In recent years, monolithic multi-surface image systems are widely concerned with the deeply development of optoelectronic imaging system and the ultra precision machining technology, most of these systems consist of multiple mirrors, and these mirrors are machined on one substrate or grouping processing on two substrates. In this paper, we discuss the optical design of visible imaging system with a filed of view 2° based on common-axial folded optical system. This study described the optical design of visible all-reflective imaging systems based on the aviation aluminum material. It works in the 0.45~0.75μm wavelength bands. The visible imaging system includes two elements, the first one is a flat mirror, and the second one is an optical element with four concentric zone aspherical mirrors, each concentric zone aspherical surfaces are 12-th order, the beam is folded and reflected between concentric zone aspherical mirrors and flat mirror, and then focused on the image plane. The surface accuracy of submicron order and position accuracy of micron order, and the technology of single point diamond turning are used to ensure the coaxality accuracy of the concentric zone aspherical mirrors. According to the optical design results, the quality of imaging arrives at the diffraction-limitation. On this basis, we design the focusing mechanism and complete system manufacturing; assembly and imaging experiment. The final system has the advantages of compactness, convenient thermal management and simple installation. It can potentially be applied to the optical system of the unmanned aerial vehicle system.
To improve the effective deformation of the unimorph deformable mirror (DM), ion beam figuring (IBF) is applied for manufacturing the initial surface figure. However, heat produced during IBF can cause comparable internal stress and thermal deformation on the adhesive layer, which causes the mirror’s figure to be unsatisfactory. Consequently, the whole manufacturing process, especially thermal distribution on the adhesive, should be monitored and controlled. A 19-unit thin-layer unimorph DM is adopted as the object to simulate and measure the distribution law of temperature field on the adhesive during the IBF process. IBF parameters are optimized according to the characteristics of the adhesive and the manufacturing simulation results. With a ϕ3-mm diaphragm integrated on IBF, the processing temperature is reduced below the adhesive’s glass transition temperature Tg. Actual figuring results report over 50% reduction on both peak-to-valley (PV) and root-mean-square (RMS) of DM with the value from 310 to 141 nm and from 38 to 17 nm, respectively. This precision has satisfied the self-corrected requirement of general unimorph DMs, which is usually <20 nm RMS. The voltage fitting coefficient of self-correcting for most electrodes is reduced to <0.05, which means the significant improvement in the effective deformation and correction ability.
The unimorph deformable mirror (DM) is favored in the field of synchrotron radiation due to its simple structure, dynamic surface figure and adaptive adjustment. The request of mirror surface accuracy on the synchrotron radiation beam focus can be up to sub-nanometer RMS. Ion beam figuring is a high precision processing method with noncontacting and roughness damage. However, because it belongs to the type of thermal manufacturing, the adhesive layer characteristic is changed and the DM’s figuring accuracy is reduced by the thermal deformation. In this paper, thermal simulation and temperature test of the adhesive during ion beam processing are carried out; The variation law of temperature and thermal stress of the adhesive layer with different ion beam diaphragms and scanning times are obtained. Therefore, the selective guideline for the diaphragm is obtained. With the optimal process parameters, the temperature of the adhesive layer is decreased with the minimum temperature between the glass transition temperature Tg and 1/2 of the Curie temperature Tc.
Single layer piezoelectric driving deformable mirror (Unimorph DM) with large deformation, simple fabrication process and low cost has been widely applied for the adaptive optics system in recent years. In the past, the optimal design of deformable mirror is often used in analytic method, and made much simplified approximation in theory. This results in large error between theoretic and real system. In this paper, the influence laws between the fitting error and the effective aperture, and the spatial distribution are studied by the dynamic–electricity coupling simulation method. The relationship between the displacement and the thickness of the mirror, the diameter and thickness of the electrode and the width of the support ring are discussed. According to these rules, a scheme of optimizing the structure of deformable mirror has been proposed, and the key parameters are designed according to the requirements of the retinal imaging system. In the end, all the fitting errors of former Zernike items 3-30 are less than 0.4 with the rated voltage of 400V.