Waveguiding properties of silica nanowires in various environments are studied by solving the eigenvalue equations of a circular cross-section waveguide numerically in cylindrical coordinates. The single-mode condition, propagation constants, poynting vector and power distribution inside and outside silica nanowire are calculated. The results show that silica nanowires in water, compared with silica nanowires in air, have higher fraction of the evanescent fields. Due to the sensitivity to surrounding environment, silica nanowires are very suitable for sensing elements, which can be used to implement a single-mode fiber optic evanescent wave sensing element of highly sensitive and accurate measurement.
The transmission spectrum of the coated phase-shifted long-period fiber gratings (LPFGs) with single and multiple phase shifts is analyzed by the coupled-mode theory and the transfer matrix method, and the influences of the film parameters on the spectral characteristics are also studied. It is shown that these parameters will affect the LPFG filtering characteristics. The loss peak of transmission spectrum decreases with the increase of film thickness, and the peak position shifts with the film refractive index. Compared with the non-coated phase-shifted LPFG, the coated one has the similar desirable filtering characteristics, and it has a flexible ability to adjust the transmission properties.
Synchronization control is a kernel technique of the laser range-gated (LRG) imaging system which controls the synchronization of the pulsed laser and the ICCD camera directly. It can achieve range gating effectively and improve the resolution of image precisely. Conventional control circuits which are composed of discrete components have a poor performance of anti-interference, and the transmitting signal has a bad delay which affects the conventional circuit’s precision and stabilization seriously. To solve these problems, a range-gated synchronization control circuit is designed. This circuit, which takes the advantages of FPGA’s high compact and flexibility, uses the phase-locking-loop (PLL) to multiply the global clock frequency. This design improves the precision and stabilization greatly, makes the precision up to a nanosecond level and provides a real-time selection of the values of pulse width and delays. Experiments results indicate that this circuit has a high precise and stable range-gated pulse.
All-optical switching has been theoretically analyzed in the 3,3′-diethyl-2,2′-thiatricarbocyanine iodide (DTTCI) carbocyanine dye that exhibits large excited-state absorption to achieve high contrast and fast switching. Switching has been analyzed both ns and ps pump pulse widths. It is shown that there is an optimum value of concentration for given peak pump intensity at which maximum modulation can be achieved. We can get 93.84% modulation of transmission of a CW probe laser beam at 532 nm at peak pumping intensity of 500 kW/cm2 at 763 nm, with Δt=1 ns and concentration of 80 μM in alcohol, resulting in switch-off and on time of 2 ns and 8 ns, respectively. The results have been also used to design all-optical NOT and the universal NOR and NAND logic gates with multiple pump laser pulses.
To overcome the limitation of low image signal swing range and long reset time in four transistor CMOS active pixel image sensor, a charge pump circuit is presented to improve the pixel reset performance. The charge pump circuit consists of two stage switch capacitor serial voltage doubler. Cross-coupled MOSFET switch structure with well close and open performance is used in the second stage of the charge pump. The pixel reset transistor with gate voltage driven by output of the pump works in linear region, which can accelerate reset process and complete reset is achieved. The simulation results show that output of the charge pump is enhanced from 1.2 to 4.2 V with voltage ripple lower than 6 mV. The pixel reset time is reduced to 1.14 ns in dark. Image smear due to non-completely reset is eliminated and the image signal swing range is enlarged. The charge pump is successfully embedded in a CMOS image sensor chip with 0.3 × 106 pixels.
A new compact optical Fano filter suitable for biological sensing is proposed, which patterns photon crystal in single crystalline silicon nanomembranes (SiNMs) and transferring onto transparent glass substrates. The effects of air hole size and silicon thickness on the transmission characteristics of new filter are numerically investigated by using three-dimensional finite-difference time-domain (FDTD) technique, the spectral response is also studied by back-filling bio-liquid. The results show that the dip wavelength will shift toward longer wavelength by either reducing air hole radius or filling bioliquid. The number of dips will increase with the increase of silicon thickness. The size of proposed filter can be less than 1 mm2.
A novel LD-pumped single-frequency micro-chip green laser is presented. By using the combination of short cavity and Loyt filter formed by Rochon prism and KTP crystal, a stable single frequency green laser is obtained with 60 mW output at 500 mW LD-pump. The optical-to-optical conversion efficiency is about 12%. The optical contact between components of the laser is adopted. This laser has the advantages of a compact structure and a low cost.
The traditional eye sensitivity function based on photopic vision is not applicable in the mesopic vision state. The mesopic vision is studied by using the photopic and scotopic vision state sensitivity functions. And the model which links the mesopic sensitivity with the photopic and scotopic states is built. Based on the model, the luminous efficacy of mesopic vision is calculated and applied to the spectrum distribution of LED light sources. The results show that the luminous efficacy of a commercial YAG phosphor converted white LED is up to 172.7 lm/W at mesopic vision, which is 67.2% higher than that of photopic vision state. We also conclude that the optimal spectral power distribution of the LED will greatly increase the mesopic luminous efficacy.
A magneto-photonic crystal (MPC) is defined as a periodic light-guided structure involving magnetic materials or a photonic crystal with some magnetic-material defects. The transfer matrices of guided optical waves (GOWs) propagating respectively in magneto-optical and non-magnetic dielectric layers are deduced according to the coupled-mode theory. The transmission spectra of GOWs in one-dimensional magneto-photonic crystals (1D-MPC) are investigated by the transfer matrix method. It is shown that the two sharp peaks in the 1D-MPC’s transmission spectra can be used for high-resolution magnetic field sensing; and a comb filter with six channels can be achieved by optimizing the 1D-MPC structure and controlling the external magnetic field.
The diamond films adherent to Si substrate are deposited with the microwave plasma CVD (MPCVD) at microwave powers of 6000 W and 4000 W from 6 h to 10 h, respectively, the internal stresses of the films are measured by XRD. Spectral peak shift and widening are applied to calculate the magnitudes of macro and micro stresses. The results show that the macro stress is tensile. The internal stress can be controlled by the microwave power. With the microwave power increasing, the intrinsic and macro stresses decrease, and the micro stress increases significantly. Also, it can be found that the macro and micro stresses increase with deposited time when the other conditions are the same.
The wavelength assignment with multiple multicast requests in fixed routing WDM network is studied. A new multicast dynamic wavelength assignment algorithm is presented based on matching degree. First, the wavelength matching degree between available wavelengths and multicast routing trees is introduced into the algorithm. Then, the wavelength assignment is translated into the maximum weight matching in bipartite graph, and this matching problem is solved by using an extended Kuhn-Munkres algorithm. The simulation results prove that the overall optimal wavelength assignment scheme is obtained in polynomial time. At the same time, the proposed algorithm can reduce the connecting blocking probability and improve the system resource utilization.
A new method is proposed to generate microwave and millimeter-wave by using polarization scrambler and polarization maintaining fiber (PMF), which is based on the coupling and the interaction between the two polarizations of the initial non-chirp Gaussian optical pulse in PMF. The expressions of the microwave and millimeter-wave are derived by couplemode theory. Moreover, the feasibility is analyzed simulatedly. At last, 0−120 GHz microwave and millimeter-wave can be produced by adjusting system parameter or input pulse duration. The project is of great simplicity, stability and high export efficiency.
This paper proposes an effective method of fault location based on a binary tree for optical burst switching (OBS) network. To minimize the monitoring cost, we divide the network into several monitor domains by introducing monitoring-cycle algorithms. In order to generate an exclusive code, we modify the monitoring cycle algorithm when two nodes have the same code. Through the binary tree algorithm, a pre-computation of faults in the OBS network can be achieved. When a fault happens, we can locate it immediately and accurately. Examples have proved that the algorithm has general applicability.
A new multiple-taps and flat microwave photonic filter, which is composed of fiber Bragg grating, M-Z modulator and erbium-doped fiber, is put forward. The flat band-pass or flat band-stop response can be realized by adjusting the coupler’s factor and the reflectivity of the fiber Bragg grating or the gain of the erbium-doped fiber. The free spectral range of the filter can be tuned by controlling the length of the erbium-doped fiber. The potential and feasibility of the proposed filtering structures have been demonstrated by simulation.
This paper presents a large field phase-shifting interference microscope for micro-surface topography measurement. A PZT is used as the Z-directional phase shifter. The interference microscope is the combination of the infinity tube microscope with the Mirau two-beam interferometer. Two-dimensional precision motorized stage is aligned as the scanning system in the X- and Y-direction to extend the test surface measurement range to 12.5 mm × 12.5 mm. The minimum displacement is 0.039 m and the overlapped proportion is 0.22. A fast stitching algorithm is proposed based on grid matching. According to the reflectivity of the core and the ferrule, the plate with the transmission/reflectivity ratio of 70/30 is selected to balance the interference intensity. The instrument is proved to be valid by actual measurement of the end surface of an optical fiber connector.
To detect the laser doppler signal, the unknown signal is tracked by the known signal using the concept of topological contravariance. The unknown topological space U and known space M are founded, and then the unknown signal’s transformation is tracked dynamically according to this mapping relationship between the two spaces. The system equation is obtained by gradient-descent method, and the conditions of stability are given by Poincaré mapping. The proposed method is applied to measure the in-plane displacement signal of the solid 50 m away using laser doppler, signal. The result proves that the method can detect laser doppler. signal accurately, its relative error is less than 0.7%.
This paper constructs a simulation system of near-field laser imaging for 3D grid model of target, provides some methods for the key problems, such as the modeling of target and laser transceiver, the calculation of laser echo power, the imaging algorithms and so on. A target image library is established by a new imaging method in any rendezvous conditions. The four real-time recognition algorithms which are efficient and suitable for hardware implementation are presented at the conditions of the image incompleteness, intensive noise and arbitrary attitude of target. The experimental results show that all the four algorithms can independently recognize the target effectively and a better recognition effect is obtained by the integration of four algorithms.
This paper proposes a lane detection algorithm based on multi-structure element model of morphological. The innovative point of the algorithm lies in the facts that the flexible structure has the multi-structure elements that lane model features have, and that the algorithm adopts the morphological filtering principle to extract the pixels in the image, which is similar to the lane model. In the algorithm, the interested area is extracted by a model of trapezium from original image, which is detected by the operator of Canny, and the lanes are extracted by the structure elements, which have similar characteristics to that of lane model. Several lines are detected by Hough transformation, then the traffic lanes are reconstructed. Experiments show that this algorithm is simple and robust, and can efficiently detect the lane mask accurately and quickly.
Under the framework of support vector machines, this paper proposes a new kernel method based on neighbor bands mutual information for hyperspectral datum classification. This algorithm assigns weights to different bands in the kernel function according to the amount of useful information that they contain, which makes the band with more useful information play more important role in the classification. Our research has shown that the band with greater mutual information between neighbor bands contains more useful information, and hence we use the mutual information of each band and its neighbor bands as the weights of the proposed kernel method. The experimental results show that for the support vector machines based on polynomial and radial basis function, after introducing the proposed kernel function, the average accuracy is increased more than 1.2% without using any reference map or increasing much more computational time.
An audio recovering method of spread-spectrum hidden information is proposed based on genetic algorithm. In this method the embedded sequence length is confirmed firstly, then the best estimated sequence with the confirmed length is got by genetic algorithm, finally the confidential message hidden in stego-audio can be recovered. Using this approach, the hidden information can be recovered without any information from the transmitter. The presented method has been implemented on PC, and the experimental results show that the average recovering correct rate is higher than 90%.
The golden films with various subwavelength hole arrays on the film surface are designed and fabricated on glass substrate by electron beam lithograply (EBL), focused ion beam (FIB), and reactive ion etching (RIE), respectively. The influences of the hole array symmetry and the hole shape on the light-enhanced transmission through the films are observed and simulated. The experimental results show that when the array lattice constant and the hole diameter are the same in the different array structures which are 1 m and 350 nm respectively, the square hole arrays exhibit two transmission peaks at 1170 nm and 1580 nm with the transmissivities of 3% and 6%, respectively, while the hexagonal hole arrays exhibit an enhanced peak of 14% at 1340 nm; when the lattice constant and the duty cycle are the same for different array stucture, the transmission peaks are different for different hole shapes, which are at 763 nm with transmissivity of 12% for rectangular holes and at 703 nm with the one of 9%, respectively. The numerical simulation results by using the transfer matrix method (TMM) are consistent with the observed results.