By utilizing the opposite thermo-optical characteristics of silicon oxynitride (SiON) and polymer materials, a hybrid integrated SiON/polymer waveguide total internal reflection (TIR) thermo-optic (TO) switch has been designed. The operation of the suggested switch is using an electrode heater, which is fabricated on a trench that is located in the center part of SiON waveguide X-junction and filled with the same polymer material as the cladding used, to adjust the refractive index of the polymer filled in the trench so as to realize TIR effect. Theoretical results show that, the suggested switch can realize an extinction ratio more than 36 dB and a crosstalk lower than -36 dB with very low driving power of 2.3 mW for TE and TM polarization by choosing the suitable polymer material which index matches that of SiON, and then by optimizing the design parameters of the single waveguide, the cross angle between the two waveguide, the width of the trench, and the structure of the electrode heater.

According to the morphological structures of leukocyte, the double layer eccentric-sphere model is established for a kind of single-nuclear cell. Based on the Mie scattering theory and interface transfer theory, the expressions of amplitude functions are revised by the geometrical-optics approximation. Results of numerical calculation are consistent with the results from the VirtualLab imitation system which calculate by finite element method. Results of numerical calculation also show that three kinds of intensity modulations with different frequencies can be found in the angular distribution. The physical mechanism about these three modulations has been analyzed. The relations between the modulation characteristics and the physical and optical parameters of the cell are obtained. The modulation distortion phenomenon will appear in the case of nuclei close to the cell. These provide a useful theory foundation for improving the measuring and identification technique of single cells.

The forming process of the photoacoustic signal excited by the intensity-modulated continuous-wave laser and the effects of modulation pulse width on photoacoustic signal are researched. It is shown that the power absorbed by the biological tissue increases with the increase of the width of the modulated rectangular pulse and the amplitude of the photoacoustic signal. The effects on the axial resolution of the photoacoustic signal excited by the modulated rectangular pulse are also researched. It is shown that the width of the photoacoustic signal increases with the increase of the width of the modulated rectangular pulse, and the axial resolution of the photoacoustic imaging becomes worse. The modulated rectangular pulse of the continuous-wave laser (laser diode) is used to induce the acoustic signal. The laser power density is raised to obtain photoacoustic imaging with higher signal-to-noise ratio (SNR) and resolution when it is hard to raise the laser power. The research on the influential factor of photoacoustic signal excited by intensity-modulated continuous-wave laser in biological tissue can be used to provide a portable and lower cost instrument.

Multislice computed tomography (MSCT) is noninvasive and 3D imaging compared with the traditional coronary angiography (CAG). An optimal CAG viewing angle algorithm based on MSCT vessel analysis is proposed. First, a local vessel enhancement based on optimal oriented flux and locally adaptive threshold region growing is applied to extract the 3D coronary arteries model and then 3D thinning is performed and segment of interest is selected. According to the parameters during CT and CAG data acquisition, a perspective projection is performed to simulate the CAG procedure and the optimal viewing angle is calculated with the minimum foreshortening and minimum overlapping principle. Experimental results illustrate that the foreshortening percent is less than 1% in the obtained angle,which is close but superior to the working view angle. Therefore it can be applied to coronary artery disease intervention planning.

The histological changes of bone defect sites created surgically in rat femur treated by low level laser therapy (LLLT) are evaluated. Thirty rats are randomly divided into 3 groups according to different methods of laser irradiation: multi-irradiated group, single-irradiated group and control group with no irradiation. The total doses of both of the irradiation groups are the same. A round bone defect is created on the femur of each rat. The rats are killed on the 15th day and the 30th day after the surgery. The results show that after drawing materials and HE staining, the inflammation and bone formation of each group are analyzed under an optical microscope. The inflammation scores of irradiated groups are lower than those of control group with significant difference, meanwhile, the bone formation scores of irradiated groups are higher than those of control group with significant difference. However, there is no significant difference between the two irradiation groups. It is concluded from the study that LLLT with proper dose may alleviate inflammation and promote bone formation. There is no difference between multi-irradiated group and single-irradiated group.

A method based on thermo-optical modulation of ultrasonic surface waves generated by laser for detecting crack of aircraft engine blade is presented. Crack closure on the blade due to laser-heating is considered in this method, thus two series of ultrasonic pulses including closure situation and original situation are both detected by interferometer when scanning the line source focused from NdYAG laser. The signals under heating by modulation signed with Sheat are compared with the cooling ones signed with Scool. The difference value between Sheat and Scool exhibits the effect of the crack closure because of the optical-thermal modulation. The results demonstrate that the crack on aircraft engine blade can be detected with reliability and high sensitivity.

A set of mild steel thin plate specimens used for automotive industry are used as laboratory samples. Different types of distortions are analyzed. Radial basis function neural network (RBFN) models have been developed to predict transverse shrinkage and longitudinal bending distortion of welded plates. Response surface method is used to set up the experimental parameters matrix. Pulse frequency, pulse width, focal distance, defocus distance, moving speed of welded plates, shielded gas, workpiece temperature fluctuation and laser power fluctuation are used as input variables of these models to increase the prediction accuracy. Six different types of RBFN models have been developed to predict the distortion of welded plates. The best one is selected from them and resulted in better output prediction.

Based on the theory of laser transmission welding, the feasibility of laser welding the polycarbonate (PC) sheet plastics is researched. The experimental scheme for laser transmission welding is plotted, which includes the selection of laser equipment and welding materials. Metallographic microscopy is conducted for experimental samples in order to investigate the influence of welding parameters on welding quality. Orthogonal experiment method is used to study the welding results under different conditions of laser power, welding speed and the content of carbon black in polycarbonate. The results show that the laser power is the primary influencing factor, followed by the welding speed, and the last is the content of carbon black.

Hot wire is used as the filler metal of high beam quality and long focal distance fiber laser for narrow gap welding. The austenite stainless steel base metal is molten by laser, and the Ni-based alloy wire is heated up by wire current. Both the stability and efficiency are improved a lot by using the hybrid heating sources. High speed camera is used to observe the movement of filler wire during laser welding and analyze the effect of welding parameters on wire transition. The solidification microstructure and the element distribution of narrow gap laser weld are studied. Consequently, it is found that wire current and filling wire speed are the two key processing parameters for laser hot wire welding quality. The side wall of base metal is bonded well with weld metal when defocused laser spot with a diameter close to the width of narrow gap is used. The laser reflection mainly contributes to the melting of side walls, rather than the laser beam itself. The solidification microstructure shows obvious epitaxial growth, while the dendrites grow vertically to the side wall due to the rapid cooling speed. No macro segregation is found. However, lack of fusion is found in the bottom of narrow gap with a 90° angle. This problem is solved by using U type narrow gap with arc transition in the bottom. The narrow gap laser weld is finally obtained without macro weld defects.

When machining metal parts with laser metal deposition shaping (LMDS) method, if the temperature gradients and energy distributions of different areas inside cladding layer and that between cladding layer and substrate can be effectively controlled with optimal process parameters, then the probability of internal defects of cladding layer can be reduced, and the mechanical properties will be greatly improved. To the problem whether the metal parts made by LMDS contain internal defects, rotatable orthogonal experiments are designed for acquiring the distributions of internal defects of the metal parts under different process parameters. A logistic regression model is built based on these experimental data. Finally an authentication test is taken with the process parameters calculated by the logistic regression model, and no internal defects are found. The results show that the logistic regression model is in good agreement with the actual situation. The logistic regression model proposed in this paper is proved to have the guiding significance for selecting LMDS process parameters.

A central composite rotatable experimental design (CCRD) is conducted to design experiments of laser transmission welding of thermoplastic-polycarbonate (PC). The genetic algorithm-artificial neural network (GA-ANN) and response surface methodology (RSM) models which establish the relationships of the laser transmission welding process parameter (laser power, scanning speed, clamping pressure, scan times) and joint strength are established, and then the welding strength is predicted and the welding parameters is optimized by using the developed models respectively. The modeling capabilities, generalization and optimization capabilities of the two models are systematically compared. The result shows that GA-ANN and RSM are not significantly different on the maximum experimental joint strength, but the modeling, generalization and optimization abilities of GA-ANN are better than that of RSM, so GA-ANN is a more effective way to optimize the PC joint strength.

The surface of X80 pipeline steel welded joints is processed with laser shock wave, the tensile mechanical properties of the welded joints before and after laser shock processing (LSP) are analyzed with tensile tests. The fracture morphologies and the distributions of chemical components are observed with scanning electric microscope (SEM) and energy dispersive spectrometer (EDS) respectively, and the fracture mechanism of X80 pipeline steel welded joints is discussed. The results show that the X80 pipeline steel welded joints in primitive state have the continuous yield feature, without obvious yield flat, the elongation rate is higher, and the tensile fracture appears the clear delaminated cracking; the strength of X80 pipeline steel welded joints by LSP has not increased, the dimple size and depth become bigger, that improves the tensile properties of the fractures.

The effect of cross-section shape and geometrical parameters of the channel on heat transfer and thermal deformation of the microchannel water-cooled mirror is studied by analyzing the temperature field obtained by using finite volume method to solve the three-dimensional steady laminar flow and heat transfer equations, and the deformation obtained by coupling the temperature field to ANSYS software. Three different cross-section shapes of microchannel, i.e., rectangle, trapezoid and circle, are investigated in this paper. Average heat transfer coefficient, temperature inereasing and thermal deformation of mirror of each shape examined with three geometrical dimensions, are simulated. It is found that for the same channel, temperature distribution is not symmetrical, the highest temperature moves to the downstream, the heat transfer coefficient of each interface is also different, the heat transfer coefficient of side wall is the biggest, heat transfer coefficient of other walls decreases along the water flow direction. For the mirror using the same shape microchannel and hydraulic diameter, the heat transfer coefficient decreases as the distance of the channel from water inlet increases. The average heat transfer coefficient and thermal deformation are related to hydraulic diameter and channel shape. Reducing hydraulic diameter may help to induce high heat transfer coefficient. The trapezoid channel mirror has the smallest thermal deformation among the three shapes channel mirrors. At the condition of heat flux of 14730 W/m2, hydraulic diameter of 239 μm and water inlet velocity of 2.54 m/s, the thermal deformation of the mirror with trapezoid channel is only 0.016 μm.

A cladding pumped passively Q-switched Yb-doped fiber laser with Cr4+:YAG saturable absorber is reported and stable nanosecond pulse trains is gotten. Two laser configurations of linear cavity and ring cavity are set up, and both of them can effectively restrain the generation of stimulated Brillouin scattering (SBS) and the generation of self-pulse. A ring cavity with Cr4+:YAG inside the cavity to obtain stable 1 μs pulse trains is established. The amplitude fluctuation and timing jitter are below 5% (RMS). Further more, stable pulse trains by using a high reflective fiber Bragg grating (FBG) as a resonator mirror in a linear cavity is reached. The tunable pulse repetition rate is from 9.1 kHz to 30.3 kHz and the minimum pulse duration is 156 ns which is much less than microsecond pulses reported before. Although the average output power is only hundreds milli-watts now, it is convinient to boost the power with a stage of fiber amplifier because the laser uses a fiber coupler as the output of pulse trains. This kind of pulse laser can be used as a seed source and amplified to tens of watts for practical applications in the future.

Based on the condition of realizing a fundamental mode and thermal stable cavity, with the help of the computer software, a resonator to realize the fundamental mode and thermal stable output of 447 nm blue lasers is devised. By using the way of high power laser-diode side-pumped, NdYAP crystal as gain medium and choosing class I angle matching LBO and class II angle KTP separately used for second harmonic generation and sum frequency mixing, the fundamental mode and thermal stable output of 447 nm blue lasers is basically realized the acquired continuous stable output is 83.5 mW and the output stability is 1.5%.

That homogeneously broadened fiber laser, which can output two wavelengths simultaneously, is demonstrated by using net gain equalization method which makes each wavelength′s loss equals to gain in order to suppress mode competition. This linear-cavity Yb-doped fiber (YDF) laser realizes simultaneously single wavelength and two wavelengths stable output with linewidth of 0.012 and 0.020 nm respectively at room temperature. Each of the two wavelengths can be tuned approximately from 1013 nm to 1078 nm by the spectra separation and charateristics of selected wavelengths. The maximum and minimum wavelength spaces are 65.00 and 1.04 nm. The suppression effect to each other is stronger with smaller wavelength spacing. The output power of each wavelength equilibrates with the total maximum output power is 40.7 mW. This tunable two wavelengths laser can generate THz based on the beat frequency and also can be used as the optical source of optical coherence tomography (OCT) due to its tunable wavelength.

Mutual injection phase-locked fiber lasers combining technique based on a corner-cube is proposed and studied. The coherent combination output of two fiber laser beams is obtained by using four different kinds of phase locking structures. These experimental results are analysed contrastively. Furthermore, the latest experimental results of coherent combination of four fiber laser beams are presented.

A pulsed Nd:YAG laser with high average power is presented. The influence of offset angle of rods in six rods series connection resonator and the master oscillator power-amplifier (MOPA) system consisting of four rods oscillator and two rods amplifier are investigated theoretically. And the tolerances of offset angle are compared. It can be seen from the investigation results that MOPA system reduces the requirement of precision of series connection. With the same offset angle, the deviation of optical axis of the MOPA system is less than that of six rods resonator. It is helpful to improve the security performance of multi-rod pulsed laser, and obtain high average output power and high pulse energy. A MOPA system with four rods oscillator and two rods amplifier has been used in the experiment, and the offset angle of all rods is adjusted in the tolerance. With input electric power of 87 kW and a duty cycle of 17%, a maximum average output power of 3011 W, a peak power of 17.7 kW, a maximum single pulse energy of 67 J and a beam parameters product of 25.2 mm·mrad have been obtained. The electro-optical conversion efficiency is 3.46%, and instability of the laser is less than 2%.

Reasonable approximations and simplifications of the coupled wave equations of stimulated Brillouin scattering (SBS) in fibers are carried out. Based on the coupled wave equations of transient SBS, a numerical model is built. As these coupled wave equations of SBS are solved, especially in the tapered fiber with variable core diameter, the powers of the pump wave and the Stokes wave in the process of SBS are obtained, including the variation laws of them and the distinctions of the SBS in the fibers with different parameters. Based on the analyses, the parameters of the tapered fiber, which is used as a phase-conjugating mirror in high power and high repetition rate laser diode pumped solid state lasers, are optimized. It provides parameter optimization rules of the system in the applications for beam quality improvement. In addition, the rationality of the model is verified by comparing simulation results with experimental results.

Prism beam expander (PBE) is widely used in the spectral narrowing module of excimer lasers. The beam divergence and fluence could be reduced by the prism beam expander. The prism number, magnification of single prism and apex angle of the PBE should be optimized to improve the efficiency of the laser. Based on the magnification theory of the prism, the impact of the incidence angle, apex angle and exit angle of the prism on magnification are analyzed by numerical simulation. The dependence of magnification on incidence angle is demonstrated experimentally. Furthermore, to achieve a given linewidth of the laser, the minimal magnification of the line narrowing module is deduced. In addition, CaF2 prism beam expander with magnification of 13.3 is designed. Finally, 0.915 pm linewidth ArF laser is obtained using the designed PBE. The experimental results agree with the theoretical analysis.

The carbon nanotube as a saturable absorber is used in the passively Q-switched and Q-switched mode-locking (QML) of a laser diode (LD) pumped Tm:YAP operating at 2 μm. As high as 507 mW average output power of Q-switched pulses laser is obtained with a pump power of 8.64 W at the cavity length of 30 mm. The maximum pulse energy, pulse width and pulse repetition frequency are 18.8 μJ, 262 ns and 26.91 kHz respectively. When the whole cavity length increases to 80 mm, the QML laser is obtained. The maximum average output power and the pulse repetition frequency of Q-switched envelope are 387 mW and 34.61 kHz, respectively, while the pulse repetition frequency of the mode locking is 1.87 GHz.

The fluorescence spectrum of Yb:YAG crystal is analyzed and its gain characteristics are discussed. A regenerative amplifier is built, which works under a low temperature. The gain material is Yb:YAG crystal with the doping concentration of 8% back-end pumped by a laser diode. Through a signal pulse injection, we can get a 10.3 mJ laser pulse output with the repetition rate of 10 Hz and the pulse width of 10 ns at -90 ℃, and the magnification exceeds 107.

A monolithic single-frequency non-planar ring oscillator (NPRO) laser is studied. Continuous-wave (CW) output power of 1.01 W with 1.83 W pump power is achieved. The slope efficiency is about 60%. The laser linewidth is measured by beat frequency measurement method with another narrow linewidth single frequency laser, and the linewidth is less than 2 kHz. Besides, the suppression technique of intensity noise and frequency tuning characteristics are studied for the laser. The relaxation oscillation peak noise is suppressed by 30 dB through feedback control of pump laser diode driver current. The laser frequency can be tuned slowly by temperature tuning and quickly by piezoelectric transducer (PZT) loaded on the laser crystal. The laser frequency can change 15 GHz when the crystal temperature changes 10 ℃. Meanwhile, the laser frequency PZT tuning range exceeds ±200 MHz, and the response time is 45 μs when the frequency is tuned over 200 MHz.

Beam quality of the passive coherent beam combination system is studied using the ring cavity passive phase-locking experimental platform of four fiber lasers in two-dimensional distribution. With the times-diffraction-limited factor β as the evaluation method, the impact of duty ratio of sub-beams and different phase-locked patterns on the β factor is analyzed theoretically; and the β factor corresponding to different output power levels is measured in the experiment. The results show that although the β factor can reflect the difference in beam quality under different experimental conditions to some extent, it can not reflect the characteristics of coherent beam patterns in the far-field because the focus of the β factor measurement is to determine the bucket size of 83.8% encircled energy (power) ratio at the focal plane, therefore it is not suitable for the evaluation of the beam quality of a passive coherent beam combination system. A comparative analysis of the β factor and beam quality is done, beam quality can better reflect the characteristics of the coherent beam combination.

A master oscillator power amplifier (MOPA) structured pulsed fiber laser is reported. The single-frequency pulse seed, with the average power of 0.5 mW, is obtained by externally modulating a continuous wave laser with linewidth of 20 kHz. The pulse seed is firstly pre-amplified to about 2.7 W of average power with three Yb-doped fiber (YDF) amplifiers. The main amplifier is based on a large-mode-area (LMA) double clad YDF with core diameter of 30 μm and cladding diameter of 250 μm. When the pump power of the main amplifier is 87.1 W, a single-frequency pulsed laser with pulse duration of 10 ns and peak power of 486.7 W is generated. The average output power is 58.4 W.

The optical properties of ZnO thin-film ridge-waveguide are studied, and the reduction of scattering loss inside the random cavities can also be obtained by covered ZnO films with MgO capped layer. Additionally, the finite difference time domain(FDTD) method for numerical calculation is utilized. The simulation results show that random laser with low scattering loss and directional optical output from the facets can be reached by employing annealed ZnO thin-film ridge-waveguide with a MgO capped layer.

Three novel stilbene derivatives with high two-photon cross-section are designed and synthesized as two-photon chromophores. Three-dimensional (3D) optical data storage experiments are carried out by two-photon photobleaching with a femtosecond laser in three stilbene derivatives doped polymethylmethacryate film. Research on the two-photon photobleaching ability of three two-photon chromophores shows that the chromophore with larger two-photon cross-section could be photobleached at lower excitation power. The effects of excitation power on two-photon fluorescence behaviors are also analyzed. The characters of optical data storage reveal that the resolution in two-photon photobleaching could be increased by lowing excitation power when exposure time is kept the same or by lowing exposure time when excitation power is kept the same. However, larger excitation power is often used to obtain high data storage rate. Two-photon writing and two-photon reading experiment realizes 3D ultrahigh optical data storage with a theoretical storage density of 14 Gbit/cm3 in doped film under higher excitation power (13.4 mW) and shorter exposure time (20 ms). The cubic dependence of two-photon photobleaching dynamics on excitation power indicates that the mechanism of two-photon photobleaching concerns the joint action of three photons.

HfO2 thin films have been deposited by ion assisted deposition (IAD) with End-Hall and APS ion source respectively. Comprehensive characterization of these films such as transmittance spectra, optical constants, crystal structures, surface topography and absorption (1064 nm) have been studied via Lambda 900 spectrophotometer, variable angle spectroscopic ellipsometry (V-VASE), X-ray diffraction (XRD), scanning electron microscopy (SEM), ZYGO interferometer, and laser calorimeter. The results show that thin film properties have a close relationship with ion source and starting material. The films deposited with End-Hall ion source presents slightly inhomogeneous. These films made with End-Hall and APS ion sources respectively show high refractive index and low absorption loss, and the crystal structures of these films are monoclinic. Under deposition with different ion sources, the films prepared with hafnium as a starting material show even surface, low root mean square roughness and total integrated scattering. Compared with End-Hall ion source, the films deposited with APS ion source show lower absorption.

The grazing incidence X-ray reflection spectra of a Mo/Si multilayer annealing at a temperature of 250 ℃ at different time are measured and the relative shifts in Bragg peak positions are extracted, from which the relative period thickness changes of the Mo/Si multilayer at pm-accuracy are calculated by fitting Bragg formula. A diffusion limited model is applied to account for the growing interfaces between Mo and Si, which states that the thickness of a compound interface grows quadratically over time. From this model the diffusion constant figures out to be 0.33×10-22 cm2/s. Then the grazing incidence X-ray reflection spectra are fitted by genetic algorithm using four-layer model, with the densities of Mo, Si and MoSi2 determined to be 9.3, 2.5 and 5.4 g/cm3. Accordingly, the diffusion constant is modified to be 1.88×10-22 cm2/s, which gives a quantitative criterion for investigating the thermal stability of the Mo/Si multilayer.

ZrO2/SiO2 multilayer mirrors at normal incidence are deposited on the infrared quartz substrates for the application of holmium laser. The deposition process is optimized to overcome the water intrinsic absorption, surface scattering loss, mechanical stress of thin film materials. The transmittance and the surface roughness of mirror is less than 0.1% at the wavelength of 2.1 μm and 1nm, respectively. The deposited mirrors show long-term stability and high reliability in the application of holmium-laser system.

Phase measuring profilometry (PMP) has received great attention in modern life with the advantages of high accuracy and non-contact. However, the application of PMP is limited by the complicated manufacturing technique of sinusoidal grating. Based on the basic theory of PMP, the paper presents the PMP based on the triangular-pattern grating, which is of more practical significance because its manufacturing technique is easier compared to the sinusoidal grating. In this paper, the accuracy of the two methods mentioned above are compared and analyzed. At the same time, the influence of grating period and contrast ratio as well as the maximum height of different objects on the measuring accuracy is analyzed both in ideal and practical conditions. The computer simulations and experiments show that the PMP based on triangular-pattern grating is feasible for its high accuracy.

The numerical model of the cross-correlation between pulses of the femtosecond laser sequence propagating in air is developed to investigate the temporal coherence characteristic of the femtosecond laser ultrashort pulse sequence. The model is based on the propagation theory of the femtosecond pulse sequence and the refractive index of air Ciddor formula. The auto-correlation patterns between pulses of the femtosecond pulse sequence in different spectral distribution with different optical path differences under different atmospheric conditions can be obtained from the model. The simulation results show that the auto-correlation patterns become broadening and chirp with the peak power decreasing due to dispersion, as the optical path difference between the pulses increases. However when the atmospheric conditions are changed with the same optical path difference, the correlations patterns only shift without any extra linear broadening or chirp. The femtosecond optical frequency comb has very high temporal coherence. The formation of the cross-correlation function between the femtosecond pulses only depends on the spectral distribution of the laser source.

Atomic force microscopy (AFM) is the main technique for measuring surfaces of sub-nanometer root-mean-square roughness, but its results always vary with the sampling conditions (sampling interval and sampling points) and measuring position. As a practical example of a supersmooth substrate random surface, an effective method based on accumulated power spectral analysis is proposed and evaluated for appropriate sampling term selecting. It is shown that this method can avoid the loss or redundancy of roughness information. A optimized measuring position selection strategy according to global and local topography analysis is proposed. It can reduce the uncertainties in surface roughness characterization due to characteristic differences of different local surfaces and the required number of measurements to obtain reliable results. The above researches provide an effective method for testing optical supersmooth substrate surface by atomic force microscopy.

Because the training serials are unipolar in multi-input multi-output free space optical communication (MIMO-FSO) systems, which leads to the signal energy loss easily, the result of traditional singular value decomposition (SVD) channel estimation algorithm is inaccurate. A kind of modified adaptive SVD estimation algorithm is put forward which can compensate for the estimation errors of SVD algorithm. So the modified adaptive SVD estimation algorithm can be better fit for MIMO-FSO systems. The simulation results indicate that compared with the SVD algorithm, the mean square error (MSE) performance of the modified algorithm is improved by two and three orders of magnitude when the signal-to-noise ratio (SNR) is 15 dB and 30 dB, respectively. Compared with the average value modified SVD algorithm, the modified algorithm has 1 dB improvement of the MSE performance under the same condition. The modified algorithm possesses strong transplanting property and can be adopted in other channel estimation methods.

A 40 GHz or 60 GHz millimeter wave phase-modulated signal is generated from a low-frequency phase-modulated optical signal injected into a distributed feedback laser diode (DFB-LD) and the frequency-multiplication factor varies from 4 to 16. The N-th modulation sideband of injection light results in wavelength locking of DFB-LD, simultaneously, the N-th modulation sideband is also amplified in the DFB-LD. Therefore, these two coherent optical fields interact in LD cavity to form stable millimeter wave phase-modulated signal. Via theoretical analyses and experimental demonstrations, the 40 GHz and 60 GHz millimeter wave phase-modulated signals are obtained by injecting 2.5, 5 and 10 GHz sine phases-modulated signal into the DFB-LD. The frequency-multiplication factor varies from 4 to 16 and the stability of the generated millimeter wave is established and proved by single sideband phase noise measurement.

An optical voltage transducer for the electric power system based on modular interference in dual-mode two-hole photonic crystal fiber (PCF) is designed. A quartz crystal cylinder wrapped with two-hole photonic crystal fiber is used as the voltage sensor head. The intensity of the two interference output lobes of the two-hole photonic crystal fiber is modulated with the converse piezoelectric effect of quartz crystal. In low voltage part, a piezoelectric ceramics (PZT) which wrapped with a piece of double core PCF is used for adjusting the static phase difference at orthogonal status. The experimental results show that the measurement precision is 0.5% by rated voltage in laboratory conditions.

In resonator micro-optic gyro (RMOG), square-wave frequency modulation implemented by applying serrodyne waveforms on phase modulators is one of the most frequently used techniques. However, in order to realize ideal square-wave frequency modulation, perfect linear phase modulation waveform is required, which is hard to achieve in analog systems. The influence of the nonlinearity of modulation waveform on the output of the resonator is analyzed. Moreover, the resonant curve shift and distortion induced by the second and third order modulation nonlinearity are theoretically calculated. Furthermore, the relationship between demodulated output and input rotation rates is presented. A RMOG experimental system is set up, and the generated triangle wave is tested and fitted to a nonlinear cubic curve. The coefficients of the second and third order nonlinearity are in the opposite directions, which counteracts part of the error. The testing result of the scale factor shows the feasibility of the modulation waveform generating method.

A high temperature fiber Bragg grating (FBG) sensing network based on wavelength modulation is highly developed on the basis of FBG high temperature sensing characters. A new packaged high temperature FBG sensor head is designed in this system. A high reliable distributed sensing network structure is also proposed to overcome the low reliability of the traditional FBG sensing network. Diffraction technique based on InGaAs image sensing is used to demodulate reflected wavelength. The results show that the average goodness-of-fit of sensing system′s temperature curve is 0.9991, the sensitivity is 0.0258 nm/℃, the accuracy is ±0.6 ℃ and the response time is less than 16 s. Moreover, the sensing network is steady enough for high temperature measurement.

An intensity compensating method for time division multiplexing (TDM) scheme of fiber-optic hydrophone using a 3×3 coupler as path-matched differential interferometer is proposed. The fiber-optic hydrophone is made by a 2×2 coupler. In this demodulation method, the non-interferential pulse is used as reference optical intensity. The signal is demodulated from two outputs by simple calculations and digital arctangent approach. The signal distortion caused by optical intensity fluctuation is suppressed efficiently. There is no carrier in this demodulation scheme. In addition, fiber-optic hydrophone can form a nearly zero path difference interferometer which is good for reducing system phase noise. The demodulation method is very simple and feasible for a general asymmetric 3×3 coupler. Correspondingly, it is easy to get a large dynamic range. A TDM experiment system composed of 8 sensors is set up. For a 10% intensity variation, the total harmonic distortion can be decreased by 30 dB by using the intensity compensating method. Noise floor of the TDM experiment system is less than 30 μrad/Hz1/2 at 1 kHz.

The polarization shift keying modulation has high reliability since the polarization properties of beam light change relatively small while propagating through the atmoshpere. The bit error rate(BER) performace of the circle polarization shift keying modulation in the satellite-to-ground laser communication is studied. Considering the effects of the atmospheric turbulence, the Hufnagle-Valley refractive index structure constant mode is adopted. By comparing the BER performace of the circle polarization shift keying modulation and the on-off keying (OOK) modulation under the weak and strong turbulence fluctuation, with the values of the Rytov variance are 0.082 and 1.11, it comes to a conclusion that the former is superior to the latter on the BER performace.Especially when the BER of 10-7, is to be achieved, their signal to noise ratio are 21.65 dB and 30 dB, the circle polarization shift keying modulation reduces 8.35dB of the signal to noise ratio under the Rytov variance is 0.082.In addition, the effects on the BER of three factors,which are the near-surface refraction structure constant, the zenith angle and the ground wind speed are analyzed . The simulation results show that the BER of the circle polarization shift keying modulation is lower than the OOK modulation at least two magnitudes. Therefore, it has broad prospect in the satellite-to-ground laser communication in future.

In fiber gas sensor systems, in order to improve the detection sensitivity, it is vitally necessary to make intensive efforts to restrain various noises of the system. Designing low-noise preamplifier and light driving circuit can effectively reduce the system noise, but cannot reduce the noise caused by the changes of optical path. This kind of noise is called background noise, which influences the measuring sensitivity of fiber gas sensor system. Therefore, how to filter the background noise affects the improvement of measurement accuracy. This paper puts forward a method based on least logarithm square method which can easily reduce the background noise of optical gas sensor system. By using reference grating and Fabry-Perot etalon, it can reconstruct the output spectra. A modified least square method is used to fit the envelope of gas absorption lines by using the data of absorption peaks on both sides. Dividing the gas absorption lines by the envelope line of absorption lines, the normalization of output is realized and thus the drift of the background noise curve due to the change of experimental environment can be reduced. This method can avoid data collection again when the background noise is drifting, and brings convenience to measurement.

Phase modulation of the single frequency laser to attain the multi-tone laser costs less and is easy to carry out. It has been proved to be an effective way to suppress stimulated Brillouin scattering (SBS) in narrow-linewidth fiber amplifiers. Relationships between modulation signals and constitutions of the modulated laser are studied theoretically. When the modulation frequency is small, for example 100 MHz, the multi-frequency laser can be attained and SBS threshold is effectively enhanced. Experimental researches are done to study effects of 100 MHz phase modulation on SBS mitigation of high power narrow linewidth fiber amplifiers. SBS threshold output powers are 2.5 times and 3.7 times of that of the corresponding unmodulated amplifiers with 16 and 26.5 m delivery fiber respectively. Experimental results show that SBS in narrow-linewidth fiber amplifiers can be effectively suppressed with phase modulation and the suppression effect depends on amplifiers′ parameters. The lower the SBS threshold without modulation, the better the suppression effect.

In order to better understand the mechanism of surface enhanced Raman spectroscopy (SERS) and further improve the Raman enhancement factor, a strategy which combines SERS and mechanical controllable break junctions (MCBJ) is employed. With such a strategy, the gap width between two nanoelectrodes can be adjusted precisely during the period of SERS measurement. The dependence of SERS intensity on the gap width and the incident laser polarization are investigated. Moreover, a nano gate-electrode with adjustable bias voltage is introduced, and the gate electrode effect to the Raman signal intensity is investigated in system. The experimental results demonstrate that the Raman signal intensity critically depends on the biased gate voltage, which provide a new method to enhance the Raman signal and benefit the theory investigation for the Raman enhancement mechanism.

The spectroscopy emission characteristics of trace heavy metal lead in water enriched with graphite is studied based on laser induced breakdown spectroscopy technique. With a 1064 nm wavelength NdYAG laser as excitation source, the echelle spectrometer and an intensified charge coupled device are used for spectral separation and high sensitive detection with high resolution and wide spectral range. The characteristic spectral line of 405.78 nm with detection delay time 900 ns and gate time 1600 ns is selected for lead in the experiment. The calibration curve of Pb is plotted based on the different concentration measurement results, and the limit of detection with 0.0665 mg/L is obtained for Pb in water. Carbon as the internal standard element effectively eliminates the spectral instability of the analytical results, and the detection limits and stability are improved.