Dual Multiplexing of Wavelength and Orbital Angular Momentum for Expanded Information Capacity With a Single Freeform Micro‐Structured Element

ABSTRACT Optical multiplexing is an important method for expanding information capacity. Here, we propose and experimentally demonstrate dual multiplexing of wavelength and orbital angular momentum (OAM) for expanded information capacity with a single freeform micro‐structured element (FME) in full visible band, in which a 3D focuses cubic (FC) and an encrypted holography images cubic (EHIC) are achieved by the proposed FC‐FME and EHIC‐FME, respectively. The dual multiplexing is achieved by the coherent phase superposition of complex optical fields of focusing, holography, and vortex corresponding to different wavelengths and OAMs, from which 3D FC and EHIC with 12 topological charges (TCs) multiplied 12 wavelengths are realized, respectively. The proposed two FMEs with sizes of 4 and 6 mm are fabricated and demonstrated by 3D laser direct writing technique, from which 12 × 12 vortex focuses and 12 × 12 encrypted holographic images with 12 designed TCs at 12 designed wavelengths are simultaneously generated, respectively, resulting in a square‐expanded information capacity. The proposed dual multiplexed method with freeform micro‐structured elements provides a new idea for multiplication of information capacity with large element size and less fabrication complex in various fields of optical communication, encryption, and storage.