Thank you very much for your respond.
I still have another 3 questions.
1.Setting the boundary to PML, which have no symmetry BC, I got modes like this, can I think that mode 1 (neff= 1.437225, TE polarization fraction=100%) is fundamental TE mode, mode 2 is fundamental TM mode?

2 You said, the fundamental mode of TE and TM for fiber have the same neff and intensity, but have different polarization.
Does the intensity mean the fiture here(2)?
Then, how to tell which are TE modes, which are TM modes?
Does TE polarization fraction (3) geater than 1% mean it is TE mode? Does TE polarization fraction equal to 0 mean it is TM mode?

3.I find in the download example of "grating coupler", the mode by "user select" for PML and "anti-symetric" BC is different. It seems that the mode by "anti-symetric" is wrong, then why use anti-symetric BC in grating coupler example?
For "anti-symetric" BC