使用QM,PQM的光纤通信质量监测,监控,管理的系统

介绍一种无源,高速,高灵敏的光电转换器件ＰＱＭ及根据ＰＱＭ设计的控制板着手,提出了了可实时,在线进行光纤通信质量监测,管理系统设计方案。     

High-speed InSb photodetectors on GaAs for mid-IR applications

We report p-i-n type InSb-based high-speed photodetectors grown on GaAs substrate. Electrical and optical properties of photodetectors with active areas ranging from 7.06/spl times/10/sup -6/ cm/sup 2/ to 2.25/spl times/10/sup -4/ cm/sup 2/ measured at 77 K and room temperature. Detectors had high zero-bias differential resistances, and the differential resistance area product was 4.5 /spl Omega/ cm/sup 2/. At 77 K, spectral measurements yielded high responsivity between 3 and 5 /spl mu/m with the cutoff wavelength of 5.33 /spl mu/m. The maximum responsivity for 80-/spl mu/m diameter detectors was 1.00/spl times/10/sup 5/ V/W at 4.35 /spl mu/m while the detectivity was 3.41/spl times/10/sup 9/ cm Hz/sup 1/2//W. High-speed measurements were done at room temperature. An optical parametric oscillator was used to generate picosecond full-width at half-maximum pulses at 2.5 /spl mu/m with the pump at 780 nm. 30-/spl mu/m diameter photodetectors yielded 3-dB bandwidth of 8.5 GHz at 2.5 V bias.     

Production and probing of atomic wavepackets with ultrafast laser pulses: applications to atomic and molecular dynamics

We demonstrate that atomic wavepackets can serve as sensitive detectors for investigating atomic and molecular dynamics. In concert with parametric four-wave mixing, the interference between coherent superpositions of atomic excited states produced by ultrafast (/spl sim/150 fs) pump and probe pulses provides a new and powerful tool with which fundamental processes, such as molecular dissociation and Rydberg-Rydberg atomic collisions, can be observed with the extraordinary sensitivity afforded by a coherent nonlinear optical process. Experiments are described in which the dissociation of an electronically excited molecule (Rb/sub 2/) and the distribution of atomic fragments into excited states spanning >10 000 cm/sup -1/ are observed. Also, resonant collisions between Rb atoms in the 7s and 5d states are detected by monitoring the shift in the frequency of an atomic wavepacket induced by the dipole-dipole interaction.     

光纤通信质量监督与管理系统的分析和设计

从光纤通信系统质量监督和管理的基本要求出发,分析比较了基于ＯＴＤＲ的和采用泄漏测量法的光纤通信质量监管系统的性能和优缺点,介绍了一种采用泄漏测量法并基于ＰＣ机进行点对点测量和通信的光纤通信质量监管系统的设计方案。     

Optical Separation of Cells on Potential Energy Landscapes: Enhancement With Dielectric Tagging

We review the emergent techniques of microfluidic sorting of colloidal and cellular samples using optical forces. We distinguish between what we term as passive and active forms of particle sorting where we can sort either with the use of a fluorescent marker (active) or based on physical attributes alone (passive). We then examine cell sorting with optical potential landscapes such as a Bessel light beam and a multibeam interference pattern. For both forms of optical potential energy landscape, we further present the possibility of enhancing the optical sorting process by tagging dielectric microspheres onto the cells. The results suggest that the methodology of tagging can enhance the sorting of cells as they subsequently respond more strongly to an applied optical field or potential energy landscape. This technique presents a simple method to enhance the sorting process.     

Optimizing particle collection for enhanced surface-based biosensors

In this article, electrode structures that combine dielectrophoretic effects with electrohydrodynamic fluid flow to concentrate particles on active sensor surfaces were presented. To optimize the collection effect on a surface, a novel electrode configuration called zipper electrodes has been developed. The local enrichment effect of these electrodes is such that particles at local concentration of 5/spl times/10/sup 3/ spores/mL can be collected using a single electrode pad. The fluid flow induced in the bulk flow is an efficient mechanism especially for very small particles, since the dielectrophoretic forces working on these particles are normally very small and do not penetrate the liquid as far as the vortex induced by combined dielectrophoresis/fluid flow does. The bulk flow makes it also a very versatile method that can extract a wide range of particles out of the liquid.     

Analysis of noise mechanisms limiting the frequency stability of microwave signals generated with a femtosecond laser

Excess phase noise is observed in the spectrum of the microwave signal extracted from a photodetector illuminated by a train of ultrashort light pulses from the femtosecond laser. This noise affects the stability of frequency transfer from optical to microwave domains with the femtosecond laser. Some contributions to the excess phase noise are related to intrinsic beam-pointing fluctuations of the femtosecond laser and optical power fluctuations of the detected light. These factors contribute to excess phase noise at the harmonics of the pulse repetition rate due to power-to-phase conversion in the photodetector, spatially dependent time delays, and photodiode nonlinearities that distort the pulse shape. With spatial filtering of the laser beam and active control of its power, the additional fractional frequency fluctuations of pulse repetition rate associated with the excess noise of the photodetection process were reduced from 6/spl middot/10/sup -14/ to approximately 3/spl middot/10/sup -15/ over 1 s of averaging. The effects of other noise mechanisms, such as laser shot noise and phase noise introduced by a microwave amplifier, were also examined but were found to be at a less significant level.     

An Energy-Efficient ASIC for Wireless Body Sensor Networks in Medical Applications

An energy-efficient application-specific integrated circuit (ASIC) featured with a work-on-demand protocol is designed for wireless body sensor networks (WBSNs) in medical applications. Dedicated for ultra-low-power wireless sensor nodes, the ASIC consists of a low-power microcontroller unit (MCU), a power-management unit (PMU), reconfigurable sensor interfaces, communication ports controlling a wireless transceiver, and an integrated passive radio-frequency (RF) receiver with energy harvesting ability. The MCU, together with the PMU, provides quite flexible communication and power-control modes for energy-efficient operations. The always-on passive RF receiver with an RF energy harvesting block offers the sensor nodes the capability of work-on-demand with zero standby power. Fabricated in standard 0.18-$mu$ m complementary metal–oxide semiconductor technology, the ASIC occupies a die area of 2 mm $times$ 2.5 mm. A wireless body sensor network sensor-node prototype using this ASIC only consumes $≪$ 10-nA current under the passive standby mode, and $≪10 mu$A under the active standby mode, when supplied by a 3-V battery.      

Sol-gel derived la modified PZT thin films: structure and properties

Lanthanum modified PZT thin films with compositions, namely 8/60/40, 8/70/30, 10/70/30 and 12/70/30 were deposited on platinized silicon substrates by sol-gel spin coating technique. Characterization of these films by XRD and SEM show that the films possess perovskite phase with submicron crystallite size. The saturation polarization (Ps), remnant polarization (PR) and coercive field (Ec) of polarization-electric field hysteresis loop are presented for all compositions. The 8/60/40 composition shows hysteresis loop with P/sub R/ = 11 /spl mu/C/cm/sup 2/. The temperature dependence of dielectric constant and dielectric loss of these films are also studied. Leakage current densities for these thin films are found to be in the range of 10/sup -/-10/sup -/ A/cm/sup 2/. To show the possible application of these thin films for micro electromechanical system (MEMS), a device incorporating an 8/60/40 PLZT thin film has been fabricated using silicon micromachining technology. This device functions satisfactorily as a vibration sensor with a resonance frequency of approximately 8.45 MHz.     

Boundary effects on the optical properties of InGaN multiple quantum wells

We examine the issues of spontaneous and piezoelectric polarization discontinuity on the optical properties of 3.0-nm-thick indium gallium nitride (InGaN) multiple quantum wells (MQWs). A quench of band-edge emission from the cap GaN layer is observed when the photoexcitation source is changed from a 355- to a 248-nm laser. The interband transitions from the InGaN wells exhibit a linear dependence on the 1) spectral blue shift of /spl sim/8.5/spl times/10/sup -18/ meV /spl middot/ cm/sup 3/ and 2) change of the internal field of /spl sim/3/spl times/10/sup -14/ meV /spl middot/ cm/sup 2/ with the injected carrier density up to N/sub inj//spl sim/10/sup 19/ cm/sup -3/ at 77 K. These observations are attributed to the redistribution of photogenerated carriers in the InGaN wells due to the polarization discontinuity at the QW interface and the surface band bending effect. By incorporating an additional boundary condition of surface Fermi-level pinning into the Poisson equation and the band-structure analysis, it is shown the emission from the InGaN-GaN MQWs is dominant by the recombination between the high-lying subbands and the screening of internal field effects.     

On the use of electrical precompensation of dispersion in optical single-sideband transmission systems

The use of electrical predistortion in optical single-sideband (OSSB) transmission systems is proposed to extend the tolerance to fiber dispersion impairment. Due to the spectral properties of OSSB signals, a simple electrical dispersive line can be used to mitigate the fiber dispersion, reducing the complexity of electrical predistortion methods proposed recently for optical modulations other than OSSB. Carrier-suppressed and carrier-unsuppressed optical modulations can be compensated by such technique, extending the range compared to previously reported works on fiber dispersion mitigation after direct detection using OSSB signals, where only carrier-unsuppressed modulations can be effectively compensated. The use of electrical precompensation is investigated for three signaling formats: Nonreturn to zero, return to zero, and alternate mark inversion (AMI). Due to distortion occurring in the sideband suppression process, signaling formats with reduced duty cycles present improved performance as a consequence of enhanced tolerance to intersymbol interference. Using such formats with electrical predistortion, the reach limitation arises not from fiber dispersion but from nonlinear impairments and optical noise accumulation. Using AMI and ideal electrical predistortion, distances greater than 1200 km of standard single mode fiber are achieved at 10 Gb/s with bit error ratio (BER) lower than 10/sup -12/, without using optical dispersion compensation. Introducing accurate models for the electrical dispersive lines, the transmission distance is reduced to 720 km for BER lower than 10/sup -12/.     

Accurate measurement of total attenuation coefficient of thin tissue with optical coherence tomography

Noninvasive accurate measurements of tissue optical properties are needed for many diagnostic and therapeutic applications. Optical coherence tomography (OCT) recently proposed for high-resolution imaging in tissue can potentially be applied for accurate, noninvasive, and high-resolution measurement of tissue total attenuation coefficient. However, confocal function (dependence of OCT sensitivity on the distance of probed site from the focal plane of the objective lens) and multiple scattering substantially limit the accuracy of the measurement with the OCT technique. We studied the influence of the confocal function and multiple scattering on the accuracy of the measurement and proposed methods that provide measurement of the total attenuation coefficient with a significantly reduced systematic error. Experiments were performed in tissue phantoms and porcine and human skin in vitro and in vivo. Our data indicate that the tissue total attenuation coefficient can noninvasively be measured in vivo with the accuracy of 5%-10% in the range from 0.5 to 17 mm/sup -1/ and about 20% in the range up to 40 mm/sup -1/. These results suggest that the proper correction of the OCT-based measurement for the confocal function and multiple scattering provides absolute values of tissue total attenuation coefficient with high accuracy and resolution that may not be achievable by other optical techniques in vivo.     

Calibration of a calorimeter for measuring the spark energy of an electrostatic discharge

This paper deals with the factors that influence the accuracy of the measurements performed with a calorimeter, developed to detect the optical signal emitted by the spark generated to facilitate experiments with electrostatic discharge. Experiments are described which were performed with a special calorimeter and a compound optical source consisting of a spark gap, a human-body-model electrostatic discharge (ESD) signal generator, and four LEDs. The spark gap was used as a versatile and more powerful source of optical emission than the human-body-model circuit; the LED source was used for calibration and alignment. For control, the spectrum of the spark discharge was measured with a spectrometer and a broadband photodetector. The calorimeter was used as a means for the determination of the energy contained in the optical signal, yielding the value of the spark-gap emission in the fundamental units for energy. The long-term stability of the system was measured, and the system response was studied for threshold optical signals. The calorimeter detectivity, defined as the overall instrument sensitivity, measured in volts per joule, was D=4.3/spl times/10/sup 7/ V.J/sup -1/ and its detection limit 2.3/spl times/10/sup -13/ J. The system's response to the IEC standard human-body-model circuit was consistent with the measurements of the system's detectivity. Most parts of the developed apparatus have been tested in an industrial environment.     

Characteristics of a saturated 18.9-nm tabletop laser operating at 5-Hz repetition rate

We report the characteristics of a saturated high-repetition rate Ni-like Mo laser at 18.9 nm. This table-top soft X-ray laser was pumped at a 5-Hz repetition rate by 8-ps 1-J optical laser pulses impinging at grazing incidence into a precreated Mo plasma. The variation of the laser output intensity as a function of the grazing incidence angle of the main pump beam is reported. The maximum laser output intensity was observed for an angle of 20/spl deg/, at which we measured a small signal gain of 65 cm/sup -1/ and a gain-length product g/spl times/l>15. Spatial coherence measurements resulting from a Young's double-slit interference experiment show the equivalent incoherent source diameter is about 11 /spl mu/m. The peak spectral brightness is estimated to be of the order of 1/spl times/10/sup 24/ photons s/sup -1/ mm/sup -2/ mrad/sup -2/ within 0.01% spectral bandwidth. This type of practical, small scale, high-repetition soft X-ray laser is of interest for many applications.     

Distributed adaptive state estimation and tracking by using active-passive sensor networks

Heterogeneous sensor networks (HSN) find a wide range of applications in the field of military and civilian environments, where sensor nodes are utilized to estimate the position of a target with both dynamics and control input being unknown for the purposes of tracking. In the HSN, nodes are considered active depending upon their ability to sense the target output while the others are taken passive. Accurate estimation requires local information exchange among the spatially located sensor nodes, so that the active nodes as well as the passive nodes converge simultaneously to the same value. The local information exchange among the nodes is dictated by a connected graph. By using the criterion of collective observability, a novel distributed adaptive estimation scheme is introduced via adaptive observer where the nodes are allowed to have different sensor modalities. Using the estimated information, a subset of active and passive nodes, referred to as mobile nodes, can track the moving target. By using a constant state feedback controller at each mobile node, the state and parameter estimation as well as the tracking errors are shown to be uniformly ultimately bounded. Simulation results verify theoretical claims.     

Recent progress in high-power blue-violet lasers

The property of GaInN-AlGaN heterostructures and GaInN multiple quantum well (MQW) gain GaInN laser diodes with low internal loss are described. GaInN blue-violet laser diodes have been developed as a light source for optical disk recording. However, the threshold current density of these diodes has been difficult to reduce and remains high at around 3-4 kA/cm/sup 2/. This is thought to be due to the large transparency current density Jt and the large optical internal loss /spl alpha//sub i/. Recently, the internal loss was successfully reduced to 13.6 cm/sup -1/ by optimizing the design of the near active region and achieved stable continuous operation under 50-mW continuous wave at 70/spl deg/C. Other laser characteristics such as far-field patterns and laser noise have also been improved for optical disk use.     

Linear phase tracking in a coherence modulation electrical sensorsystem using integrated LiNbO3 modulator/demodulator

We report an interferometric sensor system, based on coherence modulation of light and LiNbO₃ integrated optics technology. We describe a phase detection scheme designed to retrieve the absolute phase variations produced by a sensor system where the sensor signal is electronically applied to an electro-optic modulator. The system consists of an imbalanced LiNbO₃ Mach-Zehnder transducer fed by a self-powered charge generating sensor, and an optoelectronic central processing unit including a second electrooptic Mach-Zehnder working as an optical demodulator and featuring a matched path-imbalance. Electrical feedback is applied to this second interferometer in an active demodulation scheme, allowing a linear tracking of the signal phase up to 7-π radians     

A new hybrid current sensor for high-voltage applications

This article presents a new hybrid electro-optic/inductive current sensor for metering and protective relaying applications. The sensor combines a Rogowski coil with a passive integrator located in the high-voltage environment. An integrated-optic Pockels cell (IOPC) having integrated electrodes provides optical isolation. Test results from 30 A to 30 kA show the sensor to be highly linear, exceeding 0.2% linearity standards. Temperature cycling tests show the ratio error to have a maximum value of 0.3% over the -30 to +70/spl deg/C range.     

Multichannel Reflective PPG Earpiece Sensor With Passive Motion Cancellation

This paper addresses the design considerations of a novel earpiece photoplethymograph (PPG) sensor and its in-situ evaluation results. The device is encapsulated with multiple LEDs and photodiodes based on a reflective PPG design. A compact and low power circuitry was developed for signal control and conditioning. PPG signals with an averaged ac/dc ratio of 0.001-0.01 and 10% relative strength (compared to finger-based approach) were recorded from the superior and posterior auricular skins. The integrity of PPG signal and accuracy of heart rate detection were evaluated and the results showed that with adequate optical shielding and the proposed passive motion cancellation, the device was able to reliably detect heart rate both during rest and moderate exercise. The proposed sensor design is low power, easy to wear compared to conventional earlobe PPG devices.     

UV laser diode with 350.9-nm-lasing wavelength grown by hetero-epitaxial-lateral overgrowth technology

We have demonstrated a UV-laser diode with a lasing wavelength of 350.9 nm, which has a GaN-AlGaN multiquantum-well (MQW) active layer and was grown on low-dislocation-density Al/sub 0.18/Ga/sub 0.82/N template. The Al/sub 0.18/Ga/sub 0.82/N template was produced by the hetero-epitaxial lateral overgrowth technology on the low-cost sapphire substrate, and has partially low-dislocation density of approximately 2/spl times/10/sup 7/ cm/sup -2/. The lasing operation under pulsed current injection was achieved with the threshold current density of 7.3 kA/cm/sup 2/ and the operating voltage of 10.4 V.