Design and fabricate freeform holographic optical elements on curved optical surfaces using holographic printing

Freeform holographic optical elements (HOEs), due to the high degrees of design freedom, can be used to enhance performance of display systems. In this Letter, we propose a method for designing and fabricating freeform HOEs on curved optical surfaces that can be utilized to implement curved augmented reality (AR) displays. In our method, the phase profile of the freeform HOE laminated on a curved surface is first optimized to achieve a good image performance. Then, two recording wavefronts are optimized to produce the phase profile of the freeform HOE on the curved surface with a high uniformity of diffraction efficiency. The two recording wavefronts used for a curved substrate are converted into two wavefronts for a planar substrate based on a conversion relationship between the curved HOE and the planar HOE. A home-built holographic printer is used to fabricate freeform HOEs on a flat substrate, and then the freeform HOEs are laminated onto a curved optical surface. Two interesting AR display systems are presented to demonstrate the effectiveness of the proposed design and fabrication method.