THz波在金属镀层空芯波导中传输的理论和实验研究

本文基于微扰法求得不同金属镀层空心圆波导中各模式的损耗系数,对金属镀层空芯波导中THz波传输损耗随金属材料、波导结构等参数的变化关系进行了数值模拟.根据数值分析结果,优化设计并拉制了内径为1.1 mm的镀银空芯波导,实验测得当THz波的频率为2.5 THz时,传输损耗为8.6 dB/m,实现了THz波短距离的有效传输. 关键词： 太赫兹波 金属空芯波导 传输损耗     

8 mm回旋行波管和返波管的三折螺旋波纹波导色散分析

 三折螺旋波纹波导使TE11模和TE21模相互耦合,其色散曲线能够在宽频带内与电子回旋共振,因此需要对色散方程进行研究。提出了适合工程实用的行波模式和返波模式的色散方程,并对方程中的耦合系数进行了简化,误差在1%左右。利用CST软件的VBA语言对螺旋波纹波导进行建模和计算,根据模拟得到的传输特性曲线的特点,提出一种模拟方法,将模拟与理论计算得到的色散曲线作对比,误差在5%左右。     

A long-range hybrid THz plasmonic waveguide with low attenuation loss

Numerical solutions are obtained for the proposed novel hybrid terahertz plasmonic waveguide structure, namely the silicon metal silicon (SMS) waveguide. It is shown that the SMS waveguide can overcome the diffraction limit while still maintaining a sizeable propagation length. The geometric dependence of the mode characteristics of this structure is analyzed in detail, showing strong confinement and low loss with propagation lengths exceeding 14 mm at normalized mode areas of 1.72 × 10⁻². By using the FEM method (Comsol), the guiding properties of the hybrid terahertz surface plasmon polariton (HTSPP) waveguide are numerically analyzed at the THz frequency, and a combination of double-structured comparisons of the best features of the terahertz plasmonic waveguide is made. Depending on the height used and how the mode confinement is measured, various modal designs, such as double microwire structures, are developed. The structures indicate that we verified the possibility of low attenuation loss of hybrid THz plasmonics propagation. The effective mode area A_eff, energy distribution, and propagation length L_p versus height for waveguides with Si microwire and SiO₂ are shown. The numerical calculation results reveal a potential for use in applications such as optical force in trapping and transporting biomolecules, and in high-density integrated circuits.     

Compact multimode interference coupler with tapered waveguide geometry

In this paper, a novel MMI coupler, based on general interference, with tapered waveguide geometry has been proposed for reduction of coupling length. The coupling characteristics and power imbalance of the proposed structure are compared with conventional MMI structures by using a mathematical model based on sinusoidal modes. It is seen that the beat length for tapered MMI coupler with angle of taper ∼1.05° is reduced by ∼24% of that of conventional MMI coupler and the coupling characteristics obtained with the mathematical model, match well with those obtained by more sophisticated BPM computer aided design software. The power imbalance for tapered 3 dB MMI coupler is more sensitive to the wavelength than that for conventional 3 dB MMI coupler and variation of power imbalance with fabrication tolerance for both the MMI coupler is almost same.     

Grey screening-photovoltaic soliton-induced waveguides

This paper shows that waveguides induced by grey screening-photovoltaic solitons are always single mode for all intensity ratios, which are the ratio between the peak intensity of the soliton and the dark irradiance. It finds that the confined energy near the centre of the grey soliton and the propagation constant of the guided mode increase monotonically with increasing intensity ratio. On the other hand, when the soliton greyness increases, the confined energy near the centre of the grey soliton and the propagation constant of the guided mode reduce monotonically. When the bulk photovoltaic effect is neglected for short circuits, these waveguides become waveguides induced by grey screening solitons. When the external bias field is absent, these waveguides become waveguides induced by grey photovoltaic solitons.[第一段]     

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。     

Modal attenuation in metal-clad graded-index slab optical waveguides

The paper presents the influence of refractive profile shape on the distribution of modal attenuation in planar metal-clad optical waveguide structures. A calculation method has been presented in which we applied the Snyder–Love expression on modal attenuation coefficients and matrix method 4 × 4 for the analysis of planar waveguides. The obtained results are almost identical with the exact results for refractive profiles: the parabolic, exponential, Gaussian and linear ones. It has been demonstrated that the applied calculation method can be used in waveguides of any profiles of the refractive index.     

0.73～1.7μm超宽带微纳光纤波导全光调制器

提出了单层石墨烯包裹双锥形微纳光纤复合波导结构,构建了730~1 700nm超宽带微纳光纤波导全光调制器。通过火焰拉锥法将一根标准的通信单模光纤拉成具有双锥形的微纳光纤,在保证通光率的前提下可以极大的提升微纳光纤处的倏逝波与物质的相互作用。利用石墨烯的"超级特征",即单原子层厚度、线性色散的能带结构、超强的载流子带间跃迁及极短的弛豫时间和超宽带光与物质相互作用等,将单层石墨烯作为可饱和吸收体,包裹在双锥形微纳光纤波导的锥体上,以增强该复合波导表面倏逝波与石墨烯的相互作用。静态和动态全光调制实验中采用传统808nm低功率LD作为泵浦光,对谱宽为480~1 700nm的超连续谱探测光实现了光光调制,其泵浦光功率低于50mW,调制深度大于5.7dB,调制速率达到~4kHz。该微纳光纤波导全光调制器,在保证调制深度的情况下,用更低的泵浦功率实现了超宽带的全光调制,以简单、有效、廉价的方式兼容了当前高速光纤通信网络,打开了一扇未来对微纳超快光信号处理的大门。     

掺铒聚合物狭缝波导放大器的增益特性研究

设计了一种高浓度稀土铒掺杂聚合物填充硅狭缝结构的平面光波导放大器（工作波长1 550 nm,泵浦波长1 480 nm）,能够在低泵浦下获得高增益,可以应用于硅基光互联的损耗补偿。通过扫描电镜照片观察发现,合成的铒掺杂聚合物材料具有良好的纳米狭缝填充能力。考虑铒离子的合作上转换和激发态吸收,利用铒离子四能级跃迁模型,建立原子速率方程和光功率传输方程,数值仿真分析了聚合物光学性质、狭缝波导结构参数及信号光泵浦光功率等放大器增益特性的影响因素。这种具有纳米截面尺寸的光波导放大器,获得4.5 dB的信号光相对增益仅需要1.5 mW的泵浦光,展现了良好的集成光学应用前景。为了进一步提高增益,引入了多层狭缝结构,四层狭缝波导的重叠积分因子比一层狭缝的高42%。     

Fabrication of fluorinated polyimide optical waveguides by micropen direct writing technology

A novel and cheap direct writing method based on the micropen has been developed to fabricate fluorinated polyimide stripe optical waveguides on Si/SiO₂ wafers. The overall design, starting material, micropen direct writing system and fabrication processes of the stripe optical waveguides are presented. The effects of the key direct writing parameters, such as the tip-to-substrate distance, extrusive gas pressure, writing speed and viscosity of the polyamic acid, on the dimension and morphology of the stripe optical waveguides are discussed in detail. After deposition by the micropen system and baking process, the fluorinated polyimide stripe optical waveguides with good morphology and surface quality can be fabricated using the optimal parameters. The propagation losses at the wavelength of 1.55 μm are in the range of 1.4-3.5 dB cm⁻¹ as characterized by different length combinations of the strip optical waveguides.