An optical millimeter-wave generation scheme based on two parallel dual-parallel Mach–Zehnder modulators and polarization multiplexing

A novel filterless optical millimeter-wave signal generation scheme is proposed. In the scheme, the undesired sidebands are suppressed using two parallel dual-parallel Mach–Zehnder modulators (MZMs) with different modulation indexes and polarization multiplexing, and frequency multiplication factor as high as 16 can be achieved. Simulation results show that 80, 120, and 160 GHz signals are generated through a 10 GHz RF signal using the proposed method, and the performance of the generated signals is good when commercially available MZMs with extinction ratio of 20–30 dB are used. The scheme has large tunability of modulation index for frequency octupling and 12-tupling signals generation and high stability against the RF driving voltage deviation for frequency 16-tupling generation.     

Wavelength multiplexing and demultiplexing with one single volume hologram in photorefractive crystal

Based on anisotropic diffraction of a volume phase grating in a photorefractive crystal, we theoretically discuss an optical multi- and demultiplexing scheme implemented by one single grating in photorefractive LiNbO₃ crystal. It shows that our scheme can simultaneously demultiplex 93 channels in the telecommunication wavelength around 1550?nm. Using only one grating to realize WDM can avoid the multiple exposure problems encountered by multiple hologram scheme. Moreover, in our scheme, the transmitted and diffracted beams are orthogonal to each other, thus we don't need to use a normal recording and readout structure. Our theoretical results can be used in the design of a WDM device.     

Ultrasonic nondestructive evaluation of highly scattering materialsusing adaptive filtering and detection

Adaptive filtering and detection has been applied to the problem of detecting ultrasonic echo signals from test targets where the wanted signals are masked by coherent scattering from grain boundaries present in highly scattering materials. The filter is based on the normalized least mean square (LMS) error algorithm, and can be operated with either an independent reference signal or by using the delayed input signal as the reference. Tests made on a collection of 64 ultrasonic A-scans using the same processing parameters show that an up to 10 dB improvement in signal-to-noise ratio can typically be obtained. A cell-averaging constant false alarm rate (CFAR) detector is used to detect the signals automatically. The performance of the method is compared to that of split spectrum processing, both with and without polarity thresholding     

Intrinsic fiber-optic ultrasonic sensor array using multiplexed two-wave mixing interferometry

An intrinsic multiplexed laser interferometer is presented that allows for the simultaneous detection of acoustic waves by an array of fiber-optic sensors. The phase-modulated signals from each sensor are demodulated by use of an adaptive two-wave mixing setup. The light from each sensing fiber in the array is mixed with a reference beam in a single photorefractive crystal (PRC), and the output beams from the PRC are imaged onto separate photodetectors to create a multiplexed two-wave mixing (MTWM) system. The sensing fibers are embedded in graphite-epoxy composite panels, and detection of both acoustic emission and ultrasonic signals in these materials is demonstrated. The intrinsic MTWM system is an effective tool for the simultaneous demodulation of signals from a large fiber sensor array. Also, the adaptive nature of the MTWM setup obviates the need for active stabilization against ambient noise.     

Half-thickness inversion layer high-frequency ultrasonic transducers using LiNbO3 single crystal.

Half-thickness inversion layer high-frequency ultrasonic transducers were fabricated using lithium niobate (LiNbO3) single crystal plate. The transducers developed for this study used a 36 degrees rotated Y-cut LiNbO3 thin plate with an active element thickness of 115 microm. The designed center frequency was in the range of 30 to 60 MHz. Half-thickness inversion layer was formed after the sample was annealed at a high temperature, and it is shown that the inversion layer thickness can be controlled by the temperature. Silver powder/epoxy composite and parylene were used as acoustic matching layers. A lossy silver epoxy was used as the backing material. Using an analytical method, the electrical impedance for different inversion layer ratios was determined. The measured resonant frequency was consistent with the modeled data. Even-order higher frequency broadband ultrasonic transducers with a center frequency at 60 MHz was obtained using half-thickness inversion layer of LiNbO3 single crystal.     

Half-thickness inversion layer high-frequency ultrasonic transducers using LiNbO/sub 3/ single crystal

Half-thickness inversion layer high-frequency ultrasonic transducers were fabricated using lithium niobate (LiNbO₃) single crystal plate. The transducers developed for this study used a 36deg rotated Y-cut LiNbO₃ thin plate with an active element thickness of 115 mum. The designed center frequency was in the range of 30 to 60 MHz. Half-thickness inversion layer was formed after the sample was annealed at a high temperature, and it is shown that the inversion layer thickness can be controlled by the temperature. Silver powder/epoxy composite and parylene were used as acoustic matching layers. A lossy silver epoxy was used as the backing material. Using an analytical method, the electrical impedance for different inversion layer ratios was determined. The measured resonant frequency was consistent with the modeled data. Even-order higher frequency broadband ultrasonic transducers with a center frequency at 60 MHz were obtained using half-thickness inversion layer of LiNbO₃ single crystal     

The influence of external bias voltage on electrical properties of YBa2Cu3O7−x /metal point contact interface

We have investigated a change of electrical properties of YBa₂Cu₃O₇−δ/metal point contact immediately after its preparation depending on time, temperature as well as external bias voltage. The increase of the point contact differential resistance in time was experimentally observed at temperature above 200 K even if no external bias voltage was applied. The low external bias voltage considerably influences the time increase of the differential resistance indicating an important role of oxygen diffusion. It is shown on differential characteristics that for Au, In the parameters of tunneling barrier such as the average height and width are constant in time whereas for Al, Pb an evolution of the tunneling barrier was observed because of oxidation of Al and Pb. Applying of higher bias voltage (up to 1 V) enables the transport of oxygen even below 200 K (down to 4.2 K) and changes the electrical properties of YBCO/metal point contact interface. The differential characteristics change their behaviour from that typical for NIS contact with strong tunneling barrier to NS contact with a high transparency of the interface. All the above changes are reversible upon changing the bias voltage polarity.     

混凝土分层缺陷的超声检测方法研究

为解决混凝土结构中分层缺陷的在线非接触检测难题,论文提出了利用空气耦合(简称:空耦)超声导波定量检测混凝土结构中分层缺陷的新方法。首先研究了空耦超声导波在混凝土结构中的传播特性,理论分析和实验表明,利用空耦超声波以入射角8.7°入射厚度为50 mm的混凝土板时,可以激发以A0模态为主的导波。然后构建了空耦超声导波扫查实验系统,在混凝土结构单侧利用一对倾斜8.7°的空耦探头激励和接收导波信号,通过分析发现A0模态对分层缺陷敏感,且其幅度与扫查路径中的分层缺陷尺寸存在单调变化关系;在此基础上,对检测区域进行扫查,利用不同位置处的导波信号幅度实现分层缺陷的二维成像。实验结果表明,该方法不仅可以避免耦合剂对检测结果的影响,同时可实现对服役状态下混凝土结构中分层位置及尺寸的定量检测。     

Processing of ultrasonic array signals for characterizing defects. Part II: experimental work

This is Part II of the two-part paper aimed at integrating the numerical synthesis and experimental investigation of the ultrasonic wave propagation model for quantitative nondestructive evaluation. The first part of the paper focused on synthesizing and predicting measured signals using the boundary element method and the deconvolution technique based on the comparison between the signals obtained from defective and undamaged (reference) specimens. In the second part, we present an inversion technique which allows us to obtain the position and size of the defect. The inversion scheme is processing the frequency domain information rather than time-domain time-of-flights or vibration eigenmodes. This technique is tested experimentally for the case of a side-drilled hole with a non-trivial location in terms of standard pulse-echo techniques. It is shown that the scheme is particularly effective when the information of the defect is masked by other predominant signal components.     

Threshold Voltage Control of Multilayered MoS2 Field‐Effect Transistors via Octadecyltrichlorosilane and their Applications to Active Matrixed Quantum Dot Displays Driven by Enhancement‐Mode Logic Gates

In recent past, for next‐generation device opportunities such as sub‐10 nm channel field‐effect transistors (FETs), tunneling FETs, and high‐end display backplanes, tremendous research on multilayered molybdenum disulfide (MoS₂) among transition metal dichalcogenides has been actively performed. However, nonavailability on a matured threshold voltage control scheme, like a substitutional doping in Si technology, has been plagued for the prosperity of 2D materials in electronics. Herein, an adjustment scheme for threshold voltage of MoS₂ FETs by using self‐assembled monolayer treatment via octadecyltrichlorosilane is proposed and demonstrated to show MoS₂ FETs in an enhancement mode with preservation of electrical parameters such as field‐effect mobility, subthreshold swing, and current on–off ratio. Furthermore, the mechanisms for threshold voltage adjustment are systematically studied by using atomic force microscopy, Raman, temperature‐dependent electrical characterization, etc. For validation of effects of threshold voltage engineering on MoS₂ FETs, full swing inverters, comprising enhancement mode drivers and depletion mode loads are perfectly demonstrated with a maximum gain of 18.2 and a noise margin of ≈45% of 1/2 V_DD. More impressively, quantum dot light‐emitting diodes, driven by enhancement mode MoS₂ FETs, stably demonstrate 120 cd m^?2 at the gate‐to‐source voltage of 5 V, exhibiting promising opportunities for future display application.     

Microwave generation with photonic frequency octupling using a DPMZM in a Sagnac loop

A photonic microwave signal generation scheme with frequency octupling is proposed and experimentally demonstrated. The scheme is based on bi-directional use of a dual-parallel Mach–Zehnder modulator (DPMZM) in a Sagnac loop. The two sub-modulators in the DPMZM are driven by two low-frequency signals with a π/2 phase difference, and the dc biases of the modulator are all set at the maximum transmission points. Due to the velocity mismatch of the modulator, only the light wave along the clockwise direction is effectively modulated by the drive signals to generate an optical signal with a carrier and ±4th order sidebands, while the modulation of the light wave along the counterclockwise direction is far less effective and can be ignored. By properly adjusting the polarization of the light wave output from the Sagnac loop, the optical carrier can be significantly suppressed at a polarizer, and then an optical signal with only ±4th order sidebands is generated. In the experiment, a pure 24-GHz microwave signal without additional phase noise from the optical system is generated using a 3-GHz local oscillator signal. As no electrical or optical filter is used, the photonic frequency octupler is of good frequency tunability.     

Radio-frequency matched filtering by photorefractive optical holography

Matched filtering of megahertz-bandwidth signals by use of holograms recorded in a photorefractive crystal is demonstrated. Holographic recording of rapidly varying signals has heretofore been hampered by the relatively slow response of photorefractive crystals. For the first time, to our knowledge, synchronization between waveforms and short optical sampling pulses is used with acousto-optic electrical-to-optical conversion to build up static holograms of rf waveforms in a SBN crystal. Readout with a continuous input signal yields a time-resolved correlation with stored waveforms.     

Piezoelectric Microchip for Cell Lysis through Cell–Microparticle Collision within a Microdroplet Driven by Surface Acoustic Wave Oscillation

Cell lysis is an important and crucial step for the detection of intracellular secrets. Usually, cell lysis is based on strong ultrasonic waves or toxic chemical regents, which require a large amount of cell suspension. To obtain high efficiency cell lysis for a small amount of sample, a mechanical cell lysis method based on a surface acoustic wave (SAW) microchip is proposed. The microchip simply consists of a piece of LiNbO₃ crystal substrate, interdigitated transducers (IDTs) with 80 pairs of parallel electrodes and 3M Magic Tapes. The modulated input electrical signal is coupled into the substrate through IDTs, which produces an acoustic stream in the droplet on the surface of a substrate. When a biofluid droplet containing cells and microparticles is dropped on the surface of the microchip, the cells and microparticles are accelerated and collide with each other. The fluorescence staining results illustrate that the cell membrane is efficiently destroyed and that proteins as well as nucleic acids inside the cell are released. The experimental results show that this method has a high efficiency and low sample consumption. The potential application is the pretreatment of a small amount of tested sample in a hospital or biolab.     

Full-field imaging of Gigahertz film bulk acoustic resonator motion

A full-field view laser ultrasonic imaging method has been developed that measures acoustic motion at a surface without scanning. Images are recorded at normal video frame rates by using dynamic holography with photorefractive interferometric detection. By extending the approach to ultra high frequencies, an acoustic microscope has been developed that is capable of operation at gigahertz frequency and micron length scales. Both acoustic amplitude and phase are recorded, allowing full calibration and determination of phases to within a single arbitrary constant. Results are presented of measurements at frequencies of 800-900 MHz, illustrating a multitude of normal mode behavior in electrically driven thin film acoustic resonators. Coupled with microwave electrical impedance measurements, this imaging mode provides an exceptionally fast method for evaluation of electric-to-acoustic coupling of these devices and their performance. Images of 256 /spl times/ 240 pixels are recorded at 18 fps rates synchronized to obtain both in-phase and quadrature detection of the acoustic motion. Simple averaging provides sensitivity to the subnanometer level at each pixel calibrated over the image using interferometry. Identification of specific acoustic modes and their relationship to electrical impedance characteristics show the advantages and overall high speed of the technique.     

Optoelectronic implementation of a 256-channel sonar adaptive-array processor

We present an optoelectronic implementation of an adaptive-array processor that is capable of performing beam forming and jammer nulling in signals of wide fractional bandwidth that are detected by an array of arbitrary topology. The optical system makes use of a two-dimensional scrolling spatial light modulator to represent an array of input signals in 256 tapped delay lines, two acousto-optic modulators for modulating the feedback error signal, and a photorefractive crystal for representing the adaptive weights as holographic gratings. Gradient-descent learning is used to dynamically adapt the holographic weights to optimally form multiple beams and to null out multiple interference sources, either in the near field or in the far field. Space-integration followed by differential heterodyne detection is used for generating the system's output. The processor is analyzed to show the effects of exponential weight decay on the optimum solution and on the convergence conditions. Several experimental results are presented that validate the system's capacity for broadband beam forming and jammer nulling for linear and circular arrays.     

一种基于星载氢钟误差信号提取的实现方法

针对中国新一代卫星导航系统的高精度定位要求,星载氢原子钟以极其优异的长期稳定性、漂移率以及温度特性,作为频率基准大规模应用于该系统.双频方案的被动型星载氢原子钟由物理部分及电路部分两大部分组成,微波激励信号对物理部分微波腔激励后产生了腔频误差信号及高稳晶振误差信号.对于如何提取并处理这两种误差信号,提出了一种对调幅信号...     

Photorefractive processing for large adaptive phased arrays

An adaptive null-steering phased-array optical processor that utilizes a photorefractive crystal to time integrate the adaptive weights and null out correlated jammers is described. This is a beam-steering processor in which the temporal waveform of the desired signal is known but the look direction is not. The processor computes the angle(s) of arrival of the desired signal and steers the array to look in that direction while rotating the nulls of the antenna pattern toward any narrow-band jammers that may be present. We have experimentally demonstrated a simplified version of this adaptive phased-array-radar processor that nulls out the narrow-band jammers by using feedback-correlation detection. In this processor it is assumed that we know a priori only that the signal is broadband and the jammers are narrow band. These are examples of a class of optical processors that use the angular selectivity of volume holograms to form the nulls and look directions in an adaptive phased-array-radar pattern and thereby to harness the computational abilities of three-dimensional parallelism in the volume of photorefractive crystals. The development of this processing in volume holographic system has led to a new algorithm for phased-array-radar processing that uses fewer tapped-delay lines than does the classic time-domain beam former. The optical implementation of the new algorithm has the further advantage of utilization of a single photorefractive crystal to implement as many as a million adaptive weights, allowing the radar system to scale to large size with no increase in processing hardware.     

Ethernet-Based DAQ System for QUIET-II Detectors

The B-modes in cosmic microwave background polarization are a smoking gun for the inflationary universe. For the detection of the B-modes, having a large detector array is a generic approach since the B-modes is so faint pattern (T _b?0.1?μK). The Q/U Imaging ExperimenT Phase-II (QUIET-II) is proposed to search the B-modes, using an array with 500 HEMT-based polarimeters. Each polarimeter element has 4-outputs, therefore we have to manage 2000 channels in total. We developed a scalable DAQ system based on TCP/Ethernet for QUIET-II. The DAQ system is composed of the polarimeters, ADC boards, a Master Clock and a control computer (PC). The analog signals from the polarimeters are digitized on the ADC boards. On-board demodulation, which synchronizes the phase flip modulations on the polarimeter, extracts the polarized components in the digitized signal. The Master Clock distributes all necessary clocks to the ADC boards as well as the polarimeters. This scheme guarantees the synchronization of the modulations and demodulations. We employed Ethernet-based communication scheme between the data collection program (Collector) on the PC and the ADC boards as well as the Master Clock. Such an Ethernet-based communication scheme allows us to construct a simple structure of the upper level software, which results in the high scalability to increase the number of channels. All basic functions and requirements are confirmed by the laboratory tests; demonstration with test signals as well as the signals from the polarimeters, measurements of the data transfer rate, and the synchronous operation with two ADC boards. Therefore, the DAQ system is confirmed to be suitable for QUIET-II.     

Exploring strategies for classification of external stimuli using statistical features of the plant electrical response

Plants sense their environment by producing electrical signals which in essence represent changes in underlying physiological processes. These electrical signals, when monitored, show both stochastic and deterministic dynamics. In this paper, we compute 11 statistical features from the raw non-stationary plant electrical signal time series to classify the stimulus applied (causing the electrical signal). By using different discriminant analysis-based classification techniques, we successfully establish that there is enough information in the raw electrical signal to classify the stimuli. In the process, we also propose two standard features which consistently give good classification results for three types of stimuli—sodium chloride (NaCl), sulfuric acid (H₂SO₄) and ozone (O₃). This may facilitate reduction in the complexity involved in computing all the features for online classification of similar external stimuli in future.