Correcting aberrations while adjusting the focal length of holographic optical elements on a large scale

Holographic optical element (HOE) have been widely applied in many fields. However, the fixed focal length limits its application in dynamic optical systems. The existing methods have the problems of limited adjustment distance and difficulty in correcting the aberration during the adjustment. This paper proposes a method that can correct the aberration while adjusting the HOE focal length in a large range. This method modulates the illumination wave front by superposing the modulation phase factor to achieve the change of the reconstruction distance, that is, the change of the focal length of the HOE. To design modulation phase factors corresponding to different focal lengths, the relationship between the parameters of the modulation phase factor and the focal length of HOE was derived based on the Fresnel diffraction integral formula. To solve the problem of the aberration cannot be uniformly compensated at different focal length, aberrations of different types, sources, and reconstruction distances are compensated separately. The method proposed in this paper achieves a wide range of adjustment of HOE focal length and correction of aberration during the adjustment process. In the experiment, the focal length of HOE is adjusted to 30cm, 40cm, and 50cm, and the evaluation functions of abrretions have changed towards the direction of aberration reduction. This method can be used for the design and fabrication of adjustable HOE, which is expected to be used in holographic projection, structured light generation and many other fields.