In order to recognize axes-symmetric targets in the sky, based on target′s projection transform and measurement of its three dimensional (3D) orientation, a simplified approach is put forward in this paper, which is realized in the way of matching filter and coordinate transform. An appropriate projected image of a target is chosen to make a discriminating template and is encoded to a matching filter by using computer-generated hologram. After 3D orientation of the target is explored, coordinate transform of the matched filter can be carried out according to its pitching angle and azimuth angle, and then this target is detected in the way of matching correlation. By this simplified detection method, it is studied how to select template for 3D axes-symmetric object, and recognized effect is simulated for 2D arbitrary target and 3D axes-symmetric object at random angle. With the combination of only two filters, which are made from target′s projection of 45° and 90°, the minimum correlation coefficient between the target and template in various pitching angle is 0.4472 which is far more than maximal correlation coefficient of 0.06 between plane interference objects and template.

The tapered fiber as phase conjugator has the merits of high stimulated Brillouin scattering (SBS) reflectivity and high fidelity. In this paper, three self-designed tapered fibers with different dimensions were applied in a laser diode (LD) pumped high-power master oscillator power amplifier (MOPA) laser system operated at 100 Hz repetition-rate and 28 ns pulse width. Their SBS performances and influences of taper size on fiber phase-conjugator were experimentally studied. The results demonstrated that tapered fiber with core more than ?? 400 μm can be used in high-power laser system, while higher output energy and SBS reflectivity can be achieved by using a fiber phase conjugator with optimum taper size and larger fiber length of thinner side. Appling a 5.2 m-long tapered fiber with taper from ?? 400 μm down to ?? 200 μm, 85% energy reflectivity and 21 mJ output energy of double-pass can be obtained. The pulse width was compressed up to 17 ns, the peak power reached to MW.

Optical phase conjugation (OPC) is a promising optical technology that can compensate for the distortion due to dispersion and nonlinear effects simultaneously in pulses propagating through a single-mode optical fiber. The pulse propagation characteristics influenced by self-steepening (SS) on the optical fiber system using midway OPC are analyzed theoretically. Dynamic evolution of ultra-short Gaussian pulses in the system is simulated numerically. Effects of SS on the compensation for the distortion are discussed. The results demonstrate that the SS can affect pulse propagation dynamics. The distortion due to the SS cannot be compensated by the OPC. The distortion can be counteracted by the small dispersion.

A new nonlinear optical loop mirror (NOLM) constructed from a dispersion decreasing fiber (DDF) and a normal fiber is proposed. Numerical simulation shows that a ultra-short pulse with pedestal suppression and little chirp can be generated in the new optical loop mirror and the ultra-short pulse can steadily propagate over a long lossless fiber. The compression factor and pedestal energy of the compressed pulse are related to the width and peak power of the initial pulse. The compression factor and the pedestal energy are decreasing but the optimum fiber length is increasing with the growing initial optical pulse width. In the other case, the compression factor and the pedestal energy are increasing but the required optical fiber length is decreasing with the growing input peak power. When the pulse is in optimum compression, the bigger compression factor is obtained and the optical fiber used becomes shorter comparing to the nonlinear optical loop mirror constructed from dispersion-decreasing fiber.

It is difficult to exposure the square unit phase structures with sizes of several microns on diffraction patterns by using Gaussian focus spot in a laser direct writing system. A novel changeable double or single beam optical head in the laser direct writing system has been designed and investigated. A method of using projection imaging optical configuration to obtain a square shape spot has been presented for improving the quality of exposed diffraction patterns and increasing the running efficiency by dot-by-dot exposure mode. Both the diffraction optical variable images with two beam interferential fringes on the dots and the binary phase encoding patterns can be simultaneously written on the same photoresist plate. The resolution of diffraction optical variable images can be achieved up to 2540 dpi, the size of square-shaped beams is adjustable within 5～20 μm. The diffraction optical variable images and binary phase encoding patterns with two levels have been fabricated. The experimental results are given.

Differential absorption method is an important method for methane remote monitoring. Based on the methane absorption spectrum in near-infrared region, a novel kind of fiber remote sensing system utilizing fiber Bragg grating (FBG) filters and 1.31 μm superradiance light-emitting diode (SLED) was developed for real time absorption measurement. The highly sensitive technique was achieved employing the two-wavelength differential absorption method. FBG has low insert loss and can be produced easily compared with dielectric interference filters. This system has a number of advantages such as all-fiber sensor, high sensibility, simply construct and long-distance measurement. The measurement sensitivity is 0.1％. It is 2% of the lower explosion limit of methane density in air.

Based on the Mach-Zehnder interference effect between the core mode and the cladding modes, the interference fringes are formed by a pair of cascaded long-period fiber gratings (CLPFG). It is found that the spectral spacing and the wavelength of these fringes are related to the absolute value of waveguide dispersion factor of LPFG. So by measuring the characteristics of the transmission spectra of CLPFG, the absolute value of waveguide dispersion factor γ can be deduced. At the same time, the thermo-optic coefficient of effective refractive index μ can also be deduced by measured the thermo-effect of these fringes. By this method, at the wavelength of 1554 nm, the values of γ of HE14 cladding mode and μ are calculated to be 0.874 and 4.08×10-5℃-1, respectively.

The Wolf effect, i.e., the spectrum of partially coherent light generally changes on propagation even in free space unless the light obeys the scaling law, is a well-known phenomenon of the correlation-induced spectral changes. This paper deals with the influence of turbulence on the spectral shift of the Gaussian Schell-model (GSM) beam, which is taken as a typical example of partially coherent light. Based on the propagation law of partially coherent light and consideration of the presence of turbulence, an expression for the spectrum of GSM beams propagating through turbulence media is derived and numerical calculations are performed. It is shown that the turbulence affects the spectrum of GSM beams, whenever the scaling law holds or does not hold true. The stronger the turbulence is, the larger spectral shift appears in comparison to the case without turbulence. In particular, there is off-axis spectral splitting if the scaling law fails. The spectral shift of GSM beams in turbulence media depends on the beam spatial coherence, refraction index structure constant c2n and position parameter in general.

According to the more accurate Helmholtz equation, the conventional finite-difference beam propagation method (FD-BPM) is modified and a new algorithm is proposed. Compared with the old algorithm in calculation of slab waveguide, the calculated precision is improved without extending culculating time for the new algorithm

Diffuse reflectance of tissue close to source about 1 transport mean free path (MFP) can be analyzed by P3 approximation theory, the light distribution of this area is dependent on scattering phase function of tissue. The influence of the structure factor (α) of the combined phase function on the diffuse reflectance light distribution close to source is studied in this paper. The research shows that when the transport MFP is kept constant, the light distribution close to source changes with the anisotropy factor g, but almost does not change in the region of the diffusion approximation; the influence of α on the diffuse reflectance is much more than the influence of the high-order moments of phase function on it. The research is very valuable for the in vivo measurement in endoscopic mode or in superficial tissue based on the spatial-resolved diffuse reflectance.

Based on the experiment of fluorescence spectra of thioredoxin reductase (TrxR) from human brain by the excitation of ultraviolet light (UV-light), this paper studies the spectral characteristics and their origins. The experimental results show that, under the excitation of UV-light, TrxR solution emits spectra of region from 280 nm to 720 nm, including two wider bands and many sharper peaks. The wider bands and the sharper peaks represent different tendency along with the change of solution concentration. According to the theory of conversion of internal energy and resonant Raman scattering, the theoretical analyses of TrxR fluorescence spectra are educed. The results indicate that the wide band with the peak locating at 336 nm is the fluorescence from tryptophan in TrxR and the sharper peaks mostly come from the resonant Raman scattering of TrxR. These researches on the emission spectra of TrxR solution may represent an effort to better understand the conformation, structure and vibration of TrxR molecule.

A Monte Carlo model was developed to simulate laser energy transport in biological tissues photon-number-independently and mesh-independently for laser-induced interstitial thermotherapy (LITT). In addition, laser transport characters in human liver tissue and prostate tissue at 1064 nm and 850 nm as well as its main influential factors were analyzed based on the present model. The numerical results showed that the energy deposition depended paramountly on penetration depth in radial direction and on both penetration depth and active emission length in axial direction.

The radial keyhole size is acquired by processing the coaxial image of keyhole captured in Nd∶YAG continuous wave (CW) laser deep penetration welding, and its dynamic characteristics are studied in this paper. The studied results show that the radial dimension of keyhole increases with laser power for partial penetration, while it is nearly unvaried when the workpiece is fully penetrated. With welding speed increasing, the radial width of keyhole monotonously decreases, but radial length of keyhole will be fluctuated. In certain range of defocusing distance, if laser intensity is high enough, the expansion of irradiated area by laser beam can make the radial keyhole size synchronously increase with laser spot.

A method to calculate the interaction time between metal powder and laser beam during laser direct forming with the metal powder conveyed by coaxial powder feeder is introduced in detailed. A finite element method (FEM) model based on ANSYS software is established to calculate the temperature of the metal powder while it crosses through the laser beam. Under different laser power condition, after interaction with laser beam, the temperature of the 316L stainless steel (SS) powder of different size is calculated. Thus the laser energy absorbed from laser beam by metal powders is calculated. After 316L SS powders have entered laser molten pool, the energy exchange between laser molten pool and 316L SS powders is also calculated. The calculated results show that all 316L SS powders are melted after they have crossed through the laser beam with power larger than 1000 W. It is to say that the 316L stainless steel powders are turned from solid into liquid before they reach the surface of laser molten pool. The calculated results also show that during laser direct forming, approximately 5% of laser energy is used to heat and melt metal powders and 95% of laser energy is used to form laser molten pool and to compensate the heat loss due to thermal conduction.

With the home-made laser rapid forming system and suitable processing parameter, functionally graded materials (FGMs) were prepared whose compositions continuously gradually changed from 100% 316L to 100% Rene 88 DT. The microstructure of prepared materials was full dense and very fine, its composition and hardness were continuously varied in the 40-mm transition layers. In the transition layers, with Rene 88DT′s percentage composition increased, the degree of hardness and primary dendritic space were varied from 186 Hv, 12.41 μm with 100% 316L at the bottom to 458 Hv, 16.99 μm with 100% Rene 88DT in the top.

Single-longitudinal-mode (SLM) fiber lasers are attractive for optical communications and optical sensors. The fiber laser usually operates in multimode and beating noises are a serious problem due to beat between laser mode and amplified spontaneous emission mode. A novel Er-doped single-mode fiber ring laser was demonstrated. In this laser, an unpumped Er-doped fiber was served as a saturable absorber to ensure the SLM operation, and a fiber ring resonator filter was used to suppress the beating noise. With a fiber Bragg grating (FBG) as a selective wavelength component, single mode output without beating noise is obtained experimentally. Measured linewidth is narrower than 5 kHz by using a homodyne setup, which is limited by the radio-frequency (RF) analyzer. The functions of saturable absorber and fiber ring resonator are proved.

A novel external cavity laser with specific wavelength utilizing narrow-band-pass filter as wavelength selective component is presented. It consists of lensed fiber, semiconductor laser diode chip, collimating lens, narrow-band-pass filter, and high reflectivity planar reflector in series. Static characteristics of the laser are analyzed. All the calculations are based on the rate equation and the effective reflection coefficients of the compound cavity of the external cavity laser. Experimental result shows that the narrow-band-pass filter has the specifications with insertion loss about 0.5 dB, free spectral range more than 40 nm and -3 dB bandwidth less than 1.7 nm. Good single mode operation of the external cavity laser over wide injected current range is obtained with threshold current about 25 mA, side mode suppression ratio (SMSR) better than 40 dB. And the oscillation frequency of the laser can be emitted precisely according to the ITU-T wavelength nominal value. For the excellent performance of this laser, it can be really used as promising light source for Ethernet passive optical network (EPON) based wavelength division multiple access (WDMA).

A novel Er3+/Yb3+ co-doped fiber ring laser, which utilizes amplified spontaneous emission (ASE) as a secondary pump source so that it can operate in L-band, is demonstrated. Using a high-birefringence fiber loop mirror (HiBi-FLM) as the wavelength filter, which contains two-section high-birefringence fiber and two polarization controllers (PC), and by setting the polarization controllers properly, the reflection spectrum of the loop mirror can be adjusted to let the laser operate in only one mode, and the output wavelength can be tuned in a wide range of 60 nm, from 1559.2 nm to 1619.4 nm. The stability of the laser is very good, and the output power of the laser at different wavelengths can also be flatten within 0.7 dB. Under the maximum pump power of 3594.5 mW, the absorbed pump power by the fiber is measured to be 2737.37 mW and the maximum output power obtained is 300 mW, the slop efficiency is 11%. The laser emits a line with a 3-dB band width of 0.18 nm, and the side mode suppression ratio is greater than 38 dB.

An all solid state broadly tunable high-average-power laser source based on the Ti∶sapphire crystal pumped by a frequency-doubled laser diode pumped Nd∶YAG laser is reported in this paper. Without any dispersion elements in cavity, 6.44 W of Ti

The key challenge for developing high-average power solid-state lasers is thermomechanical distortions caused by waste heat deposited in the gain medium by optical pumping. If a thin laser crystal disk is used with a nearly flat-top pump profile, the heat flux can be considered to be one-dimensional. Thermal lensing and stress-induced birefringence are dramatically reduced. A nearly flat top pump profile is achieved with a good design for the four-pass optical coupling system. An average output power of 216 W is obtained from two disks with a thickness of 1 mm. The peak power of each diode array is 2000 W with 15% duty cycle. The optical-to-optical conversion efficiency of the laser system is about 36% and the electrical-to-optical conversion efficiency is more than 16%. The beam quality factor is measured to be 12×13 in a stable resonator.

A compact, all solid-state and high repetition rate as up to 105 kHz acousto-optic (A-O) Q-switched intracavity frequency-doubled 532 nm laser is demonstrated. A Nd∶YVO4 crystal is used as active media and a type-Ⅱ KTP (KTiPO4) as frequency doubler, The Q switcher is made by fused silica and driven by a driver whose maximal rf output power is 7.5 W and repetition rate is variable from 1 Hz to 105 kHz, which is made by our own. 224 mW of 532 nm average power at a repetition rate of 50 kHz was generated with a 1 W laser diode (LD) as pump source, and a high optical-to-optical conversion efficiency of 22.4% was obtained. Under low repetition rate, steady operation is achieved with pulse width of 17.2 ns, peak power of 470 W and single pulse energy of 8.1 μJ. A general formula of average-power as a function of pulse repetition rate is presented which has good agreement with the experiment results. Analysis and experimental verification showed that, even in four-level system, the effective storage time is not equal to the upper state lifetime.

With an enhanced photoacoustic cell, the surface loss of the cell is decreased obviously, thus the resonant peak broadening is mainly due to the vibrational-translational (V-T) relaxation of AsH3. The high quality factor Q value of 374 has been achieved for AsH3 gas at the pressure of 9.06 kPa. An expression for acoustic wave amplitude as a function of modulation frequency and relaxation time has been derived. This theoretical formula is fitted to the experimental data, then the relaxation process of AsH3 is studied . The results reveal that the V-T energy transfer of gas molecules is determined mainly by the molecules′ vibrational states, which contribute the most to the vibrational heat capacity; and the two-energy level double relaxation process is the most possible process for the vibrational-translation energy transfer for AsH3.

The Smith′s model and Küng′s model for calculating the threshold of stimulated Brillouin scattering (SBS) are analyzed and discussed. The more exact method is investigated. The relationship between critical gain coefficient and fiber length is obtained, which shows that the critical gain coefficient can be considered as constant only when fiber length is long enough. The SBS threshold of 25 km single mode fiber is measured by experiment. Finally, the experiment to measure SBS threshold using Brillouin optical-time-domain reflectometer (BOTDR) is done. The results are well agreed with the theoretical predication.

The influence of NCl(a1Δ) self-annihilation on the energy extraction of NCl(a1Δ)/I laser at 300 K has been simulated using a simplified continuous flow Farby-Perot (F-P) resonator model. The results show that NCl(a1Δ) self-annihilation has an important effect on the location of the cavity resonator, the profile of power density along the flow direction and the total power. The optimal location range of the cavity resonator is dramatically shorten with NCl(a1Δ) self-annihilation. The available power with NCl(a1Δ) self-quenching is much less than that obtained without NCl(a1Δ) self-annihilation at small initial density of HI but has little difference at large initial density of HI.

Based on a study optical dynamic active confocal probe, a new method of the measuring deviation focus is developed. The key point of this new method is that displacement of the turning fork is converted to time difference measurement, thus the optical and mechanical structures of the laser probe system can be simplified greatly, and its accuracy and stability are enhanced. A new high integration measurement system is designed, and systematic experiments resulted of the including linearity, measuring range and performance were carried out.

In the semiconductor intersatellite communication system, how to test the laser beams′ quality is difficult. In order to solve this problem, a basal principle of the white light lateral double-shearing interferometer is introduced firstly, and then measuring the semiconductor laser beam′s wavefront which is near the diffraction-limited by the interferometer is reported, and the formula of calculating the beam′s divergence is deduced according to the Fraunhofer diffraction. A 0.2λ wavefront error is gained experimentally. Corresponding to the wavefront error, the divergence angle is only 64.8 μrad, which indicates the beam is near the diffraction-limited. The result shows that the interferometer has high precision and wide practicability.

A novel and simple method used for the measurement of the practical value of the retardance (an overall ambiguity modulo 2π is not considered) and the determination of the fast or slow axis of a quarter-wave plate employing two polaroids and a right-angle prism is reported. The theoretical analysis of the principle is given taking Jones matrix as a mathematical tool, the uncertainty of formula is derived, the effects of each factor upon the uncertainty are simulated using a computer. The working conditions of this method are discussed. An application example is given, and the measured result of the example is verified with results of test and computer simulation, which indicates that the method is feasible. Furthermore, this method has the advantages such as easier to obtain the optical devices needed, simpler to operate, and accurate etc.

A 40 Gb/s optical transmission based on the NSFCNet 400 km×10 Gb/s system is realized without any bit error rate (BER) floor. It is shown that typical 10 Gb/s systems of middle or short distance can be upgraded to 40 Gb/s directly without change the transmission links. However, the chromatic dispersion must be compensated precisely when the system upgrades, because the dispersion tolerance of 40 Gb/s systems is much lower than that of 10 Gb/s system. Meanwhile, the influence of the optical power injected into the fiber links is also investigated. The results show that the effect of the fiber nonlinearity must be considered as well as the improvement of optical signal to noise ratio (OSNR) due to the enlarged signal bandwidth when the bit rate of transmission system is upgraded from 10 Gb/s to 40 Gb/s.

The multi-wavelength dividing element is a key element in wavelength division multipler (WDM) system. Phase-only diffractive optical element (PDOE) used as WDM element has many merits, such as easy coupling, polarization insensitivity, low cross-talk and simple structure. For the design of binary optical WDM element, the angular dispersion analysis is needed. Based on the phase binary equation, the angular dispersion and the thermal angular dispersion analysis are proposed in this paper. And the theoretical expressions of dispersion and thermal dispersion have been given after the analysis. Using the results of this theory, the destination value of Yang-Gu (Y-G) algorithm is selected, and the binary optical WDM element is also designed. The angular dispersion simulation based on Fresnel diffraction has been proceeded. The numerical simulation results validate the theoretical results.

This article analyses the model of the ATM-PON system and its downstream data structure. Based on the analysis, the layout design of ONT's physical layers is illustrated, including some important key technique, such as cell delineating, DSS, and the VHDL programming technique of FPGA, and so on. Then the implementation of the physical layer and the timing relationship of synchronization is given to prove that the design destination of the physical layer of ONT is accomplished successfully.

Based on the theory of probability, a blocking probability model is proposed to investigate the blocking performance of the individual node in wavelength division multiplexing (WDM) wavelength routed all-optical networks. The blocking performance is relevant to the number of wavelengths multiplexed in each fiber link and the number of access fiber link ports, with (full or limited) wavelength conversion. The numerical results show that the wavelength routing node equipped with the higher conversion degree of wavelength converters has the better performance than the node equipped with lower ones. To enhance service efficiency of wavelength resource and to make the all-optical networks more flexible, virtual wavelength routing, wavelength converters in all-optical networks are needed. Trade-off between the performance and the cost is found in this paper. Then to guarantee blocking performance is precondition, wavelength routing nodes deployed with the low conversion degree of the wavelength converters are able to reach the definite blocking performance. The realistic and cost-effective way to construct nodes system in WDM routing networks is to use wavelength converters with weak capability.