Based on conductive cooled slab laser amplifiers with end-pumping structure, a rectangular micro-channel water cooling heatsink as the amplifier cooling system has been designed. Optimization of the micro-channel heatsink was investigated by the finite element analysis (FEA) , which showed that the cooling performance is the best when the ratio of width of microfin valley to width of microchannel is 0.57. Comparing the experiment with the simulation of a micro-channel heatsink with 0.4 mm width of microfin valley and 0.35 mm width of microfin, the curve of heat transfer coefficient and water flow rate was fitted, resultant temperature distribution of the laser slab under cooling of the heatsink was obtained by FEA. Results indicated that low thermal resistance in the slab cooling surface was obtained even the water flow rate was slow.

A multiple diode-arrays side-pumped two-rod series connection four-mirror resonator in which has a telescope system has been demonstrated. Using two acousto-optic Q-switches and the intra-cavity frequency doubling of LBO crystal, up to 105 W output at 695.5 nm with the repetition rate of 10 kHz is obtained by resonant cavity and frequency doubling systal parameters optimal design; the optical-to-optical conversion is up to 6.6%.

A film of nanocrystalline silicon embedded in SiNx (nc-Si/SiNx)was prepared by radio-frequency magnetron sputtering technique and thermal annealing. By using the film as a saturate absorber, a 946 nm laser with passive Q-switching was achieved in a laser diode (LD) continual end-pumped Nd:YAG laser and a 473 nm blue laser pulse was generated with intra-cavity frequency doubling of LiB3O5(LBO) crystal. At the pump power of 8.5 W, the Q-switched blue laser pulses with average power of 120 mW, pulse duration of 45 ns, repetition rate of 23.8 kHz and peak power of 112 W were obtained. The conversion efficiency from pump lasers to 473 nm blue laser pulses was 1.41%. The changes of average powers, pulse repetition rates and pulse duration of the blue laser pulses with pump powers were experimentally studied. Theoretical analysis showed that the two-photon saturate absorption at 946 nm laser pulse in nanocrystalline silicon embedded in SiNx films caused the passive Q-switching of Nd:YAG 946 nm lasers.

In this paper, thermal blooming of high power laser affected by the convective wind has been simulated numerically and studied. Turbulences are simulated with the RANS/LES hybrid method, coupled with the J-B model. The duel time steps method is used for solving unsteady flow problems. The wave optics method is adopted to simulate beam propagation through both flow field and free space. Based on far field spot, qualitative and quantitative analysis has been carried out. Thermal blooming of Gauss beam with power of 0.1 MW and diameter of 0.1 m, affected by the convective wind at different velocities as follows 1, 5 and 10 m/s, has been investigated. Results show that thermal blooming affected by the wind is unsteady. The lower velocity of the convective wind, the stronger thermal blooming. And especially which of the velocity of 1 m/s is the strongest and aberration of whose far field spot is the most severe. The unsteady property of thermal blooming is more visible as the velocity is lower. For example, thermal blooming at the velocity of 1 m/s is still changing in 5 s, but those at the 5 m/s or 10 m/s have trended to steady state after 3 s.

According to three composite wave-plate theory and simulated annealing algorithm, a mica achromatic half wave-plate used in visible range is designed. Theoretical analysis shows that the retardation deviation of this device is within 2% covering the spectrum scope of 400～700 nm. This device has been measured over the visible range by normalized polarizing modulation measurement. The retardation deviation is within 4.8% based on the average equivalent fast axis. The retardation deviation of the device is within 2.9% based on the equivalent fast axis corresponds to the measuring wavelength. This mica achromatic half wave-plate can be applied in many fields.

A dual-stage optical single side band (DSSB) modulation scheme to combat chromatic dispersion for the terahertz over fiber (ToF) systems application is proposed. In the scheme, terahertz wave is obtained via carrier-suppression double sideband (DSB) modulation, one sideband of terahertz wave then undergo the fisrt single sideband (SSB) modulation and the second baseband SSB modulation in the process of data modulation, which achieves cascade SSB modulation. As can ben seen from the sumulation result, for mid-frequency carrier of 0.1 THz, the bit error rate (BER) performance without dispersion compensation achives 1×10-11 and the sensitivity of the receiver is -26.6 dBm with a data rate of 5 Gb/s after 100 km transmission. Through comparing the power penalty of DSB and DSSB, we demonstrated the optical SSB modulation has better dispersion tolerance. This paper also shows the contrastive curves of frequency selective fading for the SSB and DSB modulated signals, which definitely demonstrates the existence of dispersion fading during the DSB transmission as well as the effective suppression of the fading implemented by the SSB modulation. The novel scheme′s preferences is excelled than the conventional scheme′s, which is demonstrated by these theory and simulation.

The experimental study on visible light enhanced supercontinuum generation pumped by Yb-doped large mode area photonic crystal fiber laser amplifier is reported. The high nonlinear photonic crystal fiber has suitable dispersion making the red shifted soliton and blue shifted dispersion wave have a same group velocity. They move together in the fiber and interact with each other through four wave mixing. A 3.95 W high power supercontinuum was obtained with 1.2 W in the visible region. The optimization of fiber structures was numerically designed. As a result, the fiber with smaller core size or larger air filling fraction can shift the wavelength to blue.

The principles of the splice loss between the germanium doped core photonic crystal fiber (PCF) and single mode fiber (SMF) at the wavelength of 1550 nm are investigated by the full-vector finite element method. The mismatch of mode field between the PCF and SMF is the main factor resulting in the high splice loss. The real structure profile is extracted to exactly simulate the splice loss due to the mismatch of mode field. Based on the arc fusion technique, a set of optimized fusion parameters are obtained from a series of experiments, and the repeat-discharge operation are used to make sure moderate collapse of the cladding air holes of the germanium doped core PCF. Then the mismatch of mode field could be reduced and the low loss splicing between PCF and SMF is realized.

A three-line structured light three-dimensional (3D) scanning method is proposed in order to achieve the purpose of measuring human faces in high resolution rapidly. Three parallel structured light strips with the same distance are projected on the human face to obtain scanning image sequences. In accordance with the location relationship of light strips between adjacent images, three light strips are grouped. Combining with the calibration result, point cloud of the human face is gained. Then, the original point cloud is fitted and resampled to obtain uniform data. Experimental results show that this method is a rapid and efficient 3D measuring method.

Laser active imaging system can obtain intensity image, range image and velocity image, and it provides more useful information than other imaging systems. According to the features of laser active imaging, a new edge detection algorithm of laser active image based on wavelet transform and multi-scale morphology is presented. The wavelet multi-resolution analysis is used to differentiate the noise and the edge detail of the image, and then a non-linear algorithm is constructed to strengthen the wake parts of the image. The concept of the multi-scale morphology is introduced to obtain the edge of the processed image, bigger morphology operator eliminating noise and smaller morphology operator is used to pick up image detail, and the better edge of the processed image is obtained. The experimental results indicate that compared with classical edge detection operator, this method has better noise immunity and performance on edge detection of laser active imaging with large noise and blurry edge.

In digitally holographic reconstruction, the reconstructed image quality is reduced by the effect of the laser speckle, the system noise and the border diffraction of the digital hologram, which restrains the application of digital holography in phase measurement. In this paper, we apply the apodization for the phase measurement in digital holography to suppress the diffraction and noise effects. Simulations and experiments show that apodization can effectively reduce the border diffraction and noise effects to the reconstructed phase information of the objected wave and improve the measurement precision.

A 3D thermal-mechanical finite element model for laser bending of Al2O3 ceramic slice is established with the ABAQUS code. Based on the fields of temperature, stress-strain and displacement from the simulation, the forming mechanism of laser bending of ceramic slice is investigated. The simulated results of different thicknesses are compared with each other, as well as the influence of specimen thickness on the fields of temperature, strain-stress and displacement. It is observed that as the thickness increased, the temperature on the bottom surface may not reach the plastic-turning temperature and the magnitude of the surface residual stress may increase. Through the analysis, it is found that the optimum thickness is between 0.18 mm and 0.31 mm under the specified processing parameters.

For three-dimensional (3D) laser cutting profile in space surface, an optimized method to disperse cutting points is presented. By analyzing the curvature of starting point of the space curve, the initial step length can be determined according to precision. Then the intersection point of the reference ball founded by using the initial step length as the radius and the profile curve is the initial cutting point. Through adjusting the radius of the reference ball, the optimized discrete points can be obtained by using dichotomy according to chord length. An automatic programming software of 3D laser cutting is developed. The functions of track extraction, rapid dispersion of curves and normal vector calculation during the 3D laser cutting can be realized.

The models of two and four result droplets as the atomizing result of a plasma droplet have been established. Contrastive analysis of these two models has been done and their application situations have been discussed accordingly. Besides, the influence of the initial droplets’ parameters on atomization process has been studied. In the investigation of laser induced films damage, the erupting time of droplet should be controlled in order to control the explosion intensity of the plasma droplet. The research has some guiding significance, particularly in understanding the plasma droplets’ bursting process and in overcoming the impact of the plasma blast.

Objective to determine the effect of transmyocardial laser revascularization (TMLR) in combined with the implantation of endothelial progenitor cells (EPCs) on cardiac function and neovascularization of myocardial ischemia. An operation of acute myocardial ischemia was created. Afterwards, the dogs were randomized into AMI group, TMLR group and TMLR+EPCs receiving TMLR with implantation of EPCs and calcium alginate into channels induced by laser. Four weeks later, all dogs underwent echocardiography and the samples of myocardial ischemia tissue underwent histochemical and immunohistologic analysis. The results show that TMLR+EPCs group regional contractility in the left artial diameter (LAD) territory revealed an improvement versus control and TMLR groups, whereas control and TMLR animals did not show any difference. Neoangiogenesis was observed in laser channels in the canine heart subjected to TMLR+EPCs treatment, the remains of clacium alginate appeared in the channels of TMLR+EPCs group, but the fibrosis in TMLR group. The result indicates TMLR in combined with EPCs improve the cardiac regional and global function in acute myocardial ischemia from advancing impariment, and augment neovascularization in channels of ischemic myocardium induced by laser.

The principle of optical tweezers array based on double-plate shearing interference and the particle separation chip by mircofluidic fabrication method is introduced. The function of particle trapping and separation of the optical tweezers array is verified by the experiments. According to the principle of multi-beam light interference, double-plate shearing interference can produce stripes with high brightness and sharp edge to insure the gradient force applied to the trapped particles. The high flexibility of the system is benefited from the easy adjustment of stripe period. The microfluidic chip made by glass is fabricated by chemical etching, with good optical property, mechanical strength and electricity insulation. And the glass microfluidic chip is suitable for the samples of cell and macromolecules, such as protein, because of weak adsorption of protein. Taking advantage of fewer sample consumption and higher efficiency, the combination of optical tweezers array with microfluidic chip could be one of important tools for micro-nano scale analytical technology in the near future.

Fiber optic white-light interferometry (WLI) possesses a considerable advantage with regard to the ability to provide absolute and unambiguous measurement, comparing to laser interferometry. The research on fiber optic white-light interferometry in recent years is reviewed in this paper, and fiber optic WLI based on phase measurement method is focused, including interference-order method, Fourier-transform WLI, Fourier-transform relative WLI, wavelength-scanning WLI, and phase-shifted WLI. The main problems, such as spectrum acquirement, measurement resolution and automatic measurement, are solved in the work in order to accelerate the technique in instrumentation and engineering application.

Micro-tube biosensor is established with hollow optical fiber and its whispering gallery mode (WGM) is analyzed theoretically. The principle of bio-sensing based on the change of refractive index is presented. With the prism of ZF13, WGM of micro-tube is successfully observed by evanescent coupling. The mixture of water and ethanol is used for experimental research on sensitivity with the change of refractive index of micro-tube biosensor. At the resonance wavelength of 1555.0 nm, 2.2 nm/RIU sensitivity is obtained with 45° incident angle and 21.2 nm/RIU is obtained with 36° incident angle.

For the standard single-mode optical fiber, the frequency shift of Brillouin scattering light is the function of the temperature or strain. The temperature or strain of the optical fiber can be obtained when Brillouin frequency shift is able to be detected. Long-distance sensing Brillouin scattering distributed optical fiber sensor (DOFS) has two structures of optical time-domain analyzer (OTDA) and optical time-domain reflectometer (OTDR). Although Brillouin OTDR only process single end of the optical fiber, it suffers short sensing distance because of weak spontaneous Brillouin scattering. Brillouin OTDA possesses the merit of long-distance sensing for the relatively strong stimulated Brillouin scattering. One key point of achieving Brillouin OTDA is to produce the frequency-shifted probe light. Here, an optical fiber laser with linewidth less than 1 MHz is employed as the single optical source, a microwave electro-optical modulator is used to produce the frequency-shifted probe light, and a method of orthogonal polarization control is adopted to reduce the effect of the optical-polarization-related problem. A laboratorial system of 50 km distributed optical sensor is achieved with 2 ℃ in temperature resolution, and 10 m in spatial resolution.

A new type of panda fiber grating coupler is proposed,which has the characteristics of fiber grating and fiber coupler, especially the capability of maintaining polarization. Fabrication technics is performed and three panda fiber grating couplers are successfully fabricated. Experimental research indicates that the polarization extinction ratio does not decrease after grating writing. The experiments of optical add multiplexing(OAM) and optical drop multipplexing(ODM) are carried out and the results show that the light with center wavelength 1536.6 nm can be add and drop multiplexing by this new device.

Thermo-optic effect of liquid materials at optical wavelength of 1550 nm is investigated by use of a side polished fiber Bragg grating (FBG) sensor with double reflective Bragg wavelengths. The relationship between the difference of double reflective Bragg wavelengths of sensor and refractive index of overlaid liquid material is measured, and the relationship between the difference of double reflective Bragg wavelengths and temperature is measured when a liquid material overlays on the polished region of sensor. By analysis of the relationships above the thermo-optic coefficients of three liquids made by Cargille Lab are obtained at optical wavelength of 1550 nm. The fiber sensor could be used for measurement of thermo-optic characteristic of liquid materials as their refractive indexes are in the range of 1.4198～1.4479.

This paper presents a temperature compensating circuit which is used in distributed optical fiber Raman temperature sensor. The temperature compensating circuit through temperature compensation for the avalanche photodiode reverse bias voltage to offset the impact of environmental temperature on the avalanche photodiode, thus reducing the temperature drift of the system. By using this technology, the system measurement error caused by ambient temperature drift can be controlled within ±0.1 ℃ from 0 to 60 ℃. Compared with traditional constant temperature device, using temperature compensating circuit can effectively reduce system power consumption and cost.

A real-time calibration method is proposed for investigation of tunable optical filter (TOF) nonlinearity. Based on the transmission characteristic of TOF, nonlinearity real-time calibration system is established. Using least mean square algorithm, the relationship between wavelength and voltage of the TOF can be obtained. Thus the nonlinearity of the TOF can be described. The wavelength random error of the TOF is measured by using wavelength blocked F-P etalons. The result shows that wavelength random error of the TOF can be reduced by 37%～95% with reference wavelength. Combined with the method, the wavelength precision in gas pressure sensing system is obviously improved in position accuracy, system error and high sensitivity.

According to the evanescent wave absorption theory, a cavity ring-down spectroscopy detection system which is immune to temperature perturbation is presented. Study has been done to explore the integration of carbon nanotubes and optical fiber apparatus. The physical absorption and desorption characteristic of carbon nanotubes is utilized to realize the measurement of gas or volatile organic solvent (VOS). When fiber cladding is partially removed, the evanescent wave theory is utilized to select the appropriate diameter of fiber cladding, thus the system is sensitive to ambient refractive index and loss can be controlled. A pulsed laser beam with width of 2.5 ns according to the nonlinear polarization dependent mode locking technique is introduced into the ring-down system, and hence, our principle is validated by the highly-sensitive temperature-insensitive measurement of evanescent wave absorption loss.

A novel and simple reference light power calibration method is proposed, which has the advantage of frequency discriminator. The difference between light power of the total output of electro-optic modulator and the intended reference light power is detected at each frequency point, and then used as the feedback signal to control the output power of microwave source to calibrate the reference light power. The feasibility of the method is analyzed theoretically and verified through simulations and experiments. It is demonstrated that, after the calibration, the maximum error between the reference light power and intended power is reduced to one-third of that observed before calibration.

The Raman-scattering-based distributed optical fiber sensor (DOFS) can realize the continuous temperature detection in one-dimension space. It has good environmental adaptability, simple system structure, and high sensitivity. But there is a conflict between the spatial resolution and the signal sensitivity in the system, namely, when increasing pulse width of the probe pulse to improve the signal to noise ratio (SNR) of the detected signal, the spatial resolution is degraded simultaneously. Simplex code is used to overcome this conflict between the SNR and the spatial resolution. Using the theoretical analysis and numerical simulation, the Simplex code′s effect on Raman DOFS has been studied. In realizing a coding DOFS, there exits a problem of how to achieve high-power coding pump light, because the usual methods, such as pulsed-laser or internal modulation, can not be used. A method based on external modulation and optical amplifier is chosen, and a 4.7 km Simplex coding Raman DOFS experimental system has been set up. The results show that the 7-bit simplex code can improve the SNR of the detecting signal by around 1.6 times.

A distributed polarization maintaining fiber (PMF) pressure sensing system is presented based on polarization mode coupling in PMF. A 1050 m long fiber is tested and the measurement sensitivity and spatial resolution are determined. The relationship between coupling intensity and the size of the force as well as the influence of temperature on the system are tested. The experimental results show that the maximum detectable fiber length is longer than 1000 m. The measurement sensitivity and spatial resolution will decrease with the increase of fiber length. The temperature impact on this sensing system is very small when it is lower than 100 ℃. The influence of birefringence dispersion of the PMF on the system is also analyzed. The measurement sensitivity can be improved by a rotatable half wave plate to adjust the rotation polarization angle of the analyzer. The measurement sensitivity of the sensing system is 85 dB and the maximum spatial resolution is 98 mm by adjusting the rotation polarization angle of the analyzer.

By using bi-direction of the fiber cross-section asymmetric CO2 laser pulses exposure approach, the long period fiber grating (LPFG) sensing characteristics can be controlled and improved. This fabrication method is to write the LPFG on one side by CO2 laser, and then write the LPFG again on the other side with the same grating pitch and exposure energy. Under the action of the two exposure directions, the fiber refractive index was periodically modulated twice. Asymmetric thermal stress analysis results shown that the resonant peak of LPFG can shift in direction of either shorter or longer wavelengths, depending on the angle difference Δθ between two exposure directions changes in the second writing process. It is confirmed by the experimental results. We found this technique could be used in wavelength tunable LPFG fabrication or fiber optic sensors design to control and improve the characteristics of the components.

We designed a new type fiber Bragg grating (FBG) tilt sensor. It can be used to detect the magnitude as well as the direction of a twodimensional inclination by using four FBGs, the temperature effect has been eliminated completely without additional temperature compensation schemes. The experimental results show that this sensor has high angle sensitivity and measurement resolution and the tilt angle accuracy and resolution of the FBG tilt sensor are very good. Resolution of about 0.009° has been achieved. Furthermore, the accuracy and resolution of the FBG tilt sensor can be easily increased by either using a heavier hanging weight, or decreasing the angle between a pair of hanging fibers. Furthermore, if the size of the designed structure is further decreased, the error caused by temperature difference of four FBGs due to air disturbance can be eliminated. It can reduce the environment temperature effect on metrical result.

Refractive distribution in fiber Bragg grating(FBG) is expanded by Fourier series. The relation between step index profile and sinusoidal distribution is analyzed, and it is reasonable for using step index profile distribution to do the calculation. Rouard numeric method is used to analyze transmission spectrum of the cascaded Fabry-Pérot (F-P) cavities with length about sub-micron level. Based on two-beam optical interference approach, the characteristics of the cascaded fiber cavity and the connection between F-P cavity and FBG are given. An advisable method is proposed in which FBG can result from the cascade of fiber cavities, and basic principle of the FBG is established by utilizing the cascaded F-P cavity approach.

In the experimental research and industry applications of the fiber Bragg grating-based Fabry-Perot interfirometric (FBG FPI) sensor, its sensitivity has been widespread concerned. Considering the linewidth of the light source, the power transmission coefficient is amended and the theoretical formula of the sensitivity is deduced. Then, the key influence factors on the sensor sensitivity are discussed, including the cavity length, the coherence length of the light source, and the reflectivity of the FBG. The results show that the smaller the ratio between the cavity length and the coherence length is, the higher the sensitivity will be. When the ratio is chosen, there is an optimum reflectivity. If the reflectivity of FBG equals the optimum, the sensitivity is the highest. The results of comparison experiment on the sensitivity with different cavity lengths and sensitivity experiment on different reflectivities verify the correctness of the theoretical simulation.

A system based on Mach-Zehnder interferometer and supercontinuum white light, which is used for ultra-broadband and high precision dispersion measurement of photonic crystal fiber, is designed and constructed by considering the shortcomings of all the available methods. A photonic crystal fiber (PCF) with core diameter of 5 μm, hole diameter of 3.54 μm and pitch of 5.52 μm, is measured respectively. The measured dispersion coefficients are well in agreement with the simulation results, and the difference between the zero dispersion wavelengths is smaller than 50 nm, which show good perfermance of the method and the experimental system.

An all fiber laser which is suitable for distributed optical fiber sensor is reported. The laser is based on the technique of master-oscillator-power-amplifier (MOPA), whose seed laser is a laser diode and amplifier is Er3+ doped fiber amplifier. The laser operates in wavelength of 1550 nm with the tunable repetition rate and the pulsewdith, and the 3 dB width is less than 0.2 nm. The maximum peak power 1.1 kW of laser pulse is obtained, and the power of amplified spontaneous emission (ASE) in the output pulse is less than 10% in all condition.

Tunable diode laser absorption spectroscopy technology is a developing technollgy on new optical gas sensor in recent years, currently there are three research methods: harmonic amplitude method, first to second harmonic signal amplitude ratio method and difference method. The harmonic peak to average power ratio (PAPR) is proposed on the base of comprehensive analyzing on the features and disadvantages of those three methods. The performance of optical methane gas sensor with new method is stable, and the detection results of the prototype are as follows: response time of sensor is 10 s, in the range of 0～5×10-3 the detection precision and sensitivity are 5% of full scale and 2×10-5, respectively.

The mechanisms of fiber Bragg grating (FBG) strain sensors and cable tension measurement are analysised, and strain distribution of cable body, connecting tube, and anchorage zone are also analysised, and then a new cable tension measurement method based on FBG strain sensing of anchorage zone is proposed. Based on the stability principle of FBG, the embedded location of FBG is studied. Scale model experiments are carried out, and the FBG is embedded in the geometrical center of three steel wires to ensure the work stability of FBG. Experimental results show that the measured strain of anchoring region is only 62% of that of measured strain outside, and the central wavelength of the FBG in anchorage zone has a good linear relationship with the tension. The correctness of the theory and feasibility of the cable force measurement method are proved.

A fiber-optic refractometer based on the multimode interference in the singlemode-multimode core-singlemode fiber structure is demonstrated. The refractive index dependence of re-imaging resonant wavelength shift of the devices is investigated. It shows that the proposed sensor has a measurement resolution of 5.4×10-5 for the change of refractive indices from 1.336 to 1.372. The proposed sensor has great potential for biological and chemical applications.

The power drift of pump source and amplified spontaneous emission(ASE) noise are the main factors that result in the fluctuation of output power of superfluorescent fiber source(SFS). In order to obtain a stable output power of the SFS, a novel hybrid controller is designed, which combines the digital fuzzy control with the analog proportional control. Because both the high and low frequency noises can be constrained by the hybrid controller efficiently, the stability of output power of the SFS is clearly improved. The experimental results show that, with the hybrid controller, the short-term stability of output power of the SFS is ±0.032%(±0.0014 dB), and the long-term stability of that is ±0.041%(±0.0018 dB).

Based on the principle of intensity interrogation, the sensitivity of the fiber Bragg grating Fabry-Perot interferometer (FBG-FPI) strain sensor is analyzed and the influences of the grating length, the effective refractive index change and the cavity length of FBG-FPI resonator on the maximum strain sensitivity are also discussed. The strain sensitivities of two structures which FBG-FPI fibers are affixed to the transducer by different ways are also considered. The comparison between FBG-FPI and single fiber Bragg grating as well as traditional fiber Fabry-Perot interferometer with intensity interrogation is also presented. It is shown that the minimum theoretically detectable strain of the FBG-FPI strain sensors with intensity interrogation should be on the order of 10-12. The corresponding experiments, in which a periodic strain stimulated by a piezoelectric (PZT) affixed to the FBG-FPI, show that such a FBG-FPI strain sensor can be used to detect weak alternating strain signal and it has good linear character after the non-linear correction.

Methods related to the design of gain flattening filters for amplified spontaneous emission (ASE) and erbium-doped fiber amplifier (EDFA) are reviewed. A novel scheme to realize the gain flattening filter by using a piece of twin-core fiber and a wavelength division multiplexing (WDM) coupler is proposed and verified experimentally. The spectrum of the twin-core fiber can be adjusted by bending, twisting and stretching to meet the filter requirement. The flexibility and tunable properties make the proposed all-fiber device a good candidate for gain flattening filter. The experimental results show that the ASE spectrum can be flattened in the wavelength region of 1527.36～1561.04 nm with ripples within ±0.5 dB. The results show the filters with twin-core fiber may offer great potential for optical communications and sensing applications.

Grating assisted coupler which consists of a mismatched coupler with a Bragg grating written in only one core over the coupling region is a kind of non-interference device, so it is stable in performance and doesn’t depend on the position of the grating in the coupler region.A coupler with uniform coupling region making of SMF-28 and photoconductive fiber is fabricated by improved fused taper technology,then a Bragg grating is written in the coupling region with 248 nm ultraviolet laser,and a narrow bandwidth grating assisted coupler with maximum about reflectivity 15 dB, transmission 4 dB and bandwidth 0.1 nm is achieved to satisfy the dense wavelength division multiplexing (DWDM) system; The effect of the uniformity of coupler on the response is studyed; Its filter performance is tested in the 10 Gb/s fiber optic transmission system, and the results show that the device has good performance.

The phase consistency between different channels of the fiber laser sensor system has great effect on beamforming and target locating in the detection of underwater acoustics and seismic wave. So it is important to study the phase consistency between different channels. The factors influencing the phase consistency of the fiber laser array system based on dense wavelength division multiplexing (DWDM) and phase generated carrier (PGC) demodulation are analyzed. The analysis and corresponding calculations show that the influence of the sensor′s wavelength difference can be neglected. An experiment is carried out on two channels distribution-feedback (DFB) fiber laser sensor array system to demonstrate the analysis, The results show that the system has high phase consistency in the situation of different sensors and the results are in accordance with the theoretical expectations.

Based on the Fourier transforming of fiber grating refractive index modulation, a new analysis method is proposed from the spectral analysis, which is suitable for non-uniform ultra-long-period fiber grating (ULPFG). Also the coupled-mode equations are derieved for the non-uniform grid distribution and modulate depth. The method points out that the non-uniform ULPFG can be equivalent to the superposition of different uniform gratings. Numerical simulation and experiment about a non-uniform ULPFG indicated that this method, based on spectrum analysis, has an obvious advantages to analyze: 1) the effection on spectrum impacted by the grid number or the chirp size; 2) the phenomenon that one location with multiple resonance peaks.

The influence of laser-conditioning on defects of SiO2 mono-layer films, which is laser conditioned by small spot laser scanning process, is investigated by the spot-size effect of laser-induced damage. The threshold and the density of defect were introduced to characterize the initiating defects in the film. It is found that the laser-induced damage threshold can be increased by a factor of 1.6 under the largest spot-size used and the defects with low threshold can be removed by laser conditioning scanning process.

In order to adapt fiber lasers and fiber devices to the application of laser engineering system, an auto-correlator based on the fiber devices is designed. The 11 fiber polarization independent beam splitter, fiber collimator, fiber polarization controller, fiber coupler with different ratios, fiber isolator, and fiber interface spectrometer are used in the system. The influence of fiber polarization effect, polarization requirement of frequency-double crystal, coupling efficiency of fiber collimator on the autocorrelation measurement are analyzed and the corresponding methods of overcoming those defects are introduced. Experimentally the output pulse width of nonlinear polarization rotation mode-locked fiber laser is measured and the auto-correlator is feasible. It is indicated that the fiber auto-correlator has the characteristics of convenient connection with fiber laser systems, simple and light structure and so on.

A laser radar based on ranging principle of gain modulation is introduced, and its distance measurement accuracy under shot noise limited circumstances is analyzed. According to the accuracy model, a method which uses techniques of image registration and superposition is presented to improve ranging accuracy in airborne applications. For differences of distance accuracy among range image sequences, a weighted processing before registration is used for the purpose of assigning high weights to pixels with high accuracy, and a registration method called up-sampled phase correlation is used to locate image sequences accurately. The range images after registration are weighted superposed to minimize range error. Theoretical analysis shows that this method can effectively integrate detected signals among different frames. If n frames range images are superposed, the range error will be 1/n of one frame. Simulation and experimental results are demonstrated to verify the effectiveness of this method.

Automatic reconstruction of unknown three-dimensional (3D) objects is one of the classical research in machine vision, which is widely used in industrial inspection, robot localization and navigation, reverse engineering, and cultural relic restoration etc. A new approach of reconstructing unknown 3D models automatically is proposed. The new algorithm incorporates the visual region of the monocular laser-vision system with the limit visual surface of unknown model and selects the suitability of viewpoints as the NBV on scanning coverage. The limit visual surface is modeled by the known surface data obtained from initial view and is used to predict the maximal unknown object surface information. Then the next view visibility is determined, correspondingly the visual rotation angle and translation zones are obtained. And the position which can obtain the maximal visual surface area in the visibility zone is selected as the next best view position. The experimental results show that the method is effective in practical implementation.