*Metalens Antennas in Microwave, Terahertz and Optical Domain Applications DOI: http://dx.doi.org/10.5772/intechopen.99034*

#### **Figure 4.**

*(a) The skeptic view of metalens antenna with SIW feeding components from the bottom. (b) Jerusalem cross is used as the unit cell of metalens (c) tapered SIW with radiation patches are used for transmit/receive feeding array unit (d) Fabricated metalens with copper elements on the polymer substrate and (e) simulated radiation pattern with different incident angles in the focus plane.*


#### **Table 1.**

*Design parameters used in MIMO Metalens antenna.*

#### **Figure 5.**

*The silicon micro-brick unit: P = 150* μ*m, h = 195* μ*m, Lx = 120* μ*m and Ly = 60* μ*m.*

#### **Figure 6.**

*Electromagnetic field presence of the Si micro-brick unit cell with Lx and Ly variations at 1.0 THz. The phase changes* Φ*x (a) and transmission amplitude tx (b) of the Si unit as a function of Lx and Ly with the x-polarized incidence. The phase changes* Φ*y (c) and transmission amplitude ty (d) as a function of Lx and Ly with the y-polarized incidence.*

fine-tuned from 30 μm to 140 μm to match the desired electromagnetic profile. Si micro-bricks array is taken as homogeneous and of infinite extent in both in-plane dimensions. The transmitted phase shifts Φx, Φy and the transmittance tx and ty of the x, y-polarized light, are shown in **Figure 6(a**–**d)**. The simulated 2π phase

*Metalens Antennas in Microwave, Terahertz and Optical Domain Applications DOI: http://dx.doi.org/10.5772/intechopen.99034*

**Figure 7.**

*The phase distribution of the designed DFM along the x direction for XLP (a) and YLP (b). The transmitted intensity distributions of the designed DFM under the XLP (c), 30o LP (d), 45<sup>o</sup> LP (e) and YLP (f) incidences respectively.*

variations with transmission over 90% are shown in **Figure 6**. Nearly any combination of phase shifts from 0 to 2π with high transmittance for two polarizations can be obtained from single unit block by setting Lx and Ly properly. Conclusively, the double-phase modulation could be realized by the modulating two polarizations separately for this structure.

In **Figure 7(c)** and **(f )**, the XLP light will be focused to the left side position at x = −x0; y = f. Parallelly, the YLP light will be focused to the right side position at x = x0; y = f. In fact, any polarized light, such as the 30° LP and 45° LP, can be decomposed to x and y polarization components and be focused separately. If designing a dual-focus metalens, there will be two focus spots in the focal plane as shown in **Figure 7(d)** and **(e)**. 30° LP and 45° LP lights can be two focusing spots corresponding to the x and y-polarization. **Figure 7** shows that the focusing intensity of y-polarization component is increased with the LP angles, and the focus intensity of x-polarization component is decreased. The result shows that the splitting energy ratio could be adjusted by manipulating the two polarization states separately.

From this example, the lattice constants of the unit cell are set to 150 μm for both directions, which is chosen to be slightly less than the half of wavelength to avoid the diffraction effect. The height of Si unit is set to 195 μm, and this is obtained from the parametric sweeping by commercial FDTD simulator. The phase profile is obtained from the resonance contribution of each Si unit cell, and the height of the unit should be enough to cover 2π phase modulation and efficient transmission.

#### **3.3 Metalens with high efficiency and numerical aperture**

An imaging system normally requires a high numerical aperture with enough efficiency to meet the requirement on the resolution and image contrast.

#### **Figure 8.**

*(a) Schematic of the THz metalens. (b) Schematic of the silicon cross resonators with the incident THz field propagating along z direction and electric field along x direction. The arm width W and the height H are 12* μ*m and 20* μ*m, respectively, by varying the arm length L. (c) Transmission amplitudes and (d) corresponding phases as functions of the arm length of the cross resonator and the frequency.*

#### **Figure 9.**

*(a) Setup schematic of the THz metalens imaging experiment. (b) Measured field distribution plane along z direction parallel to the metalens plane. (c) FWHMs of the focus spots along z direction and* Δ*z represent the different distances from the focal plane. (d) Normalized experimental curve in red and theoretical curve in blue indicate the intensity profiles along the y direction at the focal plane.*
