Fig. 1. Schematic of the tunable beam deflector. The array of resonators is loaded on the surface of hydrogel. (a) Hydrogel in water after the TLCST, (b) hydrogel in water before the TLCST, (c) hydrogel in ethanol. The letter “s” in parentheses stands for swollen hydrogel. Periodic arrays of optimized resonators are loaded on hydrogel from which the set of four resonators makes a supercell. The sizes of supercells in the x direction in each condition are denoted by Λ1, Λ2, and Λ3, respectively. θ1, θ2, and θ3 are the corresponding deflection angles in each condition, respectively. Also, Λ3>Λ2>Λ1. H is the height of the hydrogel.

Fig. 2. Design of the meta-atoms on the freestanding hydrogel dipped in solvent. (a) The meta-atoms consist of gold sector resonators patterned on the surface of the freestanding hydrogel. The arrows indicate the swelling in solvent in the x and y directions. (b) The supercell. H and h are the height of the hydrogel and sector resonator, respectively. Px=Py is the periodicity of the unit cell. Ix and Iy are the increment of the period in the x and y directions, respectively. Λ is the total size of the supercell in the x direction. The rightmost cell depicts the basic building block. (c) The top view of the optimized four resonators. The α and β are the opening angles, and R is the radius of the sector resonator.

Fig. 3. The phases (red, black, and blue lines) and amplitude values (red, black, and blue starred dash lines) of the optimized resonators in the swollen and collapsed states of hydrogel.

Fig. 4. Numerical simulation results. (a)–(c) are the phase distributions of the wavefront inside the hydrogel in a collapsed state in water, swollen in water, and swollen in ethanol, respectively. (d)–(f) are the phase distributions of the wavefront inside the glass in a collapsed state in water, swollen in water, and swollen in ethanol, respectively. θt is the refraction angle in the xy plane for the linearly y-polarized input light and the linearly x-polarized light is calculated at output.