The possibility of manipulating the properties of a light beam is a fundamental requirement of free-space optical (FSO) systems. Structured light —that is, optical beams with optimized amplitude, phase, and polarization profiles—is exploited in high-resolution imaging , in microscopy , in particle detection, localization, and manipulation , and in communications . In these applications FSO beams are conventionally generated, manipulated, and received by using bulk optics, such as classical lenses or spatial light modulators (SLMs). SLMs allow the independent control of amplitude and phase in a large number of points (pixels) in the cross-sectional plane of the beam, as in liquid-crystal on silicon (LCOS) technology , but at the price of quite large size and cost as well as loss in any amplitude modulation. However, massive connection of devices driven by the internet of things (IoT) asks for solutions where footprint, weight, and cost reduction are of primary importance, for instance, in systems for localization, positioning, and ranging for autonomous vehicles and drones, as well as artificial vision and imaging systems for portable devices. More compact SLM architectures have been recently proposed, which exploit all-solid-state tunable metasurfaces [7,8]. Although allowing a significant device downscaling, these devices are hardly integrable with other functionalities, like tuneable wavelength-selective filters, splitters/combiners, and (de)multiplexers, nor with fast time-domain modulators, which could allow evolution toward more advanced all-optical processing of FSO beams. Moreover, automated configuration of SLM systems requires interferometric phase calibration techniques and optimization algorithms, whose computational complexity scales heavily with the pixel count .
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