Fabrication and characterization of diffracto-freeform optics

The requirement of the complex surface is increasing significantly with growing needs to fulfill the demands of many challenging applications. The advancements in manufacturing technologies attract optical designers to think about more and more complex shapes. The demand for hybrid surfaces i.e. diffractive structures over spherical, aspheric and freeform surfaces is growing for many future applications e.g. hyperspectral imaging, spectroscopy, beam shaping, wavefront coding. The hybrid freeform surfaces are the most complicated and most demanding surfaces for the above applications due to the advantages of the freeform base profile and diffractive structures. The use of these components leads to significant improvement in the performance of these optical systems along with considerable miniaturization and cost reduction. Challenges in fabrication and characterization of diffracto-freeforms are a limiting factor for its realization. This work aims to explore the fabrication and characterization strategy for diffracto-freeform optics. The cubic freeform shape with diffractive structures has been chosen for the study. The slow tool servo machining is utilized for the fabrication of this hybrid surface. The tool path development strategy and the effect of process parameters are discussed. The base shape and diffractive structures are characterized separately by utilizing the optical profiler measurements. The average error in the fabricated diffractive structures height and there radial distance from center is found less than 10% and 15% respectively. The characterization of the fabricated surface and fabrication issues are discussed in this paper. The current study is helpful to understand the various issues involved in the development of such complicated surfaces.