Fig. 1. Basic principles of microlens array. (a) Compound eye optical path structure^[24]; (b) schematic of uniform illumination by lens^[25]; (c) optical interconnection system of a pair of microlenses^[26]; (d) schematic of beam shaping by microlens array^[29]

Fig. 2. Optical path diagrams in ordinary lens and microlens array for parallel light and point light source. (a) Parallel light; (b) point light source

Fig. 3. Brief development history of microlens array^{[24,31,34-35,40]}

Fig. 4. Fabricating of microlens array by inkjet printing. (a) Specific steps for preparing microlens array by droplet jetting^[55]; (b) fabrication process of morphological programmable self-aligning microlens array^[64]

Fig. 5. Schematic of manufacturing process of screen-printed microlens array^[85]. (a) Scheme of screen printing process; (b) micro-cylindrical hemisphere array fabricated using screen printing; (c) microlens arrays formed by reflowing micro-cylindrical hemisphere array; (d) microlens arrays solidified under UV light

Fig. 6. Fabricating of microlens array by photocuring method. (a) Process for manufacturing microlens by photocuring method; (b) SEM image of concave microlens array^[116]

Fig. 7. Method for preparing curved microlens array film^[161]. (a) Schematic of microlens film before preparation; (b) schematic of preparation result; (c) simulated result of curved microlens array film

Fig. 8. Flow chart for preparing microlens array based on self-assembly^[162]

Fig. 9. Flow chart for preparing grating microlens array by two replications^[166]

Fig. 10. Application examples of microlens array imaging. (a) High-performance hemispherical electronic eye camera based on single crystal silicon^[170]; (b) on-chip fluorescence microscope with random microlens diffuser^[171]; (c) mid-infrared imaging optical system with field switching based on microlens array^[179]

Fig. 11. Applications of microlens array in LED. (a) Microlens array diffuser for LED backlighting^[187]; (b) light propagation in single chip LEDs and COB-LEDs^[194]

Fig. 12. Photonic crystal microlens array used for wide viewing angle display with angle-independent inkjet printing^[199]. Inkjet printing photonic crystals on (a) flat Al foil and (b) curved PDMS surface; (c) normalized fluorescent intensity of fluorescence molecule doped photonic crystal domes and flat dots versus detection angle; (d) top-view and side-view fluorescence images of fluorescent photonic crystals

Fig. 13. Preparation process of underwater oil-resistant microlens array with self-cleaning ability^[212]