The modal cut-off properties and resonant properties of Ge-doped photonic crystal fiber Bragg grating (PCFBG) with regular octagonal cladding air holes are investigated by using the mode coupling theory and the transmission matrix method, and the modal cut-off condition and the mode of transmission are given. To meet the need of the resonant wavelength, a method is designed by changing the period of the grating based on the phase matching conditions. The reflection spectrum of the grating simulation result is obtained. It is found that with properly chosen structural parameters, needed single-mode transmission and resonance with tailored main resonant peak can be realized using the PCFBG. This kind of PCFBG can thus be better applied to fiber sensing areas.

High-power ultra-short pulse train is highly demanded in many areas, however, the limited average power and low energy utilization constrain the application of ultra-short pulse train. Our method is based on nonlinear soliton effect, which is different from locking mechanism. Using an amplitude-modulated continuous wave radiation as pumping source, we numerically simulate the stable generation of high-power ultra-short pulse train. The input parameters such as pump power, modulation depth, modulation frequency and the optical fiber parameters including nonlinear coefficient, group velocity dispersion coefficient, are studied, respectively. In order to comprehensively consider how various parameters affect the pumping efficiency, we introduce the normalized modulation frequency. The results show that choosing a fiber with a small nonlinear coefficient and a large group velocity dispersion, introducing an appropriate increase in modulation frequency and modulation depth, high average power output can be ensured and a relatively high pumping efficiency is obtained. However, a smaller pump power is beneficial to energy extraction.

When the reconstructed image is out of focus, oscillation will appear at the edge of objects, because digital holography is a coherent imaging system. Therefore, it is inaccurate to perform auto-focusing by the traditional evaluation function of definition in digital holography. It can be found through wavelet analysis that the amplitude of high-frequency coefficients out of focus is smaller than that in focus. The evaluation function of definition based on Laplacian operator and wavelet transform is improved. The maximum amplitude of high-frequency coefficients in the focal windows, instead of the sum of high-frequency coefficients, is used to evaluate the definition of the reconstructed image. In order to get a clear image that contains all relevant objects in the three-dimensional (3D) space of digital holography, a fusion algorithm is proposed. The auto-focusing and reconstructed image fusion experiments for simulated digital in-line holography and an ant detection experiment are completed. Experimental results show that the improved evaluation function of definition can accurately achieve auto-focusing for digital holography, and a series of reconstructed image can be fused into a clear image by the proposed fusion algorithm.

A new image encryption technology based on computer generated hologram (CGH) combined with the 4f system of double random phase image encryption technology is proposed. The unique spread spectrum characteristics of CGH recording encryption image is analyzed, achieving the computer simulation of using the original of phase plate, conjugate panels and the combination with them as the decryption keys of the different spectrum units or spectrum units combination. And the anti-noise ability of this image encryption method is also analyzed. This proposed method improves the security of image encryption.

The property of electrowetting on dielectric (EWOD) on the core-surface of variable-focus liquid lens with specific “conductive metal/insulation film/hydrophobic” material is one of the important research topics in optofluidics. Contact angle versus applied voltage (DC and AC) curve of conductive liquid droplets is obtained by experiment. Experimental results show that, to achieve the same effect as that obtained with DC power, what should be considered is the instantaneous maximum rather than the effective value (root-mean-square) when using low-frequency AC voltage. The variable-focus experiment of the variable-focus lens under the applied 50 Hz AC voltage is performed. A curve between the focal length of the variable-focus lens and the applied voltage is given. The experiment result agrees very well with the above analysis.

We present a method for measuring the refractive index of bio-tissues based on spectral domain optical coherence reflectometry (SD-OCR). Common-path method is used to simplify the system structure and improve the measuring speed. It has a strong anti-interference ability. Broadband light (central wavelength 850 nm) is transmitted through the Y-coupler and scattered (reflected) back to the spectrum analyzing system by the specimen through the sample arm and the Y-coupler. The system construction and optimization are then realized by virtual instruments. Fast Fourier transformation (FFT) is employed to analyze signals. This theory is verified by a standard K9 glass sample and the results show that the experimental error is 0.29%. The refractive index of a cucumber superficial slice at 850 nm is measured and the measuring time is less than 1 min.

The initial phase and wavelength response of the spatial light modulator (SLM) will be shifted with the working time and the environment variation. To solve this problem, we study the initial phase calibration and the multi-wavelength response of phase-only SLM. Four-step phase shifting interferometry is used to measure and calibrate the initial phase of SLM. Michelson interferometer is used to study the relation between the order of interference fringes and the gray scale of different wavelengths experimentally. It is shown that the initial phase is calibrated appropriately and the correction coefficient of wavelength response is achieved successfully. This investigation will provide technologic reference for using SLM in various environments.

To measure the wavefront of high-power laser with ultra-long focal length, we develop and calibrate a shearing interferometer based on spatial phase modulation. It is experimentally compared with Hartmann-Shack (HS) wavefront sensor and Zygo interferometer. The results show that the shearing interferometer can meet the requirements of precisely measuring wavefront. It has high precision and good repetitiveness.

A Q-switched Nd:YAG laser is used to fabricate micro channels in a fused silica substrate by thermal induced processing and laser-induced plasma processing. The length of micro channels by thermal induced processing can be controlled and there are many thermal cracks around the channel. The interior wall of the micro channels drilled by laser-induced plasma is smooth, and the depth of the channel is up to 4 mm. The temperature and thermal stress distributions of thermal induced processing are calculated, and the behavior of laser-induced plasma processing is studied. The results indicate that as a result of great temperature changes, the thermal stress is larger than the fracture strength of sample, which leads to the formation of the channel and the thermal cracks. The ablation of the high temperature plasma formed by plasma shielding effects leads to a micro channel of high quality with a smooth internal surface and no thermal cracks.

For the precise targeting in inertial confinement fusion (ICF), the requirements for beam transformation, beam shaping and beam control are harsh. The digital control of key technologies online can realize the automatic calibration of the laser system. This paper in detail describes the key technologies, such as nonlinear broadband propagation, broadband amplification and frequency conversion. Meanwhile, other auxiliary technologies are also taken into account, including paraxial ray tracing equations (PRTEs), vector electromagnetic field propagation, phase retrieval based on the iteration algorithm, grating analysis and finite-difference time-domain (FDTD) analysis of micrometer or nanometer devices, etc. During the derivation, some elementary examples of digital control of key technologies online are also provided which can verify the correction of the corresponding theories and the stability of the algorithm.

In order to improve the in-situ synthesized coating quality by laser cladding, in-situ laser cladding coating on TC4 titanium alloy surface is processed by laser remelting. Microstructure, phase, and microhardness of the coatings are studied by scanning electron microscope (SEM), X-ray diffractometer (XRD) and micro-hardness tester. The results show that the pore of in-situ coating bottom is eliminated and the ceramic phase of coating is distributed homogeneously by laser remelting so that microstructure becomes denser. After laser remelting, the microhardness gradient is reduced. The average microhardness and coating quality are enhanced by laser remelting.

Ultrasound modulated optical tomography combines the advantages of light imaging with ultrasound and is able to image objects embedded in turbid medium. It is a promising technique. A relation between the modulated optical signal and the optical parameters of tissue inside and outside of the ultrasound zone is given by experiment. It is discovered that the modulation depth is directly relevant to the optical properties of the tissue at the ultrasound focal zone. The modulation depth reduces as the scattering coefficient of sample increases, and increases with the increase of absorption coefficient. The modulation depth of signal in ultrasound zone is not subject to the optical properties of complex tissue outside of the ultrasound zone. All these results will provide necessary basis for the image reconstruction of ultrasound modulated optical tomography.

Based on non-imaging optics, a secondary optical lens is designed for indoor illumination of high-power LED which could illuminate uniformly in a large divergence angle. The mapping of LED onto the target plane is constructed by grid partition method, based on which the general equations of freeform surfaces are derived. The surface profiles are obtained by solving the equations using difference method. Using the profile data, the lens model is established with three-dimensional (3D) software. The optical system is simulated with ray-tracing software. This lens is fit for uniform illumination with the target divergence angle between 40° and 140°. A lens with 120° divergence angle lens is designed and simulated. The results show that it can keep the uniformity above 0.9 and the efficiency above 92% when the ratio of the lens aperture to the diameter of LED emitting surface is not less than 10, and the uniformity is not effected by the distance between the LED and the target plane. This design provides an effective way for the miniaturization and simplification of the indoor illumination system of high-power LED.

Irradiance measurement system is designed for the irradiance measurement of infrared (IR) target simulator. Its optical system is featured in improving the energy distribution of irradiating light beam and focusing the energy onto the detector. According to the different usages of dual-color and single-color infrared focal plane arrays (IRFPA), co-aperture optical systems of both a dual-color IRFPA detector and two single-color IRFPA detectors can meet the irradiance measurement requirements. Dual-color detector is difficult to obtain but the structure is simple, the modulation transfer function (MTF) response is higher, and the utility is better; on the other hand, the single-color detector is easy to obtain but the structure is relatively complicated. However, the latter still has a good imaging quality and can be used in the optical system. The design result shows that the aberrations in the wave bands of mid-IR (3~5 μm) and middle IR (8~12 μm) are simultaneously adjusted in both systems. The system distortion is small, with the maximum no more than 0.7%, and the MTF approaches the diffraction limit.

A novel optical element, step refractive index triangular prism, for generating non-diffracting linear structural beam which has higher intensity in the central spot is proposed. The problem that the energy of non-diffracting linear structural beam generated by uniform refractive index triangular prism is evenly distributed and the energy efficiency of central spot is low is solved. The formation mechanism of the non-diffracting linear structural beam which has higher intensity in the central spot is analyzed by geometric optics, and the relevant parameters are also calculated. The intensity distribution is simulated by diffraction integral theory. The results show that when a plane wave illuminates the novel optical element, a non-diffracting linear structural beam which has higher intensity in the central spot is formed.

Micro-scanning technique and its benefits in infrared focal plane array (FPA) imaging are discussed. Different micro-scanning schemes and their property are described in detail. The advantages and drawbacks of each scheme are compared. The possible schemes for engineering application are presented. The research direction in micro-scanning infrared focal plane array imaging is pointed out. As an example, we design a micro-scanning optical system suitable for long wave infrared optical system whose operating wavelength range is 8～14 μm, F number is 1, and focal length is 150 mm. It was an uncooled 384 pixel×288 pixel VOx focal plane array detector. Moreover, its image quality is evaluated with the Code Ⅴ optical design software. And the infrared mico-scanning system configuration is also introduced.

Under two distinct probability models, i.e., multiple and conditional probabilities, statistical distributions are investigated. Using measurement model and statistical approaches to simulate quantum interaction on binary level systems, multiple interactive conditions are simulated via double-path interference model. From quantum interaction, Einstein, Clauser-Horne-Shimony-Holt (CHSH) and Aspect measuring quaternion is investigated. Using multiple variable logic functions and variant principle, N bit vectors of 0-1 input/output pairs form variant quaternion to establish variant double-path simulation model. Using both multiple and conditional probabilities and symmetry/anti-symmetry and synchronous/asynchronous conditions, the simulation system generates 4 groups of 16 histograms to express the statistical distributions in relevant conditions. Simulation results show that multiple probability is associated with normal distribution, while conditional probability is related to quantum interference distribution.

Application of laser is increasing in spacecraft now, but laser systems in space already have the sudden phenomenon of failure. The optics performances composed of coatings and substrates such as crystal and glass are important elements for laser generation and output. The changes of damage performances will affect the stability, lifetime and beam quality of laser system in space. Space effects of optics have become an urgent problem to research and discuss. We summarize the variation trend, damage mechanism and some improvement measures for optics in different conditions of vacuum, temperature, contamination, solar ultraviolet radiation and proton radiation, respectively. The conclusions will be helpful to the future laser applications and research in space.

The tunable liquid crystal microlens is a novel optical component by tuning its refractive index based on electro-optical effect, which has wide potential application in optical community. The elemental structures have been described, and the operation principles have been presented. An overview of recent activities in the area of the tunable liquid crystal microlens has been given, and then the development tendency in near future has been predicted.

As holmium laser is a highly coherent radiation light source, it has wide applications in laser radar, range and medical care. According to the development history of holmium laser, we summarize the methods to improve the output power and efficiency of holmium laser, including the choice of crystal material and the study of concentration of doped impurities. Furthermore, the application details and prospects are described, and the medical applications of Ho:YAG laser are emphasized.

Gain-guided index-antiguided (GG IAG) fiber has a negative index step from cladding to core, and the gain effect plays a crucial role in guiding mode. It has attractive performance on large mode area of the high-power single-mode fiber lasers. The research progress at home and abroad of GG IAG fiber laser is summarized. At first, the theoretical details of GG IAG fiber laser including bending, mode coupling, gain saturation and thermal characteristics are summarized. Then the experiments of Nd-doped, Yb-doped fiber lasers are presented. At last, the advantages and problems of the GG IAG fiber laser in high power fiber lasers are discussed.

The development history, key techniques and applications of four-mode differential laser gyros (FMDLGs) are summarized so as to provide some reference for domestic development of FMDLG. The keys to improve the performance of FMDLG are concluded according to investigation on materials related to FMDLG, including fundamental research, technical improvement, optimization design for cavity, electronic system design and error compensation technique. In order to fully realize the potentials of FMDLG, each key aspect should be taken into account elaborately.

Terahertz spectroscopic techniques have been regarded as competitive methods for the identification of explosives and related compounds. The explosives fingerprint data of various research institutions are reviewed to establish reference databases. The detection of explosives hidden under some materials including cotton, plastic, leather, polyester, cardboard etc. is discussed. The latest research advances of the remote detection of explosives are described. Furthermore，the major issues faced with mixed explosives, complex environment conditions, remote detection on THz detecting explosives in the actual scene and so on have been analyzed. The future trends in a preliminary outlook are pointed out.

Deconvolution technique is currently available for application in spectral analysis to enhance the resolution of spectra, especially the spectra with multi-longitude modes. Iterative deconvolution and Wiener filtering techniques are discussed. The root-mean-square errors of iterative deconvolution and Wiener filtering with different spectral sampling rates are compared via computer simulation. The results indicate that the resolution of the observed spectrum is improved by using iterative deconvolution and Wiener filtering. The iterative deconvolution works better than Wiener filter at low spectral sampling rate. Experimentally, the spectra of two He-Ne lasers centered at 632.8 nm with single mode and multi-mode are deconvolved. The number of longitude modes, longitude spaces and spectral bandwidths of the He-Ne lasers are obtained by using iterative deconvolution. The deconvolved spectra of He-Ne lasers measured with a low-resolution spectrometer are in agreement with the spectra measured directly with a high-resolution spectrometer.

In the Fourier transform infrared spectrometers, the interferograms are usually sampled by means of the single-side beyond zero path difference and the interferograms are asymmetric. In order to realize the Fourier cosine transform and truly rebuild the spectrum, the phase-corrected technologies of Forman is researched and improved. In the Forman method, the convolution is used in several times so that the operation is complication and it is difficult to realize by the hardware circuits. The linear convolution is realized though three fast fourier transform (FFT) operation to reduce the quantity of computation. It is found that quantity of the short double-side data, apodization function and the times of phase correction affect the result of the corrected interferograms in the experiment. The 500 K infrared blackbody is used as the radiant source to achieve the absorption spectrum of the atmosphere in the infrared range. The single-side beyond zero interferograms is achieved by the HgCdTe dot diode detection. The interferograms are corrected and rebuilded by the improved Forman method. The spectral resolution of the rebuild absorption spectrum is 4 cm-1 and the wavenumber error is little. which show the higher accuracy of spectrometers.

With the development of high-speed semiconductor devices, the cutoff frequency of high electron mobility transistor (HEMT) can achieve sub-terahertz level, which cannot be simply measured by traditional electrical method. Therefore, the ultrafast optical method is employed to measure the cutoff frequency of HEMT. The femtosecond laser pulse, which has extremely short duration, is used to suddenly turn off the HEMT that is under saturated condition. Furthermore, the terahertz time-domain spectroscopy technology is applied to measure the change of operation current, which can persist even less than 1 ps after the HEMT is switched off. Finally, the cutoff frequency of HEMT can be directly calculated by using the relationship between the terahertz traces (i.e., the curve of the source-drain current versus time) and the cutoff frequency of HEMT which can achieve sub-terahertz level.

Broadband absorption enhancement effect induced by nanocone grating in 1 μm thick Si solar cells has been numerically investigated by rigorous coupled-wave analysis method. Even though the great antireflection performance has been achieved in the nanocone grating of P=100 nm, the higher optical generation rate and ultimate efficiency are achieved in the solar cell with nanocone grating of P=500 nm and H=350 nm, which is 1.4 times and 1.65 times higher than that in planar Si.

The 2% (mass fraction of Al2O3) Al-doped ZnO (ZnO∶Al) thin films were sputtered on glass and polyimide (PI) substrates by radio-frequency (RF) magnetron sputtering technology. The effects of substrate materials on the structural, electrical and optical properties of ZnO∶Al thin films deposited on different substrates are studied. It is found that substrate materials have significant influence on film crystallization and resistivity but little on optical transmittance. Highly c-axis oriented ZnO∶Al films in (002) direction are observed on both glass and PI. Besides, it is manifested that the average optical transmittance in the visible-light range (400～800 nm) is around 85% for both films. Films on glass presents stronger (002) diffraction peaks and lower full-width at half maximum (FWHM). The lower resistivity of 2.352×10-4 Ω·cm is obtained in samples deposited on glass. Also, films on glass show larger grain size and denser microstructures than films on PI. Meanwhile, the ZnO∶Al films deposited on PI also own good crystallinity and low resistivity of 6.336×10-4 Ω·cm, which make them suitable as window materials in flexible solar cells. Films on glass are available as transparent electrodes in flat panel displays and solar cells.