We propose and experimentally evaluate a novel approach to measure atmospheric turbulence, in which imaging of light column technology is integrated into a differential motion method. In the approach, a large acquisition scene of the light column and a narrow field of view of one pixel of the charge-coupled device respectively allow high temporal and spatial resolutions, which offer the possibility of path-integrated turbulence strength measurement with multiple paths. In addition, we describe the measurement principle of the approach. Lastly, comparative experiment is performed to verify the feasibility of the approach.

Dual-grating structure thin-film silicon solar cells with different front and back grating periodicities are designed The geometrical parameters of both gratings are investigated. The reflection is greatly reduced by the front grating, whereas the absorption in the long wavelength is increased because of the back grating. The short circuit current of the combined structure is enhanced by 16.8% for a 1-\mu m thick c-Si layer compared with that of the conformal grating structure. The short circuit current can be further increased by creating a relative lateral displacement between the front and back gratings. The displacement results in a more remarkably enhanced absorption when the thickness of the active layer is reduced, indicating its importance in the design of ultra-thin high-efficiency solar cells.

A microwave photonic filter (MPF) with reconfigurability and tunability resulting from the superposition of the transfer functions is proposed. Based on the Vernier effect between the optical frequency combs and the periodic optical filters, each comb line can be mapped into a sub-filter in the electronic field. The sub-filters are superposed to obtain the total transfer function of the MPF. By manipulating a few comb lines, we can reconfigure the passband shape, tune the bandwidth, and adjust the center frequency independently. Experiments verify that the bandwidth can be tuned from 224.8 to 674.3 MHz, and that the center frequency ranges from 1 to 4 GHz.

We propose a remotely pumped Er-doped fiber amplifier (EDFA)-based 40-Gb/s downstream and 10-Gb/s upstream transmission long-reach wavelength division multiplexing passive optical network (WDMPON) scheme with downstream and upstream transmission implemented by quadrature phase-shift keying (QPSK) transceiver and reflective semiconductor optical amplifier (RSOA)-based intensity modulation direct detection (IM-DD). Transmissions of the 40-Gb/s QPSK downstream, using a Mach-Zehnder modulator, and the 10-Gb/s non-return-to-zero on-off keying (NRZ-OOK) upstream, using a 1.2-GHz RSOA equalized by fiber Bragg grating (FBG), are demonstrated with 40-km fiber transmission.

We report a switchable dual-wavelength fiber grating laser in linear overlapping cavity. The laser features two overlapping cavities sharing a single Yb-doped gain medium fiber and two sets of fiber Bragg gratings. A coiling fiber setup is inserted into the 1035 nm laser cavity. Given that the bending loss is inversely related to the bending radius, the cavity loss of 1035-nm can be modulated. Modulating the bending loss facilitates the switching of the fiber grating laser to a single-or dual-wavelength output at 1030 or 1035 nm and convenient tuning of the power ratio of the two wavelengths. An approximately 152.6-mW output power and up to 38-dB polarization extinction ratio are observed. The simultaneous lasing at 1030 and 1035 nm is a qualified seeder source for amplification to high power scale and can be applied to difference frequency generation of a terahertz signal. This dual-wavelength fiber grating laser is a potential pump source for generating terahertz radiation using a novel approach.

A sensing structure consisting of an abrupt taper spliced uniformly in to a fiber Bragg grating (FBG) is proposed and experimentally demonstrates refractive index (RI) and temperature measurements. Cladding modes are generated in the fiber through the abrupt taper containing the FBG. Most modes are reflected by the FBG at shorter wavelengths and reenter the launch fiber after passing through the abrupt taper. Spectral integrals are used to measure the power generated by the cladding and core modes. A sensitivity of -83.97 nW/RIU for ambient RI and a temperature sensitivity of 10 pm/C are obtained. No crosssensitivity problems exist between ambient RI and temperature measurement.

A multi-view three-dimensional (3D) display provides a more realistic experience than a two-view 3D display. Therefore, a multi-view 3D display with high brightness based on a parallax barrier is proposed. The parallax barrier in the 3D display has a gradient transmittance with enhanced frequency characteristic, which indicates that the aperture ratio of the parallax barrier can be increased, thereby improving brightness. Gradient transmittance is also helpful in reducing crosstalk. A prototype of the 3D display is developed. Experimental result shows that the 3D display has higher brightness than a conventional display. In addition, crosstalk is limited at a low level.

This letter presents an autofocus (AF) method to position a high-magnification microscope lens that automatically captures hundreds of images from a single moving slide. These images are taken by a mobile clinic unit in a rural location, and are later automatically processed and revised by a remote specialist. This process requires high focus precision to enable image processing techniques to achieve proper results. Low focusing times are also required for the system to be operative. We propose a novel method that combines two focus measures with an adapted searching scheme to cope with both constraints.

Electronic speckle pattern interferometry (ESPI) is a nondestructive, whole-field optical measurement technique. The removal of speckle noise is fundamental to extract measurement information accurately. In this letter, two filtering methods based on the oriented feature of ESPI fringes, i.e., the second-order oriented partial differential equation (SOOPDE) and oriented, regularized quadratic-cost function filtering methods, are first proven to be consistent. An important question in solving partial differential equation, i.e., how to select suitable parameters in an adaptive manner, is then discussed. The computer-simulated and experimentally obtained ESPI fringe patterns and phase map are processed by the SOOPDE filtering model with adaptive selective parameters. The qualitative and quantitative analyses demonstrate that the parameters selected by the adaptive method are effective and suitable for the SOOPDE filtering model.

An edge emitting laser with two symmetrical near-circular spots located far field (FF) is demonstrated using tapered double-sided Bragg reflection waveguides (BRWs). The BRWs consist of six pairs of top p-type and bottom n-type Al0.1 Ga0.9 As/Al0.3 Ga0.7As Bragg reflectors with a period thickness of 850 nm. The device has a 4o tapered angle configuration and exhibits two stable circular beams with a separation angle of 52o. Typical FF angles of 5.87o and 7.8o in the lateral and vertical directions, respectively, are achieved. The lateral FF angle in the ridged section is independent of the injection current (>0.8 A) because of narrow ridge (~10 \mu m) confinement. By contrast, the FF angle in the tapered section shows an increase rate of 1.2–1.66o/A. The periodic modulation of the lasing wavelength is observed to be sensitive to self-heating effects.

Experiments on developing a frequency-stabilized 555.8-nm laser are presented. The 555.8-nm laser is obtained by frequency doubling of a 1111.6-nm diode laser through single-passing a periodically poled lithium niobate (PPLN) waveguide. The 555.8-nm laser is then locked to a stable high-finesse Fabry–Perot (FP) cavity by the Pound–Drever–Hall (PDH) technique. The finesse of the cavity is measured by the heterodyne cavity ring-down spectroscopy technique. The linewidth of the 555.8-nm laser is investigated. After the laser is locked, the laser line width is reduced to about 3 kHz. This frequency-stabilized 555.8-nm laser is used in experiments on the laser cooling and trapping of ytterbium atoms to develop an ytterbium optical clock.

Enhancing resonance frequency of strong optical injection-locked semiconductor lasers is experimentally studied. Resonance frequency is increased from 4.1 to 53.9 GHz by the optical injection locking (OIL) technique. We experimentally demonstrate that resonance frequency is strictly equal to the frequency spacing between the cavity modes of the master and slave lasers under strong OIL condition. This result provides valuable information to improve OIL theory.

The fluorescence spectrum and thermal properties of the mixed crystal Nd:Lu0.99La0.01VO4 are determined. The strongest emission peak located at 1065.6 nm had a full width at half maximum (FWHM) of 2.1 nm. Continuous-wave (CW) laser performance is demonstrated by a compact planar–planar cavity that is endpumped by a diode laser. The laser output characteristics are investigated by using output couplers with different transmissions. A maximum CW output power of 8.09 W was obtained at an incident pump power of 19.4 W, which corresponds to an optical-to-optical conversion efficiency of 41.7% and a slope efficiency of 54.6%. The dependence of optimum transmission on pump power is calculated theoretically and is found to be consistent with experimental results.

The spatial and temporal distribution of Q-switched diode-pumped solid-state laser (DPSSL) pulses is investigated in multimode regimes. A theory model of spatial and temporal distribution of multimode Qswitched DPSSL pulses is established. The influences of position, initial inversion population density, and mode ratio on pulse width are studied. The results show that the pulse expands in the position wherein two or more mode intensities are equivalent, and the pulse building time difference of the modes are less than one mode pulse width. These results can be applied in pulse compression and mode composition.

A laser-diode end-pumped Nd:YVO4 crystal laser is demonstrated to emit the first-order Laguerre-Gaussian (LG01) mode with 502-mW laser power and 22% slope efficiency. The LG01-mode is lased only when the pumping area locates in the central part of the laser crystal's front surface, and thereafter the symmetrical LG01-HG01-TEM00 mode transition happens when laser crystal is moved laterally inside several-tens-micron area. The possible mechanism responsible for the phenomenon of symmetrical mode transition is also discussed.

Emission enhancement at 2.7 mm is observed in Er3+/Pr3+-codoped germanate glasses when pumped by a 980-nm laser diode. Significant reductions in 1.5-mm emission and upconversion intensity indicate efficient energy transfer between Er3+ and Pr3+; the energy transfer efficiency is as high as 77.4%. The mechanisms of energy transfer are discussed in detail. The calculated emission cross-section of Er3+/Pr3+-codoped germanate glass is 8.44×10-21 cm2, which suggests that Er3+/Pr3+-codoped germanate glass can be used to achieve efficient 2.7-mm emission.

Natural light illumination system (NLIS) generates increasing research interest because of the recent trend toward green energy. Various crucial optical components used in a NLIS are analyzed, designed, and fabricated to obtain high efficiency. A large amount of light is loss because of the large viewing angle during light transmission. A tapered light pipe (TLP) is used to collimate light viewing angles. In this letter, we combine a TLP and a traditional lens as a new coupler based on Etendue theory. The original efficiency is only 17.54%, but the efficiency reaches more than 70% when the new coupler is applied.

The performance of a terahertz (THz) Brewster polarizing beam splitter on polymer substrate is studied theoretically and experimentally. Simulations by using finite-element method demonstrate that both transmittance/reflectance and their extinction ratios are better than its 45 counterpart in a broad frequency range. Especially, the reflection extinction ratio improves significantly. The results are also verified experimentally with THz time domain spectroscopy (TDS) and backward wave oscillator (BWO) measurement system.

A configuration consisting of a double slit and pipe in conjunction with moving fluid is proposed to manipulate a broadband light source through the interference spectrum. Theoretical analysis shows that, by varying the speed of the fluid, the scheme can act as a special dynamic frequency filter and produce regular dark lines that may serve as an optical frequency ruler.

Ce3+/Er3+/Bi3+ triply-doped yttrium aluminum garnet (YAG) is synthesized using co-precipitation method. The Bi3+ concentration-dependent near-infrared (NIR) emission behavior is systemically investigated. The NIR emission of Er3+ ions at 1531 nm is enhanced threefold by the addition of 7 mol% Bi3+. Bi3+doping results in the formation of exciton in YAG and the variation in the local environment of the doped rare-earth ions. The enhancement in NIR luminescence is ascribed to the combined effects of the sensitization of exciton!Ce3+ !Er3+ and the Bi3+ doping-induced adjustment of the local environment for Ce3+ and Er3+ ions.

Cephalosporins are widely used as veterinary and human antibiotics. However, cephalosporin abuse is harmful to human health and causes allergic reactions or antibiotic resistance. We investigate a method featuring Raman spectroscopy and chemometrics to quantify mixture solutions of three typical cephalosporins, namely, ceftriaxone, cefotaxime sodium, and cefazolin sodium. Partial least-squares regression models are built on spectral data that are preprocessed by various methods. With prediction relative errors within 5% and high correlation coefficients of 0.998, we demonstrate that Raman spectroscopy combined with multivariate analysis is feasible for use in the quantitative determination of cephalosporin solutions.

The evolution of terahertz (THz) waveform in air plasma driven by low-energy few-cycle laser pulses is investigated to improve the accuracy of the carrier envelope phase (CEP) determination. Based on the transient photocurrent model, a balanced spatial distribution of the Kerr and free-electron effects in the plasma is found at 109 \mu J input energy. THz inversion occurs only once at the initial CEP of 0.5\pi, in which high-precision measurement of the CEP of few-cycle laser pulses is achieved.

Lateral photovoltaic (LPV) effects are observed in Bi2Sr2Co2Oy (BSCO) thin films. Upon illumination of a 532-nm constant laser, the lateral photovoltage is observed to vary linearly with the laser position between two electrodes on the film surface, and the position sensitivity can be enhanced by coating a layer of graphite on the surface of the BSCO film as a light absorber. Results suggest that the LPV effect in the thin film is independent of the photo-generated carriers but originates from thermoelectric effects. The present work demonstrates a potential application of BSCO films in position-sensitive photo (thermal) detectors.

In this study, 15 parameters representing textile properties are evaluated by the psychophysical method of categorical judgment with samples presented either in a light booth or on a display to investigate human visual perception based on the textural features of textiles. Visual perceptions of textiles can be expressed by the properties of regularity, smoothness, and warmth, which respectively explain the geometric placement rules of primitive elements, depth information, and emotion of textiles. Textiles with large primitive elements have high regularity and coarseness, whereas textiles with subtle primitive elements exhibit randomness and smoothness. Texture analysis results of the surface samples coincide well with those of display samples.