Study On The Performance Improvement Of OAM-Based FSO Communications

As mobile communication and net technologies are on the mosquito boat of progress,the demand of data rate has tended to be increasingly high.Optical communication possessed high data rate transmission can be assimilated into the development of the main trend,and has turned into a principal support of the current transmission network,occupying a leading position in the market.Optical communication is composed of wired and wireless.The former is also described as optical fiber communication.While the latter,is known as free space optical communication(FSO)in virtue of its wireless form.Contrasted with the former,FSO owns a range of advantages such as wide bandwidth,and robust anti-interference,etc.To date,FSO has been broadly employed for multi-user LAN extension,emergency communications and interstellar laser communication field.Human society sets an even higher demand on FSO technology,whilst enjoying the huge convenience provided by information network.Within the scope of the field covered by FSO,a new multiplexing dimension has emerged with an astonishing pace,known as orbital angular momentum(OAM).FSO technology augmented with OAM can be tipped to realize the promotion of channel capacity and spectral efficiency.Hence,OAM has given rise to the extensive attention from researchers.The FSO channel is a complex time-varying channel.When the vortex beam carrying OAM is transmitted in the FSO channel,the suspended aerosol particles in which will change the propagation characteristics of the vortex beam.Then the existence of turbulence will destroy the spiral structure of the wave-front.Ultimately,the steadiness and security of communication will be influenced diametrically.For this reason,the pivotal issues have focused on researching the communication performance of vortex beams transmitted through FSO channels.According to the existing research progress,we found that the great majority of investigation bound up with the performance of the OAM-based FSO link is carried out under short-distance experimental conditions,with few theoretical research results.However,the achievable communication distance under experimental conditions is extremely limited,and the conclusions drawn are only applicable to specific experimental system configurations,which cannot be deduced by general laws.Consequently,it is highly pressing to set up an integral system architecture from a theoretical perspective to investigate the performance of OAM-based FSO communication systems.On this basis,we propose the scheme of using coherent beam combining(CBC)technology to improve OAM system links characteristics and application scope.This scheme furnishes theory fundamental and technical support for system devising and performance appraising of OAM link in turbulent environment.Thus,this paper conducts research from two aspects.We set out from an OAM based coherent detection system design.This system framework aims for theoretically analyzing the error performance of the traditional single vortex beam under the turbulence environment.Specifically,under the condition of M-ary Phase-Shift Keying(MPSK),we give the analytical expression of symbol error probability(SEP).Following by investigating the impact of various beam,channel and receiver parameters on SEP.Then,CBC technology can generate high-power vortex beams.Using CBC technology,based on different parameters,we researched the propagation properties of generated high-power vortex beams in depth.In addition,the feasibility of improving OAM system link characteristics and further enhancing FSO performance is explored.