Coating optical fibers with dual dies separated by a pressurized chamber

A proven technique is described for applying bubble-free, concentric coatings to optical fibers. An initial die backed up by a pressurized chamber blocks bubbles, while exit die sizes and centers the fiber.     

Coating optical fibers with dual dies separated by a pressurized chamber

A proven technique is described for applying bubble-free, concentric coatings to optical fibers. An initial die backed up by a pressurized chamber blocks bubbles, while exit die sizes and centers the fiber.     

Aperture properties of multimode conical optical fibers (focons)

The problem on the propagation of meridional rays in conical optical fibers (focons) has been considered in terms of the geometric optics model. A sine condition for the ray parameters at reflection points has been obtained. A general equation that relates the geometric size of a focon with the ray parameters at the entrance and exit of the focon has been deduced. The equation is valid for all physically possible taper angles of a focon. The aperture properties of two types of focons (hollow and dielectric) have been analyzed. The entrance and exit aperture angles appear to be piecewise continuous or piecewise smooth functions of the parameters, which is related to the discreteness of the number of ray reflections. The main properties of the considered types of focons with typical values of the parameters have been illustrated by numerical calculations of the aperture angles.     

光纤基底TiNi形状记忆合金薄膜制备工艺

将TiNi基记忆合金薄膜与光纤相结合可制成智能化、集成化且成本经济的微机电系统和微传感器件.本文采用磁控溅射法在二氧化硅光纤基底上制备TiNi记忆合金薄膜,系统讨论了溅射工艺参数以及后续退火处理对薄膜质量的影响.采用自研制光纤镀膜掩膜装置在直径为125μm的光纤圆周表面上形成均匀薄膜.实验表明:在靶基距、背底真空度、Ar气流量和溅射时间一定的条件下,溅射功率存在最佳值;溅射压强较大时,薄膜沉积速率较低,但薄膜表面粗糙度较小.进行退火处理后,薄膜形成较良好的晶体结构,Ti_49.09Ni_50.91薄膜中马氏体B19′相和奥氏体B2相共存,但以B19′为主.根据本文研究结果,在玻璃光纤基底上制备高质量的TiNi基记忆合金薄膜是可实现的,本工作为下一步研制微机电系统和微型传感器做了基础准备.     

光纤基底TiNi形状记忆合金薄膜制备工艺

将TiNi基记忆合金薄膜与光纤相结合可制成智能化、集成化且成本经济的微机电系统和微传感器件.本文采用磁控溅射法在二氧化硅光纤基底上制备TiNi记忆合金薄膜,系统讨论了溅射工艺参数以及后续退火处理对薄膜质量的影响.采用自研制光纤镀膜掩膜装置在直径为125μm的光纤圆周表面上形成均匀薄膜.实验表明:在靶基距、背底真空度、Ar气流量和溅射时间一定的条件下,溅射功率存在最佳值;溅射压强较大时,薄膜沉积速率较低,但薄膜表面粗糙度较小.进行退火处理后,薄膜形成较良好的晶体结构,Ti_49.09Ni_50.91薄膜中马氏体B19′相和奥氏体B2相共存,但以B19′为主.根据本文研究结果,在玻璃光纤基底上制备高质量的TiNi基记忆合金薄膜是可实现的,本工作为下一步研制微机电系统和微型传感器做了基础准备.     

Scattering of a plane electromagnetic wave by bodies of conical shape

Radiophysics and Quantum Electronics -     

Single-beam optical bottle for cold atoms using a conical lens

We report a new method to generate an optical dipole potential with a null intensity region surrounded in all directions by light walls. This is achieved with a simple scheme based on a conical lens. Applications to optical trapping of neutral atoms are discussed. Received 4 September 2000 and Received in final form 21 January 2001     

Radius variation of optical fibers with angstrom accuracy

We have developed a robust method for the unprecedentedly accurate angstrom-scale detection of local variations of the fiber radius based on the idea suggested by Birks et al. [IEEE Photon. Technol. Lett. 12, 182 (2000)]. The method uses an optical microfiber (MF) translated at a small distance along the tested fiber and periodically touching it at measurement points. At these points, the MF transmission spectrum exhibits whispering-gallery-mode (WGM) resonances shifting with the tested fiber radius. A simple and comprehensive optimization scheme, which determines the radius variation without visual recognition of resonances and treats their shifts simultaneously, is developed. The optics of WGM propagation is discussed, and the condition for the validity of the developed method is established.     

Scaling relationships in sharp conical indentation of shape memory alloys

Based on dimensional analysis and finite element calculations, several scaling relationships in the indentation of shape memory alloys with a sharp conical indenter were obtained. These scaling relationships illustrate the dependence of the indentation response on the material properties of shape memory alloys, such as phase transition and plastic deformation. It is shown that the yield stress and strain-hardening exponent of transformed martensite play important roles in the indentation response, in addition to the phase transition properties. Additionally, the general relationships between indentation hardness and phase transition stress, maximum transition strain, martensite yield stress and the strain-hardening exponent of shape memory alloys were obtained. The results show that the indentation hardness of shape memory alloys is not proportional to the phase transition stress or to the martensite yield stress, and cannot be used directly to measure the phase transition stress or the yield stress of shape memory alloys.     

Ultraviolet-induced absorption losses in hydrogen-loaded optical fibers and in presensitized optical fibers

Reduced hydroxyl formation in presensitized fibers exposed to cw 244-nm light after hydrogen outdiffusion is reported. The OH band in the presensitized fiber shifts toward 1390 nm. In the fully hydrogen-loaded fiber the OH band is centered at 1397 nm and does not shift with fluence.     

Bending-induced optical loss in random-hole optical fibers

We present the experimentally determined optical bend loss for random hole optical fibers in the spectral range 1520 to 1570 nm induced by wrapping the optical fiber around a fixed diameter mandrel. The optical losses are compared to those obtained for a single-mode fiber and a multimode fiber using the same bending procedures. The bending induced optical losses in the random hole optical fibers were several orders of magnitude lower than for the single-mode fiber and were about 1 order of magnitude lower than for the multimode fiber.     

Polycrystalline silicon optical fibers with atomically smooth surfaces

We investigate the surface roughness of polycrystalline silicon core optical fibers fabricated using a high-pressure chemical deposition technique. By measuring the optical transmission of two fibers with different core sizes, we will show that scattering from the core-cladding interface has a negligible effect on the losses. A Zemetrics ZeScope three-dimensional optical profiler has been used to directly measure the surface of the core material, confirming a roughness of only ~0.1 nm. The ability to fabricate low-loss polysilicon optical fibers with ultrasmooth cores scalable to submicrometer dimensions should establish their use in a range of nonlinear optical applications.     

Twisted optical fibers sustaining propagation of optical vortices

The mode structure (the orbital number l = 1) of a few-mode weakly guiding optical fiber with high linear birefringence and a regular twist of its anisotropy axes is investigated. It is shown that, for certain values of twist pitch, the modes with l = 1 are almost pure linearly polarized optical vortices in the local coordinate system associated with the anisotropy axes. The range of values of twist pitch in which twisted fibers sustain propagation of linearly polarized optical vortices is determined numerically.     

Few-mode step-index optical fibers with ultra-low bending losses

We propose a few-mode optical fiber for low-bending-loss applications. We demonstrate ultra-lowbending-loss operation in the fiber by tailoring the core radius and index contrast of step-index optical fibers. In addition, we investigate numerically splicing losses in single-mode optical fibers and demonstrate experimentally the ultra-low-bending-loss operation characteristics. The optical fiber elaborated provides a simple technique to realize the low-bending-loss operation.     

Generation of optical vortices in multihelical optical fibers

It is theoretically demonstrated that multihelical fibers are capable to change the topological charge of the incoming field by l units in the transmitted and reflected light. The magnitude of the change in the topological charge coincides with the number of coaxial helicoids forming the fiber core. This can be used in designing generators of optical vortices (OVs) from Gaussian beams: broadband ones in transmitted light and narrowband ones in reflected light.     

Photo-induced birefringence in semiconductors compared with optical fibers

We analyze the photon-induced birefringence in semiconductors based on pump-probe setups, within the semiconductor Bloch equations formalism and the Luttinger-Kohn model for the band structure. When the pump and probe pulses are well separated in time, the anisotropic momentum space filling of the photo-excited electrons is the only mechanism causing the induced birefringence. The birefringence ratio is then for pump and probe having perpendicular vs. parallel linear polarizations. This ratio is for opposite vs. identical circular polarization. When the pump and probe pulses overlap in time, these birefringence ratios become for linear polarizations and in case of circular polarizations. These predictions differ markedly from those for optical fibers.     

Solar hypersensitization of optical fibers

Hydrogen-loaded fibers were exposed to solar radiation for 20 days, in which time the hydrogen was allowed to out-diffuse. Gratings written in these fibers show an increased photosensitivity compared with pristine fibers. Results show the solar radiation has a similar effect on both stripped and unstripped fibers. This work agrees with the fundamental process of using low fluence, long UV sources to photosensitize hydrogen-loaded, germanium-doped fibers.