Study On Free Space Optical Communication By Supercontinuum Carriers

Free Space Optical Communication(FSO)is a wireless communication method in which a space atmosphere is used as a communication channel and a laser is used as a carrier to transmit information in an atmospheric channel.It is considered as the “last mile” solution.Compared with traditional RF communication,it has the advantages of wide spectrum transmission capacity,strong anti-electromagnetic interference capability and good confidentiality,compared with traditional optical fiber communication.It has the advantages of small size,easy deployment,and no environmental impact.It can be used as an emergency communication solution for disaster relief.Free-space optical communication has great application prospects in the stars and inter-satellite links.However,the intensity of light caused by atmospheric turbulence has always been a major obstacle to the development of long-distance high-speed transmission of free-space optical communications.There are many ways proposed to mitigate the effects of atmospheric turbulence,such as spatial diversity,aperture averaging,adaptive optics,channel coding,and the use of partially coherent beams.Among them,many theoretical calculations and numerical simulations show that part of the coherent beams is less affected by turbulence than the coherent light source in the atmosphere,and it can also reduce the light intensity scintillation index more effectively.At the same time,the supercontinuum has partial coherence characteristics under certain conditions.This thesis mainly studies the high-speed transmission of optical information in the atmosphere by using the supercontinuum as the carrier with its partial coherence characteristics.According to the characteristics of supercontinuum,combined with the experimental simulation results,the supercontinuum source suitable for atmospheric transmission is selected.And compare traditional coherent light sources,compare communication performance,minimum sensitivity,scintillation index and so on.The research results mainly include the following aspects:i.The mode-locking mechanism of the pump source for supercontinuum generation is elaborated,and two common mode-locking mechanisms are listed.The comparative analysis selects the mode-locked light source suitable for the experiment.ii.A detailed theoretical analysis of the characteristics and generation of supercontinuum is carried out.The effects of nonlinear effects and dispersion on the broadening of supercontinuum spectrum are introduced in detail,and the relevant simulation results are confirmed by experiments.At the same time,pumping light sources with different wavelengths and powers are used to pump the highly nonlinear fiber and dispersion-shifted fiber,and a supercontinuum source with partial coherence characteristics is selected as the experimental transmission source.iii.The scintillation index generated by the supercontinuum source and the coherent source in the same atmospheric turbulence channel are compared.The experimental measurements are made.It is concluded that the partially coherent beams based on the supercontinuum carrier can effectively reduce the scintillation factor 25%~41%.And variables that affect the scintillation factor of the supercontinuum source transmitted in the atmospheric turbulence channel,such as coherence and transmission wavelength,and means of transmission.