Based on the coupled-mode theory and the relation between Jones matrix and Stokes vector, we give the formulas for reflected and transmitted Stokes parameters of low-birefringence single-mode uniform optical fiber Bragg grating (FBG). The curves of reflected and transmitted Stokes parameters versus wavelength of low-birefringence single-mode uniform FBG are simulated under different birefringence values. The results show that: among the four normalized Stokes parameters, s1 is antisymmetric about the central wavelength λ0, S0, s2 and s3 are symmetric about λ0. Although spectral lines do not produce a drift, the bandwidth of reflected signals is narrowed with the growing of birefringence values. The Stokes amplitudes of reflected and transmitted signals have different changes. It is shown that birefringence values have significant influences on Stokes parameters. The curves of reflected and transmitted Stokes parameters versus the parameters of single-mode uniform FBG are measured. The theoretical analysis and experimental results coincide with each other.

Based on extended quadratic congruencies code/one coincidence sequence (EQC/OCS) the incoherent 2-D optical code-division multiple access system (OCDMA) is simulated by using fiber Bragg grating (FBG) and fiber delay line. The expected en/decoding result with four users is obtained by system simulation. It is indicated that the low cost FBG can be employed as en/decoder for EQC/OCS code, which can enhance the system capacity of 2-D OCDMA system.

Using the scalar method, the field distribution of the linear polarization in a step-index of weakly guiding and the hegeneral expression of the mixed modes are derived. The results show that, the mode field ranges of the lowed LPmn increases with the fiber core radius and the coating layer index. The mode field ranges of the lowest order LPmn modes reduces with the increase of the fiber core index. The optical strength of the mixed modes reduces with the increase of the transmission distance and the proportion of mixed modes. The M2 factor of the uncoherent mixed modes increases gradually with the increase of the proportion of the highest order LPmn modes. Howerer, the increase of M2 factor approaches a critical value when the fiber core radius is a=30 μm.

A rectangular lattice micro-structure optical fiber with a pair of large circular holes near the core is squeezed or expanded in orthogonal directions. Nonlinear variation of birefringence with wavelength is suppressed by the compensation and equilibrium among the birefringence of multiple asymmetric structures. The influence of lateral deformation on modal birefringence and polarization beat length dispersion is analyzed by full-vector finite-difference beam propagation method. A suitable expansion factor is found by optimizing the design. The wavelength sensitivity of polarization beat length is effectively reduced. The polarization beat length changes in the range of 90.7~95.3 mm and the relative variation is about 5% in the wavelength range of 1.0~2.0 μm. This fiber is very suitable for making wideband fiber-optic quarter wave plate.

To accurately locate the focal plane of object in digital holography, the overall sharpness (OS) method, which is the supplement of the edge-sharpness (ES) method, is presented. By combining above methods, the integrated gray-level gradient method is obtained. The criterion with ES is confirmed to be appropriate for large particles or small object distance. In contrast, the criterion with OS is determined to be appropriate for small particles or large object distance. The conditions of above criteria are discussed by using numerical simulation holograms of particles. At last, the integrated gray-level gradient method is applied to the real holograms of dot array target and calibration target. The experimental results demonstrate that this method can effectively extract the focal plane of particle.

In view of the bending tube residual stress measurement system based on digital speckle correlation method (DSCM), the main error elements are analyzed comprehensively. According to the theory of the error elements, the methods to reduce the errors are proposed. At the end, the error elements and the methods which reduce the errors are verified through an experiment. It is a useful reference to the similar measure system based on the digital speckle correlation method.

Based on the principle of speckle photography, with charge-coupled device (CCD) as a recorder, electrically addressed liquid crystal display (EALCD) as a read-out element, the 3D phase measurement of a deformed object is performed. Using digital technology interference fringes displayed in real-time, instead of recording media used in the traditional speckle photograpy, can leave out the chemical process of developing and fixing. Using digital image processing technology realizes four steps phase shitting and with phase-unwrapping method 3D deformation phase testing is realized. So piezoelectric translator (PZT)、phase controller and so on can be omitted, thus testing system is simplified, testing time is reduced and testing precision can easily reach up to λ/10 . The experimental result shows that the research method is not only simple and high-efficiency, but also can obtain high contrast speckle fringes.

Laser cladding is a common remanufacturing method for metal parts. However fast process planning technology of laser cladding is one of the difficulties. The content and overall program of laser cladding are brought out firstly. Then path planning and process parameter planning are discussed. Finally the method is verified by an experiment. The results show that laser cladding process is able to be fastly planned with geometric properties model.

A green laser system with high average power output is developed with high energy and narrow pulse width. With diode laser pumped Nd:YAG crystal, RTP electro-optic Q-switching and power dividing by master oscillator power amplifying (MOPA), the 532 nm green laser output with high energy, narrow pulse width and high repetition rate is realized. For the fundamental frequency output at 1064 nm, the average pulse energy is 213 mJ, the operating frequency is 100 Hz and the optical-optical conversion efficiency is 12%. While a type Ⅱ phase matching high gray track resistance KTP crystal is used for extra cavity frequency doubling, an green light output at 532 nm can be obtained, with the average pulse energy of 127 mJ, the operating frequency of 100 Hz, the pulse width of 7.2 ns, the beam quality of 20 mm·mrad and the total wall plug efficiency of 2.1%.

By using the advantage of pulsed semiconductor lasers with high peak power, a pulsed LD-pumped cavity-dumped oscillator and power amplifier is built, and the pump light and signal light of the system are matched. In addition, external cavity second harmonic experiments are also carried out. The results show that, the pulsed LD pumping system has a very compact structure, it can increase the energy output in oscillator and amplification stage oscillator, and can better eliminate thermal distortion effects. Pulse width of 3.7 ns and laser pulse energy of 4 mJ can be obtained in the stage of the oscillator. Through the power amplifier and the second harmonic generation (SHG), the second harmonic light with the pulse width of 3.4 ns, pulse energy of 3.2 mJ, SHG efficiency of 40%, pulse peak stability of 5% (root mean square) and divergence angle of 0.5 mrad is obtained.

We report a high-energy LD side-pumped Nd:YAG Q-switched laser with air cooling system. The peak power is 12 MW, and the pulse width is 11 ns when the repetition rate is 30 Hz. The repetition rate is tunable from 1 to 30 Hz with 1000 mJ pump energy. The optical-to-optical efficiency is 13.2%. The central wavelength is 1064.2 nm with bandwidth of about 1 nm. The beam quality facter M2 is 2.85. We adopt a semiconductor thermoelectricity cooling (TEC) system with fan air-cooling system, eliminating the need for a bulky cooling system as that in traditional high-power lasers. This offers the possibility of miniaturization of the whole laser system.

Dynamic focal laser marking machines usually use a collimating and beam expanding system before the focusing lens. The laser beam will always focus in the marking plane by adjusting the motion of collimating and beam expanding system according to the galvanometer scanning. But for a larger marking area, the effect of focusing is not so ideal and even out of focus at the edge. In order to satisfy large area marking, a dynamic collimating and beam expanding system is designed based on normal expander system. The focusing performance is improved by 20% by optimizing the trajectory of collimating and beam expanding system. It achieves the target of small spot size in bigger area. Using polynomial fitting to calculate the beam expander′s trajectory, the marking speed is improved. Piecewise linear interpolation look-up table is used to correct the pincushion distortion at the edge. It is shown that the machine works pretty well and conforms to specified requirements.

Using multi-photon nonlinear Compton scattering model and finite-difference time-domain method, the influences of the density and temperature characteristics of band gap for un-magnetized plasma photonic crystals produced by multi-photon nonlinear Compton scattering are studied. A new mechanism of the modulation on the photonic band gap formed by incident light, Compton scattered light and plasma density and temperature is given. The results show that the photonic band gap of plasma photonic crystals can be developed by using the change of the plasma density and temperature, but this developing effect can be decreased by Compton scattering. A larger shift to the high frequency direction of the photonic band gap than that before the Compton scattering can take place. Therefore, the high pass filter characteristic of the plasma photonic crystal can be better attained.

The methods of specification, analysis and evaluation on telescope primary mirror figure error have an important instructive meaning to mirror fabrication. A structure function analysis method is introduced. Firstly, the influence of atmospheric turbulence on image quality is analyzed and the specification on mirror figure error is determined using the structure function analysis method. Then the evaluation on mirror figure error and the guidance of mirror processing by conversion from Zernike polynomial to structure function are achieved. The conversion processes and results have been described. Finally, the analysis processes mentioned above are illustrated in detail by an example of Giant Magellan Telescope (GMT). The structure function analysis method which has a greater guiding significance can evaluate the mirror figure error accurately and perfectly and shows advantages over the root-mean-square (RMS) wave aberration method.

The situation that two identical two-level atoms initially entangled with the third atom are separately trapped in two distant single-mode optical cavities, which are coupled by an optical fiber, is considered. The entanglement between cavities is investigated. By means of numerical calculations, through comparing the results if a direct selective measurement is performed or not, the effect of the state-selective measurement on the entanglement and that of the coupling coefficient between atom and cavity on the entanglement are discussed. The results show that the entanglement between the cavities can be strengthened through the state-selective measurement on the atom outside cavities; if the coupling coefficient between atom and cavity increases, the entanglement between cavities can also be strengthened.

The mechanism of optical fiber pH chemical sensor are briefly presented. The mechanism of action and the immobilization of acid-base indicator are expatiated. The analytical performance of the proposed fiber optical pH sensors with different indicators are compared. The optical detection methods of optical fiber pH chemical sensor are illustrated. In addition, the development of pH sensing materials and the detected methods in recent years are emphasized. Finally, this paper gives expectations on the development tendency of optical fiber pH chemical sensor.

Homotaxial wires with nanoscale diameter embedded in quartz glass fibers constitute the metallic core microstructured fibers. The fibers with special structure have the characteristics of transmitting lights and surface plasma waves which enable a wide range of potential uses. Here the properties, preparation methods, and research progress of metallic core microstructured fibers are reviewed.

Random distributed feedback fiber laser (RDFFL) has been developed as a new type of fiber laser in recent years. RDFFL belongs to random lasers since the feedback of laser light depends on the random distributed fiber Rayleigh scattering, rather than reflection mirrors. It achieving gain through distributed fiber Raman scattering, is regarded as a new light source with stable, incoherent continuous-wave (CW) output, with potential applications in nonlinear optics, optical communications and sensing areas. The working principle, research progress and applications of RDFFL are introduced.

Multi-tone amplification is a novel technique to effectively suppress stimulated Brillouin scattering (SBS) effect in narrow-linewidth fiber amplifiers. The corresponding basic principles are described in detail. Multi-tone amplifications can be classified into large and small wavelength separation amplifications. Important outcomes in theoretical and experimental researches of these two kinds of amplifications are overviewed and their superiorities in SBS suppression are analyzed. It is pointed out that the large wavelength separation amplification shows great advantage in enhancing the output power of the single frequency laser and the small wavelength separation amplification is of great value to further enhance the output power of current high power coherent beam combination system of fiber lasers.

In the high resolution optical lithography technology, illumination pupil shaping is employed to enhance the lithography resolution and achieve high imaging performance by using various illumination modes according to different mask structures. In this paper, three approaches of pupil shaping techniques based on diffractive optical element (DOE), micro lens array (MLA) and micro mirror array (MMA) are summarized. The principles, design and manufacturing methods are concluded.

Fluorescence lifetime imaging microscopy (FLIM) technology has so many outstanding and unique advantages compared with other fluorescence imaging methods that it attracts more and more researchers in biomedicine engineering field. Frequency domain modulation method and time domain methods including time-gated detection and time correlated single photon counting (TCSPC), are the main ways to realize FLIM. Principles, current reaseach situation and achievements of these methods are presented as well as the comparison of their main performance parameters. Wide-field FLIM is more suitable for delay imaging. Fluorescence lifetime polarization resolved imaging and endoscope FLIM are both promising research areas of FLIM.

Large nonlinear refraction indices, ultrafast response of nonlinearities, moderate to low two-photon absorption and unique photoinducing properties make chalcogenide glasses attractive candidates for all-optical signal processing. We review the basic properties of these materials, outline the progress of chalcogenide glass waveguide, introduce its nonlinear application and discuss its prospect.

Mid-infrared fiber lasers have broad application prospects in military, atmospheric communication, medical and other fields owing to their special output wavelength and high beam quality. The latest progress of fluoride and chalcogenide mid-infrared fiber lasers is described from the perspective of different rare-earth doped ions. Meanwhile, our latest progress in mid-infrared fiber lasers is also introduced. Finally, the development trends of the mid-infrared fiber lasers are prospected.

Pain remains challenge to treat, despite advances in cellular and molecular understanding of pain. Acupuncture analgesic has been accepted by west society due to low side effect and good performance. Although the effect of acupuncture analgesic has been confirmed clinically, its mechanism is still unclear. Positron emission tomography, single photon emission computed tomography, functional magnetic resonance imaging and immunohistochemistry have been applied in the study of the mechanism of acupuncture analgesic. However, poor resolution or invasion of these techniques limits their application in further study. It is suggested that optical imaging techniques, especially laser scanning confocal microscopy, optical coherent tomography and in vivo optical imaging system, could be utilized in the study of the mechanism of acupuncture analgesic.

The density functional theory is used to calculate the vibration frequency of biodiesel and diesel, identify the vibration modes and demonstrate the correlation between terahertz spectra and cetane number. The reason that biodiesel shows higher terahertz absorption and cetane number than diesel can be comprehended to be the influence of ester group at the end of the C-chain. The terahertz absorption and centane number of biodiesel-diesel blends increase with the increase of volume percentage of biodiesel in mixture, and a congruent relationship is established between absorption curve and centane number. As a result, the cetane number of biodiesel-diesel blend will be confirmed by its terahertz spectra.