Enhancing transmission efficiency of bending waveguide based on graded sonic crystals using antireflection structures

The conventional antireflection coating (ARC) structure for sonic crystal devices is to place the cylinders at the interface between a sonic crystal device and a background medium. The radius of ARC cylinders and the distance between the ARC and the sonic crystal device are adjusted to obtain an optimal antireflection effect. We propose that ARC structures are directly designed by using the conventional ARC theory instead of scanning the geometric and spatial parameters of the conventional ARC structures. According to the concept of the effective refractive index of sonic crystals, the exact ARC structures can be implemented by sonic crystals. The transmission efficiency of a bending waveguide designed by graded sonic crystals can be enhanced by introducing the ARC structures based on sonic crystals. The performances of different ARC structure designs are compared and discussed.     

Spectral selectivity of radiation-and tunnel-coupled waveguide structures

The spectral transmission profile of systems of radiation-and tunnel-coupled waveguides is studied. It is determined how a smooth variation of the thickness of the buffer layer in a structure consisting of a pair of tunnel-coupled waveguides with strongly varying parameters will affect the spectral properties of the system as a whole. A simple physical treatment of the operation of a number of integrated and fiber-optic devices is given, and the prospects for using the proposed structure of two tunnel-coupled waveguides to realize a microlaser with waveguide output is demonstrated. Zh. Tekh. Fiz. 67, 59–65 (February 1997)     

慢光在光子晶体弯折波导中的高透射传播

研究了慢光模式在SOI(silicon-on-insulator)材料光子晶体线缺陷弯折波导中的传输特性. 通过优化波导弯折处的结构参数,慢光模式在光子晶体60°与120°弯折波导中的透射率提高10倍以上,归一化透射率分别达到80%和60%以上. 为了进一步减慢光速,设计了新颖的高Q值耦合腔弯折波导结构,在归一化透射率达到75%的基础上,光波群速度低至c/170(c为真空光速). 研究结果对于增强光子晶体的慢光效应,提高光子晶体慢光器件的微型化和集成化都有一定的积 关键词： 光子晶体 慢光 弯折波导 透射率     

A multimode model of a waveguide laser cavity with mirrors of arbitrary radius of curvature

A multimode model is developed to determine optical losses in a waveguide laser cavity of cylindrical symmetry with mirrors of arbitrary radius of curvature. Within the framework of the model, it is possible to vary the parameters of the resonator: waveguide length, distance between the waveguide and mirrors, radius of curvature of the mirrors in a wide range taking account of mutual conversion of up to 10 waveguide modes and 20 modes of free space. The model was applied successfully to determine the optimal geometry of a semiconfocal cavity. A. N. Sevchenko Scientific-Research Institute of Physical Problems, 7 Kurchatov Str., Minsk, 220064, Belarus; e-mail: v.saetchnikov@rfe.bsu.unibel.by. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 6, pp. 779–783, November–December, 1999.     

On the theory of a microwave pulse compressor based on a barrel-shaped cavity

We consider a passive microwave pulse compressor based on an open barrel-shaped cavity coupled to a waveguide with perforation in the common wall [1] and calculate the radiation decrement of the cavity mode and the transmission coefficient of the waveguide mode. Institute of Applied Physics of the Russian Academy of Sciences, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 42, No. 10, pp. 977–981, October, 1999.     

Perforated coaxial exciter of the higher-order mode of a barrel-shaped cavity

We propose to excite a mode with the rotating field structure in an axisymmetric cavity by a coaxial doubly periodic perforated waveguide. The found relationship between the parameters of the system ensures the total energy transfer from the waveguide to the cavity. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 49, No. 8, pp. 673–679, August 2006.     

Plasmonic slow light waveguide and cavity

In this work, we present a detailed analysis of optical properties of metal–insulator and metal–insulator–metal (MIM) structure-based surface-plasmon waveguides and cavities. It is shown from the dispersion relation, the field distribution, the quality factor Q, and the transmission spectrum that the MIM structure can be designed as a high-Q cavity, supporting slow light with tolerable pulse distortion and lower propagation loss in the axial direction.     

Surface plasmon resonance and field confinement in graphene nanoribbons in a nanocavity

In this work, we demonstrate surface plasmon resonance properties and field confinement under a strong interaction between a waveguide and graphene nanoribbons (GNRs), obtained by coupling with a nanocavity. The optical transmission of a waveguide–cavity–graphene structure is investigated by finite-difference time-domain simulations and coupled-mode theory. The resonant frequency and intensity of the GNR resonant modes can be precisely controlled by tuning the Fermi energy and carrier mobility of the graphene, respectively. Moreover, the refractive index of the cavity core, the susceptibility χ⁽³⁾ and the intensity of incident light have little effect on the GNR resonant modes, but have good tunability to the cavity resonant mode. The cavity length also has good tunability to the resonant mode of cavity. A strong interaction between the GNR resonant modes and the cavity resonant mode appears at a cavity length of L₁ = 350 nm. We also demonstrate the slow-light effect of this waveguide–cavity–graphene structure and an optical bistability effect in the plasmonic cavity mode by changing the intensity of the incident light. This waveguide–cavity–graphene structure can potentially be utilised to enhance optical confinement in graphene nano-integrated circuits for optical processing applications.     

A Multilayer Waveguide Window for Wide-Bandwidth Millimeter Wave Tubes

A multilayer waveguide window is demonstrated to exhibit wide bandwidth and high transmission for applications in high-frequency microwave tubes. A transfer matrix approach is employed to discretize the dielectric function profile of the multilayer heterostructure in a rectangular waveguide. The closed form has been obtained and the corresponding reflection and transmission characteristics have been carried out. The analytical calculation is also compared with the result of numerical simulation via the finite-element code HFSS. The exact calculation agrees with the numerical simulation very well. By comparison, the approach not only enhances the accuracy and efficiency, but also gives a good criterion for the design. The results show that the bandwidth for a transmission of 99%, i.e., S ₁₁ below –20 dB, can be optimized to be about 8.75 GHz at a central frequency of 35 GHz or about 25%. A wide-bandwidth waveguide window can be easily designed for Ka-band and W-band tubes, and even for higher frequency ones.     

含半圆弧形腔的量子波导中声学声子输运和热导特性

采用散射矩阵方法,研究了在应力自由和硬壁两种典型的边界条件下含半圆弧形腔的量子波导中声学声子输运和热导性质.结果表明在两种边界条件下声子透射谱和热导有着不同的特征.在应力自由边界条件下,能观察到普适的量子化热导现象,当结构为一理想的量子线时,在低温区域有一个量子化平台出现,而当半圆弧形结构存在时,非均匀横向宽度引发的弹性散射使得量子化平台被破坏;在硬壁边界条件下,不可能观察到量子化热导现象,热导随温度的增加单调上升;计算结果表明还可以通过调节半圆弧形结构的半径来调控声子的输运概率和热导. 关键词： 声学声子输运 热导 量子体系     

基于耦合T型空腔的多重法诺共振现象

提出由T型空腔和挡板组成的两种金属-电介质-金属(MIM)波导结构,分别为:正T型空腔结构和倒T型空腔结构,并应用有限元法系统地研究了该结构的透射特性.对于正T型空腔结构,仿真结果出现了双重法诺共振现象,并且共振波长可以通过改变T型空腔长度和高度进行调节.该结构有助于设计成敏感度达到1 620nm/RIU、品质因数为5.4×10~4的纳米传感器.对于倒置T型空腔,在波导中产生了多重法诺共振现象,其敏感度可达1 560nm/RIU,品质因数为9.37×104.该结构有望在光学集成回路,特别是纳米传感器、光束分路器方面具有广泛应用.     

Si-based optoelectronic devices and their attractive applications

The semiconductor photonics and optoelectronics which have a great significance in the development of advanced high technology of information systems will be discussed in this paper. The emphasis will be put on the recent research carried out in our laboratory in enhanced luminescence from low dimensional materials such as SiGe/Si and Er-doped Si-rich SiO₂/Si and Er-doped Si _x N _y /Si. A ring shape waveguide structure, used to promote the effective absorption coefficient in PIN photodetector for 1.3 μm wavelength and a resonant cavity enhanced structure, used to improve the quantum efficiency and response in heterostructure photo-transistor (HPT), are also proposed in this paper. Presented at the 1st Czech-Chinese Workshop “Advanced Materials for Optoelectronics”, Prague, Czech Republic, June 13–17, 1998.     

Broadband tunable external cavity laser using a bent-waveguide quantum-dot superluminescent diode as gain device

A broadband tunable grating-coupled external cavity laser is realized by employing a self-assembled InAs/GaAs quantum-dot (QD) superluminescent diode (SLD) as the gain device. The SLD device is processed with a bent-waveguide structure and facet antireflection (AR) coating. Tuning bandwidths of 106 nm and 117 nm are achieved under 3-A and 3.5-A injection currents, respectively. The large tuning range originates essentially from the broad gain spectrum of self-assembled QDs. The bent waveguide structure combined with the facet AR coating plays a role in suppressing the inner-cavity lasing under a large injection current.     

Visualization of low Reynolds boundary-driven cavity flows in thin liquid shells

Abstract  

Classic examples of low-Reynolds recirculating cavity flows are typically generated from lid-driven boundary motion at a solid–fluid interface, or alternatively may result from shear flow over cavity openings. Here, we are interested in an original family of boundary-driven cavity flows occurring, in contrast to classic setups, at fluid–fluid interfaces. Particle image velocimetry (PIV) is used to investigate the structure of internal convective flows observed in thin liquid shells. Under the specific configuration investigated, the soap bubble’s liquid shell is in fact in motion and exhibits sporadic local “bursts”. These bursts induce transient flow motion within the cavity of order Re ∼ O(1). The combination of PIV and proper orthogonal decomposition (POD) is used to extract dominant flow structures present within bubble cavities. Next, we show that thermally induced Marangoni flows in the liquid shell can lead to forced, (quasi) steady-state, internal recirculating flows. The present findings illustrate a novel example of low-Reynolds boundary-driven cavity flows.     

Direct laser-writing of dielectric-loaded surface plasmon–polariton waveguides for the visible and near infrared

We demonstrate flexible and low-cost fabrication of dielectric-loaded surface plasmon–polariton waveguides. The waveguide structures are fabricated by two-photon polymerization of commercially available, spin-coatable epoxy-based UV-lithographic resist on a metal covered glass slide. The excitation and guiding properties of the plasmonic waveguides are investigated in the far-field at a wavelength of 632.8 nm by imaging the leakage radiation from the waveguide modes. The optimum bending radius for right angle bends is measured to 6 μm providing a transmission of up to 70%. The functionality of more complex Y-splitters is demonstrated.     

Bioinspired Si subwavelength gratings by closely-packed silica nanospheres as etch masks for efficient antireflective surface

We experimentally investigate the antireflective properties of various silicon (Si) subwavelength grating (SWG) structures using closely-packed silica nanospheres monolayers with different sizes as etch masks and a subsequent inductively coupled plasma (ICP) etching, together with theoretical calculations based on a rigorous coupled wave analysis method. The geometric structure of Si SWGs is optimized by changing the size of nanospheres and ICP etching parameters. The antireflective properties depend strongly on the period, height, and shape of the hexagonally ordered SWG structures, especially correlated with ICP etching parameters. For an optimized Si SWG structure with a rounded cone shape, the reflectance is significantly reduced, indicating a low reflectance of <4.4% over a wide wavelength region of 300–1100 nm. From theoretical analysis, the reflectance of rounded cone-shaped Si SWG structures is minimized with a period of ∼300–350 nm and heights of >750 nm, which is reasonably consistent with the experimental results. The angle-dependent antireflection characteristics are also discussed.     

Approximate and Conditional Teleportation of an Unknown Atomic State Without the Bell-state Measurement with Multi-photon Interaction

A scheme for approximately and conditionally teleporting an unknown atomic state via multi-photon interaction in cavity quantum electro dynamics (QED) is proposed. It is the extension of the scheme of Zheng (2004) [Physical Review A69, 064302], which is based on Jaynes–Cummings model in QED and where only a time point of system evolution and the corresponding Fidelity implementing the teleportation are given. In our scheme, the cavity field may be Fock state and the multi-photon interaction Jaynes–Cummings model is used to realize the approximate and conditional teleportation. Our scheme does not involve the Bell-state measurement and an additional atom, only requiring two atoms and one single-mode cavity. The fidelity of the scheme is higher than that of Zheng (2004) [Physical Review A69, 064302]. The scheme may be generalized to not only the teleportation of the state of a cavity mode to another mode by means of a single atom but also the teleportation of the state of a trapped ion. PACS: 03.67.-Ta, 03.65.Ta, 42.50.Dv     

Infrared transmissivity of heavily doped contact layers on extrinsic silicon IR-detectors

The infrared transmissivity of heavily dopedp-type contact layers on silicon was studied in the 3–5 μm and 8–14 μm wavelength range in order to optimise the layer thickness and doping concentration for antireflection coating. The transmissivity of surface layers and buried layers was computed taking into account the free carrier optical dispersion by the Drude theory and corrections due to intervalence band transitions as well as multiple reflections and interferences in the layer. The computations are in quantitative agreement with measurements on contact layers formed by multiple boron implantation. It was found that the free carrier absorption loss completely cancels the gain due to the antireflection effect for a surface layer. Transmissivities of around 73% may be obtained by a buried heavily doped layer.     

量子点调制的一维量子波导中声学声子输运和热导

利用散射矩阵方法,比较了被一维凸形量子点、凹形量子点调制的量子线中膨胀模的声子输运和热导性质. 研究结果表明: 声子的输运概率与热导受制于量子点几何结构,具有凸形量子点结构的量子线中声子输运概率与热导K_CV大于具有凹形量子点结构的量子线中声子输运概率与热导K_CC. 两者热导之比K_CV/K_CC依赖于一维量子点的具体结构,且随着温度及主量子线与量子点横截面的边长差Δ_SL的增加而增加. 两种具有不同散射结构的一维量子线中热输运性质的区别在于凸形量子点结构中膨胀模数量总是大于凹形量子点结构中膨胀模数量的缘故. 关键词： 声学声子输运 热导 量子结构     

Cross-sectional study of femtosecond laser bulk modification of crystalline α-quartz

Bulk irradiation of crystalline α-quartz was performed with ∼170-fs laser pulses with a wavelength of 800 nm focused below the sample surface. Investigations were carried out using transmission electron microscopy on a cross-sectional specimen prepared using focused ion beam techniques. We observed alternating amorphous–crystalline structures with sharp transitions and associated density changes, surrounded by a highly strained crystalline structure. The alternating sub-surface structures are parallel to the laser’s electric field polarization and exhibit a spacing which is close to the laser wavelength in air. Cracking was also observed in the near proximity of these structures.