Abstract
A Pancharatnam–Berry optical element is designed, fabricated, and optically characterized for the demultiplexing of beams with different polarization and orbital angular momentum states at the telecom wavelength of 1310 nm. The geometric phase control is achieved by fabricating properly-oriented subwavelength gratings on a silicon substrate, inducing a spatially-variant form birefringence. The digital grating pattern is transferred to the silicon substrate with a two-step nanofabrication protocol, using inductively coupled plasma reactive ion etching to transfer the resist pattern generated with high-resolution electron beam lithography. The optical characterization of the sample confirms the expected capability to sort circularly polarized optical beams with different handedness and orbital angular momentum. Encompassing optical element design and silicon photonics, the designed silicon metasurface paves the way to innovative devices for total angular momentum mode division multiplexing with unprecedented levels of integration.
Highlights
In order to face the worldwide ever-increasing demand for bandwidth, different methods have been developed and employed to exploit the several degrees of freedom of light for encoding information and increasing the capacity of optical networks
We considered the demultiplexing method based on orbital angular momentum (OAM) mode projection, and we designed and fabricated for the first time a silicon metasurface performing both OAM-mode division multiplexing (MDM) and polarization-division multiplexing (PDM)
Fabrication, and optical characterization of a silicon metasurface for the demultiplexing of optical beams with well-defined spin and orbital angular momentum states
Summary
In order to face the worldwide ever-increasing demand for bandwidth, different methods have been developed and employed to exploit the several degrees of freedom of light for encoding information and increasing the capacity of optical networks. The combination of well-established multiplexing techniques based on wavelength, polarization, time, amplitude, and phase, the modulation of light cannot exceed the physical limit of single-mode optical fibers. On the other hand, moving to a multi-mode transmission medium opens the network to the exploitation of the different orthogonal modes as distinct propagation channels, in the so-called mode division multiplexing (MDM) [1]. In the cylindrically symmetric framework of optical fibers, modes can be labeled on the basis of the carried orbital angular momentum (OAM) and present a well-defined circular polarization state, associated with the spin angular momentum (SAM) [2].
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