Fig. 1. Principle of direct laser writing (DLW) technology based on two photon polymerization

Fig. 2. Results obtained from the writing and characterization process of a DOE lens array^[42]. (a) Parameters used for writing the structure; (b) an optical microscope image of the resulting written structure array; (c) an SEM image of an individual structure in Fig. 2(b); (d) normalized light intensity distribution at the focal plane as simulated for the proposed structure; (e) simulated intensity distribution curve and (f) experimentally measured intensity distribution curve in the light intensity distribution plot, full width at half maximum for the two curves is approximately 0.49 μm and 0.47 μm, respectively

Fig. 3. Achromatic diffractive lens. (a) Optical microscopy image; (b) normalized light intensity distribution at the focal plane as simulated for the achromatic focusing; (c) SEM image of the segmented structure; (d) enlarged profile

Fig. 4. A freeform lens structure on the end face of an optical fiber. (a)-(c) Optical images of integrated freeform lens on the optical fiber; (d) experimental result of beam shaping

Fig. 5. Vortex phase plate structure on the end face of an optical fiber. (a) (b) SEM images of vortex phase plate structure on the optical fiber; (c) intensity distribution of fiber output beam after vortex phase modulation in the experiment

Fig. 6. Schematic of super-resolution DLW system based on single-color PPI

Fig. 7. Design, fabrication, and characterization of spin-decoupled metasurface^[26]. (a) Schematic of spin-decoupled metasurface, and different spins are transformed into two separated foci; (b) nanorod orientation profile of the spin-decoupled metasurface; (c)-(e) SEM images of the metasurface fabricated by single-color PPI, with magnified views; (f) simulated and measured focusing patterns for LCP and RCP incident light; (g) simulated and measured intensity profiles for LCP and RCP incident light

Fig. 8. Comparison of the metasurfaces with the inhibition beam on and with the inhibition beam off^[26]. (a) With inhibition beam on; (b) with the inhibition beam off

Fig. 9. 3D subwavelength structured photonic crystals fabricated by single-color PPI super-resolution DLW lithography^[26]. (a) Schematic of 3D woodpile photonic crystal structure with a lateral period of a and an axial period of 2a; (b) (c) SEM images of the photonic crystal structure fabricated by single-color PPI super-resolution DLW technique with a feature size of 58 nm and lateral period of a=250 nm; (d) optical microscope image of woodpile photonic crystal under white light illumination

Fig. 10. System and applications of parallel peripheral-photoinhibition lithography (P³L) ^[27]. (a) Schematic of P³L system; (b) focal spot intensity distribution on x-y and y-z planes, dual-channel PPI direct writing achieved through 532 nm dual-beams and 780 nm dual-beams; microlens arrays with dual-focal distances of (c) 18 μm and (d) 50 μm; (e) photonic wire bonds

Fig. 11. Large-scale structures fabricated by multi-channel high-speed DLW. (a) Grating structure of 25 mm×25 mm; (b) SEM image of the grating structure; (c) iconic building of Zhejiang Lab and the slogan "Dedication to Science and National Prosperity"; (d) Fresnel lens with a diameter of 15 mm