Flexible Control of Broadband Polarization in a Spintronic Terahertz Emitter Integrated with Liquid Crystal and Metasurface

Abstract

Flexible polarization control of the terahertz wave in the wide bandwidth is crucial for numerous applications, such as terahertz communication, material characterization, imaging, and biosensing diagnosis. However, this promise is impeded by the operating bandwidth of circular polarization states, control modes, and the efficiency of the regulation. Here, we report a spintronic terahertz emitter integrated with phase complementary elements, consisting of a liquid crystal and metasurface, to achieve broadband polarization control with high flexibility. This strategy allows the broadband conversion between linear, elliptical, and circular polarization by changing the rotation angle to modulate the space-variant Pancharatnam–Berry phase. The device is characterized with a terahertz time-domain spectroscopy system, demonstrating that the ellipticity of the circular polarization state could keep greater than 0.9 in 0.60–0.99 THz. In the case of an external electro-magnetic field, further polarization modulation experiments are carried out to provide multiple conversion approaches for multi-azimuth. We first propose a method of full broadband polarization state control of the terahertz emitter based on Pancharatnam–Berry phase modulation and an external electro-magnetic field. We believe that such integrated devices with broadband working bandwidth and multiple control modes will make valuable contributions to the development and multi-scene applications of ultrafast terahertz technologies.

Coupling Broadband Terahertz Dipoles to Microscale Resonators

“…In particular, the exemplary spectrum exhibits an additional peak around 1. 35 THz which corresponds to the dispersive line-shape in the PCA component (B). A spectrally and spatially distinct mode (component (C)) is located predominantly between SRRs in the vertical direction and, for example, results in a dip at around 1.8 THz in the THz emission spectrum at the position indicated by the open red circle.…”

“…Furthermore, the quasi-two-dimensional geometry of the emitter allows for a direct emitter patterning ,,,− or a coupling of the emitter surface to metallic microstructures , and metasurfaces, , aiming for a spectral and angular tuning of the emitted radiation, an improved excitation or outcoupling efficiency, or enhanced sensitivity in local THz spectroscopy . Up to now, spectral tunability by employing two-dimensional resonators and antennas combined with large-area illumination of the spintronic emitter yielded only moderate effects.…”

Liquid Crystal-Tuned Planar Optics in Terahertz Range

“…Figure 5c shows that the combination of LCs and chiral metamaterials enabled spin conversion and electronically manipulated optical chirality [83]. With the rapid development of THz technology, many other LC-integrated THz metadevices have been designed and demonstrated, such as the THz demultiplexer [84] and the spin controllable THz source [85], and so on. Dynamic THz beam steering has great potential in high-speed wireless communication, high-resolution imaging, and radar.…”

Generation of Tunable Terahertz Waves from Tailored Versatile Spintronic Meta-Antenna Arrays

“…17−19 These devices and structures that have been introduced into the spintronic terahertz sources greatly enrich the manipulation capabilities of spintronic terahertz waves. Some of these devices achieve terahertz polarization manipulation through spin-charge currents and current confinement effects, 13,20 while others enhance terahertz pulses through antenna-coupling effects. [21][22][23][24][25]45 However, the aforementioned spintronic terahertz devices so far have only focused on implementing certain modulations, 26,27 and it still attracts a great interest to develop spintronic terahertz devices with multiple modulation modes.…”

“…These schemes can significantly enhance the emission amplitude and achieve spectral modulation; (2) patterned ferromagnetic heterostructure devices with a high design of freedom and flexible manipulation capabilities, such as stripe-patterned ferromagnetic heterostructures, − ,, subwavelength blocky patterned heterostructures, and nanolayered metallic waveguide structures. − These devices and structures that have been introduced into the spintronic terahertz sources greatly enrich the manipulation capabilities of spintronic terahertz waves. Some of these devices achieve terahertz polarization manipulation through spin-charge currents and current confinement effects, , while others enhance terahertz pulses through antenna-coupling effects. − , However, the aforementioned spintronic terahertz devices so far have only focused on implementing certain modulations, , and it still attracts a great interest to develop spintronic terahertz devices with multiple modulation modes…”