Fabrication of polydimethylsiloxane microlens array on spherical surface using multi-replication process

Abstract

In comparison to traditional planar optical devices, compound-eye structured optical elements can reduce the number of components and their volume when being applied to wide-field imaging and sensing systems. However, the fabrication process for microstructures on a curvilinear surface has many difficulties since traditional fabrication techniques are planar. In this paper, we present a cost-effective method to fabricate microlenses on a spherical surface. Microlenses, of which the fill factor was about 78%, were formed using the thermal reflow technique, followed by multiple replication processes to transfer the microlenses from the planar substrate onto a spherical surface. We produced a curved mold with concave microlenses, and it allowed this method to be replicable. A polydimethylsiloxane elastomer was employed as the material for both the microlenses and the mold. The radius of curvature of the spherical surface was approximately 6.1 mm. The variation of the microlenses was analyzed, demonstrating high uniformity. The imaging performance of the microlenses is also presented. The curved microlens arrays were combined with image sensors, and sub-images of objects at various distances are shown. The experimental results demonstrate a high potential for curved microlens arrays being applied to compact mobile camera lenses.

Wide-angle and ultrathin camera module using a curved hexagonal microlens array and all spherical surfaces

“…The fabrication of the MLA on a spherical surface by multireplication processes has been demonstrated in our previous research [6][7][8][9], and practical production of the MLA is feasible. A hexagonal microlens is used to avoid the light leakage problem.…”

“…Generally speaking, it is difficult to fit a wide-angle lens structure in such small form factor, because the thickness, light incident angle, image quality, and pixel number of a mobile phone camera influence each other [5]; furthermore, most mobile phone cameras use four to six lenses. To overcome these drawbacks, we adopt a curved hexagonal microlens array (MLA), which can be made by micromachining processes [6][7][8][9][10]. The MLA is composed of multiple lenses arranged in a two-dimensional array on a supporting substrate.…”

Biomimetic Multiaperture Imaging Systems: A Review

“…Some researchers have been actively seeking for an innovative replica molding process to fabricate an omnidirectionally aligned microlens array. (25,26) Cherng and Su made a curved mold for a concave microlens array by pressing a planar microlens array with a spherical object. (25) With this curved mold, microlens arrays on a curved shell were fabricated.…”

Wide-angle camera with multichannel architecture using microlenses on a curved surface

“…First we construct a hexagonal lens as a standard and choose a material with a refractive index of 1.45, such as polydimethylsiloxane (PDMS). The semi-diameter of the hexagonal lens is 0.25 mm, which is feasible by current fabrication technology [6].…”

“…Previous research on artificial compound eyes concentrated on planar structures, such as thin compound-eye camera designs based on the apposition compound eye [4]. In order to expand the FOV of the planar structure, a curved artificial compound eye is proposed, in which microlenses are distributed on a curved surface [5,6].…”