An extended depth-of-field imaging system with a non-rotationally symmetric phase mask

Optical imaging system offers best performance across a range of applications such as machine vision, medical examination, security, and quality inspection in a production line. A typical imaging system is commonly sensitive to the defocus variations in the object plane location, which largely loses the transversal information of volume and brings inaccuracy to the comprehensive vision. Therefore, improvement of depth-of-field (DOF) with high resolution imaging remains a challenge for the conventional imaging system. Here we introduce a newly designed optical imaging system, mainly being composed of a standard Tessar lens and a non-absorptive rectangularly separable phase mask, whose corresponding optical point spread function is greatly invariant to defocus. An extended DOF image is restored by using the Tikhonov regularization algorithm and deconvolving the response function of the optical system. The proof-of-the-concept experimental results verify significantly extended DOF exceeding 40 times compared to the common optical imaging counterparts. Future work includes the use of a durable and high-transmittance phase mask to develop various large DOF optical configurations without loss of resolution.