Research On Fresnel Lens Applied In Underwater Optical Communication

With the development of laser technology, underwater wireless opticalcommunication technology has become a hotspot in recent years. It owns advantages ofsmall transmission delay, high speed data transmission and low influence from theenvironment, which can be applied in many fields such as underwater submarinecommunication, ocean environment monitoring and underwater autonomous.In the sea water, the optical signal detection can be affected hardly by theattenuation of the laser, due to the absorption and scattering of the sea water for laser.Reflection structure optical receiving system was usually used in wireless opticalcommunication to increase the communication distance and reduce the data error rate.Reflection optical antennas are always with large volume, large weight, complexstructure and high cost. In this paper, the underwater optical communication usingFresnel lens as the receiving antenna was presented. The Fresnel lens was designed andanalyzed theoretically. The parameters of received laser signal spot focused by Fresnellens was simulated for underwater optical communication. The experimentalmeasurement was consistent with theoretical analysis. The results prove that Fresnellens owns advantages of broad width, short focal length, small thickness, light weight,small volume and low cost, which used as receiving system for underwater opticalcommunications. The main contents were organized as following.The characteristics of the communication channel was introduced and analyzed.The absorption and scattering properties of the sea water were theoretically calculated,and its fitting curves were given in this paper. The laser scattering properties of the seawater were simulated by software Lighttools. The Fresnel lens was designed to meet therequirements of the optical receiving system. The parameters of lens angles werecalculated, and the secondary condenser was designed to obtain further focus spot. Andthe convergence effect was analyzed.The Fresnel lens model was established usingSolidworks according to the preset parameters, then the model was imported intoLighttools. The focus ability of sunlight and monochromatic light were rspectivelysimulated by Lighttools. The aberration of Fresnel lens was analyzed. The seawaterscatteering body model was established in Lighttools, and Fresnel lens’ focus light fieldof the scattered532nm laser was situlated in the seawater scattering body. According tothe structure of Fresnel lens and the results of the scattering simulation, analysis of thelight loss of Fresnel condenser and the factor of impact on underwater wireless opticalcommunications concentrator optical efficiency receiving. Experiments were conducted by using Fresnel lens as a receiver to study the underwater optical transmission inlaboratory and offshore sea at Weihai respectively. The receiving spots of differenttransmitting distance were measured, and three-dimensional energy distributions ofreceiving spots were analyzed. Experimental results are consistent with theoreticalanalysis, which verified Fresnel lens can be utilized as the receiving antenna ofunderwater optical communication system.