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Achromatic annular folded lens with reflective-diffractive optics.

This paper proposes an achromatic annular folded lens (AFL) with a reflective-diffractive optical element (RDOE). We derive novel mathematical models of the diffraction efficiency and polychromatic integral diffraction efficiency (PIDE) of the RDOE and an expression for its microstructure height. An AFL with an RDOE made of an optical plastic substrate material is designed in the visible waveband. To minimize the influence of incident angle on the diffraction efficiency and PIDE, the microstructure height is optimized. The design results indicate that the lateral color of the AFL is corrected, the modulation transfer function considering the diffraction efficiency is larger than 0.25 at 111 cycles/mm for all field of views. The hybrid AFL outperforms the conventional refractive imaging system in terms of the system size, volume, and image quality under the same specifications. It can be used in new-generation miniaturized imaging systems.