Flat Supercontinuum Generation at 1550 nm in a Dispersion-Flattened Microstructure Fibre Using Picosecond Pulse

The generation of a flat supercontinuum of over 80nm in the 1550nm region by injecting 1.6ps 10 GHz repetition rate optical pulses into an 80-m-long dispersion-flattened microstructure fibre is demonstrated. The fibre has small normal dispersion with a variation smaller than 1.5 （ps·nm^-1·km^-1） between 1500 and 1650nm. The generated supercontinuum ranging from 1513 to 1591 nm has the flatness of ±1.5 dB and it is not so flat in the range of several nanometres around the pump wavelength 1552nm. Numerical simulation is also used to study the effect of optical loss, fibre parameters and pumping conditions on supercontinuum generation in the dispersion-flattened microstructure fibre, and can be used for further optimization to generate flat broad spectra.     

Broadband dispersion compensation using microstructure fibers

Beijing University of Posts and Telecommunications, Beijing 100876Dispersion and dispersion slope compensation of 10-Gb/s pulses using microstructure fibers (MFs) is demonstrated experimentally. A 26-m MF is used to compensate the dispersion of 2-km standard singe mode fiber in a 20-nm range in C band. The experimental results show that a significant improvement can be achieved in the quality of the observed pulses with the dispersion compensation. Moreover, the further research shows that the MF can compensate the anomalous dispersion of a single mode fiber within ±0.27 ps/(nm·km) over a 50-nm wavelength range from 1520 to 1570 nm.     

Detection of air target based on multi-fractal analysis in a laser radar

A novel approach for detecting laser radar target based on multi-fraction dimension (MFD) of laser clutters has been proposed. The fractal dimension (FD) of laser clutter and the echoes from the plan are estimated using box-counting dimension algorithm. The intrinsic difference in the spectrum of FD Dq between them is extracted and used to detect targets. Experimental results show that the method based on MFD is more reliable than that on FD and can improve the accuracy of detection.     

Paired interference 3-dB coupler based on SOI rib waveguides with anisotropic chemical wet etching

A 3-dB paired interference (PI) optical coupler in silicon-on-insulator (SOI) based on rib waveguides with trapezoidal cross section was designed with simulation by a modified finite-difference beam propagation method (FD-BPM) and fabricated by potassium hydroxide (KOH) anisotropic chemical wet etching. Theoretically, tolerances of width, length,and port distance are more than 1, 100, and 1 μm, respectively.Smooth interface was obtained with the propagation loss of 1.1 dB/crn at the wavelength of 1.55μm. The coupler has a good uniformity of 0.2 dB and low excess loss of less than 2 dB.     

Hydrothermal synthesis of Er-doped yttria nanorods with enhanced red emission via upconversion

(Y_0.95Er_0.05)₂O₃ single-crystalline nanorods with intense red emission via up-conversion are synthesized by a hydrothermal method under modest reaction conditions. Green and red emissions are observed for both as-synthesized sample and post-treated sample after excitation at 488 nm and with upconversion pumping (810 nm). The experimental results indicate that the stokes and up-conversion luminescence of the post-treated (500 °C for 2 h) Y₂O₃:Er nanorods is more efficient than those of as-prepared materials. The increase of the Stokes luminescence may result from the improved crystallization, smooth surface and uniform diameter distribution. The enhanced red emission via upconversion is due to removal of part of surface contaminants, such as CO₃²⁻ and OH⁻. It is believed that a new mechanism is responsible for populating the ⁴S_3/2 and ⁴F_9/2 levels.     

Determination of albumins by its quenching effect on the fluorescence of Tb-oxolinic acid complex in presence of sodium dodecyl sulphate

It is found that the fluorescence intensity of Tb³⁺-oxolinic acid (OA) complex can be greatly quenched by albumins in sodium dodecyl sulphate (SLS). Under optimum conditions, the quenched fluorescence intensity is in proportion to the concentration of proteins in the range of 5.0×10⁻⁸-1.0×10⁻⁵ g ml⁻¹ for bovine serum albumin (BSA), 1.0×10⁻⁷-1.0×10⁻⁵ g ml⁻¹ for human serum albumin (HSA) and 4.0×10⁻⁷-1.0×10⁻⁵ g ml⁻¹ for egg albumin (EA). Their detection limits (S/N=3) are 2.1×10⁻⁸, 2.5×10⁻⁸ and 5.0×10⁻⁸ g ml⁻¹, respectively. In addition, the interaction mechanism is also investigated.     

利用射线追踪法研究超短外腔半导体激光器的输出特性

基于射线追踪法，推导了外腔半导体激光器的连续输出谱的隐函表达式.在此基础上，结合载流子速率方程，对超短外腔半导体激光器的输出谱及P-I特性进行了研究.结果表明：当外腔长度发生波长量级的变化时，超短外腔激光器的P-I特性将发生显著变化；随着外腔长度的变化，超短外腔激光器的激射波长在10nm范围内呈周期性跳变，当外腔长度介于40μm—70μm范围内，激射波长跳变范围最大.理论模拟结果与实验报道结果符合.     

Orientation and Structure of Ionic Liquid Cation at Air/[bmim][BF4] Aqueous Solution Interface

The watermiscible room temperature ionic liquid 1butyl3methylimidazolium tetrafluorob orate （[bmim] [BF4]） is a model system for studying the interactions between ionic liquid and water molecules. In this work the orientational structure of the low concentrated aqueous solution of [bmim] [BF4] at the air/liquid interface was investigated by sum frequency gener ation vibrational spectroscopy. It has been found that at very low concentrations, the butyl chain exhibited a significant gauche defect, indicating a disordered conformation; and the cation ring oriented with a fairly small tilting angle at the surface. When the concentration increased, the cation ring tended to lie flat at the surface, and the gauche defects of the butyl chain decreased due to the intermolecular chainchain interactions and the consequent more ordered interfacial molecular arrangement. Additionally, the antisymmetric stretching mode in the PPP and SPS spectra exhibited a peak shift, showing that there exists more than one kind of orientation or chemical environment for the butyl CH3 group. These results may shed new light on understanding the surface behavior of watermiscible ionic liquids as well as the imidazolium based surfactants.     

Hydrolytic Ring Opening Reactions of Pyromellitic Dianhydride for Divalent Transition Metal Carboxylate Complexes

The hydrolytic ring opening reactions of pyromellitic dianhydride is an effective method to prepare transition metal carboxylate complexes. In this paper, two dinuclear complexes [Ni₂(2,2′‐bipy)₂(btec)(H₂O)₆] · 2H₂O ( 1 ) and [Cd₂ (phen)₄(H₂O)₂(H₂btec)] · H₂btec · 2H₂O ( 2 ) (H₄btec = 1,2,4,5‐benzenetetracarboxylic acid, phen = 1,10‐phenanthroline, and 2,2′‐bipy = 2,2′‐bipyridine) were synthesized by slow diffusion methods and their structures were determined byX‐ray structure analysis. In both structures metal atoms are in distorted octahedral environments and they are linked by bis‐monodentately coordinated 1,2,4,5‐benzentetracarboxylate ligands as bridging units. The crystalline compounds, which are insoluble in water as well as common organic solvents, have been characterized in the solid‐state by elemental analysis, thermogravimetric analysis, IR, and diffuse reflectance UV/Visspectroscopy. Moreover, the study of the physical properties of complex 2 demonstrates that it exhibits blue fluorescence emission in the solid state at room temperature.