Abstract
A new model, i.e., the decreasing thickness model (DTM) is proposed and employed for designing the cylindrical diffractive microlenses (CDMs). Focal performances of the designed CDMs are theoretically investigated by solving Maxwell’s equations with the boundary element method. For comparison, the CDMs designed by the traditional equal thickness model (ETM) are also studied. Theoretical simulations demonstrate that focal performances of the designed CDMs are improved a lot via replacing the traditional ETM with the proposed DTM. Concretely, the focal efficiency is heightened and the focal spot size is shrunk. Experimental measurements verify the theoretical simulations well. Especially, the above-mentioned improvements become more prominent for the CDM with a higher numerical aperture.
Highlights
The diffractive microlens, as one of the most important components in micro optical systems, is widely used in beam focusing[1,2,3,4] and object imaging[5,6,7]
Focal performances of the cylindrical diffractive microlenses (CDMs) are theoretically analyzed by the boundary element method (BEM)
The CDMs designed by the traditional equal thickness model (ETM) are analyzed for comparison
Summary
The red and blue districts represent the regions with high and low intensities, respectively Numerical results reveal that the actual focal lengths are 4.06 and 3.93 μm for the CDMs designed by the DTM and the ETM, respectively. With the increase of the preset focal length, the focal spot size for the ETM is irregularly varied because the CDM boundaries in different Fresnel zones produce destructive interference at the preset focal position. The focal spot size for the DTM monotonically increases with the increase of the preset focal length, since the CDM boundary is optimally designed based on the Fermat’s principle. The DTM is much superior to the ETM for designing the CDMs, especially for small f-numbers
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