Phase-Encoding Truncated Orbital Angular Momentum Modes for High-Security and High-Capacity Information Encryption

Vortex beams carrying orbital angular momentum (OAM) modes hold the promise of facilitating high-dimensional symbol mappings for information encryption. However, challenges persist in achieving both high-security and high-capacity encryption with OAM modes, mainly due to limitations in encoding degrees of freedom and compatible decoding methods. Herein, we present an encryption scheme that integrates truncated OAM modes with phase encoding. Truncated OAM modes are hybrid modes that emerges from mode dispersion caused by the absence of amplitude modulation during generation. By combining the generation function with phase encoding, we can modulate the mode dispersion, creating a discrete set of truncated modes. This introduces a phase degree of freedom for encoding information onto the mode spectrum, achieving high-security encryption. The exponential expansion of the phase factors enables the construction of higher-order symbol maps, thereby increasing encryption capacity. As a proof-of-concept, we implemented an optical information encrypting link using 4 OAM modes and 32-order phase encoding, resulting in over 3 × 10
⁴
modulation orders. The neural network successfully decoded the encryption information with 100% accuracy. This scheme offers the potential to incorporate additional OAM modes in the generating function and further partition the phase encoding, enabling even higher-dimensional symbol mapping. These advancements open up new possibilities for advancing high-security and high-capacity information encryption based on OAM modes.