The Research Of Free Space Optical Communication System Based On Multiplexing Singular Beams

The free space optical communication(FSO)is a technology that can transmit optical signal in free space and realize bi-direction communication.It is featured by high bandwidth,good security,no spectrum licensing and convenient construction,etc.On the other hand,the singular beam is an important part of modern optics,which consists of orbital angular momentum(OAM)beam based on phase singular and cylindrical vector beam(CVB)based on polarization singular.The orthogonality and infinity of the singular beam can provide a new multiplexing dimension for FSO system,which can improve system capacity and data rate.In this thesis,the ideas,advantages,applications and research progress of FSO system was introduced first.Besides,the generation and detection methods of OAM beam and CVB,as well as the multiplexing and demultiplexing technology was discussed.The recent advances of free space optical communication using singular beam were presented.Utilizing the principle of singular beam,we applied the singular beam based on multiplexing technology to the FSO system,which was combined with audio and video transmission.The audio and video coaxial transmission systems were designed,working at the visible and near infrared frequency bands.The research emphasis was on the implementation principle of the transmitter and receiver.The main contributions of this thesis are as follows:(1)We demonstrated an audio and video coaxial transmission system based on OAM multiplexing.The advantages and disadvantages of using light-emitting-diode(LED)and laser-diode(LD)for optical communication were compared.Then we choose LD as the light source at last.The analog modulation which is easy to implement was used to load the audio signal.The FPGA was used as the digital signal processing module for real-time transmission of image in the optical communication system.And USRP was used as the baseband signal processing module for video transmission.The transmission rate is 100 Mbit/s and the real-time transmission ofimage,text and video was realized in the FSO system.Finally,the audio and video information can be transmitted coaxially through 2 OAM multiplexing beams and restored at the receiver.(2)We demonstrated a video transmission system with CVB multiplexing based on optical transceiver.The optical transceiver was used as a digital processing module in FSO system,which was integrated with WDM system.This integration can save resources,improve system capacity,and finally realize the real-time transmission of monitoring video information based on the surveillance cameraIn conclusion,the FSO system based on singular beam was studied in this thesis,which can transmit the audio and video information in real time.Our study showed that the application of multiplexing and demultiplexing technology based on singular beam can improve the capacity and data rate of FSO system,and thus play an important role in interplanetary communication,in-building communication and underwater communication,etc.