Rydberg Atom-Based OAM-FDM Integration for High-Capacity Microwave Communications

Rydberg atoms enable ultrasensitive microwave detection through their exceptional polarizability, but their use as decoders in communications is limited by a scarcity of scalable frequency points, which arises from cross-modulation in multifrequency fields and narrow operational bandwidth of the sensor. This work introduces a digital communication framework that integrates orbital angular momentum (OAM) with frequency-division multiplexing (FDM). By mapping each FDM subcarrier to a distinct OAM, we construct a 2-D multiplexing space that combines the spectral dimension of FDM with the spatial-phase dimension of OAM. As a result, the theoretical channel capacity scales as the product of the capacities attainable in each individual dimension, thereby overcoming the inherent limit of conventional single-dimensional multiplexing. OAM features are mapped to Rydberg electromagnetically induced transparency (EIT) spectra through quadrupole-gradient coupling, enabling simultaneous OAM identification and FDM demodulation using spectral templates, without separate detectors. Simulations show greater than 98% overall recognition accuracy under the transition$|61\text {D}_{5/2}\rangle \to |63\text {P}_{1/2}\rangle $: at an SNR of under 10 dB, OAM mode 1 is identified with 99.6% accuracy (0.4% misclassification) and OAM mode 0 with 98.1% (1.9% misclassification). Meanwhile, QPSK phase recognition remains greater than 98.5%, with$\varphi _{k}=\pi /2$and$3\pi /2$being 1.5–2% lower than for$\varphi _{k}=0$and$\pi $. This work supports high-performance multifrequency microwave technologies by enhancing capacity and simplifying the architecture.