A four-level tripod active-Raman-gain scheme is analyzed for obtaining phase-controlled gain, phase shift, and group velocity at room temperature. The scheme can be used to eliminate significant probe field attenuation or distortion which is unavoidable in the scheme based on electromagnetically induced transparency. It is shown that the intensity gain, phase shift, and group velocity of a probe field can be simultaneously manipulated by changing the relative phase of two pump fields. The scheme is also different from that proposed recently by Deng et al. where a probe-field gain always exists. New features of the scheme presented here raise the possibility of designing rapidly responding optical switches and gates for optical information processing.

A free-space 1\times2 wavelength-selective switch (WSS) based on thin-film filter technology is proposed. The 1\times2 WSS is fabricated with an electromagnetic actuator, a reflecton prism, a narrow-band thin-film filter, and three fiber collimators. The working principle and the configuration of WSS are illuminated. The experimental results indicate a fiber-to-fiber insertion loss ranging from 1.109 to 1.249 dB with 2-V voltage input, which satisfies the application of optical fiber communication.

We make an experimental study on vibration frequency response of micro-bend optic-fiber sensor, and single-mode fibers and multi-mode fibers are used as the sensitive optic-fibers. Contrast between the two sensitive fibers is presented. Result shows that the micro-bend optic-fiber sensor has good frequency response characteristics and strong ability to restore the waveform. With the frequency varying in the range of 500-4762 Hz, the vibration sensors using multi-mode optic-fiber as the sensitive fiber is more sensitive than that using single-mode optic-fiber. And the former has better frequency response characteristics and stronger capacity of waveform revivification. But with the frequency in the range of 287-500 Hz, the latter is better.

The deconvolution algorithm is adopted on the fiber Raman distributed temperature sensor (FRDTS) to improve the spatial resolution without reducing the pulse width of the light source. Numerical simulation shows that the spatial resolution is enhanced by four times using the frequency-domain deconvolution algorithm with high temperature accuracy. In experiment, a spatial resolution of 15 m is realized using a master oscillator power amplifier light source with 300-ns pulse width. In addition, the dispersion-induced limitation of the minimum spatial resolution achieved by deconvolution algorithm is analyzed. The results indicate that the deconvolution algorithm is a beneficial complement for the FRDTS to realize accurate locating and temperature monitoring for sharp temperature variations.

We propose an all-optical modulation formats combination scheme that merges an amplitude-shift keying (ASK) signal and a differential phase-shift keying (DPSK) signal into a single differential phase amplitude-shift keying (DPASK) signal based on parametric amplification in a highly nonlinear fiber. By optimizing the power of the ASK channel, formats combination of ASK and DPSK to DPASK signal is successfully demonstrated by computational simulation. The demodulation process of the generated DPASK pulses is investigated and the relationship between optical signal-to-noise ratio (OSNR) penalty and the input ASK power is presented. The proposed scheme may be used for increasing spectral efficiency and all-optical logic device.

We investigate the characteristics of the dual-forward synchronously pumped L-band erbium-doped superfluorescent fiber source (SFS). The effects of pump ratio and fiber length arrangements on the output characteristics of the L-band SFS in terms of mean wavelength, spectral linewidth, and output power are analyzed. It is shown that the optimized pump ratio and fiber length arrangements provide broadening spectral linewidth and enhanced pumping efficiency, while the synchronous pump ensures stable mean wavelength operation. A new single-forward pumping scheme with a section of unpumped fiber is proposed to achieve a mean wavelength stable L-band SFS with a broadening linewidth of 50.4 nm and a pumping efficiency of 33.5%.

A novel algorithm for bridge recognition of median synthetic aperture radar (SAR) images using histogram entropy presented by Pun is proposed. Firstly, Lee filter and histogram proportion are used to denoise the original image and to make the target evident. Then, water regions are gained through histogram segmentation and the contours of water regions are extracted. After these, the potential bridge targets are obtained based on the space relativity between bridges and water regions using improved contour search. At last, bridges are recognized by extracting the feature of Pun histogram entropy (PHE) of these potential bridge targets. Experimental results show the good qualities of the algorithm, such as fast speed, high rate of recognition, and low rate of false target.

To address two challenging problems in infrared target tracking, target appearance changes and unpredictable abrupt motions, a novel particle filtering based tracking algorithm is introduced. In this method, a novel saliency model is proposed to distinguish the salient target from background, and the eigenspace model is invoked to adapt target appearance changes. To account for the abrupt motions efficiently, a two-step sampling method is proposed to combine the two observation models. The proposed tracking method is demonstrated through two real infrared image sequences, which include the changes of luminance and size, and the drastic abrupt motions of the target.

A novel adaptive watermarking algorithm in discrete wavelet transform (DWT) based on quantization index modulation (QIM) technique is presented. The host image is decomposed into wavelet subbands, and then the approximation subband is divided into non-overlapping small embedding blocks. The secret watermark bit is embedded into singular value vector of each embedding block by applying QIM. To improve the invisibility and robustness of watermarking system, the quantization step for each embedding block is set by combining statistical model with particle swarm optimization (PSO) algorithm. The experimental results show that the proposed algorithm not only preserves the high perceptual quality, but also effectively stands against joint photographic experts group (JPEG) compression, low-pass filtering, noise addition, scaling, and cropping attacks, etc. The comparison analysis demonstrates that our scheme has better performance than the previously reported watermarking algorithms.

A new technique is developed to measure the electrical resistivity of conductor with a nonuniform temperature profile. The calculation method is derived from the temperature dependence of the electrical resistivity. The apparatus consists mainly of a high temperature environmental chamber, a power circuit of heating, a twenty-wavelength pyrometer, and a scanning pyrometer. After getting the resistance from the voltage drop of the specimen, the electrical resistivity in a wide temperature range of the specimen can be obtained by our calculation model. Preliminary results of the electrical resistivity of SRM 8424 over a wide temperature range (1000-3000 K) are presented. The perfect consistency between the measurement results and the nominal values justifies the validity of this technique.

The Ronchi grating is applied to measure the large-aperture aspheric surfaces in a quantitative way on the basis of self-made software which includes Ronchi null grating design, collection of Ronchi graph, and data processing. The measured concave parabolic mirror has a diameter of 630 mm and an F number of 1.34. The measurement result is approximately the same as that of the ZYGO interferometer. This analysis software and test method establish a good foundation for the quantitative measurement of the big error about the large-aperture aspheric surfaces of the next generation telescope.

A mobile molecular Doppler wind lidar at an eye-safe wavelength of 355 nm based on double-edge technique is being built in Hefei (China) for wind measurement from 10-to 40-km altitude. The structure of this lidar system is described. A triple Fabry-Perot etalon is employed as a frequency discriminator whose parameters are optimized. The receiver system is designed to achieve compactness and stability by putting in a standard 19-inch socket bench. Simulation results show that within the wind speed dynamic range of +-100 m/s, the horizontal wind errors due to noise are less than 1 m/s below 20-km altitude for 100-m vertical resolution, and less than 5.5 m/s from 20 km up to 40 km for 500-m vertical resolution with 400-mJ laser energy, 30-min temporal resolution, and a 45-cm aperture telescope.

We show that a linear relation exists between the device sensitivity and the quality (Q) factor of a dual-waveguide coupled microring resonator optical biosensor when the optimal conditions are satisfied. We also show that the detection limit depends on the loss coefficient and signal-to-nosie ratio (SNR) of the overall system, rather than the circumference of the ring. For a microring resonator sensor whose Q factor is 20000, the detection limit is found to be about 10^{-7} with 30-dB SNR, which is in good agreement with reported experimental data. These results indicate that loss reduction is the top priority in the design and fabrication of highly sensitive microring resonator optical biosensors.

A numerical model is developed for the calculation of transient temperature field of thin film coating induced by a long-pulsed high power laser beam. The electric field intensity distribution of HfO2/SiO2 high reflective (HR) film is investigated to calculate the thermal field of the film. The thermal-mechanical relationships are discussed to predict the laser damage area of optical thin film under long pulse high energy laser irradiation.

A method to generate the optical quadruple frequency millimeter-wave with high power efficiency is proposed and demonstrated based on the combination of the injection 2nd-order rational harmonic mode-locked fiber ring laser technique and the fiber grating notch filter. In this approach, the fiber Bragg grating notch filter is inserted into the laser cavity to prevent the undesired optical carrier, so that the pump power can be converted to 2nd-order harmonic wave more efficiently. In our experiment, the power efficiency of optical quadruple frequency millimeter-wave (40 GHz) generation is ten folds of that of our previous method based only on the rational harmonic mode-locked technique.

A longer laser resonator length is benefit for laser linewidth, but harmful for single-frequency operation. A novel way is suggested to narrow the bandwidth of a Fabry-Perot (FP) cavity through increasing the derivative of one round-trip phase shift with respect to the frequency. It can be implemented by replacing one of two FP mirrors with a Gires-Tournois etalon (GTE), called FPGT, as a dispersion element. FPGT resonator has additional axial modes due to the GTE reflection phase shift. Theoretical analyses show that the bandwidth of additional axial modes can be 1% of that of a conventional FP cavity. A distributed feedback (DFB) laser diode can employ FPGT resonator to achieve ultra-narrow linewidth laser. It is shown that the effect of refractivity fluctuation in the gain medium on the linewidth is little, and kilohertz linewidth is achievable for such a device.

We present a novel high-energy, single-mode, all-fiber-based master-oscillator-power-amplifier (MOPA) laser system operating in the C-band with 3.3-ns pulses and a very widely tunable repetition rate, ranging from 30 kHz to 50 MHz. The laser with a maximum pulse energy of 25 \muJ and a repetition rate of 30 kHz is obtained at a wavelength of 1548 nm by using a double-clad, single-mode, Er:Yb co-doped fiber power amplifier.

To avoid the ill-posedness in the inverse problem of bioluminescence tomography, a moment searching algorithm fusing the finite element method (FEM) with the moment concept in theoretical mechanics is developed. In the algorithm, the source's information is mapped to the surface photon flux density by FEM, and the source's position is modified with the feedback through the algorithm of barycenter searching, which makes full use of the position information of the photon flux density on surface. The position is modified in every iterative step and will finally converge to the real source's value theoretically.

We numerically investigate the main constrains for high efficiency wavelength conversion of differential phase-shift keying (DPSK) signals based on four-wave mixing (FWM) in highly nonlinear fiber (HNLF). Using multi-tone pump phase modulation techniques, high efficiency wavelength conversion of DPSK signals is achieved with the stimulated Brillouin scattering (SBS) effects effectively suppressed. Our analysis shows that there is a compromise between conversion efficiency and converted idler degradation. By optimizing the pump phase modulation configuration, the converted DPSK idler’s degradation can be dramatically decreased through balancing SBS suppression and pump phase modulation degradation. Our simulation results also show that these multi-tone pump phase modulation techniques are more appropriate for the future high bit rate systems.

The conversion efficiency on the sixth harmonic of 1064 nm in KBe2BO3F2 (KBBF) at different gas pressures in two kinds of gases, helium and nitrogen, is measured and compared. In the both gases, maximum conversion efficiency on the sixth harmonic of 1064 nm in high vacuum is nearly 10% of 355 nm, which is almost four times higher than that in low vacuum. The maximum average output power at 177.3 nm is 670 \muW with the repetition rate of 10 Hz and the duration of 20 ps in high vacuum. It indicates that the sixth harmonic generation in high vacuum is more preferable than that in low vacuum.

Nonlinear materials have been well established as photo refractive switching material. Important applications of isotropic nonlinear materials are seen in self-focusing, defocusing phenomena, switching systems, etc. The nonlinear correction term is basically responsible for the optical switches. Mach-Zehnder interferometer (MZI) is a well-known arrangement for determining the above correction term, but there are some major problems for finding out the term by MZI. We propose a new method of finding the nonlinear correction term as well as the second order nonlinear susceptibility of the materials by using a modified MZI system. This method may be used to find out the above parameters for any unknown nonlinear material.

Theoretical and experimental research on the deconvolution algorithm of dwell time in the technology of computer controlled optical surfacing (CCOS) formation is made to get an ultra-smooth surface of space optical element. Based on the Preston equation, the convolution model of CCOS is deduced. Considering the morbidity problem of deconvolution algorithm and the actual situation of CCOS technology, the weighting spatial deconvolution algorithm is presented based on the non-periodic matrix model, which avoids solving morbidity resulting from the noise induced by measurement error. The discrete convolution equation is solved using conjugate gradient iterative method and the workload of iterative calculation in spatial domain is reduced effectively. Considering the edge effect of convolution algorithm, the method adopts a marginal factor to control the edge precision and attains a good effect. The simulated processing test shows that the convergence ratio of processed surface shape error reaches 80%. This algorithm is further verified through an experiment on a numerical control bonnet polishing machine, and an ultra-smooth glass surface with the root-mean-square (RMS) error of 0.0088 \mum is achieved. The simulation and experimental results indicate that this algorithm is steady, convergent, and precise, and it can satisfy the solving requirement of actual dwell time.

For our KDP crystal orientation, various thermo-optic (TO) and relevant temperature-dependence parameters are defined, presented, and studied in the framework of a transverse and a longitudinal electro-optic (EO) modulation systems. This study is based on the concept of the so-called opto-electrical bias ([EQUATION] applied to the system. For both of the above EO-modulation systems, a set of original equations is extracted and investigated with regard to each of the more important TO or temperature coefficients. Using these equations, for these parameters the role of the transverse configuration is examined in comparison with its corresponding longitudinal configuration. A comparison is done with other orientation of the same KDP crystal.

We investigate theoretically two-photon absorption spectroscopy modified by a control field in a confined Y-type four-level system. Dicke-narrowing effect occurs both in two-photon absorption lines and the dips of transparency against two-photon absorption due to enhanced contribution of slow atoms. We also find that the suppression and the enhancement of two-photon absorption can be modified by changing the strength of the control field and the detuning of three laser fields. This control of two-photon absorption may have some applications in information processing and optical devices.

The performances of HfO2/SiO2 single- and multi-layer coatings in vacuum influenced by contamination are studied. The surface morphology, the transmittance spectrum, and the laser-induced damage threshold are investigated. The results show that the contamination in vacuum mainly comes from the vacuum system and the contamination process is different for the HfO2 and SiO2 films. The laser-induced damage experiments at 1064 nm in vacuum show that the damage resistance of the coatings will decrease largely due to the organic contamination.

The luminescence dynamics of a polypyridyl ruthenium II [Ru(phen)2(ip)]2+ and 5,10,15,20-tetraphenylporphyrin (H2TPP) dyad have been measured by using time-resolved fluorescence spectroscopy. The transient luminescent spectra of the dyad show an ultrafast energy transfer within 300 ps after photoexcitation of the [Ru(phen)2(ip)]2+ at 453 nm. However, no energy transfer has been observed as the excitation wavelength is 400 nm, corresponding to the absorption peak of H2TPP. The origin of the energy transfer from [Ru(phen)2(ip)]2+ to H2TPP has been analyzed according to the Forster energy-transfer theory.

The electron thermalization and relaxation processes in ferromagnetic nickel thin film and micro-nano-structure film have been studied by measuring the transient change after excitation by a femtosecond laser pulse. The measurements indicate that the electron thermalization time is between 18 and 47 fs. This is somewhat faster than the value reported before. And the thermalization time of the micro-nano-structure film is much longer than the nickel film. We deduce that it is caused by the discontinuity of the electron band close to the Fermi level in the micro-nano-structure nickel film.

The transient time-resolved reflectivity of chromium film is studied by femtosecond pump-probe technique with a 70-fs laser. Experimental results show that the reflectivity change increases with the power of the pump laser. The fast decrease of the reflectivity occurs between 0-200 fs which is mainly due to the electron-electron interaction. Subsequencely, the slower recovery of the reflectivity between 200-900 fs is mainly due to the electron-phonon coupling process. The reflectivity after 900 fs rises little to a near-constant value for the thermal equilibrium of the system. The experimental results can be explained properly with numerical simulation of the two-temperature model. It is helpful for understanding of the electron ultrafast dynamics in chromium film.

A phase modulator is employed in the scheme of soliton pulse compression with dispersion shifted fiber (DSF). Stimulated Brillouin scattering (SBS) effect, as a negative influence here, can be dramatically suppressed after optical phase modulation. The experimental result shows that the launched power required for high-order soliton pulse compression has been significantly increased by 11 dB under the condition of 100-MHz phase modulation. Accordingly, the experiment of picosecond pulse compression generated from electro-absorption sampling window (EASW) has also been implemented.