Fig. 1. Focusing optical system. (a) Schematic of tight focusing optical system; (b) structure of DOE

Fig. 2. Intensity distribution. (a) Intensity distribution on ρ-z plane; (b) line diagram distribution of main optical chain at ρ=0λ and secondary optical chain at ρ=-1.8λ along z direction

Fig. 3. Total intensity distribution in z=0 plane along ρ direction for different NA values

Fig. 4. Line diagram of main optical chain total intensity along z direction with different β

Fig. 5. Total intensity distribution in z=0 plane along ρ direction with different θ2 values

Fig. 6. Ratio of the horizontal direction two peak values of the secondary optical chain varies with θ2

Fig. 7. Total intensity distribution in z=0 plane along ρ direction with different θ5 values

Fig. 8. Total intensity distribution in z=0 plane along ρ direction

Fig. 9. Total Intensity distribution on ρ-z plane when p=1. (a) Other parameters unchanged; (b) β=1.4, θ5=0.95