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March 17, 2022 at 9:47 am
ywq
Subscriber孙老师您好,我在用fdtd仿真基于啁啾光栅(周期数为1000)的延时线时总是会发散,仿真模型如下图
March 17, 2022 at 10:34 pmGuilin Sun
Ansys Employee首先,这个发散的问题是会影响结果的正确性!
你可能需要首先检查结构是否正确:目前看结构是悬在背景材料(很可能是空气)中,是这样吗?
请做如下检查:
1:看看PML是否足够厚?至少半个波长
2:看看Port2和Port4里面监视器,场在边缘是否很小?用对数坐标看,如果振幅不小于0.001,说明仿真区横向尺寸小了,你也看看光源的模式分布。
3:这种结构一般谐振比较强,你需要减小Autoshutoff ,参见 Ansys Insight: 为什么说仿真时间要足够长才能得到正确的频域结果
4: 在光栅周期区间用均匀网格,设置Override Mesh,使得每个周期有整数个网格。假设周期是0.17um, 尺寸可能要0.0017um或者其整数倍。你图中似乎用了这样的均匀网格,但是没有必要涵盖整个结构,仅覆盖光栅区,保证周期内的网格均匀且整数个就可以。
你先修改测试看看。March 17, 2022 at 10:35 pmMarch 23, 2022 at 7:05 amywq
Subscriber孙老师您好,我按照您的建议改了一下相关参数,包括:
- 增大了FDTD的y方向尺寸和四个port的尺寸,使得模式的光场能量在边界截至;
- 将dt stability factor缩小为0.5;
- 缩小mesh的网格尺寸;
运行的结果就是,光栅周期数为100时,可以快速收敛,得到的结果很正确,光栅周期数为1000时,仍然发散。这里只是把光栅的周期数(也就是光栅的总长度)改变了,就导致了仿真的发散。对于这个现象,我不是很理解。
另外您给的一个建议是看看PML是否足够厚,至少半个波长,我不知道怎么设置PML的厚度,麻烦您详细介绍一下。March 23, 2022 at 2:23 pmMarch 23, 2022 at 2:23 pmywq
SubscriberMarch 23, 2022 at 2:23 pmywq
SubscriberMarch 23, 2022 at 2:23 pmywq
SubscriberMarch 23, 2022 at 2:23 pmMarch 23, 2022 at 5:21 pmGuilin Sun
Ansys EmployeePML厚度就是PML前面的网格尺寸成层数,你可以简单用Ruler测量,不需要非常精确,或者加监视器提取坐标计算;
"当光栅周期数为1000时,仍然会发散",每次有变化你仿真的都不是同一个器件,你需要参考发散的帖子自己琢磨如何修改才能避免发散,里面有很多建议。Viewing 9 reply threads- The topic ‘用fdtd仿真光栅延时线时总是发散’ is closed to new replies.
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