Impact of the second order dispersion on compensation of SPM in an adaptive pulse pre-shaping quasi-CPA system

A model of quasi-CPA (chirped pulse amplification) system, in which the input is the transform-limited Gaussian pulses, is set up numerically to investigate the impact of the second order dispersion on the adaptive compensation of self-phase modulation (SPM) effect. The adaptive phase pre-shaping controlled by differential evolution algorithm is introduced to the input pulse before amplification and recompression. With maximizing the peak power of the output pulse, the simulation results show th...     

Characteristics of direct-contact,skin-surface temperature sensors

Numerical simulations have been performed to determine the performance characteristics of direct-contact devices for the measurement of skin-surface temperature. Such devices consist of a thin metallic foil which serves as a heat spreader backed by a foam insulation pad. The sensor, either a miniature thermocouple or thermistor, is adhered to the heat-spreading foil. In practice, such devices operate in the transient mode, and the numerical simulations were performed in that mode. Special focus was given to three relevant parameters which contribute significantly to the accuracy of the temperature measurements: (a) the thickness of the foam pad, (b) the thermal conductivity of the pad material, and (c) the contact resistance between the device and the skin surface. It was found that the presence of the foam pad significantly degraded the accuracy of the measured temperature. Diminishing the thickness or, in the limit, elimination of the pad is believed necessary to enable the device to provide temperatures of acceptable accuracy. An alternative and suitable approach to the achievement of satisfactory accuracy is to use pad materials of higher thermal conductivity than those presently being utilized. With regard to contact resistance, the presence of an air gap between the device and the skin surface of the thickness of a sheet of paper did not cause a significant error in the temperature indicated by the device.     

Photonic crystal fiber with novel dispersion properties

Our recent research on designing microstruc-tured fiber with novel dispersion properties is reported in this paper. Two kinds ofphotonic crystal fibers (PCFs) are introduced first. One is the highly nonlinear PCF with broadband nearly zero flatten dispersion. With introducing the germanium-doped (Ge-doped) core into highly non-linear PCF and optimizing the diameters of the first two inner rings of air holes, a new structure of highly non-linear PCF was designed with the nonlinear coefficient up to 47 W-1·km-1 at the wavelength 1.55 μm and nearly zero flattened dispersion of ±0.5 ps/(km·nm) in telecom-munication window (1460-1625nm). Another is the highly negative PCF with a ring of fluorin-doped (F-doped) rods to form its outer ring core while pure silica rods to form its inner core. The peak dispersion - 1064 ps/(km·nm) in 8 nm full width at half maximum (FWHM) wavelength range and -365ps/(km·nm) in 20nm (FWHM) wavelength range can be reached by adjusting the structure parameters. Then, our recent research on the fabrication of PCFs is reported. Effects of draw parameters such as drawing temperature, feed speed, and furnace temperature on the geometry of the final photonic crystal fiber are investigated.     

Excellent initial guess functions for simple shooting method in Yb3+-doped fiber lasers

Excellent initial guess functions, providing for setting suitable initial estimates for simple shooting method, are developed to solve high power Yb³⁺-doped fiber lasers model with boundary conditions. When the guess value of slope efficiency is greater than or equal to the critical guess value of slope efficiency, the initial guess values of the forward signal power and backward pump power, generating from the excellent initial guess functions, are good initial guess values for the simple shooting method. Then, comparing the simulation results using our simple shooting method and the number sequence transition method based on MATLAB BVP solvers (NSTM-BVPs), the difference of the simulation results are less than given absolute error tolerance for different fiber length. Finally, we can conclude that the critical guess value of slope efficiency is less than 0.3 for all the fiber length, Yb³⁺-doped concentration, signal reflectivity and pump power.     

Structural changes of polyacrylonitrile precursor fiber induced by γ-ray irradiation

The structural changes of polyacrylonitrile precursor fibers under γ-ray irradiation were studied. The Fourier transform infrared spectroscopy (FTIR) results indicated that chemical reactions occurred in the irradiated fibers. The thermal and thermal mechanical behaviors of the fibers, which were characterized by differential scanning calorimetry (DSC), thermal gravimetry (TG) and thermal mechanical analysis (TMA), changed under irradiation, since ladder structure had formed in the fibers under irradiation prior to the heating process. The crystallinity and crystallite size were found to decrease with the increase of irradiation time, as the chemical reactions induced by γ-ray irradiation affected the crystal structure of the fibers. γ-ray irradiation may be useful in accelerating the thermal stabilization of PAN precursor fibers.     

基于单模-无芯-单模结构的光纤折射率传感器

提出了一种基于光纤单模-无芯-单模结构的光纤 折射率传感器。当外界折射率(SRI,surrounding refractive index)小于无芯光纤(NCF,no-core fiber)折射率,并且二者十分接 近的情况下,NCF 可以看作是具有阶跃折射率分布的弱导多模光纤(MMF),这样便构成了传统的单模-多模- 单模(SMS,single-mode multimode single-mode)光纤结构。利用线偏振模近似的方法理论分析了基于这种光 纤结构的折射 率传感器的模式激发特性以及输出特性,进而进行了相应的数值仿真及实验验证,结果表明 ,数值仿真与实验 结果均与理论分析结果相一致。在1.3～1.4的折射率范围内,实验测得传感器灵敏度达到 205.42nm/RIU。     

Temperature-insensitive fiber Bragg grating strain sensor

A fiber Bragg grating strain sensor,whose reflection bandwidth is insensitive to temperature,is presented.The cross-sec-tional area is designed to change linearly.Under axial stress,there is a linear relationship between stress and average strain.Experimental results show that when temperature increases,reflection center wavelength shifts to longer wavelength,and there is a good linear relationship between center wavelength and temperature.When stress increases,reflection center wavelength shifts to longer wavelength,and reflection bandwidth increases.There are good linear relationships between reflection center wavelength and stress as well as reflection bandwidth and stress.     

Nitrogen ion implanted graphene as thrombo-protective safer and cytoprotective alternative for biomedical applications

Nitrogen ion implanted graphene (N/graphene) was investigated for its interaction with mouse fibroblast cells, human endothelial cells and rabbit blood. The results showed that cells cultured on N/graphene displayed increased cell-viability, proliferation, and stretching when compared to those cultured on pristine graphene. An clinical acceptable hemolytic rate (below 5%) and lower platelet adhesion and prolonged kinetic blood-clotting time were also observed for N/graphene, indicating better thromboresistance than pristine graphene. Fourier transformer infrared spectrophotometry (FTIR) and X-ray photoelectron spectroscopy (XPS) measurements proved that N ion implantation induced introduction of N element and appearance of NC functional groups on N/graphene. The polarity and electronegativity induced by N-containing functional groups on the N/graphene may be related to the improved cytocompatibility and hemocompatibility.