Ultrabroadband Plasmonic Absorber for Terahertz Waves

Abstract

in high-resolution terahertz imaging and detection for security and biomedicine.By defi nition, perfect absorbers can absorb EM waves with near-unity absorbance, which are promising for applications in terahertz imaging and detection via enhanced contrast and sensitivity. Metamaterials are candidates for creating perfect absorbers owing to the possibility of tailoring the response of the structure with great fl exibility. [ 5,6 ] Landy et al. [ 7 ] fi rst demonstrated the perfect metamaterial absorber concept in the microwave range, and since then great interest in EM absorbers has extended toward optical frequencies in recent years. [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] Metamaterial absorbers typically consist of two coupled metallic layers separated by a dielectric spacer to create electric and magnetic responses for impedance matching with free space. [ 23 ] The electric response can be obtained from excitation of the top metal layer readily coupled to an external electric fi eld, while the magnetic response is provided by pairing the top layer with a metal ground plane or metal wire for an external magnetic fi eld. In the microwave and terahertz regions, these metamaterial absorbers obtain high absorption through dielectric loss and impedance matching at resonance. [ 23 ] The absorption frequency range and amplitude can be tuned by adjusting the shape, size, thickness, and properties of the metallic structure and dielectric spacer. Due to the nature of resonance response, these metamaterial absorbers usually exhibit narrowband absorption that has advantages in applications such as fi ltering, sensing, and modulation. [ 24 ] Broadband perfect absorbers are desirable for other applications such as high-effi ciency signal detection and communications. This has necessitated signifi cant research effort toward extending the absorption bandwidth. A straightforward approach is to cluster multiple resonating structures with different sizes in each unit cell to create a number of absorption bands. [ 9,22 ] Graphene has been introduced to construct broadband terahertz absorbers due to its exceptional properties, such as optical transparency, fl exibility, and tunability. [25][26][27] However, the structure is demanding in terms of cost and complexity. Another alternative promising material for terahertz absorption is a moderately doped semiconductor, which can be readily fabricated using conventional micro-fabrication techniques. At terahertz frequencies, doped semiconductors have desirable conductive loss, enabling them to sustain surface plasmon polaritons (SPPs) and correspondingly localized surface plasmon resonances (LSPRs) via periodic structures. [28][29][30] Recently, we have demonstrated that doped silicon can be engineered to attain highly Perfect absorbers that exhibit broadband absorption of terahertz radiation are promising for applications in imaging and detection due to enhanced contrast and sensitivity in this relatively untapped frequency regime. Here, terahertz plasmonics is used ...

A high-performance broadband terahertz absorber based on sawtooth-shape doped-silicon

“…The fabrication technology to construct this sawtooth structure is well established. 24,25,31,32 Our broadband wide-angle polarization-insensitive absorbers have many potential applications, such as high-resolution THz imaging, THz bolometer and high-quality THz communications.…”

“…In order to get high-efficient polarization-insensitive and wide-angle operant THz absorbers, Cheng et al realized two-dimensional cross-shaped THz absorber 24 and Yin et al proposed a THz absorber using a square array of plastic-caped silicon. 25 However, the fabrication processes of these two-dimensional THz absorbers are complicated.…”

“…[4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] In the past few years, doped silicon has been introduced to improve the THz absorption efficiency and bandwidth. [22][23][24][25][26][27] As a desirable lossy material at THz frequency, doped silicon can support surface plasmon polaritons and accordingly localized surface plasmon resonances via periodic structures. The main advantage of semiconductor materials is that they can be easily processed using conventional micro-fabrication technology.…”

Ultrathin Six-Band Polarization-Insensitive Terahertz Perfect Metamaterial Absorber Based on a Cross-Cave Patch Resonator

“…PMMAs have recently been developed rapidly in a wide electromagnetic (EM) spectrum range from microwave [1][2][3], terahertz [4][5][6][7][8][9][10][11], infrared [12][13][14][15][16], to visible region [17][18][19][20]. PMMA is not limited by the quarter-wavelength thickness and also scaled to different EM spectrum due to its geometry scalability.…”

Synthesis and Analysis of Metamaterial Structure for Microwave Frequency Applications

“…There is still a lack of investigation in the dual-band or multi-band metamaterial absorbers. Cheng et al [109] showed a design that achieves high absorption rate as well as enhanced wide-band operation.…”