Sensor-less adaptive optics based on stochastic parallel gradient descent (SPGD) is effective for the compensation of atmospheric disturbances in coherent free-space optical communication systems. However, SPGD converges slowly and easily falls into local extremes. Combining adaptive moment estimation and SPGD, we propose the AdamSPGD algorithm for efficient wavefront correction. Theoretical analysis and numerical simulations demonstrate that AdamSPGD can significantly increase the convergence speed, robustness, and dynamic ability, thereby more efficiently suppress the negative effects of atmospheric turbulence on mixing efficiency, bit error rate, and outage probability. Experimental results show that AdamSPGD reduces ∼50% of iterations. The improved performances make the proposed algorithm suitable for SLAO to improve the quality of optical communications.

Networking is an inevitable trend in developing free-space optical communications. The demand for multiple optical terminals to simultaneously establish links with and transmit to a single optical terminal has driven the integration of optical terminals. Phased arrays and rotating parabolic mirrors have been employed for beam control. However, achieving codomain detection of multiple optical spots with a single quadrant detector (QD) remains challenging in integrated detection. This paper proposes a codomain detection method for multiple beacons using a single QD based on pseudorandom code spread-spectrum modulation. This method realizes multiple beacons through code division multiple access (CDMA) by leveraging the orthogonality of pseudorandom sequences. The impact of different spread-spectrum gains on detection sensitivity and accuracy variation law under the interaction of multiple optical spots with different powers is investigated using simulation and experimental verification. The results demonstrate that when the spread spectrum gain is 1023, the detection sensitivity can reach −30 dBm@1 μm. Under conditions of equal-power interaction between two optical spots, the system deviation of position detection is less than ±60 μm, a reduction of 87.8% compared to the ±493 μm disturbance error without using CDMA. Finally, a simultaneous three spots tacking detection system was validated, achieving a detection accuracy of 1 μm, thereby proving the feasibility of CDMA multibeacon detection.

In space laser communication, the wide divergence angle of beacon light leads to substantial spatial losses, compounded by background light and detector noise; this results in compromised precision in the detection of the beacon light position. To solve this problem, a high-precision detection technique and communication composite technology employing a four-quadrant detector (QD) with beacon spread-spectrum modulation are proposed. Pseudo-random sequences (PRNs) are employed to spread the beacon communication spectrum, with the spread-spectrum signal utilized to modulate the intensity of the transmitted beacon light at the transmitter end. At the receiver, QD photocurrent signals are cross-correlated with an identical PRN that is used for modulation. The strong auto-correlation properties of PRNs, which are uncorrelated with noise, enhance the output signal-to-noise ratio (SNR), enabling precise position detection and beacon communication under high-SNR conditions. Theoretical analysis is used to explore the effects of spreading gain on the sensitivity of system detection and the precision of position detection. The experimental results demonstrate that the beacon spread-spectrum modulation scheme effectively detects the position of the light spot. At a received optical power of −37 dBm and spreading sequence PRN depths of 1023, 127, and 31, the root-mean-square error (RMSE) values are 0.983 μm, 2.876 μm, and 7.275 μm, respectively. This corresponds to improvements of 14.96 dB, 10.29, dB, and 6.26 dB compared to direct detection precision (30.811 μm). Additionally, under an identical signal bandwidth, the sensitivity improves by 14.6 dB, 10.1 dB, and 6.4 dB, respectively. The proposed beacon spread-spectrum scheme mitigates the limitations of hardware reception sensitivity and position-detection precision, demonstrating its potential application in high-precision detection in long-distance interstellar laser communication.

To realize the efficient transmission of deep space communication, single photon detection technology is used to overcome the signal attenuation and noise problems in long-distance transmission. To further achieve high-speed single-photon communication, we proposed the pulse sampling on-off keying modulation method instead of the PPM to increase the rate, and introduced the dark counting of the single-photon detector system, and a single-photon detector simulation model is set up to solve the problem of the transmission of the non-return-to-zero code in the single-photon detector. Simulation results show that the pulse sampling technique solves the transmission problem of non-return-to-zero pseudo-random sequence code in a single-photon detector, and its bit error rate is lower than 10E-4 under the condition that the non-return-to-zero code cannot allow good communication. In addition, the relationship between the dark count rate and the bit error rate of a single photon detector is analyzed. Finally, the feasibility of applying pulse sampling to single-photon detector is proved by experiments. The research results are of great significance to the study of single-photon laser communication in deep space.

The predecessor of China Optics was China Optics and Applied Optics Digest, which was founded in 1985. At that time, it was the only retrieval journal in the field of optics in China. At the end of 2008, China Optics and Applied Optics Digest was renamed 《中国光学》的前身是1985年创办的《中国光学与应用光学文摘》，当时是国内光学领域唯一的检索刊物。2008年底《中国光学与应用光学文摘》转型更名为《中国光学与应用光学》期刊，刊载内容突破了文摘的限制，正式成为学术刊物。