Optical response of high-level bandgap in one-dimensional photonic crystal applying in-plane integration

A new broadband filter, based on the high level bandgap in 1-D photonic crystals (PCs) of the form Si vertical bar air vertical bar Si vertical bar air vertical bar Si vertical bar air vertical bar Si vertical bar air vertical bar Si vertical bar air vertical bar Si is designed by the plane wave expansion method (PWEM) and the transfer matrix method (TMM) and fabricated by lithography. The optical response of this filter to normal-incident and oblique-incident light proves that utilizing the high-level bandgaps of PCs is an efficient method to lower the difficulties of fabricating PCs, increase the etching depth of semiconductor materials, and reduce the coupling loss at the interface between optical fibers and the PC device. (c) 2007 Society of Photo-Optical Instrumentation Engineers.

Optical response of high-order band gap photonic crystal applying in-plane in one-dimensional integration

A new broadband filter, based on the high-order band gap in one-dimensional photonic crystal (PCs) of the form Si vertical bar air vertical bar Si vertical bar air vertical bar Si vertical bar air vertical bar Si vertical bar air vertical bar Si vertical bar air vertical bar Si, has been designed by the plane wave expansion method (PWEM) and transfer matrix method (TMM) and fabricated by lithography. The optical response of this filter to normal-incident and oblique-incident light proves that utilizing the high-order band gaps of PCs is an efficient method to lower the difficulties of fabricating PCs, increase the etching depth of semiconductor materials, and reduce the coupling loss at the interface between optical fibers and PC device. (c) 2007 Elsevier B.V. All rights reserved.

Wavelength conversion based on degenerate-four-wave-mixing with continuous-wave pumping in silicon nanowire waveguide

We present a comprehensive numerical study on the all-optical wavelength conversion based on the degenerate four-wave-mixing with continuous-wave pumping in the silicon nanowire waveguide. It is well known that the conversion efficiency and the 3-dB bandwidth can be greatly affected by the phase-matching condition. Through proper design of the waveguide cross-section, its dispersion property can be adjusted to satisfy the phase-matching condition and therefore effective wavelength conversion can be achieved in a large wavelength range. Generally, the group velocity dispersion plays a dominant role in the wavelength conversion. However, the fourth-order dispersion takes an important effect on the wavelength conversion when the group velocity dispersion is near the zero-point. Furthermore, the conversion efficiency and the 3-dB bandwidth can also be affected by the interactive length and the initial pump power. Through the numerical simulation, the optimal values for the interactive length and the initial pump power, which are functions of the propagation loss, are obtained to realize the maximum conversion efficiency. (C) 2008 Elsevier B.V. All rights reserved.

Electro-optic coefficients of Si0.75Ge0.25/Si/Si0.5Ge0.5 asymmetric superlattice measured by polarization-maintaining fiber-optic Mach-Zehnder interferometer

Ten-period 5.5 nm Si0.75Ge0.25/10.3 nm Si/2.5 nm Si0.5Ge0.5 trilayer asymmetric superlattice was prepared on Si (001) substrate by ultrahigh vacuum chemical vapor deposition at 500 degrees C. The stability of Mach-Zehnder interferometer was improved by utilizing polarization-maintaining fibers. According to the electro-optic responses of the superlattice with the light polarization along [110] and [-110], respectively, both electro-optic coefficients gamma(13) and gamma(63) of such asymmetric superlattice were measured. gamma(13) and gamma(63) are 2.4x10(-11) and 1.3x10(-11) cm/V, respectively, with the incident light wavelength at 1.55 mu m. (c) 2006 American Institute of Physics.

Accurate mode analysis of ultraviolet-written channel waveguides

The transfer matrix method combined with the effective index method is adopted to model the silica-based channel waveguide patterned by UV writing. The effective indexes of the graded index channel waveguides with different dimension are calculated. The maximal error of the effective index is less than 3 x 10(-5). By this method, the number of the guided mode and the dimension range to guide certain modes can be obtained easily. Finally, the dimension range to guide a single mode is presented. (c) 2005 Society of Photo-Optical Instrumentation Engineers.

The intrinsic temperature effect of the Raman spectra of graphite

The Raman spectra of ion-implanted highly oriented pyrolytic graphite (HOPG) are reported, in which an additional mode at 1083 cm(-1) and three doublet structures in the positions of similar to 1350, similar to 2450, and similar to 2710 cm(-1) are revealed. Noticeable frequency shifts are observed for all the Raman bands between the spectra excited with different laser powers, which are interpreted as the pure temperature effect and a downshift in the C-C stretching frequency induced by the thermal expansion. Moreover, the pure temperature effect (d omega/dT)(V) without anharmonic contribution is achieved in pristine HOPG. The results suggest that the pure temperature effect without anharmonic contribution plays an important role in the frequency shifts with temperature. (C) 1999 American Institute of Physics. [S0003-6951(99)01313-3].

An analysis and simulation about conditioned launch for very short reach (VSR-4)

VSR4 links use graded index multimode fibers (GIMMFs) as the transmission medium with operation wavelength 850nm. For cost reasons, VCSEL has been selected as the optical source to VSR4. The minimum bandwidth specification for 62.5um GIMMF in VSR4 is only 400 MHz(.)km for over-filled-launch (OFL) condition. The distance of 300 meters is limited over transmission rates of 1.25Gbit/s on the basis of this specification. In order to overcome the OFL bandwidth limit by selective excitation of a limited number of modes, conditioned launch technique is investigated. In this paper, based on a comprehensive dispersion theory of GIMMF, a model is built to simulate the transmission of optical signal in GIMMFs and a comparison between OFL and conditioned launch is analyzed. The result can be the guidelines for the best choice of techniques for various LAN and interconnect systems also.

Optimization and comparison of single- and dual-pump fiber-optical parametric amplifiers with dispersion fluctuations

Solutions for fiber-optical parametric amplifiers (FOPAs) with dispersion fluctuations are derived using matrix operators. On the basis of the propagation matrix product and the hybrid genetic algorithm, we have optimized and compared single- and dual-pump FOPAs with zero-dispersion-wavelength variations. The simulations prove that the design of FOPAs involves multimodal function optimization problems. The numerical results show that dual-pump FOPAs are highly sensitive to dispersion fluctuations whereas dispersion variations have less impact on the gain of single-pump FOPAs. To increase signal gain and reduce ripple, dual-pump FOPAs, instead of single-pump FOPAs, have to be carefully optimized with a suitable multisegment fiber structure rather than a one-segment fiber structure. The different combinations of multisegment fibers can provide highly different gain properties. The increase in gain is at the cost of the ripple.

Facile route to fabricate large-scale silver microtubes

Large-scale uniform Ag microtubes with high length diameter ratios have been first successfully synthesized by a facile approach, using low-cost super fine glass fibers as templates. The samples were characterized by SEM and XRD. The investigations showed that calcining or adding of PEG-1000 and alcohol could greatly improve the mechanical strength of the sample. Especially the products exhibited favorable catalytic properties during the degradation of Rhodamine B by NaBH4. (c) 2007 Elsevier B.V. All rights reserved.

Sol-gel matrix modified microstructured optical fibre towards a fluoride sensitive optical probe

In this article, we report an optical fluoride probe based on microstructured polymer optical fibers (MPOFs) which is modified with morin-Al complex doped silica gel film. This probe is fabricated by sol-gel fluxion coating process. Sol solution doped with morin-Al is directly inhaled into array holes of MPOF and then forms morin-Al-gel matrix film in them. The sensing probe shows different fluorescence intensity to different fluoride ion concentrations in the aqueous solution. The range of response is 550 mmol/L, under the condition of pH 4.6. Crown Copyright (C) 2009 Published by Elsevier B.V. All rights reserved.

Tellurium enhanced non-resonant third-order optical nonlinearity in a germano-silicate optical fiber

碲掺杂的高非线性石英光纤

All-optical switching application of germano-silicate optical fiber incorporated with Ag nanocrystals

银纳米晶体掺杂的高非线性石英光纤的全光转换应用

Yb3+-doped 200 mu m diameter core, gain guided index-antiguided fiber

The lasing in an end-pumped gain guided index-antiguided (GG-IAG) Yb3+-doped silicate glass fiber with a 200 mu m diameter core is demonstrated. Laser beams with similar beam propagation factors M (2) and mode field diameters W (0) (> 160 mu m) were observed at the output end of the GG-IAG fibers under different pump powers, which indicated that single mode behavior and excellent beam quality were achieved during propagation. Furthermore, the laser amplifier characteristics in the present Yb3+-doped GG-IAG fiber were also evaluated.

Ultra-dry oxygen atmosphere to protect tellurite glass fiber from surface crystallization

In this study we report on surface crystallization phenomena and propose a solution for the fabrication of long and robust tellurite glass fibers. The bulk tellurite glasses of interest were prepared by melting and quenching techniques. Tellurite glass preforms and fibers were fabricated by suction casting and rod-in-tube drawing methods, respectively. The surfaces of the tellurite bulk glass samples and of the drawn fibers prepared under different controlled atmospheres were examined by X-ray diffraction. When the tellurite glass fibers were drawn in ambient air containing water vapor, four primary kinds of small crystals were found to appear on the fiber surface, alpha-TeO(2), gamma-TeO(2), Zn(2)Te(3)O(8) and Na(2)Zn(3)(CO(3))(4)center dot 3H(2)O. A mechanism for this surface crystallization is proposed and a solution described, using an ultra-dry oxygen gas atmosphere to effectively prevent surface crystallization during fiber drawing. (C) 2010 Elsevier B.V. All rights reserved.

La2Zr2O7的增韧及陶瓷纤维的制备

La2Zr2O7是一种近年来才提出的新型热障涂层材料，该材料熔点高，在熔点以下不发生相变，热导率低，抗烧结及没有氧传输发生，这些特点使得它作为一种高温下应用的热障涂层材料越来越引起人们的重视。但是，由于该材料的热膨胀系数和断裂韧性比较低，它的实际应用受到了限制。 在本论文中，使用高压烧结的方法获得了致密化的纳米La2Zr2O7块体材料，并对其断裂韧性和热膨胀系数进行了研究。得到的La2Zr2O7纳米材料的断裂韧性和热膨胀系数分别为1.98MPam1/2和9.6×10-6K-1 (200-1000℃)，这些数值明显高于非纳米的La2Zr2O7陶瓷(断裂韧性和热膨胀系数分别为1.40 MPam1/2 和 9.1×10-6 K-1，该结果表明纳米化是一种提高材料断裂韧性和热膨胀系数的有效方法。在La2Zr2O7纳米粉末中加入8YSZ纳米颗粒，高压烧结后使其颗粒充分生长，在得到的复相化合物中观察到形成了类似棒状晶体的自增韧相，使得复合材料的断裂韧性(1.88 MPam1/2)比La2Zr2O7有所提高，甚至超过了同样条件下制备的8YSZ样品的断裂韧性。 La2Zr2O7的断裂韧性也可以通过在基体中添加BaTiO3铁电材料得到明显的提高。当添加BaTiO3的体积含量达到10vol％时，4.5GPa，1450℃高压烧结10min得到的复合材料断裂韧性达1.98 MPam1/2，明显高于同条件下烧结的La2Zr2O7 (1.60MPam1/2)。应力诱导下BaTiO3的电畴转向是主要的增韧原因。随着BaTiO3颗粒添加的体积含量增加，复相化合物的热膨胀系数也明显提高。当掺杂20vol％BaTiO3时，得到的复合材料平均热膨胀系数达到10.2×10-6K-1 (150~1200℃)。 我们通过在4.5GPa, 1650℃高压烧结5min的方法还获得了掺杂YAG纳米颗粒的La2Zr2O7纳米复相陶瓷。在室温下测量了材料的维氏硬度，并通过压痕裂纹长度计算出了材料的断裂韧性。随着YAG纳米颗粒体积含量的增加，纳米复相陶瓷的断裂韧性和维氏硬度都依次增加，当添加20vol％的YAG纳米颗粒时达到最大，分别为1.93 MPam1/2和11.45GPa。断裂韧性增加的机理可归结为以下三点：一是YAG纳米颗粒的添加提高了La2Zr2O7基体的晶界强度，二是基体晶粒尺寸变化的影响，三是YAG纳米颗粒对裂纹的偏转和钉扎作用。添加微米YAG颗粒的复相化合物因为和纳米复相陶瓷具有不同的增韧机制，因此断裂韧性的变化趋势也不相同，在掺入10vol％的YAG微米颗粒时，复合材料的断裂韧性最大，而后降低，当掺入YAG微米粒子的体积含量达到20vol％时，断裂韧性甚至低于La2Zr2O7。 从20世纪90年代开始，电纺作为一种合成纤维的办法越来越吸引人们的注意。其合成的纤维长度长，直径均匀，并且组成范围很广。最初，电纺只是被用来合成一些有机聚合物的纤维，最近，很多研究组开始致力于使用电纺的方法合成复合纤维或者陶瓷纤维。 在本论文中，我们使用电纺的方法获得了La2Zr2O7纳米纤维和SiC单晶纳米线。1000℃煅烧得到的La2Zr2O7纳米纤维具有烧绿石结构，直径在200~500nm之间。同样的温度煅烧时得到的La2Zr2O7纳米纤维的比表面积要明显高于粉末样品的，表明纤维的抗烧结性能比粉末的高。得到的SiC纳米线直径在50~100nm之间，表面有一约5nm厚的无定形的SiO2薄层。 使用电纺的方法，恰当的控制煅烧条件，我们获得了La2Ce2O7， La2(Zr0.745Ce0.386)2O7.524和8YSZ中空纤维。这种中空结构减小了粒子之间的接触面积，提高了材料的抗烧结性能。在扫描电镜分析的基础上，我们总结了这些中空纤维的形成过程。