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

Abstract:On the start occasion of the New Year, 2011, we would like to extendour sincere appreciations and compliments to all readers, authors, 更多还原

Abstract:In order to reduce transmission loss of the optical waveguide in Mach-Zehnder (M-Z) electro-optical (EO) polymer modulator, the basic iterative formula of semi-vector finite-difference beam propagation method (FD-BPM) is obtained from the scalar wave equation. The transition waveguide is combined with S-type bend branch waveguide for the M-Z EO modulator in the branch waveguide. The effects of structure parameters such as ridge width, length of the branch waveguide and interferometer spacing on the transmission loss are systematically studied by using the semi-vector FD-BPM method. The structure is optimized as an S-sine bend branch waveguide, with rib width w=7 μm, length of branch waveguide L=1200 μm and interferometer spacing G=22 μm. The results show that the optimized structure can reduce transmission loss to 0.083 dB, which have a certain reference value to the design of optical waveguide in M-Z polymer modulator.

Abstract:The bending efficiencies of three-dimensional (3D) horizontal single- and multiple-slot waveguide microrings are analyzed using the effective index and modified transfer matrix methods. The effects of waveguide parameters, low-index material, high-index material, asymmetric structure, and asymmetric slots on the bending loss are studied. The results show that the bending efficiency can be enhanced by applying asymmetric structures and asymmetric slots. In addition, it is demonstrated that the bending loss increases with the increase of the number of slots. However, by using proper thicknesses for different high-index layers of the horizontal multiple-slot waveguide, it is possible that the horizontal multiple-slot waveguide can provide a lower bending loss than the single-slot one.

Abstract:Multi-e-phase-shifted fiber Bragg gratings and e-phase-shifted sampled fiber Bragg gratings (SFBGs) with dual wavelength filtering properties are compared. Results show that both of these gratings have the dual wavelength reflective spectra. However, the side lobe of the reflective spectrum of e-phase-shifted SFBGs is lower than that of multi-e-phaseshifted gratings. By adjusting the duty cycle in the range of 0.66 0.80, the filtering properties of e-phase-shifted SFBGs are optimized, and the side lobe suppression ratio (SLSR) is the lowest when the duty cycle is 0.75. The application of the e-phase-shifted SFBGs in the dual-wavelength laser is also demonstrated.

Abstract:A new method is presented to fabricate the triangular fiber Bragg grating (TFBG). The fabrication device is simple, only requires a single exposure and does not need to write complicated program. The transfer matrix method is used to design the fiber Bragg grating, and the grating resonant wavelength and the grating reflectivity can be controlled in order to achieve the triangular spectrum. With different fiber tilt angles, the available bandwidth of TFBG, the linearity and the oblique gradient are also different. In the experiment, the angles 1°, 1.5° and 2° are chosen. The results show that the best angle value is 1.5°, and the TFBG has a good linearity, greater gradient and wider available bandwidth.

Abstract:An amplitude modulator for the terahertz (THz) range is designed. The Drude model is adopted, in which the collision damping is independent of the carrier energy. The Si block with 808 nm laser is illustrated, and it will generate the photocarriers. The injected photo-carriers will change the conductivity and dielectric of the sample, which have direct relationship with the absorption coefficient of the THz wave, hence to control the characteristics of the THz wave in the sample. By changing the light intensity, due to the different photon-generated carrier concentrations, the single transmission of the THz wave in the silicon substrate is changed remarkably.

Abstract:The gas-sensitive film coated -phase-shifted long-period fiber grating (LPFG), consisting of two same long-period fiber gratings cascaded by a regular fiber with length of half of the grating period, is proposed for gas sensing. The sensitivity of the sensor is defined by the change rate of the transmission at specific wavelength with respect to the film refractive index. The qualitative and numerical analyses show that to get a high sensitivity, the optimal coupling strength of each long-period fiber grating is $ \sqrt 2 $ \sqrt 2 π/4. With this coupling strength, the longer the grating is, the higher sensitivity the sensor has. By choosing appropriate grating period, a high sensitivity for the film with a certain refractive index and thickness can be attained.

Abstract:A novel fiber Bragg grating (FBG) sensor with simultaneous sensing of displacement and temperature is presented. The FBG is affixed on the cantilever inclinedly. The midpoint of FBG exactly coincides with the zero strain layer of a rectangular beam. The vertical displacement can be measured by the broadened bandwidth of FBG as the bandwidth is insensitive to temperature, while the temperature can be measured by the center wavelength shift as the wavelength shift is insensitive to vertical displacement. With 0.1 nm spectral resolution of the analyzer, sensitivities of bandwidth-displacement and center wavelength-temperature are 0.48 nm/mm and 0.05 nm/°C, resolutions are 0.2 mm and 2.0 °C, and sensing ranges of displacement and temperature are up to 8.5 mm and 45°C respectively. Experimental results match theoretical analyses very well.

Abstract:Top-contact organic field effect transistors (OFETs) based on poly(3-hexylthiophene) (P3HT) with different concentrations in chloroform (CHCl₃) are fabricated. The output characteristics indicate that the P3HT concentration has significant influence on the OFET devices. The performance of the devices firstly is enhanced with increasing the P3HT concentration, and then decreases. The optimized devices with the P3HT concentration of 2 mg/mL show the best performance. The field0effect mobility is up to 1.4×10⁻² cm²/Vs, the threshold voltage (V _t) is as low as −20 V, and the current on/off ratio (I _on/off) is close to the order of 10⁴. The results suggest that the P3HT aggregation patterns induced by different concentrations can improve the performance of the OFETs.

Abstract:A novel polarization splitter based on photonic crystal fibers (PCFs) with three cores of high birefringence is proposed. The 45° linearly polarized light is launched into a core. After a coupling length (about 1500 μm), the xand y-polarized light beams are separated into different cores. When the light is launched into another core, the xand y-polarized light from different cores can be obtained and the degree of separation can be also adjusted. The polarization splitter is highly flexible and adjustable. The length of the polarization splitter is about 1500 μm which is just the coupling length. So it has appreciate significance of manufacturing mini-type photonic apparatus in integrated optics.

Abstract:A programmable transversal equalizer for electronic dispersion compensation (EDC) in optical fiber communication systems is developed. Based on the SiGe technology with a cut-off frequency of 80 GHz, the equalizer consists of 6 seriesparallel amplifiers as delay units and 7 Gilbert variable gain amplifiers as taps, which ensure that the equalizer can work at the bit rate of 10 Gb/s. With different tap gains, the forward voltage gain of the transversal equalizer varies, which demonstrates that the equalizer has various filtering characteristics such as low pass filtering, band pass filtering, band reject filtering, and notch filtering, so it can effectively simulate the inverse transfer function of dispersive channels in optical communications, and can be used for compensating the inter-symbol interference and other nonlinear problems caused by dispersion. The equalizer (including pads) occupies an area of 0.40 mm×1.08 mm, and its total power dissipation is 400 mW with 3.3 V power supply.

Abstract:Based on the rapid genetic algorithm (RGA), the band gap structures of square lattices with square scatters are optimized. In the optimizing process, gene codes are used to express square scatters and the fitting function adopts the relative values of the largest absolute photonic band gaps (PBGs). By changing the value of filling factor, three cell forms with large photonic band gaps are obtained. In addition, the comparison between the rapid genetic algorithm and the general genetic algorithm (GGA) is analyzed.

Abstract:Al and F co-doped ZnO (ZnO:(Al, F)) thin films on glass substrates are prepared by the RF magnetron sputtering with different F doping contents. The structural, electrical and optical properties of the deposited films are sensitive to the F doping content. The X-ray analysis shows that the films are c-axis orientated along the (002) plane with the grain size ranging from 9 nm to 13 nm. Micrographs obtained by the scanning electron microscope (SEM) show a uniform surface. The best films obtained have a resistivity of 2.16×10⁻³ù cm, while the high optical transmission is 92.0% at the F content of 2.46 wt.%.

Abstract:ZnSe multipod-based structures, including tetrapod-like microrods, long microwires, and short nanorods, are selectively prepared by atmospheric pressure thermal evaporation of ZnSe nanoparticles without using any catalyst. The morphologies could be well controlled by simply adjusting the deposition position. The phase structures, morphologies, and optical properties of the products are investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (TEM), and photoluminescence (PL) spectroscopy. A vapor-liquid mechanism is proposed for the formation of ZnSe multipod-based structures. The presented route is expected to be applied to the synthesis of other II-VI groups or other group’s semiconductor materials with controllable morphologies.

Abstract:The adaptive polarization mode dispersion (PMD) compensation in high-speed transmission system has become more and more necessary for the link PMD causing strong signal distortions. A dynamic adaptive PMD compensator in 40 Gb/s polar-multiplex differential quadrature phase shift keying (PM-DQPSK) system is reported. Experimental results show that the PMD compensator can track the average polarization state variation at 65 rad/s without any lost of the optimum tracking. The 1st-order PMD compensation is demonstrated experimentally, and the compensator can increase the maximal tolerable PMD value by 26 ps from 17 ps to 43 ps in an optical transmission system.

Abstract:A new kind of single-polarization photonic crystal fiber (PCF) is proposed. Two kinds of multi-component glasses and the air are selected as working materials. Through using the full vector finite element method (FEM) and the perfectly matched layers (PML), the polarization-maintaining characteristic and the confinement loss of the fiber are analyzed, respectively. In addition, the single-polarization region of the fiber around 1.55 ìm is discussed. Numerical simulations show that the fiber maintains single-polarization operation within the wavelength range of 1.421 1.696 ìm. The birefringence can reach 6.988×10⁻³, and the confinement loss is as low as 0.012 dB/m when 7 layers of ring holes are arranged in the cladding at ?=1.55 ìm.

Abstract:A novel technique for calibrating crucial parameters of chassis components is proposed, which utilizes the machine vision metrology to measure 3D coordinates of the center of a component’s hole for assembling in the 3D world coordinate system. In the measurement, encoding marks with special patterns will be assembled on the chassis component associated with cross drone and staff gauge located near the chassis. The geometry and coordinates of the cross drone consist of two planes orthogonal to each other and the staff gauge is in 3D space with high precision. A few images are taken by a high-resolution camera in different orientations and perspectives. The 3D coordinates of 5 key points on the encoding marks will be calculated by the machine vision technique and those of the center of the holes to be calibrated will be calculated by the deduced algorithm in this paper. Experimental results show that the algorithm and the technique can satisfy the precision requirement when the components are assembled, and the average measurement precision provided by the algorithm is 0.0174 mm.

Abstract:The laser induced breakdown spectroscopy (LIBS) is an element analysis technique with the advantages of real time detection, simultaneous multi-element identification, and in-situ and stand-off capacities. To evaluate its potential of ocean applications, in this paper, the time resolved laser-induced breakdown spectroscopy for calcium concentration detection in water is investigated. With the optimum experimental parameters, the plasma emission lifetime is determined to be about 500 ns with 532 nm laser excitation, and 1000 ns with 1064 nm laser excitation. The lowest detection concentration of 50 ppm is achieved for calcium detection in CaCl₂ water solution using the 532 nm LIBS. Even better detection sensitivity is achieved using the 1064 nm LIBS, and the resulted lowest detection concentration of calcium is 25 ppm. The results suggest that it is feasible to develop LIBS as an on-line sensor for metal element monitoring in the sea.

Abstract:During the 3D shape measurement, there are noises in the images that are obtained by the capture system. The traditional method, Fourier transform profilometry (FTP) technique, improves the accuracy only by the filtering method in the frequency domain. In this paper, the curve fitting method is used for the light field distribution calculation before the filtering process applied in the frequency domain by choosing a suitable filter window, and then the higher quality of the basic frequency component signal is got. This method can avoid the frequency overlapping caused by the noise, so the improvement of the measuring accuracy of FTP is realized.

Abstract:Compared with the Arnold transform, the image scrambling method based on bit shuffling pixels is much more secure, and has higher efficiency and speed. However, the key space of this bit shuffling pixels based method is too small to resist exhaustive search attack. Therefore, an improved method based on chaos is proposed in this paper. The security of the improved scheme is enhanced by increasing the number of the keys. Theoretical analysis and experimental results show that the proposed method is effective and has higher security.

Abstract:Within the framework of the correlation theory of electromagnetic laser beams, the far field cross-spectral density matrix of the light radiated from an electromagnetic Hermite-Gaussian model source is derived. By utilizing the convergence property of Hermite polynomials, the conditions of the matrices for the source to generate an electromagnetic Hermite-Gaussian beam are obtained. Furthermore, in order to generate a scalar Hermite-Gaussian model beam, it is required that the source should be locally rather coherent in the spatial domain.