Deep-Space Optical Communication Receiver Based on Single Photon Coherent Beam Combination

TL;DR

This work tackles photon-starved deep-space optical links by replacing a single large receiving telescope with a cascaded coherent beam–combining (CBC) array to boost SNR while enabling a coherent output beam for advanced processing. The authors develop a two-beam CBC block with MAP-based phase tracking and extend it to multi-stage cascaded CBC, analyzing performance under phase diffusion and background noise for PPM-based SCPPM transmission. Key findings show that cascaded CBC can match a single large aperture in nighttime conditions and offer daytime throughput gains due to effective noise filtering, with performance highly dependent on the first-stage efficiency and noise level; the study also provides aperture-size and stage-optimization guidelines, validated through Psyche mission-inspired simulations. The results point to CBC as a scalable, potentially cost-saving ground-receiving architecture for future deep-space missions, with implications for AO integration and quantum-enhanced signal processing.

Abstract

We introduce an alternative receiver architecture for deep-space optical communication, in which a single large aperture is replaced by an array of smaller ones with outputs combined coherently, employing phase stabilization based on photon counting events. We show that it allows to increase the signal to noise ratio, thus potentially attaining higher information transmission rates in the regime of large noise, typical for daytime communication. We analyze its practical performance by simulating pulse position modulation-based communication from the recently launched Psyche mission. Under nighttime conditions the achieved performance is comparable to that offered by a single large aperture, whereas in daytime conditions the single photon coherent beam combination architecture provides an advantage in the information transmission rate.

Figures (7)

• Figure 1: Binary coherent beam combination in the photon-starved regime. The optical signal is received by two separate apertures resulting in two light beams that are then interfered on a $50\mathpunct{:}\!50$ beam splitter, whose dark port is monitored by a photodetector. To ensure maximum amount of light leaving the scheme through the bright port, discrete detected photocounts are used to reduce the phase difference between the input beams --- which may result, for instance, from turbulent propagation in the atmosphere --- through a feedback loop.
• Figure 2: Scheme of the proposed deep-space optical communication reception based on a pulse position modulation format (a) received by an exemplary array of $4$ telescopes with coherently combined beams in the cascaded scheme (b).
• Figure 3: Schematic representation of k-stage CBC defined in Sec. \ref{['sec:early']}, where despite performing full cascaded CBC, information decoding is optimized by the choice of a threshold stage $k$. Dark port clicks that happen after stage $k$ of cascaded CBC are treated as a detection of the signal. In the depicted example, 8 beams are combined and (no)-detection events that happened in the given communication slot are annotated next to their respective detectors. If 1-stage CBC is assumed, the slot is counted as occupied by the signal because of the detection in a dark port in stage 2 and despite a lack of detection in the final detector. On the other hand, if 2-stage CBC is assumed, the slot is considered empty as no detections happened from stage 3 onwards. The choice of the optimal $k$ for information decoding can be made in post-processing if one saves the information on individual slot-by-slot detector clicks.
• Figure 4: Single photon coherent beam combination efficiency for (a) $2$ and (b) $16$ input beams for $I_0^\text{in}=5$ [photons/ms], $D_I=0, \Delta t=0.05$ ms as a function of phase diffusion parameter $D_p$ and the ratio of the the background noise and the total input intensity $I_\text{noise}/I_0^\text{in}$. (c), (d) Fraction of time steps for which final output intensity drops below $5\%$ of total initial value for respective cases.
• Figure 5: (a) Diameter $d_{\textrm{eff}}$ of an effective single large aperture that collects the same optical power as the output of a CBC scheme with a given total collection area represented by its equivalent diameter $d_{\textrm{tot}}$ for different individual CBC apertures sizes $d_{\textrm{CBC}}$. Number of apertures $N$ is indicated by the number of CBC stages $n=\log_2 N$ above respective points and lines are drawn only to guide the eye. (b) Efficiency $\eta_{\textrm{tot}}$ of cascaded coherent beam combination as a function of the number of apertures for different diameters.