Monte Carlo simulation of laser pulse after underwater propagation

In this paper, we study influences of inherent optical properties (IOP) of seawater and parameters of laser pulse on characteristic of laser pulse after underwater propagation. Besides, achievable transmission distances under different conditions are simulated. Regard single pulse energy, initial duration and far field divergence angle of the transmitted laser pulse as inputs, and energy, temporal and spatial distribution on receive plane as outputs, underwater optical channel can be treated as a linear time invariant (LTI) system. The response of the underwater optical channel to the laser pulse with unit energy, far-field divergence angle of 0 and duration of 0 is impulse response. For different inputs, corresponding outputs are the convolution of the inputs and impulse response. Firstly, by using Monte Carlo method, the impulse responses of the underwater optical channel after transmission under a series of seawater performance conditions are studied. Through convolution, the influences of initial duration and far field divergence angle on temporal and spatial distribution are simulated. Simulation results show that influences of initial duration and far-field divergence angle of transmitted laser pulse are not obvious. And, the effects of IOP of seawater, such as absorption coefficient, scattering coefficient and asymmetry factor, on energy value, temporal and spatial distribution on receive plane are analyzed and compared. At last, according to proposed reasonable receive condition and detection threshold, achievable transmission distance of different parameters of laser pulse and different IOP of seawater are simulated. Simulation results show that, achievable transmission distance depends mostly on IOP of seawater, less on parameters of laser pulse. Simulation results provide a certain reference for underwater optical communication.