摘要
针对无线光通信存在光束对准耗时长的问题,提出一种发射端采用图像跟踪,接收端采用二维反射镜控制的光束快速对准方法。依据几何光学理论计算了激光经二维反射镜后出射的扫描轨迹,并在无线光通信强度调制/直接检测系统上开展实验。实验结果表明:当通信距离为1.3km时,光斑型心在x(y)方向的方差由跟踪前的12.5734pixel^(2)(5.1393pixel^(2))降至跟踪后的2.2770pixel^(2)(1.3697pixel^(2)),探测器输出电信号的幅值为92.4mV;当通信距离为10.3km时,光斑型心在x(y)方向的方差由跟踪前的18.8653pixel^(2)(10.5290pixel^(2))降至跟踪后的14.4970pixel^(2)(8.0287pixel^(2)),探测器输出电信号的幅值为74.4mV。所提方法无需将控制信号由接收端回传至发射端,在快速建立下行链路的同时即可实现上行链路的建立。
Objective When the laser signal is transmitted through the atmospheric channel,the fluctuation of atmospheric refractive index caused by atmospheric turbulence causes beam expansion,beam drift,and wavefront distortion,which harms the reception of the optical signal and even leads to the interruption of communication in severe cases.In a wireless optical communication system,the gaze-gaze,gaze-scan,and skip-scan are used to achieve the coaxial alignment of the beam between the transmitting and receiving antennas,which increases the preparation time of system communication.In practice,a fast acquisition,tracking,and alignment mechanism must establish links.The wireless optical communication system’s coaxial alignment demands that the optical axis of the transmitting and receiving antennas completely coincide in space.The detector must return the measured parameter data to adjust the transmitting antenna to keep the beam stable coarse alignment for a long time and fine alignment on this basis.Atmospheric turbulence affects long-distance data return and position adjustment,making the traditional long-axis beam alignment process uncertain.In this paper,an acquisition tracking and pointing system with independent transceiver control is developed.The transmitter calibrates and tracks the target position by the calibration camera to realize the course alignment of the beam;at the receiving end,a two-dimensional mirror is used to control the position as the spot center feedback,suppress the atmospheric turbulence,and realize the fine alignment of the beam.The non-common sight axis control avoids the inconvenience of transmitting control instructions from the receiving end to the transmitting end,and it is not necessary to use a space stable platform for the moving base,which greatly facilitates the promotion of wireless optical communication.Methods Fig.1(b)shows the wireless optical communication using a two-dimensional mirror-assisted alignment.The system comprises the calibration coarse alignment from the transmitting antenna to the two-dimensional mirror and the minor axis fine alignment from the two-dimensional mirror to the receiving antenna.The coarse alignment from the transmitting antenna to the two-dimensional mirror is directly positioned and calibrated by the calibration camera at the transmitting end,and the transmitting antenna is adjusted with the image as feedback;fine alignment from the two-dimensional mirror to the receiving antenna is adjusted by the two-dimensional mirror based on the detector feedback information at the back end of the receiving antenna.As the calibration coarse alignment and minor axis fine alignment can be operated at a single end,the calibration alignment at the transmitting end does not require data return.Fig.4depicts the construction of a wireless optical communication IM/DD system that uses a two-dimensional mirror to achieve rapid alignment.The transmitting end loads the source by intensity modulation,and the output is collimated by the transmitting antenna.To complete the initial calibration,the aiming platform at the transmitting end and the calibration camera connect with the two-dimensional mirror at the receiving end,so that the beam completely covers the two-dimensional mirror at the receiving end,thus,adjusting the two-dimensional mirror to align the reflected beam coaxial with the receiving antenna.The parallel light emitted by the receiving antenna passes through the optical prism is divided into two beams.The focusing lens converges to one of the beams,which is coupled into the photosensitive surface of the photodetector for system communication;the other beam is focused,and the infrared camera detects the spot position in real-time to complete the beam tracking.Results and Discussions After course alignment,the beam is tracked based on the relative deviation between the calibration point and the imaging coordinate position of the two-dimensional mirror.Fig.7shows the beam course tracking curve of the position coordinate of the two-dimensional mirror under the 1.3km experimental link,in which the pitch and azimuth angles are adjusted twice and once in four hours,respectively.The beam drift is caused by atmospheric turbulence;the gravity subsidence and mechanical vibration of the optical-mechanical structure makes frequently adjusting the coarse alignment in a short time unnecessary.Fig.10shows the 1.3km beam-tracking curve,the corresponding time-domain waveform,and power spectral density estimation.The step angle of the two-dimensional mirror is adjusted to 10.92μrad.With the increase of the iteration numbers,the center of the spot is gradually adjusted from the first quadrant of the detection surface to the center.After tracking,the variations of the spot centroid at the center of the camera in the x and y directions are 2.2770and 1.3697pixels^(2),respectively.The time required to perform one closed loop is 0.05s,which is sufficient to compensate for the drift rate of the spot.Fig.14shows the bidirectional alignment experiment for a 10.3km wireless optical communication link.After the beam emitted by the laser reaches the receiving end through atmospheric turbulence,the two-dimensional mirror at the receiving end is adjusted to reflect the beam to the receiving antenna.The detector at the receiving end can detect the source information from the transmitting end after converging by an antenna and focusing lens.Laser B emits a light beam at the focus position of the receiving antenna,which is reflected by the two-dimensional mirror and reaches the transmitting end through atmospheric turbulence.To achieve the two-way alignment of the light beam,the antenna and the focusing lens at the transmitting end converge the light beam,and detector B can detect the source information transmitted by the receiving end.By adjusting the two-dimensional mirror at the receiving end,the beam alignment from the receiving to the transmitting end can be accomplished while completing the entire alignment from the transmitting to the receiving end because the optical path is reversible.Conclusions This study presents a method for achieving rapid beam alignment using image calibration at the transmitting end and a two-dimensional mirror control at the receiving end,thus,addressing the problem of long timeconsuming beam alignment in traditional wireless optical communication.The image calibration coarse tracking at the transmitting end can ensure that the spot effectively covers the two-dimensional mirror,and the coupling spot coarse tracking at the receiving end can effectively suppress the beam drift caused by atmospheric turbulence;the uplink can be established simultaneously with the downlink.The non-common sight axis control avoids the inconvenience of transmitting control instructions from the receiving end to the transmitting end,and it is not necessary to use a space stable platform for the moving base,which greatly facilitates the promotion of wireless optical communication.
作者
杨尚君
柯熙政
吴加丽
刘旭光
Yang Shangjun;Ke Xizheng;Wu Jiali;Liu Xuguang(School of Automation and Information Engineering,Xi’an University of Technology,Xi’an 710048,Shaanxi,China;Shaanxi Civil-Military Integration Key Laboratory of Intelligence Collaborative Networks,Xi’an 710048,Shaanxi,China;School of Physics and Telecommunications Engineering,Shaanxi University of Technology,Hanzhong 723001,Shaanxi,China;Department of Communication Engineering,School of Automation and Information Engineering,Xi’an University of Technology,Xi’an 710048,Shaanxi,China)
出处
《中国激光》
EI
CAS
CSCD
北大核心
2022年第11期95-108,共14页
Chinese Journal of Lasers
基金
陕西省科研计划项目(18JK0341)
陕西省重点产业创新项目(2017ZDCXL-GY-06-01)
西安市科技计划项目(2020KJRC0083)。
关键词
光通信
光束扫描
捕获跟踪对准
二维反射镜
optical communications
beam scanning
acquisition tracking alignment
two-dimensional mirror
