| Underwater wireless communication plays an important role in observing the evolution of underwater species and ecology,exploiting underwater resources and national defense.Underwater wireless optical communication is expected to become the mainstream technology in the future because of its characteristics.To solve the problems such as short propagation distance and limited transmission rate when LED is used as communication light source,and the following research results are obtained:1.The light distribution characteristics of LED light source with Lambert distribution of light intensity are simulated and calculated under the lens and paraboloid spotlight models,and the spotlight optimization scheme is proposed.According to the characteristics of the paraboloid model,for the 3535 package light source,when the device height is 110mm,the optimal diameter is 100mm;for the lens model,by increasing the refractive index of the material,the thickness of the lens,and the curvature of the lens,the light efficiency of the model can be improved;For the paraboloid model,when the diameter of its bottom is 16 times of the diameter of the circular surface light source,the surface light source can be approximately a point light source.2.The visible light communication performance of blue LED with superlattice periods of 6,15 and 32 is studied.The results show that the response frequency of the three samples is 242mhz,292mhz and 282mhz respectively at the driving current of 300mA and-30dB,and the BER of the three samples is 0.0036,0.0020 and 0.0030 respectively at the communication rate of 2.4Gbit/s.The sample with 15 periods of superlattice has the best communication performance.The RSM of GaN(105)asymmetric surface of the three samples shows that the larger the number of superlattices,the larger the relaxation of InGaN Quantum Well on GaN,which is conducive to the improvement of the communication performance of the samples;the SEM of the samples shows that the size of V-shaped pits in the three samples are 103.7nm(6SLs),137.7nm(15SLs),205.0nm(32SLs).The results show that the communication rate of the samples with V-shaped pits is 0.75Gbit/s,while that of the samples without V-shaped pits is 1.05Gbit/s,which further proves the influence of V-shaped pits on the communication performance.Therefore,under the influence of the above two factors,the communication performance of 15 samples with superlattice period under 300mA driving current is the best.3.The visible light communication performance of InGaN/GaN green LED with multiple quantum well periods of 3,4,5 and 6 is studied.The results show that the response frequencies of the four samples are 338MHz,322MHz,320MHz and 304MHz respectively at the driving current of 400mA and-30dB,and the BER of the three samples are 0.0024,0.0029,0033,0.0037 respectively at the communication rate of 2.4Gbit/s.It shows that the communication performance of the sample with small period number of MQW is better.4.The quantum well thickness is 23A,25A,27A and 29A respectively.The results show that when the driving current is 400mA,the response frequencies of the four samples are 322mhz,308mhz,298mhz and 294mhz at-30dB,and when the communication rate is 2.4Gbit/s,the BER of the three samples are 0.0032,0.0035,0.0065 and 0.0136 respectively,which indicates that the lower the QW thickness is,the better communication performance.5.Designed the LED source of underwater visible light communication system.The results show that the communication performance of 27mil chip is significantly better than that of 45mil chip in the short distance(1.2m)high-speed communication environment;in the long distance communication,in order to ensure the transmission distance,the large size of LED array light source should be selected as much as possible enough light energy can be transmitted;the amount of phosphor will affect the optical communication performance of LED,and the color temperature of phosphor white LED should be controlled at about 7000K. |
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