Energy transport in plasmon waveguides on chains of metal nanoplates

An interest in energy transport in 3D chains of metal nanoparticles is oriented towards future applications in nanoscale optical devices. We consider plasmonic waveguides composed of silver nanoplates arranged in several geometries to find the one with the lowest attenuation. We investigate light propagation of 500-nm wavelength along different chains of silver nanoplates of subwavelength length and width and wavelength-size height. Energy transmission of the waveguides is analysed in the range of 400–2000 nm. We find that chain of short parallel nanoplates guides energy better than two electromagnetically coupled continuous stripes and all other considered nonparallel structures. In a wavelength range of 500–600 nm, this 2-μm long 3D waveguide transmits 39% of incident energy in a channel of λ × λ/2 cross section area.     

Enhancing Bremsstrahlung production from ultraintense laser-solid interactions with front surface structures

A new type of a coaxial multi-layer plasmonic waveguide is proposed. The mode propagation properties are analyzed at the communication working wavelength. Theoretical investigations reveal that the enhanced optical confinement can be achieved in the two low-index dielectric media layers. The mode size can be sub- or deep sub-wavelength scale. The mode propagation loss can be well compensated by replacing the high-index dielectric media with gain material to achieve longer propagation length with better mode confinement. The comparisons of the mode properties between the proposed waveguide and waveguides studied in the published literatures are also considered. These investigations potentially lay the groundwork for the further applications of nanowire type multilayer hybrid structures. This structure could also enable various applications such asnanophotonic waveguides, high-quality nanolasers, and optical trapping and biosensors.     

Tunnelling leaky modes on optical waveguides

The lossless dielectric waveguide of circular cross section with an index of refraction greater than its surround supports trapped modes in addition to two subclasses of leaky modes: refracting and tunnelling modes. Refracting modes leak because their fields are formed by waves that undergo refraction at the core-cladding interface. Tunnelling modes leak because their fields are formed by waves that undergo a form of electromagnetic tunnelling at the core-cladding interface due to the curvature of its cross section. Tunnelling modes have a very slow leakage compared to refracting modes and are therefore important for the understanding of propagation in multimode, optical waveguides of circular cross section.     

Two-dimensional light confinement in cross-index-modulation plasmonic waveguides

We report a numerical study of plasmonic waveguides that localize light in two dimensions at a cross section of 4.2 nm × 2.1 nm with the propagation length of 38 μm. By varying the geometrical parameters, strong mode confinements (range from λ(2)/3352 to λ(2)/2557525) are achieved with controllable propagation distance (44.68-40.988 μm), and mode size below 1 nm(2) has been demonstrated for the first time. Furthermore, a cross-index-modulation mechanism is proposed to explain the strong field localization behavior, providing guidelines for future waveguide designs.     

Synthesis of a fluorinated photoresist for optical waveguide devices

A linear fluorinated bis-phenol-A novolac resin (LFAR) for optical waveguide was synthesized based on 4,4′-(hexafluoro-isopropylidene)diphenol, epoxy chloropropane and formaldehyde. Negative fluorinated photoresist (FP) was made by composing the LFAR, diphenyl iodonium salt and solvent. The film, which was made by spin-coating FP, had good UV light lithograph sensitivity, large hardness and high glass transition temperature (T _g >170°C, after crosslinking). Low-loss optical waveguides with very smooth top surface were fabricated from the resulting FP by direct UV exposure and chemical development. For waveguides without upper cladding, the propagation loss of the channel waveguides was measured to be 0.21 dB/cm at 1550 nm.     

Enhancement of single mode operation in coaxial optical waveguide using DB boundary conditions

In this study, a competent numerical strategy to compute the dispersion of optical waveguides is presented and propagation of electromagnetic waves in a coaxial optical waveguide with DB boundary conditions is instigated. For this intend, cylindrical coordinates are here being used to derive the DB boundary conditions and to obtain field components for the modes. The propagation constant for the waveguide to be studied is determined by solving the Bessel and the modified Bessel functions. The cutoff frequencies for various lower order modes have been calculated and their dispersion characteristics are plotted correspondingly. The behavior of the coaxial optical waveguide under DB boundary conditions is shown to be significantly different from that of coaxial optical waveguide and conventional optical waveguide under traditional or tangential boundary conditions. Finally, the effect of waveguide dimensions on the mode cutoff frequencies and fabrication issues are also addressed.     

Nanofiltering via integrated liquid core waveguides

We demonstrate and describe how nanoporous liquid core waveguides can exclude scattering particles, making them an ideal integrated platform for analysis of turbid solutions. Milk with 0.5% fat showed an optical propagation loss of 0.05?dB/mm at 633?nm in nanoporous waveguides compared to the 10.6?dB/mm loss in standard cuvette measurements. To examine the nanofiltering effect, waveguides were infiltrated with solutions containing Rhodamine B molecules (1?nm) and 22?nm red fluorescing polystyrene beads. With fluorescence spectroscopy we show that 22?nm beads are excluded, while Rhodamine B molecules penetrate the waveguides. This is further confirmed by fluorescence microscopy, also revealing a homogenous distribution of Rhodamine in the waveguide volume.     

Interference microscopy of femtosecond laser written waveguides in phosphate glass

By focusing fs-laser radiation in the volume of a transparent material the refractive index can be changed locally, leading to 3-dimensional waveguiding structures. Waveguides are written in phosphate glass (IOG from Schott) at a depth of 100 μm below the surface. The pulse energy and the scan velocity are varied. For the first time the optical path difference caused by the waveguides and therefore the refractive index distribution of the waveguides and their cross sections are determined using interference microscopy. The optical path difference measured in the written structures and their cross sections is analyzed by a phase-shift algorithm. Thus, the refractive index distribution both along a line perpendicular to the waveguide and in the plane of a cross section is determined. The results are visualized as 2-dimensional graphics. Several regions of opposite sign of the refractive index change are observed in the cross sections of waveguides generated by femtosecond laser pulses. The number and the size of these regions are increasing with increasing pulse energy and decreasing scan velocity.     

Four layer polymeric mode polarization filter for integrated optics

We report on our systematic study of fabrication and characterization of four-layer polymer waveguides. Various optical properties (such as refractive index, birefringence, and propagation loss) of polycarbonate and polystyrene waveguides are presented. The thin film structure consisting of glass/polycarbonate/polystyrene/air has been used for demonstrating polarization filter action because the two polymers are quite different with respect to their optical anisotropy. Modal electric field plots for both TE and TM are generated to support the observed behavior. It is also observed that the four-layer lightguide exhibits relatively low loss values compared to the monolayer configuration.     

梯形截面脊波导的特性分析

提出了用有效折射率法结合转移矩阵理论对梯形截面脊波导进行数值分析的新方法。对梯形截面脊波导中模式传播常数和模式间耦合系数的分析表明,梯形截面脊波导与稍宽的矩形截面脊波导行为相同。这一结论有利于简化梯形截面脊波导的设计,提高实际器件的精度。     

Low-loss polymeric optical waveguides with large cores fabricated by hot embossing

A simple low-cost method of fabricating polymeric optical waveguides with large core sizes for plastic optical fibers is presented. The waveguides are fabricated by hot embossing with an ultraviolet-cured epoxy resin stamper. The stamper is fabricated by replication of a rectangular groove mold that is made from silicone rubber replicated from a ridged original silicon master. The master is fabricated by anisotropic etching of (110) single-crystal silicon. Optical waveguides with large core sizes of 100-500 microm have been fabricated, and a low propagation loss of 0.19 dB/cm at 650 nm was achieved.     

Synthesis of photosensitive poly(methyl methacrylate-co-glycidyl methacrylate) for optical waveguide devices

Photosensitive poly(MMA-co-GMA) for optical waveguide was synthesized, and the refractive index of the polymer film was tuned in the range of 1.481–1.588 at 1550 nm by mixing with bis-phenol-A epoxy resin. The film, which was made by spinning coated the poly(MMA-co-GMA) with photo initiator, had good UV light lithograph sensitivity, high glass transition temperature (T _g : 153°C, after crosslinking) and good thermal stabilities (T _d : up to 324°C, after crosslinking). The optical waveguides with very smooth top surface were fabricated from the resulting polymer by direct UV exposure and chemical development. For waveguides with cladding, the propagation losses of the channel waveguides were measured to be below 3 dB/cm at 1550 nm.     

Fabrication of hollow optical waveguides in fused silica by three-dimensional femtosecond laser micromachining

We report on the fabrication of hollow optical waveguides in fused silica using femtosecond laser micromachining. We show that in such hollow waveguides, high-intensity femtosecond laser beams can be guided with low optical loss. Our technique, which was established earlier for fabrication of optofluidic structures in glass, can ensure a high smoothness at the inner surfaces of the hollow waveguides and provide the unique capability of fabrication of hollow waveguides with complex geometries and configurations. A transmission of ∼90% at 633 nm wavelength is obtained for a 62-mm-long hollow waveguide with an inner diameter of ∼250 μm. In addition, nonlinear propagation of femtosecond laser pulses in the hollow waveguide is demonstrated, showing that the spectral bandwidth of the femtosecond pulses can be broadened from ∼27.2 to ∼55.7 nm.     

L波段紧凑型TEM-TE11模式转换器

设计了一种适用于窄带高功率微波源系统的紧凑型TEM-TE11模式转换器。该结构首先将同轴波导沿角向分区使微波在各分区内相位传播常数不同,然后将相位传播常数较大的分区进行横向折叠设计以缩短系统轴向长度。分区传播的微波在模式转换器末端相位差达到180时,合成同轴波导中TE11模式。为L波段磁绝缘振荡器设计了模式转换器,并采用数值仿真程序进行计算,在1.31 GHz中心频率上,模式转换器转换效率为95%;在1.23~1.40 GHz频率上,模式转换器效率大于90%,相对带宽13%。将模式转换器应用于磁绝缘振荡器,并测量了天线的定向辐射能力,所得结果与设计一致。     

Proposal for a 4-channel all optical demultiplexer using 12-fold photonic quasicrystal

In this work, 12-fold photonic quasicrystal (PQC) with cross section equals to 138 μm² has been used to design a 4-channel optical demultiplexer. The size of structure promises its applications in optical integrated circuits (OICs) and also, wavelength division multiplexing (WDM) communication devices. Finite difference time domain (FDTD) method has been employed in order to investigate the structure's band gap and output waveforms of each channel. Four channels, with spacing less than 1 nm and cross-talk level better than ? 2.8 dB have been separated by introducing defects in L-shaped and line defect waveguides (LDWs) in the crystal's structure. It has been shown that, L-shaped waveguides (LWs) are quite more frequency selective than line defect waveguides. Also, it has been found that the exact tuning of the central wavelength of each channel is possible by making use of defects with different radiuses and sites in the waveguides.     

硅衬底上锗硅合金光波导设计及工艺的优化考虑

报道用射频加热化学气相沉积法制备Ｓｉ／ＧｅＳｉ／Ｓｉ大断面单模脊形光波导中设计和工艺的进一步完善，ＧｅＳｉ合金层中Ｇｅ的含量Ｘ要满足脊形光波导是单模，光波导的数值，孔径接近单模光纤值，脊高小于临界厚度值等，计算表明兼顾上述三项要求应取ｘ＝１～３％，脊的高与宽受大断面及单模的制约。Ｓｉ的晶体结构使脊的二个腐蚀侧壁是斜坡，为此起始脊宽取５～６μｍ为宜；腐蚀液，抛光液的选取人保证脊则壁及波导面端的优良镜     

数码照相法测量离子交换平面光波导损耗特性

利用数码相机对离子交换平面玻璃光波导传输线进行数字成像,根据传输线上的光强分布拟合出光强传输衰减曲线,计算出波导的传输损耗.对光波导进行退火处理,研究了波导退火前后的传输损耗特性.退火后0阶模式下传输损耗由2.148 9 dB·cm－1降为0.746 0 dB·cm－1.结果表明,波导的传输损耗是随着模阶数的增加而递增,适当的退火处理明显改善了离子交换波导的质量.     

Determination of refractive index profiles of gradient optical waveguides by ellipsometry

Ag⁺-Na⁺ and K⁺-Na⁺ ion-exchanged optical waveguides in soda-lime glass are characterised by ellipsometry. Refractive index profiles of the waveguides are calculated from ellipsometric multiple angle of incidence data using the Newton-Kantorovitch type iterative procedure and compared with those reconstructed by inverse WKB method. It is demonstrated that such continuous profiles with relatively small index gradient (of the order of 0.1 and 0.01), extending to few micrometers in depth, can be determined by ellipsometric measurements. A good agreement is found between results obtained by ellipsometry and by the inverse WKB method at depths above 500–600 nm, while there is a difference in the subsurface region, where ellipsometry is more sensitive to the quality of the surface. The profiles obtained by the two methods are consistent if the surface thin layer is etched.     

扩散平面光波导的传递函数方法

引入一种计算光波导传播特性的新方法传递函数方法。给出了公式推导,计算了扩散各向同性及扩散各向异性平面光波导的传播特性,并与其它方法所得结果进行了比较。结果表明用传递函数方法处理折射率渐变分布的光波导问题,计算相对简单,可以得到精确的数值结果。