• Photonics Research
  • Vol. 9, Issue 11, 11002196 (2021)
Maziyar Milanizadeh1, Fabio Toso1, Giorgio Ferrari1, Tigers Jonuzi1、2, David A. B. Miller3, Andrea Melloni1, and Francesco Morichetti1、*
Author Affiliations
  • 1Dipartimento di Elettronica, Informazione e Bioingegneria-Politecnico di Milano, Milano 20133, Italy
  • 2Current address: VLC Photonics, Universidad Politécnica de Valencia, 46022 Valencia, Spain
  • 3Ginzton Laboratory, Stanford University, Stanford, California 94305, USA
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    Abstract

    In technologies operating at light wavelengths for wireless communication, sensor networks, positioning, and ranging, a dynamic coherent control and manipulation of light fields is an enabling element for properly generating and correctly receiving free-space optical (FSO) beams even in the presence of unpredictable objects and turbulence in the light path. In this work, we use a programmable mesh of Mach–Zehnder (MZI) interferometers to automatically control the complex field radiated and captured by an array of optical antennas. The implementation of local feedback control loops in each MZI stage, without global multivariable optimization techniques, enables an unlimited scalability. Several functionalities are demonstrated, including the generation of perfectly shaped beams with nonperfect optical antennas, the imaging of a desired field pattern through an obstacle or a diffusive medium, and the identification of an unknown obstacle inserted in the FSO path. Compared to conventional devices used for the manipulation of FSO beams, such as spatial light modulators, our programmable device can self-configure through automated control strategies and can be integrated with other functionalities implemented onto the same photonic chip.

    1. INTRODUCTION

    The possibility of manipulating the properties of a light beam is a fundamental requirement of free-space optical (FSO) systems. Structured light [1]—that is, optical beams with optimized amplitude, phase, and polarization profiles—is exploited in high-resolution imaging [2], in microscopy [3], in particle detection, localization, and manipulation [4], and in communications [5]. 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 [6], 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 [9].