A 2 kW single-mode fiber laser with two cascade home-made cladding light strippers (CLSs) has been demonstrated by employing bidirectional-pump scheme. 2.009 kW signal power is obtained when pump power is 2.63 kW and the slope efficiency is 76.6%. Raman Stokes light is less than -47 dB at 2.009 kW even with a 10-m delivery fiber with core/inner cladding diameter of 20 μm/400 μm. The beam quality M2≤1.2 and the spectral FWHM bandwidth is 4.34 nm. There is no transverse mode instability and the output power stability of ±0.14% is achieved by special thermal management for a more uniform temperature distribution on the Yb-doped gain fiber.

The design and optimization for lens group in spectral domain optical coherence tomography (SD-OCT) system is fairly important to improve the imaging quality. The field lens in sample arm and the focus-ing lens in spectrometer are designed based on Zemax, and the imaging quality is evaluated according to spot diagram and wavefront map. The results show that the field lens can provide ideal imaging quality and good lat-eral resolution. And the focusing lens in the spectrometer makes the size of focal spot smaller than the pixel width of CCD to avoid the interference in each pixel of CCD. In this way, we observe considerable improvement in the resolution of the spectrometer.

The target tracking algorithm in compression domain based on compression perception is studied. To meet the specific application requirements, the shortcomings of original algorithm are improved. At the same time, based on the design idea and demand of miniaturized target position detector, a real-time image pro-cessing platform with TMS320DM6437 digital signal processor as the core is designed and implemented, and the algorithm is implemented and optimized on the DSP platform. The simulation and experiment results show that after the combination of Kalman filter, LBP feature and adding adaptive learning rate update strategy, the stability of the algorithm is improved. For the implementation in DSP, after a series of optimizing measures, as for an image with resolution of 960×960, taking the target window of 80×80 into account, the computation speed can be up to 25 fps, which can meet the requirement of real-time tracking. The embedded tracking system can track the selected moving objects continuously and stably, and can meet the target localization and tracking require-ments under specific applications, which has a real practical value. Moreover, the method in this paper has a certain reference value for the research and applications of this kind of target tracking method in the embedded platform.

In order to compensate disturbance and accomplish the stabilized tracking control for airborne plat-form mounted on multi-rotor unmanned aerial vehicle (MUAV), a self-adjusting tracking control method based on an improved disturbance observer (DOB) and radial basis function (RBF) neural network approximation is pro-posed. First, a compensated control is introduced into feedback loop in the structure of original disturbance ob-server, an improved disturbance observer is established based on velocity signals, and the ability of disturbance compensation and robustness are analyzed. Second, aiming at the compensation problem of nonlinear un-known disturbance, a method based on the RBF neural network (RBFNN) approximation properties is utilized. Finally, a composite compensation control structure is designed based on Lyapunov stability theory. The experi-mental results show that after applying the proposed method, the disturbance of airborne opto-electronic plat-form is compensated effectively. The proposed method has high precision and stable tracking control perfor-mance, and it can fully meet the requirement of airborne opto-electronic platform stability control.

Two-dimensional strip is a common flow control method to accelerate flow transition. The wavefront distortion resulting from hypersonic boundary layer has been investigated in virtue of theoretical analysis and wind tunnel experiments. Wavefront measurement system is used to measure the wavefront distortion of hyper-sonic boundary flow, and compare the distribution of flow wavefront with and without strip. The results prove that high-precision wavefront measurement system can present not only wavefront but also density distribution be-fore the flow transition of boundary layer. In addition, the experimental results show that the wavefront distortion increases quickly when the flow is obviously unstable. Finally, comparing the distribution of wavefront induced by strip with the corresponding data without strip, we find that the mean wavefront, root mean square and peak-valley value of wavefront with strip are much larger than that without strip.

Fourier transform infrared (FTIR) spectroscopy Si―OH group is widely used in Si―OH content meas-urement of fused silica optics. However, the measurement accuracy is influenced by water molecular absorption bands in low Si―OH content samples and absorption saturation in high Si―OH content samples, leading to lim-ited measurement range. FTIR spectroscopy is employed to measure 2500~5000 cm-1transmittance spectra of fused silica samples with different OH contents and thicknesses. The interference of water molecular absorption band to 3673 cm-1is eliminated. Then Si―OH contents, corresponding measurement errors and limits of detec-tion at 3673 cm-1and 4522 cm-1bands are calculated. Based on the experimental results and Beer’s law, a model to correlate Si―OH content, sample thickness, measurement error of transmittance, and measurement error of Si―OH content is established. From this model, by using 3673 cm-1band for fused silica samples with Si―OH content less than 8.17×10-4and 4522 cm-1band for samples with Si―OH content more than 8.17×10-4to meas-ure the Si―OH content, a dynamic range from 0.4×10-6to 10-2Si―OH can be achieved with optimized accuracy for fused silica samples with 2 mm thickness.

In order to realize the high-precision measurement of the thermal expansion coefficient of the infrared material under the cryogenic vacuum environment, a measurement scheme of solid material is proposed. Based on the self-collimation principle, this scheme designs a microstructure, establishes the relationship between structural deformation and angle, and deduces the formula of thermal expansion coefficient measurement. Us-ing the measurement formula, this article analyzes the relationship between the measurement error transfer function of the scheme, and also uses the error sensitivity function to analyze the design accuracy of cryogenic thermal expansion coefficient measuring device for infrared materials, and finally the relative error of the scheme is calculated. The thermal expansion coefficient of the scheme is measured to be only 0.76%, which satisfies the nanometer measurement requirement.

To improve the detection efficiency, the optical components of modern infrared detection system generally need to be cooled. The determination of the thermal expansion coefficient of the infrared material at low temperature can provide the theoretical basis for the study of infrared optical system. Some institutes from home and abroad had researched the thermal expansion coefficient of common solid material in the past. But few people explored the thermal expansion coefficient of infrared materials in low temperature environment. When the infrared material is in minus 250 degrees Celsius, the deformation of material is very small. If the accuracy of the device is not high enough, measurements would become very difficult. So the thermal expansion coefficient of the infrared material is lacking. In order to realize the high-precision measurement of the thermal expansion coefficient of the infrared material un-der the cryogenic vacuum environment, a measurement scheme of solid material is proposed. Based on the self-collimation principle, this scheme designs a microstructure. The scheme uses a sample column made of infra-red material and two support columns to support a plane mirror, and the three cylindrical rods are placed in a trian-gular manner. A collimator is placed at the top of the plane mirror to measure the angle of the mirror. When the tem-perature changes, the length of the sample column will change. So the angle of the plane mirror will change. The co-efficient of thermal expansion of the solid material is estimated by measuring the angle change of the plane mirror through the collimator. Then the article establishes the relationship between structural deformation and angle, and deduces the formula of thermal expansion coefficient measurement. As the measurement accuracy is relatively high, it is necessary to analyze each error source. In order to calculate the magnitude of the thermal expansion coefficient error, the article calculates the error sensitivity function for each factor and integrates all errors. So using the meas-urement formula, this article analyzes the error transfer formula theoretically, and also uses the error sensitivity function to analyze the design accuracy of the system. Calculation shows that the effect can be ignored when the squareness tolerance between sample column and the platform reaches 6 levels. Finally, the precision of the scheme is measured to be only 0.76% which satisfies the nanometer measurement requirement. The scheme can achieve not only measurement of thermal expansion coefficient in low-temperature vacuum and high-temperature environments, but also other high-precision nano-sized measurements of linear deformation.

Surface plasmon polaritons (SPPs) is a type of collective electron oscillation along metal-dielectric interface. Based on the coupling between the incident light and the free electrons metal surface, it can propagate along the interface with an exponentially decaying field distribution on both sides. SPPs may be one of the most promising candidates in the area of nano integrated optics because of the subwavelength optical confinement with the ability of breaking the diffraction limit. During the past years, advancements in novel plasmon waveguide configurations have led to the proposal and demonstration of numerous plasmon waveguide structures, which combine the advantages of both semiconductor and plasmon waveguides and enable light transmission in the deep sub-wavelength scale to achieve long distance propagating with very tight mode confinement. Among these waveguides, the metal-insulator-metal (MIM) waveguides have attracted considerable interests because of their smaller mode size, stronger confinement of SPPs and lower propagation loss. They are promising structures for design of nanoscale all-optical devices due to their relatively easy fabrication according to the current state of the art. Optical resonant cavities based on the MIM structures are crucial structural components in plasmonic wavelength-selective devices and plasmonic all-optical switches owing to their simplicity. A plasmonic Y-shaped metal-insulator-metal (MIM) plasmonic waveguide struc-ture with two side-coupled Fabry–Perot (FP) resonant cavities is proposed. The finite element method (FEM) is used to study the transmission properties of the waveguide. Simulation results show that two stopbands occur respec-tively on the transmission spectrum of each output port and which is helpful to the potential applications of nar-rowband filter. In addition, at other locations in the spectra away from the stopbands, the transmission rates of the two output ports are always equal indicating obvious effect of optical splitting. By tuning the lengths of the two cavi-ties, the locations of the stopbands can be effectively controlled, and an interesting phenomenon is that the trans-mission peak of one output port corresponds to the transmission dip of another output port. Based on this result, the effect of all-optical directional transmission, switching and filtering can be obtained and adjusted by changing the geometry parameters. Finally, the applications of the structure in the area of refractive index sensing are investigated. For this purpose, the sample to be measured can be filled in two the cavities. During the simulation, the refractive index of the medium filled in the cavities is changed from 1.00 to 1.05 with a step of 0.01. It is found that the trans-mission spectra of the two output ports have a clear redshift, and the calculated sensitivity can reach 1280 nm/RIU with the quality factor up to 208. The proposed compact waveguide structure has potential applications in the field of integrated photonic devices, such as plasmonic filters, switches, power splitters and refractive sensors.

Surface plasmon polaritons (SPPs) is a type of collective electron oscillation along metal-dielectric interface. Based on the coupling between the incident light and the free electrons metal surface, it can propagate along the interface with an exponentially decaying field distribution on both sides. SPPs may be one of the most promising candidates in the area of nano integrated optics because of the subwavelength optical confinement with the ability of breaking the diffraction limit. During the past years, advancements in novel plasmon waveguide configurations have led to the proposal and demonstration of numerous plasmon waveguide structures, which combine the advantages of both semiconductor and plasmon waveguides and enable light transmission in the deep sub-wavelength scale to achieve long distance propagating with very tight mode confinement. Among these waveguides, the metal-insulator-metal (MIM) waveguides have attracted considerable interests because of their smaller mode size, stronger confinement of SPPs and lower propagation loss. They are promising structures for design of nanoscale all-optical devices due to their relatively easy fabrication according to the current state of the art. Optical resonant cavities based on the MIM structures are crucial structural components in plasmonic wavelength-selective devices and plasmonic all-optical switches owing to their simplicity. A plasmonic Y-shaped metal-insulator-metal (MIM) plasmonic waveguide struc-ture with two side-coupled Fabry–Perot (FP) resonant cavities is proposed. The finite element method (FEM) is used to study the transmission properties of the waveguide. Simulation results show that two stopbands occur respec-tively on the transmission spectrum of each output port and which is helpful to the potential applications of nar-rowband filter. In addition, at other locations in the spectra away from the stopbands, the transmission rates of the two output ports are always equal indicating obvious effect of optical splitting. By tuning the lengths of the two cavi-ties, the locations of the stopbands can be effectively controlled, and an interesting phenomenon is that the trans-mission peak of one output port corresponds to the transmission dip of another output port. Based on this result, the effect of all-optical directional transmission, switching and filtering can be obtained and adjusted by changing the geometry parameters. Finally, the applications of the structure in the area of refractive index sensing are investigated. For this purpose, the sample to be measured can be filled in two the cavities. During the simulation, the refractive index of the medium filled in the cavities is changed from 1.00 to 1.05 with a step of 0.01. It is found that the trans-mission spectra of the two output ports have a clear redshift, and the calculated sensitivity can reach 1280 nm/RIU with the quality factor up to 208. The proposed compact waveguide structure has potential applications in the field of integrated photonic devices, such as plasmonic filters, switches, power splitters and refractive sensors.

Si―OH group is the most common impurity in fused silica, which has a significant impact on the optical perfor-mance of fused silica optics from infrared to ultraviolet spectral regions. The Si―OH content can be directly meas-ured from Si―OH stretching band at 3673 cm-1with molar absorptivity of (77.5±1.5) L/(mol·cm). However, meas-urement range is limited by interference of absorption bands from water molecule in low Si―OH content samples and absorption saturation in high Si―OH content samples. Fourier transform infrared (FTIR) spectroscopy is em-ployed to measure 2500 cm-1~5000 cm-1transmittance spectra of fused silica samples with different Si―OH con-tents ranging from 0.0 to 10-3and thicknesses ranging from 2.0 mm to 8.0 mm. Since 3000 cm-1~3100 cm-1absorp-tion bands from H2O molecule is not covered by other infrared (IR) absorption bands, absorption at 3673 cm-1from H2O molecule can be eliminated using transmittance from 3000 cm-1~3100 cm-1region and line shape of H2O band obtained by Gaussian fit from low Si―OH content samples. Compared with 4522 cm-1absorption peak which is not interfered by any absorption bands, the Si―OH content calculated from 3673 cm-1 band without influence of water absorption band has a relative error about 2.5% lower than that directly calculated by 3673 cm-1 band in Suprasil 501 sample with about 5.0×10-5Si―OH content and 2.0 mm thickness. After eliminating the influence of water ab-sorption band, corresponding measurement errors and limit of detection for Si―OH content at 3673 cm-1and 4522 cm-1bands are calculated. Based on experimental data and Beer’s law, a model to correlate Si―OH content, sample thickness, measurement error of transmittance, and measurement error of Si―OH content is established. From this model, Si―OH content measurement error is mainly influenced by logarithm of transmittance and influence of water absorption band in low Si―OH content samples, and absorption saturation in high Si―OH content samples. Since the molar absorptivity at 4522 cm-1is nearly 50 times weaker than that at 3673 cm-1, the corresponding transmit-tance at 4522 cm-1is much lower than that at 3673 cm-1, leading to a lower relative root mean square error for Si―OH content measurement at 4522 cm-1than that at 3673 cm-1in high OH content samples. With 2.0 mm thick-ness, a relative error less than 0.13% can be achieved in sample with 10-2Si―OH content at 4522 cm-1absorption band. As a result, by eliminating water absorption band at 3673 cm-1for low Si―OH content samples and employing 4522 cm-1band for high Si―OH content samples to measure the Si―OH content, the measurement range is increased from (6.0~1810.0)×10-6to (0.4~10000.0)×10-6at 2.0 mm thickness with improved measurement accuracy.

Aero-optical effects caused by hypersonic boundary layer transition are always challenges in improving the accu-racy of directed energy weapon. In order to avoid hypersonic boundary transition in the optical detection window, which can generate large scale structures and cause wavefront distortion, researchers have tried many flow con-trol methods to accelerate or delay transition. We investigate the effects of 2D strip to the hypersonic boundary layer in the virtue of theoretical analysis and wind tunnel experiments. A radial shearing interference system is used to measure the wavefront distortion.The experiment is conducted in FD-03 tunnel of China Academy of Aerospace Aerodynamics. Free stream total pressure is 1.05 MPa, total temperature is 350 K, Mach number is 5.01, Reynolds number is 2.45×107, and aero-dynamic noise is 0.3%. We use plane model as an experimental model, the size of plane model is 250 mm×120 mm, the thickness of leading edge is 1 mm, and attack angle is 0. The plane is 30 mm above the bottom of the en-trance of nozzle. The roughness is 0.8 μm~1.6 μm. The strip is attached on the plane 35 mm away from leading edge. The size of strip is 20 mm×120 mm×0.5 mm.High-precision wavefront measurement system is used to measure the wavefront distortion of hypersonic boundary layer. This system based on the radial shearing interference system can measure the wavefront of flow filed precisely. We measure the wavefront of circular region with diameter of 0.9 mm and space of 3.9 mm, to re-veal the development of hypersonic boundary flow and compare the distribution of wavefront induced by strip with the corresponding data without strip. After the calculation of data analysis program, we get the mean wave-front, root mean square and peak-valley value of wavefront, which are reflections of density distribution of hy-personic boundary flow.The results prove that high-precision wavefront measurement system can present not only wavefront but also density distribution before the flow transition of boundary layer. In addition, the experimental results show that the wavefront distortion increases quickly when the flow is obviously unstable. Finally, comparing the distribu-tion of wavefront induced by strip with the corresponding data without strip, we find that the mean wavefront, root mean square and peak-valley value of wavefront with strip are much larger than that without strip. It means the strip may accelerate the development of hypersonic boundary flow, and make the flow unstable earlier. The conclusions have some reference values to flow control of the guidance system on the hypersonic aircraft.

Recently, multi-rotor unmanned aerial vehicle (MUAV) has been widely used in military and civilian fields. Airborne opto-electronic platform (AOEP) is the key to the application of MUAV, such as target reconnaissance, identification and tracking. The imaging quality, recognition accuracy and tracking accuracy of airborne opto-electronic devices, to a large extent, depend on the stable control performance of the AOEP. Unfortunately, the AOEP is vulnerably affected by air disturbance, vibration and other unknown disturbance factors during the flight operation process, which se-riously influences the stability and accuracy, and even leads to reconnaissance and tracking tasks failure. Therefore, how to improve the anti-disturbance ability of the AOEP has become the key problem, which restricts the develop-ment and applications of the MUAV severely. It has been one of the hot research directions in recent years.For the problem of disturbance compensation of airborne stabilized platform, the control method based on dis-turbance observer (DOB) has been widely used. To a certain extent, the stability control performance of the airborne stabilized platform is improved. However, the compensation effect of DOB on high frequency noise is not ideal. Simultaneously, disturbance usually has strong nonlinearity. It is difficult to obtain ideal tracking control perfor-mance by using DOB method only. Fortunately, neural networks and fuzzy systems are real-time, robust, and can approximate any function. They have been widely used in the tracking control system of stabilized platform.Aiming at the disturbance compensation and stability control of AOEP, a composite compensation control method for AOEP mounted on MUAV is proposed. First, to eliminate the effects of high frequency noise, by introducing a compensation control into the original DOB structure, an improved disturbance observer (IDOB) based on the ve-locity signal is proposed. Second, considering the nonlinearity of the disturbance, the radial basis function neural network (RBFNN) is used to estimate and compensate the nonlinear disturbance. In order to realize the stable con-trol of AOEP, a composite compensation control system based on IDOB and RBFNN is designed by using Lyapunov stability principle. It is proved that the proposed control system is asymptotically stable and the tracking error is bounded. It has good stability and robustness. Finally, the effectiveness of the method is verified by experiments. The experimental results show that the IDOB structure has better disturbance rejection ability and has higher stabil-ity accuracy. The proposed method can restrain the effect of disturbance to the AOEP system. The AOEP has higher stability and tracking precision. The composite compensation control system completely satisfies the requirements of tracking control of AOEP.

Recently, multi-rotor unmanned aerial vehicle (MUAV) has been widely used in military and civilian fields. Airborne opto-electronic platform (AOEP) is the key to the application of MUAV, such as target reconnaissance, identification and tracking. The imaging quality, recognition accuracy and tracking accuracy of airborne opto-electronic devices, to a large extent, depend on the stable control performance of the AOEP. Unfortunately, the AOEP is vulnerably affected by air disturbance, vibration and other unknown disturbance factors during the flight operation process, which se-riously influences the stability and accuracy, and even leads to reconnaissance and tracking tasks failure. Therefore, how to improve the anti-disturbance ability of the AOEP has become the key problem, which restricts the develop-ment and applications of the MUAV severely. It has been one of the hot research directions in recent years.For the problem of disturbance compensation of airborne stabilized platform, the control method based on dis-turbance observer (DOB) has been widely used. To a certain extent, the stability control performance of the airborne stabilized platform is improved. However, the compensation effect of DOB on high frequency noise is not ideal. Simultaneously, disturbance usually has strong nonlinearity. It is difficult to obtain ideal tracking control perfor-mance by using DOB method only. Fortunately, neural networks and fuzzy systems are real-time, robust, and can approximate any function. They have been widely used in the tracking control system of stabilized platform.Aiming at the disturbance compensation and stability control of AOEP, a composite compensation control method for AOEP mounted on MUAV is proposed. First, to eliminate the effects of high frequency noise, by introducing a compensation control into the original DOB structure, an improved disturbance observer (IDOB) based on the ve-locity signal is proposed. Second, considering the nonlinearity of the disturbance, the radial basis function neural network (RBFNN) is used to estimate and compensate the nonlinear disturbance. In order to realize the stable con-trol of AOEP, a composite compensation control system based on IDOB and RBFNN is designed by using Lyapunov stability principle. It is proved that the proposed control system is asymptotically stable and the tracking error is bounded. It has good stability and robustness. Finally, the effectiveness of the method is verified by experiments. The experimental results show that the IDOB structure has better disturbance rejection ability and has higher stabil-ity accuracy. The proposed method can restrain the effect of disturbance to the AOEP system. The AOEP has higher stability and tracking precision. The composite compensation control system completely satisfies the requirements of tracking control of AOEP.

Target tracking is the key technology of many computer vision systems, and has important application value in a range of military and civil fields such as weapon guidance, intelligent transportation system, medical image system, virtual reality and so on. The essence of target tracking is to determine the position of the target in successive frames of a video. Classic ideas of target tracking in videos are based on the surface model representing the target object, which translates the tracking problem into the problem of maximizing the similarity coefficient between the model and the candidate distribution. This kind of method is often with large computation complexity, and as for the plat-form with limited resources, the robustness, accuracy and real-time performance are difficult to achieve a good bal-ance. On the other side, tracking method based on decision model is the research hot spot in the field of target track-ing. It treats the target localization as a binary classification problem, by designing classifiers to distinguish the tar-get from the background effectively to achieve the aim of target tracking. This method is often able to achieve a high-er frame rate, but in embedded system, relative research and applications are still very imperfect. Target tracking algorithms based on compress sensing in compression domain fuses these two types of target tracking methods, and often have low computational complexity, high accuracy and stability. However, there are still some problems to be solved in some applications. The target tracking algorithm in compression domain based on compression percep-tion is studied, and in order to meet the specific application requirements, the shortcomings of original algorithm are improved. At the same time, based on the design idea and demand of miniaturized target position detector, a re-al-time image processing platform with TMS320DM6437 digital signal processor as the core is designed and imple-mented, and the algorithm is implemented and optimized on the DSP platform. The simulation and experiment re-sults show that after the combination of Kalman filter, LBP feature and adding adaptive learning rate update strategy, the stability of the algorithm is improved. For the implementation in DSP, after a series of optimizing measures, as for an image with resolution of 960×960, taking the target window of 80×80 into account, the computation speed can be up to 25 f/s, which can meet the requirement of real-time tracking. The embedded tracking system can track the selected moving objects continuously and stably, and can meet the target localization and tracking requirements under specific applications, which has a real practical value. Morevoer, the method in this paper has a certain refer-ence value for the research and applications of this kind of target tracking method in the embedded platform.

Spectral domain optical coherence tomography (SD-OCT) is a non-invasive cross-sectional imaging method that has been developed to obtain high-resolution tomographic images of biological, organic and inorganic objects. The high resolution, imaging depth, acquisition speed, and sensitivity of the SD-OCT system are significant for medical imag-ing. However, there are many negative factors which will result in lower system resolution. For example, if the field lens in sample arm is not appropriate, the lateral resolution will decrease. Similarly, if the focusing lens in spec-trometer cannot provide the focal spot with a smaller size comparing with the pixel width of CCD, it will bring inter-ference in each pixel of CCD, and the resolution of the spectrometer will decrease. As a result, the design and optimi-zation for lens group in SD-OCT system are fairly important to the resolution and imaging quality. The aim of this study is to provide higher resolution of the system by designing and optimizing the lens group in sample arm and spectrometer based on Zemax, which can provide the optical designer with spot diagram, geometric aberration, op-tical transfer function and other means of analysis used to assess the imaging quality. The field lens in sample arm and the focusing lens in spectrometer are designed, and the imaging quality is evaluated according to spot diagram and wavefront map. The results indicate that the field lens can bring ideal lateral resolution of 7.9 μm, which is suf-ficient for high-resolution imaging. And the focusing lens in the spectrometer makes the size of focal spot smaller than the pixel width of CCD to avoid the interference in each pixel of CCD. In this way, we observe considerable im-provement in the resolution of the spectrometer, and the signal-to-noise ratio of the system is improved, too. After design and optimization with Zemax, we measured the lateral resolution of the system with the USAF1951 resolution board. The results show that the lateral resolution is 12 μm, which differs from the simulation value by 5.1 microns. Then we calculate the resolution of the spectrometer with the focusing lens we designed. It turns out that the resolu-tion of the spectrometer determined by the pixel width of CCD is 0.0363 nm. In conclusion, the simulation results, experimental results and calculation results show that the lens group we designed can achieve good resolution and imaging quality, and provide a strong theoretical basis for the processing of the device.

Spatial resolution is an important property of remote sensing image. As an important branch of remote sensing, the moderate resolution imaging spectroradiometer (MODIS), mounted on Terra and Aqua satellites, is an important instrument for observing global biological and physical processes in the Earth observation system (EOS) program. It is widely used in the fields of ground detection, cloud classification and climate research because it contains rich information. However, due to sensor limitations and external interference, MODIS image resolution is still limited to a certain level. Therefore, using super-resolution technology to improve resolution of the MODIS image has a great practical significance.Recently, although the method based on sparse representation has tackled the ill-posed problem effectively, two fatal issues have been ignored. First, many methods ignore the relationships among patches, which will result in some unfaithful output. Second, the high computational complexity of sparse coding using l1 norm is needed in re-construction stage. We proposed a single image super-resolution (SISR) method to predict a high-resolution (HR) MODIS image from a single low-resolution (LR) input. As is known to us, infinitely many HR patches will result in the same LR patch when blurred and down-sampled. This is an extremely ill-pose problem. Therefore, we group the LR patches with the similar semantic and the corresponding HR patches into topics in the training stage and find the HR patch with the most similar semantic from all possible HR patches for a given LR patches in the reconstruct stage by pLSA.In the training stage, we discover the semantic relationships among LR patches and the corresponding HR patches and group the documents with the similar semantic into topics. Then, we can learn dual dictionaries for each topic in the low-resolution (LR) patch space and high-resolution (HR) patch space and also pre-compute corresponding re-gression matrices for dictionary pairs. In the reconstruction stage, for the test image we infer locally which topic it corresponds to and adaptive to select the regression matrix to reconstruct HR image by semantic relationships. With above processing, we can get the optimal reconstruction for the HR image.Our method discovered the relationships among patches and pre-computed the regression matrices for topics. Therefore, our method can greatly reduce the artifacts and get some speed-up in the reconstruction phase. Experi-ment manifests that our method performs MODIS image super-resolution effectively, results in higher PSNR, recon-structs faster, and gets better visual quality than some current state-of-art methods.

A high power single-mode fiber laser is an attractive laser source which has various application fields such as mate-rials processing and long-distance laser energy transmission. In the last decades, the output powers of monolithic fiber lasers have increased remarkably. However, the power scaling of the single-mode fiber lasers is limited by the traditional fiber nonlinear effects and transverse mode instability (TMI). Among fiber nonlinear effects, the stimu-lated Raman scattering (SRS) is the main limiting factor for continuous-wave fiber lasers. SRS results in the output power instability of the fiber laser. Backward SRS is also damagingly raised by the reflected light from the optics or the work piece in a practical laser system. Therefore, a laser with high SRS suppression is desired for stable opera-tion of a laser system. Besides, photodarkening is also found in Yb-doped high power fiber laser, which can cause the decrease of output power, long term stability and operation life of the fiber laser. Koponen has observed a sev-enth-order dependence of the PD rate on the excited-state Yb concentration for two different fibers. This result im-plies that PD of an Yb-doped fiber source fabricated using a particular fiber will be strongly dependent on the Yb in-version rate and lower inversion rate can be obtained by using 976 nm pump light as compared to 915 nm. A sin-gle-mode fiber laser employing bidirectional-976 nm pump scheme and high SRS suppression and high power sta-bility are demonstrated without any TMI. We investigate the signal power vs. pump power (S-P) performances, beam distribution and quality, output spectrum and output power temporal characteristic of the fiber laser oscillator with bidirectional-pumping configuration. The forward-pumping is firstly utilized and then bidirectional-pumping is uti-lized to further scale the output laser. Besides, the performance of the homemade CLS used in the 2 kW system is described. By employing bidirectional-pumping, the TMI is remarkably mitigated and when the output power is fur-ther scaled to 2 kW with a slope efficiency of 76.6%, the Raman stokes light is ~47 dB below the signal power even with a 10-m delivery fiber with core/inner cladding diameter of 20 μm/400 μm. Nearly diffraction-limited beam quality is also confirmed with the measured M2below 1.2 and no residual pump and cladding light are observed. Beside, remarkable power stability is also demonstrated because of more uniform temperature distribution on Yb-doped gain fiber by a special thermal management. From the experimental results and theoretical evaluation, an output power of 3 kW is believed to be achieved by further increasing pump power.

Compared to electron beam welding, the penetration depth of high power laser welding is smaller due to the attenua-tion effect of the plasma plume on laser power deposition. To date, numerous researches on the suppression of laser plasma plume had been undertaken, such as pulse laser welding, weaving laser welding, change the shielding gas compositions, and apply the side-assistant gas and electromagnetic fields. However, the increase of the penetration depth and the improvement of the weld quality were inconspicuous. Compared with conventional laser welding, the welding formation and quality was improved significantly while the laser welding was conducted under vacuum. In this work, the influences of ambient pressure on the laser welding penetration depth, surface formation and porosity defect were summarized. The domestic and overseas research findings on mechanism of laser welding under vacu-um were elaborated from the aspects of plasma plume, keyhole and molten pool behaviors. In addition, the applica-tions of laser welding under vacuum in the industry were introduced. Finally, the problems of reported researches were analyzed and the prospects of the technology were discussed. The previous researches on the laser welding under vacuum indicated that the penetration depth of the weld seams increased sharply, the welding formation was improved and the porosity defects were suppressed effectively. Critical vacuum degree enough for improving the weld penetration depth and quality was detected for aluminum alloy, titanium alloy, nickel-base alloy and steel. The laser welding characteristics under vacuum was related to the plasma plume, keyhole and molten pool flow behav-iors. The planet wheel carrier in the power station had been welded successfully by applying this technology. The laser welding under vacuum exhibits the wonderful application prospects to weld the thick plates in the shipbuilding, nuclear instrument and pressure vessel industries. In the future works, the authors suggest that the laser power deposition mechanism should be investigated systematically by considering the physical properties of the materials and the collision characteristics of the ions in the plasma plume. Besides, the heat and mass transfer characteristics, solidification behavior of the molten pool should be studied. In order to expand the application fields of laser weld-ing under vacuum, the low vacuum and local subatmospheric pressure laser welding equipments should be devel-oped towards higher adaptability and integration. Local subatmospheric pressure laser welding equipments with the excellent pressure maintaining property should be developed. Moreover, the feasibility of laser welding with filler and laser hybrid welding under vacuum is of vital interest for the development this technology.

Compared to electron beam welding, the penetration depth of high power laser welding is smaller due to the attenua-tion effect of the plasma plume on laser power deposition. To date, numerous researches on the suppression of laser plasma plume had been undertaken, such as pulse laser welding, weaving laser welding, change the shielding gas compositions, and apply the side-assistant gas and electromagnetic fields. However, the increase of the penetration depth and the improvement of the weld quality were inconspicuous. Compared with conventional laser welding, the welding formation and quality was improved significantly while the laser welding was conducted under vacuum. In this work, the influences of ambient pressure on the laser welding penetration depth, surface formation and porosity defect were summarized. The domestic and overseas research findings on mechanism of laser welding under vacu-um were elaborated from the aspects of plasma plume, keyhole and molten pool behaviors. In addition, the applica-tions of laser welding under vacuum in the industry were introduced. Finally, the problems of reported researches were analyzed and the prospects of the technology were discussed. The previous researches on the laser welding under vacuum indicated that the penetration depth of the weld seams increased sharply, the welding formation was improved and the porosity defects were suppressed effectively. Critical vacuum degree enough for improving the weld penetration depth and quality was detected for aluminum alloy, titanium alloy, nickel-base alloy and steel. The laser welding characteristics under vacuum was related to the plasma plume, keyhole and molten pool flow behav-iors. The planet wheel carrier in the power station had been welded successfully by applying this technology. The laser welding under vacuum exhibits the wonderful application prospects to weld the thick plates in the shipbuilding, nuclear instrument and pressure vessel industries. In the future works, the authors suggest that the laser power deposition mechanism should be investigated systematically by considering the physical properties of the materials and the collision characteristics of the ions in the plasma plume. Besides, the heat and mass transfer characteristics, solidification behavior of the molten pool should be studied. In order to expand the application fields of laser weld-ing under vacuum, the low vacuum and local subatmospheric pressure laser welding equipments should be devel-oped towards higher adaptability and integration. Local subatmospheric pressure laser welding equipments with the excellent pressure maintaining property should be developed. Moreover, the feasibility of laser welding with filler and laser hybrid welding under vacuum is of vital interest for the development this technology.

High-bit-rate long-distance quantum communication is a proposed technology for future communication net-works and relies on high-dimensional quantum entan-glement. While the spatial modes of light provide an avenue for high-dimensional entanglement, photon states can decay over long distances, thus a way to am-plify the signal is needed. Comparable to classical re-peaters, entanglement swapping is used to generate remote quantum correlations between particles that have not interacted, thus reducing the effects of decay and loss.

Grain boundaries separate crystallites in solids and influence material properties, as widely documented for bulk materials. In nanomaterials, however, investi-gations of grain boundaries are just beginning.

Optical communications, laser science, microscopy and metrology demand control of light polarization. Metamaterials have recently been developed to act as efficient passive polarization components of subwave-length dimensions. However, active polarization con-trol has so far been mainly limited to microwave and terahertz wavelengths, and current electronic methods used to control polarization are reaching physical speed limits.