Circularly Polarized Terahertz Research Articles

Twisted Stacking Metasurface for Complete Amplitude and Phase Control of Circularly Polarized Terahertz Waves

AbstractTerahertz (THz) metasurfaces have emerged as a powerful tool for manipulating THz wavefronts, typically achieved by adjusting various geometric parameters. In this study, an approach is introduced by incorporating interlayer coupling into twisted stacking metasurface design to completely control the amplitude and phase of circularly polarized THz waves. By leveraging the interlayer coupling effect and the Pancharatnam–Berry phase, the study achieves efficient control over transmission phase and amplitude by simply adjusting the relative twist angle between paired C‐shaped split‐ring resonators. To validate the concept, a holographic metasurface is fabricated and characterized, providing experimental evidence of its THz wavefront manipulation capabilities. This design strategy presents a versatile and tunable solution for THz wave control, promising applications in a wide range of functional devices.

Efficient manipulations of circularly polarized terahertz waves with transmissive metasurfaces

The unrestricted control of circularly polarized (CP) terahertz (THz) waves is important in science and applications, but conventional THz devices suffer from issues of bulky size and low efficiency. Although Pancharatnam–Berry (PB) metasurfaces have shown strong capabilities to control CP waves, transmission-mode PB devices realized in the THz regime are less efficient, limiting their applications in practice. Here, based on Jones matrix analysis, we design a tri-layer structure (thickness of ~λ/5) and experimentally demonstrate that the structure can serve as a highly efficient transmissive meta-atom (relative efficiency of ~90%) to build PB metadevices for manipulating CP THz waves. Two ultrathin THz metadevices are fabricated and experimentally characterized with a z-scan THz imaging system. The first device can realize a photonic spin Hall effect with an experimentally demonstrated relative efficiency of ~90%, whereas the second device can generate a high-quality background-free CP Bessel beam with measured longitudinal and transverse field patterns that exhibit the nondiffracting characteristics of a Bessel beam. All the experimental results are in excellent agreement with full-wave simulations. Our results pave the way to freely manipulate CP THz beams, laying a solid basis for future applications such as biomolecular control and THz signal transportation.

Circularly polarized terahertz radiation monolithically generated by cylindrical mesas of intrinsic Josephson junctions

We report emissions of circular polarized electromagnetic waves from cylindrically shaped mesa structures of the high-temperature superconductor Bi2Sr2CaCu2O8+δ. The frequency range of circularly polarized emission of a cylindrical mesa with notched sides is between 400 and 430 GHz, which is wider than expected by the patch antenna theory. Three maxima recognized in emission intensity are presumably attributed to excitations of fundamental orthogonal modes and circularly polarized modes. Along with the demonstration of circularly polarized emission from truncated edge square mesas, the obtained results provide a wide variety of engineering designs of compact and solid-state electromagnetic sources which are able to generate circularly-polarized terahertz waves.

Monolithic Superconducting Emitter of Tunable Circularly Polarized Terahertz Radiation

We propose an approach to control the polarization of terahertz (THz) radiation from intrinsic Josephson-junction stacks in single crystalline high-temperature superconductor $Bi_2Sr_2CaCu_2O_{8+\delta}$. By monolithically controlling the surface current distributions in the truncated square mesa structure, we can modulate the polarization of the emitted THz wave as a result of two orthogonal fundamental modes excited inside the mesa. Highly polarized circular terahertz waves with a degree of circular polarization of more than 99% can be generated using an electrically controlled method. The emitted radiation has a high intensity and a low axial ratio (AR<1 dB). The intuitive results obtained from the numerical simulation based on the conventional antenna theory are consistent with the observed emission characteristics.

Emission of Circularly Polarized Terahertz Wave From Inhomogeneous Intrinsic Josephson Junctions

We have theoretically demonstrated the emission of circularly-polarized terahertz (THz) waves from intrinsic Josephson junctions (IJJs) which is locally heated by an external heat source such as the laser irradiation. We focus on a mesa-structured IJJ whose geometry is slightly deviate from a square and find that the local heating make it possible to emit circularly-polarized THz waves. In this mesa, the inhomogeneity of critical current density induced by the local heating excites the electromagnetic cavity modes TM (1,0) and TM (0,1), whose polarizations are orthogonal to each other. The mixture of these modes results in the generation of circularly-polarized THz waves. We also show that the circular polarization dramatically changes with the applied voltage. The emitter based on IJJs can emit circularly-polarized and continuum THz waves by the local heating, and will be useful for various technological application.

Scattering of Circularly Polarized Terahertz Waves on a Graphene Nanoantenna

We present a surface current method to model the graphene rectangular nanoantenna scattering in the terahertz band with Comsol. Compared with the equivalent thin slab method, the results obtained by the surface current method are more accurate and efficient. Then the electromagnetic scattering of circularly polarized terahertz waves on graphene nanoantennas is numerically analyzed by utilizing the surface current method. The dependences of the antenna resonant frequency with the circularly polarized wave on width and length are consistent with those for the linear polarized waves. These results are proved to be useful to design efficient nanoantennas in terahertz wireless communications.

Publisher’s Note: Tunable Circularly Polarized Terahertz Radiation from Magnetized Gas Plasma [Phys. Rev. Lett.114, 253901 (2015)

Received 6 July 2015DOI:https://doi.org/10.1103/PhysRevLett.115.049902© 2015 American Physical Society

Tunable Circularly Polarized Terahertz Radiation from Magnetized Gas Plasma.

It is shown, by simulation and theory, that circularly or elliptically polarized terahertz radiation can be generated when a static magnetic (B) field is imposed on a gas target along the propagation direction of a two-color laser driver. The radiation frequency is determined by √[ω(p)(2)+ω(c)(2)/4]+ω(c)/2, where ω(p) is the plasma frequency and ω(c) is the electron cyclotron frequency. With the increase of the B field, the radiation changes from a single-cycle broadband waveform to a continuous narrow-band emission. In high-B-field cases, the radiation strength is proportional to ω(p)(2)/ω(c). The B field provides a tunability in the radiation frequency, spectrum width, and field strength.