Fabrication of hybrid optical line generator by direct machining.

Toni Saastamoinen,Juha Väyrynen,Hemmo Tuovinen,Jarkko Mutanen,Markku Kuittinen,Kari Mönkkönen,Anni Eronen

doi:10.1364/oe.26.002335

Abstract

In this study, a mold of a line generator consisting of a cylindrical lens array with a triangular diffractive grating was ultra-precision diamond machined with Moore 350FG 5-axis ultra-precision machine. The design and the simulation of the hybrid structure were performed using ray tracing and exact electromagnetic theory. The machined hybrid lens structure was replicated to a UV-curable polymer and was then characterized and tested. The optical measurements show that the hybrid element works as designed.

Highlights

Multi-axis ultraprecision diamond machining can be used to fabricate optical components such as microlenses, mirrors, light guides, lens arrays, Fresnel lenses and refractors [1, 2]
The measured surface roughnesses from the lenses (Table 2) are well below the requested surface roughness values for SPI A-1 standard (Ra: 12 – 25 nm)
The measured roughness values prove that the surface is smooth enough for optical applications

Summary

Introduction

Multi-axis ultraprecision diamond machining can be used to fabricate optical components such as microlenses, mirrors, light guides, lens arrays, Fresnel lenses and refractors [1, 2]. Machining a diffractive grating on top of a freeform surface is possible, the part shape and feature sizes are limiting factors [6, 7]. Freeform machining holds many advantages over lithographical processes: an ability to pattern 3D-surfaces [9,10,11], good shape of the pattern, high patterning speed, a capacity to process different materials, manufacturing process observed in real time, and on-fly adjustments are possible [12, 13]. Lithographical processes are conventionally used in making diffractive gratings and even hybrid diffractive phase element for line generator [14] but they lack the ability to pattern three-dimensional surfaces. We attempt to overcome this limitation by generating diffractive gratings on a cylindrical lens array with ultra-precision diamond machining. The idea is to establish an industrial-like manufacturing process for making and replicating hybrid structures. The handling of a large amount of optical and manufacturing data creates challenges [15, 16]

Design

Manufacturing

Surface roughness measurements

Imaging of the hybrid structure

Measurement of the intensity distribution

Discussion & Conclusion