High resolution refractive index sensing with cladded multimode tapered optical fibre

A new fibre-optic refractive index sensor is presented. It is based on the radiation losses introduced by the sample medium in a cladded multimode tapered fibre. A simple light transmission measurement setup is used to test some samples. It is demonstrated that the sensor is suitable for measuring RI in the range 1.36 to 1.46, as well as RI changes below 10/sup -4/.     

Refractive index sensing with long-period grating fabricated in biconical tapered fibre

A single long-period fibre grating was written in a biconical fibre taper made from standard communications step-index optical fibre, resulting in an interferometric fibre sensor device that provided a resolution of 1/spl times/10/sup -4/ for refractive indices in the range of 1.30 to 1.34, suggesting that these devices may be suitable for use with aqueous solutions.     

基于Zemax紫外气体检测仪中的光学系统设计

基于Cassegrain望远镜系统并借助光学设计软件Zemax设计了一种收发同置的SO2气体浓度检测仪的光学系统,采用Cassegrain望远镜系统,把发射和接受安放在同一个装置中,使得装置结构紧凑、体积小、易加工。给出了光学系统的设计参数和指标,以及理论及实验测得的光源能量使用效率和距离之间的变化曲线。使用该光系统的SO2气体浓度检测仪的测量精度及指标可与美国MonitorLabs公司的ML9850B仪器相比。     

All-silica package for tapered couplers

The primary packaging of singlemode tapered couplers, by fusing the fibre leads with a negligible loss to a silica substrate, is reported. This procedure eliminates adhesive, and ensures matched coefficients of thermal expansion throughout.<>     

熔锥光纤器件的锥区特性

从理论和实验两方面研究了熔锥光纤器件的锥区的传输、耦合、偏振和调制特性.用耦合模理论分析给出了锥形光纤传输和耦合效率与锥区结构的关系.实验上测定了实际锥形光纤在不同锥角、不同长度下的偏振特性,得出偏振光经实际锥形光纤传输或耦合后,再传输其终端,得到均是椭圆偏振光的结论.测定了载波光脉冲经过锥形光纤耦合后其脉冲的变化特性,实验表明,光脉冲在经过锥形光纤耦合传输后其形状保持不变.     

Approximate variances for tapered spectral estimates

We propose an approximation of the asymptotic variance that removes a certain discontinuity in the usual formula for the raw and the smoothed periodogram in case a data taper is used. It is based on an approximation of the covariance of the (tapered) periodogram at two arbitrary frequencies. Exact computations of the variances for a Gaussian white noise and an AR(4) process show that the approximation is more accurate than the usual formula.     

A novel approach to high-speed high-resolution on-chip mass sensing

The state-of-the-art mass sensing so far has been rather developed along the resolution axis, reaching atomic-scale detection, than into the direction of high-speed. This paper reports a novel self-calibrating technique, making high-speed inertial mass sensors capable of instant high-resolution particle detection and weighing. The sensing nanoelectromechanical resonator is embedded into a phase-locked loop and the sensor-inherent nonlinear phase–frequency relation is exploited for auto-calibration. A tunable on-chip carbon nanotube based mass balance serves as a case study of small-size and low-cost environmental and healthcare applications. Tunability and a phase-locked loop topology make the system widely universal and invariant to nanotube characteristics. Operational for tube eigenfrequencies up to 385 MHz, the circuit integration in a 180 nm technology achieves instantaneous zeptogram resolution, while yoctogram precision is obtained within the tenth of a second. These figures of merit range at the physical limits of carbon nanotube resonators, in both mass- and time-resolution.     

Self-consistent vector coupled-mode theory for tapered opticalwaveguides

A nonorthogonal coupled-mode theory for nonparallel waveguides is derived. An orthogonal coupled-mode theory is developed based on the exact local array modes. The relation between the two formulations is established. Closed-form solutions are obtained for the two-guide synchronous tapered coupler. The formalism obeys power conservation     

Flexible pillars for displacement compensation in optical chip assembly

In chip-to-chip optical interconnect systems with surface mounted light-sources and detectors, thermal and mechanical effects can cause lateral displacements of the assembled devices. These displacements can result in optical signal losses that can critically deteriorate the bit-error-rate of the digital system. We demonstrate that, for a given loss budget of 1 dB, the use of flexible optical pillars with 150-/spl mu/m height and 50-/spl mu/m diameter can double the lateral displacement tolerance from about 15 to 30 /spl mu/m. The pillars fabricated from Avatrel polymer form an air-free path between the light source and the substrate and cause maximum optical power losses less than 0.2 dB.     

Optimum tapered buffer

Driver stages in MOS circuitry have been extensively investigated during the last decade. recently a tapering rule for CMOS buffers was derived showing that the tapering factor (β) is determined by the ratio of output to input capacitance. The derivation fails to account for the correlation between the short-circuit current and β. As a result, the derived formula consistently overpredicts the value of optimum β, especially for large input/output capacitance ratios. The authors present a modified formula and a method to account for the effect of the short-circuit current that is viable for buffer stages over a wide range of output/input capacitance ratios; this newly derived formula accurately predicts the optimum tapering factors for BiCMOS as well as CMOS buffer chains     

CMOS tapered buffer

Jaeger's buffer comprises a string of tapered inverters. Each inverter is molded by a capacitor and a conductor. In this work, the capacitor is split into inherent and load components (C_x and C_y), and it is shown that the value of the optimal taper depends on the C_x/C_y ratio: the best taper exceeds Jaeger's 2.72 slope, but only moderately     

Assessment of coupled-mode theory for tapered optical coupler

The accuracy and the scope of validity of different coupled-mode formulations for a tapered optical waveguide coupler are assessed by comparison with the beam propagation method (BPM). It is demonstrated that the coupled-mode theory (CMT) based on local modes is valid only for small tilt angles, whereas an improved formulation that takes into account the wavefront-tilt effect yields highly accurate results for relatively large tilt angles. The radiation loss at the input and the output junctions can also be estimated by a simple mode-matching method combined with the improved CMT. The coherent coupling between two junctions,which is neglected in the coupled-mode formulations, is observed in the BPM simulations.<>     

Compact linear tapered slot antenna for UWB applications

A novel ultra-wideband (UWB) antenna consisting of a linear tapered slot in the ground plane and a microstrip to slotline transition is investigated. The antenna possesses a wide bandwidth from 2.95?14 GHz for |S₁₁| < - dB and shows stable radiation patterns with an average gain of 3 dBi throughout the band. Measured group delay and transmission characteristics indicate that the antenna has good pulse handling capabilities.     

Investigation of tapered multiple microstrip lines for VLSIcircuits

The analysis of tapered, coupled microstrip transmission lines is presented. These lines, used as interconnects between integrated circuit devices, are modeled using an iteration-perturbation approach applied in the spatial domain. From this model, a frequency-dependent scattering parameter characterization is determined. A time-domain simulation of pulse propagation through the tapered, coupled microstrip lines is performed. The frequency-domain scattering parameters are inverse Fourier transformed to obtain the time-domain Green's function. The input pulse is convolved with the Green's function, and a Newton-Raphson algorithm is applied to account for nonlinear loads. Some experimental results are shown, and a simulation approximation is proposed     

A unified design methodology for CMOS tapered buffers

In this paper, the various disparate approaches to CMOS tapered buffer design are unified into an integrated design methodology. Circuit speed, power dissipation, physical area, and system reliability are the four performance criteria of concern in tapered buffers, and each places a separate, often conflicting, constraint on the design of a tapered buffer. Enhanced short-channel tapered buffer design equations are presented for propagation delay and power dissipation, as well as a new split-capacitor model of hot-carrier reliability of tapered buffers and a two-component physical area model. Each performance criterion is individually investigated and analyzed with respect to the number of stages and tapering factor, and the interaction of the four criteria is examined to develop both a qualitative and a quantitative understanding of the various design tradeoffs. The creation of process dependent look-up tables for optimal buffer design is described, and a methodology to apply these look-up tables to application-specific tapered buffers for both unconstrained and constrained systems is developed     

Integrated uniplanar transition for linearly tapered slot antenna

This paper presents the design, fabrication, and numerical modeling of two new uniplanar microstrip-to-coplanar strip (CPS) line transitions and a new variant of the linearly tapered slot antenna (LTSA). This new variant with an integrated uniplanar microstrip-to-coplanar strip line feed is called a V-LTSA. The advantages of these transitions in packaging and monolithic microwave integrated circuits (MMIC) integration are listed. The two transitions and the feed are modeled using finite difference time domain (FDTD) method. The overall agreement between the measured and modeled return-loss and insertion-loss characteristics of two back-to-back transitions is good. The resonance frequencies predicted by the FDTD method are within a few percentage points of the measurements. Furthermore, the V-LTSA with the feed is experimentally shown to have a wide return loss (⩽-10 dB) bandwidth, good radiation patterns, and low cross-polarization. The gain of the V-LTSA is 9 dB at the design frequency of 10 GHz. A proof-of-concept package to house the feed is experimentally evaluated and shown to have negligible effect on the antenna characteristics. This type of antenna readily integrates with MMIC packages in an array having a brick architecture. The V-LTSA has potential applications in phased arrays     

Load balancing multipath routing protocol for mass remote sensing data downlink in LEO satellite network

LEO satellite networks can provide seamless real-time data communication for all kinds of users,which developed rapidly in recent years.At the mean time,the massive payload data down-link system of space data sources,such as remote sensing satellites,still make use of traditional storage and forward mode.The real-time performance of space mission data will be improved effectively,if such satellites are connected to LEO satellite networks equipped with inter satellite links.However,it is necessary to design a specialized satellite network load balancing routing algorithm.Satellite parallel edge-disjoint multipath routing protocol (SPEMR) was designed for remote sensing satellite real-time down-link applications.OPNET simulation results indicate that the performance degradation index(DI) of the multipath scheme implemented by SPEMR is 0.32,which is only 32% of the TLR and 21% of the traditional DSP scheme.It is demonstrated that SPEMR has the better capability of transmitting massive data in real time.     

二级倒立摆的模糊控制

研究了二级倒立摆系统的模糊控制问题,提出了一种结构新颖的模糊控制律。通过对控制律的参数寻优和调整,实现了二级倒立摆的稳定控制。仿真研究表明：本文提出的模糊控制算法无论是动态指标还是稳态精度方面都有明显的优越性。     

The five pillars of organizational excellence

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Adiabatic fused tapered couplers

Pre-fattening of one fibre is shown to be a vehicle for achieving wavelength independent adiabatic fused tapered couplers. Compared with the conventional pre-tapered fused tapered coupler, this adiabatic coupler has a significant improvement in its ease of manufacture