Research On Optical Beam Forming System And The Applications Of RF Orbital Angular Momentum

With the rapid development of digital media,dense coding and channel sharing techniques can no longer meet the growth of communications in radio band,while the proposal of MIMO can relieve the pressure of information explosion largely.Microwave photonics,as a new branch of science in telecommunications,can effectively improve channel capacity in transmitting and processing microwave signals,by utilizing the unique advantages of low loss and large bandwidth of optical system.As one of the main research contents of microwave photonics,the optical controlled beam forming technology combines the multi-antenna technology of MIMO system,which ensures that the high-speed broadband signal processing can be effectively applied in the existing communication and radar systems.Therefore,the technology of optical controlled beam forming has become a research hotspot.In addition,the radio frequency beam with orbital angular momentum(OAM),resulted from optical controlled beam forming system,has a broad prospect in applications of microwave communications,phased array radar and multi-dimensional detection.At present,the complete optical controlled beam forming system mainly consists of three parts.The first part is the optical controlled delay or phase shift module,which is used to generate and control the beam forming.Meanwhile,special beam forming effects such radio frequency OAM are also produced in this part.The second part is the antenna array.The function of beam forming is realized by radiating signals with the relations of delay and phase from the antenna array.The last part is the driving module of photoelectric conversion between the above two parts.It is working to improve the system efficiency and offsetting the link errors in photoelectric conversion.The first two parts are the core techniques of the system.Therefore,the principle and structure of the optical controlled beam forming system are deeply studied in this paper.A new design scheme is proposed,and the applications of OAM beams is verified in experiments.The main innovations in this dissertation are listed as follows.1.A scheme of phase shift and time delay is proposed with photonic integration technique.Time delay and phase shift can be realized simultaneously with a chip incorporating array waveguide grating(AWG)structure,which is appropriate in beam forming and OAM applications.The time delay can be obtained in a 12.5 ps range,and a 0 to 360 °continuous phase shift can be implemented with a 12 to 20 GHz signal.The RF OAM beam generated in this system is simulated and analyzed.2.A new transmission mode of coupled OAM beams is proposed.It can be found that when OAM beams couple in the positive and negative states,the signal precisions of OAM beams are improved.The requirement of the antenna amounts is released in this transmission mode.A contrast experiment of two modes has been made,and the OAM beams are demodulated with the same conditions.Experimental results show that the power of coupled OAM beam is increased by 3dB,and the signal-to-noise ratio is also improved.3.A new type of patch antenna is designed for the optical controlled beam forming system.The antenna is designed with multi-layer structure,which combines aperture coupling and inset feeding.Simulation results show that the antenna can effectively improve the bandwidth from 2%to 5%.The design can work in multiple frequency bands.In addition,the antenna array can be formed and applied in RF OAM beam control system easily.4.The measurement of angular velocity is realized with radio frequency OAM beams.In this experimental scheme,a method called"accumulation amplification"is proposed to measure the frequency offset and obtain the angular velocity of the object.Till now,most of detections with OAM beam are achieved in optical domain.The rotational Doppler effect of OAM beam is used to measure the rotational velocity of spinning object.The Doppler frequency shift can be measured directly in optical OAM system through a photodetector.However,there is no corresponding devices in RF system.In order to solve this problem,I set up a relationship between the spatial phase of OAM beam and the Doppler frequency shift using"accumulation amplification".In the RF OAM detection system,the frequency shift is successfully measured.The rotational velocity of the obj ect is calculated.