光波束形成中色散延时的非线性修正

Nonlinear modification of dispersion delay for optical beam forming

光波束形成网络是光控相控阵雷达中的重要组成部分,有助于提升系统的宽带宽角扫描能力。利用光开关的切换,改变各收发通道间的相对延时量,从而实现波束指向的变化。在常用的技术中,色散延时是一种简洁的光波束形成实现方法,而色散线性项仅适用于色散量小且通道数少的情况。随着延时量的增加,非线性色散延时积累,会引起波束畸变。因此引入相对色散斜率(RDS)作为其非线性因子,并通过调整商用激光器波长来抵消色散介质的非线性效应。当RDS为0.003 nm^(-1)时,激光器阵列的最大波长间隔从0.796 nm "拉伸"到0.862 nm,波长也整体"平移"-0.31 nm,修正波长与商用激光器波长的最大调整量为0.2 nm,可满足商用波分复用器的通带带宽,大扫描角时主瓣与副瓣之比从5 dB提升至12.9 dB。通过分析,RDS数值越小,激光器波长的修正量越小。因此,RDS是选择色散介质和调整激光器波长的重要参数,从而能够恢复波束畸变,以提升相控阵系统的成像、识别能力。

Optical beam forming network is an important part in optically controlled phased array radar,which could improve the beam scanning ability with large bandwidth and direction angle.The direction of beam is usually controlled by optical switches to change relative delay of transmitting and receiving channels.Among commonly-used techniques,dispersion delay is a concision way to realize optical beam forming network.Linear dispersion is only applicable to beam forming with limited dispersion delay and channels.With the increase of delay,nonlinear dispersion delay accumulates,which distorts the beamform.Therefore,relative dispersion slope(RDS)was used as a nonlinear factor.Moreover,adjusting wavelengths of commercial lasers was raised to compensate the nonlinearity.If RDS was 0.003 nm^(-1),the maximum wavelength interval stretched from 0.796 nm to 0.862 nm and wavelengths shifted-0.31 nm.In this case,maximum difference between modified and commercial laser wavelengths was 0.2 nm,which was suitable for the passband of commercial wavelength division multiplexing devices.In the meantime,ratio of main to side lobe improved from 5 dB to 12.9 dB with large scanning direction.Based on the analysis,the smaller RDS value was,the less wavelengths modifications of lasers were.Therefore,RDS is a key parameter in choosing dispersion material and adjusting wavelengths of lasers.In this way,distorted beamform could be recovered.The abilities of imaging and identifying thus could be improved in phase arrayed systems.