Fig. 1. Traditional diffractive lens. (a) Continuous phase; (b) multi-step phase

Fig. 2. Dispersion of two kinds of lens. (a) Traditional refraction lens; (b) diffraction lens

Fig. 3. Equal width diffractive achromats (EWDA) and equal area diffractive achromats (EADA). (a) Equal width; (b) equal area

Fig. 4. Diagram of diffractive achromats. (a) Partition diagram; (b) relationship between focal length and wavelength

Fig. 5. Distribution of PSF. (a) Ordinary diffractive lens; (b) EWDA; (c) EADA

Fig. 6. Spot at the focal point of the three lenses at different wavelengths

Fig. 7. Diffraction efficiency of the three kinds of lenses working at RGB triband respectively and working at triband together

Fig. 8. Normalized point spread function at the focal plane of three lenses

Fig. 9. Energy contrast at the imaging plane. (a) PSF working in RGB band; (b) PSF working in G band

Fig. 10. Simulation and analysis of eight-level structure. (a) PSF of continuous structure and eight-level structure; (b) diffractive efficiency of eight-level DOE and PDA