High Precision Fabrication Method of Fresnel Diffractive Lenses on Ultrathin Membrane for Imaging Application

Abstract

The microstructures on flexible membrane substrate prepared by the traditional methods may introduce large morphology and position errors, making it hard to achieve clear imaging. In this paper, we present a high precision fabrication method composed of two steps: unstressed fixation of the polyimide membrane and high precision fabrication of diffractive microstructures on the flexible membrane substrate. By using precise spincoating technology, we get 25 μm thick polyimide membranes, whose coefficient of thermal expansion is almost zero. To prepare high precision microstructures, we propose an aerated membrane method, by which the flexible membrane substrate and the photoresist on it can attach tightly to the mask under the air pressure difference between the upper and lower surfaces of the membrane substrate during the contact lithography. The results show that the wave-front error obtained by this method is less than 1/30λ RMS (F# = 25@632.8 nm) at 400 mm aperture, indicating the microstructures have excellent morphologies and high position accuracy.

Membrane–Fresnel Diffractive Lenses with High-Optical Quality and High-Thermal Stability

“…Because the processing was not mature enough, the M-FDL on the PI membrane that they finally fabricated has only two levels, and the diffraction efficiency was only 33%. In 2020, the Institute of Optics and Electronics, Chinese Academy of Sciences, proposed an aerated-membrane method for directly fabricating M-FDL [ 13 , 14 ]. The wave-front error of the M-FDL they finally fabricated can reach 0.035λ at 632.8 nm.…”

Microprismatic Fresnel Lens for Formation of Uniform Light Circle

“…Distant object tracking is an important application of Fresnel lenses [1][2][3]. The lens is also used to form precise visual images [4][5][6][7], even with a varying focal distance [8], for Image rectification [9], signal enhancement [10], imaging systems [11], lens distortion models [12], and other applications [13,14]. Different methods have been proposed for designing focusing lenses, including flat focusing Fresnel structures.…”