Design, analysis, and manufacturing of a glass-plastic hybrid minimalist aspheric panoramic annular lens

TL;DR

This work tackles the challenge of bulky, heavy panoramic lenses by introducing a glass-plastic hybrid minimalist ASPAL that stacks four lenses to deliver a 360° by 35°–110° FoV with near-diffraction-limited imaging. It combines a compact ray-tracing PAL model to guide structural compactness, an annular-surface tolerance framework using Fringe Zernike and Standard Zernike models, and mid-spatial-frequency surface analysis to define robust manufacturing tolerances. The authors validate the approach by batch-fabricating 20 ASPAL units via precision glass molding and injection molding, achieving about 8.5 g per unit, RMS spot radius ~2.1 μm, and MTF ≈0.47 at 133 lp/mm, while reducing height and weight relative to conventional SPALs. The results demonstrate practical viability for space- and weight-constrained sensing (e.g., micro-UAVs, micro-robots) and offer a scalable pathway for ultra-wide FoV panoramic imaging with glass-plastic hybrid optics and an enforced local-tolerance framework.

Abstract

We propose a high-performance glass-plastic hybrid minimalist aspheric panoramic annular lens (ASPAL) to solve several major limitations of the traditional panoramic annular lens (PAL), such as large size, high weight, and complex system. The field of view (FoV) of the ASPAL is 360°x(35°~110°) and the imaging quality is close to the diffraction limit. This large FoV ASPAL is composed of only 4 lenses. Moreover, we establish a physical structure model of PAL using the ray tracing method and study the influence of its physical parameters on compactness ratio. In addition, for the evaluation of local tolerances of annular surfaces, we propose a tolerance analysis method suitable for ASPAL. This analytical method can effectively analyze surface irregularities on annular surfaces and provide clear guidance on manufacturing tolerances for ASPAL. Benefiting from high-precision glass molding and injection molding aspheric lens manufacturing techniques, we finally manufactured 20 ASPALs in small batches. The weight of an ASPAL prototype is only 8.5 g. Our framework provides promising insights for the application of panoramic systems in space and weight-constrained environmental sensing scenarios such as intelligent security, micro-UAVs, and micro-robots.

Figures (21)

• Figure 1: The optical path diagrams and coordinate distribution of maximum lens diameter $D_{\max}$ and total length $TL$ of seven panoramic imaging systems designed with an imaging circle diameter of 3.6 mm as the design criteria. Compared with other imaging systems, PAL has significant advantages in maximum lens diameter and total length and has the least number of lenses.
• Figure 2: Establishment of PAL physical structure model and implementation of ray tracing. (a) The surface name and refractive index definition of the imaging rays passing through PAL. (b) The tracking points and surface thickness definition of the marginal and chief rays passing through the interior of PAL. (c) Physical structure model of PAL in Matlab constructed by point-by-point ray tracing.
• Figure 3: Numerical relationship among PAL physical structure parameters and compactness ratio $CR_1$. (a) Curvature radii $R_2$, $R_3$, and compactness ratio $CR_1$. (b) Refractive index $n_{2}$, $n_{3}$, and compactness ratio $CR_1$. (c) Incidence angle $\theta$, Y-axis offset distance from initial incidence position $D$, and compactness ratio $CR_1$.
• Figure 4: Workflow of the high-performance glass-plastic hybrid minimalist ASPAL.
• Figure 5: Design compromise due to manufacturing challenges. (a) In the initial ASPAL design, due to the small reflection surface area, it was difficult to expel air from the lens during the molding process near the minimum FoV of 35°. (b) The improved design shifts the first transmission surface of ASPAL to the left, increases the area of the first reflection surface, and solves the difficulty of expelling air in the small FoV. However, the optical design indicators are compromised.