Progress of Grating Couplers for Light Exchange between Space and On‐Chip

In photonic integrated chips, grating couplers, as core components enabling optical exchange between on‐chip and spatial domains, directly impact the overall functionality of chips. This paper conducts a systematic study on grating couplers, first outlining their research background, reviewing current research progress and achievements, and analyzing the parameter performance of relevant grating couplers. At the material level, this paper explores the influence mechanisms of various materials—from basic silicon‐based materials to various new types of materials—on the performance of grating couplers. At the structural level, it systematically introduces the development context of grating couplers with different structures, starting from traditional gratings, extending to specially structured gratings, and finally focusing on subwavelength gratings. Meanwhile, this paper elaborates on the wavelength application range of photonic chips, including design adaptability from visible/infrared bands to terahertz–microwave bands. It also provides a detailed analysis of the structural evolution of terahertz grating couplers on metasurfaces and the application of inverse design methods in the research and development of grating couplers. Looking ahead, with continuous breakthroughs in nanotechnology and materials science, grating couplers are expected to achieve significant progress in improving efficiency and reducing loss, thereby playing an irreplaceable key role in emerging fields.