Research On Laser Optical Signal Temporal Spreading Through Inferior Atmospheric Layer

Free space optical communication system has quick architecture with its equipment, high capacity, high security and many other characteristics much better than optical fiber communication systems that it becomes an international research focus. Horizontal link laser optical communication system uses laser propagating through the atmosphere to communicate, its communication performance is influenced largely by the atmosphere, because the laser signal will be affected in the way of the energy attenuation and broadening occurred in the time domain and so on. The free space optical communication system's further communication rate enhanced is restricted by the laser signal broadening in time domain. Free space optical communication systems generally use the IM/DD or DPSK phase modulation methods to communicate, under which modes the laser signal broadening in time-domain caused by the atmosphere were also different. Therefore, it is of great importance to study the impact of the laser signal broadening in time-domain caused by the atmosphere.In this paper, we do the research on effects of the horizontal link of laser communication signal's time-domain broadening caused by atmosphere. Monte Carlo simulation method is used to simulate the transmission of the laser signal in the horizontal link, and simulations are carried out respectively in pulse-width modulation and phase modulation. After that we discuss the parameters such as the transmission distance, the concentration of aerosol particles, the beam divergence angle on the signal broadening.Research works are done by the following aspects:1. Analyze the details of time-domain broadening of the laser signal generated by atmosphere, discuss the mechanism respectively in IM/DD mode and DPSK phase modulation mode.2. In the design of Monte Carlo algorithm of the laser signal broadening in time domain, we improve the previous calculation of photon free path length, using a normal model of scattering coefficient as random volume instead of a fixed value to calculate each photon path length.3. Implement Monte Carlo simulation of the laser signal broadening in time domain in IM/DD mode, and analyze parameters such as the transmission distance, the concentration of aerosol particles, beam divergence angle on the laser signal time-domain broadening respectively. 4. Implement Monte Carlo simulation of the laser signal time-domain broadening in DPSK phase modulation, and analyze parameters such as the transmission distance, the concentration of aerosol particles, beam divergence angle and the receiving aperture on the laser signal time-domain broadening respectively.This research work has the instructible value to the design and optimization of horizontal link laser optical communication system.