many broadband scenarios. Taking the commonly used beam splitter [23,24] as an example, the reported terahertz circularpolarization beam splitter, [25] all dielectric splitter with variable split ratio, [26] terahertz beam splitter based on I-shape metasurface [27] and optically controlled dynamic splitter, [28] though work in broadband, produce significantly different steering angles in different frequencies resulting from chromatic aberration. Luckily, researches on achromatic metasurfaces in visible and infrared light have made a big progress in recent years, realizing the phase control as well as the dispersion engineering. Several types of achromatic metalens [29-36] have been demonstrated in visible and infrared light by engineering the dispersion and the phase of the unit cells simultaneously to meet the multilevel condi
In recent years, as a promising new method, integrating nanostructures to improve the power of photoconductive antennas has received widespread attention. However, there are few reports on the application of artificial electromagnetic structures to regulate the spectral features of photoconductive antennas. Herein, it is demonstrated that by integrating split‐ring resonator (SRR)‐like metallic structures onto the coplanar lines of the photoconductive antenna transmitter, one can significantly manipulate the spectral feature of the generated terahertz (THz) radiation. The guided THz wave along the coplanar lines is scattered by the SRRs to the far field and interferes with the THz pulse radiated from the photoconductive antenna gap, leading to enhancement of the photoconductive antenna's energy and modulation in the spectrum. Further studies have shown that the strength, frequency, and band‐pass/band‐stop characteristics of the modulation can be altered by changing the geometry and placement of the SRRs. Water vapor absorption is also discussed to exemplify the benefit of this novel meta‐antenna over the ordinary photoconductive antenna in sensing scenario. The photoconductive antenna proposed here takes the lead in using artificial structures to manipulate the spectral domain behavior of photoconductive antennas, which is of great significance for THz spectroscopy, imaging, and sensing.
In recent years, metasurface-based focusing elements have gradually become an indispensable type of terahertz lenses. However, the meta-lens often suffers from chromatic aberration due to the intrinsic dispersion of each element, especially in the broadband application scenarios. In this paper, we design and demonstrate a silicon-based achromatic meta-lens working from 0.6 to 1.0 THz, which is polarization insensitive because of the adopted symmetrical structures. The simulated focal length and the full width at half maximum (FWHM) of the foci at different frequencies prove the achromatic behavior of our meta-lens compared with the chromatic counterpart. We also show that the focus shift incongruence of our design originates from the transmission amplitude distribution of the meta-lens. This article not only provides an achromatic planar lens working at terahertz domain but also reveals the importance of the amplitude distribution in the achromatic metasurface design.
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