High-responsivity intersubband infrared photodetector usingInGaAsP/InP superlattice

A 4-7-μm infrared detector made of an InGaAsP/InP short-period superlattice is demonstrated with materials grown by metalorganic chemical vapor deposition (MOCVD). A single current blocking layer of InP is used to reduce the dark current. At 40 K, the detector shows a low dark current of less than 4 pA at a bias voltage of 4 V. At 35 K, a peak responsivity of 4.0 A/W is obtained at 5.6 μm at a bias of 1 V     

High-responsivity optical FET's fabricated on a FET-SEED structure

Optical detectors with responsivity of 1000 A/W and response time of 10 μs at 50 nW optical input power were fabricated using the AT&T FET-SEED process     

Surface micromachined accelerometers

Surface micromachining has enabled the cofabrication of thin-film micromechanical structures and CMOS or bipolar/MOS integrated circuits. Using linear, single-axis accelerometers as a motivating example, this paper discusses the fundamental mechanical as well as the electronic noise floors for representative capacitive position-sensing interface circuits. Operation in vacuum lowers the Brownian noise of a polysilicon accelerometer to below 1 μg/√(Hz). For improved sensor performance, the position of the microstructure should be controlled using electrostatic force-feedback. Both analog and digital closed-loop accelerometers are described and contrasted, with the latter using high-frequency voltage pulses to apply force quanta to the microstructure and achieve a very linear response     

High-responsivity and low-operation-voltage edge-illuminatedrefracting-facet photodiodes with large alignment tolerance forsingle-mode fiber

We demonstrate a novel edge-illuminated refracting-facet photodiode (RFPD), in which the incident light parallel to the up-side surface is refracted at an angled facet and absorbed in a thin absorption layer. Although the absorption layer is thin, the absorption length is effectively increased by making the light transit at a certain angle to the absorption layer, resulting in an increase in internal quantum efficiency. The fabricated RFPDs with an absorption layer thickness of 1.5 μm have a responsivity as high as 0.95 A/W even at a bias voltage of 0.5 V for a flat-ended single-mode fiber. The 1-dB-down misalignment tolerances for vertical and horizontal directions are as large as 9.5 and 33 μm, respectively. A 3-dB bandwidth of more than 6 GHz is obtained     

Bridge configurations in piezoresistive two-axis accelerometers

In piezoresistive two-axis accelerometers with two proof masses suspended by cantilever beams, there are generally many ways to configure the Wheatstone bridges. The configurations are different both with respect to functionality and performance. The main distinction is between bridges that contain resistors belonging to both proof masses, and the one bridge that doesn’t. We compare the different bridge configurations by analytical calculations of bridge non-linearity, robustness towards manufacturing variations and electronic noise. We consider accelerometers where the ratio between the sensitivity to acceleration normal and parallel to the chip plane vary over a wide range. For numerical examples we use representative values for p-type silicon. The performance of the configuration with one bridge connected to each proof mass is superior to those that combine resistors belonging to different proof masses.     

PLZT fiber-optic switch

This paper describes a nonmechanical two-input two-output (2 × 2) optical switch using the electrooptic effect in PLZT ceramics. An alkoxide process and a hot-pressing technique are used to obtain homogeneous PLZT ceramics. This switch has low insertion loss (<1.9 dB) and fast response (<70 ns), and it is easily applicable to multimode fibers with connectors.     

New fiber-optic depolarizer

A new type of single mode fiber-optic depolarizer is proposed and demonstrated. The new depolarizer consists of a Mach-Zehnder interferometer with one arm used as a delay line with respect to the other. Light having a 100-MHz spectral width, for example, can be depolarized with high coupling efficiency to single mode fibers by using a polarization-maintaining fiber-delay line of a few meters in length.     

Frustrated-total-internal-reflection fiber-optic pressure sensor

In this work the design and construction of a simple fiber-optic pressure sensor based on the principle of frustrated-total-internal-reflection in a fiber cut beyond the critical angle are described. The characteristic of the device is obtained and compared with the predictions of a simple theory. Modifications to alter its sensitivity by the use of different wavelengths and fiber cut angle are discussed.     

Microbend fiber-optic phase shifter

The use of spatially periodic microbend transducers to produce phase shift in single-mode fibers has been investigaed. Phase shift of32deg/mum²of transducer displacement per centimeter of trans-3.7deg/mum². cm for a 1023-μm peroid. Phase shifts as large as 560°/cm of transducer length were obtained with the shorter period transducer. These results are compared with predictions based on coupled-mode theory.     

光纤陀螺的发展现状

介绍了光纤陀螺的原理特点和发展过程,着重描述和总结了光纤陀螺在国内外发展的技术趋势和产业化情况。可以看到,随着现代微电子技术、光电子技术和信号处理技术的发展,光纤陀螺在未来惯性测量领域中占据越来越重要的位置。     

A fiber-optic magnetic gradiometer

A fiber-optic magnetic gradiometer capable of measuring both ac and dc magnetic-field gradients has been designed and demonstrated. An approach using real-time magnetic balancing and trimming has been deployed. A device sensitivity of 0.1 gamma (10^-6Oe) per centimeter of sensor head separation for 1 m of magnetically active fiber is achievable.     

A fiber-optic DC magnetometer

An interferometric fiber-optic magnetometer capable of measuring dc magnetic fields is demonstrated. Sensitivity on the order of 10^-6Oe per meter of sensor fiber at 1-Hz bandwidth has been achieved.     

A fiber-optic interferometric seismometer

A fiber-optic interferometric sensor has been developed which consists of a seismic mass of 520 gm supported by two rubber mandrels, each wound with a single layer of single-mode optical fiber 6.5 m long. One end of each fiber is cleaved to enhance reflection. The other ends are interconnected via a fiber-to-fiber 3-dB coupler, forming a Michelson interferometer. When the case of the sensor is displaced, the fiber around one mandrel extends in length while the other contracts. The resulting "push-pull" mechanical operation of the sensor allows both legs of the interferometer to be active, providing good common mode rejection of spurious effects, as a reference leg is not required. This, together with the fact that the light traverses each leg of a Michelson interferometer twice due to reflection, provides the sensor with four times the sensitivity of a conventionally constructed interferometric sensor. Sensitivities of 8500 rad of optical phase shift per micrometer of case displacement have been measured above the mass-spring resonance, where the sensor operates as a seismometer. Below resonance the sensor operates as an accelerometer with a measured sensitivity of 10 500 rad/g, the highest reported to date. Including both thermodynamic and demodulator noise sources (approx 10 murad/sqrt{Hz}), below resonance the sensor has a detection threshold of 1 ng/sqrt{Hz}, a 20- dB improvement over the best existing conventional low noise vibration sensors.     

Air-core photonic-bandgap fiber-optic gyroscope

We report the demonstration of the first air-core photonic-bandgap fiber gyroscope. Because the optical mode in the sensing coil travels largely through air, which has much smaller Kerr, Faraday, and thermal constants than silica, far lower dependencies on power, magnetic field, and temperature fluctuations are predicted. With a 235-m fiber coil, we observe a minimum detectable rotation rate of /spl sim/2.7/spl deg//h and a long-term stability of /spl sim/2/spl deg//h, which are consistent with the Rayleigh backscattering coefficient of the fiber and comparable to that measured with a conventional fiber.     

Side-projected fiber-optic velocity sensors

Side-projected dual-fiber velocity sensors with various fiber core separations for in vivo measurements were developed and tested. Good linearity between the flow velocity and the Doppler shift frequency is obtained with this sensor in both the forward (toward the sensor tip) and reverse (away from the sensor tip) flow directions. Experimental and numerical analysis of the data showed that the boundary layer along the side wall of the fiber sensor varies with the flow velocity     

光纤系统的屏蔽

在无保护的设计中．光纤元件可能引发巨大的电磁或射频干扰     

Numerical prototyping methods in microsystem accelerometers design

The authors of this research would like to present the numerical prototyping methods in reference to design of microsystem silicon accelerometer. As an example device the capacitive accelerometer was taken into account. The accelerometer was prepared as a FEM parametric model. The model was then processed by the numerical optimization algorithms in order to find the optimal design parameters. For this purpose, the so-called numerical multi-objective optimization process was carried out. The idea was to find the optimal solution in reference to more than one optimizing criterion. As a result the set of optimal solutions was obtained and this method seems to be promising for similar purposes.     

光纤流量传感器的进展

光纤流量传感器是一种基于光信号的新型流量传感器.光纤中传输的光信号受到流量的作用,其强度、相位、波长等参数都会发生变化,通过检测光信号相关的变化可得到相应的流量大小.文章就几种类型的光纤流量传感器的工作原理及特性进行了阐述,对它们的优缺点进行分析比较,并提出了改进方案.     

高g值加速度传感器校准数值模拟

通过传感器动态校准理论分析,给出对不同谐振频率的加速度计动态校准时所允许的最大脉冲宽度以及脉冲宽度与传感器谐振频率之间的关系式。在有限元分析软件ABAQUS中建立霍普金森杆数值模型,产生窄脉冲,并提出了一种产生且复现脉宽在10μs以下的窄脉冲信号的方法。分析了子弹的不同撞击速度、不同端部形状等因素对数值模拟结果的影响。对988压电式加速度计进行频率特性分析,发现数值模拟结果与实际实验结果十分接近,验证了所建立方法的有效性。