Broadband Terahertz Near-Perfect Absorbers

Abstract

Broadband terahertz (THz) absorbers are highly desired in detection, modulation, receiving, and imaging devices. We report the design and successful implementation of a novel broadband THz metasurface with a near-perfect absorption. Different from the traditional metal/dielectric/metal three-layer structures, the as-designed THz absorber has one more metal layer and a dielectric spacer on top, both of which are 200 nm thick. Although the total thickness increased by ∼7%, the near-perfect THz absorption band significantly broadened by 4×, achieving a broadband absorption of 270 GHz. Broadband, polarization-insensitive, and near-perfect THz absorptions were also observed over wide incident angles in these meta-absorbers, where the electric field and power loss were mainly concentrated in the additional thin dielectric layer. Such a broadband THz absorption was achieved through electromagnetic coupling between the top and middle metal layers and the resultant overlapping of the resonance frequencies. This strategy can be adapted to other spectrum-shaping devices.

Design and Fabrication of a Triple-Band Terahertz Metamaterial Absorber

“…The polarization performance of the designed structure under TE and TM polarization is shown in Figure 8a,b, respectively. The simulated results clearly presen in TM polarization, under which the resonator maintains high absorptivity [23,39] for incident angles up to 70°, as shown in Figure 8d. The results in Figure 8c,d show that when the incident angle exceeds 10°, two additional weak absorption peaks are observed in TE and TM polarization.…”

“…Figure 5 a–c show the distributions of the electric field in the x – y plane, and Figure 5 d–f show the distributions of the magnetic field in the x – y plane at the three resonance frequencies of 0.337, 0.496, and 0.718 THz, respectively. As shown in Figure 5 a,d, the electric and magnetic fields are concentrated mainly on the outer ring and its edge, indicating strong electrical and magnetic resonances [ 23 , 39 ]. The distribution of the electric and magnetic fields proves that the first absorption peak is excited by the outer ring resonator.…”

“…The reason is that the direction of the electric field varies with the incident angle, which leads to the decrease of the electric resonance intensity [ 23 , 39 ]. However, there is no change in direction of the electric field in TM polarization, under which the resonator maintains high absorptivity [ 23 , 39 ] for incident angles up to 70°, as shown in Figure 8 d. The results in Figure 8 c,d show that when the incident angle exceeds 10°, two additional weak absorption peaks are observed in TE and TM polarization. The extra resonance peak is caused by the higher resonance mode, which has been confirmed in experiments [ 4 , 42 , 43 ].…”

All-Metal Terahertz Metamaterial Absorber and Refractive Index Sensing Performance

“…Figure 2c,d show that the electric and magnetic field is focused primarily on the air slot of the ring metamaterial layer. The local enhancement of electric and magnetic fields indicates strong electrical and magnetic resonances [35,36]. The resonance mode can be obtained by the decomposition of dipole scattered powers [37].…”

Broadband THz Absorption of Microbolometer Array Integrated with Split-Ring Resonators

“…However, metallic thin film exhibits limited absorption (≤ 50%), while antenna-coupled micro-bridge structure generally has a narrow absorption peak of THz wave. In order to achieve high THz absorption in a wide spectrum range, a thin dielectric layer and a thin metal layer can be added on the top surface of a conventional three-layer absorber [19]. The phasecoupled method and strong coupling response can also improve the absorption bandwidth or realize multiband absorption [20][21][22][23].…”