Dynamic evolution of the spectrum of long-period fiber Bragg gratings fabricated from hydrogen-loaded optical fiber by ultraviolet laser irradiation

Long-period fiber Bragg gratings fabricated by exposure of hydrogen-loaded fiber to UV laser light exhibit large-scale dynamic evolution for approximately two weeks at room temperature. During this time two distinct features show up in their spectrum: a large upswing in wavelength and a substantial deepening of the transmission minimum. The dynamic evolution of the transmission spectrum is explained quantitatively by use of Malo's theory of UV-induced quenching [Electron. Lett. 30, 442 (1994)] followed by refilling of hydrogen in the fiber core and the theory of hydrogen diffusion in the fiber material. The amount of hydrogen quenched by the UV irradiation is 6% of the loaded hydrogen.     

Reaction of germanium tetrachloride with oxygen under MCVD fiber preform fabrication conditions

The GeO₂ yield in the reaction between GeCl₄ and oxygen has been determined as a function of the reaction time under typical MCVD fiber preform fabrication conditions. It is shown that the yield increases steadily over time and may attain 100%. In the case of the cooxidation of germanium and silicon tetrachlorides under the same conditions, there is an optimal reaction time corresponding to a maximum in GeO₂ yield. The temperature profile along the reaction zone has been optimized in terms of germania yield.     

Polarization-multiplexed diffractive optical elements fabricated by subwavelength structures

Polarization-multiplexed phase-only diffractive optical elements with subwavelength structures are proposed and fabricated. The differences among the phase modulations result from the differences among the effective indices exhibited in the subwavelength structures with various filling factors and surface profiles, and the phase retardations are obtained by the relief depth of the structures. The polarization-selective property is achieved by the polarization dependence of the effective indices exhibited in the one-dimensional subwavelength structures and the polarization independence exhibited in the two-dimensional structures. Additionally, the polarization contrast of our polarization-multiplexed elements, defined as the cross talk between the two polarization incidences, is independent of the relief depth. The principle of the polarization multiplexing by use of the subwavelength structures is described, and the fabrication results for the polarization-multiplexed computer-generated holograms are demonstrated.     

Long-period grating fabricated by periodically tapering standard single-mode fiber

We fabricated an asymmetric long-period grating (LPG) by periodically tapering a section of standard single-mode fiber using a resistive filament heating. The LPG exhibits large peak transmission attenuation of -30.31 dB with only 22 periods in a 1.0 cm long optical fiber and possesses unique characteristics for sensing applications. The bending and strain sensitivities are 1.74 nm m and 1.11 pm/mu epsilon, respectively. The polarization dependent loss is large, up to 11.65 dB, which is caused by an asymmetric index profile in the cross section of the tapered LPG.     

Properties of fluorosilicate glass prepared by MCVD

Multilayer and two-layer fiber preforms with a fluorosilicate glass core have been produced by the modified chemical vapor deposition (MCVD) process with SiF₄ as a fluorination agent. The fluorine profile across the preforms has been studied, the fluorine concentration in the glass has been determined as a function of the initial vapor mixture composition, and the effect of the fluorine concentration on the refractive-index difference between the fluorosilicate and silica glasses and on the mechanical stress in the glass has been examined. Comparison of the present results with literature data demonstrates that the above parameters depend significantly on the fluorosilicate glass preparation process: MCVD or plasma chemical vapor deposition (PCVD). This is tentatively attributed to the difference in structure between the glasses made by MCVD and PCVD.     

High optical quality InP-based nanopillars fabricated by a top-down approach

Dense and uniform arrays of InP-based nanopillars were fabricated by dry etching using self-assembly of colloidal silica particles for masking. The pillars, both single and arrays, fabricated from epitaxially grown InP and InP/GaInAsP/InP quantum well structures show excellent photoluminescence (PL) even at room temperature. The measured PL line widths are comparable to the as-grown wafer indicating high quality fabricated pillars. A stamping technique enables transfer with arbitrary densities of the nanopillars freed from the substrate by selectively etching a sacrificial InGaAs layer.     

Responses of a long-period grating fabricated in a graded-index optical fiber to temperature and refractive-index changes

Sensing experiments with a long-period grating (LPG) inscribed by a CO₂ laser in a single-mode fiber with an inverted-parabolic index profile in the fiber cladding were done. A single LPG with a period of 500 μm was used in experiments and spectral changes of the attenuation band centered at ≈1520 nm were measured. Responses of the LPG to temperature changes and temperature-induced refractive-index changes were investigated. An average shift of 0.56 nm/°C was obtained for the bare LPG and of 0.86 nm/°C for the LPG recoated with a polymeric layer. An overall shift of the central wavelengths was observed in experiments repeated after two weeks that can be attributed to post-curing processes in the polymeric layer.     

使用光纤实现荧光定量PCR检测

阐述了光纤在荧光定量PCR检测中的应用特点和荧光产生机理,给出了光纤耦合效率的计算公式。介绍了试验装置的构成和工作原理,列举了限制荧光检测的实际问题并提供了消除模块背景的方法。试剂检测的结果证实了使用光纤的检测系统具有很高的检测分辨率和8个数量级以上的动态线性范围,完全满足荧光定量PCR检测的要求。     

Waveguide properties of optical structures fabricated by oxidation of porous silicon

Results of an investigation of the optical properties of channel waveguides fabricated by oxidation of porous silicon are described. The waveguide parameters are estimated and the existence of optical anisotropy is established. The effective refractive index of the dominant quasi-TM waveguide mode is measured. The results suggest that a buffer layer exists between the waveguide and the silicon substrate. It is hypothesized that a second refractive index peak exists within this layer. Pis’ma Zh. Tekh. Fiz. 23, 86–89 (May 26, 1997)     

Laterally graded porous silicon optical filter fabricated by diffusion-limited etch process

We report a method of producing a lateral gradient in the optical properties of anodically etched porous silicon layers. Lateral gradation details of the porous silicon layer are governed by the etch mask pattern involved. Unlike other methods that rely on uneven hole current distribution, we believe that in our method the diffusion of reactive ions in the etchant plays a key role. As an implementation of the proposed method, we demonstrate a linearly graded optical bandpass filter operating at the lambda=1550 nm range by employing a tapered etch window opening. The resultant optical filter exhibited a approximate 60 nm tuning range with a sharp transmission bandwidth of approximately 3 nm. Computer simulations indicate that an uneven hole current distribution cannot be the reason for the observed gradient along the taper axis, supporting the view that the diffusion-limited etch process plays the key role.     

High-throughput optical quality control of lipid multilayers fabricated by dip-pen nanolithography

Surface supported phospholipid multilayers are promising materials for nanotechnology because of their tendency to self-organize, their innate biocompatibility, the possibility to encapsulate other materials within the multilayers, and the ability to control the multilayer thickness between ～ 2 and 100 nm during fabrication. Dip-pen nanolithography (DPN) is an atomic force microscopy (AFM) based fabrication method that allows high-throughput fabrication and integration of a variety of micro- and nanostructured materials including lipid multilayers, with areal throughputs on the scale of cm(2) min(-1). Although multilayer thickness is a critical feature that determines the functionality of the lipid multilayer structures (for instance as carriers for other materials as well as optical scattering properties), reliable height characterization by AFM is slow (on the order of μm(2) min(-1)) and a bottleneck in the lithographic process. Here we describe a novel optical method to reliably measure the height of fluorescent multilayers with thicknesses above 10 nm, and widths above the optical diffraction limit based on calibrating the fluorescence intensity using one-time AFM height measurements. This allows large surface areas to be rapidly and quantitatively characterized using a standard fluorescence microscope. Importantly, different pattern dimensions (0D dots, 1D lines or 2D squares) require different calibration parameters, indicating that shape influences the optical properties of the structured lipid multilayers. This method has general implications in the systematic and high-throughput optical characterization of nanostructure-function relationships.     

Relief optical microelements fabricated with dichromated gelatin

Relief microlenses and micromirrors are fabricated in dichromated gelatin layers. Microelements typically have diameters of approximately a few hundred micrometers and have focal distances ranging from 4 to 15 mm.     

光纤水听器调制激光光源的一种实现方法

在干涉型光纤水听器的信号检测技术中,采用相位载波零差检测方式,直接调制激光光源,具有明显的优越性。提出了一种实现方法,通过产生高频正弦波,对激光光源(多量子阱分布反馈激光器),进行直接驱动调制。光源调制输出波形精确多样(正弦波、三角波(包括锯齿波)和方波),输出频率大范围(0～20MHz),连续可调。实验表明达到了水听器对光源的要求。此调制技术也可在光纤通信等其它领域得以应用。     

Single-mode optical waveguides fabricated from fluorinated polyimides

Buried channel optical waveguides were fabricated from fluorinated polyimides. They operated in single mode and showed an optical loss of less than 0.3 and 0.7 dB/cm for TE and TM polarizations, respectively, at a wavelength of 1.3 mum. Moreover, these waveguides had high heat and moisture resistance; the optical loss did not significantly change after heating at 380 degrees C for 1 h or after exposure to 85% relative humidity at 85 degrees C for over 200 h.     

Bismuth activated alumosilicate optical fibers fabricated by surface-plasma chemical vapor deposition technology

Plasma chemical technology is experimentally applied to the fabrication of a Bi-activated alumosilicate-core pure-silica-cladding fiber preform. To the best of our knowledge, this is the first time this technology has been applied in this way. We measure gain efficiency at pumping by a 1058 nm wavelength Yb fiber laser in a piece of a newly obtained fiber 20 m in length within 100-1200 nm wavelengths band. The gain efficiency reaches as high as 0.2 dB/mW. Bi-activated alumosilicate-core pure-silica-cladding fiber that is not more than 12 m in length serves a basis for a 1 W output power fiber laser emitting at the wavelength of 1160 nm with 8% slope efficiency. We also measure the photoluminescence spectrum and kinetics of Bi centers responsible for laser emission under the excitation of 193 nm wavelength ArF laser pulses.     

Measuring optical fiber length by use of a short-pulse optical fiber ring laser in a self-injection seeding scheme

A method for measuring the length of an optical fiber by use of an optical fiber ring laser pulse source is proposed and demonstrated. The key element of the optical fiber ring laser is a gain-switched Fabry-Perot laser diode operated in a self-injection seeding scheme. This method is especially suitable for measuring a medium or long fiber, and a resolution of 0.1 m is experimentally achieved. The measurement is implemented by accurately determining the pulse frequency that can maximize the output power of the fiber ring laser. The measurement results depend only on the refractive index of the fiber corresponding to this single wavelength, instead of the group index of the fiber, which represents a great advantage over both optical time-domain reflectometry and optical low-coherence reflectometry methods.     

A few-mode optical fiber retaining optical vortices

The ability of an optical fiber with axial losses to selectively suppress the fundamental HE ₁₁ mode, as well as the TE and TM waveguide modes, and, simultaneously, to transmit optical vortices with almost zero energy losses is considered. The attenuation coefficients for the corresponding eigenmodes and vortices are determined. It is shown that such a fiber operates as a mode filter for the feeding beam.     

Polarimetric optical fiber refractometer

An optical fiber refractometer based on a photometric return-path birefringence sensor is proposed. For measuring the refractive index, the phase shift between polarization components on total internal reflection inside a refractometric prism is used. Several kinds of refractometric prism are described. It is shown that a refractive-index sensitivity of 0.0001 and higher for a wide range of index values is attainable.     

Practical circular-polarization-maintaining optical fiber

The author describes a new idea for making circular-polarization-maintaining optical fiber with an existing fabrication technique. The method simply requires one to spin at a constant rate a special preform consisting of only one off-axis stress-applying element in addition to the on-axis core. Measurements taken with such a fiber specimen verify the existence of circular eigenmodes, the ease of joining or splicing two fiber segments, the tolerance to macrobending with a small radius, etc. Good agreement exists between the experimental data and the theoretical analysis. Prospective applications are discussed.