Bionic compound eye optical element composed of multi-dimensional sub-eye microlenses plays an important role in miniaturizing the volume and weight of an imaging system. In this manuscript, we present a novel structure of the bionic compound eye with multiple focal lengths. By the division of the microlens into two concentric radial zones including the inner zone and the outer zone with independent radius, the sub-eye which is a multi-level micro-scale structure can be formed with multiple focal lengths. The imaging capability of the structure has been simulated. The results show that the optical information in different depths can be acquired by the structure. Meanwhile, the parameters including aperture and radius of the two zones, which have an influence on the imaging quality have been analyzed and discussed. With the increasing of the ratio of inner and outer aperture, the imaging quality of the inner zone is becoming better, and instead the outer zone will become worse. In addition, through controlling the radius of the inner and outer zone independently, the design of sub-eye with different focal lengths can be realized. With the difference between the radius of the inner and outer zone becoming larger, the imaging resolution of the sub-eye will decrease. Therefore, the optimization of the multifocal structure should be carried out according to the actual imaging quality demands. Meanwhile, this study can provide references for the further applications of multifocal microlens in bionic compound eye.
The high-precision fabrication of micro-/nano-structure is a challenge. In this paper, we proposed a new fabrication method of high-precision structure based on an etching resistance layer. The high-precision features were fabricated by photolithography technique, followed by the etching process to transfer the features to the substrate. During this process, the etching uniformity and error lead to the feature distortion. We introduced an etching resistance layer between feature layer and substrate. The etching process will stop when arriving at the resistance layer. Due to the high precision of the plating film, the high-precision structure depth was achieved. In our experiment, we introduced aluminum trioxide as the etching resistance layer. The structures with low depth error of less than 5% were fabricated.
According to the exposure pattern distortion in contact printing caused by the photoresist and sometimes has a rough surface with impurity particles on it, we propose a new flexible hybrid mask for contact printing. The mask consists of three layers: a flexible polymer buffer layer, a polymer structure layer of high Young's modulus, and a metal masking layer. Because the hybrid mask skillfully combines the characteristics of flexible polymer and high Young's modulus polymer, it has two advantages: high flexibility and high resolution. The flexible hybrid mask can attach closely with the photoresist under the condition of vacuum adsorption. So the fabrication of micro-nano structures with high precision and high resolution can be realized. In this paper, a new flexible hybrid mask with critical dimension of 2um was fabricated. The photoresist structure with high precision was manufactured using this mask by photolithography and it verified the feasibility of the mask for lithography.
With the advantages of small structure and high efficiency, the diffractive element is widely used in the construction of a structured light 3D measurement system. But the working wavelength of diffraction element is single, and the light field generated by the diffraction element is only one channel. We make the original single channel into three channels, so as to achieve from the serial algorithm to parallel algorithm to improve the measurement speed. Based on the lattice light field and the design method of multi wavelength diffraction elements, and in the premise of ensuring the number of points, the traditional lattice points of light field are divided into three channels. These channels are regarded as the target fields, and the diffraction element for generating color structure light field is designed.
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