Metrology Data-Based Simulation of Freeform Optics

Ingo Sieber,Allen Yi,Ulrich Gengenbach

doi:10.3390/app8122338

Ingo Sieber, Allen Yi + Show 1 more

Open Access

https://doi.org/10.3390/app8122338

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Abstract

This paper describes the approach to use measurement data to enhance the simulation model for designing freeform optics. Design for manufacturing of freeform optics is still challenging, since the classical tolerancing procedures cannot be applied. In the case of spherical optics manufacturing, tolerances are more or less isotropic, and this relationship is lost in case of freeform surfaces. Hence, an accurate performance prediction of the manufactured optics cannot be made. To make the modeling approach as accurate as possible, integration of measured surface data of fabricated freeform optics in the modeling environment is proposed. This approach enables performance prediction of the real manufactured freeform surfaces as well as optimization of the manufacturing process. In our case study this approach is used on the design of an Alvarez-optics manufactured using a microinjection molding (µIM) process. The parameters of the µIM process are optimized on the basis of simulation analysis resulting in optics, with a performance very close to the nominal design. Measurement of the freeform surfaces is conducted using a tactile surface measurement tool.

Highlights

With the advancement of modern precision optical fabrication technologies, freeform optical components can be manufactured with a sufficiently high accuracy [1,2]
Freeform optics can be seen as an enabling technology since they allow completely new designs of optical systems
Since freeform optics are lacking symmetry, such simple tolerance parameters cannot be found. This makes the estimation of shape tolerances nearly impossible as well as the estimation of the impact of manufacturing tolerances on the optical performance

Summary

Introduction

With the advancement of modern precision optical fabrication technologies, freeform optical components can be manufactured with a sufficiently high accuracy [1,2]. Quality of optical surfaces can be evaluated and characterized using a variety of measures: Root mean square (RMS) errors as well as peak to valley (PV) errors are used to describe low-spatial frequency (LSF) errors, power-spectra density analysis can be used to analyze mid-spatial frequency (MSF) errors like spokes or ripples [24,25] Based on these figures the manufacturing accuracy can be characterized but no conclusions can be drawn regarding the optical performance in the case where freeform optics are used in a manufactured subsystem. The performance prediction based on a model enhancement by means of metrology data can be used to optimize manufacturing parameters This might be useful to improve the performance of freeform optics designed-for-manufacture by low-cost mass fabrication methods such as replication technologies (like μIM) [28].

Manufacture of the Freeform Optics

Surface

Analysis and Results

Conclusions