Ultraprecision Machining-based Micro-Hybrid Lens Design for Micro Scanning Devices

摘要

This paper presents design of a refractive-diffactive hybrid lens for use in micro optical scanning systems. To achieve the target focal length with minimized aberration, the refractive lens was optimally designed with consideration of reducing transverse ray aberration. The diffactive efficiency was calculated in terms of depth and period of the Fresnel pattern via rigorous coupled wave-analysis (RCWA). The geomeuy of the V-shaped diamond tools limits the depth of Fresnel edge of the diffactive lens due to the interference, which eventually determines the whole size of the lens. In this study, two types of hybrid lenses for micro scanning system were compared and designed in consideration of optical performance and machining limit. Therefore, the designed diffractive lens was optimized for 300 pm focal length with minimum aberration. The depth of Fresnel edge and the diameter was determined to be 0.94 mu m and 423.4 mu m within the machining limit, respectively The lens base mold was fabricated using a 5-axis ultraprecision machine, and the lens was imprinted through a hot embossing process. The measured focal length and the calculated NA are 336 pm and 0.63 respectively Lastly, Imaging tests and diffractive efficiency are measured to evaluate the optical performance of the micro-hybrid lens.