We demonstrate a wireless transmission link at 3.9 THz over a distance of 0.5 m by employing a terahertz (Hz) quantum-cascade laser (QCL) and a THz quantum-well photodetector (QWP). We make direct voltage modulation of the THz QCL and use a spectral-matched THz QWP to detect the modulated THz light from the laser. The small signal model and a direct voltage modulation scheme of the laser are presented. A square wave up to 30 MHz is added to the laser and detected by the THz detector. The bandwidth limit of the wireless link is also discussed.

We present a high-transmittivity non-periodic sub-wavelength high-contrast grating (HCG) with large-angle beam-steering ability for transmitted light. The phase front profile of transmitted light is a decisive factor to the beam-steering property of the HCG. By designing the structural parameters of the HCG, both beam steering and high transmittivity can be achieved. The properties of the beam steering and transmission are numerically studied with the finite element method. The results show that the transmittivity is up to 0.91 and the steering angle is 27.42° which is consistent with the theoretical 30°.

We propose and demonstrate a visible light communication (VLC) scheme based on space-division multiple access (SDMA) optical beamforming to accommodate multiple user devices in the VLC based on optical beamforming. SDMA optical beamforming is a technique which separates light-emitting diode light spa-tially and focuses each part on different target devices simultaneously. We show the experimental results of the VLC signal amplitudes, the optical power densities, and the bit-error rate performance as a function of transmission distance before and after the SDMA optical beamforming. The results show that the VLC signal amplitudes and optical power densities are improved by 8–2 and 3.8–5 dB, respectively, with the help of SDMA optical beamforming.

An approach to reducing the harmonic distortion in frequency-doubled triangular-shaped pulse train generation is proposed. It requires a dual-parallel Mach–Zehnder modulator followed by a section of dispersive fiber, as the key component. The basic principle is to make the expression of optical intensity approximately equal to the Fourier expansion of idea triangular-shaped waveform. A detailed expression of the final optical intensity is given by theory and then verified by simulation. It is found that the impact of the undesired harmonic distortion is greatly reduced.

We propose a novel iteration-free blind phase noise estimation scheme for coherent optical orthogonal frequency division multiplexing (CO-OFDM) systems. In the new algorithm, the cost function is selected as the similar expression with real and imaginary parts as that in the modified constant modulus algorithm, and the new cost function is derived under some assumptions, where it is infinitely approximated by the sine and cosine functions. By means of the analytical formula of the cost function, the initial coarse common phase error can be obtained with only some samples, where the algorithm avoids computational complexity of conventional blind phase noise compensation scheme. In CO-OFDM systems with high-order modulation format (32 quadrature amplitude modulation) and narrow linewidth lasers, it is proved by the simulation results that the phase noise can be effectively compensated with the proposed blind estimation method.

We demonstrate a novel all-fiber cavity ring-down (CRD) magnetic field sensing method that uses frequency-shifted interferometry, and does not require any optical pulse and fast electronics compared with conventional CRD schemes. The sensing element in the ring-down cavity is a fiber taper surrounded by magnetic fluid, whose refractive index varies as an external magnetic field is applied. Magnetic field strength measurement is successfully achieved within a range from 8 to 850 Gs. A resolution of 0.00105 ± 0.00003 dB/Gs is obtained in the approximately linear segment from 423.2 to 766.6 Gs. The sensing method is potential for sensing other physical and chemical parameters.

We report an extrinsic Fabry–Perot interferometer-fiber Bragg grating (EFPI-FBG) hybrid sensor in this letter. The interferometric cavity of the proposed hybrid sensor is composed of a glass capillary tube, a section of single-mode fiber, and a section of single-mode metal fiber with one FBG. The FBG processed by high-temperature annealing is used to measure temperature, whereas the fiber EFPI is adopted for strain measurement. One of the two aligned fibers is free along the axial direction, which is different from the traditional structure that both the fibers are fixed to glass capillary tube. Experimental results show that the sensor can measure high temperature and large strain simultaneously. The measuring range of temperature and strain for the hybrid sensor is up to 500 °C and 10,000 μ.., respectively. Effective temperature compensation of the hybrid sensor is realized, too.

The resolution of the parallax image is inversely proportional to the view number in the horizontal direction for the traditional autostereoscopic display based on a parallax barrier. To balance the resolution in the vertical and horizontal directions, two parallax interleaved barriers are designed. The liquid crystal display panel provides the synthetic image with square pixel units, and the pixels in a unit are distributed to different horizontal views. Two parallax interleaved barriers work together to modulate pixels in vertical and horizontal directions. 3D display with uniform resolution and low crosstalk is demonstrated.

We apply graph matching method to detect infrared small moving targets using image sequences. Candidates (interest points) detected in the first frame form one graph and the same candidates in the last frame form another one. The real moving targets are extracted by matching these two graphs. Experimental results demonstrate that the proposed method is robust and efficient to the translation and rotation of the background.

The grating fringe on the reference plane is broadened in the intersecting axis system because of oblique-angle projection. In order to solve this problem, we study the theoretical model of the temporal phase unwrapping method based on the fringe cycle correction. We also study the 3D shape measurement theoretical model of the larger complex objects after considering the coordinate deviation and lens distortion. Experimental results demonstrate that the fringe cycle on the reference plane can be corrected to a constant value, the lens distortion can be corrected, and 3D shape of larger complex objects can be accurately measured.

In this letter, we propose a voltage-controlled optical filter based on electrowetting. The device is made of a transparent cubic cell filled with two immiscible liquids having three indium tin oxide electrodes fabricated on the bottom substrate of the cell. A conductive droplet carrying a color filter is placed on the ITO electrode and the surrounding liquid is density-matched silicone oil. Under zero bias, the droplet is placed in the middle of the substrate and white light passes through the filter and we can see red light on the screen. When a voltage is applied to the device, the filter moves with the liquid based on electrowetting effect, we can see the white light on the screen. Due to the movement of the liquid, our device functions as an optical switcher. The switch time of the device is ~70 ms. The proposed device has a wide application in optical communication, electronic display, and optical switch.

We develop a self-adaptive algebraic tomography algorithm (SAATA) to investigate the simultaneous reconstruction of concentration and temperature distributions in larger temperature range from two views. The simplified optical arrangement with fewer projections is realized by extension of spectral information at multiple wavelengths, resulting in great potential in applications of practical combustion diagnosis. The results show SAATA can perform much better reconstructions in 300–3000 K temperature range than genetic simulated annealing algorithm and least-square orthogonal-triangular decomposition method with two-wavelength scheme. More phantoms are created to demonstrate the capability of SAATA to capture the peaks and adapt for both flat and sharp temperature distributions. Meanwhile, the advantage of high stability ensures better reconstruction performance at noise levels from 0.1% to 10% in projections.

We develop a new calibration method in lab by measuring the absolute spectral irradiance responsivity of Sun photometer sun channel. The absolute power responsivity of Sun photometer is obtained when a white laser double monochromator system serve as a source, and a standard transfer detector calibrated against cryogenic absolute radiometer is assembled to measure the absolute power of laser beam. The effective area of aperture is measured through laser raster scanning method, and the relative spectral irradiance responsivity of the corresponding channel is obtained by using tungsten–halogen lamps double monochromator system. On the basis of the above results, the top of the atmosphere responsive constants V0 (500, 675, and 870 nm) are obtained by integration with extraterrestrial solar spectral irradiance data. Comparing the calibration results with that of CIMEL, France in November 2011, the relative differences are 4.38%, 2.23%, and 2.45%, respectively. The calibration uncertainty reaches to 2.048×10-2, which shows a remarkable consistency with the Langley plot method. Further, our scheme can overcome the limits of space and atmospheric conditions which are only available at a high-altitude calibration site in particular date. The advantages lie in not only shortening the experiment period but also being of high precision. This new scheme definitely plays an important role in supporting the current and future sun photometry calibration activities which are significant to earth observation.

To improve ophthalmic adaptive optics (AO) speed and compensate for ocular wavefront aberration of high temporal frequency, the AO wavefront correction is implemented with a control scheme including two parallel threads: one is dedicated to wavefront detection and the other conducts wavefront reconstruction and compensation. With a custom Shack–Hartmann wavefront sensor that measures the ocular wave aberration with 193 subapertures across the pupil, AO achieves a closed-loop updating frequency up to 110 Hz, and demonstrates robust compensation for ocular wave aberration up to 50 Hz in an AO scanning laser ophthalmoscope.

We present detailed analysis of calibration process error for electro-optical detection systems, which can be simplified as the plane rotation around a non-orthogonal axis. By means of octonions it firstly proves that the plane rotation around a non-orthogonal axis can be decomposed into rotations around two perpendicular axes. The rotation is further divided into three steps, and the calibration error is hence discussed and obtained. The simulation and test results indicate that there are large calibration errors in calibration process. The pointing error can be effectively improved after separating error components, which provides a more accurate set data for further compensation.

We experimentally demonstrate efficient frequency doubling of a telecom 1560 nm distributed feedback diode laser with a 3 cm long MgO:PPLN waveguide with a conversion coefficient of 114%/W. We investigate optical inhomogeneities by measuring the quasi-phase-matching temperature curve. The ~2.7 mW of second-harmonic power at 780 nm is sufficient to detect the Rb D2 features using modulation transfer spectroscopy. The laser frequency is locked to a hyperfine transition of Rb D2 line and typical residual frequency fluctuation of ±86 kHz (rms) is achieved within 30 min. Our experimental scheme can be used for realizing robust, compact, and highly accurate Rb stabilized 1560 nm laser systems for fiber-optic communication applications.

We present a doping method to improve the femtosecond laser ablation rate and promote ablation selectivity. Doping transition metal ions, Co2+ or Cu2+, in silicate glass apparently change absorption spectroscopy and induce resonant absorption at wavelengths of 600 and 800 nm, respectively. Comparing with femtosecond laser processing of the same glass without doping, we find that the threshold fluence decreases and the ablation rate increases in resonant absorption in doped silicate glass. Resonant absorption effectively increases multiphoton ionization for seed-free electron generation, which in turn enhances avalanche ionization.

We demonstrate the laser performances of Nd, Y:SrF2 crystals with Nd3+ concentrations of 0.15 and 0.43 at.%. The sample with 0.43 at.% Nd3+ concentration yields a maximum output power of 1.023 W at 1056.9 nm with a slope efficiency of 53%. The focal length of the thermal lens is analyzed for the 0.15 at.% Nd3+-doped crystal sample. An improved cavity is designed considering the thermal lens. The maximum output power is 464 mW at 1056.9 nm, with a slope efficiency of 36.1%. The wavelength is tuned within the range of 1049.74–1059.13 nm.

We report the experimental demonstration of an ultranarrow bandwidth atomic filter by optically induced polarization rotation in multilevel electromagnetically induced transparency systems in hot Rb vapor. With a coupling intensity of 2.3 W/cm2, the filter shows a peak transmission of 33.2% and a bandwidth of 10 MHz. By altering the coupling frequency, a broad tuning range of several Doppler linewidths of the D1 line transitions of 87Rb atoms can be obtained. The presented atomic filter has useful features of ultranarrow bandwidth, and the operating frequency can be tuned resonance with the atomic transition. Such narrowband tunable atomic filter can be used as an efficient noise rejection tool in classical and quantum optical applications.

We report a compact Ho:LuAG ceramic laser intracavity pumped by a diode-pumped Tm:YAG ceramic laser. The laser oscillation is accomplished by using a common linear cavity configuration containing Tm:YAG and Ho:LuAG ceramics. The 1.0 at.% Ho:LuAG ceramic laser yields 1.15 W of maximum output simultaneously at 2094 and 2100 nm with a beam quality factor of M.2.~.2.8.

We develop a compact and high-energy Nd:YAG slab laser system consisting of an oscillator and an amplifier for space applications. The oscillator is a diode-side-pumped electro-optically Q-switched slab laser with a cross-Porro resonator. The KD*P Pockels cell with a low driving voltage of 950 V is used to polarization output coupling. The amplifier is a Nd:YAG zigzag slab pumped at bounces. The maximum output pulse energy of 341 mJ with 13 ns pulse duration is obtained from the system at the repetition rate of 20 Hz and the beam quality factors are M 2 x = 3.1 and M 2 y = 3.5. The beam pointing stabilities of the laser system are 3.05 μrad in the X-direction and 3.99 μrad in the Y-direction, respectively.

We propose a scheme for carpet anti-cloak based on the transformation optics. An anti-cloak layer is designed, which can make the external electromagnetic waves break the carpet cloak shielding. The external electromagnetic waves can be detected under the carpet cloak, while not affecting the role of carpet cloak of stealth. The Jacobian transformation tensor is calculated by numerically solving the Laplace equations with proper boundary condition. Thus, it is possible to design the anti-cloak layer of irregular shape. The simulation results demonstrate the feasibilities and flexibilities of the structure. Design details and full-wave simulation results are provided.

Photoacoustic microscopy (PAM) is recognized as a powerful tool for various microcirculation system studies. To improve the spatial resolution for the PAM images, the requirements of the system will always be increased correspondingly. Without additional cost of the system, we address the problem of improving the resolution of PAM images by integrating a deconvolution model with a directional total variation regularization. Additionally, we present a primal-dual-based algorithm to solve the associated optimization problem efficiently. Results from both test images and some PAM images studies validate the effectiveness of the proposed method in enhancing the spatial resolution. We expect the proposed technique to be an alternativeresolution enhancement tool for some important biomedical applications.

Elliptic vortex solitons are investigated in anisotropic nonlocal media with more general formulations. We address the existence and dynamics of such solitons analytically and numerically. The solution of elliptic vortex solitons depends on the eccentricity of both the input beam and nonlocal response function. With different degrees of nonlocality, we numerically investigate the evolution of the elliptic vortex solitons, and find that, typically, the elliptic vortex solitons with single and double charges collapse into spiraling dipole- and tripole-like soliton clusters, respectively.

The steady-state stimulated Raman scattering (SRS) gain with different excitation wavelengths ranging from 400 to 1100 nm of tungstate crystals, SrWO4 and BaWO4, is systematically researched. As excitation frequency is close to electronic transition frequency, molecular polarizability is not a constant, which has to be taken into account in our work. The experiment and theory agree well with each other and show that SRS gain is not only proportional to Stokes light frequency, but is also inversely proportional to biquadratic excitation frequency.

The spectrum of an electromagnetic light wave on scattering from a semisoft boundary medium is discussed within the accuracy of the first-order Born approximation. It is shown that spectral shifts and spectral switches are affected both by the polarization of the incident light wave and by the characters of the scattering medium. Moreover, numerical results show that the direction at which the spectral switch occurs is governed by the characters of the scattering medium, whereas the magnitude of the spectral switch is affected by the polarization of the incident light wave.

In trace Li analysis with degenerate four-wave mixing (DFWM) method, acid anions and major metallic elements are dominant interferences in Li-containing samples. To better use DFWM technique to analyze trace Li in actual samples, we study their effects on Li DFWM signal intensity. It is found that K, Cs, and Ni can enhance the Li DFWM signal, SO2-4..., PO3-4..., Cl-, and Ca can cause significant suppression, and NO3-, Mg, Ba, Sr, and Na almost have no effects. Finally, we use H3BO3 to eliminate the depressive effects of chlorides on Li DFWM signal. The result is also of reference in other trace elements analysis with DFWM.

The most general model of elliptical birefringence in an optical fiber is extended to describe a transient Brillouin interaction including both gain and loss. The effects of elliptical birefringence cause a Brillouin spectral shape distortion, which is detrimental for fiber sensing techniques. The model investigates the effects of birefringence and the corresponding evolution of spectral distortion effects along the fiber, and also investigates regimes where this distortion is minimal.

Quantitative knowledge of the film thickness and mass fraction of the urea–water solution is very crucial in many practical applications. Film thickness or mass fraction can only be determined individually by conventional measurement techniques. We develop a novel measurement method to measure the film thickness and mass fraction of urea–water solution simultaneously. The absorption coefficients of urea–water solution (5–50 wt%) are measured, a pair of optimized wavelengths is then chosen to achieve high measurement sensitivity. Cross validation is also performed and uncertainties of the technique are smaller than 0.68% for thickness measurements and 1.86% for mass fractions.

We report a design for one nanometer X-ray focusing by a complex refractive lens, which is capable of focusing 20 keV X-rays down to a lateral size of 0.92 nm (full-width at half-maximum (FWHM)) and an axial size of 98 nm (FWHM) with intensity gain of 49050. This complex refractive lens is comprised of a series of kinoform lenses, whose aperture is gradually matched to the converging trace of the X-ray beam so as to increase the numerical aperture (NA). The theoretical principle of the proposed complex refractive lens is presented. The NAs of these lenses are calculated. The numerical simulation results demonstrate that the proposed design can focus the X-ray beam into sub-nanometer while remaining high gain.