Objective Pulse position modulation, which is a modulation method obtained from the onoff keying (OOK) after encoding, has the characteristic of a high energy efficiency ratio, which increases peak optical power by reducing the duty cycle to overcome the adverse effects of factors such as atmospheric turbulence and dark counts on the signal. It also increases the signaltonoise ratio, giving it better channel interference immunity, which is important in a wide range of applications in atmospheric and even deepspace optical communications. In pulse position modulation communication systems, classical receivers usually use direct detection to detect pulse position modulated signals, and their bit error rate (BER) performance is limited to the standard quantum limit (SQL). However, in quantum theory, their counterparts, which can obtain more information than classical communication systems, increase the BER performance to the Helstrom limit. However, there is a lack of relevant studies on the effects of practical factors on the BER performance of pulse position modulated quantumenhanced receivers. In this study, we analyze the effects of the main practical factors, interference visibility, dark counts, and detection efficiency on the BER performance of a single pulse position modulated joint detection quantumenhanced receivers based on 4 -PPM (PPM, pulse position modulation) signal modulation. We also provide a theoretical reference for the subsequent development of quantumenhanced receiver design and experiments.Methods First, the structure of the joint detection quantumenhanced receiver system for pulse position modulated signals is introduced. Second, a decisiontree model of the corresponding feedback control strategy is established, from which the theoretical BER performance of the joint detection quantumenhanced receiver is obtained. Then, the effects of practical factors such as interference visibility, dark counts, and detection efficiency on the system performance are analyzed by Monte Carlo simulation and compared with SQL, the Helstrom limit, and the ideal performance of the receiver to determine the influence mechanisms of various practical factors.
Results and DiscussionsThe simulation results show that as the average number of photons increases, the nonideal interference visibility causes the bit error to first decrease and then increase, and its minimum point value is positively correlated with the interference visibility (Fig. 3). The existence of dark counts causes the bit error rate to converge to a fixed value, which is a monotonically decreasing function of dark counts (Fig. 4). Moreover, the nonideal detection efficiency causes the bit error rate to decrease exponentially and the deceleration rate to increase with the detection efficiency (Fig. 5).
ConclusionsIn the experiment, by adjusting the moderate numbers of average photons of input signals and the intensity and polarization of the local oscillator to obtain high interference visibility, and applying the single photon detector with high dete...
