Abstract:An efficient surface-enhanced Raman scattering (SERS) substrate is developed based on silver nanoparticles decorated anodic aluminum oxide (Ag/AAO). The AAO templates were fabricated using a two-step anodization approach, and silver nanoparticles (AgNPs) were obtained by thermal decomposition of Ag nitrate in AAO. The structure of Ag/AAO hybrid substrate is characterized by scanning electron microscopy (SEM). The results show that the as-prepared SERS substrates consist of high-density AgNPs with sizes of tens of nanometers. The AgNPs are adsorbed on the surface of AAO template in the form of network structure which is called “hot spot”. The SERS enhancement ability of the nanostructure is verified using thiram as probing molecules. The limit of detection is as low as 1×10-9 mol/L. The results indicate that the as-prepared substrate possesses excellent SERS sensitivity, high stability and uniformity enhancement.

Abstract:In this paper, a 64 mm×64 mm matrix polymer solar cell (PSC) was fabricated by air-brush spray deposition. Although the open-circuit voltage (Voc) and the fill factor (FF) both need to be improved, the efficiency of matrix PSCs still reaches about 1.82%, and especially the current density achieves nearly 20 mA/cm2. The results verify that air-brush spray deposition is a suitable method to prepare large area PSC devices, and the process we use in this paper can be easily transplanted to roll-to-roll production.

Abstract:The GaN based blue light emitting diodes (LEDs) with a thin AlInN layer inserted in front of the electron blocking layer (EBL) are experimentally studied. It is found that inserting a thin EBL can improve the light output power and reduce the efficiency droop compared with the conventional AlGaN counterparts. Based on numerical simulation and analysis, the improvement on the electrical and optical characteristics is mainly attributed to the reduction of the electron leakage current, which increases the concentration of carriers in the quantum well (QW) when the thin AlInN layer is used.

Abstract:In this paper, the Čerenkov radiation of light pulse in a microring and gratings is simulated and investigated. The system design consists of a two-defect grating incorporating a microring, connected with a uniform grating. In simulation, the continuous wave (CW) light pulse with wavelength centered at 1.55 µm is input into the microring device via the two-defect grating. The resonant outputs from the two-defect grating propagate through the microring and uniform grating, where the time delays of those two input pulses with different wavelengths through the system are distinguished by the output uniform grating. From the obtained resonant output pulses, we find that the red-shifted and blue-shifted Čerenkov pulses are observed. In applications, such a proposed system can be used to form two different optical delay pulses, in which the change in Čerenkov radiation of them, i.e., time delay within a microring device system, can be useful for Čerenkov radiation imaging and sensing applications.

Abstract:A nonlinear optical loop mirror (NOLM)-based linear cavity switchable multi-wavelength erbium-doped fiber (EDF) laser is proposed and experimentally demonstrated. Due to the characteristics of the intensity-dependent transmissivity, the NOLM can effectively mitigate the mode competition of the homogenous broadening gain medium, so that the multi-wavelength lasing can be achieved at room temperature. By adjusting the states of the polarization controllers (PCs), the number of the lasing wavelengths in the proposed laser can be adjusted flexibly from 11 to 13 with a wavelength spacing of 0.4 nm around the wavelength of 1 530 nm.

Abstract:The surface morphology of ZnO films at different annealing temperatures and the performance of polymer solar cells (PSCs) with ZnO as the electron transport layer are studied. The low temperature sol-gel processed ZnO film has smoother surface than that in higher temperature, which results in the best photovoltaic performance with a power conversion efficiency (PCE) of 3.66% for P3HT:PC61BM based solar cell. With increasing annealing temperature, the photovoltaic performance first deceases and then increases. It could be ascribed to the synergy effects of interface area, the conductivity and surface energy of ZnO film and series resistance of devices.

Abstract:By using poled-polymer/silicon slot waveguides in the active region and the Pockels effect of the poled-polymer, we propose a kind of Mach-Zehnder interferometer (MZI) electro-optic (EO) switch operated at 1 550 nm. Structural parameters are optimized for realizing normal switching function. Dependencies of switching characteristics on the slot waveguide parameters are investigated. For the silicon strip with dimension of 170 nm×300 nm, as the slot width varies from 50 nm to 100 nm, the switching voltage can be as low as 1.0 V with active region length of only 0.17–0.35 mm, and the length of the whole device is only about 770–950 μm. The voltage-length product of this switching structure is only 0.17–0.35 V.mm, and it is at least 19–40 times smaller than that of the traditional polymer MZI EO switch, which is 6.69 V.mm. Compared with our previously reported MZI EO switches, this switch exhibits some superior characteristics, including low switching voltage, compact device size and small wavelength dependency.

Abstract:A new large-scale three-dimensional (3D) reconstruction technology based on integral imaging with color-position characteristics is presented. The color of the object point is similar to those of corresponding points. The corresponding point coordinates form arithmetic progressions because integral imaging captures information with a senior array which has similar pitches on x and y directions. This regular relationship is used to determine the corresponding point parameters for reconstructing 3D information from divided elemental images separated by color, which contain several corresponding points. The feasibility of the proposed method is demonstrated through an optical indoor experiment. A large-scale application of the proposed method is illustrated by the experiment with a corner of our school as its object.

Abstract:Cadmium sulfide (CdS) buffer layers with the scale of 10 cm×10 cm are deposited by chemical bath deposition (CBD) with different temperatures and thiourea concentrations under low ammonia condition. There are obvious hexagonal phases and cubic phases in CdS thin films under the conditions of low temperature and high thiourea concentration. The main reason is that the heterogeneous reaction is dominant for homogeneous reaction. At low temperature, CdS thin films with good uniformity and high transmittance are deposited by adjusting the thiourea concentration, and there is almost no precipitation in reaction solution. In addition, the low temperature is desired in assembly line. The transmittance and the band gap of CdS thin films are above 80% and about 2.4 eV, respectively. These films are suitable for the buffer layers of large-scale Cu(In,Ga)Se2 (CIGS) solar cells.

Abstract:The Cu2ZnSnS4 (CZTS) powders are successfully synthesized by using ZnS and Cu2SnS3 as raw materials directly without any intermediate phase at 450 °C for 3 h in Ar atmosphere. The crystalline structure, morphology and optical properties of the CZTS powders are characterized by X-ray diffraction (XRD), Raman spectrum, field emission scanning electron microscopy (FESEM) and ultraviolet-visible (UV-vis) spectrophotometer, respectively. The results show that the band gap of the obtained CZTS is 1.53 eV. The CZTS film is fabricated by spin coating a mixture of CZTS powders and novolac resin with a weight percentage of 30%. The photoelectrical properties of such CZTS films are measured, and the results show an incident light density of 100 mW.cm-2 with the bias voltage of 0.40 V, and the photocurrent density can approach 9.80×10-5 A.cm2within 50 s, giving an on/off switching ratio of 1.64.

Abstract:Based on the space diversity reception, the binary phase-shift keying (BPSK) modulated free space optical (FSO) system over Málaga (M) fading channels is investigated in detail. Under independently and identically distributed and independently and non-identically distributed dual branches, the analytical average bit error rate (ABER) expressions in terms of H-Fox function for maximal ratio combining (MRC) and equal gain combining (EGC) diversity techniques are derived, respectively, by transforming the modified Bessel function of the second kind into the integral form of Meijer G-function. Monte Carlo (MC) simulation is also provided to verify the accuracy of the presented models.

Abstract:A novel radio-over-fiber (ROF) scheme to simultaneously generate and transmit the 3rd generation telecommunication (3G) and millimeter-wave (MMW) signals by using a single dual-electrode Mach-Zehnder modulator (MZM) is proposed. There is no apparent nonlinearity induced by the ROF system. By employing this analog ROF signal transmission technique, highly transparent fiber-wireless convergence networks can be realized, which are ideal for multi-standard wireless system operation.

Abstract:To enhance the communication quality of OpenFlow controlled all-optical networks, an optical signal-to-noise ratio comprehensive-awareness (OSNR-CA) model based lightpath control scheme is proposed. This approach transforms main physical-layer optical impairments into OSNR value, and takes this comprehensive OSNR value of the optical signal along the lightpath into consideration, when establishing the lightpath for the connection request using OpenFlow protocol. Moreover, the proposed scheme makes full advantages of the OSNR monitoring function in each node, and assigns the lightpath according to the comprehensive-OSNR value by extending messages of OpenFlow protocol, in order to guarantee the reliable establishment of the lightpath. The simulation results show that the proposed scheme has better performance in terms of packet loss rate and lightpath establishment time.

Abstract:The mode theory is the main way to study the propagation characteristics of light in fiber so far, but it is not suitable for analysis of light in duct. By using ray-tracing method, the rotary propagation characteristics of light in multimode-single mode-multimode (MSM) fiber structures are analyzed in this paper. Firstly, the light ray in fiber can propagate around an inscribed circle, and the central axis of this fiber is the propagation axis. Secondly, the radius of the inscribed circle is decided by both incident angle and incident position, and its variation is between 0 and RM, where RM is the radius of the multimode fiber. Lastly, the bigger the ratio of core and cladding diameter is, the higher the propagation efficiency is.

Abstract:A portable dual-channel digital/analogue hybrid lock-in amplifier (LIA) is developed, and its amplitude detection error is less than 10% when the signal-to-noise ratio (SNR) is larger than −12 dB. Then, a differential mid-infrared methane (CH4) detection device is experimentally demonstrated based on a wideband incandescence wire-source and a multi-pass spherical reflector. The experiments are carried out to obtain the sensing performance of the device. With the absorption length of only ~4.8 cm, the limit of detection (LoD) is about 71.43 mg/m3, and the detection range is from 0 mg/m3 to 5.00×104 mg/m3. As the concentration gets larger than 714.30 mg/m3, the relative detection error falls into the range of −5%—+5%. Two seven-hour-measurements are done on the CH4 samples with concentrations of 1.43×103 mg/m3 and 4.29×103 mg/m3, respectively, and the results show that the maximum relative error is less than 5%. Because of the cost effective incandescence wire-source, the small-size and inexpensive dual-channel LIA, and the small-size absorption pool and reflector, the developed device shows potential applications of CH4 detection in coal mine production and environmental protection.

Abstract:In the three-dimensional (3D) contour measurement, the phase shift profilometry (PSP) method is the most widely used one. However, the measurement speed of PSP is very low because of the multiple projections. In order to improve the measurement speed, color grating stripes are used for measurement in this paper. During the measurement, only one color sinusoidal fringe is projected on the measured object. Therefore, the measurement speed is greatly improved. Since there is coupling or interference phenomenon between the adjacent color grating stripes, a color correction method is used to improve the measurement results. A method for correcting nonlinear error of measurement system is proposed in this paper, and the sinusoidal property of acquired image after correction is better than that before correction. Experimental results show that with these correction methods, the measurement errors can be reduced. Therefore, it can support a good foundation for the high-precision 3D reconstruction.

Abstract:Because texture images cannot be directly processed by the gray level information of individual pixel, we propose a new texture descriptor which reflects the intensity distribution of the patch centered at each pixel. Then the general multiphase image segmentation model of Potts model is extended for texture segmentation by adding the region information of the texture descriptor. A fast numerical scheme based on the split Bregman method is designed to speed up the computational process. The algorithm is efficient, and both the texture descriptor and the characteristic functions can be implemented easily. Experiments using synthetic texture images, real natural scene images and synthetic aperture radar images are presented to give qualitative comparisons between our method and other state-of-the-art techniques. The results show that our method can accurately segment object regions and is competitive compared with other methods especially in segmenting natural images.

Abstract:Based on the angular spectrum method and the circular Gaussian distribution (CGD) model of scattering media, we numerically simulate light focusing through strongly scattering media. A high contrast focus in the target area is produced by using feedback optimization algorithm with binary amplitude modulation. It is possible to form the focusing with one focus or multiple foci at arbitrary areas. The influence of the number of square segments of spatial light modulation on the enhancement factor of intensity is discussed. Simulation results are found to be in good agreement with theoretical analysis for light refocusing.

Abstract:Using spontaneous parametric down conversion, polarization post selection and coincidence counting technique, the polarization Einstein-Podolsky-Rosen (EPR) entangled states are prepared. Experimental studies on the efficiency, contrast and fidelity with different pump laser intensities are performed systematically. The results show that the pump laser intensity distinctly influences the quality of entangled photons, especially the contrast and the fidelity. On the other hand, the pump efficiency of entangled photons is almost invariable, namely the entangled source brightness increases linearly with the increase of pump laser power.