Fabrication and analysis of 2x2 thermo-optic SOI waveguide switch with low power consumption and fast response by anisotropy chemical etching

A low power consumption 2 x 2 thermo-optic switch with fast response was fabricated on silicon-on-insulator by anisotropy chemical etching. Blocking trenches were etched on both sides of the phase-shifting arms to shorten device length and reduce power consumption. Thin top cladding layer was grown to reduce power consumption and switching time. The device showed good characteristics, including a low switching power of 145 mW and a fast switching speed of 8 +/- 1 mus, respectively. Two-dimensional finite element method was applied to simulate temperature field in the phase-shifting arm instead of conventional one-dimensional method. According to the simulated result, a new two-dimensional index distribution of phase-shifting arm was determined. Consequently finite-difference beam propagation method was employed to simulate the light propagation in the switch, and calculate the power consumption as well as the switching speed. The experimental results were in good agreement with the theoretical estimations. (C) 2004 Elsevier B.V. All rights reserved.

Unveiling the morphology of buried In(Ga)As nanostructures by selective wet chemical etching: From quantum dots to quantum rings

The three-dimensional morphology of In(Ga)As nanostructures embedded in a GaAs matrix is investigated by combining atomic force microscopy and removal of the GaAs cap layer by selective wet etching. This method is used to investigate how the morphology of In(Ga)As quantum dots changes upon GaAs capping and subsequent in situ etching with AsBr3. A wave function calculation based on the experimentally determined morphologies suggests that quantum dots transform into quantum rings during in situ etching. (c) 2007 American Institute of Physics.

Chemical etching of a GaSb crystal incorporated with Mn grown by the Bridgman method under microgravity conditions

A GaSb crystal incorporated with Mn has been grown by the Bridgman method on the Polizon facility onboard the FOTON-M3 spacecraft. Structural defects and growth striations have been successfully revealed by the chemical etching method. By calculating various parameters of the convection, the striation patterns can be explained, and the critical value of the Taylor number, which characterizes the convective condition of the rotating magnetic field induced azimuthal flow, was shown. The stresses generated during crystal growth can be reflected by the observations of etch pit distribution and other structural defects. Suggestions for improving the space experiment to improve the quality of the crystal are given.

静动结合的化学腐蚀法制备近场光学探针的理论分析

理论上分析了静动结合的化学腐蚀法制备探针的具体机理及过程。在静态腐蚀的过程中, 利用流体力学Young-Laplace方程的一级近似解获得了光纤插入到HF酸中形成的新月形高度。在动态腐蚀过程中, 详细分析了当静态腐蚀时间和动态腐蚀时间分别取不同值时, 光纤移动速度对光纤探针结构的影响。利用此法可制备出尖端锐利、大锥角或多锥体等各种结构的光纤探针。这为实验上制备出性能优良的探针, 为拓宽扫描近场光学显微镜的应用范围奠定基础。将上述理论分析的结果与本文实验中所得初步结果进行了比较, 所得结果一致。

Design and fabrication of compact nonblocking 4X4 optical matrix switch on silicon-on-insulator by anisotropic chemical etching

A folding nonblocking 4 X 4 optical matrix switch in simplified-tree architecture was designed and fabricated on a silicon-on-insulator wafer. To compress chip size, switch elements (SEs) were connected by total internal reflection mirrors instead of conventional S-bends. For obtaining smooth interfaces, potassium hydroxide (KOH) anisotropic chemical etching of silicon was employed. The device has a compact size of 20 X 3.2 mm(2) and a fast response of 8 +/- 1 mu s. Power consumption of 2 x 2 SE and excess loss per mirror were 145 mW and -1.1 dB, respectively. (c) 2005 Society of Photo-Optical Instrumentation Engineers.

Changing the size and shape of Ge island by chemical etching

Self-assembled Ge islands were grown on Si (1 0 0) substrate by Si2H6-Ge molecular beam epitaxy. Subjected to a chemical etching, it is found that the size and shape (i.e. ratio of height to base width) of Ge islands change with etching time. In addition, the photoluminescence from the etched Ge islands shifted to the higher energy side compared to that of the as-deposited Ge islands. Our results demonstrated that chemical etching can be a way to change the size and shape of the as-deposited islands as well as their luminescence property. (C) 2001 Elsevier Science B.V. All rights reserved.

Comparisons of static, quasi-static and dynamic 3D porous media scale network models for two-phase immiscible flow in porous media

A dynamic 3D pore-scale network model is formulated for investigating the effect of interfacial tension and oil-water viscosity during chemical flooding. The model takes into account both viscous and capillary forces in analyzing the impact of chemical properties on flow behavior or displacement configuration, while the static model with conventional invasion percolation algorithm incorporates the capillary pressure only. From comparisons of simulation results from these models. it indicates that the static pore scale network model can be used successfully when the capillary number is low. With the capillary increases due to the enhancement of water viscosity or decrease of interfacial tension, only the quasi-static and dynamic model can give insight into the displacement mechanisms.

Thermo-optic variable optical attenuator with low power consumption fabricated on silicon-on-insulator by anisotropic chemical etching

A thermo-optic Mach-Zehnder (MZ) variable optical attenuator based on silicon waveguides with a large cross section was designed and fabricated on silicon-on-insulator (SOI) wafer. Multimode interferometers were used as power splitters and combiners in the MZ structure. In order to achieve a smooth interface, anisotropic chemical etching of silicon was used to fabricate the waveguides. Isolating grooves were introduced to reduce power consumption and device length. The device has a low power consumption of 210 mW and a response time of 50 mus. (C) 2004 Society of Photo-Optical Instrumentation Engineers.

Low power 2 x 2 thermo-optic SOI waveguide switch fabricated by anisotropy chemical etching

A 2 x 2 thermo-optic (TO) Mach-Zehnder (MZ) switch based on silicon waveguides with large cross section was designed and fabricated on silicon-on-insulator (SOI) wafer. The multi-mode interferometers (MMI) were used as power splitter and combiner in MZ structure. In order to get smooth interface, anisotropy chemical wet-etching of silicon was used to fabricate the waveguides instead of dry-etching. Additional grooves were introduced to reduce power consumption. The device has a low switching power of 235 mW and a switching speed of 60 mus. (C) 2004 Elsevier B.V. All rights reserved.

Integrated folding 4x4 optical matrix switch with total internal reflection mirrors on SOI by anisotropic chemical etching

A folding rearrangeable nonblocking 4 x 4 optical matrix switch was designed and fabricated on silicon-on-insulator wafer. To compress chip size, switch elements (SEs) were interconnected by total internal reflection (TIR) mirrors instead of conventional S-bends. For obtaining smooth interfaces, potassium hydroxide anisotropic chemical etching of silicon was utilized to make the matrix switch for the first time. The device has a compact size of 20 x 1.6 mm(2) and a fast response of 7.5 mu s. The power consumption of each 2 x 2 SE and the average excess loss per mirror were 145 mW and -1.1 dB, respectively. Low path dependence of +/- 0.7 dB in total excess loss was obtained because of the symmetry of propagation paths in this novel matrix switch.

Novel folding large-scale optical switch matrix with total internal reflection mirrors on silicon-on-insulator by anisotropy chemical etching

A compact optical switch matrix was designed, in which light circuits were folded by total internal reflective (TIR) mirrors. Two key elements, 2 x 2 switch and TIR mirror, have been fabricated on silicon-on-insulator wafer by anisotropy chemical etching. The 2 x 2 switch showed very low power consumption of 140 mW and a very high speed of 8 +/- 1 mus. An improved design for the TIR mirror was developed, and the fabricated mirror with smooth and vertical reflective facet showed low excess loss of 0.7 +/- 0.3 dB at 1.55 mum.

Measurement of threading dislocation densities in GaN by wet chemical etching

We demonstrate a technique based on wet chemical etching that enables quick and accurate evaluation of edge- and screw/mixed-type threading dislocations (TDs) in GaN. Large and small etch pits are formed by phosphoric acid on the etched surfaces. The large etch pits are attributed to screw/mixed TDs and the small ones to edge TDs, according to their locations on the surface and Burgers vectors of TDs. Additionally, the origin of small etch pits is confirmed by a transmission electron microscopy. The difference in the size of etch pits is discussed in view of their origin and merging. Overetching at elevated temperatures or for a long time may result in merging of individual etch pits and underestimating of the density of TDs. Wet chemical etching has also been proved efficient in revealing the distribution of TDs in epitaxial lateral overgrowth GaN.

Increasing the photoluminescence intensity of Ge islands by chemical etching

Self-assembled Ge islands were grown on Si(100) substrate by Si2H6-Ge molecular beam epitaxy. After being subjected to chemical etching, it is found that the photoluminescence from the etched Ge islands became more intense and shifted to the higher-energy side compared to that of the as-deposited Ge islands. This behaviour was explained by the effect of chemical etching on the morphology of the Ge islands. Our results demonstrate that chemical etching can be a way to change the luminescence property of the as-deposited islands.

DELINEATION OF DEFECTS IN SIMOX STRUCTURES USING A CHEMICAL ETCHING TECHNIQUE

Residual defects in the overlayer of fully annealed SIMOX material have been studied by means of a chemical etching technique. The etching procedure has been calibrated and an optimum recipe is reported. Observations using optical microscopy and transmission electron microscopy have been used to quantify the defect densities and good agreement between the two techniques has been established, confirming that the optimised chemical etching process can be used with confidence to determine the dislocation density for values < 10(7) cm-2.

Application of static and dynamic enclosures for determining dimethyl sulfide and carbonyl sulfide exchange in Sphagnum peatlands: Implications for the magnitude and direction of flux

A static enclosure method was applied to determine the exchange of dimethyl sulfide (DMS) and carbonyl sulfide (OCS) between the surface of Sphagnum peatlands and the atmosphere. Measurements were performed concurrently with dynamic (flow through) enclosure measurements with sulfur-free air used as sweep gas. This latter technique has been used to acquire the majority of available data on the exchange of S gases between the atmosphere and the continental surfaces and has been criticized because it is thought to overestimate the true flux of gases by disrupting natural S gas gradients. DMS emission rates determined by both methods were not statistically different between 4 and >400 nmol m−2 h−1, indicating that previous data on emissions of at least DMS are probably valid. However, the increase in DMS in static enclosures was not linear, indicating the potential for a negative feedback of enclosure DMS concentrations on efflux. The dynamic enclosure method measured positive OCS flux rates (emission) at all sites, while data using static enclosures indicated that OCS was consumed from the atmosphere at these same sites at rates of 3.7 to 55 nmol m−2 h−1. Measurements using both enclosure techniques at a site devoid of vegetation showed that peat was a source of both DMS and OCS. However, the rate of OCS efflux from decomposing peat was more than counterbalanced by OCS consumption by vegetation, including Sphagnum mosses, and net OCS uptake occurred at all sites. We propose that all wetlands are net sinks for OCS.