The transmitting beams are usually approximated as plane wave or spherical wave in free space optical communication (FSO) systems. But the actual beam is a Gaussian beam, and there are many differences when we study the performance of FSO system with the approximation model. By using the methods of theoretical analysis and simulation, without considering the impact of the inner and outer scales of turbulence, we analyze the difference of aperture averaging effect among different transmitting beams. The differences of bit-error rate (BER) performance are then analyzed. The results show that Gaussian wave has apparent impact on the improvement of BER performance by aperture averaging, and saturation is reached firstly, followed by spherical wave. Plane wave is relatively gentle.

A high-birefringence holey fiber geometry is proposed, in which the cladding holes form a round lattice array. The birefringence properties are simulated by the finite difference beam propagation method. The influence of the cross-section structure parameters on birefringence is analyzed. The birefringence performances from round, quadrilateral and octagonal lattice arrays are compared. The results show that the modal birefringence of the holey fiber with round lattice can reach the order of 10-2 in 1.7~2.0 μm wavelength range. In the cross-section under the same structural parameters, the holey fiber with round lattice has a higher birefringence than those with quadrilateral and octagonal lattices. The polarization beat length is in sub-millimeter level in the 0.6~2.0 μm wavelength range. This fiber is suitable for making polarization interferometric fiber devices and sensors.

Thermal effect of ultraviolet laser in fabricating and spectrum of fiber Bragg grating (FBG) was experimentally researched by phase mask method. Results indicated that, getting the same photosensitive fiber had accumulative exposures by the way of phase mask straight exposure, the grating reflectivity will not be linearly increased with the exposure level, but will be diminished, which is called “bleaching”. The process of bleaching had some connection with the interval of multiple-exposure. The shorter of interval was, the longer time of bleaching process will take. On the condition of having the same quantity of illumination, the higher exposure frequency rate of laser was, and the less time the exposures take, the grating reflectivity will be higher. During scanning exposal to make uniform FBG, on the condition of having the same exposure parameter, differ of scanning directions leads to different regularities of distribution of side lobes. Thermal-induced chirping in FBG fabrication was proposed for the first time.

A novel design of Photonic Crystal Fiber (PCF) was present in order to simultaneously achieve high nonlinearity, ultra-flattened dispersion, and low confinement loss. The software COMSOL based on finite element method with anisotropic perfectly matched layers is used to analyze the effective mode area, dispersion properties, and confinement loss of PCF with eight-ring air holes. Numerical results show that a small effective mode area corresponding to a high nonlinear coefficient of the order 36.2 W-1·km-1 at 1.55 μm wavelength is obtained. Moreover, ultra-flattened dispersion of (0.3±0.3)ps/(nm·km) is also obtained over 330 nm bandwidth from 1.37 μm to 1.70 μm with low confinement losses less than 0.1 dB/km within the band of 1.37 μm to 1.62 μm.

In order to improve the fabrication efficiency of micro fiber pressure sensors, an optical fiber sensor based on Fabry-Perot (F-P) interferometer fabricated by using 157 nm laser micromachining is proposed and demonstrated. The sensor head consists of a short air F-P cavity near the tip of a single-mode fiber and the fiber tip. Tracking the phase signal, the variation of pressure can be obtained. In the pressure measurement range of 0~60 MPa, the sensitivity and long-term stability of the sensor are 0.01 rad/MPa and ±0.04 MPa, respectively. For ten sensor samples tested, the tolerance of sensitivity of the sensors for 60 MPa measurement range is ±5%. This sensor has great potential to realize mass-production of good reproducibility and the application prospect in industry measurement is wonderful.

Aiming at improving the quality of reconstructed images of digital holography, based on the analysis of the reconstruction light intensity of digital hologram, a method combining light intensity subtraction and median filtering is proposed. The principles of light intensity subtraction and median filtering are described. Light intensity subtraction based on HRON substraction diminishes the zero-order image and background light. The median filter process effectively minimizes the background noise light. From the comparison of quality of experimentally reconstructed images obtained by different methods, it is shown that the proposed method could effectively improve the quality of reconstructed image of digital hologram.

As the unmanned aerial vehicle (UAV) image has large data amounts and high resolution, the stitching error cannot be ignored during the image mosaic process which involves multiple images. Furthermore, with the number of mosaic images increasing the errors will continue to accumulate. The main error sources of UAV image mosaics are analyzed. A deep study is made on the image overlap and the error accumulation problem. The optimal overlap of UAV image mosaic is determined, and the original image is sparsed according to the optimal overlap. Aiming at the error accumulation problem during splicing process, the block splicing method is proposed. The experimental results show that the number of images can be reduced according to the optimal overlap, and the stitching error can be reduced effectively as the block splicing method is adopted to splice sparsed image. The vision effect of image splicing can be improved, with the efficiency of image processing enhanced in a certain extent.

With the increase of ball firing times, multiple flaws will appear in the gun bore, due to the impact of high temperature-high pressure powder gas and the attrition of pills, which influences the fire accuracy and the fire safety. Through analyzing the gradient and direction characteristics of indentation, rust corrosion and burning corrosion, the gun bore flaw images are separated into spread flaw images and regional flaw images. Then the classification factor of the spread flaw image and the regional flaw image is defined according to the sensitivity to direction of Radon image transformation and the edge gradient of Susan operation. This classification offers basis for the following analysis. Experimental results show that the algorithm could classify the gun bore flaw image accurately through computing the flaw characteristics and thus realize the quantitative classification.

When the test wavefront is strongly aspheric, the minimum fringe spacing is too small to acquire the phase value for interferometry. A technique for the measurement of free surfaces based on multiple test beams is presented. Multiple test beams under different in cident angles illuminate the free surface. When the incident angle matches with the curvature of an area under test, the fringe density in this area is reduced. In this way, the full-aperture measurement of free surfaces can be performed. The advantage of the method is that no null and no mechanical movements of the test surface are needed. In order to support the system design, the interferogram of the system is simulated and analyzed.

According to existing theory of laser shock forming, using finite element analysis software ANSYS/LS-DYNA, through the reasonable simplification and modeling, and by carefully setting up the material properties, selecting elements, meshing, applying constraints, and controlling the solving steps, a finite element model for TC4 titanium alloy sheet forming by single synchronized two-station laser shocking is established and the forming process is simulated. In the post-processing, the dynamic response curve in the forming process is drawn and the characteristics of the shock wave propagation and attenuation in the target are analyzed. By using path operation, the formed contour curve is given and the stress distribution is further studied and analyzed. The study provides reference for the investigation and application of synchronized laser shock forming.

We design a yellow light multi-wavelength tunable Raman laser by multi-stage stimulated Raman scattering in fiber and acousto-optic tunable filter, which can output a single wavelength. We get six wavelengths of yellow laser from 558 to 583 nm. Pulse energy of a single wavelength is about 5 μJ, the full-width at half-maximum of the laser is less than 5.4 nm, the pulse width is about 2.5 ns, and the divergence angle is less than 1\O. This work provides a new direction for new wavelength Raman tuning laser using tunable AOTF.

An effective depth measurement method based on desktop vision system (DVS) with high precision is proposed. For this purpose, rectification techniques for stereo image pairs are proposed and derived, which mainly consist of geometric distortion correction, reprojection transformation by central projection, zooming transformation, vertical translation transformation and brightness and color correction. The reprojection transformation can change the stereo image pairs captured by a binocular converged camera system with different camera intrinsic parameters into those captured by binocular parallel camera system with the same camera intrinsic parameters (except geometric distortion coefficient). For depth measurement, firstly, the stereo image pairs captured by a DVS are rectified and corrected into perfect ones. And then, horizontal parallax of the corresponding points of interest is gotten by stereo matching. Finally, the depth information of the spatial point of interest is calculated based on horizontal parallax and the parameters obtained by camera calibration. Experimental results show that the proposed depth measurement method is simple and practical, and the relative error is demonstrated for depth measurement of the near distant objects to be no more than 0.31%.

40 Gb/s polymer electro-optic modulators with microstrip line traveling-wave electrode are designed, fabricated and tested. Assuming that the electro-optic coefficient γ33 of the core polymer is 30 pm/V, the performance parameters of the designed modulator are half-wave voltage Vπ=4.94 V and modulation bandwidth 42 GHz. The modulator is fabricated using the second-order nonlinear optical polymer material BPAN-NT with a completely independent intellectual property as the core layer material of the polymer electro-optic modulator. After that, the performances of the modulators in direct current (DC), low frequencies and microwave regions are tested. The low-frequency (237 Hz) Vπ values at 1.31 and 1.55 μm wavelengths are 32.1 and 40.5 V, respectively. The electro-optic coefficient of core layer material γ33 is thus obtained as 3.856 pm/V. The extinction ratio is measured to be 20 dB. Within the frequencies ranging from 50 MHz to 40 GHz, the actual measured microwave attenuation coefficient α0 of the electrode system is 0.6 dB·cm-1·GHz-1/2, Using this value, the modulation bandwidth of the modulator is calculated to be 42.70 GHz. The modulation indices are measured by using optical spectrum analyzer in the frequency range from 7.5 to 16 GHz and from 32 to 40 GHz. And the frequency response curve of the modulation index M of the electro-optic polymer modulator is also obtained. The 3 dB bandwidth of the 40 Gb/s modulator is 30 GHz.

The walk-off angle, interaction angle and refractive index are calculated with numerical methods under type I frequency-doubling phase-matching direction, while the fundamental frequency wavelength is 1064 nm in LBO crystal. The walk-off angle of the fundamental frequency wavelength is 0°~1.35°. The walk-off angle of the doubling frequency wavelength is 0°~1.52°. The interaction angle between fundamental frequency and doubling frequency waves is 0°~1.15°. The coupled wave equations and the conversion efficiency are numerical calculated considering the change of walk-off angle, the interaction angle and the refractive index. The results show that the conversion efficiency has maximum value (3.35%) when the phase matching direction is about (42.2°, 19°). In addition, the conversion efficiency is proportional to the square of the crystal length.

In order to better explain the basic principle of coherent anti-Stokes Raman scattering (CARS) microscopy and facilitate image processing of CARS micrograph, the method of angular spectrum is proposed to study the optical field distributions of CARS microscopy. Based on this method, lateral and axial optical field distributions as a function of the numerical aperture of objective and the spot size of incident beam are calculated, respectively. Calculations indicate that the full-width at half-maximum (FWHM) of the optical field decreases as the numerical aperture increases, and the bigger the waist radius of incident beam is, the higher the resolution of CARS imaging is. Theoretical calculations lay a solid foundation for the future experiments.

Illumination system is the key factor influencing both the luminous efficiency and the size of the optical engine of a projector. The traditional illumination system aims at the collection and distribution only for Lambert source, failing to radically overcome the disadvantages of low luminous efficiency or big size. A design in illumination system using Gradient-Index (GRIN) lens arrays for single chip digital light processing (DLP) laser projector is introduced. The complex optical components of traditional illumination system are substituted by single-stage lens. Also, the optical performance is simulated and evaluated by the ray tracing software. The results show that the luminous efficiency of the entire illumination system is 69.5%, the uniformity of illumination is 90.9%, and the volume is only 3.06 cm3, reaching the goal of improving the luminous efficiency and reducing the size of optical engine.

In order to meet the market demand of optical zoom camera for mobile phone with low cost and high zoom ratio, the zoom system with three movement groups and the optical plastic-glass composite structure are used to design a camera lens for mobile phone with 4.6 times optical zoom, and 5 megapixels (5×106 pixel) resolution. The zoom system is optimized with computer-aided design software Zemax. In the whole field of view (FOV), the modulation transfer functions (MTFs) at 20 lp/mm are higher than 0.8, and the MTFs at half Nyquist frequency of CMOS in most part of the FOV are greater than 0.4 lp/mm at the wide-angle end (short focus) and the telephoto end (long focus). The relative distortion is less than 3.2%. The relative illumination at the wide-angle end is greater than 67%, and it is higher than 89% at the telephoto end. The moving curves change smoothly. The camera system has the advantages of high resolution, low manufacturing cost, and high zoom ratio.

The temporal-spatial evolution behaviors of the dimensionless energy flux density is calculated by means of transfer matrix method and Fourier transform when the optical pulse passes through one-dimensional photonic crystals. It will help us to know the details of energy transportation at any position and any time. The energy transportation behavior is a result of the coherent superposition of all Fourier components which experience different phase shifts and different amplifications in the medium. The electric field of a Gaussian pulse at the output port is also discussed as a function of time.

Ultra-short optical pulses and pulse trains are of considerable importance in many applied science fields such as physics, chemistry and biology because of their excellent spatial and temporal characteristics. The pulse shaping technology which is a part of ultra-short pulse research has drawn more and more attention. The pulse shaping technology based on fiber devices has also been proposed because the fiber devices have many strong points such as low insertion loss, easly integration, and so on. In this paper, we review the progress of pulse shaping technology based on optical fiber devices that is used in ultra-short optical pulse generation, arbitrary wave generation and microwave/millimeter-wave generation.

Optical fiber devices based on fiber Bragg grating Fabry-Perot structures have attracted considerable research interest in the recent years for their many important applications in optical communications and fiber-optic sensing areas. Their developments as multi-wavelength filters, tunable dispersion compensators, distributed Bragg reflection (DBR) lasers, multi-parameter sensors and high-sensitivity hydrophone have been reviewed.

This paper describes the theory of using coupled-resonator-induced transparency (CRIT) to control the speed of light and introduces several different types of slow light structures composed of ring resonators. The applications and research progress of rotation sensors and gyroscopes with high sensitivity and compact integration are given as well.

It is noteworthy that terahertz time-domain spectroscopy (THz-TDS) has been pioneered as a spectral measurement tool, which has drawn much attention in the field of terahertz (THz) wave. Conventional THz-TDS systems employ a stepped delay line for their optical delay line scan and utilize lock-in amplifier (LIA) for the acquisition of THz signals. In this approach, the speed of THz signals sampling is too slow to be introduced into some applications which require a high-speed performance. And the THz waveforms can be acquired in rapid scan THz-TDS system. Therefore, numerous practical applications for THz-TDS systems can be entered much more easily. In this review, we describe the technique for rapid scan THz-TDS and illustrate the various implementations of the technique with recent domestic and oversea examples. In addition, an improved method for rapid scan is proposed.

We analyze the principle of wide spectrum film thickness monitoring and design a portable embedded wide spectrum monitoring system of film thickness. This system is based on ARM9 core processor S3C2440 and Linux operating system with real-time monitoring interface developed on cross platform Qt2. The system collects spectral data by the USB fiber spectrum instrument, and the S3C2440 processor processes spectral data by methods such as wide spectral scanning, evaluation function, and single wavelength extremum. Thus the purpose of monitoring the film thickness of optical coating is reached. The testing result of the system indicates that this system has high precision, fast response and convenience in carrying and operating.