Self-cleaning effect of sealing caps for infrared hollow fiber delivering pulsed Er:YAG laser light

A sealing cap had been proposed as an output device for hollow optical fibers in delivering laser light underwater. Properties of sealing cap were experimentally discussed when used in ablation on soft tissue for Er:YAG laser. A self-cleaning effect of the sealing cap was observed when various targets were used for different laser light power. Debris from pork fat formed a uniform oil layer on the output surface of the cap, and the oil layer is relatively transparent in Er:YAG laser light wavelength band. When the target was pork muscle, almost no debris could attach on the surface of the cap. The self-cleaning effect was more obvious when ablation was conducted underwater because of the protection of the water film between the target and the cap's surface.     

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.     

Temperature sensor based on etched optical fiber with a metal coating

Presented in this work is a new class of optical fiber temperature sensor, of which the heat-expansion thin film is coated on the etched fiber. It uses the method that combine thermal carving technique with chemical etching. The sensitivity of the sensor is increased and the shape size is decreased. This sensor possesses the linear temperature response and the good repeatability. These sensors can be used to measure finely the temperature which is lower than 200°c.     

Study of non-linear properties of hollow core photonic crystal fiber

A highly non-linear hollow core photonic crystal fiber (PCF) having three ring-hexagonal structure is designed. The full vector finite element method with perfectly matched layer is used to investigate the non-linear properties of hollow core PCF effectively. The effective area of modal pattern is also studied for the same newly designed structure. It is found that when effective area is very small the non-linearity is very high.     

Characteristics of radio transmission over polymer optical fiber for indoor wireless coverage

The characteristics of radio over polymer optical fiber (RoPOF) are evaluated for indoor or in-building wireless coverage. The frequency responses and the third order intermodulation distortion products of the RoPOF link are investigated. The eye diagrams and EVM values of signals carrying quadrature-phase-shift-keyed (QPSK) data and global system for mobile (GSM) signals are measured to evaluate the transmission performance. The interference measurements with FDM are also carried out. The results show that although the nonlinear distortion and power loss deteriorate the system to some extent, making use of passband transmission, RoPOF can provide fairly good transmission performance for wireless applications.     

Cleaving of solid single mode polymer optical fiber for strain sensor applications

Single mode polymer optical fibers (smPOFs) can be applied for measuring large strains in numerous applications, such as civil engineering infrastructure assessment and health monitoring. Because of the large light attenuation of solid smPOFs, small lengths of the fiber would need to be coupled to silica optical fibers (SOFs) for practical applications of the smPOF as a strain sensor. This coupling requires smooth cleaving of the smPOFs. In this work, several cleaving techniques previously demonstrated to provide smooth cross-sections of multimode POFs were applied to the smPOF. From these techniques, hot-knife cutting was determined to be a feasible method for cleaving when the blade was heated to 80 °C and the smPOF heated in the range of 30 °C to 40 °C. In addition, focused ion beam machining which produces high-precision cleaves of the solid smPOF cross-section, was performed to set a bench mark and thus evaluate the quality of cleaving from other methods used in this study.     

Design of a highly nonlinear twin bow-tie polymer photonic quasi-crystal fiber with high birefringence

A twin bow-tie polymer-based photonic quasi-crystal fiber with high birefringence, high nonlinearity and low dispersion as well as maintaining single mode operation is presented in the wavelength range 1.8–2.2 μm. Through optimizing fiber structure parameter using a full-vector finite-element method combined with perfectly matched layers boundary condition, the birefringence is as high as 2.43 × 10⁻³, the nonlinearity is as high as 118 W⁻¹ km⁻¹, and the dispersion is only 25 ps/nm/km at 2 μm with the holes pitch of 3.3 μm. From the point of fabrication, the influences of deviation of each air hole diameter are discussed to verify the robustness of the photonic quasi-crystal fiber designed.     

A polymer photonic crystal fiber with high and flattened birefringence

A novel high birefringence polymer photonic crystal fiber (PCF) is proposed in this work. This PCF is composed of a polymer core and a cladding with elliptical air holes and squeezed triangular lattice. The high birefringence is introduced on the combined effect of elliptical air holes and the squeezed lattice. Our numerical results based on the supercell lattice method indicate that the birefringence can reach as high as 0.0018 at 650 nm wavelength with a properly designed cladding structure. We also analyze the dependence of the birefringence on structure parameters. And we design a PCF that has high and flattened birefringence.     

Highly resolved transmission infrared microscopy in polymer science

Over the last few years, the use of synchrotron-based IR sources for high-resolution microspectroscopy has been a subject of great interest. The special characteristics of synchrotron radiation allow one to obtain high quality IR spectra at high spatial resolution using commercial grade IR microscopes situated at IR beamlines. The application of this technique to the study of polymeric materials is discussed, with examples from a series of heterogeneous polymeric materials, which include polymer blends and fibre-reinforced polymer composites, from studies undertaken at the MIRAGE Beamline, LURE, Paris, France.     

聚酰亚胺(PI)薄膜用于光纤布拉格光栅湿度传感器的特性分析

研究了湿敏聚合物--聚酰亚胺(PI)薄膜用于光纤布拉格光栅湿度传感器的原理及应用,并对其传感特性进行了分析与测量.实验表明:镀有聚酰亚胺(PI)薄膜的光纤布拉格光栅的反射峰位置漂移量与湿度呈线性关系,容易标定,实现了对湿度的高精度测量.用这种材料制作的湿度传感器比其他类型湿度传感器性能优越.     

Analytical one-dimensional model for laser-induced ultrasound in planar optically absorbing layer

Ultrasound generated by means of laser-based photoacoustic principles are in common use today and applications can be found both in biomedical diagnostics, non-destructive testing and materials characterisation. For certain measurement applications it could be beneficial to shape the generated ultrasound regarding spectral properties and temporal profile. To address this, we studied the generation and propagation of laser-induced ultrasound in a planar, layered structure. We derived an analytical expression for the induced pressure wave, including different physical and optical properties of each layer. A Laplace transform approach was employed in analytically solving the resulting set of photoacoustic wave equations. The results correspond to simulations and were compared to experimental results. To enable the comparison between recorded voltage from the experiments and the calculated pressure we employed a system identification procedure based on physical properties of the ultrasonic transducer to convert the calculated acoustic pressure to voltages. We found reasonable agreement between experimentally obtained voltages and the voltages determined from the calculated acoustic pressure, for the samples studied. The system identification procedure was found to be unstable, however, possibly from violations of material isotropy assumptions by film adhesives and coatings in the experiment. The presented analytical model can serve as a basis when addressing the inverse problem of shaping an acoustic pulse from absorption of a laser pulse in a planar layered structure of elastic materials.     

用于ICF靶的空心玻璃微球的干凝胶法制备

 为用干凝胶法制备用于ICF靶的空心玻璃微球（HGM）,研究了载气组份、温度和压力对成球过程和HGM品质的影响,优化了制备工艺参数。结果表明：提高载气中氦气的含量,有利于增加干凝胶粒子的成球率和HGM的纵横比;适当提高载气中氩气的含量,有利于提高HGM的表面质量。降低载气压力可以提高HGM的纵横比;升高载气温度可以提高干凝胶粒子成球率和HGM品质。当载气中氦气的体积分数在50%~80%,载气压力在(0.75~1.00)×10⁵ Pa,载气温度在1 500~1 650 ℃时,干凝胶粒子的成球率较高,HGM的球形度、同心度和表面光洁度较好。制备得到了直径100~500 μm、壁厚0.5~3.0 μm的HGM,其耐压强度、抗大气侵蚀性能和表面粗糙度等指标均满足ICF物理实验要求。     

一种简易的光纤光栅涂覆装置

阐述了对裸光纤光栅进行涂覆的原理和必要性。设计了一种简易可行的光纤光栅涂覆装置。该装置简单灵活,成本较低,尤其适合于长度较长的光纤光栅的一次性涂覆,涂层厚度灵活可调。以啁啾光纤光栅为例进行了涂覆实验,涂层光滑均匀,涂覆后的光栅强度得到了增强,抵抗机械应力的能力得到了提高,使用起来更方便。对光栅在涂覆前后分别作了特性参数测试。结果表明,光栅特性基本上不发生变化,性能未劣化,光纤光栅的涂覆简单易行。     

Metal oxide buffer layer for improving performance of polymer solar cells

We report the application of aluminum doped ZnO (ZnO:Al) layer as a buffer on ITO glass for fabrication of non-inverted polymer solar cells. The ZnO:Al thin film was deposited using DC magnetron sputtering, with the thickness being varied from 23 to 100 nm. The devices showed most discernible improvements in their efficiencies when a thin layer of ZnO:Al film of thickness ∼40 nm was introduced. The observed enhancement in short circuit current density and open circuit voltage is likely attributed to the role of the ZnO:Al film as an optical tuner and an interfacial diffusion barrier. The result suggests that a metal oxide layer inserted between ITO and polymer layers can be a route for improving both efficiency and stability of polymer solar cells.     

Low-velocity impact damage characterization of carbon fiber reinforced polymer (CFRP) using infrared thermography

Carbon fiber reinforced polymer (CFRP) after low-velocity impact is detected using infrared thermography, and different damages in the impacted composites are analyzed in the thermal maps.The thermal conductivity under pulse stimulation, frictional heating and thermal conductivity under ultrasonic stimulation of CFRP containing low-velocity impact damage are simulated using numerical simulation method. Then, the specimens successively exposed to the low-velocity impact are respectively detected using the pulse infrared thermography and ultrasonic infrared thermography. Through the numerical simulation and experimental investigation, the results obtained show that the combination of the above two detection methods can greatly improve the capability for detecting and evaluating the impact damage in CFRP. Different damages correspond to different infrared thermal images. The delamination damage, matrix cracking and fiber breakage are characterized as the block-shape hot spot, line-shape hot spot, and “

” shape hot spot respectively.     

Deformation of a tethered polymer in uniform flow

Static properties of a single polymer fixed at one end and subjected to a uniform flow field are investigated for several polymer models: the Gaussian chain, the freely jointed chain, and the FENE (Finitely Extensible Nonlinear Elastic) chain. By taking into account first the excluded-volume interaction and subsequently also the hydrodynamic interaction, the polymer models are gradually completed and the relevance of each effect for the polymer deformation can be identified. Results from computer simulations of these bead spring chains are compared with analytical calculations using either the conformational distribution function or blob models. To this end, in contrast to the blob model with non-draining blobs introduced for a tethered polymer by Brochard-Wyart, we here develop also a model with free-draining blobs. It turns out that a limited extensibility of the polymer – described by nonlinear spring forces in the model – leads to a flow velocity dependence of the end-to-end distance, segment density, etc. which agrees with the power law predictions of the blob model only for very long chains and in a narrow range of flow velocities. This result is important for comparison with recent experiments on DNA molecules which turn out to be still rather short in this respect. The relative importance of finite extensibility, the excluded-volume effect, and hydrodynamic interactions for polymers in flow is not fully understood at present. The simulation of reasonably long chains becomes possible even when fluctuating hydrodynamic interactions are taken into account without employing averaging procedures by introducing efficient numerical approximation schemes. At medium velocity of the uniform flow the polymer is partially uncoiled and simulations show that the effects of excluded-volume and hydrodynamic interactions are position-dependent. Both are stronger near the free end than near the tethered end of the polymer. A crossover from a nearly non-draining polymer at small flow velocities to a free-draining almost uncoiled chain at large velocities is found in the simulations. Accordingly, models assuming the polymer to be composed of either free- or non-draining subunits, like the two blob models, cannot correctly describe the extension and shape of a tethered polymer in flow, and simple power laws for the polymer extension, etc. cannot be expected. Received 21 June 1999     

Dispersion compensation in transmission using uniform long period fiber gratings

It is proposed that the high dispersion at the transmission band edges of uniform long period gratings (LPG) fabricated on relatively high Δ fibers can be used for efficient dispersion compensation. Since the transmission of LPG varies with length of the grating or refractive index modulation, we show that it is possible to tailor the transmission spectrum to obtain high transmission with constant dispersion and negligible delay ripple over a reasonable bandwidth. Since the proposed structure works in transmission it should be suitable for fiber optic communication links.     

Rugged distal tips for CO2 laser medicine

Low-loss and rugged distal tips for CO₂ laser have been proposed and fabricated based on a commercially available stainless steel (St) pipe. A method of smoothening the inner surface of the St pipe with a rough inner surface is put forward. Fabrication parameters, transmission properties, and mechanical strength of the cyclic olefin polymer-coated silver hollow St distal tip are experimentally discussed.