We propose the integration of a tapered spot-size converter for coupling between a narrow air-core hollow waveguide and a single-mode fiber (SMF). The linear taper waveguide consisting of SiO2 is integrated with a hollow waveguide composed of highly reflective multilayer mirrors. Light is guided with total internal reflections at a SiO2 taper surface and the multiple reflections in the multilayer mirror. The core thickness of a taper SiO2 waveguide is linearly changed from 15µm to 0.6µm. The modeling result shows a coupling loss of less than 1dB between a SMF and a hollow waveguide with an air-core thickness of 1µm. A taper waveguide-induced loss is less than 0.1dB for a two-dimensional linear taper waveguide with a length of less than 1mm. Using the proposed structure, we can expect the dramatic reduction in coupling losses by 10dB. The device structure can be formed by fully planar fabrication processes based on lithography, etching and coating. The proposed spot-size converter enables us to achieve a large tunability of over 10% in propagation constant in hollow waveguides with a variable air-core.
An adaptive fuzzy internal model control (IMC) scheme is proposed to control nonlinear systems with inherent time delay. A Takagi-Sugeno (TS) fuzzy modeling with adaptive tuner is used to obtain the plant model. TS model is obtained using experimental data of step responses at different input levels and the model accuracy is improved using the normalized least mean squares (nLMS) based online adaptive tuner. Adaptive inverse of the plant is established using adaptive inverse control scheme on TS model with adaptive tuner. The scheme is implemented on a laboratory scale heating process. The experimental results indicate that the heating process output tracks the reference signal.
The thermo dynamical stability of a boron atom at the Si/SiO2 interface was studied by using ab initio calculation to investigate a mechanism of boron pile-up at the interface during thermal annealing. The B atom is stable in bulk Si site of the interface without any interface defect, which contradicts the experimental observations. By introducing an oxygen vacancy at the interface, the mechanism of B segregation into SiO2 layer at the atomic scale was verified.
A theory has been developed to calculate fixed polarity Reed-Muller spectra over GF(5) from disjoint cubes representation of 5-valued functions. The algorithm makes use of the properties of disjoint cubes and allows the determination of the spectral coefficients in an independent way. It is simple and can be implemented with small amount of storage space. The algorithm is interactive so the users can manually determine the generation of a part of a spectrum. At the end of the article, experimental results of the algorithm for several 5-valued test files are shown.
A small, low-cost FM-CW demonstrator system has been designed to investigate the feasibility of the application of FM-CW SAR in the field of airborne earth observation. A Ka-band backscatter model function and an algorithm for measurement of the wind vector over the water surface by this demonstrator system in the scatterometer mode have been developed. The principle considered, backscatter model and measuring algorithm proposed can be used for creating an airborne radar system for operational measurement of the sea roughness characteristics and for safe landing of an amphibious airplane on water, in particular under search and rescue missions in coastal areas.
An object mounting structure has been developed for use in millimeter-wave scanning near-field microscopy in order to efficiently reduce both unwanted signal fluctuations caused by surface waves within the object to be imaged and reflections from outside the object. The object mount comprises a hemispherical lens with an anti-reflection (AR) layer covering the spherical surface. An object mount for use at a millimeter-wave frequency of 60GHz has been designed and fabricated. Experiments performed at 60GHz show that signal fluctuations resulting from the above two factors can be dramatically reduced using this object mounting structure.