Using an improved inexion point method (IIPM), we investigate atmosphere boundary layer (ABL) height evolution over Hefei during the total solar eclipse on July 22, 2009. A lidar ceilometer is used in ground-based observations. Estimations of ABL heights before, during, and after the solar eclipse are analyzed using the IIPM. Results indicate that the IIPM, which is less sensitive to background noise, is more suitable in detecting ABL height and temporal evolution. Data demonstrate that the total solar eclipse resultes in a decrease in ABL height, indicating a suppression of turbulence activity, similar to that observed during the sunset hours. Changes in ABL height are associated with a slow change in temperature, indicating a significant weakening of penetrative convection and a time lag between ABL response and the reduction in solar radiation.

A natural gas leakage detector based on scanned-wavelength direct absorption spectroscopy is described. The sensor employs a multi-channel scanned-wavelength direct absorption strategy. It has the potential to simultaneously monitor methane and hydrogen sulfide in open path environment. Traditionally, scanned wavelength direct absorption spectroscopy is the technique choice for natural gas leakage applications because of its simplicity, accuracy, and stability. We perform the gas sensor using direct-absorption wavelength scans with isolated features at 1-kHz repetition rate and the center wavelength is stabilized at the center of the 2 \nu 3 band R(3) line of methane (1.65 \mu m) and the (\nu 1 +\nu 2 +\nu 3) combination band of hydrogen sulfide (1.57 \mu m), respectively. The influence of light intensity fluctuations can be eliminated by using scanned-wavelength direct absorption spectroscopy. Because of the fast wavelength scanning, the sensor has a response time of less than 0.1 s. The sensor can be configured to sense leakages in path-integrated concentrations of, for example, 100-ppm·m hydrogen sulfide and 10-ppm·m methane.

A guided-mode resonance (GMR) filter with the same material (Ta2O5) for both the grating layer and the waveguide layer is designed and fabricated. This simple structure is easy to fabricate and can avoid the defects at the grating/waveguide interface using different materials. The spectral response measured with a Lambda 900 spectrophotometer under normal incidence for TE waves exhibits a peak reflectance exceeding 80% at the wavelength of 1040 nm with a full-width half-maximum (FWHM) linewidth of 23 nm. We evaluate the deviations of the fabricated structure from the designed parameters.

We propose a novel and simple all-optical 160-Gb/s orthogonal frequency division multiplexing (OFDM) symbol generator which is based on discrete triangle waveform driving-LiNbO3 modulators to realize largerange linear optical shift. The entire system needs 64 discrete modulators: at the transmitter, a 2.5-Gb/s optical duobinary (ODB) modulator for data modulation and a 2.5-Gb/s triangle waveform driving-LiNbO3 phase modulator for phase shift to generate each subcarrier; and at the receiver, a 2.5-GHz optical band pass filter (OBPF) using Faraday anomalous dispersion optical effect to separate them. Excellent bit error rate (BER) is observed after 1060 km of transmission without any dispersion compensation.

A novel scheme for ultra-wideband (UWB) monocycle pulse generation is proposed based on a dual-output push-pull Mach-Zehnder modulator (MZM). The MZM is driven by a non-return-to-zero (NRZ) data sequence and biased at the nonlinear point to generate edge-triggered pulses. To combine the complementary pulses forming a monocycle UWB pulse, two schemes are used to implement incoherent summation structure. A proof-of-concept experiment of UWB-over-fiber down-link system is set up. Further, by using digital signal processing (DSP) to calculate the bit error rate (BER), the transmission performance of two system configurations is studied.

A cascaded ytterbium-doped all-fiber master oscillator power amplifier (MOPA) with 1064-nm pulsed laser is demonstrated, and it can produce up to 20-W average power and 0.1-mJ pulse energy at tunable repetition rates from 10 to 200 kHz. Two main di±culties of the all-fiber configuration are overcome: all fiber isolator and mode field adapter between single mode fiber (SMF) and double cladding fiber (DCF). Gain saturation and nonlinear effect are analyzed theoretically, and the possibility of further power-scaling of this cascade scheme is predicted.

A novel heuristic algorithm that considers transmission impairment (especially amplified spontaneous emission (ASE) noise) is developed for traffic grooming in wavelength division multiplexing (WDM) optical networks. Span constraints, which are determined by the impairment, are added to constrain the maximal transparent reach limit of a lightpath. Under span constraints, a series of short lightpaths will be built up explicitly to relay traffic when a single lightpath cannot meet the requirement of transmission quality. Both problem formulations and heuristic algorithms are given for impairment-aware traffic grooming. Numerical results show that the successful routing of each low-speed traffic stream is guaranteed and the efficiency of wavelength channels and lightpath usage are both improved by considering transmission impairment.

We study the performance of an orthogonal modulation system with frequency-shift keying (FSK) label and optical Manchester-coded (MC) payload. Simulation result shows that by introducing an optical MC payload, the available extinction ratio (ER) value of a FSK and intensity modulation (IM) orthogonal modulation system can be improved from 5 to 9 dB for system optimization, exhibiting great advantages over the traditional non-return-to-zero (NRZ) payload. Besides, the bit error rate (BER) characteristics of both label and payload show a more remarkable advantage than that of NRZ coding, verifying itself as a perfect candidate for the payload coding method in orthogonal modulation systems.

An approach to generate a flat optical comb with tunable comb spacing and adjustable comb number is proposed. In the proposed approach, a Mach-Zehnder modulator (MZM), being biased to generate two carrier-suppressed first-order sidebands, is cascaded with a phase modulator. The two optical sidebands are then sent to the phase modulator to generate two identical, but frequency-shifted phase-modulated spectra. Thanks to the complementary nature of the two adjacent comb lines in the phase-modulated spectra, the overlapping of the two spectra would lead to the generation of a flat optical comb. Since only the phase modulation index or the microwave power is needed to be adjusted, the system is easy to be implemented with tunable comb spacing and adjustable comb number. Numerical simulations are performed, and the approach is verified by an experiment.

Two compensating methods about solitons transmition systems at 40 Gb/s in a photonic crystal fiber are investigated. The maximum transmission distance of the system is calculated numerically by sliding filters and synchronic modulation technology. The maximum transmission distance increases evidently which occasionally is three times longer than before. The results show that the actions of high order dispersion, polarization mode dispersion, and high order nonlinearity are weakened by the two methods. The compensating effect of synchronic modulation technology is better than that of the other one. The capability of the compensated system is ameliorated, which is shown by eye patterns.

Utilizing the intersecting cortical model (ICM) to enhance degraded images under poor illumination is presented. As the key point, the general mapping function (MF) for image enhancement is deduced firstly on the basis of the nature-firing ICM (NF-ICM), which restrains the traditional autowave effect of blurring details and contrast. Then, the sigmoid MF is especially proposed to map the input gray-level to a more proper range for visual looking, and it solves over-enhancement and artifact by the classical logarithm one. For image enhancement application, the optimized parameters, initial threshold, and stopping condition in NF-ICM are all analyzed in detail. Simulation results prove that the proposed method has more contrasted, colorful, and good-visual performance.

The two-dimensional (2D) compound parabolic concentrator's (CPC) characteristics are analyzed. It is shown that CPC's height is taller and its light collecting ability is stronger with the CPC's field of view decreasing when the bottom radius is unchanged. According to the ZEMAX analysis, CPC is good at collecting optical signal, and the antenna combining CPC with hemispherical lens can gather more optical signal than a single CPC or CPCs combined in series. The light propagation of scattering optical communication based on multiple scattering is simulated by Monte Carlo method, and the results show that using CPC as receiving antenna can strengthen communication system's signal collecting ability and increase its communication distance.

An optical fiber evanescent wave methane gas sensor based on core diameter mismatch is reported. The sensor consists of a multimode fiber in which a short section of standard single-mode fiber, coated with the inclusion of cryptophane molecules E in a transparent polysiloxane film, is inserted. The sensing principle is analyzed by optical waveguide theory. For different sensing film thicknesses and interaction lengths, the sensor signal is investigated within the methane concentration range of 0-14.5% (v/v). It is shown that the sensor signal with the thickness of 5 \mu m and the interaction length of 3 mm strengthens linearly with the increasing concentration of methane, with a slope of 0.0186. The best detection limit of the sensor for methane is 2.2% (v/v) with a response time of 90 s. This sensor is suitable for the detection of methane concentration below the critical value of 5%.

We investigate the dispersion properties of nanometer-scaled silicon waveguides with channel and rib cross section around the optical fiber communication wavelength and systematically study their relationship with the key structural parameters of the waveguide. The simulation results show that the introduction of an extra degree of freedom in the rib depth enables the rib waveguide more flexible in engineering the group velocity dispersion (GVD) compared with the channel waveguide. Besides, we get the structural parameters of the waveguides that can realize zero-GVD at 1550 nm.

The characteristics of fiber laser coherent beam combination are investigated by using a 2×2 fiber laser array with a self-Fourier cavity. The experimental results show that with a certain output width the power ratio of the center spot is increased with the increase of space duty cycle, meanwhile the number of secondary spots is decreased correspondingly. The results are in agreement with theoretic analysis.

Asymmetric broad-waveguide separate-confinement heterostructure (BW-SCH) quantum well (QW) laser diode emitting at 808 nm is analyzed and designed theoretically. The dependence of the optical field distribution, vertical far-field angle, and internal loss on different thicknesses of the upper waveguide layer is calculated and analyzed. Calculated results show that when the thicknesses of the lower and upper waveguide layers are 0.45 and 0.3 \mu m, respectively, for the devices with 100-\mu m-wide stripe and 1000-\mu m-long cavity, an output power of 7.6 W at 8 A, a vertical far-field angle of 37°, a slope efficiency of 1.32 W/A, and a threshold current of 189 mA can be obtained.

Two extended-cavity diode lasers at 780 nm which are longtime frequency-stabilized to Rb87 saturated absorption signals are reported. A high-performance frequency-locking circuit module using a first-harmonic detection technique is designed and achieved. Two lasers are continuously frequency-stabilized for over 100 h in conventional laboratory condition. The Allan standard deviation of either laser is estimated to be 1.3×10^-11 at an integration time of 25 s. The system environment temperature drift is demonstrated to be the main factor affecting long-term stability of the stabilized lasers based on our correlation study between beat frequency and system environment temperature.

A high power continuous-wave (CW) 914-nm Nd:YVO4 laser at room temperature is presented. Using an end-pumped structure and employing an 808-nm diode-laser as the pump source, the maximum output power of 15.5 W of the 914-nm laser is achieved at the absorbed pump power of 40.2 W, with a corre-sponding average slope efficiency \mathrm s=65.6%. To the best of our knowledge, this is the highest output power of diode-pumped 914-nm laser. A beam quality factor M2=2.8 at the output power of 15 W is measured by using the traveling knife-edge method.

Mode radiation loss for microdisk resonators with pedestals is investigated by three-dimensional (3D) finite-difference time-domain (FDTD) technique. For the microdisk with a radius of 1 \mu m, a thickness of 0.2 \mu m, and a refractive index of 3.4, on a pedestal with a refractive index of 3.17, the mode quality (Q) factor of the whispering-gallery mode (WGM) quasi-TE7;1 first increases with the increase of the radius of the pedestal, and then quickly decreases as the radius is larger than 0.75 \mu m. The mode radiation loss is mainly the vertical radiation loss induced by the mode coupling between the WGM and vertical radiation mode in the pedestal, instead of the scattering loss around the perimeter of the round pedestal. The WGM can keep the high Q factor when the mode coupling is forbidden.

A high-average-power, high-repetition-rate dual signal optical parametric oscillator based on periodically poled MgO-doped lithium niobate (PPMgLN) with a phase-reversed grating is reported. The pump laser is an acousto-optically Q-switched Nd:YVO4 laser with a maximum average power of 7.6 W. When the repetition rate is 50 kHz and the pulse width of the pump source is 23 ns, the maximum average dual signal output power is about 1.9 W, leading to a conversion efficiency of 25%. Over a 30-min interval, the instability of the signal power measured is less than 0.5%.

A simple and efficient templating method in combination with hot embossing technique is developed for fabricating large-area two-dimensional (2D) microlens arrays (MLAs) with uniform shape. By utilizing a modified microchannel method, a 2D large-area hexagonal close-packed (HCP) array of silica colloidal microspheres is prepared and serves as a template in the following hot embossing treatment to create a polycarbonate (PC) microcavity array. Then, with the obtained PC microcavity structure serving as a mold, a hot embossing process is applied to finally achieve a polymethylmethacrylate (PMMA) MLA. The effect of annealing time during the mold preparation process on the dimensions and shapes of the prepared microlens is investigated. The imaging performances of the prepared PC concave microcavities and PMMA convex microlenses are characterized by carrying out projection experiments. Our method provides a rapid and low cost approach to prepare large-area MLAs.

Integral imaging is a true, three-dimensional (3D) display technology that captures and reconstructs 3D scenes using two-dimensional (2D) micro-lens arrays. The manufacturing technique of micro-lens arrays is complicated and expensive, thus limiting the application of the technology. An imitating micro-lens array for integral imaging is presented in this letter. Imitating micro-lens array is composed of a cheap lenticular lens and a parallax barrier. The relationship of the parameters of the imitating micro-lens array is analyzed and the parameter formulae are deduced. The arrangement of pixels under a cell of the imitating micro-lens array is presented. The imitating micro-lens array is simulated using ASAP software, and the results prove that the designed imitating micro-lens array is effective. A 3D scene is reconstructed on a 3D display that consists of the imitating micro-lens array and a 17-inch flat panel display.

The natural sedimentation method combining with the isothermal heating evaporation induced self-assembly is presented to fabricate three-dimensional (3D) colloidal crystals in the curved cavity of the fiber end face. A-50 \mu m-deep cavity is etched by hydrofluoric acid. The colloidal crystals are characterized by optical and scanning electron microscopy. A 1380-nm stop band is observed by measuring their transmission spectra at normal incidence by an optical spectrum analyzer (OSA).

The far-field analytical expressions for the electromagnetic fields of a cylindrically polarized vector beam propagating in free space are obtained based on the vector angular spectrum and the method of stationary phase. The far-field energy flux distributions and the beam quality by the power in the bucket (PIB) in the nonparaxial regime have been investigated. The PIB of the cylindrically polarized beam depends on the ratio of the waist width to wavelength, the order of the Laguerre polynomial, and the angle between the electrical vector and the radial direction. The analyses show that azimuthal polarization compared with radial polarization has better energy focusability in the far field.

Tight focusing properties of partially coherent radially polarized vortex beams are studied based on vectorial Debye theory. We focus on the focal properties including the intensity and the partially coherent and polarized properties of such partially coherent vortex beams through a high numerical aperture objective. It is found that the source coherence length and the maximal numerical aperture angle have direct influence on the focal intensity, as well as coherence and polarization properties. This research is important in optical micromanipulation and beam shaping.

The pairwise entanglement dynamics in a multipartite open system consisting of three entangled cavity photons locally coupled with independent N-mode reservoirs is studied via concurrence. The initial states of cavity photons are prepared in two types of W-like states while the corresponding reservoirs are prepared in the factorable vacuum state. The result shows that all the pairwise concurrences of the total system including cavities and reservoirs undergo qualitatively different dynamical behaviors. Among the two W-like states, only one could exhibit entanglement sudden death (ESD) leading the corresponding reservoirs to exhibit entanglement sudden birth. In addition, by taking the entanglement of the corresponding reservoirs into account, entanglement invariants are constructed for the W-like state that does not undergo ESD.

We propose a scheme to prepare the Bell states for atomic qubits trapped in separate optical cavities via atom-cavity-laser interaction. The quantum information of each qubit is encoded on the degenerate ground states of the atom, so the entanglement between them is relatively stable against spontaneous emission. The proposed scheme consists of a Mach-Zehnder interferometer (MZI) with two arms, and each arm contains a cavity with an N-type atom in it. It requires two classical fields and a single-photon source. By controlling the sequence and time of atom-cavity-laser interaction, the deterministic production of the atomic Bell states is shown. We also introduce the generalization of the present scheme to generate the 2N-atom Greenberger-Horne-Zeilinger state.