Space-variant Pancharatnam-Berry Phase Research Articles

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

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.

Generation and Manipulation of Orbital Angular Momentum by All-Dielectric Metasurfaces

We propose the design of a planar dielectric metasurface to overcome the ohmic loss and discrete phase profile of metallic metasurfaces. The proposed metasurface is composed of annular subwavelength gratings, which can be taken regard as a space-variant Pancharatnam-Berry phase optical element. Consequently, the OAM-carrying beams with topological charge a"" = +/- 2 is generated with the efficiency high up to 90 %. In addition, we demonstrate a method to produce fractional, quasi-focusing, and quasi-non-diffracting OAM-carrying beams by adopting appropriate width modulation of the annular gratings. The proposed metasurfaces offering superiorities in high efficiency, phase continuity, and manipulative diversity may have potential applications in integrated-photonics and optical communication system.

Observation of photonic spin Hall effect with phase singularity at dielectric metasurfaces.

Observation of photonic spin Hall effect (SHE) near the phase singularity at dielectric metasurfaces is presented. The structured metasurface works as a space-variant Pancharatnam-Berry phase element and produces a vortex beam with phase singularity. The dynamical vortex phase is introduced to eliminate or enhance the phase singularity, thus realizing the manipulation of spin-dependent Pancharatnam-Berry phase. The spin-orbit coupling near the singularity of the Pancharatnam-Berry phase leads to the observation of the photonic SHE which manifests itself as spin-dependent splitting. The underlying mechanism is significantly different from previously reported cases. It thereby provides an alternative way to manipulate the spin states of photons.

Realization of Tunable Photonic Spin Hall Effect by Tailoring the Pancharatnam-Berry Phase

Recent developments in the field of photonic spin Hall effect (SHE) offer new opportunities for advantageous measurement of the optical parameters (refractive index, thickness, etc.) of nanostructures and enable spin-based photonics applications in the future. However, it remains a challenge to develop a tunable photonic SHE with any desired spin-dependent splitting for generation and manipulation of spin-polarized photons. Here, we demonstrate experimentally a scheme to realize the photonic SHE tunably by tailoring the space-variant Pancharatnam-Berry phase (PBP). It is shown that light beams whose polarization with a tunable spatial inhomogeneity can contribute to steering the space-variant PBP which creates a spin-dependent geometric phase gradient, thereby possibly realizing a tunable photonic SHE with any desired spin-dependent splitting. Our scheme provides a convenient method to manipulate the spin photon. The results can be extrapolated to other physical system with similar topological origins.

Ladder operators formalism for optical angular momentum transfer and space-variant Pancharatnam-Berry phase

Ladder operators are introduced in SU(2) parameter space to analyze the space-variant Pancharatnam-Berry (PB) phase. The spin and orbital angular momentum transfers to a wave passing through the PB phase optical elements are understood in terms of the PB phase. Space-variant PB phase structures are identified in polarization grating and cholesteric liquid crystal, providing an explanation for the beam propagation direction alteration. A simultaneous occurrence of the wavefront shaping and the beam propagation direction alteration is demonstrated experimentally.

Formation of helical beams by use of Pancharatnam–Berry phase optical elements

Spiral phase elements with topological charges based on space-variant Pancharatnam-Berry phase optical elements are presented. Such elements can be achieved by use of continuous computer-generated space-variant subwavelength dielectric gratings. We present a theoretical analysis and experimentally demonstrate spiral geometrical phases for infrared radiation at a wavelength of 10.6microm .

Space-variant Pancharatnam–Berry phase optical elements with computer-generated subwavelength gratings

Space-variant Pancharatnam-Berry phase optical elements based on computer-generated subwavelength gratings are presented. By continuously controlling the local orientation and period of the grating we can achieve any desired phase element. We present a theoretical analysis and experimentally demonstrate a Pancharatnam-Berry phase-based diffraction grating for laser radiation at a wavelength of 10.6microm.