Abstract:Submission of a manuscript implies: that the work described has not been published before (except in the form of an abstract or as part of a published lecture, review, or thesis): that it is not under 更多还原

Abstract:The whispering-gallery-mode (WGM) photonic crystal microcavity can be potentially used for miniaturized photonic devices, such as thresholdless lasers. In this paper, we use plane wave expansion (PWE) method and study the WGM of H2 photonic crystal microcavities which are formed by removing seven center air holes in a photonic crystal. The WGM in these large-size cavities has some advantages compared with single defect WGM in the view of real device applications. We analyze the nearby air hole e...

Abstract:The goal of Optoelectronics Letters is to rapidly report original,new and important results in the fields of photonics and optoelectronics in English, to advance the international academic exchanges. 更多还原

Abstract:A new aqueous chemical growth method for generation of ZnO flowerlike and spindlelike nanostructures, transformed from layered basic zinc acetate (LBZA) nanobelts, is developed. The novel as-synthesized ZnO flowerlike and spindlelike nanostructures are mainly due to the pH. They are characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The X-ray diffraction peaks indicate that these ZnO nanostructures prefer to grow along the C-axis. Photoluminescence (PL) measurements show that the ZnO flowerlike nanostructures have strong ultraviolet (UV) emission properties at 380 nm, while no defect-related visible emission can be detected. The good performance for photoluminescence emission makes the ZnO flowerlike nanostructures to be promising candidates for photonic and electronic device applications.

Abstract:The high-density carbon nanotubes (CNTs) are synthesized on Fe/Si substrate in the mixture of acetylene and hydrogen gas by radio frequency plasma enhanced chemical vapor deposition (RF-PECVD) method. The effects of substrate temperature on the growth of CNTs are studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy. The quality of CNTs is improved considerably by increasing the substrate temperature while the beam density is increased and graphitization degree (I _D/I _G) is enhanced. The best aligned CNTs are prepared at 750 °C, the beam D density is about 1.6 × 10³/μm², and I _D/I _G is about 0.93. Temperature influence is also discussed.

Abstract:Highly ordered nanocomposite arrays of Rh6G-Au-AAO are formed by filling anodized aluminum oxide (AAO) with Rhodamine 6G (Rh6G) and gold nanoparticles. The optical properties of Rh6G-Au-AAO are studied by visible absorptive and fluorescent spectroscopy. Compared with the fluorescence spectra of Rh6G-Au in the solution environment, the fluorescence peak intensities of Rh6G-Au-AAO are significantly enhanced, the maximum enhancement rate is 5.5, and a constant blue shift of ∼12 nm of peak positions is presented. The effects come from the spatial confinement of AAO and the inhibition of the fluorescence quenching effect induced by gold nanoparticles. The results show that the nanocomposite structures of fluorescence molecules-metal nanoparticles-AAO have a considerable potential in engineering molecular assemblies and creating functional materials of superior properties for future nanophotonics.

Abstract:The emergence angle of specialty solid coupled (SSC) optical taper is numerically studied by using ray-tracing method, which depends on the shape curve function. The relationships between the taper length, shape factor, large-end and small-end radii and the emergence angle are analyzed, respectively. The results show that the variation of small-end radius has great influence on the range of emergence angle for SSC optical taper. Therefore, given the shape curve function of the SSC optical taper, the emergence angle can be used for analyzing the transmission loss of SSC optical taper.

Abstract:The conversion efficiency and noise figure (NF) of the silicon-on-insulator (SOI) waveguide-based wavelength converter are investigated with the coupled equations. The effects of the pump power, the nonlinear absorption and the waveguide length on the conversion efficiency and noise figure are discussed. The conversion efficiency decreases with the increasing pump power and the noise figure is degraded due to the two-photon absorption (TPA) and the TPA-induced free-carrier absorption (FCA) at the higher pump power. With the increasing of the free carrier lifetime, the conversion efficiency will decrease and the noise figure will increase accordingly. The optimal waveguide length depends on the pump power and the free carrier lifetime. In practical applications, the high conversion efficiency and low noise figure can be achieved by choosing suitable parameters of the silicon waveguide.

Abstract:To enhance the electro-optic (EO) modulation efficiency and realize the impedance-matching, a polymer-on-silicon multimode interference (MMI) Mach-Zehnder interferometer (MZI) -based electro-optic (EO) switch is designed and optimized. Under the central operation wavelength of 1550 nm, the driving voltages of the designed switch are 0 and ±1.375 V, respectively, with a short active region length of 5 mm, and the characteristic impedance of the electrode is about 49.6 Ω. The manufacture tolerance is analyzed for instructing the device fabrication. The results show that to realize ideal switching function, high fabrication accuracy on the buffer thickness, core thickness, electrode width and MMI waveguide width is extremely required, and a small voltage drift of −0.03 0.05 V is also expected for reducing the crosstalk to less than −30 dB. The allowed 3 dB bandwidth is 60 nm, and within this spectrum range, the insertion loss and crosstalk are less than 6.71 dB and −30 dB, respectively.

Abstract:Many theoretical studies have been developed to study the spectral response of a fiber Bragg grating (FBG) under nonuniform strain distribution along the length of FBG in recent years. However, almost no experiments were designed to obtain the evolution of the spectrum when a FBG is subjected to non-uniform strain. In this paper, the spectral responses of a FBG under non-uniform strain distributions are given and a numerical simulation based on the Runge-Kutta method is introduced to investigate the responses of the FBG under some typical non-uniform transverse strain fields, including both linear strain gradient and quadratic strain field. Experiment is carried out by using loads applied at different locations near the FBG. Good agreements between experimental results and numerical simulations are obtained.

Abstract:A tunable microwave photonic bandpass filter with high mainlobe-to-sidelobe ratio (MSR) based on a phase modulator and a dispersive device is proposed. The multi-tap characteristics of the filter are realized by slicing a broadband source using a Mach-Zehnder interferometer (MZI) which results in a high MSR of 25 dB. The tunability of the filter is realized by an optical variable delay line (OVDL) in one arm of the MZI, which changes the wavelength spacing of the sliced broadband source and results in a tunable free spectrum range (FSR) of the filter. The central frequency of the bandpass filter is tunable from 10.7 GHz to 27 GHz by changing the wavelength spacing from 0.145 nm to 0.054 nm.

Abstract:In this paper, thermal characteristics of the high-power LED spot lamp are reported. The emphasis is placed upon optimizing design of the heat sink of LED spot lamp using the optimization module and the orthogonal-experiment method. Results demonstrate that the weight of the heat sink is decreased to 46.1% of that for the initial structure, and the influence of each factor on junction temperature and weight of the heat sink is acquired by range analysis. Finally, the influence of ambient temperature and natural convection coefficient on the LED maximum temperature is analyzed. The results and the optimizing methodology are of great importance to the thermal design of LED lamps.

Abstract:Based on the analysis of carrier dynamics in quantum dots (QDs), the numerical model of InAs/GaAs QD laser is developed by means of complete rate equations. The model includes four energy levels and among them three energy levels join in lasing. A simulation is conducted by MATLAB according to the rate equation model we obtain. The simulation results of PI characteristic, gain characteristic and intensity modulation response are reasonable. Also, the relations between the left facet reflectivity of laser cavity and threshold current as well as modulation bandwidth are studied. It is indicated that the left facet reflectivity increasing can result in reduced threshold current and improved modulation bandwidth, which is in accordance with experimental results. The internal mechanism of QD lasers is fully described with the rate equation model, which is helpful for QD lasers research.

Abstract:Blue top-emitting organic light-emitting devices (TEOLEDs) are demonstrated by employing Alq₃ as phase shift adjustment layer (PSAL) to increase the phase shift on reflection of the top electrode within a range, which also improves the light out-coupling. By adjusting the thickness of PSAL, the CIE _x,y of devices, which utilize 2, 7-Di-pyrenyl-9, 9-spiro-bifluorene (DPSF) as emitting layer, changes from (0.16, 0.50) to (0.18, 0.37). The maximum current efficiency of 7.1 cd/A is acquired under 4.5 V with an increasing luminance of 139 cd/m². Compared with adjusting the total thickness of organic layer, it is more beneficial for achieving blue TEOLEDs with high efficiency.

Abstract:The light propagation characteristics through the annular coupled-resonator cavity waveguides are systematically analyzed by the finite-difference time-domain (FDTD) method. It is found that this kind of waveguide has more minbands owing to the increasing of the cavity’s size, compared with the traditional line-typed coupled-resonator waveguide. The group velocity of light propagation can be reduced for a further degree when the adjacent annular cavities are interlaced in the perpendicular direction, and a group velocity about 0.00067c (c is the light speed in vacuum) can be obtained.

Abstract:Optical and electrical properties of composites formed by mixing porous silicon (PS) and poly (9, 9-diocty-2, 7-fluoreneco-4, 4′-butoxydiphenyl) (PFP) have been studied by Fourier transform-infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and photoluminescence (PL) spectroscopy. The optical spectra show that porous silicon is incorporated into the polymer without significant change in the polymer properties. The FT-IR spectroscopy has detected the existence of specific interactions, which may be attributed to non-conjugated alkoxy segment. By fitting the current-voltage (I-V) curve of PFP/PS structure with the modified standard equation, the n factor and I ₀ are determined.

Abstract:Single crystals of glycinium oxalate (GLO) are grown by solution growth technique. The Z scan technique is used to elucidate the third order nonlinearity in the material. The results indicate that the compound exhibits reverse saturable absorption (RSA) and self-defocusing performance. The second harmonic generation (SHG) efficiency of the crystal evaluated by Kurtz and Perry technique is compared with that of the standard KDP crystal. Attempt is made to correlate the SHG efficiency with the crystalline perfection in the material.

Abstract:Aiming at the unidirectional links coming from nodes with different transmitting power and the obstacle blocking in UV mesh wireless communication network and the traditional ant colony algorithm only supporting bidirectional links, a new ant colony based routing algorithm with unidirectional link in UV mesh communication wireless network is proposed. The simulation results show that the proposed algorithm can improve the overall network connectivity and the survivability by supporting the combination of unidirectional link and bidirectional link.

Abstract:All-optical analog-to-digital conversion (ADC) has been extensively researched to break through the inherently limited operating speed of electronic devices. In this paper, we use the photonic crystal fiber (PCF) for time-stretch (TS) analog-todigital (A/D) conversion system through generating low noise, linear chirp distribution and flat super-continuum (SC). Based on the radio frequency (RF) analog signal modulated to the linearly chirped super-continuum, the large-dispersion photonic crystal fiber is used for time-domain stretching.

Abstract:A new decoding scheme for product accumulate (PA) code over a space optical Poisson/pulse-position modulation (PPM) channel is investigated. In this scheme, the PPM and the accumulator of the PA code are taken as a single inner code, decoded with an iterative demodulating-decoding technique based on Bahl-Cocke-Jelinek-Raviv (BCJR) algorithm, rather than belief propagation (BP) algorithm in the original scheme. Simulation results show that this scheme provides much better bit error rate (BER) performance. At a BER of 10⁻⁵, the new scheme has a gain of 1.8 dB more than the original one. In addition, extrinsic information transfer (EXIT) charts are employed to analyze and compare the performance. The results indicate that the new scheme has not only better BER performance, but also lower error floor.

Abstract:A new modulation format in optical fiber communication system, the eight differential phase shift keying (8DPSK) of multi-phase modulation technology based on carrier-suppressed return-to-zero (CSRZ) is proposed in this paper. The formulae of CSRZ-8DPSK modem methods are derived theoretically and the methods are demonstrated. Spectra based on CSRZ and CSRZ-8DPSK modulation methods and their eye diagrams by simulation with MATLAB are obtained. The results show that the CSRZ-8DPSK modulation methods have narrower spectra with higher efficiency. The performance of eye diagrams is also much satisfactory after demodulation, suggesting some possible applications of the methods in the next generation of optical fiber communications.

Abstract:To estimate the shape of tapered fibers using tapering machines with movable large-zone furnaces, a new calculation method is proposed based on the discrete deducing method and the principle of the volume conservation of the fiber materials. This method can estimate the tapering results, i.e., the shape of the tapered fibers, based on arbitrary moving parameters of the large-zone furnace and the fiber holders. The theoretical estimated results agree with the experimental measuring shape of the tapered fibers quite well.

Abstract:The mixed solutions of brilliant blue and indigotine are prepared and the fluorescence spectra of them are experimentally measured. The serious overlapping spectra of brilliant blue and indigotine are solved by means of the first-derivative fluorescence spectrometry. The wavelet coefficients, obtained by compressing the spectral data using wavelet transformation (WT), are taken as inputs to establish the radial basis function neural network (RBFNN). The neural network model can realize simultaneous determination of brilliant blue and indigotine, and the mean relative errors of both compounds are 1.84% and 1.26%, respectively.