Abstract:Nanotrees ZnO films are synthesized by thermal evaporation method on silicon and glass substrates. PbS powder (5 wt%) is used to obtain the nanostructure and growth modifications. ZnO films are compared with non-doped ones (ZnO film was dense structure without nanotrees). The deposited PbS:ZnO films exhibit polycrystalline orientation using X-ray diffraction (XRD), but the films without doping was less crystalline quality. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to characterize the morphology. SEM images (surface and cross section) was confirmed the nanotrees form for doped ZnO film. Energy dispersive X-ray detector (EDX) was used to verify the composition of prepared films. Ultraviolet-visible (UV-Vis), photoluminescence (PL) and micro Raman techniques were used to investigate the optical properties. The PL spectra intensities were found to increase for PbS:ZnO nanotrees. Up to our knowledge, no work has been published regarding the obtained ZnO nanotrees using PbS as dopant via simple thermal evaporation method.

Abstract:A Fabry-Perot micro-cavity is fabricated by on-line fiber cutting-welding method. The asymmetrical fiber Fabry-Perot micro-cavity is designed and produced by cutting a standard single-mode fiber and welding the fiber end with the core-offset structure. The length of the Fabry-Perot micro-cavity could be controlled within a certain range of accuracy based on the on-line fiber cutting-welding method. According to this method, a micro-machined Fabry-Perot micro-cavity with a length of about 147 μm is achieved and its spectral characteristic is also investigated in our experiment. This proposed method is suitable to produce a micro-fiber-optic structure with improved and controlled precision, which is attractive for the fiber processing field. Moreover, the fabricated Fabry-Perot micro-cavity also has potential application in the microfluidic system and biochemical detection area.

Abstract:We demonstrate a period poled tapered lithium niobate waveguide and study second harmonic generation (SHG) in this device for the purpose of broadening the quasi-phase matching (QPM) acceptance bandwidth. The finite-difference beam-propagation method is used to simulate the guided modes and calculate the effective indices. The simulation results show that by tapering the width of the cross section linearly, the phase mismatch between a specific input wavelength and its SHG signal can be varied along the propagation length. Ideal SHG phase-matching conditions for a wide range of input wavelengths in communication band from 1 542.5 nm to 1 553.5 nm can be satisfied in different positions of the waveguide.

Abstract:A Mach-Zehnder interferometer (MZI) based on two spherical structures is proposed and temperature and humidity are measured simultaneously. The device is fabricated by inserting two spherical structures into a single mode optical fiber (SMF). The results of the experiment indicate that the temperature sensitivities are 0.079 nm/ºC and 0.090 nm/ºC from 10 ºC to 60 ºC, respectively. When the humidity changes from 30% to 70%, the humidity sensitivities are 0.148 nm/%RH and 0.06 nm/%RH, respectively. Therefore, temperature and humidity are measured simultaneously by the sensitive matrix. The new structure is demonstrated to be a particularly useful approach to detect temperature and humidity.

Abstract:Theoretical design of a neotype fluidic controlling sensor system based on side-polished optical fiber is proposed. Numerical investigations demonstrate that the higher birefringence and resonance coupling can be achieved by flexible design of the polishing shape and depth in the research wavelength. The fluidic system is beneficial to selective integration of functional materials. The material is integrated into the fluidic system, which can achieve a birefringence up to 6.98×10-5, and the application of Sagnac thermometer in temperature sensing is studied, and a group of dips with different temperature sensitivities would be observed in the transmission spectra, which is about 1.6 nm/°C by calculating. furthermore, by introducing resonant coupling, single mode single polarization at 1 310 nm is realized. The refractive index (RI) response of the sensing system for a low RI range of 1.39—1.37 is approximately linear, and exhibits a sensitivity of 6 338 nm/RIU. The results show that the proposed neotype fluidic controlling system can be used as a flexible polarization filter or as a potential two-parameter sensor.

Abstract:Virtually imaged phased array (VIPA) has the advantages of insensitive to polarization, simple structure and high in spectral resolution. Compared with commonly used dispersive devices, such as diffraction gratings or Fabry-Pérot (FP) interferometers, VIPA is self-aligned and has high transmission efficiency. In this paper, the dispersion mechanism of the VIPA is introduced in detail, the influence of incident angle and VIPA thickness on the dispersion performance near 532 nm is calculated and analyzed with MATLAB. According to the calculated results, the selected VIPA device has a thickness of 6 mm and an incident angle of 4°. The spectral dispersion system, in combination with corresponding optical devices, is designed and simulated with ZEMAX, then the experimental system was built. The spectral dispersion system based on VIPA, at a central wavelength of 532 nm, has the free spectral range of 15.08 GHz and the spectral resolution of 0.87 GHz. The system designed in this paper can be applied to high-resolution spectral detection such as Brillouin scattering, Raman scattering, laser fluorescence, laser-induced plasma and so on.

Abstract:Focus on the tracking target for detection indoor, the angle peak characteristics are analyzed based on uniform circular motion and the void-zone is proposed. The sine angular trajectory is used to transform the actual target into the infield, which improves the value adaptability of the peak angular acceleration to velocity and accommodates the mobility condition of photoelectric turntable. Fight trajectory is generated by a tri-axial optical target and the tracking experiment is carried out by theodolite to realize the physical simulation of trajectory, which provides powerful conditions for evaluating the tracking performance of photoelectric turntable under the mobility index.

Abstract:The low internal quantum efficiency (IQE) of AlGaN-based deep ultraviolet light emitting diode (DUV-LED) limits its wider application. The main reasons for low IQE include low carrier concentration, poor carrier location and large defects. The bending of energy band between AlGaN electron blocking layer and conduction layer obstructs transport of holes to multiple quantum wells. In this paper, we propose a gradual Al-composition p-type AlGaN (p-AlGaN) conduction layer to improve the light emitting properties of AlGaN-based DUV-LED. Increased carrier concentration in the active region enhances the effective radiative recombination rate of the LED. Consequently, the IQE of our optimazited DUV-LED is increased by 162% in comparison with conventional DUV-LEDs.

Abstract:Different characteristics of fundamental mode of hybrid dielectric loaded plasmonic waveguide have been explored at 1 550 nm wavelength, to resolve the issue of large propagation loss and diffraction limit with minimal waveguide dimension.Propagation length of 432 µm has been achieved with the optimal dimension of 200 nm×40 nm. Through the numerical simulation results, the effective area of 0.021μm2 and normalized intensity of 40.71 μm-2in the spacer region of the waveguide have been realized. To accomplish the ultra-compact directional coupler, the smaller coupling length of about 1.42 µm has been achieved. PTFE-based waveguide can be highly beneficial for the realization of monolithic integration with active optical devices.

Abstract:In this article we report the development of 10×10 photodiode array by realizing heterojunction between mercury cadmium telluride (HgCdTe) quantum dot (diameter ~14 nm) and silicon responsive in mid wave infrared (MWIR) range (l=3—5 μm) at room temperature. Performance of this optical sensor has been evaluated experimentally and Detectivity of 1.6×108 cm /W has been achieved at spectral wavelength of 3.5 μm at 300 K. This work ascertains the compatibility of chemically synthesized HgCdTe quantum dots with commercially available direct injection type readout integrated circuits (ROIC) for the development of low cost large format MWIR focal plane array (FPA).

Abstract:The influence of polyvinylpyrrolidone (PVP) and monoethanolamine (MEA) as surfactants on photoluminescence (PL) of Eu-doped ZnO (ZnO:Eu) has been studied. X-ray diffraction (XRD) results show that there are more Eu3+ ions to replace Zn2+ ions into ZnO lattice for ZnO:Eu in the presence of surfactant MEA. From the spectral analysis for ZnO:Eu with different surfactants by Gaussian deconvolution, it can be seen that the use of MEA as a surfactant affects the energy transfer from ZnO host to Eu3+ ions and leads to three new emission peaks, including UV emission (389 nm), violet emission (411 nm) and green emission (506 nm).

Abstract:Ge films were prepared at different deposition temperatures and ion source bias voltage using the electron beam evaporation. The infrared refractive index was obtained by spectral inversion. Results show that the refractive index becomes larger as the deposition temperature increases. The maximum refractive index at the wavelength of 4 000 nm is 4.274 with the deposition temperatures of 210 °C. The refractive index of film decreases first and then increases as the bias voltage increases. When the ion source bias voltage is 120 V, the refractive index of the film is the smallest. The difference in extinction coefficient of Ge films prepared by different process parameters is small.

Abstract:Coherent optical orthogonal frequency division multiplexing (CO-OFDM) is considered as a key solution for long haul optical fiber communication systems thanks to its high spectral efficiency and robustness against chromatic dispersion. We have investigated a CO-OFDM based on quadrature phase shift keying (QPSK)-OFDM and 16 quadrature amplitude modulation (16QAM)-OFDM over 500 km uncompensated fiber links. The simulation results show that the proposed system is a promising solution to meet the aggregate data rate demands cost effectively in future high-speed optical communication systems.

Abstract:To achieve the real-time detecting and localization of hypervelocity impact events, a monitoring and localization system was designed based on fiber Bragg grating (FBG) sensor network. First, the simulation model was built to study the damage evolution and wave propagation process. Subsequently, based on the response mechanism of FBG to strain, the corresponding high frequency demodulation system was designed. Furthermore, a hypervelocity impact experiment was performed to verify the effectiveness of the designed system. Finally, combined with the diamond sensor array localization algorithm, the accurate position of hypervelocity impact source can be achieved.

Abstract: In this paper, we focus on the detection of prohibited items with small size, and establish an automatic detection model based on feature fusion single shot multibox detector (FSSD) architecture. Two modifications are carried out to improve the detection accuracy. Firstly, the semantic enrichment module (SEM) with dilated convolution is applied to extract the low level feature with strong semantic information. Secondly, a residual module (Res) with residual blocks is added in the multibox detection architecture in order to extract more adequate features for target detection. The simulation results have demonstrated a better performance of the proposed detection model for prohibited items with small size compared with the state-of-the-arts.

Abstract:The excitonic spin polarization in dependence of the size of semiconductor quantum well (QW) was investigated by observing the two different circular polarizations of photoluminescence (PL). From the measurements of PL in QWs, it was found that there is a difference between the two different polarization conditions, which is caused by spin-dependent phase-space filling. The PL spin polarization was estimated from the signals of the left and right circularly polarized PL and was found to depend on the size of the wells as well as on the strength of the bias field. The effects of the size of the well and applied electric field on the excitonic PL spin polarization were studied.