Dynamic Control of THz Wavefronts by Rotating Layers of Cascaded Metasurfaces

A metadevice for dynamically controlling the THz wavefront by rotating layers of cascaded metasurfaces.Credit: Shanghai University

Cascade metasurface for dynamic control of THz wavefront

Electromagnetic waves (EM) in the terahertz (THz) regime contribute to critical applications in communications, security imaging, and biological and chemical sensing. Such widespread applicability has brought about significant technological advances. However, traditional THz devices are usually bulky and inefficient due to the weak interaction between natural materials and THz waves. Ultra-small active THz devices exist, but current electronic and photonic approaches to dynamic control are inefficient.

Recently, the rapid development of metasurfaces has opened up new possibilities for creating highly efficient and ultra-compact THz devices for dynamic wavefront control. Metasurfaces, ultrathin metamaterials formed by sub-wavelength planar microstructures (ie, metaatoms), allow for a tuned optical response to control the EM wavefront. Scientists are fascinated by anomalous light deflection, polarization manipulation, photonic spinholes, holograms, etc. by constructing a metasurface with a specific phase profile pre-designed for transmitted or reflected waves. Demonstrated the wave operation effect.

Dynamic beam steering meta device

Demonstration of dynamic beam steering metadevice: (a) Schematic diagram of a metadevice consisting of two layers of transparent metasurface aligned by an electric rotating stage. SEM photographs of (b) top view (left) and (c) bottom view (right) of the manufactured metadevice. (D) Schematic of the experimental equipment shown to characterize the metadevice. Simulated far-field scattering power distribution using (e) experiments and (f) metadevices that are illuminated by 0.7 THz LCP light and evolve along Path I at various points in time. (G) The change in the direction of the transmitted wave on the sphere in the k direction as the metadevice moves along path I and path II. The solid line (star) shows the simulation (experimental) result. Here, the blue area shows the solid angle of the beam steering coverage. Credit: X. Cai et al. , Doi 10.1117 / 1.AP.3.3.036003

In addition, the integration of active elements with individual metaatoms in passive metasurfaces enables “active” metadevices that can dynamically manipulate the EM wavefront. Deep sub-wavelength active elements are easily found in the microwave region (such as PIN diodes and varicaps) and contribute well to beam steering, programmable holograms, and active metadevices for dynamic imaging, but at frequencies above THz. It’s difficult to create. .. This problem is due to size restrictions and significant ohm loss in the electronics. The THz frequency can control the THz beam uniformly, but usually the THz wavefront cannot be manipulated dynamically. This is ultimately due to a flaw in the local tuning function at deep sub-wavelength scales in this frequency domain. Therefore, developing a new approach that avoids reliance on local tuning is a priority.

As reported in Advanced photonicsResearchers at Shanghai University and Fudan University have developed common frameworks and metadevices for dynamic control of the THz wavefront. Instead of locally controlling the individual metaatoms in the THz metasurface (for example, via a PIN diode, varicap, etc.), the rotating multilayer cascade metasurface alters the polarization of the light beam. When they rotate different layers in a cascaded metadevice (each showing a particular phase profile) at different velocities, they dynamically change the effective Jones matrix characteristics of the entire device, the wavefront of the THz beam and It shows that abnormal manipulation of polarization characteristics can be realized. Two metadevices are shown. The first metadevice can efficiently redirect vertically incident THz beams to scan a wide solid angle range, and the second metadevice can dynamically manipulate both the wavefront and polarization of the THz beam.

This work offers an attractive alternative for achieving low-cost dynamic control of THz waves. Researchers hope that this research will inspire future applications of THz radar, as well as biological and chemical sensing and imaging.

Reference: “Dynamic control of terahertz wavefront by cascade metasurface”, Xiaodong Cai, Rong Tang, Haoyang Zhou, Qiushi Li, Shaojie Ma, Dongyi Wang, Tong Liu, Xiaohui Ling, Wei Tan, Qiong He, Shiyi Xiao, Lei Zhou , June 26, 2021, Advanced photonics..
DOI: 10.1117 / 1.AP.3.3.036003

Dynamic Control of THz Wavefronts by Rotating Layers of Cascaded Metasurfaces Source link Dynamic Control of THz Wavefronts by Rotating Layers of Cascaded Metasurfaces

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