Optoelectronic oscillator (OEO) is a hot topic recently and the tunability is one of its important performances. The step of the tunable performance at present is about 125 MHz and the step is long, which can be defined as coarse tuning. An experiment is made to prove the OEO based on phase shifter which can be finely tuned. By changing the voltage of the phase shifter, the phase shift of the oscillation frequency in the ring cavity can be tuning. The time delay in the loop will be changed which will change the oscillation frequency. Because the amount of phase shift of the phase shifter can be fine-tunned by the voltage, we can achieve a fine tunability. In the experiment we use an electrical phase shifter whose maximum phase shift is 180° realizing a fine-tunning OEO with the step of 70 KHz from about 10.02 GHz to 10.025 GHz,the range of 5.5 MHz.

In inversion endoscope surgery, high-accuracy tracking for medical instruments is demanded. Traditional electromagnetic tracking (EMT) methods are confined by their low robustness and high complexity, which restrict EMT from clinical application. To solve the problems, an inertial measurement unit (IMU) is added to EMT system to realize multi-sensing tracking. The effective fusion techniques provide anti-interference ability for the tracking system. At the same time, IMU can also help to simplify EMT and improve practicality on system level. The experimental results show that orientation error is less than 1°, and position error is less than 3 mm. Even under disturbances, orientation error can be controlled under 3.5°, which meets the clinical requirements.

The aim of the present study is to examine whether low level Ga-Al-As laser irradiation has an effect on hedgehog signaling pathway during osteoblast proliferation in vitro. The molecular mechanism of how low level Ga-Al-As laser irradiation promotes bone formation is explored. This study provides a theoretical basis for the clinical application of low level Ga-Al-As laser irradiation in oral implant. Mouse osteoblastic cell line MC3T3-E1 is cultured in vitro. The cultures after laser irradiation are treated with recombinant N-terminals sonic hedgehog (N-Shh) or hedgehog inhibitor cyclopamine respectively. The experiment is divided into 4 groups. The proliferation activity is detected by cell counting, MTS, flow cytometry at 12, 24, 48, 72 h after laser irradiation. Proliferation activity of laser irradiation and N-Shh group is remarkably increased compared with those of laser irradiation group. Proliferation activity of laser irradiation and cyclopamine group is remarkably decreased compared with those of laser irradiation group, meanwhile proliferation activity of laser irradiation and cyclopamine group is remarkably increased compared with those of control group. These results suggest that low level Ga-Al-As laser irradiation activate hedgehog signaling pathway during osteoblast proliferation in vitro. hedgehog signaling pathway is one of the signaling pathways by which low level Ga-Al-As laser irradiation regulates osteoblast proliferation.

Gabor on-axis digital holography is suitable for the situation that light transmission energy is much more than the energy blocked by the target. Therefore, the reconstruction study on the small target at different lateral positions has important application value. The experiments on 2.52 THz Gabor on-axis holographic imaging at different lateral positions are conducted, the Tukey window function and the angular spectral method are combined to realize two-dimensional reconstruction, and the results are compared and analyzed. The experimental results show that the algorithm proposed inhibits the aperture effect and also improves the contrast ratio of the whole image. The reconstruction performance of the target close to the central position of the detector is slightly better than that near the edge.

The remote sensing image is susceptible to the clouds and fog. In order to improve the output quality of low contrast image and maintain the details, an image enhancement algorithm based on Gaussian mixture modeling (GMM) is proposed. The histogram of original image is smoothed with a 1×3 filter. The best parameters of GMM is got by fitting the histogram with the expectation maximization (EM) algorithm, and the histogram is separated into sub-histograms based on the optimal intersections. The mapping of output image is got according to the Gaussian parameters, and the final enhanced image is obtained. Results of experiments show that the algorithm can determine the optimal number of clusters adaptively and improve the speed of the histogram fitting which costs 0.37 s averagely. Comparing with traditional methods, the enhancement result is superior in terms of objective evaluations of related information entropy and texture information. It can improve the contrast of the remote sensing image while maintaining the details effectively.

The method of using the continuously adjustable terahertz optical asymmetrical demultiplexer (TOAD) structure to tailor the duty ratio of return to zero (RZ) code is proposed. And the dependence of the additional window on the recovery time of semiconductor optical amplifier (SOA) in the TOAD loop is analyzed. For 2.5 Gb/s RZ code, experiments are demonstrated to compress the duty ratio from 50% (200 ps) to 25% (100 ps) and then 10% (40 ps), and broaden from 25% to 50%. The experiments indicate that with the TOAD structure, the duty ratio can be broadened up to 100% (RZ to NRZ), and can be narrow to picosecond or even sub-picosecond, if the switch window of the TOAD is tuned narrower.

Based on the experiments of fiber laser beam welding 6061 aluminum alloy with 2.5 mm thickness, the effects of heat input on full penetration weld appearance are investigated. The results show that the weld width of the penetration weld increases with increasing the heat input, and the change amplitude of the weld back is greater than that of the weld front. When the stable fully penetration weld is used, a higher laser power results in a broader adjustable range of the heat input. Fine columnar microstructure is formed near the fusion zone, and the mixed microstructures (including columnar grains and equiaxed grains) is distributed in the center of the weld. When the heat input is reduced, the microstructures of the weld zone tend to fine, and the proportion of the equiaxed grains in the mixed microstructures decreases. In addition, with the heat input decreasing, the microhardness of the weld zone increases slightly, and the microhardness data dispersity between the weld up and weld bottom decreases. When the heat input is about 90 J/mm, the microhardness symmetry of weld up and weld bottom is best.

Ceramic materials have excellent properties, but their surface qualities are poor. The surface quality of ceramic materials can be effectively improved using short-wavelength laser polishing technique. Experiments are conducted according to existing different forms, such as melting, vaporization, micro-cracks, splashes of molten material and photochemical effects etc, while ultraviolet (UV) laser is polishing Al2O3 ceramics. Through observing polished surface morphology, the mechanism of UV laser polishing Al2O3 ceramic is studied, and the morphology, adhesive force, elementary composition and main crystalline phase of white powder in high energy density are analyzed. The mechanism of UV laser polishing Al2O3 ceramics is further confirmed.

Ni-based composite coatings with different nano-TiC/C additions are prepared by laser cladding on the 38CrMoAl steel substrate. The influence of nano-TiC/C on the microstructure and properties of the coatings is investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), Vickers hardness tester, and friction wear testing machine. The results show that the composite coatings mainly consist of γ-Ni, Ni3B, and M23C6 phases. But what changes is that with the increase of the nano-TiC/C additions, the numbers of the primary γ-Ni dendrites present the trend of first increasing and then decreasing, whereas their sizes change is reversed. The TiC particles are observed as the nano-TiC/C addition mass fraction is higher than 3.5%, and their sizes and number gradually increase with the further increase of the nano-TiC/C addition. The hardness values of the composite coatings gradually increase with increase of the nano-TiC/C additions, as a result of the refinement of the solidified structure and the reinforcement of the TiC particle. Whereas the wear resistance is the highest as nano-TiC/C addition is 5.0%, which results from high surface and internal perfections of the fine TiC particle, as well as its good compatible deformation capability with the surrounding matrix.

The laser beam with pre-gasification pulse is used in titanium Ti6Al4V laser spot weld bonding test. The influence of residual carbon from adhesive pyrolysis on microstructure and properties of titanium laser spot weld-bonded joint is studied. The results show that lots of TiC appear in the titanium weld-bonded joint because of residual carbon from adhesive pyrolysis, and interface reaction zone compose mainly by TiC appear in the interface between spot-welded joint and adhesive layer. The residual carbon that affects the microstructure of titanium laser spot weld-bonded joint is mainly from the pyrolysis in the pre-gasification pulse, and the residual carbon which composes interface reaction zone is from the back flow of adhesive after the joining process. The advent of TiC increase the hardness of titanium weld-bonded joint, but also has an adverse effect on the tensile-shear load of titanium weld-bonded joint.

Laser cutting liquid crystal display (LCD)-glass is a complex process of interaction between laser and material. In thermal cracking method laser cutting, the size of the crack tip stress intensity factor (SIF) decides whether the crack extends in the whole cutting process. The size of the crack tip SIF during cutting process is calculated using thermal weight function, comparing with the fracture criterion judges the crack′s extension situation. The effects of laser power, spot radius, the cutting speed and crack length on the crack tip SIF are studied. It is concluded that the greater the laser power, the smaller the cutting speed, and the smaller the spot radius, the faster the crack tip SIF increaseing the bigger the peak value. Under different crack lengths, the crack tip SIF increase speed and the peak value are also different. The experimental verification illustrates the feasibility of this technology.

Microstructure evolution of Ni-33%Sn (mass fractiion, similarly hereinafter) alloys during laser remelting is investigated by placing on the copper plate, titanium plate and refractory brick, respectively. The result shows that the microstructure of samples on three different cooling plates is quite similar as for thoroughly melting of Ni-33%Sn alloy and the anomalous eutectic structure can be obtained at the bottom of the molten pool. The area of anomalous eutectic on copper plate is significantly larger than those on the other two cooling plates. Free nucleation at the bottom of the molten pool and rapid growth lead to the generation of anomalous eutectic. The epitaxial growth behavior on both sides of the molten pool and the epitaxial growth conditions after high speed free nucleation and growth at the bottom of the molten pool lead to the small area of the anomalous eutectic at the bottom of the pool. The greater thermal conductivity of copper plate makes faster cooling rate and larger nucleation region at the bottom of the sample, which leads to larger area of anomalous eutectic than those of the other two cooling plates.

The nonlinear propagation characteristics of intense laser with circular aperture diffraction in Kerr medium are stuied by experiments. We experimentally observe the formation of small-scale filaments, the evolution of single filament and the interaction between filaments. Results show that modulation growths take place at particular spatial positions and lead beam breakup into multi-filamentation during nonlinear propagation. The single filament intensity is not growing indefinitely, but to release the excess energy by the cone emitting after reaches a certain value. At the same time, new filaments form owing to the interaction between the background energy and the released energy. The filaments in close proximity through the interference interaction, make new filaments form in their neighborhood.

A high-repetition-rate electro-optic Q-switched single longitudinal mode laser has been developed. Using a fast electronic circuit negative feedback control system, the laser cavity generates dissipation varying with laser intensity and the quasi-continuous prelase is established, then the Q-switch is turned on based on this prelase. Stable single longitudinal mode laser output is generated with the mode selection of the resonant reflector. The laser has produced pulse with width of 15 ns, maximum pulse energy of 2 mJ at 1 kHz repetition rate, and single longitudinal mode probability of 100% within 30 min. The laser system is compact, simple, reliable and has been used as a master oscillator of master oscillator power-amplifier (MOPA) systems.

Based on the extended scalar nonlinear Schrdinger equation, the influence of pumping schemes on the properties of dissipative solitons is investigated theoretically in passively mode-locked ytterbium-doped fiber laser with positive dispersion cavity. The results show that, under the condition of the same initial overall gain, the dissipative solitons obtained in the backward-pumped fiber laser have narrower spectral width, shorter pulse duration and higher pulse peak power than those of forward pumping scheme for the given gain saturation energy. Moreover, the linear fitting degree of the pulse chirp is lower. For the forward pumping and backward pumping schemes, the pulse energies of the dissipative solitons are equal with the same gain saturation energy, but the differences of the output spectral and temporal waveforms increase as the incrense of the gain saturation energy.

Continuous-wave tunable deep ultraviolet (UV) laser is commonly realized by extra-cavity frequency doubling of near infrared ray (NIR) or visible laser, but the bandwidth of cavity locking circuits limits the tunability of laser. A feed-forward control method is applied in the frequency quadrupled UV laser, which is used for laser cooling of neutral mercury atom; that is to say, synchronous adjust ment two series frequency doubling cavity when tuning the frequency of fundamental laser. By this method, not only the power noise is induced by laser frequency tuning reduced, but also the frequency tuning range of the UV laser is enhanced. Hence, the tunability of UV laser is considerably increased. When the laser frequency on the Doppler-free dichroic locking spectroscopy of neutral mercury atom is locked, it is found that the laser frequency noise can be reduced by the application of feed-forward control circuit. The enhancement of the tunability and stability of UV laser provides a lot of advantages in the experiments of laser spectroscopy and laser cooling of mercury atom.

In order to realize the high-power narrow linewidth of vertical cavity surface emitting laser (VCSEL), the shallow surface relief rectangular structure (SR VCSEL) is designed. The difference of the current density distribution leads to the mode distribution different. Calculation results show that, compared with circular mesa VCSEL, the uniformity of the current density distribution of rectangular mesa VCSEL is not changed when the active area is increased. And theoretical results indicate that the threshold gain of high-order mode increases greater than that of the fundamental mode when etching shallow relief of surface. In the experiment, the power of 5.87 mW when current is continuous, spectral width of 0.1 nm, power polarization degree of 10, and transverse mode suppression ratio more than 30 dB are obtained.

A simple photonic approach to generate tunable microwave signal with a Brillouin fiber ring laser in a figure of eight configuration is proposed and experimentally demonstrated. A dual wavelength optical signal with about 20 GHz or 0.16 nm frequency spacing is achieved by removing the odd-order Stokes lines. The power variation of the first order Stokes and third order Stokes is less than ±0.35 dB. The optical signal is heterodyned at the high speed photodetector (PD) to produce a 21.39 GHz microwave signal. The signal-to-noise rate (SNR) of the microwave signal is about 20 dB. The 3 dB linewidth is estimated as 2 MHz. The power variation of microwave signal is less than ±0.75 dB. 3 dB linewidth of microwave signal is also about 2 MHz by beating Brillouin pump and the second order Stokes. Tunable microwave signal under ±0.28 GHz can be obtained by adjusting the wavelength of pump laser. ~20 GHz tunable microwave signal can be achieved by the proposed scheme, and the result can be used to improved microwave signal in future.

The spatial coherence properties of high power vertical cavity surface emitting lasers (VCSELs) are studied based on the theorem of partially coherent light proposed by Van Cittert-Zernike. The interference stripe patterns are gauged using the Young′s double-slit experiment for the devices of 980 nm wavelength VCSEL single emitters. Then interference patterns are switched to grayscale by intensity distribution patterns for data collection. In this paper, the integral average value method is proposed to calculate the degree of spatial coherence. The proposed integral average value method and traditional average method are used respectively to calculate the light intensity of the pattern. The results are compared with those calculated by the theoretical value of Van Cittert-Zernike theorem. The VCSEL optical apertures′ influence on coherent characteristics are also discussed. The experimental results show that, a relative error within 2.5%～9.4% is reached by our integral average value method. On the contrary, a relative error of 7.5%～67.4% are got from the traditional average method. Apparently, traditional average value method causes the error generally 1.5～27 times worse than our integral average value method. Moreover, for single emitter VCSELs with optical aperture from 200 μm to 500 μm, the smaller the optical aperture are, the larger the coherent degrees (between 0.731～0.426) are. The conclusion can be wildly used on theoretical and experimental design for VCSEL coherent arrays.

Multi-pass amplification beam path alignment is based on cavity mirror alignment. To optimize multi-segmental parallel cavity mirror alignment algorithm of high power solid-state lasers, a new algorithm of multi-pass beam path cavity mirror alignment based on diffraction symmetry is proposed, and the algorithm avoids the problem of low alignment accuracy caused by image quality. The accuracy of multi-pass amplification beam path alignment is improved from 8 μrad up to 3.96 μrad. It has been verified on SG-Ⅲ facility.

Linear structured light scanning is a common method for three dimensional (3D) detection, which is used to detect the targets both in water and air. A method for achieving simultaneously 3D and color information is proposed based on the line scanning system. The true color and 3D information of underwater object can be reconstructed based on the principle of color mixing and color space transformation, red, green, and blue are used as three colors light sources. Experiments demonstrate that the targets can be 3D reconstructed with true color texture at millimeter scales.

Metallic nanoparticles can be synthesized by photochemical reduction method with controllable shape and size, hence the photochemical reduction method has become one of the hot topics in the area of metallic nanoparticle synthesis. A method for fabricating large area metallic grating is provided. Gold nanoparticles are synthesized via photochemical reduction method. Nanoparticle gratings are deposited on the glass substrate under illumination of two coherent beams. Surface plasmon polaritons (SPP) are excited by the grating efficiently. The period and the surface features of metal-gratings can be controlled by adjusting the introduced light beams. After half hour annealing treatment under 400 ℃, the grating become smoother and the excitation angle of SPPs gets closer to the theoretical value.

Optical gas sensor material adsorption gas molecules lead to changes in optical properties to detect environmental gas composition, which is called optical gas sensing effect. Microscopic characteristics of rutile titanium dioxide (110) surface adsorption H2S molecules are studied, under the first-principles plance-wave ultrasoft pseudopotential method based on density functional theory (DFT) system, and adsorption energy, charge density, density of states and optical properties of TiO2 (110) surface are calculated. The results show that, the most stable surface is TiO2 (110) surface which terminated on the two coordinated O atoms; only containing oxygen vacancy surface can stably adsorb H2S molecules; the higher of the oxygen vacancy concentration, the higher adsorption energy; the main way of surface adsorption H2S molecules is horizontal adsorption. When oxygen vacancy concentration reach 33%, adsorption energy is 0.7985 eV. The adsorption essence is surface oxygen vacancies oxidation H2S molecule. In the visible light range of 400~760 nm, the surface optical properties can be improved only when H2S molecules adsorption on containing oxygen vacancies surface, moreover, the higher concentration of oxygen vacancy, the more obvious improvement of absorption, reflection ability and optical gas sensing performance.

A kind of polymer/SiO2 hybrid Mach-Zehnder interferometer (MZI) variable optical attenuator (VOA) is designed and fabricated. The VOA has lower power consumption than the VOA based on inorganic materials and faster response than the polymer VOA. The cross section size of the single mode waveguide is designed and optimized according to the single mode transmission conditions of ridge waveguide, and the structure of device is also simulated. The VOA with low power consumption and fast response is obtained by using the photolithography and wet-etching fabrication processes. With 1550 nm optical communication wavelength, the dynamic attenuation range of the fabricated VOA is 23 dB and the maximum power consumption is 14 mW. The rise and fall times of the device are 252 μs and 384 μs. The experimental results show that the VOA has a lower power consumption and a faster response with using the organic/inorganic hybrid structure and optimizing the device structure.

The edge effect appears at the edge of workpiece as a result of the uneven distribution of pressure in computer controlled optical surfacing (CCOS) and this restricts the fabrication accuracy in practice seriously. The edge effect has become one of the urgent problems of numerical control machining technology. Theoretical simulation and experimental verification are done based on liner pressure distribution model and skin pressure distribution model. The experimental results show that when the distance between the workpiece and the tool borders is relatively large (the distance is 1/3 of aperture of removal function in experiment) or short (the distance is 1/24 of aperture of removal function in experiment). Little difference between removal functions based on both of the models is observed and the effectiveness of the models is proved that when the distance is medium(the distance is 1/6 of aperture of removal function in experiment), the removal function based on linear model is closer to the experimental result and the skin model has a biggr deviation with the experiment result in the central area.

Interferometry is among the widely-used precise metrologies in varieties of science and engineering fields. An easy-to-control moire interferometric angular measurement method based on multi-diffraction of dual gratings is proposed, to facilitate tilt remediation and in-plane angle adjustment between mask and substrate in proximity lithography, as well as related applications in micro/nano devices and micro-optoelectronics system etc. This method aims to take advantages of symmetric and similar orders generated from dual-gratings diffractions to realize the (m, -m) and (m, 0) interferometry, in which fields with phase distribution associated with tilt and in-plane angle are formed. The fundmental of presented moire interferometry is derived in detail and related schemes of (m, -m) and (m, 0) interferometric measurement are introduced. Specifically, both schemes monitor the tilt and in-plane angle according to the fringe deflection and frequency variation in an on-axis and off-axis manner respectively. Corresponding composite gratings are designed for experimental verification. Experimental and analytical results indicate that the tilt and in-plane angle can be adjusted with an accracy below 10-3 rad and 10-4 rad, respectively.

Mid-infrared spectrum region is the fundamental absorption band of molecules. Tunable diode laser absorption spectroscopy (TDLAS) technology can be applied to detect greenhouse gas sensitively by scanning a single molecular absorption line. A miniaturized system based on the combination of direct absorption method and a 2704 nm band laser is presented, which is utilized to monitor carbon dioxide. Also, the digital signal processor (DSP) data acquisition system can be applied to acquire and process the absorption signal, as well as to revise the concentration according to the environment temperature and altitude. In order to eliminate the shift of wavelength and ensure the detection accuracy, the wavelength locking module is used and finally a SD card is used for data storage. The system is powered by a battery, the response time is 1.6 s and the detection limit is 5×10-7. It takes a long time to test the system, which ensures its stability and feasibility.

A new pixel matching method is proposed based on two-dimensional empirical mode decomposition (2D EMD). It combines with five steps of unequal step algorithm and is applied to the on-line three-dimensional shape measurement. A sinusoidal fringe is projected on the measured object moving with a constant speed. The object′s movement can produce the corresponding phase shifting deformed patterns. And five arbitrary deformed patterns are captured by CCD within a duty cycle of the grating pattern. The deformed patterns are decomposed with 2D EMD method. The mode patterns which is consistent with the object′ surface shape are obtained. And then Otsu algorithm is used to do the binarization. The higher reliability of the area is segmented to be regarded as a template to realize the pixel matching. And the equivalent shifted phase deformed patterns in which the points are one-to-one corresponding are calculated. Then, the five unequal steps phase shifting algorithm is used to obtain the wrapped phase, which forms unwrapped phase by the phase unwrapping algorithm. And the surface information of the measured object is retrieved via the phase-height formula. The computer simulations and experiments prove the feasibility of this method.

In order to improve the situation of laser ranging signal extraction problem and degree of automation, the feature of laser ranging data are listed, considering these feature and combination of binary image analysis a new method extracting the signal from the laser ranging data that contain a lot of noise is proposed. Before removing the noise the original data should be mapped into a binary image matrix in the method. According to the density of signal is higher than noise, the first step is done to remove the noise in the image matrix. The second step is done to remove the noise based on the feature that the signal is similar to a line in the image. The result of the image which has been processed should be inversely mapped back. The experimental results show that it is a potential method which can extract signal automatically and replace artificial methods.

Random changes of atmospheric turbulence have restrictions on the performance of satellite-to-ground laser communication. High-speed laser communication proposes new requirements on the description of turbulence characteristics in a short period. A direct, real-time measurement of atmospheric coherent length method based on lateral shearing interferometry is proposed. By measuring the sheared phase distribution of the phase distortion caused by atmospheric turbulence, considering that the time average of phase structure function is equal to the ensemble average when the turbulence is an ergodic random process and combining the Fried phase structure function, the atmospheric coherent length can be measured. Experiments are conducted by using a 635 nm laser wave through a 1.2 km distance. The results demonstrate the feasibility of this method, and solve the constraints in time accumulation and statistical analysis of the traditional measurements.

A method for a workpiece surface mass loss detection is presented based on wavelet transform. In order to obtain the surface morphology information, two-dimensional laser sensor is applied to measure the workpiece. The three-dimensional point cloud data obtained are analogous to the pixel point cloud in the grayscale image. The wavelet transform edge detection method is used to extract and locate the workpiece surface characteristics area and then to calculate the volume loss and mass loss on the surface of the workpiece. The detection experiment is performed for the damage on the surface of the steel material workpiece. The experiment for the steel material workpiece surface mass loss proves the feasibility of the solution. The results show that the tested workpiece damage quality detection accuracy can reach milligram level. The system is suitable for the measurement of big volume or big mass workpiece surface damage and evaluation of the material properties.

Refractive index of D-Glucose solution in many areas such as scientific research and industry has very important applications. It′s very important to measure the refractive index accurately. The beam splitter prism interferometry is used to measure refractive index of D-Glucose solution at different temperatures with different concentrations. The basic principle of this method and apparatus is introduced. The refractive index of a sample of known calcium chloride solution is measured by the system and contrasted with literature values to verify its reliability. The accuracy is up to 10-4. In order to research the characteristics of D-Glucose solution, diversifications of D-Glucose solution′s refractive index at different temperatures measured and plotted into graphs. Error analysis is conducted as well. The results can provide help for medicine and biology.

In order to make quantitative analysis to the accuracy crystal thickness in the birefringent filters, based on the fundamental filter theory, by introducing the birefringent dispersion of crystal, the exact relationship of crystal thickness accuracy, phase retarder deviation and spectrum shift is built up. Theoretical analysis and simulation are put forward strictly. The results show that the birefringent dispersion cannot be neglected when using LiNbO3 as the materials of plates and that the crystal thickness accuracy can ensure a good transmission spectrum, which may be useful for constructing high-performance birefringent filer.

Probing the liquid film at two wavelengths with different absorption cross-sections allows eliminating the effect of additional broadband signal losses, e.g., minor beam steering. However, severe beam steering effects due to the shrinking of the liquid film at the end of the evaporation process can not be avoided. The effect is studied by measuring the film thickness on quartz plate during film evaporation process with two-color tunable diode laser absorption spectroscopy (TDLAS) method, and shadowgraphy images are simultaneously taken to track the change of film shape. Severe beam-steering effects are reduced in the developed two-line TDLAS film-measurement sensor by using an integrating sphere in front of the detector. The sensor is then applied to obtain the film thickness variation in the flow channel during the film build-up by impinging of water droplets and the evaporation of liquid film.

In order to suppress the third-order crosstalk caused by the nonlinearity of the IQ modulator in the recirculating frequency shifter (RFS), and to improve the flatness of the multi-carriers and carrier to noise ratio (CNR), a modified RFS scheme based on linear IQ modulator (LIQM-RFS) is presented to generate multi-carriers. According to theoretical analysis, the range of driving voltage of linear IQ modulator (LIQM) radio frequency (RF) source which can be selected is twice of that of IQ modulator, with the premise of effective suppression of the third-order crosstalk. In particularly, the third-order crosstalk loss can still be repressed in a range where the first-order harmonic component of LIQM is shifted at a higher efficiency. With this feature, LIQM-RFS-based multi-carrier generator ensures the flatness of subcarriers, meanwhile it requires lower erbium-doped fiber amplifier (EDFA) gain. Therefore, the power of amplified spontaneous emission noise caused by the optical amplifier is lower, by which the CNR is improved. The simulation results show that CNR of multi-carrier generated by LIQM-RFS multi-carrier generator increases by about 9 dB compared to traditional RFS, and the subcarrier flatness of about 2.95 dB can be ensured.

According to the definition of the orbital angular momentum (OAM) density, it can be deduced that the high-order Bessel beams have the OAM just as the high-order Laguerre-Gaussian beams and its divergence angle is zero. Based on this theory, an optical fiber of ring refractive index distribution is proposed to transmit the high-order Bessel OAM beams. A theoretical analysis of the OAM modes which can propagate in this optical fiber is presented and graphs of the intensity and phase distributions of these modes are obtained by simulation. The analysis result is that the number of the OAM modes transmitted in the fiber does not vary linearly with the change of any single parameter, and it depends on the number of all Bessel function roots between the normalized frequency range of the inner and outer diameter of the ring fiber.

With the configuration of two-stage amplifying, the high power fiber amplifier with gain clamping and gain flattening is constructed. It makes gain flattened and gain clamped using fiber loop mirror (FLM) combined with two fiber Bragg gratings (FBGs). The output performance of the amplifier is tested, which shows that the maximum output power is 1.399 W and the gain fluctuation is reduced to ±0.75 dB in the range from 1535 nm to 1547 nm. Under the conditions of inputing small power and high power signals, the gain control characteristics of amplifier are researched, respectively. As the input power of channel 2 changing from -33.7 dBm to -2.5 dBm or -14.8 dBm to 16.4 dBm, the excursion ranges of channel 1 can be 0.04 dB and 0.06 dB, respectively.

Aiming at the shortcomings of the existing multiplexers, a pattern of the asymmetric planar waveguide type mode division multiplexer/demultiplexer is designed, based on the effective refractive index matching effect. Waveguide structure consists of a main boom and two waveguide branches. The parametric principle to design the asymmetric planar waveguide type mode division multiplexer/demultiplexer is discussed. The performance of mode multiplexing/de-multiplexing is simulated under different waveguide width ratios, and the best waveguide width ratio is determined. The transmission process and the light field energy flow processes of fundamental mode and first-order mode are analyzed. The simulation results show that the asymmetric planar waveguide type mode division multiplexer/demultiplexer has a good performance of mode division multiplexing/demultiplexing, and the mode conversion can be realized efficiently. The properties, such as simple structure, high mode conversion efficiency, easy integration, make it more suitable for mode division multiplexing communication.

In order to meet the requirement of determining the azimuth angles in fabricating optical devices from photonic crystal fibers (PCFs), a method based on analyzing the forward scattering patterns is proposed. The PCF sample is illuminated transversely by a laser of 650 nm, and the forward scattering patterns and the tip microscopic images are simultaneously recorded. The summary of local intensities of the forward scattering patterns is chosen as the characteristic value. The characteristic value presents good correspondence to the azimuth angles of photonic crystal fiber by comparing the half-image summarized intensities of the forward scattering patterns. Based on this correspondence, the special azimuth angle can be determined. The accuracy within 0.5° obtained in the applications to three kinds of PCFs proves that the proposed method is effective and universal. This method is simple in operation, accurate in determination, and is expected to play an important role in the axial orientation in the fabrication of PCF based devices.

The waveguide structure of the large-mode microstructure fiber is designed in view of the efficient coupling and laser output quality during the practical application of the high-power fiber laser. It employs the bundle drawing technology to prepare the ytterbium-doped microstructure fibre with the core diameter of 41 μm, inner-cladding numerical aperture of 0.62, core numerical aperture of 0.05 and effective mode area of 530 μm2. The output power of the single-mode laser is 19.1 W, the slope efficiency is 55.2% and the beam quality factor of M2 is less than 1.01, on the condition that the pump power is 35.0 W.

In Brillouin optical time domain reflectometer (BOTDR) system, the Brillouin scattering signal is so weak that the sensing distance is usually limited and thus the signal to noise ratio and measurerent precision are influenced in system. Therefore, the forward and backward Raman amplification of Brillouin scattering signal in BOTDR system is studied. The experimental results show that the stimulated Brillouin scattering (SBS) threshold by the backward pump Raman amplification is higher than that by the forward pump Raman amplification. When the pump power is 700 mW, the gain of the forward pump is about 13.78 dB, then the amplified gain will decrease because of the occurence of the second order Brillouin scattering spectral line. When the pump power is 1000 mW, the gain of the backward pump is about 16.33 dB, and it still has the growth trend subsequently, which is beneficial to the continuous amplification of the Brillouin backscattering signal.

Kerosene, diesel and gasoline are taken as research objects without considering each oil′s components. By fluorescence spectroscopy analysis, a dimension reduction method that turns three-dimensional spectrum into two-dimensional spectrum is proposed by linking the spectral datum matrixes end to end , drawing its envelope and extracting the apparent statistic (the standard deviation, coefficient of kurtosis and coefficient of skewness are chosen). The method is applical to the systems of certain degree of spectral overlap but low spectral shape similarity. The recognition rate of the oils is over 98% with clustering analysis. According to the Lambert-Beer law, fitting curve of fluorescence intensity and concentration is used for quantitative analysis and standard addition recovery rate is over 95%. Distinguish efficiency is increased by 43%, compared with the parallel factor method used commonly.

A transversely chirped volume Bragg grating (TCVBG) is used as an external cavity diode laser to realize a simple, narrow line width, wavelength stability and continuous tunable external cavity diode laser. The wavelength stability and narrow spectral width characteristics of the external cavity diode laser using TCVBG is demonstrated. The wavelength tuning characteristics and power characteristics of TCVBG is analyzed. Experimental results indicate that the wavelength of the diode laser is locked and the linewidth is narrowed sharply under the effect of TCVBG external cavity. The continuous tuning output spectra is achieved by moving laterally relative position TCVBG. The continuous tuning range from 800 nm to 815 nm is implemented. The spectral line width (full width at half maximum, FWHM) is less than 0.3 nm. An output power of 2.01 W is also obtained and the power stability is less than 1.5% over the investigated tuning range.

The aim of this study is to develop a rapid offshore eutrophication assessment technique by parallel factor analysis (PARAFAC) and partial least squares regression (PLSR) based on fluorescence excitation-emission matrix spectroscopy (EEMs) of chromophoric dissolved organic matter (CDOM), UV-visible spectroscopy of CDOM, dissolved oxygen (DO), chlorophyll a (Chl a) and turbidity (Tur). EEM-PARAFAC model identifies three fluorescent components, two humic-like (C1 and C2) and one protein-like (C3). a220, a254, a270, a350, C1, C2, C3, DO, Chl a and Tur are selected to study their correlations with total phosphorus (TP) and total nitrogen (TN). Using trophic index (TRIX) as the reference, the model for rapidly evaluating eutrophication status is developed by PLSR. The correlation coefficients of the PLSR model are 0.9721 for the training data and 0.9827 for the validation data，and the classification accuracy is 89.0% for the validation data. The results prove that optical parameters of CDOM can be as substitutes for TP and TN in rapid assessment of offshore eutrophication.

Laser tweezers Raman spectroscopy (LTRS) is used for real-time investigation of the overexpression of broad bean 14-3-3b soluble protein and inclusion body protein in the single living Escherichia coli cell at different temperatures after induction with isopropyl thiogalactoside (IPTG). The results show that 14-3-3b soluble protein and inclusion body protein have significantly different Raman characteristic peaks, which reflects that the two kinds of proteins have distinct conformations in their main chains and side chains. Intensity of the characteristic peaks of the inclusion body protein, including 900, 1033, 1328, 1415 and 1446 cm-1, gradually increases as the function of the culture time after IPTG is added at 28 ℃, however, intensity of the peaks of the soluble protein, including 763, 1002, 1363, 1451 and 1665 cm-1, increases in small increments relatively. Conversely, the growth rate of soluble protein peaks is higher than that of the inclusion body peaks obviously at 16 ℃, indicating that the recombinant protein is mainly formed as inclusion body at 28 ℃, and mainly as soluble protein at 16 ℃. Under lower temperature, the information of protein folding in precision can be reflected by the spectral changes and the correct protein folding into certain configuration is conducive to the formation of soluble protein in E. coli cells. In addition, the non-recombinant protein of the bacteria expression at 16 ℃ contains more cystine, which may be associated with protein folding. The LTRS is a useful tool for nondestructive, unmarked, efficient, real-time monitoring of overexpression processes of soluble protein and inclusion body protein in a single living E. coli cell.

In mass flow measurement system, harmonic component of wavelength modulation spectroscopy signal, especially the second harmonic component is commonly used as test object, it is used for the inversion of gas concentration, velocity and other information. Based on the principle of wavelength modulation, using oxygen (O2) molecules in the vicinity of 764.28 nm absorption lines, the full width at half maximum (FWHM) of common line profiles is analyzed, and the range of application of the Lorentzian line profiles at different temperature and pressure is obtained; absorption spectral lines of O2 molecules are studied under different conditions of temperature, pressure, and the second harmonic peak change relation between them is studied as well; the error of the second harmonic peak inversion is analyzed under different temperatures and pressures, and error correction methods are put forward; in the experiment，when the optimal modulation depth is impossible to immediately adjust with the temperature and pressure changes, the optimal modulation coefficient application range under different temperatures and pressures is analyzed, and the error correction method is given.