The influence of structural parameters on laser wavelength continuous tuning range in external cavity semiconductor laser with Littrow configuration is studied. The influence of allowed machining errors at the key points such as the mirror rotation axis on laser wavelength continuous tuning range is calculated. The details of designing external cavity semiconductor laser are presented. An external cavity semiconductor laser is designed, and with a commercial semiconductor laser tube it can produce qualified 780 nm laser, with line width less than 1 MHz and wavelength continuous tuning range of 3 GHz. The semiconductor laser is frequency stabilized by use of the third and fifth harmonics of Rb saturated absorption spectra. The method for optimizing the laser frequency short-term stability is proposed, and the choice of modulating depth is explained theoretically in detail. With the proposed frequency stabilizing method, the stability of laser reaches 10-12 at 780 nm wavelength.

With a homemade semiconductor saturable absorber mirror (SESAM), different cavities have been designed to achieve mode-locking. Linear cavity continuous-wave mode-locking (CWML) lasers of single output beam with average power of 5 W, double output beams with average power of 5 W and adjustable output transmission have been presented. Bi-directional operation ring cavity passively continuous wave (CW) mode-locked laser end-pumped by a fiber coupled laser diode has been constructed. By placing the semiconductor absorber mirror in a special location, a new mode-locking technique for multiplying the pulse repetition rate of a picosecond passively mode-locking laser was successfully demonstrated. And 4 W mode-locking output of LD end-pumped Nd∶YVO4 laser was achieved by using a nonlinear mirror, which is constituted by a combination of a KTP frequency-doubling crystal and a dichroic mirror with high reflectivity for the second harmonic and partial transmission for the fundamental.

The two-dimensional (2D) Galerkin vectorial finite-element method (FEM) with 2nd transparent boundary conditions (2nd TBC) is reported and the modes of fibers with arbitrary cross-section shape and arbitrary refractive indices distribution are analyzed. By 2nd TBC the confinement loss (CL) of modes of photonic crystal fibers (PCF) is solved more accurately than by 1st TBC. The relative error between results of FEM with 2nd TBC and multipode method (MM) is no more than 10%. After the temperature properties of a single mode PCF is numerically simulated, the approximate formulas for the change of effective refractive index neff, effective radius Reff and CL of PCF with temperature are constructed. When the temperature coefficient of refractive index ξ varies slowly within the range of wavelength and temperature, as temperature inceases, neff inceeases linearly and the increment has nothing to do with wavelength λ, diameter of air hole d and distance between two nearest holes Λ; Reff decreases linearly and the decrement is in proportion to ξ, temperature increment ΔT, Λ2 and λ2, and inverse proportion to d; CL decreases linearly and the decrement is in proportion to ξ, ΔT, and CL, CL varies more rapidly with larger d/Λ at a longer wavelength. The dispersive properties of PCF are not affected by temperature change.

Nano-Al2O3 coating was prepared on the surface of H13 steel by nano-composite plating (NCP) and then treated by high power continuous wave CO2 laser. Scanning electron microscope (SEM) was used to observe the surface and cross section morphologies of coating before and after laser treatment. Energy dispersive X-ray spectroscope (EDS) was utilized to analyze elements distribution on the surface of coating before and after laser treatment. X-ray diffractometer (XRD) was employed to analyze the microstructure of coating before and after laser treatment. The changes of micro-hardness and coefficients of friction before and after laser treatment were observed. The results revealed that strengthened coating had good performance such as flat surface, uniform component, fine microstructure and metallurgical bonding with parent metal. Nano-Al2O3 particles were distributed on the surface of strengthened coating uniformly. The micro-hardness of the strengthened coating was 1.5～1.8 times of untreated coating, while its coefficient of friction was about half of untreated coating and one third of parent mental. For the surface of strengthened coating and parent metal, grain-abrasion was dominate, however the NCP Al2O3 coating included grain-abrasion and sticking abrasion.

The temperature field, molten flow and gas jet induced convection and heat exchange boudary conditions are important for material surface formation quality and tissue transformation in laser texturing. Then a three-dimensional transient numerical model is developed for the heat transfer, convection heat transfer and morphology evolvement of the molten pool during laser surface texturing. Based on the software Fluent, the model adopts the enthalpy and volume of fluid (VOF) methods to solve the solid-liquid phase boundary and free surface flow numerically. The evolution of phase interface and free surface, and the effect of assist gas on the surface profile are analysed. The heat transfer and fluid motion, as well as the surface shape and scale of the molten pool are numerically approached for the pulse laser texturing with different processing parameters. The numerical simulation was consistent with the result of laser texturing experiments.

The femtosecond laser (800 nm, 50 fs, 1 kHz) induced damages in Si wafer and fused silica are studied by experiments. The morphologies of structural changes in the two inorganic silicon materials have been investigated by means of charge coupled device (CCD) camera and scanning electron microscopy (SEM). Furthermore, the relationship of damage threshold to laser pulse duration and photon energy is studied. The main process during laser-induced damage in Si wafer is that avalanche ionization which is seeded by electrons due to defects, while that avalanche ionization is seeded by electrons excited by multi-photon ionization is the main process during laser-induced damage in fused silica. The energy deposition is initiated by multiphoton ionization rather than impurities or defects to start an electron avalanche in transparent materials.

The most effective factors to the dimensions of deposit layers in the laser rapid forming (LRF) processing have been achieved through using orthogonal regression design (ORD) and regression analysis method. The most effective factors on the height of deposition layer are powder feeding rate and scanning velocity. And the most effective factors on the width are spot diameter, scanning velocity, and interaction between laser power and spot diameter. The approximate relations between the deposition layer dimensions and their most effective factors are obtained and validated.

AZ91HP magnesium alloy was treated by laser melting in vacuum. The results showed that with high power laser and rapidly scanning speed, the melted layers mainly consisted of α-Mg dendrite and lath-shaped β-Mg17Al12 distributing in the inter-dendrite, and the melted layer contained more β-Mg17Al12 than that of as-received Mg alloy. With the increase of laser powers, the grain dimension of the melted layer increased, and the increased amplitude along the long direction was 10 times of that along the width direction. Because of the grain refinement and the enhancement of the hard phase β-Mg17Al12, the microhardness of the melted layer was increased by 90%, the wear resistance was increased by 78%, and the corrosion resistance was significantly improved compared with as-received Mg alloy.

The autocorrelation characteristics of the super-Gaussian optical pulse and their variations with the edge sharpness parameter, linear chirp parameter, noise-pulse and random noise are investigated by use of numerical analysis method, and compared with the relevant parameters of the original pulse. A useful method of filtering random noise is given and validated by experiments. When the edge sharpness parameter increases, the curve of intensity autocorrelation becomes narrow, and the autocorrelation spectral curve broadens without chirp, noise-pulse and random noise. When the linear chirp parameter increases, the temporal waveform of the pulse and the curve of intensity autocorrelation keep unchanged; the curve of pulse spectra broadens and the oscillatory structures appear at its edges and increase; the autocorrelation spectral curve broadens and its edges are still smooth. The variation of pulse autocorrelation characteristics is complex when noise-pulse or random noise exists.

The phase matching angle and the non-collinear angle for ultrashort and mid-infrared optical parametric amplification (OPA) in MgO∶LiNbO3 are calculated. With pump light wavelength fixed at 800 nm, the non-collinear angle should be optimized between 1.74° and 2° when the seeded signal wavelength is 1053 nm, and the non -collinear angle should be optimized between 1.05° and 2.18° when the seed signal wavelength changes between 1046 and 1067 nm. Especially, when the seeded signal wavelength is 1057 nm and the non-collinear angle is 1.76°, the group velocities mismatching can be almost completely compensated with the pump light wavelength fixed at 800 nm. The series of signal light wavelength, mid-infrared light phase matching angle and non-collinear angle are also achieved when the group velocities are almost completely compensated with the pump light changing between 780 and 810 nm.

A cylindrical microcavity was made by immersing a silica capillary in a solution of rhodamine 6G whose refractive index is lower than capillary′s. Whispering-gallery-mode (WGM) laser was observed in the cylindrical microcavity by evanescent wave exciting and coupling dye gain. Due to dye gain was excited by a pumping evanescent wave, the gain was limited around the cylindrical microcavity closely, and the pumping efficiency was then improved greatly. The pumping threshold for laser emission was reduced to 9.5 μJ in this method compared with a value of 200 μJ in a method of only evanescent wave coupling dye gain. Wave number intervals of whispering-gallery-modes between measured and theoretic values matched very well. The calculated positions of structural resonances of whispering-gallery-modes matched the experimental results very well too. All those indicated when silica fiber was replaced by silica capillary as cylindrical microcavity, the same whispering-gallery-mode could also be obtained.

An integrable optic-fiber coherent state quantum identification system is presented. In the scheme, the Stokes vectors of polarization coherent state are employed as quantum signal carrier, the dynamic polarization controller serves as a modulation device, and the inherent quantum noise guarantees the security. The driving circuit of laser pulses, detection circuit for weak narrow laser pulses, and signal synchronous module, are self-designed. Classical communication needed by quantum secret communication is implemented by Socket network communication program running on the TCP/IP local area network. The running key employed in the system is 12 bit. The transmission rate of identity picture is 8 kbit/s, the bit error rate between legal users is less than 10-4, and the information I(Alice,Eve) per bit obtained by an attacker is less than 10-14.

The thickness, refractive index and transmission loss of films are important parameters in determining electro-optical coefficients and designing optical waveguide devices. The guest-host polymer disperse red 13 (DR13)/poly-methylmethacrylate (PMMA) thin films with three different concentrations were prepared by the spin-coating method, whose absorption spectra were obtained using a spectrophotometer. Their refractive index and thickness were measured with a prism coupler and the dispersion curve was plotted by fitting their refractive indices at different wavelengths. The experimental apparatus for an imaging technique were set up, by which the films′ transmission losses were measured with the help of image processing program written by ourselves. From the absorption spectra, there are two large absorption peaks at about 300 nm and 500 nm and no absorption peak in the telecommunication wave band, so this material can potentially be used in telecommunication devices. Thicknesses of the films are about 1～2 μm. It can be seen that at the same input wavelength, the refractive index becomes greater as the mass ratio increases, and when the wavelength of the input laser increases, the refractive index of the same mass ratio reduces. The error values of thickness and refractive index of the films are about 3.2×10-1 μm and 1.5×10-3. The transmission losses of three different mass ratio (10%, 15%, 20%) are 1.5269 dB/cm, 2.7601 dB/cm and 3.6291 dB/cm, respectively. It is shown that the transmission loss increases as the mass fraction increases, that is, DR13 is more important for the transmission loss than PMMA.

During the coating process, the metal contamination in the vacuum chamber is one of the significant factors to reduce the optical properties of thin films. The gas composition during coating process was tested by high-vacuum residual gas analyser. It is found that when applying brass pedestal in the vacuum chamber, zinc will sublime from the pedestal under high temperature and deposit in the thin film, thus reducing its laser-induced damage threshold (LIDT). The composition of the coatings was studied by surface analysis technology which proved the zinc impurity in the coatings. And the laser-induced damage experiment also showed that its LIDT was distinctly reduced.

By KrF pulsed excimer laser deposition (PLD), the high quality diamond like carbon (DLC) films have been deposited on ZnS substrate to improve its environment reliability. The plasma excited by the laser is also analyzed. And the helpful particles in plasma are filtered and deposited. The adhesion strength of DLC film with ZnS substrates was improved without narrowing the spectral range and decreasing the transmission. The uniformity of films is improved to 95% in 80 mm area by off-axis rotating-substrate method. The spectral range of DLC/ZnS sample is 0.53～12 μm, especially the transmission is higher than 70% in the spectral range of 1.3～11 μm, moisture-resistance is 95%～100%, and working temperature is -45～85 ℃. The adhesion strength has achieved requirement of “General specification for optical coatings” (GJB2485-95). The research shows that the environment reliability of ZnS has been improved obviously by depositing DLC film.

In order to recognize an object and determine its spatial position, 180 training images are divided into four image sets, and the feature vectors of all image sets are calculated. It is shown that each image set can be represented with three feature vectors, so the total four feature spaces can be constructed with only twelve feature vectors. The object decomposition and reconstruction are simplified greatly. Based on the relation between object vector and its reconstructed vector, the object can be determined as true or false, and its spatial position can be located. Simulation results show that the method of constructing multiple feature spaces and the object recognition rule are effective, and object recognizing and spatial position determining under out-of-plane rotation can be achieved.

A fiber optic hydrophone based on Sagnac interferometer with saw-tooth active phase biasing technique is proposed and demonstrated experimentally. The influence of 2π reset error of saw-tooth wave on system is analyzed. A phase bias around π/2 is obtained by use of a saw-tooth modulation signal with frequency at 94.05 kHz, and reset voltage of 10.84 V. Acoustic signal is gotten directly by A/D converter trigged by a pulse signal synchronized with saw-tooth modulation signal, and the influce of 2π reset error is depressed. The results show that when the system frequency is 10 kHz, the average amplitude of the signal is 0.067 rad, with variance of 3.08×10-5 rad and ralative variational amplitude of only 0.046%. The phase bias of system is quite steady.

The influence of mode mismatch on measurement in continuous-wave cavity ring-down technology was theoretically analyzed and experimentally studied. According to q-conversion of Gauss beam and mode coupling theory, the influence of light beam radius mismatch and phase front curvature mismatch on measurement was numerically simulated and experimentally confirmed as to general stable cavity with large Fresnel number. The results show that mode mismatch mainly affects the cavity ring-down signal output power rather than its ring-down feature when the cavity′s Fresnel number is large. Under the same case of mode coupling, a laser of higher power and a detector of larger focal area can improve the measuring accuracy.

In sinusoidal phase modulating (SPM) interferometry, the spectrum leakage is generated due to the frequency variation of modulating signal or sampling signal. The spectrum leakage induces errors in the measurement result by reducing values of harmonic components. The spectrum leakage in a SPM interferometer and its influence on measurement accuracy are analyzed theoretically with the discrete Fourier transform method. The mathematical expression of the measurement error induced by frequency leakage is obtained. In experiments, when the frequency shift is -0.3～0.3 Hz, the induced measurement error is 0.3～7.9 nm. Beyond the range, the measurement error increases obviously. The experimental and theoretical data agree well with each other.

According to the refractive index change of glass, sliver and polystyrene for different incident wavelengths, the sensitivity of surface plasmon resonance (SPR) sensor for different wavelengths were analyzed. The experimental data are used to fit the refractive index change of glass, sliver and polystyrene with wavelength, and the SPR sensor sensitivity under different wavelengths was achieved by application of the fit result in theoretical calculation. The optimized wavelengths under different sensitivity requirement of SPR sensor were proposed. To prove the theoretical result, the light sources with wavelengths of 568 nm and 632.8 nm were applied to SPR sensor. The two light sources were used to achieve sample surface morphology, and the result was found that the detail of sample was better presented by the light source with wavelength of 632.8 nm than that with 568 nm wavelength.

The key technology of single CCD image based non-contact measurement is three-dimensional (3D) reconstruction. The 3D surface model is usually obtained directly through shape from shading (SFS) method. But when the resolution of an input image is low, the resolution of the 3D surface model reconstructed by the above way would be poor and can not meet practical demmand. To resolve this problem, an improved 3D reconstruction method is proposed. First, the B-spline interpolation method is used to improve the image resolution, and the parameter mapping method of pixels is applied to avoid the image distortion and high frequency missing; then the SFS method is adopted to reconstruct the amplified image according to the gray gradient of image. The experimental results demonstrate that the proposed method can conserve the detail of an image, and improve the resolution and smoothness of the reconstruction model effectively. It will help improve the precision of non-contact measurement based on single CCD image.

The coherently coupled nonlinear Schrdinger equation is used to study the modulation instability of laser pulses propagating in fiber Bragg gratings with raised cosine apodization function in both anomalous and normal dispersion regimes. The results show that modulation instability is produced in both anomalous and normal dispersion regimes. The obvious regular gain spectra have been produced when the input power reaches a certain value in anomalous dispersion regime. The modulation instability in normal dispersion regime rises from a fixed value to infinite when the input power is in the range that can produce modulation instability. Furthermore, the gain spectra have been restrained by raised cosine apodization function in both dispersion regimes.

A full-duplex radio-over-fiber (RoF) system with optical millimeter-wave generation utilizing optical phase modulator was designed and experimentally demonstrated. Carrier suppression double sideband optical signal with 40 GHz repetitive frequency is generated by using an optical phase modulator along with optical filtering technique. An optical interleaver was employed to separate the two first-order sideband carriers, one of the carriers was used to carry 2.5 Gbit/s downstream data, while the other was sent to base station for reuse for modulating upstream data. It was experimentally demonstrated that the 2.5 Gbit/s data for bidirectional transmission were transmitted over 40 km standard single mode fiber (SMF-28) with less than 0.5 dBm power penalty. By using optical phase modulator along with optical interleaver to generate optical mm-wave, and adopting the wavelength reuse technique, the proposed RoF system becomes simple and cost-effective.

It is a promising approach to achieving high-speed all-optical signal processing based on the combination of semiconductor optical amplifier (SOA) and optical bandpass filter (OBF). The inverted wavelength conversion (WC) of the nonreturn to zero (NRZ) and the format conversion from NRZ to pseudo return to zero (PRZ) are demonstrated synchronously based on single SOA and an optical bandpass filter with 0.32 nm bandwidth. The conversion results depend on the OBF detuning as respect to the probe carrier. When the OBF detuning is -0.24 nm, the output will be the inverted WC and the filter is used to accelerate the SOA gain recovery. When the detuning is +0.41 and -0.48 nm, the output result will be the NRZ to PRZ format conversion and the generated PRZ pulses appear at the leading edge and trailing edge of the NRZ signal respectively. The filter completes phase modulation to intensity modulation conversion. The converted PRZ signal realizes wavelength conversion as well.

The key technologies of achieving room-temperature stable multi-wavelength fiber lasers (MWFLs) are how to restrain the homogeneous broadening effect of the doped fiber at room temperature. We summarize the main technologies and methods reported recently to realize the room-temperature MWFLs, and introduce our innovative works in this field, including proposing several novel structures and operable technologies of switchable multi-wavelength fiber lasers using special fiber Bragg gratings (FBG) with several resonance peaks, such as FBG in multimode fiber, FBG in polarization maintaining fiber and sampled FBG. Switchable multi-wavelength fiber lasing oscillations with less than 2 nm wavelength spacing, tunable wavelength and spacing and excellent room-temperature stability were demonstrated and realized. Two other erbium-doped MWFL designs are proposed respectively by using nonlinear polarization rotation (NPR) effect and a nonlinear optical loop mirror (NOLM) to induce intensity-dependent loss. As a result, power-stable, broad bandwidth and uniform multiwavelength operations are obtained for both laser sources. Up to 50 wavelengths lasing oscillations with wavelength spacing of 0.8 nm within a 3 dB spectral range of 1562～1605 nm have been achieved. The measured power fluctuation of each wavelength is about 0.1 dB within a two-hour period.