Low-loss highly overcoupled fused couplers: fabrication andsensitivity to external pressure

A flame brush technique for fabrication of optical directional couplers that maintain low loss over many coupling cycles is discussed. Couplers with excess losses less than 3% and with 2500 power transfer cycles in the coupling are reported. Such couplers, which have a narrow wavelength band transmission (0.12 nm), can be tuned by applying an external hydrostatic pressure. The long fused couplers can also have application as optical fiber sensors     

Fabrication of polarisation-maintaining [3×3] single-mode-fibre couplers

[3×3] fused fibre couplers have been fabricated with polarisation-maintaining and absorption-reducing (PANDA) fibres. The couplers can hold linear polarisation along the principal axis of the fibre branches, showing an extinction ratio better than ?15 dB.     

Explaining strain [in silicon]

Large effects of elastic strain on the electrical resistance of silicon were discovered not long after the recognition of silicon as the material for the development of solid-state electronics. The effects were shortly employed as the basis of a variety of mechanical sensors. More recently, the use of strain to improve the performance of field-effect transistors (FETs) has drawn increased attention to its role as a part of the arsenal of silicon electronic technology. Attention to unwanted strain as a source of problems is also increasing. This article is aimed at explaining the basis of the effects of strain on the electrical properties of n-silicon and how these effects produce both good and bad results.     

CCDing in the dark [thermal imaging sensors]

A new generation of thermal imaging sensors based on charge-coupled devices (CCDs) is described, and their use in night vision systems is discussed. The advantages of custom analog CCD technology over the earlier digital approach and its noise performance are examined. Some military night vision systems are described     

Fiber wavelet filters [and planar waveguide couplers for full-wavelength demultiplexers]

The passive optical networks proposed by Marhic and Siegman to evaluate the discrete Fourier transform (DFT) of a linear array or a pixellated image (parallel input) are redesigned for the discrete wavelet transform or the wavelet packet (WP) decomposition. Using only asymmetric optical couplers, with a suitable power coupling ratio, it is shown that it is possible to optically implement Mallat's pyramidal decomposition scheme with a compactly supported wavelet basis function. The case of a serial input has a larger number of potential applications to optical communications systems or optical computing, and simple passive optical networks are presented that evaluate the DFT or the wavelet transform of a stream of optical digits, by using only Mach-Zehnder interferometers with output asymmetric couplers. In particular, an all-optical implementation of the WP-division demultiplexer for a waveform coded transmission system is given. The proposed networks are full-wavelength demultiplexers, as they split the spectrum of the incoming signal into a set of closed frequency channels; the filters have identical bandwidth and span the whole input spectrum. Using the WP-decomposition method, different subband filtering schemes can be designed, fabricating trees of quadrature mirror filters with the fiber or the integrated optics technology.     

Multiplexing of fibre optic intensity sensors using fused biconicalwavelength selective couplers

Fused biconical wavelength division multiplexers have been used to replace standard couplers in an intensity-sensor multiplexing network. The wavelength-selective power splitting and the low insertion losses of these devices (<0.2 dB) improve the power budget, while providing network overall optical isolations >30 dB. With this isolation, crosstalk effects in the network are proven to be negligible     

Large wavelength shifts in UV-exposed 3 dB and WDM fused taperfibre couplers

The spectral response of 3 dB and 1300/1550 nm wavelength division multiplexing fused taper fibre couplers can be shifted by over 100 nm by exposing the entire coupler with intense UV light at a wavelength of 193 nm and without prior hydrogenation. There is no discernable increase in excess loss. The major contribution to these shifts for these couplers originates in the down- and up-taper regions     

Computer-aided design tool for electromagnetic sensors - [instrumentationnotes]

Numerical simulation is an invaluable tool for the designer of any device. By providing a model of the sensor within the design parameters, simulation can substantially speed up and simplify the design process and give a reliable estimation. The use of optimization algorithms can lead to much better sensor characteristics and reduce sensor costs and operation.     

提高应变式力传感器综合性能的措施

分析了应变式力传感器虚变片粘粘位置选取的内在机理,提出了提高应变式力传感器的测试灵敏度,减小其非线性误差的实用措施。     

Letter to the editor [Use of periodic functions for equipmentdesign]

It is pointed out that there has long been unease about using a periodic function, such as a sinusoid, as an input to determine the response of a network or of a structure excited by an electromagnetic field. It has been argued that periodic functions have infinite energy and violate causality because there is no way that one cycle of a periodic function differs from any other. An argument that shows that the traditional method of using sinusoids or other periodic functions to design equipment is asymptotically correct is presented     

Effects of grating heights on highly efficient unibond SOIwaveguide grating couplers

We report the first successful experimental evaluation of the effect of grating height upon the output efficiency of grating couplers as predicted using perturbation theory. In addition, we have also produced a grating with an output efficiency of 70%, which is the highest efficiency yet reported for a silicon-on-insulator waveguide grating coupler     

Measurement method for determination of optical phase shifts in3×3 fibre couplers

The phase characteristics of 3×3 fibre couplers are investigated with a self-homodyne experiment of 1.3 and 1.5 μm. A 2×2 fibre coupler, a fibre delay line and the 3×3 fibre coupler under test form a Mach-Zehnder interferometer. The measurement results are compared with values from S-matrix theory for lossy couplers     

采用信号调理IC驱动应变片电桥传感器

目前可以提供的应变片具有较宽的零应变电阻选择范围,可以选择的传感器材料和相关技术也非常广泛,但在大量应用中主要采用了儿类数值(如120Ω和350Ω).过去,标准值很容易实现与基本磁反射计的连接,这些反射计含有匹配输入阻抗网络,从而简化了应变测量.     

Use of multimode interference couplers to broaden the passband of wavelength-dispersive integrated WDM filters

We describe how multimode interference couplers (MMI) may be used to broaden and flatten the passband of integrated wavelength-dispersive filters. We discuss the approach and demonstrate its effectiveness with a passband-broadened InP arrayed waveguide filter operating at 1.5 /spl mu/m.     

Sensor survey: Part 2 sensors and sensor networks in five years [Sensor Survey Results]

This article shows where the survey respondents think sensors and sensor networks are going within the next 5 years.     

一种光纤传感器温度与应变同时解调的方法

文章分析了一种利用外差检测所得微波信号的电场振幅和频率来计算后向布里渊散射光功率及频移的方法.该方法通过对功率较强的微波信号进行数值拟合,利用得到的直流分量和交流分量计算出后向散射光功率、频移及其随温度、应变变化的系数矩阵.数值结果表明,温度、应变的解调精度分别为1℃、100 με,但也受到一定采样频率的限制.