Abstract:One dimension (1D) ordered titanium dioxide (TiO₂) nanostructured photocatalysts sensitized by quantum dots (QDs) are fabricated. Their morphologies, crystal structures and photocatalytic properties are characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and ultraviolet-visible-near infrared (UV-vis-NIR) absorption spectroscopy, respectively. Compared with the original TiO₂ nanostructure, the nanostructured TiO₂ sensitized by QDs exhibits a good photocatalytic activity for the degradation of methyl orange (MO). The QDs with core-shell structure can reduce the photocatalytic ability due to the higher potential barrier of carrier transport in ZnS shell layer. The results indicate that the proposed photocatalyst shows promising potential for the application in organic dye degradation.

Abstract:In order to study the depolarization properties of an improved Lyot depolarizer with monochromatic light, the theory of multi-beam superposition is adopted. The dependences of degree of depolarization (D) on vibration azimuth angle (VAA) and total retardation (TR) are analyzed. The results show that D is ideal for any VAA when TR is δ=(N+1/2)π (N is an integer) on the basis of wedge angle large enough. And when δ=Nπ, VAA makes the most significant impact on D. When δ is assigned to the other values, the impact on D made by VAA is between the former two. Using a 405 nm semiconductor laser, experiments for measuring D of the sample with wedge angle of 6° are conducted. The theoretical results are well verified by experiments. D is over 98.8% when TR is nearly δ=(N+1/2)π by changing the incident angle.

Abstract:A hole-blocking layer (HBL) of 4,7-diphenyl-1,10-phenanthroline (BPhen) is incorporated between the emitting layer (EML) and the electron transport layer (ETL) for a tris-(8-hydroxyqunoline)aluminum based organic light-emitting device (OLED). Such a structure helps to reduce the hole-leakage to the cathode, resulting in an improved current efficiency. The BPhen improves the balance of hole and electron injections. The current efficiency is improved compared with that of the device without the blocking layer. The highest luminous efficiency of the device with 6 nm BPhen acting as a blocking layer is 3.44 cd/A at 8 V, which is improved by nearly 1.5 times as compared with that of the device without it.

Abstract:Based on poled guest-host electro-optic (EO) polymer DR1/SU-8, a Mach-Zehnder interferometer (MZI) EO modulator operated at 1.55 μm is proposed. For achieving high response speed and high EO modulation efficiency, both waveguide structure and electrode structure are especially optimized. The impedance match and less index mismatch are achieved. The final characteristic impedance of electrode is about 49.4 Ω, and the microwave index and the light-wave index are 1.5616 and 1.6006, respectively. The device is fabricated using wet-etching technique and inductively coupled plasma (ICP) etching technique, and its performance is measured at 1.55 μm. Experimental results show that when the applied voltage is tuned, the modulator can be changed from ON state to OFF state. The insertion loss at ON state is 12 dB and the extinction ratio between ON and OFF states is about 10 dB. The high response speed is in nanosecond level for a square-wave signal. Therefore, the modulator possesses potential applications in high-speed optical networks on chip.

Abstract:A novel scheme for all-optical ultra-wideband triplet signal pulse generation based on the cross-gain modulation (XGM) in a single semiconductor optical amplifier (SOA) is demonstrated. In this scheme, only one optical source and one SOA are needed, so the configuration is simple. Due to only one wavelength is included in the generated triplet pulse, no time difference between output signal light and probe light is introduced during the transmission process. By using the software of Optisystem 7.0, the impacts of the input signal width, the optical power and the wavelength of the optical source on the generated triplet pulse are numerically simulated and studied. The results show that the proposed scheme has better triplet signal pulse when the input signal pulse width is larger, and it is insensitive to the wavelength change within a certain range.

Abstract:Flexible TiO₂ memory devices are fabricated on a plastic substrate at room temperature. The metal-insulator-metal (MIM) structure is grown on polyimide (PI). Several metals with different ductilities, such as Al, W, Cu and Ag, are selected as electrode. The test results show that the samples have stable resistive switching behaviors, and the electric characteristics can stay stable even after the radius of substrate is bent up to 10 mm. After 10³ times of substrate bending, the memory cells with W as bottom electrode on PI still show stable resistive switching characteristics and low switching voltages. The set voltage and reset voltage can be as low as 0.9 V and 0.3 V, respectively.

Abstract:A metamaterial based on complementary planar double-split-ring resonator (DSRR) structure is presented and demonstrated, which can optically tune the transmission of the terahertz (THz) wave. Unlike the traditional DSRR metamaterials, the DSRR discussed in this paper consists of two split rings connected by two bridges. Numerical simulations with the finite-difference time-domain (FDTD) method reveal that the transmission spectra of the original and the complementary metamaterials are both in good agreement with Babinet’s principle. Then by increasing the carrier density of the intrinsic GaAs substrate, the magnetic response of the complementary special DSRR metamaterial can be weakened or even turned off. This metamaterial structure is promised to be a narrow-band THz modulator with response time of several nanoseconds.

Abstract:A new integrated optical three-dimensional (3D) electric field (E-field) sensing system is shown in this paper. In the system, the method of tuning laser’s wavelength is used for controlling the working point of the integrated optical E-field sensor to keep it always in linear working area. The sensing system contains three independent E-field sensors, and the tuning of their working points and the sensing of electric signal are completed by adopting time-division multiplexing (TDM) technique. Then, the theoretical analysis and simulation of the working mechanism of the E-field sensing system are done in this paper. The results show that the bandwidth of electric signal is directly related with the tuning time of working point, and also determines the working rate of the controlling system.

Abstract:We adopt the post-additional thermal annealing (PATA) process to optimize the performance of the polymer solar cells (PSCs) with an active layer composed of a blend of regioregular poly (3-hexythiophene) (RR-P3HT) and fullerenes. It is found that compared with general annealing process, the crystallinity of RR-P3HT by PATA is enhanced, and the absorption peak is raised obviously at ～500 nm after PATA. With the optimized annealing conditions, the device shows an enhancement of 31% in short circuit current density, 5% in open circuit voltage (V _oc), and 11% in the power conversion efficiency (PCE) compared with that of the general annealing device.

Abstract:The properties of ZnO thin film on sapphire (0001) substrate fabricated by single source chemical vapour deposition (SSCVD) method are studied. X-ray diffraction (XRD) analysis demonstrates that the film exhibits hexagonal structures but with preferential nonpolar (100) plane orientation, which is different from the crystalline structure of substrate, and its formation mechanism is also analyzed. The film has the characteristic of p-type conductivity originating from excess of oxygen, and its p-type conductivity is comparatively stable due to its nonpolar plane orientation. A strong ultraviolet (UV) emission and a high light transmission in visible wavelength region are observed from photoluminescence (PL) spectrum and transmittance spectra at the room temperature, and the strong ultraviolet emission originates from the recombination of free and bound excitons. Compared with the ZnO film on silicon substrates, the exciton emission peaks of the film on sapphire substrate show a slight blue shift about 50 meV, which might be related to the different crystallite sizes or surface stress of the films.

Abstract:A novel white-bluish emitting phosphor of (Ba_0.49Sr_0.49)₂B₂P₂O₁₀:0.02Eu²⁺ is synthesized by the solid state reaction. (Ba_0.49Sr_0.49)₂B₂P₂O₁₀:0.02Eu²⁺ can be effectively excited by 370 nm ultraviolet (UV) light, and exhibits two emission bands at 430 nm and 522 nm which are attributed to the d-f transitions of the Eu²⁺ ions in two different cation sites in the host lattices. And the chromaticity coordinate of (Ba_0.49Sr_0.49)₂B₂P₂O₁₀:0.02Eu²⁺ phosphor is (0.29, 0.25).

Abstract:Laser crystals of LiYF₄ (LYF) singly doped with Er³⁺ in 2.0% and co-doped with Er³⁺/Yb³⁺ in about 2.0%/1.0% molar fraction in the raw composition are grown by a vertical Bridgman method. X-ray diffraction (XRD), absorption spectra, fluorescence spectra and decay curves are measured to investigate the structural and luminescent properties of the crystals. Compared with the Er³⁺ singly doped sample, obviously enhanced emission at 1.5 μm wavelength and green and red up-conversion emissions from Er³⁺/Yb³⁺ co-doped crystal are observed under the excitation of 980 nm laser diode. Meanwhile, the emission at 2.7 μm wavelength from Er³⁺ singly doped crystal is reduced. The fluorescence decay time ranging from 18.60 ms for Er³⁺ singly doped crystal to 23.01 ms for Er³⁺/Yb³⁺ co-doped crystal depends on the ionic concentration. The luminescent mechanisms for the Er³⁺/Yb³⁺ co-doped crystals are analyzed, and the possible energy transfer processes from Yb³⁺ to Er³⁺ are proposed.

Abstract:In near-zero-permittivity operation range, the position-dependent extraordinary optical properties of a one dimensional (1D) Fibonacci quasi-periodic superconducting photonic crystal (PC), which consists of alternating superconductor and dielectric layers, are theoretically investigated by using the transfer matrix method. Based on the calculated reflectance spectrum, it is shown that the extraordinary optical properties depend on the relative positions of the threshold wavelength and the photonic band gaps (PBGs). By suitably choosing the thickness of the superconducting or dielectric layer, a transmission narrow band filter or resonator can be designed without introducing any physical defect in this structure.

Abstract:A method of color mixture for white light is presented with Sr₃MgSi₂O₈:Eu²⁺, Mn²⁺ shell coated on Sr₂SiO₄:Eu²⁺ core by spray pyrolysis procedure. Upon near ultraviolet (NUV) excitation, a 550 nm band emission of Eu²⁺ from core host combines with the simultaneous emissions of Eu²⁺ at 457 nm and Mn²⁺ at 683 nm based on energy transfer in the shell lattice to generate warm white light with color rendering index (CRI) of 91. With such a core-shell-like structure, the re-absorption of blue light from shell layer can be effectively suppressed, and the chemical stability of the phosphor is verified experimentally to be superior to that of the Sr₂SiO₄:Eu²⁺. This new proposed phosphor provides great potential in the color mixture of blending-free phosphor converted white NUV light emitting diode (LED) devices.

Abstract:A new optical label switching system with coherently detected implicit spectral amplitude code (SAC) labels is proposed in this paper. The implicit SAC labels are recognized using a frequency-swept local light source oscillator. An explicit SAC-label switching system with 40 Gbit/s intensity modulation (IM) payloads and 156 Mbit/s label and an implicit SAC-label switching system with 2.5 Gbit/s IM payloads and 156 Mbit/s label are both considered. Label and payload bit error rate (BER) performance is assessed and compared by simulations. The results reveal that after 80 km transmission and at the BER of 10^?9, the received optical power (ROP) values of label and payload are ?8.3 dBm and ?23.5 dBm in implicit SAC-label switching system, respectively, while those are ?18.2 dBm and ?18.6 dBm in explicit SAC-label switching system, respectively. As a result, the payloads of 40 Gbit/s and 2.5 Gbit/s in explicit/implicit SAC-label switching system have little influence on the received payload quality at the BER of 10^?9 after 80 km transmission. Finally, a payload of 40 Gbit/s can obtain 12.5 dB optical signal-to-noise ratio (OSNR) after 80 km transmission.

Abstract:Atmospheric turbulence and platform vibration in the space optical communication can cause the offset and jitter of beam, which further result in the fluctuations of received optical power. To resist this effect, a communication system with fine tracking systems in the receiver and transmitter is designed. The system is used in the experiment of laser communication between high-rise buildings over a distance of 3.5 km. After adding a vibration source to the transmitter, the centroids of spots captured by the camera of the transmitter and the optical power of receiver are recorded for the purpose of analysis. When the vibration source works at the designated frequency, a peak appears at the corresponding frequency in the spectrum of the spot centroids and the optical power of receiver. Then the peak disappears once the fine tracking system begins to work. Compared with the condition without the fine tracking system, the minimum value of the optical power of receiver is increased by 5 dB, and the standard deviation is decreased by 30%.

Abstract:An improved multiplier-free feed-forward carrier phase estimation algorithm is proposed for dual-polarization quadrature-phase-shift-keying (DP-QPSK) with coherent detection. The bit error rate (BER) performance, block length effect and linewidth tolerance of the proposed algorithm are evaluated for a 112 Gbit/s DP-QPSK system. A linewidth symbol duration product of 2.9×10^?4 is demonstrated for 1 dB optical signal-to-noise-ratio (OSNR) penalty at BER of 10^?3 for the proposed algorithm. The hardware complexity of the proposed multiplier-free algorithm is demonstrated to be much lower than that of the 4th power algorithm.

Abstract:A novel full-duplex single-sideband (SSB) wavelength division multiplexing radio over fiber (WDM-RoF) system with selected mapping (SLM) technique for decreasing peak-to-average power ratio (PAPR) is proposed in this paper. At the central office (CO), the generated SSB signal carrying 10 Gbit/s 16-ary quadrature amplitude modulation orthogonal frequency division multiplexing (16QAM-OFDM) downstream signal with SLM technique is sent to the base station, and 60 GHz SSB optical signal carrying 10 Gbit/s 16QAM-OFDM upstream signal is sent back to CO utilizing the wavelength-reuse technology. Simulation results show the proposed method for PAPR reduction can effectively improve the sensitivity of receiver, and the power penalty of the 16QAM-OFDM downlink (uplink) signal is about 2 dB (3 dB) at BER of 1×10^?3 after 42 km standard single-mode fiber (SSMF) transmission.

Abstract:A differential optical absorption spectroscopy (DOAS) method is presented and used for the air pollutant detection. The novel measurement frame employs a Cassegrain telescope and a combined fiber bundle. The emitting and receiving fibers are bundled together at one port. The common port is placed at the focus of the Cassegrain telescope. The total length of the prototype is reduced to about 1/2 of the traditional one. Air pollutants of SO₂, NO₂ and O₃ are monitored by the prototype, and the concentrations are inverted. Results show that the correlation coefficients are 0.9490, 0.9614 and 0.9301, respectively. And there is a good consistency between the measured results and the reference data.

Abstract:The effect of temperature on the dynamics of a laser-induced cavitation bubble is studied experimentally. The growth and collapse of the cavitation bubble are measured by two sensitive fiber-optic sensors based on optical beam deflection (OBD). Cavitation bubble tests are performed in water at different temperatures, and the temperature ranges from freezing point (0°C) to near boiling point. The results indicate that both the maximum bubble radius and bubble lifetime are increased with the increase of temperature. During the stage of bubble rapidly collapsing in the vicinity of a solid surface, besides laser ablation effect, both the first and second liquid-jet-induced impulses are also observed. They are both increased with liquid temperature increasing, and then reach a peak, followed by a decrease. The peak appears at the temperature which is approximately the average of freezing and boiling points. The mechanism of liquid temperature influence on cavitation erosion is also discussed.