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Integrated optical phased arrays (OPAs) have emerged as a promising technology for various applications due to their ability to dynamically control free-space optical beams in a compact and non-mechanical manner. While integrated OPAs have traditionally focused on the infrared spectrum, advancements in visible-light integrated OPAs have been relatively limited despite their potential benefits for applications such as displays, 3D printing, trapped-ion quantum systems, underwater communications, and optogenetics. Moreover, integrated visible-light grating-based optical antennas, one of the crucial devices that forms a visible-light integrated OPA, have been relatively underexplored, especially for more advanced designs. In this paper, we address this gap by providing a thorough explanation of the design principles for integrated visible-light grating-based antennas and applying them to design and experimentally demonstrate five different antennas with varying advanced capabilities, including the first visible-light unidirectionally-emitting grating-based antennas for integrated OPAs. Specifically, we develop and experimentally demonstrate integrated visible-light exponentially-emitting single-layer, uniformly-emitting single-layer, exponentially-emitting dual-layer, uniformly-emitting dual-layer, and unidirectionally-emitting dual-layer grating-based antennas. This work aims to provide a thorough design guide for integrated visible-light grating-based antennas, facilitating future widespread use of integrated OPAs for new and emerging visible-light applications. 

Integrated optical phased arrays (OPAs) have enabled cutting-edge applications where optical beam steering can benefit from chip-scale integration. However, the majority of integrated OPA demonstrations to date have been limited to showing far-field beam forming and steering. There are, however, many emerging applications of integrated photonics where emission of focused light from a chip is desirable, such as in integrated optical tweezers for biophotonics, chip-based 3D printers, and trapped-ion quantum systems. To address this need, we have recently demonstrated the first near-field-focusing integrated OPAs; however, this preliminary demonstration was limited to emission at only one focal plane above the chip. In this paper, we show the first, to the best of our knowledge, spiral integrated OPAs, enabling emission of focusing beams with tunable variable focal heights for the first time. In the process, we develop the theory, explore the design parameters, and propose feed-structure architectures for such OPAs. Finally, we experimentally demonstrate an example spiral integrated OPA system fabricated in a standard silicon-photonics process, showing wavelength-tunable variable-focal-height focusing emission. This work introduces a first-of-its-kind integrated OPA architecture not previously explored or demonstrated in literature and, as such, enables new functionality for emerging applications of OPAs that require focusing operation.