Abstract
In this paper, the implementation of optical elements in the form of Pancharatnam-Berry optics is considered. With respect to 3D bulk and diffractive optics, acting on the dynamic phase of light, Pancharatnam-Berry optical elements transfer a phase that is geometric in nature by locally manipulating the polarization state of the incident beam. They can be realized as space-variant sub-wavelengths gratings that behave like inhomogeneous form-birefringent materials. We present a comprehensive work of simulation, realization, and optical characterization at the telecom wavelength of 1310 nm of the constitutive linear grating cell, whose fabrication has been finely tuned to get a π-phase delay and obtain a maximum in the diffraction efficiency. The optical design in the infrared region allows the use of silicon as candidate material due to its transparency. In order to demonstrate the possibility of assembling the single grating cells for generating more complex phase patterns, the implementation of two Pancharatnam-Berry optical elements is considered: a blazed grating and an optical vortices demultiplexer.
Highlights
Metasurfaces based on high-index dielectric materials have gained increasing attention due to their ability to locally manipulate the amplitude, phase and polarization of impinging light achieving high spatial resolution, low intrinsic losses and showing potential compatibility with standard industrial processes [1]
In order to demonstrate the possibility to assemble the single grating cells for the generation of more complex phase patterns, besides a simpler blazed grating, we considered the realization for the first time of a PB mode-division demultiplexer for the sorting of optical beams carrying orbital angular momentum (OAM) of light [26]
We focus on the optimization of a linear sub-wavelength grating as constitutive basic unit for the design and implementation of high-efficient Pancharatnam-Berry Optical Elements in silicon working in the infra-red range
Summary
Metasurfaces based on high-index dielectric materials have gained increasing attention due to their ability to locally manipulate the amplitude, phase and polarization of impinging light achieving high spatial resolution, low intrinsic losses and showing potential compatibility with standard industrial processes [1]. The basic principle of metasurfaces optics is based on the generation of spatially-variant artificial birefringence by properly structuring the substrate surface. The local rotation of the gratings is proportional to the geometric phase, known as Pancharatnam–Berry (PB) phase, whose local control allows the design of the phase map over the full area of the optics surface. The key-element of such a Pancharatnam-Berry optical element (PBOE) is varied pixel-by-pixel in order to transfer the desired geometric-phase pattern to the incident light, providing the space variety of grating orientation that can be viewed as continuously rotating wave plates with constant retardation and continuously space-varying fast axis
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