Determination of nitrites and nitrates in plasma-activated deionized water by microchip capillary electrophoresis

In this work, we present the application of a fast and sensitive microanalytical method, microchip capillary electrophoresis (MCE), for the determination of NO₂⁻ and NO₃⁻ ions in deionized water treated by atmospheric pressure plasma jet (APPJ). The MCE technique consisted of an online combination of isotachophoresis with zone electrophoresis, both performed on the microchip. The argon plasma has been characterized by optical emission spectroscopy (OES) and Fourier transform infrared spectroscopy (FTIR). OES confirmed the presence of argon excited species (Ar I) emission (4p → 4s) lines, N₂ emission bands (second positive system C³Π_u → B³Π_g), and OH band (A²∑⁺ → X²Π Δv = 0), as well as the presence of NO and excited NO₂. The presence of NO₂ molecules was also confirmed by FTIR absorption spectroscopy. The performance of the developed MCE method was evaluated for linearity, limit of detection, limit of quantitation, precision, and accuracy, and the concentration of NO₂⁻ and NO₃⁻ in the water as a function of the water treatment time was monitored.     

Novel electroabsorption modulator monolithically integrated with spot-size converter

A novel 1.55-μm spot-size converter integrated electroabsorption modulator was designed with conventional photolithography and chemical wet etching process. A ridge double-core structure was employed for the modulator, and a buried ridge double-core structure was incorporated for the spot-size converter. The passive waveguide was optically combined with a laterally tapered active waveguide to control the mode size. The figure of merit is 4.1667 dB/V(/100 μm) and the beam divergence angles in the horizontal and vertical directions were as small as 11.2°and 13.0°, respectively.     

Novel electroabsorption modulator monolithically integrated with spot-size converter

A novel 1.55-μm spot-size converter integrated electroabsorption modulator was designed with conventional photolithography and chemical wet etching process. A ridge double-core structure was employed for the modulator, and a buried ridge double-core structure was incorporated for the spot-size converter. The passive waveguide was optically combined with a laterally tapered active waveguide to control the mode size. The figure of merit is 4.1667 dB/V(/100μm) and the beam divergence angles in the horizontal and vertical directions were as small as 11.2° and 13.0°, respectively.     

All-optical sampling with a monolithically integrated Mach-Zehnder interferometer gate

An all-optical sampler consisting of a polarization-independent monolithic Mach-Zehnder interferometer with integrated semiconductor optical amplifiers and a temporal resolution of 1 ps is presented. As an example, a simple 320-Gbit/s pattern has been successfully sampled, demonstrating the functionality of this scheme for high-bit-rate waveform characterizations in light-wave systems.     

A scanning laser induced fluorescence detection system for capillary electrophoresis microchip based on optical fiber

In this paper, a scanning laser induced fluorescence detection system for capillary electrophoresis microchip based on single-mode optical fiber has been established using a green diode pumped solid-state laser as excitation source. It includes laser induced fluorescence detection subsystem, capillary electrophoresis microchip, mechanical scanning platform, channel identification unit and fluorescent signal processing subsystem. Two V-shaped detecting probes composed of optical fiber for transmitting the excitation light and detecting the induced fluorescence were constructed. Parallel four-channel signal analysis of capillary electrophoresis was performed by this system using Rhodamine B sample solution. Furthermore, the separation and distinction of different concentrations of Rhodamine B sample were achieved with the constructed detection system. The lowest detected concentration is 1.0 × 10⁻⁵ mol/L for Rhodamine B sample. The results show that the constructed detection system possesses some advantages of compact structure, low cost, and better stability which could be used as reference to the design and optimization of laser induced fluorescence detection system for capillary electrophoresis microchip.     

Nonreciprocity of counterpropagating signals in a monolithically integrated Sagnac interferometer

We demonstrate nonlinearly induced nonreciprocity of counterpropagating waves in a monolithically integrated Sagnac interferometer that employs a semiconductor optical amplifier as the nonlinear element. We show that the dependence of the linewidth enhancement factor on charge injection can influence the third-order nonlinearity in the semiconductor gain medium to a surprisingly large degree. This effect is utilized to control the phases of the counterpropagating signals in the interferometer. A theoretical model is used to explain the experimental observations. We show that these effects have significant practical implications by demonstrating an all-optical controlled-NOT gate.     

Gel-based optical waveguides with live cell encapsulation and integrated microfluidics

In this Letter, we demonstrate a biocompatible microscale optical device fabricated from agarose hydrogel that allows for encapsulation of cells inside an optical waveguide. This allows for better interaction between the light in the waveguide and biology, since it can interact with the direct optical mode rather than the evanescent field. We characterize the optical properties of the waveguide and further incorporate a microfluidic channel over the optical structure, thus developing an integrated optofluidic system fabricated entirely from agarose gel.     

A germanium photodetector array for the near infrared monolithically integrated with silicon CMOS readout electronics

Near infrared (NIR) detectors, operating in the 1.3–1.6 μm region, are key elements in a number of applications ranging from optical communications to remote sensing. InGaAs and Ge are currently the materials of choice for the fabrication of NIR detectors due to their good absorption and transport properties. However, as the required performances increase (bit-rate in optical communications, number of pixels in imaging, etc.), it becomes more and more important to reduce the separation from detectors and driving/biasing and amplifying electronics, by integrating the two components on the same chip.We demonstrate an array of NIR detectors monolithically integrated with standard silicon CMOS readout electronics. The employed low temperature process allowed the integration of the detectors as the last step of chip fabrication. The integrated micro-system consists of a linear array of 120×120 μm² pixels, an analog CMOS multiplexer and a transimpedance amplifier. The chip exhibits a good photoresponse in the NIR, with responsivities as high as 43 V/W at 1.3 μm, dark currents of 1 mA/cm² and inter-pixel cross-talk better than −20 dB.     

Optoelectronic properties analysis of silicon light-emitting diode monolithically integrated in standard CMOS IC

Si p~+n junction diodes operating in the mode of avalanche breakdown are capable of emitting light in the visible range of 400–900 nm. In this study, to realize the switching speed in the GHz range, we present a transient model to shorten the carrier lifetime in the high electric field region by accumulating carriers in both p and n type regions. We also verify the optoelectronic characteristics by disclosing the related physical mechanisms behind the light emission phenomena. The emission of visible light by a monolithically integrated Si diode under the reverse bias is also discussed. The light is emitted as spatial sources by the defects located at the p–n junction of the reverse-biased diode. The influence of the defects on the electrical behavior is manifested as a current-dependent electroluminescence.     

Vectorial wave-matching mode analysis of integrated optical waveguides

For mode fields of integrated optical waveguides with piecewise constant and rectangular permittivity profile, Maxwell's equations reduce to the two-dimensional Helmholtz wave equation, supplemented by continuity requirements on the boundaries between different media. Two basic components of the mode field are expanded into factorizing harmonic or exponential functions, separately on each rectangular region. We determine approximations for guided modes and propagation constants by means of a minimization procedure based on a least squares expression for the mismatch in the continuity requirements. Results for the hybrid mode fields of typical sample waveguides classify this approach as competitive with and superior to alternative methods for vectorial mode analysis, although some open questions remain.     

Morphological stability in epitaxy of semiconductors — application to optoelectronic monolithically integrated structures

A simple selection rule for epitaxial growth techniques, which is based on morphological stability of the substrate surface is proposed. According to this rule a certain growth technique should be used for preparing a specific device structure of a three-dimensional monolithically integrated optical or electronic circuit. The formulae for morphological stability functions for LPE, MO, VPE, and MBE growth techniques are given. Calculations performed for the GaAs/Al _x Ga_1–x As material system by using the linear morphological stability theory of Mullins and Sekerka suggest that from the point of view of morphological stability the most suitable growth technique for fabrication of three-dimensional monolithically integrated optical and electronic device structures is the MBE technique.On leave from the Institute of Physics, Polish Academy of Sciences, PL-02-668 Warsaw, Poland     

Sensitive detection and separation of fluorescent derivatives using capillary electrophoresis with laser-induced fluorescence detection with 532 nm Nd:YAG laser

Capillary electrophoresis with laser-induced fluorescence detection (CELIF) is a powerful tool for separation and sensitive determination of fluorescent species. Biologically active compounds, such as amino acids, peptides and proteins may exhibit native fluorescence, which is however often low and/or an expensive laser is required for excitation in UV. Therefore, labelling of the analytes with a fluorescent dye is usually necessary.In this work, a home-built CELIF instrument with diode pumped frequency-doubled continuous wave Nd:YAG excitation laser with feedback power regulation (532 nm) was constructed. The suitability of this type of laser for LIF detection in a separation method was found excellent. A limit of detection (LOD) (S/N=3) of 2×10⁻¹³ mol/l was achieved with rhodamine B, which is comparable to those obtained using similar instruments with Ar⁺ laser [Y.F. Cheng, N.J. Dovichi, Science 242 (1988) 562, E.S. Yeung et al., J. Chromatogr. 608 (1992) 73]. LOD of a protein derivatized according to modified procedures [M.J. Little et al., Anal. Chim. Acta 339 (1997) 279, A. Chersi et al., Biochim. Biophys. Acta 1336 (1997) 83] was determined. Detection of the derivatives was found to be limited by insufficient reaction recovery at low analyte concentration, chemical noise, separation efficiency and quality of the derivatizing reagent rather than by the detector performance. As a consequence, a huge gap between the detection ability of CELIF instruments and LOD determined in real samples is revealed.     

Facet-embedded thin-film III-V edge-emitting lasers integrated with SU-8 waveguides on silicon

A thin-film InGaAs/GaAs edge-emitting single-quantum-well laser has been integrated with a tapered multimode SU-8 waveguide onto an Si substrate. The SU-8 waveguide is passively aligned to the laser using mask-based photolithography, mimicking electrical interconnection in Si complementary metal-oxide semiconductor, and overlaps one facet of the thin-film laser for coupling power from the laser to the waveguide. Injected threshold current densities of 260A/cm(2) are measured with the reduced reflectivity of the embedded laser facet while improving single mode coupling efficiency, which is theoretically simulated to be 77%.     

Propagation of X-ray femtosecond pulses through tapered nanometer-scale capillary waveguides

It is shown that temporal broadening of an X-ray femtosecond pulse under propagation through a tapered nanometer-scale waveguide is negligible small for the wide region of the guide and pulse parameters. The output pulse has the step-like transverse intensity distribution. The conventional waveguide theories do not predict this phenomenon.     

单片集成微环反射器可调谐半导体环形激光器理论和数值模型(英)

设计了一种新颖的快速可调谐激光器。这种激光器在恒定电流泵浦的有源微环组成的半导体环形激光器腔外部集成一个可调谐的无源微环反射器,其结构将决定激光器激射腔模的有源腔和无源可调谐部分分离,有助于提高调谐速度。与光栅结构的激光器相比,该激光器结构简单,具有强烈的选模功能,不需要相位匹配部分,输出波长不受调谐部分热效应的影响。基于多模速率方程建立了激光器的理论和数值模型,数值仿真结果表明该激光器能在选取的15个腔模范围内完成数字调谐,且具有40 mA的较低阈值电流和适中的边模抑制比。     

单片集成微环反射器可调谐半导体环形激光器理论和数值模型(英)

设计了一种新颖的快速可调谐激光器。这种激光器在恒定电流泵浦的有源微环组成的半导体环形激光器腔外部集成一个可调谐的无源微环反射器,其结构将决定激光器激射腔模的有源腔和无源可调谐部分分离,有助于提高调谐速度。与光栅结构的激光器相比,该激光器结构简单,具有强烈的选模功能,不需要相位匹配部分,输出波长不受调谐部分热效应的影响。基于多模速率方程建立了激光器的理论和数值模型,数值仿真结果表明该激光器能在选取的15个腔模范围内完成数字调谐,且具有40 mA的较低阈值电流和适中的边模抑制比。     

Application of capillary electrophoresis in anion binding studies: Complexation and separation of nitrate and nitrite by an azacryptand

Capillary electrophoresis (CE) was employed for studying the complexation of an azacryptand with nitrate and nitrite in aqueous solution. CE separation of a mixture of nitrate and nitrite with 10 mM acetate buffer (pH 3.3) showed two peaks at the retention times of 2.8 and 3.1 min for nitrate and nitrite, respectively. However, when the ligand (2 mM) was added to the running buffer, the peaks emerged in the reverse order and at shorter retention times of 2.7 and 2.5 min for nitrate and nitrite, respectively. The longer retention time for nitrate compared with nitrite indicates a stronger complex formation between the ligand and nitrate, that reduces the migration speed of nitrate as compared with the less strongly bound nitrite. The (1)H NMR titrations of L with these two anions at the pH 3.3, gave the binding constants (log K), 3.75 and 4.23, for nitrite and nitrate, respectively which were in consistence with the results obtained from the CE method.     

Chalcogenide glass waveguides integrated with quantum cascade lasers for on-chip mid-IR photonic circuits

We demonstrate on-chip hybrid integration of chalcogenide glass waveguides and quantum cascade lasers (QCLs). Integration is achieved using an additive solution-casting and molding method to directly form As(2)S(3) strip waveguides on an existing QCL chip. Integrated As(2)S(3) strip waveguides constructed in this manner display strong optical confinement and guiding around 90° bends, with a NA of 0.24 and bend loss of 12.9dB at a 1mm radius (λ=4.8μm).     

单片集成放大反馈激光器的脉冲包络动力学实验研究

实验研究了由分布反馈激光器区(DFB区)、相位控制区(P区)以及放大反馈区(A区)所构成的三段式单片集成放大反馈激光器(AFL)所产生的脉冲包络(PPs)的动力学特征,并分析了P区电流I_P和A区电流I_A对PPs的重复频率νPP以及包络规则性的影响.研究结果表明:DFB区电流IDFB相对较大时,AFL存在两个模式,此时通过选取合适的I_P和I_A可使AFL工作在PPs动力学状态;对于一给定的I_P,I_A在两个分离区域内可使AFL呈现PPs状态.随着I_A的增加,在I_A相对较小的区域,AFL输出PPs的重复频率νPP以及表征PPs规则性的时间序列自相关函数的次最大值σ均呈现单调下降趋势.而在I_A相对较大的区域,νPP呈现出先减小然后小幅波动的变化趋势,而σ则总体呈现先增加后减小的趋势;对于一给定的I_A,I_P的变化也会对AFL输出PPs的特性产生显著影响,在AFL呈现PPs状态所要求的I_P的变化范围内,随着I_P的增加,νPP呈现出先减小后增大而σ则呈现先增加后减小的变化趋势.通过观测I_A,I_P连续变化时AFL的动力学特性,确定了AFL呈现PPs在I_A和I_P构成的参量空间的分布图谱.     

Analysis of DNA sequencing systems based on capillary electrophoresis

A method for characterization and optimization of DNA sequencing systems based on capillary electrophoresis is proposed. A model is developed that relates the read length of a sequencing run and the parameters of DNA sequencing systems such as the properties of the separation medium, capillary length, injection time, concentration of the injected DNA sample, detection sensitivity, system noise, and the illumination power. The optimization of DNA sequencing systems will allow determination of optimum regimes for preparation, injection, and separation of DNA samples needed for achieving a read length required. The method proposed is applied to the characterization of capillary-electrophoretic DNA sequencing systems based on single-photon detection.