Alternative Design of Binary Phase Diffractive Optical Element with Non-π Phase Difference

Cheng Xu,Hui Pang,Qiling Deng,Axiu Cao

doi:10.3390/app11031116

Abstract

It was found that binary phase diffractive optical element (DOE) with non-π phase difference had higher diffraction efficiency and adjustable zero-order intensity than a 0-π one. However, existing design methods are all based on the simulated annealing algorithm and thus computationally expensive. In this paper, a simple and efficient method using the iterative Fourier transform algorithm (IFTA) is proposed. In this method, the target pattern is first modified via reducing the zero-order intensity. Then, the IFTA is adopted to design the conventional 0-π DOE. Subsequently, the phase distribution remains unchanged and the phase difference is carefully adjusted to increase the zero-order intensity so that the reconstructed pattern is consistent with the target. To verify this method, several typical DOEs for beam splitting were designed and fabricated, and the result showed that the proposed method is effective.

Highlights

In the past two decades, diffractive optical element (DOE) has received more and more attention due to its superior wavefront manipulation capability and unique advantages of high design flexibility, small size, and mass productivity. It expands the capabilities of conventional optics based on refraction or reflection and is widely used in a broad range of applications, such as beam shaping [1,2,3], beam splitting [4,5,6], structured light projectors [7,8,9,10], pattern generation [11,12,13,14], optical security [15,16,17], and so on
LargeFrom number orders, itwhen is recom a target light field contains a small number of diffraction orders, a non 0-π DOE design can be considered to improve the diffraction efficiency
The experimental results are in good agreement with the numerical simulation, which showed that the proposed method is effective for non 0-π DOE design

Summary

Simulation

To further verify the effectiveness of the proposed method, a variety of DOEs were designed to generate different patterns. For the fourth 7 × 5 beam splitter design, the results were similar This indicates that in some cases, the non-π DOE can improve the diffraction efficiency, and in another cases, it cannot. When the phase difference is less than the optimal value, it means that the phase difference is farther from π, so the zero-order will be enhanced This unique zero-order adjustable character is very useful in the fabrication process because we can judge whether the etching depth is smaller or larger than the target by comparing the intensity of the zero order with other orders, especially for DOEs with small feature size, where it is difficult to accurately measure the etching depth with step meter or white light interferometer.

Simulated

Experiment

Diffraction of the

Conclusions

design designed non of