Study On Transmission And Communication Characteristics Of Ince Gaussian Beam In Ocean Channel

With the development of ocean space information network,massive data transmission between nodes has put forward great requirements for underwater communication technology.Underwater Optical Communication had attracted more and more attention because of its advantages such as high transmission rate,large communication capacity and good security.However,the complex environment of ocean channel,especially the ocean turbulence effect,seriously damaged the beam structure and reduced the communication quality.Aiming at the problems of optical communication transmission and communication deterioration in complex ocean environment,the scientific community used special beams and spatial diversity to improve the transmission and communication performance.Ince-Gaussian(IG)beams with anti-turbulence ability had become one of the research hotspots recently.In order to improve the optical communication performance in the ocean complex channel environment,a series of studies were carried out based on IG beams,including theoretical basis of laser ocean channel transmission,modeling and simulation of IG beams ocean turbulent channel transmission and communication,IG beams generation principle and experimental study,IG beams ocean channel transmission experimental study,focusing on its performance in the ocean turbulent channels.Specific research contents are as follows:1.The basic theories of laser ocean channel transmission,including ocean absorption,sea water scattering and ocean turbulence channel theoretical models were studied.On this basis,common laser ocean turbulence channel transmission methods,including Rytov approximation,generalized Huygens-Fresnel principle and random phase screens method,were compared and studied.The application scope and difference of various methods were analyzed.2.The transmission and communication characteristics of IG beams in ocean turbulence channel were simulated.Firstly,the transmission model of IG beams and HIG beam in ocean turbulence channel was constructed based on random phase screens method and power spectrum inversion method.On this basis,the relationship between related parameters(transmission distance,turbulence intensity)and performance indexes(scintillation index,centroid drift,overlap and bit error rate)was analyzed.Then the influence of HIG beam parameters on transmission and communication performance was optimized.The results showed as follows: 1)IG beams and HIG beam had better anti-turbulence ability at different distances,and HIG beam had more significant advantage.2)With the increase of ocean turbulence intensity,the transmission and communication performance of HIG beam decreased gradually.Compared with Gaussian beam,the improvement ability of HIG beam was weakened.3)The ellipticity,order and degree of HIG beam had optimal performance values,and the order was the most sensitive.3.The generation principle and experimental method of IG beams were explored.Firstly,the generation methods of IG beams were compared and analyzed,and the evolution of the light intensity of IG beams generated by Liquid crystal spatial light modulator(LCSLM)was calculated based on the diffraction principle.Then the experimental platform was designed and constructed,and the phase grayscale maps were constructed by shining grating,and IG beams with controllable parameters were generated.On this basis,Partially coherent Ince Gaussian(PCIG)beams were generated by Rotating ground glass disk(RGGD).Finally,IG beams modulated square wave signal were generated by signal generator.The results showed that: 1)The intensity distribution of IG beams with different parameters generated by LCSLM was in line with expectations.The generated HIG beam was basically in line with expectations.2)PCIG beams could be generated by RGGD,and PCIG beams with different coherence degrees could be obtained by adjusting the position of RGGD.The coherence of partially coherent beams decreased as the distance between RGGD and the common focus of the lens group increased.Due to the diffusion action of ground glass,the size of the spot increased continuously.3)The IG beams modulated square wave signal of 0.5～5MHz could be generated by the signal generator.When the modulation frequency reaches 3MHz,the calculated Waveform distortion degree was 22.4%.When the modulation frequency was4 MHz or above,the Waveform distortion degree was serious,the Waveform distortion degree reached and exceeded 28.7%.In order to reduce the influence of the performance of the laser itself on the results in the subsequent experiments,the modulation frequency was set to0.5～3MHz in the subsequent experiments.4.The transmission characteristics of IG beams in ocean channel were studied experimentally.On the basis of simulation,the experimental platform of IG beams transmission in simulated ocean environment was designed and built by using materials such as water tank,water drawing pump,hot water and salt.The scintillation index,centroid drift,power jitter and modulation signal waveform distortion of IG beams and Gaussian beam in different ocean channel environments were experimentally studied,especially in ocean turbulent environment.The results showed as follows: 1)Compared with Gaussian beam,IG beams showed advantages in scintillation index,centroid drift and power jitter performance in different intensity ocean turbulence.With the increase of ocean turbulence intensity,the transmission performance of IG beams improvement ability was partially enhanced: the scintillation index and centroid drift improvement ability were enhanced,while the power jitter improvement ability was weakened.When the water temperature increased from 40.1℃to 60.2℃,the performance advantage between IG beams and Gaussian beam scintillation index increased from 15.5% to 21.8%,between centroid drift increased from 11.6% to 18.3%,but the performance advantage between power jitter variance decreased from 12.9% to 3.7%.2)With the increase of modulation frequency and turbulence channel intensity,the waveform distortions of IG beams were lower than that of Gaussian beam due to the multipath delay effect caused by scattering,while the improvement ability of waveform distortion decreased.At the modulation frequency of 3MHz,when the water temperature increased from 40.1℃to 60.2℃,the performance advantage between IG beams modulation square wave signal waveform distortion and Gaussian beam waveform was reduced from 6.3% to 5.6%.The overall variation trend of the measured data was consistent with that of the simulation results,which can verify the superiority of IG beams in the ocean channel,especially in the turbulent channel.