## 3 Lens Construction
### Monolithic Lens
When a voltage is applied to the lens, its intermediate disc-type DEA produces deformation to drive the lens deformation to achieve zoom, and its zoom ratio can reach a maximum of 181%, with a shortest response time of up to 80 ms.  
Figure 6: Planar actuator-driven biconvex DETL. (**a**) Circular DEA-driven liquid lens: (**a1**) lens physical diagram; (**a2**) lens structure and zoom principle schematic diagram; the upper and lower diagrams,  
respectively, show the effect before and after applying voltage to the lens [50]. **(b)** Circular DEA-driven solid lens: (**b1**) lens physical top view; (**b2**) lens structure schematic diagram; (**b3**) lens zoom. The schematic diagram of the principle, as well as the upper and lower diagrams, shows the focal length change after applying voltage to the lens, respectively [51]. **(c)** Disc-shaped DEA-driven solid lens: (**c1**) top view of the lens object; (**c2**) schematic diagram of the lens driving principle; (**c3**) diagram of the lens morphology change, where the left and right diagrams show the side view of the lens morphology before and after applying voltage, respectively [54]. The core principle of dielectric elastomer-driven droplet lenses is to fill liquid droplets on the surface of small pores or hydrophobic layers, creating biconvex or monoconvex surfaces through the liquid's surface tension. When a voltage is applied to the DE to deform it, the droplet curvature changes with the deformation of the DEA. [PERSON] et al. [55] prepared two small droplet lenses with different scales by filling glycerol droplets into the holes of a DE film, as shown in Figure 7a. After applying a voltage, the lens's aperture decreases, thereby causing the lens's focal length to change. This lens has a zoom ratio of up to 140%, but it is significantly affected by gravity, and the gravity effect needs to be suppressed by reducing the lens size. [PERSON] et al. [56] prepared a droplet lens by placing a glycerol-sodium chloride mixture droplet into the middle of an annular hydrophobic layer, and the droplet curvature control was realised by modulating the infiltration region with an electric field. [PERSON] et al. [57; 58] designed two different droplet prehensile ratio lenses, as shown in Figure 7b, and the zoom ratio reached up to 252% through a disc-type DEA. In planar DEA-driven DETL, the lenses are made of monoconvex soft solids like silicone rubber, which offer excellent impact resistance and a simpler preparation process. However, compared to biconvex lenses, they have a smaller field of view and poorer im  
Figure 7: Planar actuator-driven droplet DETL. **(a)** Annular DEA-driven biconvex lens: **(a1)** top view of the lens object; **(a2)** schematic diagram of the lens zoom principle, the upper and lower diagrams show the focal length change of the lens before and after the application of the voltage, respectively; **(a3)** diagram of the lens zoom effect, the left and the right diagrams are the lens imaging images before and after the application of the voltage, respectively [55]. **(b)** Disc-shaped DEA-driven biconvex lens: **(b1)** top view of the lens object; **(b2)** schematic diagram of the lens structure; **(b3)** schematic diagram of the lens zoom principle; the left and right figures show the focal length change of the lens before and after applying the voltage, respectively [58]. age quality. Biconvex lenses, on the other hand, use soft solids or liquids as lens materials, resulting in superior imaging quality. Moreover, substituting the material of the biconvex lens with a conductive substance (e.g., NaCl solution or conductive gel) can further simplify its preparation process and reduce lens power. The droplet lens is easy to prepare due to its non-encapsulated structure, and the protruding droplets formed under surface tension possess a uniform spherical crown shape. In comparison to encapsulated lenses, droplet lenses typically provide higher imaging quality.