For wavefront sensorless adaptive optics (AO) systems, the efficiency of close-loop control methods is of greate importance. In this paper, a gradient descent algorithm with Hadamard model is proposed. The working principle of AO close-loop based on the algorithm is introduced. The working process and feasibility of this method are analyzed by comparing with the serial gradient descent algorithm and stochastic parallel gradient descent algorithm. The numerical simulation model with this method is setup, and the close-loop corrections with random generated aberrations are performed to verify its precision and convergence speed. The results show the gradient descent algorithm with Hadamard model can be used in wavefrontless adaptive optics, and compared with the stochastic parallel gradient descent algorithm, it is not only easier to be implemented but also more efficient.

Phase screen can reflect the change of refractive index correctly. Constructing an accurate atmospheric turbulence phase screen with small calculation amount is the key of numerical simulation. According to the statistical characteristics of turbulence, square atmospheric turbulence phase screen is calculated using fractal model. The simulation results complying with Kolmogorov atmospheric turbulence are obtained by analyzing the simulation results and theoretical values of phase structure function. Performance of atmospheric turbulence phase screen simulation based on fractal method is also analyzed. Analysis results show that square atmospheric turbulence phase screen simulation based on fractal method is consistent with the theoretical values in statistical properties. The simulation error of phase screen increases with fractal iterations from the area of low-frequency to the one of high-frequency. With the increasing grid numbers of phase screen, the accuracy of phase screen simulation is reduced. Besides, the number of phase screen needed is increased. As the number of phase screens increases, the simulation accuracies of atmospheric turbulence phase screens with different intensities turn similar.

The effects of the expansion angle of partially coherent Gaussian-Schell (GSM) beam on the receiving optical power are analyzed, numerical calculation and simulation are used in the laser extension angle and the receiving optical power of the laser communication link, and at the same time the influence of the beam′s expansion angle on the power of the laser communication link is analyzed quantitatively. The results show that, the receiving power of partially coherent GSM beam is inversely proportional to the beam waist radius, as well as the spatial coherent length and transmission distance. Besides it is proportional to the wavelength. Based on that, when comparing partially coherent GSM beams with coherent Gaussian beams, it turns out that the power loss of the partially GSM coherent light caused by beam expansion is less than coherent Gaussian light. Under the certain condition of initial parameters, the receiving power of partially coherent beam is completely 2.65 times larger than coherent beam.

A system including underwater green light laser transmitter and receiver is designed. The optical transmission experiment is made in coastal waters of Weihai and a photomultiplier tube is used as a detector. Different waveforms and signal strengths under different distances are measured by using different receiving loads. The results show that a bigger load will get an increased distance. The effective transmission distance is 26 m when the load is 1 MΩ. Data is fitted under different distances, and it is found that the attenuation in coastal waters appears e exponential decay, the coefficiency is 0.5 m-1. It can be deduced that the system will get a better performance in sea with smaller attenuation.

A solution of optical system to receive laser echo light based on the configuration and transmission properties of fiber bundle is proposed. This system just needs a detector with diameter of 3 mm for realizing the panoramic detection. The system consists of three parts: front coupling system, fiber bundle and rear focusing optical system. 8 sets of coupling subsystem couple the eight sectors′ laser echo lights into the fiber bundle. Then, fiber bundle as a device to collect light, converts the 8 rectangular fields of incident light into a circular field of emergent light matching the circular detector. The emergent light from the fiber bundle is converged on the detector by the rear focusing optical system. The energy receiving efficiency is more than 80% and the difference between each view is less than 8% through simulation. The result indicates that the system′s detection range is far and consistent in each direction. Due to requiring only one infrared detector to realize no blind spot panoramic detection. It facilitates subsequent processing.

Q-switched Er:YAG laser and free-running Er:YAG laser are used to study the laser ablation for the fresh porcine thighbones tissue in vitro. The ablation threshold range of the Q-switched laser and the free-running laser are 1.80~2.40 J/cm2 and 3.46~5.00 J/cm2, respectively. The results indicates that the ablation threshold of the Q-switched laser is lower. The fresh porcine thighbones tissue in vitro is irradiated by the two laser modes under the conditions of repetitive rate of 3 Hz, pulse energy of 200 mJ, and pulse number of 15 times. In addition, the morphologic changes of the tissue crater are observed by a scanning electron microscope (SEM). The morphology and the microstructure of the incision surface of the tissue ablated by the two laser modes are compared. Meanwhile, in the process of laser ablation, temperature distribution of the irradiation region with the two lasers for the tissue is measured by thermal infrared imager. Results show that after laser ablation for the tissue by the Q-switched laser, the lancing is smooth and the thermal damage for the surrounding histocyte is slight. Thus, in the process of the laser ablation for the porcine thighbones tissue in vitro, the Q-switched laser has a significant advantage.

A C-scanning photoacoustic imaging system is designed with a pulsed laser diode, which has the properties of low cost, small size, compact structure, and high repetition frequency. The 3D-visual reconstruction algorithm is employed to observe the 2D and 3D photoacoustic image. During the experiments, the laser diode and the ultrasonic transducer keep the fixed positions using a front side detection configuration. The experimental results show that lateral resolution of the imaging system is determined as 0.5 mm, and the speed of A-scanning is 0.16 s/div with a signal-to-noise ratio of 20.6 dB. The laser diode is only 10 cm×3 cm×3 cm with a pulse energy output as low as 14 μJ. The proposal method has the potential to be developed as a configuration of inexpensive, real-time, and portable noninvasive photoacoustic imaging system for biomedical tissue.

The synthetic aperture (SA) imaging based on multi-images fusion is dynamically focused in both transinission and receiving yielding an improvement in resolution. But this imaging technique sets high demands on processing capabilities, data transport and storage. It also makes the implementation of a SA system very challenging and costly. The proposed method is specifically for this issue. The method uses the focused image lines as input data, and takes advantage of the synthetic aperture imaging based on multi-images fusion which picks out the coherent samples of the recorded echoes and sums these samples, thus obtaining a high resolution image. The proposed method is dynamically focused in both transmission and receiving, and a range independent lateral resolution is obtained. With Field II software, simulations on scatters and phantom are made and compared with broadband minimum variance (MV) beamforming and SA imaging based on multi-images fusion, the feasibility of the method named a fast synthetic aperture (FSA) imaging is verified.

A picosecond laser machining system is designed, which can output 355、532、1064 nm picosecond laser. The maximum single pulse energy is 1.5 mJ and the pulse width is 9.12 ps. Through the axial aberration compensation design, the maximum distance of axial focus compensation is 0.4 mm, the diameter of minimum focal spot is 3 μm and the maximum peak power density is 0.6×1015 W/cm2. With this system, the machining experiment of different wavelengths and different materials is completed. The results show that 1064 nm picosecond laser can be used to cut mobile phone screen, 532 nm picosecond laser can be used to product photoelectricity detector and 355 nm picosecond laser can satisfy micro-machining requirements of metal materials.

The morpha and spectral character of damaged CCD, which has been irradiated by picosecond pulsed laser, are studied by using scanning electron microscope and micro-Raman spectrometer. Morphological damaged images of different layers are observed on the surface of CCD. The damage sequence is decided by comparing different layers′ conditions with a scale as small as a single pixel. The damage status of W-shield and poly-Si around one pixel is observed. On the cross section, the red-shift of Raman spectrum of bulk silicon material is measured and it means that bulk silicon melts, which brings a short-circuit between surface poly-Si electrode and substrate. The short-circuit explains the thermal mechanism of complete failure.

In order to enrich the preparation methods of biomedical porous Ti, a technology of selective laser melting is used to prepare porous Ti. The effect of spot diameter/scan space (D/d) and powder on the structure of porous Ti and the formation mechanisms of big holes and small holes are investigated. The results demonstrate that when the experiment is 95%Ti+5%TiH2 (95%, 5% are mass fractions) and D/d=1, porous titanium holes are comprised of big holes and small holes, small holes make part of the big holes connected, to be there-dimensional connectivity structure. Laser beam irradiates preset powder selectively, and the area without irradiated form big holes. Big holes are decided by D/d. Big holes are formed under D/d=1, while under D/d=2, are not. TiH2 is decomposed and produces H2 under the irradiation of laser beam, with the rapid solidification and “Piston Effect”, and some H2 does not have enough time to overflow from weld pool and thus form small holes; the effect of small holes on porosity is not obvious, but the existence of small holes improve the open ratio of the sample dramatically.

Three-dimensional laser milling is based on the single layer milling. So, the depth of single milling determines the quality of the three-dimensional laser milling. There are many mutual factors affecting the laser milling, which can not be expressed as a linear relationship. Based on the artificial neural networks, the bidirectional feed-forward back propagation (BP) neural network models of milling width and depth are set up with Matlab platform. The neural network models are tested using samples obtained from the laser milling experiments. The results show the feed-forward BP neural network with hidden layer can predict and optimize the process parameters. Which is helpful to reduce the times of experiments.

Welding of 5083-H116 aluminum plate with thickness of 4 mm using IPG YLS-6000 fiber laser is presented. The influence of parameters on the weld forming and weld defects is carried out in this paper. Also, microstructure and mechanical properties of joint is analyzed. It indicates that laser power, speed and defocus have great effects on penetration state. The main problems of weld of 5083-H116 aluminum plate are sag and undercut. Under the condition of penetration, using high power of 5 kW and 6 kW and speed range from 6 m/min to 9 m/min can get ideal weld formation. With the optimal parameters of zero defocus, 6 kW power and 9 m/min welding speed, metallographic observations indicate that crystalline morphology near the fusion line is dense columnar, and in center of the weld which is isometric dendrite. Besides, the segregation of weld is more visible. The test shows that the micro-hardness of weld fluctuates and the mean value is less than the parent material. Tensile strength of joint is up to 287 MPa, about 83.9% of parent material. Yield strength is about 227 MPa. Elongation is about 3.57%. The tensile fracture happens in weld, and belongs to ductile fracture.

After the multiwall carbon nanotubes are irradiated by a 1064 nm wavelength fiber laser, connection phenomenon is found by scanning electron microscope (SEM) observation. The SEM images clearly demonstrate the melting and solidified phenomenon between the two overlapping multi walled carbon nanotubes. Two or more multi wall carbon nanotube fuse together, and the tube wall is smooth and complete without any sign of damage. Through the transmission electron microscopy (TEM), the new graphite layers are found in the connection. Besides, It is found that in the case of a certain power density, as the laser irradiation time increases, the present multi-walled carbon nanotubes show the trend of melting connecting to destruction.

In order to improve the powder convergent characteristics of flow field of the inside-laser powder feeding nozzle in laser metal direct forming (LMDF) and obtain longger converging focal length, smaller converging diameter and divergence angle, the powder converging parameters are studied by experiments with different shielding gas pressure under unloading and carrier gas conditions. The experimental results indicate that the powder converging focal length increases, converging diameter and divergence angle decrease with the growth of shielding gas pressure under unloading conditions. The powder convergent characteristics gets better. The powder converging focal length firstly gets longger then gets shorter, converging diameter and divergence angle decrease with the shielding gas pressure increasing under carrier gas state. The effect is preferred when the shielding gas pressure is equal to the carrier gas pressure. It has an important guiding significance for process optimization during LMDF with the inside-laser powder feeding way.

Alumina engineering ceramics have been widely used in modern industry for their superior thermal physical and mechanical properties. In order to study the surface quality of alumina ceramics during pulse-laser assisted turning, experimental investigations are conducted on pulse-laser assisted turning of hot-pressed 96 alumina ceramics. Based on the orthogonal experiment method, optimum operating conditions are achieved, and the influences on surface roughness and defects during pulse-laser assisted turning of alumina ceramics are attained under different parameters such as laser power, pulse frequency, rotational speed and feed. The results indicate that the feed makes the major contribution to overall turning performance, which reaches 41.97%. Good surface roughness and less surface defects can be achieved under the optimum operating conditions, which are laser power of 50 W , rotational speed of 510 r/min, pulse frequency of 50 kHz and feed of 0.01 mm/r.

In this paper, picosecond laser drilling of quartz glass is studied. The 532 nm picosecond laser induced ablation threshold of quartz glass is explored and the basic parameters of the picosecond laser processing of glass, including the laser power, repetition rate and processing time, are investigated. From the study, the ablation threshold of quartz glass at picosecond pulse width is concluded to be around 2.01 J/cm2. It is found that the diameter and depth of the holes drilled in quartz glass are proportional to the laser fluence and processing time, but the rate of increase levels off finally. Meanwhile the laser repetition rate also has an important influence on the machining quality. Picosecond laser crack-free processing of quartz glass is achieved by optimizing the laser parameters based on the ablation threshold and the processing rules obtained in our research.

As the direct tool of metal deforming in rolling, the quality and operational life span of mill roll are of high significance. Mill roll is the main consumption component with a high ratio in steel rolling production costs. In this paper, the indefinite chilled cast-iron roller is surface-modified by laser cladding, using Cr2C3 and NiCr powder. The results indicates that, the cladding layer and base materials are a good metallurgical bond, and the microstructure of cladding layer is finer than base materials. The average microhardnesses of base materials and cladding layer are 506 HV and 1137 HV, respectively. Compared with the base material hardness, cladding layer hardness increases by 25%, so the wear resistance of the cladding layer is significantly improved. Microcrack in cldding layer includes solidification crack and low plasticity crack, and the microcrack is effectively decreased by the secondary scanning and adjusting chemical composition of the powder.

The dispersion-managed passively mode-locked Yb-doped fiber laser is designed, using negative group velocity dispersion characteristics of photonic crystal fiber at 1 μm wavelength. The net group velocity dispersion of the fiber laser is normal. Larger pulse energy can be generated from this laser. The generation of the dissipative dispersion-managed soliton is studied through numerical simulation. The amplitude modulation of the saturated absorber and the gain dispersion of the Yb-doped fiber play significant roles in the formation of the soliton. The effects of the positive and negative dispersion elements on the pulse width and spectrum width are analyzed. The time bandwidth product increases gradually with the net group velocity dispersion value decreasing. The shortest pulse of 90 fs width is obtained through further compression.

This paper reports a passively mode locked fiber laser from a linear cavity. It consists of semiconductor saturable absorption mirror (SESAM) and fiber Bragg grating. Another function of the SESAM is to achieve passive mode locking based on saturable absorption. The polarization of picosecond pulses is maintained by polarization maintaining fiber. All-fiber structure of fiber laser is achieved by a homemade fiber coupled SESAM. Repetition rate of mode locked trains of 40 MHz, pulse width of 25 ps, spectral width of 0.12 nm, mode locked threshold average laser power of 8 mW, and the maximum laser power of 19 mW are obtained. Mode locked train without Q-switched mode locking is proved by radio frequency (RF) spectrometer.

The continuous-wave single-frequency single-end-pumped Yb:GdCOB crystal laser is designed and experimentally demonstrated. A novel output method is proposed to achieve the spatial and fiber output with compact sandwiched structure, and the single-frequency operation is realized in an ultrashort cavity. The maximum output power is 40.9 mW and the slope efficiency is 13.7% at 1083.2 nm with 360 mW incident power and a 1-mm-thick crystal, and the fiber output power is 337 μW. Meanwhile, the maximum single-frequency output power is 4.5 mW at 1078.2 nm with 380 mW incident power and a 0.2-mm-thick crystal.

AbstractBlue semiconductor laser pumped Pr:YLF orange laser at 607 nm is reported. Compared to laser diodes (LDs), the optically pumped semiconductor lasers (OPSLs) have better beam quality, higher output power and higher absorption efficiency. So pumping with OPSLs can help to improve the laser performance. The polarized emission spectra of Pr:YLF in the orange band at 12 K and 300 K are measured, showing that the orange transition 3P0→3H6 consists of 6 emission lines. An OPSL providing output power of up to 1.9 W and centered at 479.2 nm is used as the pump source. With a 5 mm-long Pr:YLF crystal with a doping concentration of 0.5% and a plano-concave cavity, orange laser emission at 607 nm with an output power of 524 mW is obtained, corresponding to a slope efficiency of 39.1%.

For the nozzle throat ablation problem existing in the gain generator of high power DF/HF chemical lasers, there is a way called film cooling, to protect the wall and the throat of the nozzle. The differences of flow characteristic are numerically simulated under the different mass fluxes of the helium film and the influence of film on main stream is analyzed. The relationship between the throat width of the helium film, the main stream and the nozzle′s throat width is important for the design of nozzle′s throat with gaseous film cooling through the slot.

An all-fiber configuration linearly-polarized fiber laser reported, with one pair PM fiber Bragg grating for wavelength and polarization selection. The maximum linearly-polarized laser output power is 30.2 W, which respects to the launched pump power of 50 W from a 975 nm diode laser pumper. The optical-to-optical efficiency is 60%, and polarization extinction rate (PER) is better than 22 dB. The output central wavelength as well as the full width at half maximum (FWHM) of spectrum can be precisely adjusted by controling the temperature of the fiber Bragg grating.

The systematic research on tilt-tip control in coherent beam combining using delayed-stochastic parallel gradient descent (D-SPGD)algorithm is demonstrated. The control effects are compared with those of the traditional stochastic parallel gradient descent (SPGD) algorithm. The theoretical research results reveal that the D-SPGD algorithm can weaken the limitation of time-delay on control bandwidth, and improve the tilt-tip control effect of long-distance system obviously. D-SPGD algorithm is a promising method to be applied in practical system of coherent beam combining over long distance.

Photodarkening (PD) is recognized as an important factor that affects the reliability and lifetime of many fiber lasers and amplifiers. Temporal characteristics of the fiber laser and a self-recovery phenomenon with time dependence in darkened fibers are observed. A feasible method to measure PD is designed and several domestic fibers are tested. A 638 nm laser diode (LD) is utilized to bleach the darkened fiber. Experimental result indicates that the excess loss caused by PD can be considerably mitigated by 638 nm irradiation and one reasonable explanation is demonstrated.

Dual-wavelength solid laser pumped NdYAG in miser configuration combined with the iodine absorption frequency stabilization technology and the external cavity-enhanced second harmonic generation technology is constructed to develop 266 nm ultraviolet (UV) laser wavelength standard device. The iodine absorption frequency stabilizing system read by a single dual-wavelength solid-state laser of 532 nm can give a reference frequency. When the output frequency of the 532 nm laser departs from the reference frequency, the cavity length of this laser will be controlled by a feedback signal from the iodine absorption frequency stabilizing system through a servo control system, so that the output frequency of the 532 nm can be locked to the reference frequency provided by the frequency stabilizing system. Because the laser at 532 nm is obtained from the frequency-doubled 1064 nm laser through PPKTP frequency doubling crystal, the frequency stability of the laser at 1064 nm can be assured. The single dual-wavelength solid-state laser of 1064 nm can provide a frequency stable UV laser output at 266 nm through double frequency doubling process.

Semiconductor optical amplifier-based ring cavity laser (SOA-RL), which has been widely used in optical communications, optical fiber sensing, and bio-photonics fields, can be tuned at an ultra high speed up to megahertzs over 100 nm bandwidth range with high signal-to-noise ratio (SNR) and good flatness output. A steady-state model and segmentation algorithms are employed to investigate the gain spectra of the SOA and the laser wavelength of the SOA-RL when the SOA is driven by some non-uniform injections, such as linear, quadratic, exponential, or square root functions. The results show that the laser wavelength changes slowly with the change of injection current when its average is greater, and there is a minimum value when the injection current is exponentially distributed along the SOA, which exhibits high wavelength stability.

A new structure based on carbon nano-tubes (CNTs) and nano-gold particles is presented for surface enhanced Raman scattering (SERS) substrate. By chemical vapor deposition (CVD) method and spin coating, CNTs arrays and films are prepared. Different sizes of gold sol are obtained through chemical reduction method. Order and disorder CNTs are modified. After the decorating, the CNTs and nano-gold particales samples are conducted as SERS substrate. In the experiment, R6G is served as the detecting molecule. Raman spectrum measurement indicates that the Raman intensity of CNTs array is higher than CNTs film, because it can absorb more nano-gold particles. These reinforcing effects are reduced while particles′ diameters decrease from 80 nm, which is better than other groups at 65 nm.

Two different doping concentrations Nd, Y∶CaF2 crystals (0.6%Nd, 5%Y∶CaF2 and 0.8%Nd, 5%Y∶CaF2, represented by fraction of number of atoms) are obtained by the temperature gradient technique (TGT) method. The absorption and emission spectra, emission lifetimes, laser properties are studied. It is found that codoped Y3+ ions can effectively inhibit the concentration quenching effect and improve the spectral properties of the crystal. The broad and flat emission spectra around 1.06 μm is observed in Nd,Y∶CaF2 crystals, and the emission bandwidths is 26 nm, which is very close to the Nd-glass. While the strongest emission line is at 1054 nm, the fluorescence lifetime, emission cross section, and quantum efficiency of 0.6%Nd, 5%Y∶CaF2 are estimated as 333 μs, 3.6×10-20 cm2, and 76.7%, respectively. The room temperature continuous wave (CW)-laser oscillation is achieved using 0.6%Nd, 5%Y∶CaF2 crystal. The maximum output power is about 413.3 mW, with the slope efficiency of 28.5%.

The modification of multi-walled carbon nanotubes on the surface of silicon solar cells without antireflection layer is studied. The modification craft is realized by dropping uniform mixture of multi-walled carbon nanotubes and ethanol on the surface of polycrystalline silicon solar cells. The short-circuit current increases by 5.61%, but open circuit voltage, maximum output power and the fill factor decreases by 4.36%, 6.15% and 7.11% respectively when the modification reaches the best state. For polycrystalline silicon solar cell, both advantages and disadvantages of the modification of multi-walled carbon nanotubes exist, and this indicates the existence of optimization point of modification. With PC1D simulation software, the principles of modification are analyzed from aspects of theoretical and numerical analyses, and the reasons for the change of electrical parameters are explained. Through experiments and analyses, a way of reducing the concentration of multi-walled carbon nanotubes is proposed to optimize the effect of modification.

Self-supporting carbon nanotube films (CNFs) with light absorption in broadband frequency field are prepared by the method of vacuum filtration, and the films can be applied to a variety of environments, such as metal and plastic. Carbon nanotubes aqueous solutions with stable dispersion are prepared with the assist of surfactant. CNFs with different thicknesses are prepared on mixed cellulose membrane filter by vacuum filtration method. Perfect separation of the films is achieved with xenon lamp heating method. The results show that entangled and continuous isotropy CNFs with staggered planar mesh structure are formed from carbon nanotube dispersion solution and the film thickness is proportional to the amount of deposition carbon nanotubes; the light absorption rate increases with the increase of sheet resistance, which is consistent with optical absorption characteristics in electromagnetic field theory. The light absorption rate in the wavelength region of 350~2500 nm is 94%~98%, which has certain potential.

To retrieval the instantaneous phase of the fringe pattern accurately in Fringe Projection Profilometry, the fringe pattern should be denoised. Based on OWT_SURE_LET wavelet denoising method, using stationary wavelet substitute for orthogonal wavelet, using DB8 substitute for Sym8, and using a shrinkage function with six parameters substitute for that with four parameters, an improved wavelet de-noising algorithm is proposed. Compared with other de-noising methods, the new method is very fast and robust. Experiments show that this new method is effective in the sense of peak signal-to-noise ratio (PSNR) and root square mean error (RSME) of the instantaneous phase of fringe pattern, no matter what types of the fringe pattern or the carrier frequency in the fringe pattern.

A novel high-precision measurement method for simultaneously measuring three-dimensional small angles is presented. The collimated beam is normally incident upon the hypotenuse-surface of rectangular-prism with splitting film. The displacements of the reflection beam and transmitted beam are measured by quadrant photoelectric detectors QD1 and QD2, respectively. The direction change of the reflection beam is double that of yaw and pitch and the direction change of the transmitted beam is double that of pitch. So the displacement introduced by roll can be measured by differential measurement based on two quadrant photoelectric detectors. This method can avoid crosstalk of straightness errors, yaw and pitch errors and enhance the anti-interference ability of the system. Feasibility of the method is verified by theoretical analysis and experiments. When the system parameters are set, the angular resolution for the yaw, pitch and roll can reach to 0.1″ and 0.3″, respectively, and the measuring accuracies are about 1″ and 2″, respectively.

Terahertz (THz) scattering measurement is of great importance in many research areas such as THz imaging. To gain high-collimated, broad light and reduce loss of energy, off-axis parabolic mirrors are used during the measurement. However, the introduction of off-axis parabolic mirrors causes troubles in alignment. By using of optical design software Zemax, analyzing collimation system and collection system in the optical system. Through analysis of tilt angle and eccentricity of three off-axis parabolic mirrors, the maximum permissible alignment errors of off-axis parabolic mirrors in 118.83-μm THz emitter system are obtained.

Testing of the large-aperture convex aspheric mirror is a very difficult task in the aspherical testing. The null lens compensator is one of the efficient methods for testing the large-aperture convex aspheric mirrors. However, with the aperture increasing, some unavoidable errors are induced in the fabrication and adjustment of the compensator. In this paper, a method using a standard sphere mirror is proposed to calibrate the error of the compensator. The system error in the compensator is tested and calibrated. The calibrated compensator is used to measure the large-aperture aspheric mirror. The calibration error is also analyzed. The root-mean-square (RMS) error before calibration is 0.097 λ (wavelength λ=632.8 nm), which significantly deteriorates the testing accuracy in the null lens testing. The final testing RMS error after calibration is smaller than 0.0046 λ, which satisfies the designed precision requirement of the large-aperture convex aspheric mirror.

A novel method for measuring the photo-thermal effect of fiber Bragg gratings (FBGs) is presented. The photo-thermal effect of an UV-written FBG is studied by using the novel method. A distributed Bragg reflector (DBR) fiber laser is built up by using a 980-nm semiconductor laser as the pump laser, two UV-written FBGs as reflector and a 10-m-long Er-doped fiber as the gain medium. The reflection optical spectrum of the FBG used is obtained while the DBR fiber laser is working. The experimental result shows that the optical reflection spectrum of the FBG shifts by 0.034 nm towards longer wavelength when the pump power is 100 mW, which is induced by the photo-thermal effect. The novel method is applicable in measuring the photo-thermal effect of FBGs.

For the holey fiber with diamond lattice, the influence of the special holes near the core, the bottom holes and the pitch of diagonal holes on the wavelength sensitivity of polarization beat length is analyzed. The preliminary optimal cladding structure parameters are obtained. Then two new asymmetric structures are introduced through the lateral deformation. The holey fiber original non-linear variation of birefringence with wavelength is further suppressed. The wavelength sensitivity of the polarization beat length is reduced while a larger error tolerance of the cladding structure geometrical parameters is obtained. The results show that the median value of polarization beat length is about 132.5 mm and the relative variation of polarization beat length is less than ±4% in wavelength range of 1.2~1.7 μm while the error tolerance of optimized geometric parameters is greater than 0.1 μm. The more feasible process structure parameters are provided for drawing the achromatic holey fiber wave plates with broadband.

A novel bend-insensitive optical fiber is proposed. Low-index rods are included in the cladding to reduce the bending loss, and low refractive index ring surrounding the core is used to remove the higher-order mode. Index-contrast between the core and the low-index ring is conserved to ensure low splicing loss in standard single-mode optical fiber. The bending loss of the fundamental mode and the confinement loss of the higher-order mode are investigated by the finite-element method. The splicing losses between the bend-insensitive optical fiber and the single-mode optical fiber are investigated by the beam propagation method. The results show that the bending loss of the proposed fiber can meet the G.657 A1 standard and the splicing loss between the bend-insensitive optical fiber and the single-mode optical fiber is less than 0.08 dB.

Confined-doped fiber is an effective way to obtain high power output and maintain the beam quality. Differences about mode distribution and beam quality between confined-doped and conventional fibers are obtained by numerical simulation. Output mode distributions caused by off-axis, slant or mixed-modes launch field are also given, respectively.

The large evanescent field of optical micro-nano fiber (OMF) has enormous prospect in optical fiber sensing. In this paper, the factors that affect OMFs profile during taping process are analyzed. Accurate OMFs profile can be tapered by improved art and choosing proper parameters. Two OMFs is tapered and their profiles coincide well. The relationship between adhered particulates and additional loss of OMF is theoretically simulated, and the corresponding experiments are carried out by using dust in air and 2 μm-in-diameter alumina particulates. The relationship between absorption coefficient of liquid and additional loss of OMF is also calculated, and the absorption coefficient of different kinds of liquids are tested.

A high voltage sensor based on optical fiber Fabry-Perot interferometer and insulating oil is proposed. When high voltage is applied on insulating oil in the container, liquid flow caused by high voltage changes the cavity of the Fabry-Perot interferometer in the oil. High voltage information can be demodulated by using the change of the reflected light intensity. In our experiments, pulse voltage, with the peak of dozens kilovolt in amplitude, the full width at half maximum time of 1 ms and power frequency voltage of 7 kV, are measured. Experimental results show that the output light intensity of the sensor can respond sensitively to such kind of liquid turbulence. The light waveform is nearly pulsed under a pulse voltage. Moreover, the frequency of the output waveform is 50 Hz when the power frequency voltage of 7 kV is applied to the sensor. The sensing method based on optical fiber sensor and liquid flow has a potential application in the measurement of millisecond even microsecond pulse voltage and power frequency high voltage.

In order to compensate the influence on the inter-satellite laser communication system caused by the vibration of the satellite platform, a space-borne platform vibration compensation system is designed and constructed based on the reflection liquid crystal light modulator. Compared with the traditional vibration compensation system, it has the advantages of non-mechanical structure, high pointing accuracy, small volume, light weight, low power consumption and compensation for the higher-order aberration, so that many problems of the traditional compensation method can be overcome. As shown in the experimental results, the compensation factor is better than 0.8, and the residual error is less than 2 μrad when the frequency of angular vibration ranges from 10~100 Hz and the amplitude is lower than 10 μrad, which meet the high dynamic accuracy demands of inter-satellite laser communication system.

The method of extracting Brillouin spectrum characteristics by using the general regression neural network is proposed based on the relationship between the optical fiber strain and the Brillouin spectrum frequency shift. The Brillouin spectrum frequency shift and gain are taken as the input vector and target vector of general regression neural network, respectively. Then the general regression neural network is trained and simulated. The more accurate Brillouin spectrum frequency shift can be calculated with the obtained weight and threshold. Experimental results and theoretical analysis show that the Brillouin spectral feature and optical fiber strain obtained by using the general regression neural network are more accurate compared with the nonlinear least square method、back propagation neural network and radial basis function network, and the corresponding optical fiber strain error is the least (within 1%).

Generation and coherence of the supercontinuum (SC) in all-normal dispersion photonic crystal fiber are numerically and experimentally investigated. Different pumping pulses are used in the investigation. In the case of high power short pulse, self-phase modulation plays a crucial role in the SC generation. Spectra are symmetrically spreading at both sides of the pump wavelength, and the SC is highly coherent. When the width of the pump pulse is as large as 600 ps, stimulated Raman scattering is the main nonlinear effect, so supercontinuum is transfered towards the longer wavelengths with respect to pumping wavelength.

The characteristics of soliton self frequency shift of ultra-short pulse propagation in fluoride fibers are investigated. Modulation instability, soliton self frequency shift and the dispersive waves generated in the short wavength direction play improtant roles in the spectral evolutions in fluoride fibers when pumped at 1550 nm. The output spectrum is mainly dominanted by soliton self frequency shift when the soliton order of the pump pulse is small. The effects of the length of fluoride fiber, peak power of pump pulse and initial chirp on soliton self frequency shift are discussed. By adjusting the peak power of the pump pulse at 1550 nm, the central wavelength of maximum red shifted Raman soliton can be tuned to above 2.6 μm. Combined with some special rare earth doped fiber amplifiers, a widely tunable fluoride infrared fiber laser can be realized through the method of cascaded Raman soliton self frequency based on soliton self frequency shift effect in fluoride fibers.

Terahertz technology is widely used in the radar cross section (RCS), because the wavelength of terahertz can help downsize the model to a proper range and the measurement of scale model can help decrease the cost of time and the expenditure of the experiment. In the calculation of the RCS of a rough surface, sometimes, the question is deduced into the calculation of the boss on a flat plate and the monostatic radar is the one that mass of radar system adopted. However, a plane wave is usually assumed in most of the RCS estimation, while in real measurements, the energy of the incident beam obeys the Gaussian distribution. In the estimation, the influence of 2.52 THz collimated Gaussian beam on monostatic RCS is studied in details and the relatively error is analyzed.

The choice of the accurate and proper signal is the key to enhance the sensitivity and contrast of ultrasound-modulated optical tomography（UOT）. Fast Fourier transform (FFT) is used in the digital frequency analysis of modulation signal. Spectral intensity of zero frequency (I0) represents the unmodulated light intensity, and the sum total of spectral intensity (If) from 0.2 MHz to 1.8 MHz depended on the frequency range of ultrasonic probe represents the ultrasound-modulated light intensity. Compared with the in-time signal, If has the higher sensitivity to optical properties of media, but it is easy to be influenced by the non-target media. The modulated depth of in-frequency signal (M2=If/I0) is not easy to be influenced by non-target media, but it has low sensitivity to optical properties of the target media. The results indicate that the result of in-frequency signal is not better than the in-time signal for image reconstruction and processing.

Ultraviolet detecting technology, based on the atmospheric transmission characteristics of ultraviolet radiation, is a new imaging technique. It broadens and develops the available electromagnetic spectrum in military field. Based on spectrum radiation characteristics and image enhancement, a new ultraviolet scene simulation method is proposed. The infrared scene simulation of target and background is created. The radiation temperature of each pixel in the target model is calculated. The corresponding radiation exitance and image grayscale in ultraviolet spectrum are acquired by using Plank formula. By introducing image enhancement, practical ultraviolet scene simulation images are obtained. The experimental results show that the simulation effect is good.

Polarization detection characteristics of the electro-optic crystal ZnTe in the terahertz time-domain spectroscopy (THz-TDS) system are investigated. The differential current associates with three factors which are direction of crystal axis, THz polarization direction and probe beam polarization direction. According to theoretical analysis, the differential current is relevant to the angle (α) between the THz polarization and the crystal axis and the angle (φ) between the probe beam polarization and the crystal axis. Experiments and caculations are conducted in the cases of α=φ,α=φ+π/2, α=φ+π/4, and the experimental results agree well with the calculation results.