Rotational Offset Microlens Arrays For Highly Efficient Structured Pattern Projection

This article reports the diffractive optical elements of rotational offset microlens arrays for generating highly efficient structured light patterns in active stereoscopic 3D imaging. The double-side configuration of microlens arrays increases the uniformity of diffraction patterns by using two successive refractions on microlens surfaces. In addition, the rotational offsets between the frontside and the backside microlens arrays with rectangular or hexagonal arrangements control the contrast and the density of structured dot array patterns. Two layers of microlens arrays with high curvature and high fill-factor are microfabricated on both sides of the glass wafer by using ultrathin fluorocarbon encapsulation, thermal reflow, and parylene gap filling. The rotational offset angles of 22.5 degrees, 28 degrees, and 37 degrees in rectangular and 13.25 degrees, 21.75 degrees, and 27.75 degrees in hexagonal arrangements efficiently provide diffractive dot arrays with high uniformity, contrast, and density by minimizing the overlapping of diffractive patterns. The active stereo imaging using rotational offset microlens arrays successfully acquire high-resolution depth map for 3D plaster objects with smooth and curved surfaces. The structured light pattern projection using rotational offset microlens arrays will provide promising opportunities for compact advanced imaging systems in industrial, medical, or military applications.