本文选用蓝绿波段激光作为载波，研究了跨介质光无线通信系统中的关键技术，并从调制和编码角度对系统误码率进行优化。首先，根据信道的光学传输特性对跨介质光无线通信的三个信道——水下信道、大气信道和海气界面建模。本文对海气界面选用海面坡度分布和三维模拟海面两种建模方式。三维海面主要是利用基于经验观测的海面方向谱来描述，通过将海面看作多个余弦波的叠加来反演海面，很好的模拟了三维海面在时空中的高度分布。根据水下和大气的光学特性，将水下信道看作衰减信道，光线在大气中直线传输。其次，通过蒙特卡洛仿真了接收平面的光强分布。对大量光子进行追踪统计，分析风速、发射器倾斜角、时间变化、水下传输距离对接收平面光强分布的影响，主要包括光斑中心的偏移和光斑半径的变化。不同风速下，光斑中心的偏移不明显，光斑半径会随着风速的增大而增大；发射器倾斜角的增大会造成光斑中心的偏移和半径的增大；光斑中心和半径随时间的变化不明显；随着水下传输距离的增大，光斑半径增大，光强减小明显。最重要的是，在海面处发生全反射时，大部分光子无法到达接收平面，导致信号中断。最后，本文对光信号在海气界面处发生全反射的情况进行了分析。在一般海面条件下，风速为15 m/s，发射器倾斜角为30°时，中断概率高达5.62%，平均中断时间为0.294 s。全反射给通信带来的影响不容忽略，因此本文将采用脉冲位置调制和喷泉码来消除全反射的影响。在海面处，6-PPM对误码率的优化效果与其他调制方式对比更为明显。但是优化效果有限，特别是在风速较大时，误码率仍高达5-6%。采用喷泉码，只需要在接收端接收到足够的编码符号即可恢复源信息，与丢失信号的数量和内容无关，因此非常适用于擦除信道。本文分析了喷泉码在不同编码冗余和译码开销情况下的性能，编码冗余为1.4时，译码开销为1.2，此时能实现误码率为的通信。本文工作重点集中在海面处光学特性的分析，特别是全反射对通信质量的影响。并采用脉冲位置调制和喷泉码对系统误码率进行优化，选取合适的编码冗余和译码开销，能起到明显的优化效果。

In this paper, the blue-green laser is selected as the carrier to study the critical technologies in the air-water optical wireless communication system and optimize the bit error rate of the system from modulation and coding. Firstly, three channels of optical wireless communication across the medium: underwater channel, atmospheric channel, and sea surface, are modeled according to their optical transmission characteristics. In this paper, two modeling methods of the sea surface, slope distribution and three-dimensional simulation of the sea surface, are selected for the air-water interface. Three-dimensional sea surface is described using the sea surface direction spectrum based on empirical observation. The sea surface is inverted by taking the sea surface as the superposition of multiple cosine waves, which simulates the height distribution of the three-dimensional sea surface in space-time. According to the optical characteristics of underwater and atmospheric, the underwater channel is regarded as an attenuation channel, in which the light transmits in a straight line in the atmosphere. Secondly, the intensity distribution of the receiving plane is simulated by Monte Carlo. A lot of photons were tracked and statistically analyzed to analyze the influences of wind speed, emitter inclination Angle, time variation, and underwater transmission distance on the light intensity distribution of the receiving plane, including the shift of spot center and the change of spot radius. Under different wind speeds, the shift of the spot center is not apparent, and the radius of the spot will increase with the increase in wind speed. The rise in the emitter inclination Angle will lead to the deviation of the spot center and the radius increase. The change of spot center and radius with time is not apparent; With the rise of underwater transmission distance, the spot radius increases, and the light intensity decreases. Most importantly, when there is a total reflection at the sea surface, most of the photons cannot reach the receiving plane, causing the signal to be interrupted.Finally, the total reflection of the optical signal at the sea surface is analyzed. When the wind speed is 15 m/s, and the inclination angle of the transmitter is 30°, the interrupt probability is as high as 5.62%, and the average interrupt time is 0.294 s. The influence of total reflection on communication cannot be ignored, so this paper will use pulse position modulation and fountain code to eliminate the influence of total reflection. At the sea surface, the optimization effect of 6-PPM on the bit error rate is more evident than in other modulation methods. However, the optimization effect is limited, especially with a large wind speed. The bit error rate is still as high as 5-6%. Using fountain code only needs to receive enough coded symbols at the receiving end to recover the source information. It has nothing to do with the amount and content of lost signals, so it is very suitable for erasing channels. This paper analyzes the performance of fountain code under different coding redundancy and decoding cost. When the coding redundancy is 1.4 and the decoding cost is 1.2, communication with a bit error rate can be realized.This paper focuses on analyzing optical properties at the sea surface, especially the effect of total reflection on communication quality. Furthermore, pulse position modulation and fountain code are used to optimize the bit error rate of the system, and the appropriate coding redundancy and decoding cost can achieve an obvious optimization effect.