The concept of synthetic dimensions has emerged as a powerful framework in photonics and atomic physics, enabling the exploration of high-dimensional physics beyond conventional spatial constraints. Originally developed for quantum simulations in high dimensions, synthetic dimensions have since demonstrated advantages in designing novel Hamiltonians and manipulating quantum or optical states for exploring topological physics, and for applications in computing and information processing. Here, we provide a comprehensive overview of progress in synthetic dimensions across photonic, atomic, and other physical platforms over the past decade. We showcase different approaches used to construct synthetic dimensions and highlight key physical phenomena enabled by the advantage of such a framework. By offering a unified perspective on developments in this field, we aim to provide insights into how synthetic dimensions can bridge fundamental physics and applied technologies, fostering interdisciplinary engagement in quantum simulation, atomic and photonic engineering, and information processing.

Integrated optical phased arrays (OPAs) have attracted significant interest to steer laser beams for applications including free-space communications, holography, and light detection and ranging. Although many methods have been proposed to suppress grating lobes, OPAs have also been limited by the trade-off between field of view (FOV) and beamforming efficiency. Here, we propose a metasurface empowered port-selected OPA (POPA), an OPA steered by port selection, which is implemented by an aperiodic waveguide array with an average pitch less than the wavelength and phase controlled by coupling among waveguides. A metasurface layer above the POPA was designed to increase wide FOV steering, aliasing-free by polarization division. As a result, we experimentally demonstrate beam scanning over a ±41.04°×7.06° FOV. The aliasing-free POPA with expanded FOV shows successful incorporation of the waveguide-based OPA technique with an emerging metasurface design, indicating much exploration in concepts for integrated photonic devices.

Self-imaging is an important function for signal transport, distribution, and processing in integrated optics, which is usually implemented by multimode interference or diffractive imaging process. However, these processes suffer from the resolution limit due to classical wave propagation dynamics. We propose and demonstrate subwavelength optical imaging in one-dimensional silicon waveguide arrays, which is implemented by cascading straight and curved waveguides in sequence. The coupling coefficient between the curved waveguides is tuned to be negative to reach a negative dispersion, which is an analog to a hyperbolic metamaterial with a negative refractive index. Therefore, it endows the waveguide array with a superlens function as it is connected with a traditional straight waveguide array with positive dispersion. With a judiciously engineered cascading silicon waveguide array, we successfully show the subwavelength self-imaging process of each input port of the waveguide array as the single point source. Our approach provides a strategy for dealing with optical signals at the subwavelength scale and indicates functional designs in high-density waveguide integrations.