Ge Ren

The macroscopic Fourier ptychography (FP) is regarded as a highly promising approach of creating a synthetic aperture for macro visible imaging to achieve sub-diffraction-limited resolution. However most existing macro FP techniques rely on the high-precision translation stage to drive laser or camera scanning, thereby increasing system complexity and bulk. Meanwhile, the scanning process is slow and time-consuming, hindering the ability to achieve rapid imaging. In this paper, we introduce an innovative illumination scheme that employs a spatial light modulator to achieve precise programmable variable-angle illumination at a relatively long distance, and it can also freely adjust the illumination spot size through phase coding to avoid the issues of limited field of view and excessive dispersion of illumination energy. Coupled with a camera array, this could significantly reduce the number of shots taken by the imaging system and enable a lightweight and highly efficient solid-state macro FP imaging system with a large equivalent aperture. The effectiveness of the method is experimentally validated using various optically rough diffuse objects and a USAF target at laboratory-scale distances.

Excellent disturbance rejection ability is essential for a photoelectric tracking system (PTS) based on the Charge-Couple Device (CCD) sensor, which is a premise guarantee for obtaining highly accurate tracking, especially under the condition of moving carriers with intense disturbances. The feedforward control method based on disturbance estimated from the system model output and sensor output is currently a commonly used strategy for disturbance compensation due to its ability to directly counteract the disturbances. This disturbance feedforward compensation method behaves sensitively in case of model mismatch caused by internal disturbances, which may lead to a significant reduction in the disturbance compensation effect or even cause system instability. In this paper, unlike disturbance feedforward compensation, a pure disturbance sliding-mode feedback control (DSMFBC) based on disturbance observation without additional sensors is proposed, ensuring faster and precise compensation for disturbance. In case of model mismatch, the observed disturbance is used to build the disturbance feedback control to maintain a more efficient disturbance compensation through the robustness that feedback naturally possesses. To achieve a stronger anti-disturbance capability, a sliding-mode nonlinear control method is used to design the control law. The experimental setup of PTS based on the fast-steering mirror (FSM) demonstrates that the method has better dynamic performance and disturbance rejection ratio.

We investigate niobium-silicon mixed films prepared by plasma-assisted reactive magnetron sputtering. Multilayer films composed of niobium-silicon oxide with various Nb fractions were fabricated. The Nb fractions were calculated using the Brüggemann model and measured by x-ray photoelectron spectroscopy. The morphology of the samples shows that the stress in mixed monolayers depends on the Nb fraction and annealing temperature. A high-reflectivity (HR) multilayer film was fabricated from two mixed-oxide materials with Nb fractions of 20% and 95%, which are optimal for stress self-compensation and a maximum difference in refractive index to facilitate film design. The residual stress of this mixed-oxide multilayer HR film is completely self-compensated through annealing. Although annealing this film redshifts the transmission spectra and increases the surface roughness of the film, the results of cavity ring-down tests indicate that the reflectance remains high in the wavelength band of interest (1064 nm) and spatially uniform over the substrate surface. This detailed characterization of these films shows that the mixed-oxide multilayer HR mirror with self-compensated stress would be appropriate in numerous applications.

This study concerns the problem of integrated optimization of structure and control based on a fast steering mirror, aiming to achieve simultaneous optimization of the mechanical structure and control system. The traditional research and development path of the fast steering mirror involves a lengthy process from the initial design to the final physical manufacture. In the prior process, it was necessary to produce physical prototypes for repeated debugging and iterative optimization to achieve design requirements, but this approach consumes a significant amount of time and cost. To expedite this process and reduce unnecessary experimental costs, this study proposes an integrated optimization of structure and control (IOSC) method. With the use of IOSC, it is possible to achieve simultaneous optimization of structure and control. Specifically, the use of non-dominated sorting genetic algorithm II (NSGA-II) obtains globally optimal controller parameters and mechanical structure parameters under certain performance indices. This achieves an effective balance between the resonance frequency generated by the system and the working bandwidth, providing a high-precision reference for the research and development of fast steering mirrors.

It is a crucial issue to realize real-time piston correction in the area of sparse aperture imaging. This paper introduces an optical diffractive neural network-based piston sensing method, which can achieve light-speed sensing. By using detectable intensity to represent pistons, the proposed method is capable of converting complex amplitude distribution of the imaging optical field into piston values directly. Differing from the electrical neural network, the way of intensity representation enables the method to obtain the predicted pistons without imaging acquisition and electrical processing process. The simulations demonstrate the feasibility of the method for point source, and high accuracies are achieved for both monochromatic light and broadband light. This method can greatly improve the real-time performance of piston sensing and contribute to the development of the sparse aperture system.

The space-agile optical composite detection (SOCD) system with a pointing mirror possesses flexible and fast response ability. Like other space telescopes, if the stray light is not properly eliminated, it may result in a false response or noise that floods the real light signal due to the low illuminance and large dynamic range of the target. The paper shows the optical structure layout, the decomposition of the optical processing index and roughness control index, the stray light suppression requirements, and the detailed stray light analysis process. The pointing mirror and ultra-long afocal optical path increase the difficulty of stray light suppression in the SOCD system. This paper presents the design method of a special-shaped aperture diaphragm and entrance baffle, black baffle surface testing, simulating, selection, and stray light suppression analysis process. The special-shaped entrance baffle has a significant effect on the suppression of stray light and reduced dependence on the platform posture of the SOCD system.

The space-agile optical composite detection system with pointing mirror possesses flexible and fast response ability. Just like other space telescopes, if the stray light is not properly eliminated, it may result in a false response or noise flooding the real light signal due to the low illuminance and large dynamic range of target. The paper shows the optical structure layout, the decomposition of the optical figure profile and roughness profile index, the stray light suppression requirements, and the detailed stray light analysis process. Pointing mirror and ultra-long afocal optical path increase the difficulty of stray light suppression in space-agile optical detection system. This paper will present the design method of special shaped aperture diaphragm and heterosexual entrance baffle, black baffle surface testing, simulating and selection, and stray light suppression analysis process. The special-shaped entrance baffle has a significant effect on the suppression of stray light, and reduced dependence on platform posture.

The space-agile optical composite detection system with pointing mirror possesses flexible and fast response ability. Just like other space telescopes, if the stray light is not properly eliminated, it may result in a false response or noise flooding the real light signal due to the low illuminance and large dynamic range of target. The paper shows the optical structure layout, the decomposition of the optical figure profile and roughness profile index, the stray light suppression requirements, and the detailed stray light analysis process. Pointing mirror and ultra-long afocal optical path increase the difficulty of stray light suppression in space-agile optical detection system. This paper will present the design method of special shaped aperture diaphragm and heterosexual entrance baffle, black baffle surface testing, simulating and selection, and stray light suppression analysis process. The special-shaped entrance baffle has a significant effect on the suppression of stray light, and reduced dependence on platform posture.

A noised phase-unwrapping method is presented by using the Wigner distribution function to filter the phase noise and restore the gradient of the phase map. By using Poisson’s equation, the unwrapped phase map was obtained. Compared with the existing methods, the proposed method is theoretically simple, provides a more accurate representation, and can be implemented in light-field hardware devices, such as Shack-Hartmann sensors.

The image-based piston sensing method using the convolutional neural network (CNN) is an advanced technique which has good applicability. However, acquiring a large amount of the training dataset required to train a network is difficult to handle in practice. In this letter, we demonstrate the possibility of using a neural network trained by the simulation dataset to accurately sense pistons directly from experimental images. As a demonstration of the proposed scheme, a single CNN developed by computer-generated images is applied for piston measurement of an experimental setup with three sub-apertures. This is particularly helpful for the sparse aperture system with more sub-apertures. We believe that the study in this letter will contribute to the applications of the CNN-based technique for piston sensing.