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The diffraction limit of light greatly limits the development of conventional optical devices, which are difficult to be miniaturized and integrated with high density. Surface plasmons, electromagnetic modes at the metal-dielectric interface, can concentrate light into deep subwavelength dimensions, enabling the manipulation of light at the nanometer scale. Surface plasmons can be used as information carrier to transmit and process optical signals beyond the diffraction limit. Therefore, nanodevices based on surface plasmons have received much attention. By modulating surface plasmons, the modulation of optical signals at nanoscale can be realized, which is important for the development of on-chip integrated nanophotonic circuits and optical information technology. In this article, we review the modulations of propagating surface plasmons and their applications in nano-optical modulators. The wave vector of propagating surface plasmons is very sensitive to the dielectric function of the metal and the environment. By tuning the dielectric function of the metal and/or the surrounding medium, both the real and imaginary part of the wave vector of surface plasmons can be modified, leading to the modulation of the phase and propagation length of surface plasmons and thereby modulating the intensity of optical signals. We first introduce the basic principles of different types of modulations, including all-optical modulation, thermal modulation, electrical modulation, and magnetic modulation. The all-optical modulation can be achieved by modulating the polarization and phase of input light, pumping optical materials, changing the dielectric function of metal by control light, and manipulating a nanoparticle by optical force to modulate the scattering of surface plasmons. The modulation based on thermal effect depends on thermo-optic materials and phase-change materials, and the temperature change can be triggered by photothermal effect or electrical heating. For electrically controlled modulation, Pockels electro-optic effect and Kerr electro-optic effect can be employed. Electrical modulation can also be realized by controlling the carrier concentration of semiconductors or graphene, using electrochromatic materials, and nanoelectromechanical control of the waveguide. The modulation of surface plasmons by magnetic field relies on magneto-optic materials. We review recent research progresses of modulating propagating surface plasmons by these methods, and analyze the performances of different types of plasmonic modulators, including operation wavelength, modulation depth or extinction ratio, response time or modulation frequency, and insertion loss. Finally, a brief conclusion and outlook is presented.

A two-point touch method for three-dimension space is proposed through introducing true three-dimension display and unmarked spatial orientation,while a two-point touch for true three-dimension display system is built.Interactive approach,which offers the solution of spatial orientation,tracking and gesture recognition,has been considered.Demonstrated in the experiments,optical-based two-point touch system meets the needs of human-computer interaction without any markers and sensors and changes of ambient light does not interfere with the operation of the human-computer interaction.

Microfluidic is of great significance for biomedical research and chemical engineering. The mixing of liquids is an essential and necessary procedure for the sample preparation. Due to the low Reynolds number, laminar flow is dominant in a microfluidic channel and it is difficult to mix the fluids in the microchannel quickly and effectively. To improve the mixing efficiency of the liquids in microfluidic channels, we develop an acoustic mixer based on single microbubble oscillation. By designing the cylinder structure on the bottom surface, when the fluid flows through cylinder structure with a diameter of 40 m, the microbubble can be generated by the surface tension of the liquid. The device is fabricated by using standard soft lithography and the replica moulding technique, ensuring the stability and repeatability of the mixing. A piezoelectric transducer (PZT) with a resonant frequency of 165 kHz is attached to the polydimethylsiloxane microfluidic device on the glass substrate by ultrasound coupling gel. When the microbubble is excited by the PZT at a resonant frequency of 165 kHz, microbubble oscillates immediately. To verify whether ultrasound can induce microbubble cavitation, a passive cavitation detection system is established. The results show that the higher harmonics can be detected, indicating that the stable cavitation occurs. The microstreaming induced by the oscillating microbubble disturbs the fluid dramatically, achieving the mixture of liquids. Particle image velocimetry method is utilized to characterize the microstreaming, and a pair of counter-rotating vortices in the microchannel is detected. Furthermore, to test the performance of the device, the deionized water and rhodamine B are injected into the Y-shape microchannel. Relative mixing index is used to quantitatively analyze the mixing performance by measuring the grayscale values of the optical images. The results indicate that with the increase of the input power, mixing time can be shortened correspondingly. When the input power is 14.76 W, the mixing process is ultrafast, within 37.5 ms the high mixing uniformity can be achieved to be 92.7%. With the advantages of simple design, high efficient and ultrafast mixing, and low power consumption, this oscillating microbubble-based acoustic micromixer may provide a powerful tool for various biochemical studies and applications.

A new frequency dependent finite difference time domain (FD-FDTD) method using digital signal processing (DSP) is proposed. The dispersive media is characterized as an infinite-impulse response (IIR) filter, directly leading to FDTD equations. The representation of a dispersive medium is therefore converted to a problem of digital IIR design. It is shown that the numerical results are consistent with analytic solution.

A functional field effect transistor with self-organized In0.15Ga0.85As/GaAs quantum wires (QWRs) as a channel was achieved by molecular beam epitaxy on a (553)B GaAs substrate. Both the three-dimensional image of atomic force microscopy and the polarization of the photoluminance peaks reveal that the channel of the device is a self-organized QWR structure. The device with a gate length of 2 µm and a source-drain spacing of 5 µm performed a good enhancement-mode characteristic and a maximum transconductance of 65 mS/mm was obtained at the gate voltage of 1.0 V by the geometric gate width at room temperature. The saturated drain current is as high as 5.6 mA. The device exhibited a much larger current capacity due to the high density of the self-organized QWRs in its channel layer. In addition, the effective gate width was discussed in comparison with the geometric gate width of the device, from which a larger maximum transconductance of 130 mS/mm could be estimated.

The single-phase earth fault usually happens in power distribution line, but it is very difficult to detect most earth fault locations. The traditional methods have great difficulty in detecting earth fault, cannot quickly resume supplying power for customers and affect reliability of power supply. Tongzhou Power Supply Company of Beijing Electric used signal infusion, detection and other international advanced fault location technology to organize a large scale experiment. The results prove that the technology has a great effect on detecting earth fault and can meet the needs of real application. It introduces the technology in the experiment and test process in detail and reaches primary conclusions, which is of great importance to resolve problems in China.

This paper proposes the microwave equivalent circuit models of the tuned MEMS shunt-capacitive switches and presents their down-state resonance choice formulation and upstate impedance matching formulation. The design method of this kind of MEMS switches is developed based on the analysis of microwave equivalent circuits. The circuit simulation results of the MEMS switch for X band based on those equivalent models are described and compared with the results of HFSS software. The good agreement verifies the effectiveness of those formulations. Those simplified models help to design high-performance RF MEMS switches in an easier way.

A new method for modeling wave propagation in arbitrary frequency-dispersive dielectric media using FDTD and DSP is discussed. This approach involves modeling the simulation region of dispersive media as an IIR digital filter, whereby the difference equations in the time domain are obtained directly and are used to model the transform function /spl epsiv/(t). In order to verify this approach, the authors simulate Gauss pulse plane wave propagation on an air/water interface and compare the numerical reflection/transmission coefficients with analytic results. The study shows that the numerical results are consistent with the analytic solution.