In recent years, space laser communication has gradually replaced traditional microwave communication as a key research field in various countries owing to its high-speed transmission rate, excellent anti-interference and anti-interception abilities, and good confidentiality. Quadrature phase shift keying (QPSK) is widely used in space laser communication systems owing to its high spectrum utilization and strong anti-interference ability. Owing to the long-distance transmission of high-speed QPSK optical signals through the space channel, the signal power is severely attenuated, and the signal is therefore amplified at the transmitting node with high power to overcome the loss of long-distance transmission in space. However, the high-power QPSK signals show significant phase degradation under the influence of the fibre optic nonlinear effect inside the transmitting node. To relay the degraded QPSK high-speed optical signals under the premise of meeting the current application requirements, a dual-pumped nonsimplex phase-sensitive amplifier based on a microcavity optical frequency comb is proposed to relay QPSK high-speed optical signals.

A coupled-wave model of signal optical and pump optical phase locking was established (Fig. 2). A numerical analysis was conducted based on this model. Based on the numerical analysis, a QPSK all-optical regeneration and multicast experimental system for a dual-pump non-simplex phase-sensitive amplifier with a microcavity optical frequency comb was designed (Fig. 5). First, a 10 Gbit/s QPSK all-optical regeneration and multicast simulation system was constructed using the VPI simulation platform to carry out a simulation analysis of the experimental system. Then, experimental verification was carried out based on the simulation analysis (Fig. 9), and conclusions were drawn.

The results of the numerical analysis (Fig. 4) show that the pump optical power P_m affects the phase sensitivity fluctuation that and the input relative phase φ_r affects the phase compression effect. By controlling these parameters, the phase noise can be compressed to improve the quality of the signal. Moreover, the results of the VPI simulation analysis show that the three signals have the best integrated performance when the input relative phase is 20° and the pump optical power is 24 dBm [Fig. 7(a) and Fig. 7 (b)]. The phase-sensitive gain fluctuation is approximately 6.1 dB [Fig. 7(c)]. The final results show that the optical signal-to-noise ratio (OSNR) values of the three signals improve by 1.5 dB, 2.1 dB, and 0.6 dB, respectively, compared with the degraded signals when the BER is 10^-3 and the overall performance of the three signals is optimal Fig. 8(e). Additionally, experimental verification based on simulation is carried out. First, the phase-sensitive amplification characteristics are verified by changing the relative phase by changing the pump optical phase. The results show that the signal optical power fluctuates periodically with the change of the relative phase [Fig. 11(a)] and that the phase-sensitive gain fluctuates by approximately 7.5 dB [Fig. 11(b)]. The experimental system is optimized by adjusting the phase of the pump optical within a certain range, and the three signals have the best overall performance when the phase of the pump optical is 90°, with the signal optical and one of the multicast optical signals improving by three orders of magnitude in terms of bit error rate, compared with the phase-deteriorated optical signals. The other multicast optical signal improves by one order of magnitude. When the bit error rate is 10^-3, compared with the phase-degraded optical signal, the receiving sensitivities of the all-optically regenerated optical signal and the two-way multicast optical signal are improved by 1.1 dB, 1.8 dB and 0.4 dB, respectively. Hence, the simulation analysis and experimental verification show that the all-optical regeneration and multicasting scheme designed in this study simultaneously achieves the phase regeneration of QPSK optical signals and wavelength multicasting. Moreover, the performance achieved by the three optical signals is better than that of the original degraded signal.

In this study, a dual-pump nonsimplex phase-sensitive amplifier based on a microcavity optical frequency comb is proposed to relay degraded high-speed QPSK. A coupled wave model of the optical signal and pump optical phase locking is constructed. First, a numerical analysis is carried out, and the results show that the effect of phase regeneration can be optimized by controlling the pump optical power, relative phase, and other parameters. The QPSK all-optical regeneration and multicast experimental system are designed based on these results to regenerate the degraded QPSK high-speed optical signals all-optically and generate two multicast optical signals. The simulation analysis and experimental verification show that the proposed scheme achieves phase compression for phase-degraded signals, improves the signal performance, and simultaneously copies two optical signals containing the same modulation information for multicast output. This scheme significantly improves the quality of transmitted signals and provides an innovative solution for the multiplexing of signals in space networks, thereby providing strong support for the enhancement of the reliability and scalability of future space laser communication networks.