Spectral imaging of flexible terahertz coding metasurface

Abstract

Coding metasurfaces have emerged as a promising venue for terahertz (THz) beam steering and beamforming. In this study, we designed a transmission metasurface with a complementary structure based on Babinet's principle. The beam-steering capability of the coding metasurface is implemented by encoding “0” and “1” elements with different phase responses and by controlling the coding sequences. The deflection angle can be controlled by changing the period of these 0 and 1 elements. Despite the development of beam-steering technology, measurements of the direction pattern of steered THz beams remain challenging. Systems for THz time-domain spectroscopy and spectral imaging are used to characterize the flexible coding metasurfaces. The THz imaging system can provide information on the directional pattern of the beam. To verify the performance of the proposed metasurface, the experimental measurements of beam deflection were found to be consistent with the values yielded by a simulation. Our study provides an effective platform for the design and measurement of THz beam steering.

Perfect Control of Diffraction Patterns with Phase-Gradient Metasurfaces

“…In the first sample, the +1 and −1 diffraction orders share an energy ratio of 1:2, as illustrated in Figure d. Although they are the most common diffraction orders, the energy of the beams is usually equal in the current literature. ,,, According to eqs and , the number of unit cells in a period is set to s = 2|1 – (−1)| = 4. Then, we put the unit number and preset ratio together into eq and set the phase difference between the two beams to π/2.…”

“…This design method can also be regarded as a discrete continuous grating, but it is more straightforward and easy to accomplish. − However, it has some limitations in applications. Most studies focus only on the one single diffraction order where the incident wave can be reflected or refracted in a single target direction. − When multiple beams pointing in different directions are desired, the existing PGM-based method that only modulates a phase response is not capable of efficiently simulating different diffraction orders. , The excited beams are still in the same order mode, and their corresponding energy distribution cannot be arbitrarily controlled. , In addition, an excited low-order mode may produce a high-order mode in the opposite direction beyond the critical angle θ c which can be explained by the Fabry–Pérot resonator mechanism . Although introducing amplitude modulation in the PGM approach can allow achieving different diffraction orders and arbitrary energy ratios, a part of the incident energy will be inevitably lost in such a procedure due to the normalization of the superimposed complex reflection or transmission coefficients. − …”

Multi-frequency terahertz coding metasurfaces based on vanadium dioxide

“…proposed an H-shaped resonator metasurface that achieved effective and versatile control of spoof surface plasmon polaritons 19 . In recent years, coding metasurfaces have received significant attention in the terahertz frequency band, with applications including terahertz beam deflection, 20 – 24 spectral imaging, 25 – 27 polarization manipulation, 28 – 31 focusing, 32 – 34 and other functionalities. In 2020, Chen et al.…”

The bound state in the continuum in flexible terahertz metasurfaces enabled sensitive biosensing

“…As such, flexible BIC metasurfaces offer a versatile platform for efficient light manipulation and open up a new range of applications. 25,26 To date, although much research has focused on the structure design of BIC metasurfaces, [27][28][29][30] much less effort has been made to explore flexible BIC metasurfaces, which promise great potential both for fundamental study and photonic applications.…”