Overview: Aluminum Oxynitride (AlON) transparent ceramic has high transparency from the ultraviolet to mid-infrared range, excellent mechanical properties, high temperature resistance and excellent chemical stability. It’s a new structure-function integration optical material and an ideal material for photoelectric windows, missile domes, and transparent armors. The fabrication of AlON transparent ceramic mainly includes synthesis of the AlON nanopowders, forming nanopowders to green body, sintering of the green body into a dense transparent ceramic, grinding and polishing. The preparation of green body with high density and homogeneous microstructure is the key technical procedure for fabricating AlON transparent ceramic. Generally, cold isostatic pressing is used for fabricating AlON green body. However, AlON nanopowders possess high specific surface area and are easy to form non-uniform agglomeration. If the nanopowders are directly formed by cold isostatic pressing, the density of the green body will be poor, and finally resulting in poor performance of the sintered AlON ceramic. In order to solve the problem of non-uniform agglomeration of AlON nanopowders, the AlON powders can be granulation processed into uniform, dense, good fluidity spherical particles, and then dense green body can be obtained by cold isostatic pressing. Spray granulation is an effective method to realize nanopowders micro-spheroidization, but, there is no report on dealing with spray granulation of AlON nanopowders. In this paper, we aimed to improve density and homogeneity of AlON green body by spray granulation combined with cold isostatic pressing, and fabricate AlON ceramics with larger size and more complex structure. First, single phase AlON powders were prepared by solid-state reaction method and ball-milled into nanopowders with an average particle diameter of 320 nm, and narrow size distribution. Second, We optimized the spray granulation process. The effect of solid content of AlON slurries on properties of spray granulated particles were investigated. When the solid content of AlON slurry was 50 wt%, dense spherical particles with a diameter greater than 10 μm and good fluidity were obtained. Third, The effect of cold isostatic pressing pressure on density, microstructure, average pore diameter of green bodies and optical transmittance of sintered ceramics were intensively investigated. The results showed that when cold isostatic pressing pressure was increased to 200 MPa, the density of AlON green body reached to 2.17 g/cm3, the relative density increased to 58.8%, and the green body had small pore and uniform microstructure. The in-line transmittance of AlON ceramic fabricated by cold isostatic pressing and pressureless sintering reached 83% at 2000 nm for the thickness of 2 mm. Last, we have demonstrated our work on fabricating AlON transparent ceramics with a diameter of Φ170 mm plate and Φ110 mm dome. Those spray granulation, cold isostatic pressing and pressureless sintering techniques can be used to fabricate high quality, large size AlON transparent ceramics in the future. AlON transparent ceramic is a new structure-function integration optical material with excellent optical, thermal, and mechanical properties, which can be widely used in missile domes, and transparent armors and other fields. The preparation of green body with high density and homogeneous microstructure is the key technical procedure for fabricating AlON transparent ceramic. However, nanopowders possess high specific surface area and are easy to form non-uniform agglomeration, resulting in poor density of formed green body. In order to improve density and homogeneity of green body, micro-spheroidization of nanopowders and dense spherical particles with a diameter greater than 10 μm and good fluidity were obtained by optimizing the spray granulation process. The effect of cold isostatic pressing pressure on density, microstructure, average pore diameter of green bodies, and optical transmittance of sintered ceramics were intensively investigated. Green bodies with relative density of 58.8% were obtained. The in-line transmittance of sintered ceramics reached 83% at 2000 nm (thickness 2 mm). AlON transparent ceramics with diameter of Φ170 mm plate and Φ110 mm dome were obtained by cold isostatic pressing and pressureless sintering.

Overview: In order to achieve the desired performance a compact and lightweight isogrid fully integrated into the Altitude Structure is proposed. This structure is adapted to the mirror interfaces of the 30 m Chinese Future Giant Telescope. The aim of the M1 Support Structure is to provide stiff support for the Primary Mirror and, at the same time, contribute to the stiffness of the Altitude Structure, using a lightweight solution so that the unbalance of the altitude structure does not increase in an important way. Besides, the M1 Cell needs to offer an adequate interface to the different mirrors and thus avoid the generation of important local displacements at their support due to the weight of that mirrors. Furthermore, the M1 Cell must allow easy access for maintenance. The isogrid consists of a series of top and bottom plates welded to each other using a series of ribs extending in different directions and using a triangular pattern, resulting in a structure behaving like a lightweight isotropic material. The isogrid will have a constant thickness of 3200 mm to be accessed and will follow the same curved surface as the mirrors. Apart from being a lightweight solution, the fabrication and assembly of such an isogrid are simpler than those of a conventional space frame, which is the traditional solution for M1 Support Structures. Besides, the isogrid allows more open room below the mirrors, so that access from below to the mirrors for maintenance can be achieved easily and even carts up to 1 m height would be able to drive below the mirrors, which is difficult to achieve in the case of a space frame. This can be achieved using a continuous floor on the bottom plate. In order to avoid the fact that the ribs are an obstacle to the continuous floor, we propose using a modular and puzzle-like grating made of galvanized steel that can be mounted easily and the top surface is at the same height as the ribs. A grating based on 40 mm × 4 mm steel members with a spacing of 50 mm ×50 mm is proposed to fulfil the requirements. The different elements of the grating will be planar elements. Due to the low curvature of the surface containing the mirrors, it is expected that carts will be able to travel through it.In recent years, with the fast development of astronomical science and higher requirements for astronomical telescope's performance, the ground-based extremely large astronomical optical telescopes with aperture 20 m~40 m in diameter are being actively studied and constructed internationally. With the increase of the telescope aperture, these telescopes should face even greater challenges. In order to make them meet their optical design requirements, new solutions are needed to provide adequate load sharing. In this paper, several design methods of the main structures and key components of the extremely large telescopes are summarized, the advantages and disadvantages of various schemes are analyzed, a lightweight sheet metal welding structure for the 30 m Chinese Future Giant Telescope (CFGT) is put forward, and the finite element model design and analysis are carried out. The results show that when the telescope points to the zenith, the first modal frequency is 2.3 Hz and the maximum deformation of the structure is 3.8 mm. While the telescope points in the horizontal direction, the first modal frequency is reduced to 2.1 Hz and the maximum deformation of the structure is 2.9 mm, which meets the technical requirements of CFGT. The design provides a technical reference for the development of extremely large telescopes in China in the future.

Overview: With the development of the computer and the artificial intelligence technology, the orbital angular momentum shift keying system decoding method based on the machine learning has emerged. The orbital angular momentum demodulation scheme using machine learning has advantages of the simple structure, wide recognition range and high recognition accuracy. The development of deep learning has further improved the recognition accuracy of orbital angular momentum. And the development of deep learning has further improved the recognition accuracy of orbital angular momentum. In order to speed up the training speed of the orbital angular momentum beam recognition model based on deep learning, this paper proposes to use the transfer learning method to identify the orbital angular momentum beam, and build the transfer learning recognition model based on the VGG16 architecture. To simulate the transmission of orbital angular momentum beams in a turbulent environment, this paper use the sub-harmonic method to generate an atmospheric turbulence phase screen and build a simulated turbulent environment by loading the phase screen with the spatial light modulator. The orbital angular momentum recognition task was carried out in a weakly turbulent environment with D/r0=1.5 and a medium turbulent environment with D/r0=4. And high recognition rates of 98.62% and 94.37% were obtained in weak turbulence environment with D/r0=1.5 and a medium turbulence environment with D/r0=4, respectively. The feasibility of an orbital angular momentum recognition system based on the transfer learning is proved. At the same time, in terms of the model training speed and recognition rate, this paper compares the performance of the transfer learning model and the original VGG16 model, and visualizes the recognition results of each beam by using the confusion matrix. The VGG16 model obtains the recognition rates of 99.39% and 94.81% in the weak turbulence environment with D/r0=1.5 and the medium turbulence environment with D/r0=4, respectively. The recognition rate is reduced by less than 1%, but the model training speed is improved by 2.3 times. This paper proves the feasibility of the orbital angular momentum recognition system based on transfer learning. At the same time, it is proved that the orbital angular momentum recognition system based on transfer learning model can greatly reduce the time required for model training under the condition of maintaining high recognition rate. This paper provides an idea for the rapid construction of orbital angular momentum shift keying system which based on convolutional neural network in the future. This paper proposes a transfer learning method to recognize the orbital angular momentum beam to speed up the training speed of the orbital angular momentum beam recognition model based on deep learning. In order to simulate the atmospheric turbulence, we generate the atmospheric turbulence phase screen by the sub-harmonic method and build the simulated turbulence environment by loading the phase screen on the spatial light modulator. The orbital angular momentum beam recognition system based on transfer learning has achieved a recognition rate of more than 90% in both weak and medium turbulent environments. Compared with the traditional deep learning method in the aspects of model training speed and recognition rate, it is proved that the orbital angular momentum beam recognition method based on transfer learning can reduce the training time while maintaining a high recognition rate in the weak and medium turbulent environment.

In the end, the demodulation method of Fabry-Perot sensors ultimately serves for practical application. The complex environment in engineering applications affects the performance of the Fabry-Perot sensors. So, the research on the demodulation method should not be limited to the laboratory environment. Developing a demodulation method with engineering application value is vital.Fiber optic Fabry-Perot sensors have attracted a lot of attention in many fields such as medical detection, underwater acoustic detection, and electric power monitoring due to their high sensitivity and strong anti-interference ability. The parameters of the light source, the structure of the sensing head, and the demodulation methods are the main factors that restrict the detection ability of fiber optic Fabry-Perot sensors. Demodulating the fiber optic Fabry-Perot sensors is to extract cavity length from the output optical signal which indicates the information of vibration, displacement, acceleration, temperature, and other parameters sensed by the sensor's head. An excellent demodulation method can improve the demodulation speed, resolution, and dynamic range of the fiber optic Fabry-Perot sensor. However, there are dozens of demodulation methods for the fiber optic Fabry-Perot sensor, and it is difficult to choose the appropriate demodulation method for specific application scenarios. In this paper, firstly, the characteristics of the signal output from the optical fiber Fabry-Perot sensor are reviewed. Then, the influencing factors of the common demodulation methods are described in detail, and the improvement methods proposed by domestic and foreign research institutes are also introduced. Finally, the choice principle of the demodulation is proposed from two aspects: the applicable condition and the multiplexing of the optical fiber Fabry-Perot sensor.

Overview: Atmospheric polarization mode has important application value in the field of the autonomous navigation because of its stable meridian characteristics. However, its acquisition is limited by the physical characteristics of the acquisition device and is easy to be blocked by the surrounding environment of the acquisition location and thin clouds, resulting in the reduction or disappearance of the local atmospheric polarized light between the acquisition device and the shelter (buildings, trees, thin clouds, etc.). When capturing the atmospheric polarization information, it often produces the degradation of the atmospheric polarization characteristics in irregular areas and destroys the overall structure of the atmospheric polarization mode. As a result, the accuracy of its meridian decreases. To solve this problem, this paper proposes a neighborhood constrained atmospheric polarization mode generation network, which combines the neighborhood constraint characteristics of the atmospheric polarization information. It carries out multi-step neighborhood feature reasoning through the neighborhood feature repair module, and gradually propagates the continuous distribution characteristics of the atmospheric polarization information to the missing region, so as to increase the feature constraints in the reconstruction process. In addition, this paper further puts forward the constraint condition on the physical characteristics of the atmospheric polarization mode - Solar meridian angle loss. The solar meridian feature that generates atmospheric polarization information is extracted by the solar meridian feature constraint, and compared with the solar meridian feature of the real atmospheric polarization mode, so as to guide the generation process and improve the meridian accuracy of reconstruction results. Finally, because the acquisition of atmospheric polarization modes is limited by time, space and the number of the acquisition equipment, it is difficult to directly obtain the local atmospheric polarization modes under different conditions at the same time. Therefore, this paper proposes a binary mask data set containing four distribution types, which combined with the measured global atmospheric polarization data. It can also simulates the local effective atmospheric polarization information under different conditions and improves the diversity of local atmospheric polarization mode data. In this paper, experiments are carried out on the measured atmospheric polarization data and compared with other latest methods. The experimental results show the robustness and superiority of this method.Atmospheric polarization mode supports the polarization navigation application by virtue of the "∞" feature containing the solar meridian information. However, due to the limitation of the physical characteristics of the acquisition device, the surrounding environment of the acquisition location and the occlusion of thin clouds, the obtained atmospheric polarization information is partially distorted and the accuracy of the solar meridian is reduced. In order to solve this problem, this paper proposes an atmospheric polarization pattern generation network based on neighborhood constraints. The network mines the continuity of atmospheric polarization pattern distribution, increases the constraints of reconstruction process through multi-step neighborhood feature reasoning, and accurately generates global atmospheric polarization information from local effective polarization information. In addition, according to the physical characteristics of the atmospheric polarization mode, the angle loss of solar meridian is proposed to further improve the accuracy of the solar meridian. In this paper, experiments are carried out on the measured atmospheric polarization data, and compared with other latest methods. The experimental results show the robustness and superiority of this method.

Overview: Gas-liquid two-phase flow is widely used in the industrial field, and one of the typical flow patterns is bubble flow. Therefore, measuring the bubble flow phase distribution parameters is of great significance for studying the characteristics of two-phase flow and industrial production. Optical technology is widely used in small-channel gas-liquid two-phase flow detection, and it can be divided into invasive and non-invasive. Invasive optical detection methods will affect the characteristics of gas-liquid two-phase flow to a certain extent, so non-invasive measurement is an important research direction of optical technology. Some scholars have proposed a method of measuring phase distribution based on the characteristics of single-wavelength light intensity distribution, but the established model is only suitable for the horizontal pipeline, and the resulting error is large. To solve this problem, a dual-wavelength measurement model of bubble flow phase distribution parameters is proposed in this paper, to obtain more optical signal characteristics of laser passing through bubble flow in small channels and reduce the measurement error of phase distribution parameters. The phase distribution and parameter distribution of vertically rising gas-liquid two-phase bubble flow in a small channel are measured and studied by the dual-wavelength transmission method. The light intensity distribution of dual-wavelength laser passing through gas-liquid two-phase flow is calculated based on the principle of the geometric optics, and then the characteristic quantity of dual-wavelength light intensity distribution is extracted. An identification model of bubble flow phase distribution parameters based on the dual-wavelength measurement theory is established. Trace Pro is used to trace the refraction trajectories of 445 nm and 635 nm laser passing through the pipe section containing bubbles with different phase distribution parameters, and the corresponding light intensity distribution curves are obtained. The key features of the corresponding double wavelength light intensity distribution curves are studied, and three kinds of characteristic parameters are extracted: missing part length, missing part offset, and double wavelength interval length. The neural network is trained by using the simulated feature data set, and the trained neural network is used to predict the phase distribution parameters of bubble flow in the experiment. The simulation results show that the prediction results are in good agreement with the simulation data, and the relative error is within ± 5%. The average absolute errors of the established model for the prediction of bubble center position and radius are 0.018 mm and 0.007 mm respectively. The results show that the dual-wavelength method has higher accuracy and is more suitable for the measurement of gas-liquid two-phase flow. Finally, a dual-wavelength gas-liquid two-phase flow measurement system is built. The bubble flow in the small vertical rising channel with the small gas flow is measured by using a dual-wavelength laser light source. The bubble flow is obtained by injecting gas into the stagnant liquid column. The experimental research is carried out, and the bubble sizes distribution curve is counted. In general, the dual-wavelength measurement method provides good results and is an alternative method for the measurement of bubble phase distribution parameters. This technology is helpful to measure and monitor bubble flow parameters online.Aiming at the deficiency of the existing single-wavelength method in measuring the phase distribution parameters of the vertically rising gas-liquid two-phase bubble flow in a small channel, a dual-wavelength method is proposed. Based on the principle of geometric optics, the light intensity distribution of dual-wavelength laser passing through gas-liquid-two-phase-flow is calculated, and the characteristics of light intensity distribution of dual-wavelength laser are extracted. An identification model of bubble flow phase distribution parameters based on the dual-wavelength measurement theory is established. Trace Pro is used to simulate 445 nm and 635 nm laser passing through bubbles with different phase distribution parameters, and then the features of the dual-wavelength light intensity distribution curves can be extracted. The characteristic quantity data set of simulation is used to train the neural network. The trained neural network is used to predict the phase distribution parameters of bubble flow in the experiment. The simulation results show that the average absolute errors of the model for predicting the bubble center position and radius are 0.018 mm and 0.007 mm respectively, which are better than the single-wavelength method, which proves the effectiveness and accuracy of the model. The bubble flow was measured on the experimental platform, and the three-dimensional diagram of bubble flow was reconstructed.