We create a Bose-Einstein condensate (BEC) of ⁸⁷Rb atoms by runaway evaporative cooling in an optical trap. Two crossed infrared laser beams with a wavelength of 1064 nm are used to form an optical dipole trap. After precooling the atom samples in a quadrupole-Ioffe configuration (QUIC) trap under 1.5 \mu K by radio-frequency (RF) evaporative cooling, the samples are transferred into the center of the glass cell, then loaded into the optical dipole trap with 800 ms. The pure condensate with up to 1.5×10⁵ atoms is obtained over 1.17 s by lowering the power of the trap beams.

An asynchronous optical sampling scheme based on four-wave mixing (FWM) in highly nonlinear fiber (HNLF) is experimentally demonstrated. Based on this scheme, 10-GHz input pulse train with 1.8-ps pulse width is successfully sampled in 100-m HNLF. A single pulse at 10 GHz with 2.3-ps pulse width is rebuilt by using a 50-MHz frequency tunable free-running fiber laser as the sampling pulse source (SPS). 40-GHz pulse train is used as the input signal. The rebuilt waveforms, together with the low-jitter eye diagram, are also presented.

Schemes integrating inter-carrier interference (ICI) self-cancellation and common phase error (CPE) compensation for coherent optical orthogonal frequency division multiplexing (CO-OFDM) systems are investigated. The purpose of our research is to counteract the impacts of laser phase noise and fiber nonlinearity. We propose two ICI self-cancellation-based CO-OFDM schemes, and adopt a pilot-aided decision feedback (DFB) loop for CPE compensation. The proposed schemes are compared with conventional CO-OFDM schemes at the same spectral efficiency. Simulations show that our schemes can not only enhance laser linewidth tolerance of the CO-OFDM system, but also present strong robustness against fiber nonlinearity.

A polarization-mode dispersion (PMD) measurement system using a pair of polarization-state generators (PSGs) is demonstrated. Based on the saturation characteristics of magneto-optic rotators, the PSG can be digitally controlled, ensuring high-speed and highly repeatable generation of five distinct polarization states. Thus, the PSG can make full use of the advantage of the Mueller matrix method of PMD measurement. The experimental result shows that the system has good measurement repeatability and potential for field testing.

A novel approach is used to implement optical carrier suppression and separation (OCSS) labeling. Then, the performance of 10/40-Gb/s duobinary payload with 2.5-Gb/s amplitude shift keying (ASK) or duobinary label by numerical simulations is studied. Influencing factors, such as demultiplexer bandwidth and fiber Bragg grating (FBG) filter bandwidth, are investigated. Simulation result shows that the received sensitivity of ASK label is higher than that of the duobinary label, while the received sensitivity of duobinary payload with duobinary label is higher than that with ASK label.

Simple single-lens equivalent systems for graded-index (GRIN) lenses in inhomogeneous medium obtained using matrix optics are proposed in this letter. Due to its simplicity, the equivalent optical system enables quick analysis of the imaging properties of GRIN lens rod immersed in inhomogeneous medium. This facilitates the optical analysis of complicated optoelectronics systems in inhomogeneous medium utilizing GRIN lens rods.

A novel speckle reduction technique for digital holography is proposed. Multiple off-axis holograms are recorded using a circularly polarized illumination beam and a rotating linearly polarized reference beam. The speckle noise in the reconstructed images is suppressed by averaging these fields. We demonstrate the effectiveness of this technique experimentally and conduct additional statistical evaluation.

We introduce a new spectrum transform into the image fusion field and propose a novel fusion method based on discrete fractional random transform (DFRNT). In DFRNT domain, high amplitude spectrum (HAS) and low amplitude spectrum (LAS) components carry different information of original images. For different fusion goals, different fusion rules can be adopted in HAS and LAS components, respectively. The proposed method is applied to fuse real multi-spectral (MS) and panchromatic (Pan) images. The fused image is observed to preserve both spectral information of MS and spatial information of Pan. Spectrum distribution of DFRNT is random and uniform, which guarantees that good information is reserved.

We propose a fragile watermarking scheme capable of image tamper detection and recovery with a block-wise dependency mechanism. Initially, the image is divided into blocks with size of 2×2 in order to improve image tamper localization precision. By combining image local properties with human visual system, authentication data are acquired. By computing the class membership degree of each image block property, data are generated by applying k-mean clustering technique to cluster all image blocks. The recovery data are composed of average intensity obtained by truncating the two least significant bits (LSBs) of each pixel within each block. Finally, the logistic chaotic encrypted feature watermark consisting of 2-bit authentication data and 6-bit recovery data of image block is embedded into the two LSBs of each pixel within its corresponding mapping block. Experimental results show that the proposed algorithm does not only achieve superior tamper detection and locate tiny tampered positions in images accurately, it also recovers tampered regions effectively.

Based on structured-light vision measurement technology, we study a measuring method for microdiameter. The measurement principle and mathematical model are described. A novel grayscale barycenter extraction algorithm along the radial direction is proposed, which can precisely gather the image coordinates of the ellipse-shaped light-stripe centers. The accuracy of the measurement result shows marked improvement by using the algorithm. The method executes circle fitting to the measured three-dimensional (3D) data using linear least square method, which can acquire the diameter, surface profile, and other information of the object effectively. On the scene, a line-structured light vision system using the presented method is applied to measure the curvature radius of metal blades. Experimental results show that the measurement precision of the system is higher than 2 \mu m.

A conductively cooled, laser diode (LD) end-pumped, injection-seeded single frequency Nd:YAG laser is designed and implemented. The laser utilizes Nd:YAG rod as gain medium and compact dual-end-pumping arrangement using two fiber-coupled LDs with a maximum output of 150 W. The optimized ramp-fire technique is applied to build reliable single longitudinal mode oscillating. The laser is capable of producing a 10-mJ Q-switched pulse with 13-ns pulse width at 1064 nm at a pulse repetition rate of 250 Hz. The output beam qualities M2 of approximately 1.19 and 1.22 in horizontal and vertical directions are detected, respectively.

The transverse trapping forces on a dielectric sphere located at an oil-water interface are theoretically investigated with the ray-optics model. The transverse trapping forces rely on the internal property of the particle-interface system, and increase with either the decrease of three phase contact angles at the oil-water interface or the use of oil phase with low refractive index. The numerical results also show that the transverse trapping forces can be improved by either decreasing the numerical aperture of the microscope objective or shrinking the diameter of the trapping laser beam.

Ultrafast spectroscopy of semiconductor saturable absorber mirror (SESAM) is measured using a femtosecond pump-probe experiment. This allows dynamic responses of SESAM in the cavity to be concluded by ultrafast spectroscopy. Change in reflection is measured as a function of pump-probe delay for different pump excitation fluences. Change of nonlinear reflection of SESAM is measured as a function of incident light energy density. When the excitation fluence increases, nonlinear change in ultrafast spectroscopy of SESAM becomes increasingly significant. When SESAM is pumped by an ultrahigh excitation fluence, the energy density of which is approximately 1400 \mu J/cm², two-photon absorption can be observed visibly in its ultrafast spectroscopy.

We experimentally demonstrate the phase locking of a two-dimensional (2D) array of four fiber lasers using an improved self-imaging resonator with a spatial filter. The high visibility interference round stripes of the coherent beam profile are observed. The coherent output power of the fiber array exceeds 134 W. The entire system operates quite stably, and no thermal effects observe in the spatial filter, indicating that the coherent output power can be increased using this method.

We report a photoluminescence observation of the coupling of donor-bound excitons and longitudinal optical phonons in high-quality ZnO crystals at 5 K. The first-order phonon Stockes line of donor-bound excitons exhibits a distinct asymmetric line shape with a clear dip at its higher energy side, suggesting that quantum mechanical interference occurs during the annihilation of donor-bound excitons. The donor binding energy is determined to be 49.3 meV from spectral featural.

The fundus camera used in imaging retina includes two parts: fundus imaging path with a positive focusing lens and annular Kohler illuminating path. We present a pupil joint equation and a focus equation based on the internal focusing manner to analyze its configuration. Using these equations, the configuration of the camera is given in detail. The design result of the fundus imaging path shows compact initial configuration at a total length of about 123 mm. The focusing range is -10-10 diopter, and the movement of the focusing lens is nearly linear at displacement of more than a sub-millimeter per diopter.

Theoretical analyses are presented on the critically phase-matched second-harmonic generation (SHG) in a biaxial crystal with the focused fundamental Gaussian beams. The dependence of the second-harmonic light power on the phase matching conditions, focused geometries, walk-off effects, and absorptions are discussed in detail. Expressions are presented for calculating the light power of the types I and II SHGs in the biaxial crystal, applied to optimize the blue light generation with the LiB3O5 crystal. A maximum conversion efficiency of around 37% is obtained with 798-nm laser power of 500 mW.

A four-wave mixing (FWM) model is used to analyze the polarization control of terahertz (THz) pulse generated by a two-color laser field in air. The analytic formula for the THz intensity varying with the THz polarizer angle, and the relative phase between the two pulses, are obtained. The corresponding numerical results agree well with both numerical result obtained from a quantum model and measured data reported. Moreover, possible phenomena are predicted for variables not found in other experiments. Compared with the quantum model, the FWM model gives analytic formulas and clear physical pictures, and has the advantage of efficient computing time.

A method for the design of an unobscured reflective zoom system with three mirrors is described. This method applies the vector aberration theory, which helps designers analyze third-order aberrations for optical systems with decentered and tilted surfaces. As the vector aberration theory presents the variation of third-order aberrations in asymmetric systems through analytic expressions, real ray tracing is unnec-essary. Hence, the design with vector aberration theory is faster, and the analytic expressions are more comprehensive and intuitive. To demonstrate the practicability of the method, a design example is given, which shows that the presented method can guide designers achieve a good unobscured reflective zoom system with three mirrors.

We exhibit a three-dimensional (3D) photonic nanojet based on a dielectric microsphere irradiated by a plane wave with the finite-difference time-domain (FDTD) method. We investigate the influence of the refractive index of the surrounding on the properties of the nanojet by simulating the electric field distributions in it. The simulation results show that, by optimally choosing the size of the sphere and the ratio of the refractive indices of the sphere and the surrounding, the focus point can occur just on the surface of the sphere even if the refractive index of the surrounding is changed. Additionally, the peak amplitude of the nanojet increases with increasing the refractive index of the surrounding. However, the decay length and the jet width of the nanojet decrease simultaneously. These effects may have potential applications in observation or manipulation of nano-objects such as antibodies in biology. In nanojet-enabled optical data storage, the photonic nanojet may be also helpful for improving data-storage capacities and retrieval speed by controlling the field amplitude, the decay length, and jet width of the nanojet.

By using CdSe/ZnS quantum dots (QDs), we study the effect of cavity quantum electrodynamics on the coupling of the microtoroid cavity. When with whispering gallery (WG) modes, the microtoroid cavity demonstrates high quality factor and small mode volume at visible wavelengths. Accordingly, fiber tapers allow QDs to adhere into the cavity and further permit the control of site-selected coupling. From the luminescence spectra, QDs are modulated effectively by cavity modes. Variable modulations are observed by changing QD coupling conditions. Therefore, based on experimental and theoretical research, strong and tunable Purcell enhancement can be realized by this system.The authors thank Jinming Cui and Chunhua Dong for their helpful discussion. This work was supported by the National Fundamental Research Program of China (No. 2006CB921900), the National Natural Science Foundation of China (Nos. 60537020 and 60621064), and the Knowledge Innovation Project of the Chinese Academy of Sciences.

A 1550-nm all-fiber monostatic lidar system based on linear chirp amplitude modulation and heterodyne detection for the measurements of range and velocity is presented. The signal processing method is given, after which the relationship between the peak frequency values in the final signal spectrum, the target's range, and the line-of-sight velocity is obtained in the presence of the fiber end-face-reflected signal plaguing many monostatic lidar systems. The range of an electric fan as well as the line-of-sight fan speed of different levels is tested. This proposed system has a potential application for the space-borne landing system.

Effect coatings have the unique property of large change of appearance under different viewing conditions. This results in quality control problems of related products. In this letter, samples of metallic panels with effect coatings are visually assessed and measured. Based on experimental results, we propose formulae to predict precisely the total differences of effective samples in terms of variations in color, coarseness, and glint. Under diffused illumination, the total difference formula includes color difference and coarseness difference. Under directional illumination, the total difference formula includes color difference and glint difference.

Diamonds are wide-gap semiconductors possessing excellent physical and chemical properties; thus, they are regarded as very appropriate materials for optoelectronic devices. Based on the Kerr effect, we introduce a simple and feasible method for measuring the third-order nonlinear optical susceptibility of synthetic diamonds. In the experiments, synthetic type I diamond samples and transverse electro-optic modulation systems are utilized. As for the laser with the wavelength of 650 nm, the third-order susceptibility and Kerr coefficient of the diamond samples are obtained at χ⁽³⁾₁₂₁₂=2:17×10^-23 m²=V² and S₄₄= 1.93×10^-23 m²=V², respectively.