高性能Ag/AgI红外空芯光纤的研究

采用液相化学镀膜法研制了内面镀有银膜和碘化银膜(Ag/AgI)的高性能空芯红外光纤.分析了绿色导航光和红外激光同时低损耗传输的光纤结构参量.长度1 m、内直径0.7 mm的Ag/AgI空芯光纤不仅在红外有低损耗传输特性,而且首次在波长530 nm处获得了7 dB/m的低传输损耗特性.满足可见光作为导航光的同轴传输要求.通过分析和改进实验工艺参量,有效降低Ag和AgI薄膜的表面粗糙度.给出了高性能Ag/AgI空芯光纤的介质镀膜的具体工艺参量.     

Coupling external cavity mid-IR quantum cascade lasers with low loss hollow metallic/dielectric waveguides

We report on the optical coupling between hollow core waveguides and external cavity mid-IR quantum cascade lasers (QCLs). Waveguides with 1000???m bore size and lengths ranging from 2 to 14?cm, with metallic (Ag)/dielectric (AgI or polystyrene) circular cross-section internal coatings, have been employed. Our results show that the QCL mode is perfectly matched to the hybrid HE₁₁ waveguide mode, demonstrating that the internal dielectric coating thickness is effective to suppress the higher losses TE-like modes. Optical losses down to 0.44?dB/m at 5.27???m were measured in Ag/polystyrene-coated waveguide with an almost unitary coupling efficiency.     

Silver/polystyrene-coated hollow glass waveguides for the transmission of terahertz radiation

We have applied techniques developed for IR waveguides to fabricate Ag/polystyrene (PS) -coated hollow glass waveguides (HGWs) for transmission of terahertz radiation. A loss of 0.95 dB/m at 119 microm (2.5 THz) was obtained for a 2 mm bore, 90 cm long Ag/PS HGW. We found that TE modes are supported in HGWs with thin PS films, while hybrid (HE) modes dominate when PS film thickness increases. The lowest losses are obtained for the thicker PS films and the propagation of the HE modes.     

Loss reduction of dielectric-coated metallic hollow waveguides for CO2 laser light transmission

A condition for reducing transmission loss of a dielectric-coated metallic hollow waveguide is shown theoretically when the inner metallic surface is not perfect. It is also shown that the transmission loss for CO₂ laser light is 10.6 μm wavelength is able to be estimated from an attenuation spectrum of a short waveguide. By fabricating a ZnSe coated Ag hollow waveguide of short length, we have shown that it has a lower loss than a Ge coated waveguide for CO₂ laser light.     

Dependence of the optical properties of UHV deposited silver thin films on the deposition parameters and their relation to the nanostructure of the films

Silver films were deposited on glass substrates under different deposition conditions, i.e. different film thicknesses, deposition rates and deposition angles. Their optical properties were measured by spectrophotometry in the spectral range of 185–3300 nm. The Kramers–Kronig method was used to analyze the reflectivity curves of the silver films to obtain their optical constants. The influence of substrate temperature on the microstructure of thin metallic films, the structure zone model (SZM), is well established, whereas there has been some previous work on the influence of film thickness and morphology, deposition rate and deposition angle on the microstructure and morphology of thin films. An effective medium approximation (EMA) analysis was used to establish the relationship between the atomic force microscopy results, SZM predictions and EMA results, and hence the optical properties of silver thin films. The predictions of the Drude free-electron theory are compared with experimental results for dielectric functions of Ag films produced under different deposition conditions. The real part of the dielectric constant increases with film thickness and decreases with increasing deposition rate and with increasing incidence angle, whereas the imaginary part of the dielectric constant decreases with increasing film thickness and deposition rate and with decreasing incidence angle over the whole energy range measured, including the interaband and interband regions.     

介质镀膜空芯光纤在THz频段的传输特性

 理论分析了介质镀膜空芯光纤在THz频段的传输特性，得出了该光纤的特征方程及模式分布。利用射线光学原理计算了介质膜材料为聚酰亚胺、介质膜厚度为0.05 mm的光纤的衰减常数随介质膜内直径的变化情况。得出其主模在THz频段的衰减常数小于1 dB/m，该值远小于相同内径的金属圆波导在这一频段的衰减常数。模拟计算了介质膜厚度为0.05 mm、内径为1 mm，金属膜内径为1.05 mm的介质镀膜空芯光纤在0~1 THz的S参数，模拟结果显示该光纤在THz频段有很宽的通带，且在通带内衰减常数小于0.5 dB/m，可用于THz频段电磁波远距离传输。     

THz波段介质涂敷空芯金属圆波导的传输特性

针对THz波段介质涂敷空芯金属圆波导传输特性的精确分析问题,基于波导中场方程及边界条件建立关于传播常数的特征方程,并且采用改进的Muller法求解特征方程得到涂敷圆波导主模HE11模的传播常数。计算中对THz波段的非理想导体电导率采用经典弛豫效应模型。仿真结果表明:内径为1.8 mm的银波导,当聚苯乙烯涂敷层厚度为17 m时,HE11模在1.5~3.0 THz的衰减常数在1 dB/m以下,且具有较好的色散特性;内径为2.2 mm的银波导,在2.5 THz时其衰减常数随涂敷层厚度的增加先增大后减小,且存在最佳介质涂敷层厚度,可实现THz波低损耗传输。     

银薄膜对光学基底表面粗糙度及光散射的影响

为了研究金属银薄膜与光学基底表面粗糙度和光散射的关系,提出了通过对光学薄膜矢量散射公式积分来获得界面粗糙度完全相关模型和完全非相关模型下其表面的总反射散射的方法.理论计算了光学基底上两种模型在不同厚度银膜下的总反射散射和双向反射分布函数.结果表明,当沉积在光学基底上的银薄膜的厚度大于80 nm后,两种模型下计算的银薄膜的表面总反射散射都等于基底的总积分散射,银薄膜能较好地复现出基底的粗糙度轮廓.实验研究表明为了复现基底的粗糙度,银薄膜的最佳厚度应在80~160 nm之间.     

Experimental analysis of metal coated dielectric waveguides

This paper concerns the experimental characteristics of metal coated dielectric waveguides with a rectangular surface corrugation. Waveguide are designed to operate at a second Bragg frequency of 90 GHz. The period, height and the duty cycle of a rectangular grating were calculated using the chosen frequency. A metallic layer of aluminum is sputtered on one side of the slab waveguide. The purpose of the metallic layer is to simulate a layer of high density plasma on the surface of the waveguide similar to that obtained by optical excitation of semiconductor structures. Experiments were performed to examine the far field radiation pattern, attenuation constant and the dispersion relation. Due to the presence of the plasma layer there will be an angular shift in the far field radiation pattern. We have observed angular shifts of about 20 in the radiation pattern of the waveguide before and after coating. Measurements are made in the frequency range of 88–95 GHz. This waveguide structure can be used to design an electronically steerable antenna and an electronic phase shifter operating in the millimeter-wave frequency band.Supported in part by the Army Research Office.     

Surface plasmon–exciton transition in ultra-thin silver and silver iodide films

Silver thin films in the thickness range 2–10 nm produced by thermal evaporation onto glass substrates were systematically iodized and carefully characterized by X-ray diffraction, atomic force microscopy (AFM) and optical absorption spectroscopy. While the uniodized films are X-ray amorphous in keeping with their quasi-continuous nature and 2D islanded structure, briefly iodized films showed characteristic beta AgI structure. Most interestingly, AFM of Ag films revealed uniform triangle-shaped embryos whose shape does not change appreciably upon iodization. Optical absorption spectra of uniodized Ag films show intense surface plasmon resonance (SPR) features with maxima at 440, 484 and 498 nm for the films of thicknesses 2, 5 and 10 nm, respectively, with 5 nm films showing properties characteristic of optimally matched dielectric and electronic properties of the substrate and sample, respectively. Finally, an interesting and unique SPR–exciton phase transition is observed as the ultra-thin films are progressively iodized. These Ag and AgI films could be promising candidates for plasmonic and nanophotonic applications. PACS 78.66.-w; 73.20.Mf; 71.35.Cc; 42.70; 68.37.Ps; 42.82.-m     

Infrared reflectivity and dielectric permeability of ultra-thin Cu and Al films

In this report we present an experimental investigation of the reflectivity (R) and the dielectric permeability () for Cu and Al ultra-thin films ranging in thickness from a few monolayers to 12 nm at infrared and visible wavelengths. The metal films were prepared by RF-sputtering on SiO₂ (glass) and Si substrates. IR reflectivity was measured at 9.2 μm, while was measured with the help of laser ellipsometer at a wavelength of 632.8 nm. Two types of oscillations on R(d) and (d) were discovered for two thickness regions determined by the critical thickness value d*. Oscillations at d<d* with periods near 0.3 nm for Al and Cu films were observed on R(d) and (d) due to quantum sized effects (QSEs). At d>d* (thickness between 6–12 nm) we discover a new type of strong oscillation of R(d) and (d) with an oscillating period of 0.2 nm. For thickness larger than 12 nm all the oscillations tend to disappear and R and behave almost as their volume values. A possible explanation for the appearance of these two kinds of oscillations is based on the introduction of the critical film thickness d*.     

Theoretical study of polymeric metal clad optical waveguide polarizer

Planar optical waveguides consisting of thin dielectric films and buffer layers with metal cladding have been investigated theoretically. A computer program was written to calculate the exact zeroes of complex eigenvalue equation for TE and TM modes in multilayer metal clad waveguide polarizer. Numerical results and illustrations are given for Polycarbonate waveguide with other polymers as buffer and Al, Ag and Au as cladding metals at . It is also shown that, using thin (finite) films of metal produce more efficient polarizers as compared to semi-infinite metal films. Effect of low index buffer layer on attenuation of TM/TE modes is also investigated.     

Low loss smart hollow waveguides with new polymer coating material

A new kind of cyclic olefin polymer COP-E48R has been selected as the dielectric material for a silver hollow glass tube. Owing to its lower extinction coefficient at the wavelength of 10.6 μm, transmission losses for the CO₂ laser light has been reduced significantly in the COP-E48R-coated silver (COP-E48R/Ag) hollow glass waveguide. By properly selecting the film thickness of COP, Er:YAG and CO₂ laser light are shown to be transmitted with low loss simultaneously or independently. Delivery properties of red and green pilot beams were also evaluated.     

Er3+-Yb3+共掺磷酸盐玻璃光波导的FD-BPM分析

阐述了三维波导结构的FD-BPM原理,并用FD-BPM法模拟了波长为1.54μm和0.98μm的高斯光束在Er³⁺-Yb³⁺共掺磷酸盐玻璃光波导内光场分布.与沟道光波导相比,掩埋型光波导内的泵浦光和信号光的散射都非常小,光场分布非常均匀.研究结果表明,掩埋型光波导是制作Er³⁺-Yb³⁺共掺磷酸盐玻璃光波导激光器和放大器的理想波导.     

Waveguide trapping of hollow glass spheres

Microparticles can be trapped and propelled by the evanescent field of optical waveguides. As the evanescent field only stretches 100-200?nm from the surface of the waveguide, only the lower caps of the microparticles interact directly with the field. This is taken advantage of by trapping hollow glass spheres on waveguides in the same way as solid glass spheres. For the chosen waveguide, numerical simulations show that hollow microspheres with a shell thickness above 60?nm can be stably trapped, while spheres with thinner shells are repelled. The average refractive index of the sphere-field intersection volume is used to explain the result in a qualitative way.     

粉末靶制备的AZO/Ag/AZO透明导电薄膜的光电性能

室温下,采用射频磁控溅射AZO粉末靶和Ag靶在玻璃基底上制备Ag层厚度分别为12 nm和15 nm两组对称结构掺铝氧化锌/银/掺铝氧化锌(AZO/Ag/AZO)透明导电薄膜,研究了Ag层和AZO层厚度对薄膜光电性能的影响。结果表明:3层薄膜的可见光区平均透光率达到了80%,550 nm处的最高透过率达到了88%,方块电阻小于5 Ω/□。Ag层厚度是影响AZO/Ag/AZO薄膜光电性能的主要因素,AZO层的厚度对薄膜光学性能影响较大。     

The structure of dielectric β-SiC thin films of hollow glass waveguide for CO2 laser power delivery

A novel type of hollow glass waveguide with β-SiC dielectric films was manufactured by a modified chemical vapor deposition method. FTIR absorption spectra and SEM results show that the change of film structure is responsible for the phenomena of the blue shift and the narrow width of the fundamental absorption band of β-SiC, and that the microfissures at the films provide the heterocrystallization centers for promoting the formation of β-SiC crystal. The influences of the concentration of hydrogen gas passed through the system and the reaction temperature are discussed with regard to the film structure.     

Effects of substitution of Ti for Fe in BiFeO3 films prepared by sol–gel process

Ti substituted BiFe_1−xTi_xO_3+δ films have been prepared on indium–tin oxide (ITO)/glass substrates by the sol–gel process. The films with x=0.00–0.20 were prepared at an annealing temperature of 600 °C. X-ray diffraction patterns indicate that all films adopt R3m structure and the films with x=0 and 0.10 show pure perovskite phase. Cross-section scanning shows the thickness of the films is about 300 nm. Through 0.05 Ti substitution, the 2P_r increases to 8.30 μC/cm² from 2.12 μC/cm² of the un-substituted BiFeO₃ film and show enhanced ferroelectricity at room temperature. The 2P_r values are 2.63 and 0.44 μC/cm² for the films with x=0.01 and 0.2, respectively. Moreover, the films with x=0.05 and 0.10 show enhanced dielectric property since the permittivity increases near 150 at the same measuring frequency. Through the substitution of Ti, the leakage conduction is reduced for the films with x=0.05–0.20.     

Robust hollow devices and waveguides for Er:YAG laser radiation

Fluorocarbon-polymer (FCP) coated silver hollow stainless steel (St) devices and waveguides have been developed for Er:YAG laser radiation. Full liquid phase techniques have been adopted to coat the silver and FCP layers inside the stainless steel hollow structure. Both straight and bent robust hollow devices have been fabricated as the output optical elements for the delivery system of medical Er:YAG lasers. A robust hollow waveguide with the length of about 1.6 m has also been realized as an actual delivery system.     

Reverse-symmetry waveguides: theory and fabrication

We present an extensive theoretical analysis of reverse-symmetry waveguides with special focus on their potential application as sensor components in aqueous media and demonstrate a novel method for fabrication of such waveguides. The principle of reverse symmetry is based on making the refractive index of the waveguide substrate less than the refractive index of the medium covering the waveguiding film (n_water=1.33). This is opposed to the conventional waveguide geometry, where the substrate is usually glass or polymers with refractive indices of ≈1.5. The reverse configuration has the advantage of deeper penetration of the evanescent electromagnetic field into the cover medium, theoretically permitting higher sensitivity to analytes compared to traditional waveguide designs. We present calculated sensitivities and probing depths of conventional and reverse-symmetry waveguides and describe schemes for easy implementation of reverse symmetry. Polymer waveguides are demonstrated to be candidates for cheap, mass-producible reverse-symmetry sensor modules. The grating-coupled waveguiding films of controlled thickness are produced by soft lithography. The resulting films are combined with air-grooved polymer supports to form freestanding single-material polymer waveguides of reverse symmetry capable of guiding light. Received: 20 December 2001 / Published online: 14 March 2002