波子(SPP)的纳米Y分支波导的传输特性。结果表明,该新型Y分支波导在光通信波段可以实现大角度的分光功能,且在180°分支情况下,传输效率仍高达92.8%以上。另外,该波导还具有导波性能良好、对分叉处间隙缺陷大小不敏感及制作容差较大和器件尺寸在纳米量级等特点。对该新型光波导器件的研究为未来纳米集成光学器件的研制和应用有一定的指导意义。     

A photonic crystal L-shaped bend based on ring resonators

We propose a new type of two-dimensional （2D） photonic crystal L-shaped bent waveguides based on ring resonators with an acceptable bandwidth. The proposed structure mechanism is based on coupling between a waveguide and a ring resonator. This structure is designed and verified by finite-difference time-domain （FDTD） computation. Our simulation using this method gets over 90% output.     

Optimization the coupling coefficient of large mode area PCF using 2D FDTD method

The 2D FDTD method is used to design a tapered photonic crystal fiber, where large mode area is prominently coupled to optical fiber. For the first time, we observed that the mode area is stabilized with respect to possible fabrication tolerance by implementing a secondary surrounding waveguide with configuration of large air holes in the outer ring. The mode field area can be obtained in tapered region using a full vectorial H field technique. Beside these, the coupling coefficient can be optimizing by using least square boundary residual technique.