Catering to emerging satellite-based free-space optical (FSO) communication networks and exploiting polarization encoding via Stokes operators, we propose a novel simultaneous quantum-classical communications (SQCC) protocol. The protocol enables the coexistence of secure quantum communications and high-throughput classical communications with minimal alterations in both the infrastructure and the energy input. Compared to the conventional SQCC protocol, our new approach provides superior practicality in the real world, eliminates the need for a separate local oscillator, and allows for the simple readout of both quantum and classical information using direct detection. The protocol also minimizes the undesirable interplay between the quantum and the classical parts of communication. We provide a detailed mathematical formulation of the protocol, along with theoretical and numerical analysis of its performance, illustrating a promising path to practical and effective realization of combined classical-quantum communications.

Catering for the emerging satellite-based free-space optical (FSO) communication networks, exploiting polarization encoding via Stokes operators, we propose a novel simultaneous quantum-classical communications (SQCC) protocol that enables the coexistence of secured quantum communications and high-throughput classical communications under minimal alterations in both infrastructure and energy input. Relative to the conventional SQCC protocol, our new protocol provides superior real-world practicability by eliminating the need for a separate local oscillator, allowing for the simple readout of both quantum and classical information using direct detection, and minimizing the undesirable interplay between the quantum and classical parts of communication. We provide a detailed description, along with theoretical and numerical analyses on the feasibility and performance of our protocol, illustrating a promising pathway towards the practical and effective realization of combined classical-quantum communications.