High sensitivity gravimetric sensor made of unidirectional carbon fiber epoxy composite on （1-x）Pb(Zn1/3Nb2/3)O3-xPbTiO3 single crystal substrate

We have derived a general formula for sensitivity optimization of gravimetric sensors and have used it to design a high sensitivity gravimetric sensor using unidirectional carbon fiber epoxy composite(CFEC) waveguide layer on(1- x)Pb(Zn1/3Nb2/3)O3-xPbTiO3(PZN-xPT) single crystal substrate with the carbon fibers parallel to the x1 and x2axes, respectively. The normalized maximum sensitivity Sfm λ maxexhibits an increasing tendency with the decrease of(h/λ)optand the maximum sensitivity Sfm λ maxincreases with the elastic constant cE66 of the piezoelectric substrate material. For the CFEC/[011]c poled PZN-7%PT single crystal sensor configuration, with the carbon fibers parallel to the x1 axis at λ = 24 μm, the maximum sensitivity Sfm maxcan reach as high as 1156 cm2/g, which is about three times that of a traditional SiO2/ST quartz structure gravimetric sensor. The better design selection is to have the carbon fibers parallel to the direction of propagation of Love wave in order to obtain the best sensitivity.     

Highly sensitive fiber refractive index sensor based on side-core holey structure

We propose a side-core holey fiber （SCHF）-based surface plasmon resonance （SPR） sensor to achieve high refractive index （RI） sensitivity. The SCHF structure can facilitate analyte filling and enhance the overlapping area of the core mode and surface plasmon polariton （SPP） mode. The coupling properties of the sensor are analyzed by numerical simulation. The maximum sensitivity of 5000 nm/RIU in an RI range of 1.33-1.44, and the average sensitivity of 9295 nm/RIU in an RI range from 1.44 to 1.54 can be obtained.     

Micro Extrinsic Fiber-Optic Fabry-Perot Interferometric Sensor Based on Erbium- and Boron-Doped Fibers

Micro extrinsic Fabry-Perot interferometers （MEFPIs）, with cavity lengths of up to ~ 9 μm and maximum fringe contrast of ~19 dB, are fabricated by chemically etching Er- and B-doped optical fibers and then splicing the etched fiber to a single-mode fiber, for the first time to the best of our knowledge. The strain and temperature responses of the MEFPI sensors are investigated experimentally. Good linearity and high sensitivity are achieved. Such a type of MEFPI sensor is cost-effective and suitable for mass production, indicating its great potential for a wide range of applications.     

基于银膜孔阵列超强透射效应的相敏表面等离子体共振传感器的仿真研究

A high spatial resolution, phase-sensitive Surface Plasmon Resonance（SPR） sensor based on Extraordinary Optical Transmission （EOT） is proposed to monitor the binding of organic and biological molecules to the silver surface. The 2D nanohole-array configuration is well suited ~br dense integration in a sensor chip. The optical geomeWy is collinear, which simplifies the alignment with respect to the traditional Kretschmann arrangement for SPR sensing. Various design parameters of the device have been studied by simulation. The heterodyne technique is used to improve the sensitivity. The optimization results indicate that the sensor has the advantages of achieving high resolution and a wide dynamic range simuhaneously.     

Ultraviolet laser-induced photovoltaic effects in miscut ferroelectric LiNbO3 single crystals

This paper investigates the photovoltaic properties of miscut LiNbO 3 single crystal with different thicknesses under irradiation of a 248 nm ultraviolet laser pulse with 20 ns duration without an applied bias.Nanosecond photovoltaic response is observed and faster rise time is obtained in thinner samples.In accord with the 248 nm laser duration,the full width at half maximum of the photovoltaic signals keeps a constant of ～ 20 ns.With decrease of the crystal thickness,the photovoltaic sensitivity was improved rapidly at first and then decreased,and the maximum photovoltage occurred at 0.38 mm-thick single crystal.The present results demonstrate that decreasing the LiNbO3 single crystal thickness can obtain faster response time and improve the photovoltaic sensitivity.     

Tetragonal Distortion of GaN Epilayer with Multiple Buffer Layers on Si （111） Studied by RBS/Channelling and HRXRD

Rutherford backscattering （RBS）/channelling and high resolution x-ray diffraction （HRXRD） have been used to characterize the tetragonal distortion of a GaN epilayer with four Alx Ga1-xN and single AIN buffer layers grown on a Si （111） substrate by metal-organic vapour phase epitaxy （MOVPE）. The results show that a 1000nm GaN epilayer with a perfect crystal quality （Xmin = 1.54%） can be grown on the Si （111） substrate in virtue of multiple buffer layers. Using the RBS/channelling angular scan around an off-normal （1213） axis in the （1010） plane and the conventional HRXRD θ - 20 scans normal to GaN （0002） and （1122） planes at the 0° and 180° azimuth angles, the tetragonal distortion eT, which is caused by the elastic strain in the epilayer and different buffer layers, can be obtained respectively. The two experiments are testified at one result, the tetragonal distortion of GaN epilayer is nearly to a fully relaxed （eT = 0）.     

Temperature-insensitive fiber cantilever vibration sensor based on a fiber-to-fiber structure

A simple optical fiber cantilever vibration sensor consisting of two opposite aligned bare optical fibers sealed in a quartz capillary is presented.The fiber with the longer bare section is suspended in air and acts as a cantilever.By detecting the transmission power of the sensor directly,the environmental vibrational frequencies and amplitudes may be obtained.By adjusting the cantilever's natural deflection angle,the sensor can achieve high sensitivity,good response linearity,and a wide dynamic range.Coupling conditions are optimized to minimize temperature effects by simply setting an appropriate air gap between the bare fibers.     

High-power terahertz pulse sensor with overmoded structure

Based on the hot electron effect in a semiconductor, an overmoded resistive sensor for 0.3-0.4 THz band is investi-gated. The distribution of electromagnetic field components, voltage standing wave ratio （VSWR）, and the average electric field in the silicon block are obtained by using the three-dimensional finite-difference time-domain （FDTD） method. By adjusting several factors （such as the length, width, height and specific resistance of the silicon block） a novel sensor with optimal structural parameters that can be used as a power measurement device for high power terahertz pulse directly is proposed. The results show that the sensor has a relative sensitivity of about 0.24 kW 1, with a fluctuation of relative sensitivity of no more than ±22%, and the maximum of VSWR is 2.74 for 0.3-0.4 THz band.     

Subwavelength Imaging in a One-Dimensional Metal-Dielectric Structure

We analyse the dispersion relation of a one-dimensional （1D） metal-dielectric （MD） structure for H-polarized light （i.e. the magnetic field is parallel to the interfaces of the layers） and use the transfer matrix method to simulate the subwavelength image effect through the 1D-MD structure. The structure operates in the self-collimation regime, and does not involve negative refraction or amplification of evanescent waves. The Fabry-Perot resonance effect is studied in order to obtain optimum parameters for maximum transmission. A resolution of ）λ/10 for a single point source is achieved when the thickness of the 1D-MD is about 300 nm. Taking into account the actual values of the dielectric constants of the metal （silver） and the dielectric （HfO2） layers, we find that a silver/HfO2 stack, with suitable parameters, has a resolution of λ/5 at visible wavelengths.     

Polarized Micro-Raman Study of the Temperature-Induced Phase Transition In 0.67 Pb（Mg1/3Nb2/3）O3-0.33PbTiO3

Polarized Raman spectra of ferroelectric relaxor 0.67Pb（Mg1/3Nb2/3）O3-0.33PbTiO3 （0.67PMN-0.33PT） single crystal are systematically investigated in a wide temperature range from -196 to 600℃ by micro-Raman scattering technique. The results clearly reveal that there are two structural phase transitions in such composite ferroelectric relaxor： the rhombohedral-tetragonal （R- T） phase transition and the tetragonal-cubic （T- C） phase transition. The former occurs at about TR-T =34℃, corresponding to the vanishing of the soft A1 mode at 106cm^-1 recorded in the parallel polarization. The latter appears at about TT-C = 144℃, which can be verified with the vanishing of mode at 780cm^-1 measured in the crossed polarization.     

The transverse laser induced thermoelectric voltages in step flow growth （1- x）PD（Mg1/3Nb2/3）O3-xPbTiO3 thin films

This paper reports that the transverse laser induced thermoelectric voltages （LITV） axe observed for the first time in the step flow growth （1- x）PD（Mg1/3Nb2/3）O3-xPbTiO3 （PMN-PT, x = 0.20, 0.33, 0.50） thin films deposited on vicinal-cut strontium titanate single crystal substrates. Because lead magnesium niobate-lead titanate is a solid solution of lead magnesium niobate （PMN） and lead titanate （PT）, there are two types of signals. One is wide with a time response of a microsecond, and the other superimposed with the wide signal is narrow with a time response of a nanosecond. The transverse LITV signals depend on the ratio of PMN to PT drastically. Under the irradiation of 28-ns pulsed KrF excimer laser with the 248-nm wavelength, the largest induced voltage is observed in the 0.50Pb（Mg1/3Nb2/3）O3-0.50 PbTiO3 films. Moreover, the effects of film thickness, substrates, and tilt angles of substrates are also investigated.     

Refractive index sensor based on tapered PCF in-line interferometer

A simple and compact refractive index sensor is demonstrated by tapering a photonic crystal fiber (PCF) in-line interferometer. The PCF is spliced between two single-mode fibers and tapered via hydrofluoric acid etching. Its sensitivity in liquid is more than an order of magnitude larger than the untapered one. By optimizing the etching process, we can fabricate more uniformly and thinly tapered PCF interferometers with higher sensitivity in the future.     

High-sensitivity FBG microphone with static pressure equalization and optimized response

We present a high-sensitivity fiber Bragg grating(FBG)-based microphone with a flat response and static pressure equalization. A very high dynamic sensitivity of the microphone is achieved by a pressure sensing structure based on a carbon fiber diaphragm. Static pressure equalization is realized by a balance structure with a capillary glass tube. The resonances of the sensor are suppressed by air damping structures, and a broadened flat response is achieved. An acoustic-solid interaction model was used to analyze the response characteristics of the microphone. An experimental prototype was produced and tested, and the results are well consistent with the design.The tested sensitivity was-10 d B re 1 pm/Pa from 10 Hz to 2.5 kHz with a fluctuation of less than ±1.5 dB.Combined with the phase-generated-carrier-based coherent detection scheme, the microphone can achieve a sound resolution of the milli-pascal level. The static pressure sensitivity is measured to be-0.27 pm/atm, which is 100 dB lower than the dynamic sensitivity.     

A fiber micro-vibration sensor based on single-mode fiber ring laser

A new micro-vibration sensor based on single-mode fiber ring laser is put forward. The Mach-Zehnder interferometric （MZI） detection technique is presented for interrogating laser frequency shift due to the measurand （piezoelectric transducer （PZT） is used to simulate the micro-vibration） induced laser cavity strain from both single- and multi-mode lasers. In the experiment, compared with multi-mode laser sensors, the single-mode laser sensor is proved to be a sensor with high resolution. When the PZT is driven by the analog signal （0.03 rad near 2 kHz）, the signal-to-noise ratio （SNR） of output signal from the single-mode laser sensor is close to 55 dB and the sensitivity of the sensor is about 5 ×10^-5 rad/Hz1/2.     

Pressure effects in AlAs/Inx Ga1-xAs/GaAs resonant tunnelling diodes for application in micromachined sensors

This paper reports the current-voltage characteristics of [001]-oriented AlAs/InxGa1-xAs/GaAs resonant tunnelling diodes （RTDs） as a function of uniaxial external stress applied parallel to the [110] and the [1^-10] orientations, and the output characteristics of the GaAs pressure sensor based on the pressure effect on the RTDs. Under [110] stress, the resonance peak voltages of the RTDs shift to more positive voltages. For [1^-10] stress, the peaks shift toward more negative voltages. The resonance peak voltage is linearly dependent on the [110] and [1^-0] stresses and the linear sensitivities are up to 0.69 mV/MPa, -0.69 mV/MPa respectively. For the pressure sensor, the linear sensitivity is up to 0.37 mV/kPa.     

Growth of Atomically Flat Ultra-Thin Ag Films on Si（111） by Introducing a √3×√3-Ga Buffer Layer

Growth of high-quality ultra-thin Ag film is of great interest from both scientific and technological viewpoints. First, ultra-thin metal fihns are model systems utilized to investigate quantum size effects （QSE）. When the film thickness is comparable to the Fermi wavelength of an electron, quantized energy lev- els known as quantum well states are produced in the surface normal direction. High-quality metal films with uniform thickness can effectively suppress in- homogeneous broadening of the thickness-dependent quantum levels to manifest quantum size effects. Secondly, Ag is the most widely used material for sur- face plasmonic devices, and high-quality Ag films have already shown the capability of supporting surface plasmon propagation fbr an extremely long distance. Moreover, ultra-thin Ag films can act as an excel- lent substrate for integrating various nano and low- dimensional structures. For instance, silicene, which is a two-dimensional （2D） sheet composed of silicon similar to graphene, has recently attracted intense attention. Ag （111） surface is widely recognized as the most important substrate suitable for the growth of silicene, while Ag films are much more cost-effective candidates for expensive single crystal Ag（111） sub- strates.     

Oscillatory electron phonon coupling in Pb/Si（111）deduced by temperature-dependent quantum well states

Photoemission study of atomically flat Pb films with a thickness from 15 to 24 monolayers （ML） have been performed within a temperature range 75-270K. Well-defined quantum well states （QWSs） are observed, which exhibit interesting temperature-dependent behaviours. The peak position of the QWSs shifts towards higher binding energy with increasing substrate temperature, whereas the peak width broadens linearly due to enhanced electron-phonon coupling strength （λ）. An oscillatory A with a period of 2ML is deduced. Preliminary analysis shows that the oscillation can be explained in terms of the interface induced phase variations, and is thus a manifestation of the quantum size effects.     

Vibration analysis of a new polymer quartz piezoelectric crystal sensor for detecting characteristic materials of volatility liquid

We present a new polymer quartz piezoelectric crystal sensor that takes a quartz piezoelectric crystal as the basal material and a nanometer nonmetallic polymer thin film as the surface coating based on the principle of quartz crystal microbalance (QCM). The new sensor can be used to detect the characteristic materials of a volatile liquid. A mechanical model of the new sensor was built, whose structure was a thin circle plate composing of polytef/quartz piezoelectric/polytef. The mechanical model had a diameter of 8 mm and a thickness of 170 μ. The vibration state of the model was simulated by software ANSYS after the physical parameters and the boundary condition of the new sensor were set. According to the results of experiments, we set up a frequency range from 9.995850 MHz to 9.997225 MHz, 17 kinds of frequencies and modes of vibration were obtained within this range. We found a special frequency f_sp of 9.996358 MHz. When the resonant frequency of the new sensor’s mechanical model reached the special frequency, a special phenomenon occurred. In this case, the amplitude of the center point O on the mechanical model reached the maximum value. At the same time, the minimum absolute difference between the simulated frequency based on the ANSYS software and the experimental measured stable frequency was reached. The research showed that the design of the new polymer quartz piezoelectric crystal sensor perfectly conforms to the principle of QCM. A special frequency value f_sp was found and subsequently became one of the most important parameters in the new sensor design.     

Sensitivity and detection limit of dual-waveguide coupled microring resonator biosensors

We show that a linear relation exists between the device sensitivity and the quality （Q） factor of a dual- waveguide coupled microring resonator optical biosensor when the optimal conditions are satisfied. We also show that the detection limit depends on the loss coefficient and signal-to-nosie ratio （SNR） of the overall system, rather than the circumference of the ring. For a microring resonator sensor whose Q factor is 20000, the detection limit is found to be about 10-7 with 30-dB SNR, which is in good agreement with reported experimental data. These results indicate that loss reduction is the top priority in the design and fabrication of highly sensitive microring resonator optical biosensors.     

A high figure of merit localized surface plasmon sensor based on a gold nanograting on the top of a gold planar film

We investigate the sensitivity and figure of merit （FOM） of a localized surface plasmon （LSP） sensor with gold nanograting on the top of planar metallic film. The sensitivity of the localized surface plasmon sensor is 317 nm/RIU, and the FOM is predicted to be above 8, which is very high for a localized surface plasmon sensor. By employing the rigorous coupled-wave analysis （RCWA） method, we analyze the distribution of the magnetic field and find that the sensing property of our proposed system is attributed to the interactions between the localized surface plasmon around the gold nanostrips and the surface plasmon polarition on the surface of the gold planar metallic film. These findings are important for developing high FOM localized surface plasmon sensors.