Design and analysis of coplanar waveguide optical modulator using finite element method

An analysis is given on the finite element method (FEM) for calculating the various parameters of optical modulators and a computer program is written to solve the finite element equation. Based on this method, a Mach-Zehnder type electro-optic modulator with coplanar waveguide (CPW) electrode is designed and fabricated. When compared with the Fourier series method, small differences on the 3-dB bandwidth, characteristic impedance and half-wave voltage, etc. are obtained.     

High-power multi-mode laser to single-mode pump conversion

A novel pump-sharing module for multi-channel amplifiers based on integration of high-power multimode semiconductor lasers and planar waveguide circuits is proposed. The feedback-free modules are designed for optimum coupling, throughput and power uniformity on silicon using BPM method and fabricated via the sol-gel process of photo patternable precursors. Modal properties of the multimode lasers are considered by studying spectrum and spatial distribution of laser output power at different temperatures. Employing an 1500 mW 980 nm multimode laser (TE polarized), via lens and Butt coupling up to 1250 mW of laser output is coupled into the multimode channel waveguides, which are tapered and branched to four single mode waveguides. The measured pump power from splitter outputs, randomly polarized, exceeds 600 mW. At constant temperatures ranging from 22 °C to 30 °C, the pump-sharing modules exhibit good stability with a power uniformity of <0.5 dB over hours.     

Solvent detection using porous silicon optical waveguides

Since the first report on the use of porous silicon as an optical waveguide medium in 1995, significant development has been made towards the understanding and applicability of such material. Here, the introduction of solvents (acetone, methanol, and propan-2-ol) into the pores is shown to dramatically reduce the loss of the waveguides, in a reversible manner. Both the magnitude and duration of this effect are sensitive to the solvent introduced. In some waveguides, for example, the measured loss (at 0.633 μm) falls by as much as 34 dB cm⁻¹ on the introduction of acetone. Theoretical estimates of the effect of solvents on the interfacial scattering loss confirm this as the origin of the observed reductions. These results, combined with the fact that a substantial portion of the guided-mode field interacts with the solvent, indicate an enhanced sensitivity for sensor applications may be achievable.     

BESOI光波导的研制

本文通过大量实验,采用键合及背腐蚀方法研制成功 SOI 光波导,传输损耗仅0.85dB/cm.     

Simulations of flows and water depth in a dendritic river system

This paper presents the development of a channel hydrodynamic model for simulating the behaviour of flows and water depths in a river network that may consist of any number of joined and branched rivers/streams, including both tidal and non-tidal rivers. The model employs a numerical method—an integrated compartment method (ICM). The method greatly facilitates the set-up of algebraic equations for the discrete field approximating the corresponding continuous field. Most of the possible boundary conditions that may be anticipated in real-world problems are considered. These include junctions, prescribed flow, prescribed water depth (or cross-sectional area), and rating curve boundaries. The use of ICM makes the implementation of these four types of boundary conditions relatively easy. The model is applied to two case studies: first to a single river and then to a network of five river branches in a watershed. Results indicate that the model can simulate the behaviour of the hydrodynamic variables that are required to compute chemical transport in a river-stream network.     

0.5μm X-ray lithography: Developments in microstructure processes

Summary X-ray lithography is a 1∶1 shadow printing technique, so that both patterning and resist performance, in the mask fabrication process, are critical to this technology. In this paper, results of resist performance are presented, which meet immediate mask copying requirements and those of prospective printing applications. Furthermore, a single-layer resist process is presented, for master mask fabrication by electron beam lithography, resulting in high-quality, high-resolution patterns down to 0.5μm (1∶1 lines and spaces) and even 0.2 μm (single lines). 8000 ? thick Au absorber structures are obtained, exhibiting vertical walls and sharp edges, suitable for X-ray lithography with relatively hard radiation in general, and synchrotron radiation in particular. Boron nitride substrates are utilized, under conditions in which negligible scattering effects are observed. The results are discussed in the light of Monte Carlo calculations.

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Riassunto La litografia a raggi X è una tecnica di proiezione 1∶1, cosicché sia il pattering che la prestazione dei resist, nel processo di fabbricazione delle maschere, sono critici per questa tecnologia. In questo articolo sono presentati dei risultati relativi a prestazioni di resist che soddisfano i requisiti necessari alla copiatura della maschere e, in prospettiva, anche i requisiti di una litografia per produzione. Inoltre, si presenta un processo che utilizza un singolo strato di resist, nella fabbricazione di maschere mediante litografia a fascio elettronico, che porta a risultati di alta qualità: righe fino a 0.5μm (nel caso di linee e spazi 1∶1) e 0.2μm (linee singole). Gli assorbitori di oro, di spessore 8000 ?, sono adatti per una litografia a raggi X con radiazione relativamente dura: in particolare, con luce di sincrotrone. Vengono utilizzati substrati di nitruro di boro in condizioni nelle quali si osservano trascurabili effetti di scattering elettronico. I risultati sono analizzati alla luce di calcoli di scattering effettuati col metodo Monte Carlo.

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Резюме Рентгеновская литография представляет технику 1∶1 теневых отпечатков, так что копирование и изготовление сопротивления существенно зависят от теънологии. В этой работе приводятся результаты по изготовлению сопротивлений. Предлагается процесс изготовления одно-слойного резистора с помощью электронно-лучевой литографии, результаты характеризуются высоким качеством, высоким разрешением до 0.5 микрон и даже до 0.2 микрон (отлельные линии). Получаются структуры Au поглотителя толщиной 8000 ?, имеющие вертикальные стенки и острые края, подходящие, в общем случае, для рентгеновской литографии с относительно жестким излучением и, в частности, с использованием синхротронного излучения. Используются подложки из нитрида бора при условиях, когда наблюдаются пренебрежимо малые эффекты рассеяния. Полученные результаты обсуждаются в свете моделирования по методу Монте Карло.

     

Planar leaky light-guides and couplers

A quantitative theory of light propagation in a dielectric slab guide with general cladding media is presented. It is based on a plane wave which bounces in a zigzag fashion along the guide as a result of total or partial reflections at the two surfaces of the film. Two mechanisms are considered which contribute to the attenuation of the guide: losses due to absorption in the slab and cladding materials, and radiation losses if the guide is a leaky one. We point out the significance of the Goos-H?nchen effect for all questions relating to the power flow in the slab guide. The theory is illustrated by discussing dispersion and attenuation of guides with various low-index and high-index claddings, operating above and below cutoff. The low-index leaky guide is considered particularly in detail. Its high attenuation by leakage can be reduced to practically acceptable values (<1d B/cm) by increasing the film thickness to ≳ 40λ. One application of this guide is in the leaky wave coupler. This coupler may be viewed as a prism-film coupler simplified by omission of the gap. It offers a new approach to the problem of broad-band coupling to thin-film light guides.     

2-dimensional localization of acoustic waves in random perturbation of periodic media

In this work we study internal band edges localization of acoustic waves in 2-dimensional space obtained by random perturbation of some periodic media. Our results rely on the study of Lifshitz tails for the integrated density of states for random acoustic operators of the form . Localization is then deduced by the standard multiscale argument.     

Design of organic 3D microresonators with microfluidics coupled to thin-film processes for photonic applications

We report on the design and realization of photonic integrated devices based on 3D organic microresonators (MR) shaped by an applied fluid mechanism technique. Such an interdisciplinary approach has been judiciously achieved by combining microfluidics techniques and thin-film processes, respectively, for the realizations of microfluidic and optical chips. The microfluidic framework with flow rates control allows the fabrication of microresonators with diameters ranging from 30 to 160 μm. The resonance of an isolated sphere in air has been demonstrated by way of a modified Raman spectroscopy devoted to the excitation of Whispering Gallery Modes (WGM). Then the 3D-MR have been integrated onto an organic chip and positioned either close to the extremity of a taper or alongside a rib waveguide. Both devices have proved efficient evanescent coupling mechanisms leading to the excitation of the WGM confined at the surface of the organic 3D-MR. Finally, a band-stop filter has been used to detect the resonance spectra of organic resonators once being integrated. Such spectral resonances have been observed with an integrated configuration and characterized with a Δλ = 1.4 nm free spectral range (FSR), appearing as stemming from a 78 μm-radius MR structure.     

Design, simulation and characterisation of integrated optics for a microfabricated flow cytometer

Flow cytometry is widely used for analyzing micro-particles such as cells and bacteria. Microfabricated flow cytometers promise reduced instrument size and cost with increased robustness and have application in medicine, life sciences and environmental metrology. Further miniaturisation and robustness can be achieved if integrated optics are used instead of traditional free space optics. We present designs simulation and experimental characterisation of integrated optics for a microfabricated cytometer made from SU-8 resin on a glass substrate. The optics constructed from combinations of optical fibres (positioned with microgrooves), waveguides, and microlenses enable analysis of scattered light and fluorescence from particles positioned near the centre of a microchannel using one dimensional sheath flow. Four different methods for directing the incident light onto the particles are examined and the optimum design discussed.