Core size scaling of helical-core optical fibres

The mode-area, scaling properties of helical-core optical fibres are numerically studied and the limit of core size for achievable single-mode operation is explored. By appropriate design, helical-core fibres can operate in a single mode with possible scaling up to 300 mu m in core diameter with numerical aperture 0.1.

Gain characteristics of Er3+-doped phosphate glass fibres

An erbium-doped phosphate glass fibre has been drawn by the rod-in-tube technique in our laboratory. The gain for the Er3+-doped phosphate glass fibre with different pump powers and with different input signal wavelengths is investigated. The 2.2-cm-long fibre, pumped by a single-mode 980-nm fibre-pigtailed laser diode, can provide a net gain per unit length greater than 1.8dB/cm. The pump threshold is about 50 mW at the wavelength of 1534 nm, and below 70 mW at 1550 nm. The gain linewidth of the Er3+-doped phosphate glass fibre is greater than 34 nm and can cover the C band in optical communication networks.

Nd3+ doped silicate glass photonic crystal fibres

We report on the fabrication of two kinds of large core area Nd3+ doped silicate glass photonic crystal fibres, and demonstration of the fibre waveguiding properties. The measured minimum loss of one kind of fibres is 2.5 db/m at 660nm. The fibres sustain only a single mode at least over the wavelength range from 660nm to 980nm.

A novel design of grating couplers for efficient broadband coupling between silicon-on-insulator nanophotonic waveguides and fibres

A novel design of out-of-plane grating couplers is proposed for coupling between silicon-on-insulator nanophotonic waveguides and single-mode fibres. The coupler with the first-order diffraction coupling to the optical fibre is actually a second-order reflected grating with two times of period of the first-order grating. To enhance outcoupled power, a back hole is designed to form in the silicon substrate and a kind of metals is placed on the top acting as a reflection layer. The coupler is optimized using coupled-mode- based simulations, showing that, the coupling efficiency to and from tapered optical fibre can be as high as 85% with 1 dB bandwidth about 23nm.

Ridge waveguide laser integrated with spot-size converter in a single step epitaxial for high coupling efficiency to single-mode fibres

A 1.55-mum laser diode integrated with a spot-size converter was fabricated in a single step epitaxial by using the conventional photolithography and chemical wet etching process. The device was constructed by a conventional ridge waveguide active layer and a larger passive ridge-waveguide layer. The threshold current was 40 mA together with high slope efficiency of 0.24 W/A. The beam divergence angles in the horizontal and vertical directions were as small as 12.0degrees x 15.0degrees, respectively, resulting in about 3.2-dB coupling losses with a cleaved optical fibre.

Theoretical design or single-polarization single-mode microstructured polymer optical fibres

Using the full-vector plane-wave expansion method, a kind of PMMA-based polarization-maintaining microstructured optical fibre (PM-mPOF) is theoretically studied. Dependence of the cutoff wavelengths of the two orthogonal polarization states (polarized along the two principal axes of PM-mPOF) on the structure parameters of the fibre is investigated in detail. A single-polarization single-mode (SPSM) PM-mPOF working in the visible region is designed and optimized with the result of the maximum SPSM bandwidth of 140 nm.

Multi-wavelength erbium-doped fibre lasers on assistance of high-nonlinear photonic-crystal fibres

On the basis of self-stability effect of four-wave mixings (FWMs) in high-nonlinear photonic-crystal fibres, a novel multi-wavelength erbium-doped fibre (EDF) laser is proposed and demonstrated experimentally at room temperature. The proposed lasers have the capacity of switching and tuning with excellent uniformity and stability. By means of adjusting the attenuators, the triple-, four-, or five-wavelength EDF lasers can be lasing simultaneously. With the assistance of the FWM self-stability function, the multi-wavelength spectrum is excellently stabilized with uniformity less than 0.9 dB.

Silver nanocrystals modified microstructured polymer optical fibres for chemical and optical sensing

In-fibre chemical and optical sensors based on silver nanocrystals modified microstructured polymer optical fibres (MPOFs) were demonstrated. The silver nanocrystals modified MPOFs were formed by direct chemical reduction of silver ammonia complex ions on the templates of array holes in the microstructure polymer optical fibres. The nanotube-like and nanoisland-like Ag-modified MPOFs could be obtained by adjusting the conditions of Ag-formation in the air holes of MPOFs. SEM images showed that the higher concentration of the reaction solution (silver ammonia 0.5 mol/L, glucose 0.25 mol/L), gave rise to a tubular silver layer in MPOF, while the lower concentration (silver ammonia 0.1 M, glucose 0.05 M) produced an island-like Ag nanocrystal modified MPOF. The tubular Ag-MPOF composite fibre was conductive and could be directly used as array electrodes in electrochemical analyses. It displayed high electrochemical activity on sensing nitrate or nitrite ions. The enhanced fluorescence of dye molecules was observed when the island-like Ag-modified MPOF was inserted into a fluorescent dye solution. (C) 2007 Elsevier B.V. All rights reserved.

Single-crystalline nanowires of SiC synthesized by carbothermal reduction of electrospun PVP/TEOS composite fibres

Nanowires of SiC were synthesized by carbothermally reducing PVP/TEOS composite fibres obtained by electrospinning. High-resolution transmission electron microscopy (HRTEM) and selected-area electron diffraction (SAED) indicated that the SiC nanowires are single crystalline in nature. Both Fourier-transformed infrared spectroscopy and HRTEM indicated that a thin layer of SiO2 was formed on the outer surface of the nanowire as a result of post-heat treatment for the removal of residual carbon. Such SiO2 layer protects the inner SiC fibre from further oxidation. The formation mechanism of single-crystalline SiC nanowires was proposed based on our understanding and characterizations. The growth of the nanowire is believed to be along the ( 111) of its cubic cell.

趋磁细菌AMB-1培养条件优化及磁小体变化过程研究

趋磁细菌(Magnetotactic bacteria)的研究是国际微生物学研究热点之一。趋磁细菌体内含有纳米单磁畴的氧化铁/硫化铁(Fe3O4或Fe3S4)晶体，称为磁小体。由于趋磁细菌营养条件要求苛刻，在环境中需要微好氧条件，且营养类型属于化能自养，使得培养趋磁细菌时常遇到问题。 本研究首先通过正交试验优化趋磁细菌AMB-1菌株培养条件，在培养条件铁源为奎尼酸铁0.02 mmol/L，装瓶量75% ，pH值6.7，温度25 ℃时，AMB-1 OD600达到0.440(1.166×109 cells/ml)。同时运用磁收集传代法，使带有磁小体的AMB-1细胞比例占95％以上(Cmag值稳定在1.9-2.0)。 在AMB-1具有较好的生物量，同时又具有较好的含磁小体细胞比例后，研究磁小体的变化过程。通过透射电镜观察磁小体变化过程，发现培养24 h细菌体内已有较小晶体形成(平均27 nm，n=188)且沿长轴分布；48 h晶体长大(平均43 nm，n=203)且形成分段链沿长轴排列；72 h晶体进一步成熟(平均50 nm，n=191)仍以分段链沿长轴排列；随后细菌逐渐衰亡磁小体变小，168 h可见部分自溶细菌中仍有磁小体链(平均37 nm，n=186)；192 h细菌自溶磁小体链(平均33 nm，n=184)分散到环境中。 通过透射电镜在细胞水平上研究趋磁细菌细胞分裂时发现，磁小体在细菌分裂时采用两种分离方式：一种为磁小体分配到两个子细胞；另一种为磁小体只分配到一个子细胞。无磁小体的子细胞，在随后的生长过程又分为两种情况：一种为细胞逐渐产生磁小体，另一种为不再产生磁小体。这种现象的发现，解释了随着传代次数的增多，细菌磁性有所下降的原因(Cmag值降低)。 在对趋磁细菌磁小体合成机制的研究中，常使用基因敲除的办法获得缺陷型，并与野生型对比进行研究。但是，利用基因敲除获得缺陷型不仅操作繁琐并且所得缺陷型不稳定。本研究利用特殊的磁富集传代法，先将带有磁小体的菌体收集并连续传代，筛选获得了高磁菌株；利用这种方法，收集不含磁小体的菌体并连续传代，筛选获得了无磁菌株。 趋磁细菌磁小体在医疗、环保等领域具有广阔应用价值，但是目前由于趋磁细菌难以大规模培养，并且磁小体纯化存在成本高等原因，将磁小体真正实际应用尚有一段距离。通过研究磁小体在趋磁细菌中的变化过程发现，AMB-1菌株在培养192 h后自溶，并且磁小体随着细胞的破碎释放到环境中去。