In this study, we report a robust cryptographic scheme operating over noisy channels, enabled by a nonlinear detection architecture that intrinsically mitigates channel-induced phase aberrations. Difference-frequency generation (DFG) in a nonlinear crystal is employed to automatically compensate channel-induced phase aberrations, providing intrinsic noise mitigation. Spatial modes in the orbital angular momentum basis are used as high-dimensional information carriers, providing enhanced capacity and improved security. As a classical proof-of-principle, our results demonstrate that the DFG correction mechanism reliably restores the spatial mode transfer matrix to near-ideal fidelity across a broad range of aberration types and strengths, recovering projected secret key rates and mutual information metrics consistent with a secure high-dimensional channel. These findings establish nonlinear wave mixing as a viable tool for noise-resilient, high-dimensional communication, with a clear pathway toward quantum implementation using single-photon sources and detectors.

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• Angular momentum of light