However, these approaches are resonant in nature, leading to a narrow bandwidth down to several nanometers. The chip-scale generation and transmission of AM-carrying beams on silicon-integrated circuits have been realized through whispering gallery mode resonators ( 13) and resonant microring fibers ( 10). The advance of strong light-confinement nanophotonic approaches has been a major propellant of miniaturized optical circuits to harness AM of light. However, macroscale interference-based detection methods through hologram-coding ( 9, 10) or phase-shifting ( 11, 12) of AM-carrying beams have imposed a fundamental physical limit for realizing such a principle at a chip-scale footprint.
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As one of the most fundamental physical properties in both classical and quantum optics, angular momentum (AM) of light-including spin angular momentum (SAM) possessed by circularly polarized light and orbital angular momentum (OAM) manifested by the helical wavefront of light-has emerged as a physically orthogonal multiplexing approach to high-capacity optical communications ranging from free-space ( 9) to compact optical fibers ( 10).
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In the age of information technology, optical multiplexing using physical dimensions of light, including space ( 1), frequency ( 2), brightness ( 3), color ( 1, 4), polarization ( 1, 5, 6), mode ( 7), and lifetime ( 8), has played a crucial role in high-definition displaying ( 3– 5), high-capacity data storage ( 1, 6), high-speed communications ( 7), and highly sensitive biological sensing ( 8).