The Analysis and Performance of LODC-OFDM Signal in Nonlinear Rydberg Atomic Sensor

Rydberg atomic sensors have been seen as novel radio frequency (RF) measurements and the high sensitivity to a large range of frequencies makes it attractive for communications reception. However, the signal sensing process in Rydberg system involves sequential transduction from electromagnetic waves to optical signals and finally to electrical signals. The unipolar characteristic of the optical interface inherently restricts conventional OFDM reception. Therefore, adopting unipolar OFDM schemes, inspired by optical communication systems, becomes essential for compatible signal transmission. In this work, we investigate the amplitude modulation-to-amplitude modulation (AM-AM) characteristics of Rydberg atomic sensors, establishing an empirical approximation function. Building on the direct current-biased optical orthogonal frequency division multiplexing (DCO-OFDM) framework, we propose a novel local oscillator direct current-biased OFDM (LODC-OFDM) scheme specifically optimized for Rydberg-based sensing, effectively addressing the broadband OFDM reception challenge. Then, we adopt Bussgang theorem to analyze the nonlinear distortion of LODC-OFDM signals and the results in closed-form solutions are derived for AM/AM curves approximated by Taylor series expansion and for the ideal pre-distortion case. In real experiments, the experimental and theoretical results fit well.

Theoretical Analysis of Heterodyne Rydberg Atomic Receiver Sensitivity Based on Transit Relaxation Effect and Frequency Detuning

We conduct a theoretical investigation into the impacts of local microwave electric field frequency detuning, laser frequency detuning, and transit relaxation rate on enhancing heterodyne Rydberg atomic receiver sensitivity. To optimize the output signal amplitude given the input microwave signal, we derive the steady-state solutions of the atomic density matrix. Numerical results show that laser frequency detuning and local microwave electric field frequency detuning can improve the system detection sensitivity, which can help the system achieve extra sensitivity gain. It also shows that the heterodyne Rydberg atomic receiver can detect weak microwave signals continuously over a wide frequency range with the same sensitivity or even more sensitivity than the resonance case. To evaluate the transit relaxation effect, a modified Liouville equation is used. We find that the transition relaxation rate increases the time it takes to reach steady state and decreases the sensitivity of the system detection.