Showing papers in "Chinese Optics Letters in 2005"

Efficient stable simultaneous CW dual-wavelength diode-end-pumped Nd:YAG laser operating at 1.319 and 1.338 μm

Abstract: An efficient, stable diode-end-pumped simultaneous continuous-wave (CW) dual-wavelength laser operating at 1.319 and 1.338 ?m in a Nd:YAG crystal has been demonstrated. A total output power of 6.3 W is achieved at an absorbed pump power of 15 W, with a slope efficiency of 43.5%. The instability of output power is less than 1%. With a type II critical phase-matched KTP crystal inserted into the cavity as frequency doubler, a maximum outputpower of 200 mW in red region is acquired. In addition, a six-wavelength laser operation at 1.319 ?m, 1.338 ?m, 1.356 ?m, 659.5 nm, 669 nm, and 678 nm is observed.

Bright and dark optical solitons in the nonlinear Schrodinger equation with fourth-order dispersion and cubic-quintic nonlinearity

Abstract: By the use of an auxiliary equation, we find bright and dark optical soliton and other soliton solutions for the higher-order nonlinear Schrodinger equation (NLSE) with fourth-order dispersion (FOD), cubic-quintic terms, self-steepening, and nonlinear dispersive terms. Moreover, we give the formation condition of the bright and dark solitons for this higher-order NLSE.

Partially coherent vortex beams propagation in a turbulent atmosphere

Abstract: Based on the Rytov approximation and the cross-spectral density approximation for the mutual coherence function of the partially coherent field, the propagation properties of the partially coherent beams with optical vortices in turbulent atmosphere are discussed. The average intensity and the mutual coherence function of the partially coherent vortex beams propagation in weak turbulent atmosphere are obtained. It is shown that the vortex structure of the average cross-spectral density of partially coherent beams has the same helicoidally shape as that of the phase of the fully coherent Laguerre-Gauss beams in free space and the relative intensity of the beam is degraded by optical vortex.

Implementation of tristate logic based all optical flip-flop with nonlinear material

Abstract: The advantages of multivalued logic in optical parallel computation need no introduction. There are lots of proposals, already reported, where tristate, quarternary state logic operations can be performed with optics. Here we report a new approach to implement tristate logic based all optical flip-flop using optical nonlinear material. The concept and the principle of operation of this type of flip-flop are different from that of the conventional binary one.

Space optical remote sensor image motion velocity vector computational modeling, error budget and synthesis

Abstract: For space optical remote sensor (SORS) with either film or time delay and integrate charge coupled device (TDI-CCD) imaging, in order to achieve higher resolution it requires more accurate real-time image motion compensation. This primarily depends on real-time computation of the image motion velocity vector (IMVV) and error budget and synthesis on related parameters. An effective modeling scheme is introduced and the derivation of IMVV equation, error budget and synthesis by Monte-Carlo method are presented in detail. This total solution was applied to SORS system test on orbit and has been confirmed to be very accurate based on the resolution, transfer function at Nyquist frequency, signal-to-noise ratio and average gray scale of the captured images.

Design and parametric amplification analysis of dispersion-flat photonic crystal fibers

Abstract: We present a modified method to design photonic crystal fibers (PCFs) with flattened dispersion characteristic. Using this modified PCF we design a broadband fiber optical parametric amplifier (FOPA), which provides a gain of 8 dB with 1.5-dB uniformity over a 260-nm bandwidth. Both the simulation results of total dispersion of PCF and the gain spectrum of FOPA are demonstrated.

Light extinction method for solubility measurement

Abstract: A novel measurement method for chemical solubility determination is brought forward, in which the advantages of two kinds of traditional methods are united. The results show that the concentration of unsolved particles suspending in the solution can be determined by measuring I/I0 (ratio of the transmission intensity to the incident intensity) of the laser beam permeating through the solution according to Lamben-Beer law. The biggest relative deviation for the solubility data determined is less than 1.5% for the sparingly soluble substances and 0.3% for the opulently soluble substances. By comparison of the experimental solubility data with previous data, the light extinction method is demonstrated to be stable and reliable.

Particle filter based visual tracking with multi-cue adaptive fusion

Abstract: To improve the robustness of visual tracking in complex environments such as: cluttered backgrounds, partial occlusions, similar distraction and pose variations, a novel tracking method based on adaptive fusion and particle filter is proposed in this paper. In this method, the image color and shape cues are adaptively fused to represent the target observation; fuzzy logic is applied to dynamically adjust each cue weight according to its associated reliability in the past frame; particle filter is adopted to deal with non-linear and non-Gaussian problems in visual tracking. The method is demonstrated to be robust to illumination changes, pose variations, partial occlusions, cluttered backgrounds and camera motion for a test image sequence.

Determination of the effective refractive index of porous silicon/polymer composite films

Abstract: The equation for calculating the effective refractive index of porous silicon inserted polymer was obtained by three-component Bruggeman effective medium model. The dependence of the effective refractive index of porous silicon/polymer composite films on the polymer fraction with various initial porosity was given theorically and experimentally respectively. The porous silicon and polymer polymethylmetacrylate based dispersive red one (PMMA/DR1) composite films were fabricated in our experiments. It is found that the measured effective refractive index of porous silicon inserted polymer was slightly lower than the calculated result because of the oxidization of porous silicon. The effective refractive index of oxidized porous silicon inserted polymer also was analyzed by four-component medium system.

Diode end-pumped 1123-nm Nd:YAG laser with 2.6-W output power

Abstract: We present a compact and high output power diode end-pumped Nd:YAG laser which operates at the wavelength of 1123 nm. Continuous wave (CW) laser output of 2.6 W was achieved at the incident pump power of 15.9 W, indicating an overall optical-optical conversion efficiency of 16.4%, and the slope efficiency was 18%.

Color fusion of SAR and FLIR images using a natural color transfer technique

Abstract: Fusion of synthetic aperture radar (SAR) and forward looking infrared (FLIR) images is an important subject for aerospace and sensor surveillance. This paper presents a scheme to achieve a natural color image based on the contours feature of SAR and the target region feature of FLIR so that the overall scene recognition and situational awareness can be improved. The SAR and FLIR images are first decomposed into steerable pyramids, and the contour maps in the SAR image and the region maps in the FLIR image are calculated. The contour and region features are fused at each level of the steerable pyramids. A color image is then formed by transferring daytime color to the monochromic image by using the natural color transfer technique. Experimental results show that the proposed method is effective in providing a color fusion of SAR and FLIR images.

Full distributed fiber optical sensor for intrusion detection in application to buried pipelines

Abstract: Based on the microbend effect of optical fiber, a distributed sensor for real-time continuous monitoring of intrusion in application to buried pipelines is proposed. The sensing element is a long cable with a special structure made up of an elastic polymer wire, an optical fiber, and a metal wire. The damage point is located with an embedded optical time domain reflectometry (OTDR) instrument. The intrusion types can be indicated by the amplitude of output voltage. Experimental results show that the detection system can alarm adequately under abnormal load and can locate the intrusion point within 22.4 m for distance of 3.023 km.

Transfer color to night vision images

Abstract: Natural color appearance is the key problem of color night vision field. In this paper, the color mood of daytime color image is transferred to the monochromic night vision image. This method gives the night image a natural color appearance. For each pixel in the night vision image, the best matching pixel in the color image is found based on texture similarity measure. Entropy, energy, contrast, homogeneity, and correlation features based on co-occurrence matrix are combined as texture similarity measure to find the corresponding pixels between the two images. We use a genetic algorithm (GA) to find the optimistic weighting factors assigned to the five different features. GA is also employed in searching the matching pixels to make the color transfer algorithm faster. When the best matching pixel in the color image is found, the chromaticity values are transferred to the corresponding pixel of the night vision image. The experiment results demonstrate the efficiency of this natural color transfer technique.

An airborne pushbroom hyperspectral imager with wide field of view

Abstract: An airborne pushbroom hyperspectral imager (APHI) with wide field (42 deg. field of view) is presented. It is composed of two 22 deg. field of view (FOV) imagers and can provide 1304 pixels in spatial dimension, 124 bands in spectral dimension in one frame. APHI has a bandwidth ranging from 400 to 900 nm. The spectral resolution is 5 nm and the spatial resolution is 0.6 m at 1000-m height. The implementation of this system is helpful to overcome the restriction of FOV in pushbroom hyperspectral imaging in a more feasible way. The electronic and optical designs are also introduced in detail.

High resolution mosaic image of capillaries in human retina by adaptive optics

Abstract: Adaptive optics (AO) has been proved as a powerful means for high resolution imaging of human retina. Because of the pixel number of charge-coupled device (CCD) camera, the field of view is limited to 1 deg.. In order to have image of capillaries around vivo human fovea, we use mosaic method to obtain high resolution image in area of 6deg.*6deg.. Detailed structures of capillaries around fovea with resolution of 2.3 ?m are clearly shown. Comparison shows that this method has a much higher resolution than current clinic retina imaging methods.

5.3-W Nd:YVO4 passively mode-locked laser by a novel semiconductor saturable absorber mirror

Abstract: We report a diode end-pumped continuous wave (CW) passively mode-locked Nd:YVO4 laser with a homemade semiconductor saturable absorber mirror (SESAM). The maximum average output power is 5.3 W at the incident pump power of 17 W, which corresponds to an optical-optical conversion efficiency of 31.2% and slope efficiency of 34.7%. The corresponding optical spectrum has a 0.2-nm full width at half maximum (FWHM), and the pulse repetition rate is 83 MHz.

Numerical simulation of the ultrasonic waves generated by ring-shaped laser illumination

Abstract: The improvement of the generation efficiency has attracted much attention, confronted with the little amplitude of acoustic wave generated by pulsed laser in the thermoelastic regime. This paper constructed the finite element model to simulate ultrasonic waves generated by the ring-shaped laser source with the 8 mm inner radii. The numerical results demonstrate that strong focusing exists at the center axis of ring as the result of constructive interference of the waves generated by different parts of the source. Furthermore, the bulk wave includes compression, shear peak amplitudes and the surface acoustic wave magnitude drops quickly when the receiver position is away from the epicenter. Numerical simulations indicated that the low acoustic amplitudes in laser acoustics can be relieved somewhat by taking advantage of constructive interference between waves generated by different parts of an acoustic source, giving locally higher amplitude.

Biophotonics of molecular oxygen: activation efficiencies upon direct and photosensitized excitation

Abstract: With a goal of mimicking the mechanisms of the biological effect of low intensity laser radiation, we have measured the rates of oxygenation of chemical traps of singlet oxygen in air-saturated organic solvents and deuterium oxide upon direct (1270 nm) excitation of the 1Δg -> 3Σ g- transition in oxygen molecules. The data were used for estimation of the molar absorption coefficients of oxygen corresponding to this transition. The obtained values were compared with the radiative lifetimes of singlet oxygen calculated from the quantum yields of singlet oxygen phosphorescence. The quantum efficiencies (the ratios of the photoreaction rates to the irradiation intensities) of oxygenation were compared upon porphyrin-photosensitized and direct oxygen excitation.

Stable single frequency Er-doped all-fiber ring laser with fiber Bragg grating Fabry-Perot filter

Abstract: Using a fiber Bragg grating (FBG) and a Fabry-Perot cavity composed of two fiber Bragg gratings (FBGFP) as its frequency-selective components, a type of single frequency all-fiber ring laser permits oscillation only on one longitudinal mode of the main cavity without modehopping while the cavity length can be up to tens of meters The salient feature is due to the single narrowband resonance of the FBGFP filter Such a fiber ring laser is achieved experimentally, and the laser mode is limited inside the single resonance of the FBGFP

Effects of parameters on the stationary state and self-trapping of three coupled Bose-Einstein condensate solitons

Abstract: The stability of three coupled Bose-Einstein condensate (BEC) solitons is investigated by the variational approach in two conventional time-independent trapping potentials The effects of parameters of the potentials and the initial conditions of the BEC soliton system on the stationary state and self-trapping are discussed It is found that the trapping potentials play an important role in the stability of the system and change the characteristics of the system, and there are different critical potential amplitude values corresponding to different trapping potentials and initial conditions of the BEC soliton system

Time-resolved terahertz spectroscopy of explosive materials

Abstract: We studied terahertz spectra of hexanitrohexaazaisowurtzitane ('varepsilon'-HNIW and 'gamma'-HNIW), a kind of explosive materials, using terahertz time-domain spectroscopy (THz-TDS) in the 0.2-2.5 THz region. The experimental results show that explosive samples with different conformations have different intermolecular or phonon bands. For 'varepsilon'-HNIW, the observed absorption peaks were located at 0.99, 1.32, 1.43, and 2.08 THz; for 'gamma'-HNIW, the absorption peaks were observed at 1.05, 1.52, and 1.90 THz. The frequency dependent refraction index and absorption coefficients of two samples were also extracted.

Optical coherent detection Brillouin distributed optical fiber sensor based on orthogonal polarization diversity reception

Abstract: In Brillouin distributed optical fiber sensor, using optical coherent detection to detect Brillouin scattering optical signal is a good method, but there exists the polarization correlated detection problem. A novel detecting scheme is presented and demonstrated experimentally, which adopts orthogonal polarization diversity reception to resolve the polarization correlated detection problem. A laser is used as pump and reference light sources, a microwave electric-optical modulator (EOM) is adopted to produce frequency shift reference light, a polarization controller is used to control the polarization of the reference light which is changed into two orthogonal polarization for two adjacent acquisition periods. The Brillouin scattering light is coherently detected with the reference light, and the Brillouin scattering optical signal is taken out based on Brillouin frequency shift. After electronic processing, better Brillouin distributed sensing signal is obtained. A 25-km Brillouin distributed optical fiber sensor is achieved.

Finite element analysis on stress-induced birefringence of polarization-maintaining optical fiber

Abstract: Influence of thermal-mechanical properties on the features of the panda polarization-maintaining optical fiber (PMF) in fabrication process is studied in detail by finite element method (FEM). The stress birefringence is 2.13443*10^(-4) obtained by the static analysis and 2.1269*10^(-4) by dynamic analysis. The difference in simulation by two methods is around 0.4%. The non-uniformity of stress birefringence in the fiber core is about 1.6%. Predicted results demonstrate that effect of the thermal conductive parameter on fiber thermal stress dominates. The high and uniform stress birefringence in the fiber core is obtained by appropriately selecting suitable stress region area and position.

Nanostructure and thermal-optical properties of vanadium dioxide thin films

Abstract: A novel nanopolycrystalline structure of vanadium dioxide thin films is deposited on silicon or fused silica substrates by reactive ion sputtering and followed by an annealing. The characteristic analysis shows that the films have a columnar nanostructure with an average grain of 8 nm. The resistivities as a function of ambient temperatures tested by four-point probes for as-deposited films present that the transition temperature for nanostructure of vanadium dioxide films is near 35 Celsius degree which lowers about 33 Celsius degree in comparison with the transition temperature at 68 Celsius degree in its microstructure.

Effect of oxygen flow rate on the properties of SiOx films deposited by reactive magnetron sputtering

Abstract: SiOx (x=0--2) films were deposited on BK-7 substrates by a low frequency reactive magnetron sputtering system with the oxygen flow rate (OFR) changing from 0 to 30 sccm. The samples were characterized by atomic force microscopy, spectrophotometer, and X-ray photoelectron spectroscopy. The extinction coefficient and refractive index decrease, while the optical transmittance increases with the increase of OFR from 0 to 17 sccm. The root mean square surface roughness has a maximum at 10 sccm OFR. The highest deposition rate is at 15 sccm OFR. Our results show that the films deposited at 20 sccm OFR are stoichiometric silica with relatively high deposition rate, low extinction coefficient, and low surface roughness. Therefore, a precise control of OFR is very important to obtain high quality films for optical applications.

A wideband sensitive holographic photopolymer

Abstract: A novel wideband sensitive dry holographic photopolymer sensitized by rose bengal (RB) and methylene blue (MB) is fabricated, the holographic storage characteristics of which are investigated under different exposure wavelengths. The result shows that the sensitive spectral band exceeds 200 nm in visible light range, the maximum diffraction efficiency under different exposure wavelengths is more than 40% and decreases with the decrease of exposure wavelength, the exposure sensitivity is not change with the exposure wavelength. This photopolymer is appropriate for wavelength multiplexing or multi-wavelength recording in digital holographic storage.

Effect of vacuum-induced coherence on lasing without inversion in an equispaced three-level ladder system

Abstract: The effects of vacuum-induced coherence (VIC) on the properties of the absorption and gain of the probe field in an equispaced three-level ladder atomic system are investigated. It is found that lasing without inversion (LWI) is remarkably enhanced due to the effect of VIC in the case of the small incoherent pump rate.

Characteristics of an add-drop filter composed of a Mach-Zehnder interferometer and double ring resonators

Abstract: A planar lightwave circuit (PLC) add-drop filter is proposed and analyzed, which consists of a symmetric Mach-Zehnder interferometer (MZI) combined with double microring resonators. A critical coupling condition is derived for a better box-like drop spectrum. Comparisons of its characteristics with other schemes, such as a MZI with a single ring resonator, arepresented, and some of the issues about device design and fabrication are also discussed.

Effect of higher order non-linearity in frequency variation of self-phase modulation in optical fiber communication

Abstract: In optical soliton propagation through a single mode optical fiber, it is established that self-phase modulation is maintained by the third order non-linearity of the silica-based glass material of the fiber. In this paper we show that the fifth order non-linearity has also some contribution in frequency variation of self-phase modulation.

Optical bistability in tunable fiber laser using fiber Mach-Zehnder interferometer

Abstract: In this letter, a novel mechanism of hybrid optical bistability is proposed by using nonlinear mechanism in the frequency domain. This device is based on electro-optical feedback through the fiber Bragg grating on piezoelectric transducer (PZT) to tune continuous wave (CW) fiber laser. The optical bistable characteristics for two manners of separately alternating input power and bias voltage are discussed. The smallest wavelength shift of the order of 0.001 nm needed to realize a switching process in this optical bistability device is estimated. The potential applications of this device in the optical fiber sensor technique are also discussed.