适合于有线电视系统的色散补偿光纤光栅

Dispersion Compensation Fiber Gratings Suitable for CATV Systems

分析了光栅色散抖动对有线电视信号的影响 ,估计出落在信号 5 0MHz～ 5 5 0MHz范围内互调产物功率约占所有互调产物功率的 10 %～ 5 0 %。为了抑制色散抖动幅度 ,光栅的折射率变化应该从初值零渐渐升到最大值。长度为 10cm、包络为升余弦与tanh(4z)的光栅都能满足有线电视系统的要求。此外还发现 ,长光栅对应的抖动周期小 ,因此对信号的影响也小 ;具有升余弦包络的光栅比tanh(4z)光栅更能有效地抑制色散抖动。

The influence of fiber grating dispersion ripple on CATV signals is analyzed and the power of intermodulation terms fallen into the range of 50 MHz-550 MHz is estimated about 10%-50% of the total power of all the intermodulation terms. In order to restrain the amplitude of dispersion ripple, the refraction index change of fiber gratings should be made to rise from zero to its maximum value gradually. 10 cm-length fiber gratings with apodized refraction index profiles of raised-cosine or tanh (4z) shape can be used in CATV systems in theory. The longer the fiber gratings are, the smaller period of dispersion ripples they have, and subsequently the much less the influence on CATV signals. It is found that the fiber gratings with raised-cosine tapered profile have smaller dispersion ripple amplitude than those with tanh (4z) profile.