Pancharatnam-Berry Phase Metasurfaces Research Articles

Direct polarization measurement using a multiplexed Pancharatnam–Berry metahologram

Polarization, which represents the vector nature of electromagnetic waves, plays a fundamental role in optics. Fast, simple, and broadband polarization state characterization is required by applications such as polarization communication, polarimetry, and remote sensing. However, conventional polarization detection methods face great difficulty in determining the phase difference between orthogonal polarization states and often require a series of measurements. Here, we demonstrate how polarization-dependent holography enables direct polarization detection in a single measurement. Using a multiplexed Pancharatnam–Berry phase metasurface, we generate orthogonally polarized holograms that partially overlap with a spatially varying phase difference. Both amplitude and phase difference can be read from the holographic image in the circular polarization basis, facilitating the extraction of all Stokes parameters for polarized light. The metahologram detects polarization reliably at several near-infrared to visible wavelengths, and simulations predict broadband operation in the 580–940 nm spectral range. This method enables fast and compact polarization analyzing devices, e.g., for spectroscopy, sensing, and communications.

Chip-integrated metasurface for versatile and multi-wavelength control of light couplings with independent phase and arbitrary polarization

While metasurfaces are now widely considered in free-space optics, their potential for coupling and tailoring guided waves is not fully explored. Here we transfer the Jones matrix method to target versatile on-chip coupling using metasurface-patterned photonic waveguides around the telecommunication wavelength of 1.55 μm, which can accommodate both propagation and Pancharatnam-Berry phase metasurfaces for guided waves. One can either encode two arbitrary and independent phase profiles to any pair of orthogonal polarizations or deploy complete control over both the phase and polarization of coupled modes. A set of design scenarios synergizing silicon nanoantennas and low-loss silicon-nitride waveguides are proposed, including directional couplers with mode-selectivity and polarization splitters with directionality ranging from 10 to 20 dB. Furthermore, our optimization method can be further extended to cover multiple working wavelengths. Exemplary on-chip color routers are also numerically demonstrated. This chip-integrated metasurface platform further translates the concept of a metasurface into photonic integrated circuits, serving as a positive paradigm for versatile and complete control over waveguide optical signals and motivating chip-scale applications such as polarization/wavelength demultiplexers, optical switches, and multifunctional mode converters.

Detecting nanometric displacements with optical ruler metrology.

We introduce the optical ruler, an electromagnetic analog of a physical ruler, for nanoscale displacement metrology. The optical ruler is a complex electromagnetic field in which singularities serve as the marks on the scale. It is created by the diffraction of light on a metasurface, with singularity marks then revealed by high-magnification interferometric observation. Using a Pancharatnam-Berry phase metasurface, we demonstrate a displacement resolving power of better than 1 nanometer (λ/800, where λ is the wavelength of light) at a wavelength of 800 nanometers. We argue that a resolving power of ~λ/4000, the typical size of an atom, may be achievable. An optical ruler with dimensions of only a few tens of micrometers offers applications in nanometrology, nanomonitoring, and nanofabrication, particularly in the demanding and confined environment of future smart manufacturing tools.

Transformation of photonic spin Hall effect from momentum space to position space

Photonic spin Hall effect (PSHE) in momentum space can lead to a giant spin-dependent splitting (SDS). However, the SDS in momentum space increases linearly with beam propagation distance, which limits its applications. In this work, a simple method is proposed to transform the PSHE from momentum space to position space. We first theoretically analyze the feasibility of the transformation. The results show that the transformation can be realized when a light wave passes through two identical Pancharatnam–Berry phase metasurfaces. Then an experimental setup is established to verify the theoretical results. Through rational design of the optical path, only one metasurface is needed to complete the transformation of PSHE from momentum space to position space. The experimental results agree well with theoretical calculations. We believe that these results are helpful for the design of photonics devices based on PSHE.

Multidimensional Manipulation of Photonic Spin Hall Effect with a Single‐Layer Dielectric Metasurface

AbstractThe photonic spin Hall effect, originating from photonic spin–orbit interactions, has attracted considerable research interest due to its potential for applications in spin‐controlled nanophotonics. However, most research efforts have focused only on 1D modulation, including transverse or longitudinal spin‐dependent splitting. Here, a novel method is proposed for multidimensional spin‐dependent splitting on a single‐layer dielectric metasurface. Due to the interplay of the Pancharatnam–Berry phase and dynamic phase, the longitudinal focusing and transverse shifting of the different spin state photons can be simultaneously achieved. Moreover, the conjugated characteristic of the modulated phases of Pancharatnam–Berry phase metasurfaces for different spin photons can be broken, and both symmetric and asymmetric transverse spin‐dependent splitting are obtained with the proposed method. This method can be used for the multidimensional and flexible manipulation of spin photons and has potential in spin‐controlled nanophotonics, ranging from optical communication to beam shaping and optical sensors.

Generation of Bessel beam by manipulating Pancharatnam-Berry phase

Bessel beam is one of diffraction-free beams and has some peculiar properties. Varieties of its applications have been found, such as microparticle manipulating, material processing and biological studies. In this work, we propose a method of creating a Bessel beam by manipulating Pancharatnam-Berry phase. Using femtosecond laser, nano waveplatelets are written on a fused silicon glass to form a metasurface. The optical axis of waveplatelets rotating in the radial direction can produce the space-varying Pancharatnam-Berry phase. The designed metasurface acts as a planar axicon to generate Bessel beams by replacing the traditional one. A Jones calculation is employed to analyze the transformation of the metasurface. The theoretical results indicate that a left-handed circularly polarized light passing through the planar axicon is convergent, while a right-handed circularly polarized one is divergent. The intrinsic physical reason is that Pancharatnam-Berry phase is spin-dependent. Therefore, Bessel beams are generated by the planar axicon only when a left-handed circularly polarized light inputs the system. It is notable that the maximum nondiffracting distance is determined by the rate of rotation of the metasurface microstructure. By reducing the rate of rotation, we can easily obtain a longer nondiffracting distance, thus avoiding the problem that the base angle of the traditional axicon is too small to fabricate. According to the Fresnel diffraction integral, we simulate the propagation of the field emerging from the planar axicon and obtain the intensity distributions behind the planar axicon with different distances. The results show that the intensity pattern remains unchanged in the propagating process and possesses the propagation properties of Bessel beam. It implies that approximate nondiffraction Bessel beams can be achieved by employing the planar axicon with metasurface. Finally, we set up an experimental system with the Pancharatnam-Berry phase metasurface with period d=1000 upm to verify the theoretical analysis. Theoretically, the maximum nondiffraction distance is 7.9 m. In the shaded region, we measure the intensity distributions at different distances. The experimental results are in good agreement with the simulation results, so the planar axicon based on Pancharatnam-Berry phase can be an effective Bessel beam generator. We believe that these results are helpful for developing more spin-dependent photonic devices.