相位调制边带失衡问题研究

 高功率激光系统中一般利用相位调制器对单纵模激光进行频谱展宽以避免受激布里渊散射，当后继系统中的滤波器存在中心波长偏差时，则会导致相位调制产生的边带失衡，使光信号出现较为严重的高频起伏。基于前端系统模拟平台对此问题进行了数值模拟研究，结果表明滤波后的高频起伏随滤波器带宽变窄和中心波长偏差增大而加剧。分析表明0.2 nm带宽的滤波器出现0.05 nm左右的波长偏差时，将引起24.3%左右的顶部起伏。实验中根据分析将滤波器带宽从0.2 nm加大到0.4 nm，成功将脉冲顶部起伏从25.2%减小到了4.4%，对前端系统的研制起到了很好的指导作用。

Analysis of the unbalanced sidebands of phase modulation

Phase modulation was always used to prevent stimulated Brillouin scattering(SBS) which could damage the optics such as lenses in high power laser systems.Band pass filters such as fiber Bragg gratings were usually used in the optical fiber amplifiers to restrain the amplified spontaneous emission(ASE).When the phase modulated laser passes the filter,unbalanced sidebands will be caused by the wavelength mismatch between the laser and filter.The result is fast amplitude modulation on the top of the waveform.The problem is discussed and simulated with a simulation software developed by ourselves in this paper.It is obtained that the fast amplitude modulation is worsened with narrower bandwidth and larger wavelength mismatch.With 0.05 nm mismatch for 0.2 nm bandwidth filter,the modulation ratio is about 24.3%.The ratio is optimized to 4.4% by replacing the 0.2 nm filter by a 0.4 nm filter.The results are well used to direct the development of ICF driver front-end system.