| Optical wireless coherent communication is a wireless transmission optical communication technology that uses the interference principle of light to coherently demodulate the received signal using a local oscillator light source at the receiver end.Compared with intensity modulation/direct detection,it has a detection sensitivity of about 20 dB～23 dB and is more suitable for long-distance laser communication transmission.The existence of atmospheric turbulence limits the development of optical wireless coherent communication technology.Adaptive optics technology can effectively suppress the wavefront distortion caused by atmospheric turbulence by means of the phase conjugate compensation principle.In this dissertation,the adaptive optics technologies are applied to the field of optical wireless coherent communication by taking into account the above research background.The following works are carried out:Firstly,the calibration algorithms(push-pull,Hadamard matrix algorithm)and closed-loop control algorithms(proportional integral differential control,iterative control and fuzzy control algorithm)of adaptive optics are described in detail.An adaptive optics algorithm using the combination of Hadamard matrix algorithm and fuzzy proportional integral differential control algorithm is proposed.The numerical simulation and experimental research verify that the proposed algorithm is superior to the conventional single algorithm combination in the temporal correlation and spatial average of wavefront correction.Secondly,the influence of the wavefront distortion caused by atmospheric turbulence on the coupling efficiency and the power in the barrel is analyzed.According to the basic principle of adaptive optics and the closed-loop control algorithm,an adaptive optics system using a combination of fast steering mirror and deformable mirror is designed to correct the wavefront distortion.The wavefront sensor-less control algorithm and wavefront sensor control algorithm are combined to improve the spatial light to single-mode fiber coupling efficiency by eliminating the non-common optical path aberration.Thirdly,one technology for rapid acquisition,pointing and tracking of light beams using a two-dimensional mirror is proposed.The transmitter end uses camera calibration,and the receiver end uses a two-dimensional mirror to achieve rapid alignment of the non-common axis of light beam.The conventional common axis alignment of the transmitter end and the receiver end is transformed into a non-common axis alignment controlled independently by the transmitter end and the receiver end.The communication links with a distance of 1.3 km and 10.3 km/have been tested in the field.Fourthly,data measurement and data analysis are carried out for the field experiments of optical wireless coherent communication system at different distances of 600 m,1.3 km,4.5 km,10.2 km and 100 km taking the lead at domestic,and the system performance is evaluated in terms of the far-field and near-field facula,wavefront equiphase surface,intermediate frequency signal,baseband signal,etc.to verify that adaptive optics technology can effectively compensate for wavefront distortion and improve the performance of optical wireless coherent communication.The optical wireless coherent communication system independently developed in this dissertation has a detection sensitivity up to-47 dBm,which can realize uninterrupted video transmission by controlling the carrier frequency drift to not exceed 2 MHz.Combined with adaptive optics technology,with the closed-loop control,the coupling efficiency from spatial light into single-mode fiber in the turbulent environment can be improved by nearly 20%.The work of this dissertation provides a more extensive theoretical and experimental basis for the application of optical wireless coherent communication in more distant,adaptive optics in different scenes. |
PDF Full Text Request