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We theoretically study the optical bistability assisted by multipole polarizations in a semiconductor quantum dot (SQD)/metal nanoparticle (MNP) hybrid molecule. We map out bistability phase diagrams within the parameter subspace spanned by (the pumping intensity Ipu, interparticle distance, d) under dipole and multipole approximations. It is shown that the Ipu-correlated bistable region will be broadened greatly in the strong exciton–plasmon coupling regime, and the corresponding lower (upper) bistable threshold is enlarged significantly due to multipole polarization (N = 10) in comparison to that in the dipole approximation (N = 1). However, under the same conditions, the d-correlated bistable region is shrunk at high pump intensities. Our contribution not only offers a better understanding of exciton–plasmon coupling systems but also expands the application of SQD/MNP hybrid molecules in the field of optical bistable nanodevices. [ABSTRACT FROM AUTHOR]

In this study, the multiple-exposure nanosphere-lens lithography method utilizing the polystyrene nanospheres with focusing behavior is investigated and introduced to fabricate diverse photonic crystals (PCs) on indium tin oxide to enhance the optical output power of GaN-based light-emitting diode (LED). Simulated results indicate that the focused light intensity decreases with increasing tilted angle due to the shadow effect introduced by adjacent nanospheres. The fill factor of nanopattern is tunable by controlling tilted angles and exposure times. To attain quadruple PC without overlapping patterns, mathematical calculation model is used to define the optimum range of tilted angles. Angular emission patterns and three-dimensional finite-difference time domain simulated results indicate that the enhanced light extraction of PC LEDs results mainly from diffused scattering effects, and the diffraction effects of PC on light extracted efficiency increase with the increase of fill factor. Furthermore, it is confirmed that the multiple PC can extract more light from GaN into air than common PC with same period and fill factor. [ABSTRACT FROM AUTHOR]

We report a hollow type piezoelectric micromotor made of a PZT ceramic/metal composite cylinder with sizes of only 3.6 mm in diameter and 3.0 mm in length aiming at medical endoscope application. The hollow piezoelectric stator of the micromotor, acting as a nut, can excite E02-mode traveling wave along its circumferential direction, and a hollow rotor with a fine lens inside, acting as a screw, is driven to produce a spiral motion along its axis direction inside the hollow stator via the traveling wave. The features of the developed micromotors are its hollow, fine structure and submicrometer step resolution, ensuring that the optical path passes in a narrow and limited space and that the optical focal length is tuned precisely inside the endoscope, which is meaningful in medical diagnosis. [ABSTRACT FROM AUTHOR]

The authors present a facile approach to the fabrication of nanopatterned sapphire substrates (NPSS) with concave pyramid structure by a wet etching method. The silica wet-etching mask on the sapphire substrate was prepared by using a colloidal monolayer templating strategy. NPSS with two different periods were prepared by employing 660 and 900 nm polystyrene colloidal spheres. Light emitting diode (LED) structure was epitaxially grown on the NPSS by the metal-organic chemical vapor deposition method. Both structural and optoelectronic properties of LEDs grown on flat sapphire substrate and NPSS were demonstrated and compared in detail. The calculations based on x-ray rocking curves revealed that the threading dislocation densities (TDDs) were decreased and the crystalline quality of epitaxial GaN film was improved when NPSS was used. Furthermore, the decrease in the edge TDDs was more prominent than that in the screw TDDs, which could be explained by the dislocation annihilation mechanism. The LEDs grown on 660-and 900-nm-NPSS exhibited 48% and 56% enhancement in light output power compared to that of a conventional LED on a flat sapphire substrate, arising from the nanoscale patterns in the sapphire which allowed more light to reflect from sapphire substrate onto the top direction. [ABSTRACT FROM AUTHOR]

In this experiment, a flip-chip light-emitting diode with photonic crystal was fabricated at the interface of p-GaN and Ag reflector via nanospheres lithography technique. In this structure, photonic crystal could couple with the guide-light efficiently by reason of the little distance between photonic crystal and active region. The light output power of light emitting diode with embedded photonic crystal was 1.42 times larger than that of planar flip-chip light-emitting diode. Moreover, the embedded photonic crystal structure makes the far-field divergence angle decreased by 18° without spectra shift. The three-dimensional finite difference time domain simulation results show that photonic crystal could improve the light extraction, and enhance the light absorption caused by Ag reflector simultaneously, because of the roughed surface. The depth of photonic crystal is the key parameter affecting the light extraction and absorption. Light extraction efficiency increases with the depth photonic crystal structure rapidly, and reaches the maximum at the depth 80 nm, beyond which light extraction decrease drastically. [ABSTRACT FROM AUTHOR]

In this paper, a computational goal for a monaural speech separation system is proposed. Since this goal is derived by maximizing the signal-to-noise ratio (SNR), it is called the optimal ratio mask (ORM). Under the approximate W-Disjoint Orthogonality assumption which almost always holds due to the sparse nature of speech, theoretical analysis shows that the ORM can improve the SNR about 10log102 dB over the ideal ratio mask. With three kinds of real-world interference, the speech separation results of SNR gain and objective quality evaluation demonstrate the correctness of the theoretical analysis, and imply that the ORM achieves a better separation performance. [ABSTRACT FROM AUTHOR]

The propagation of surface water wave pulses over a topographical bottom with randomly arranged cylindrical steps is investigated by multiple scattering theory. It is shown that the waves within a certain frequency range can be localized due to the strong multiple scattering process. In the localized state, the wave intensity decreases exponentially as the transmitted distance increases. By making use of this effect, some components contained in the pulse can be filtered or inhibited by the cylinder ensemble and trapped for a relatively long period of time until dissipation. [ABSTRACT FROM AUTHOR]

The localization caused by multiple scattering of lightwaves provides a mode for random laser action. It is shown that once the gain surpasses a certain threshold, photons are driven to localized modes, which greatly suppresses the energy loss and leads to laser emission. Concurrent with the localization of the random laser, unique collective behaviors of the localized modes appear, as distinguished from the other modes, which reveals the “invisible” microcavities of random lasers. [ABSTRACT FROM AUTHOR]

We show some properties of the acoustic propagation in two-dimensional sonic crystals, formed by parallel rigid cylinders placed in air. The transmission through slabs of sonic crystals and the associated band structures are considered. It is shown that within partial band gaps, the waves tend to be collimated or guided into the direction in which the propagation is allowed. Such a feature also prevails in the situations in which deaf bands appear. We show that within the partial band gaps, a stable imaging effect can be obtained for flat sonic crystal slabs, in analogy to the cases with photonic crystals. [ABSTRACT FROM AUTHOR]

We synthesis uniform Au-CdS core-shell hetero-nanorods and demonstrate the effective plasmon-exciton interaction induced optical nonlinear enhancement in metal-semiconductor hetero-nanostructures. After growing CdS semiconductor shell onto the Au nanorods, the longitudinal plasmon resonance exhibits considerable red-shift with enlarged absorption intensity. Nonlinear absorption responses transform from saturable absorption to reverse saturable absorption, and effective nonlinear absorption coefficient β is increased from -7.7 to +22.2 cm/GW. The observed behaviors indicate strong plasmon-exciton interaction and great local field enhancement. [ABSTRACT FROM AUTHOR]