content_image/362009.jpg content_image/362016.jpg content_image/362017.jpg content_image/362018.jpg
<img src='content_image/362009.jpg'>

We are currently investigating the polarization mode [I]. On substituting Eqs. (2) and (13) into Eq. (19) we have 

<img src='content_image/362016.jpg'>

There exists an inherent transverse shift on propagation. This result coincides with that obtained by Li [11] with different methods. According to Eq. (24) the rotation angle is given by 

<img src='content_image/362017.jpg'>

In this case, the rotation characteristics of wavepacket centroid vanish, i.e., Ω $^{[I]}$( z ) = 0. 

We are now in a position to consider the polarization model [II]. On substituting Eqs. (2) and (14) into Eq. (19) we can determine 

<img src='content_image/362018.jpg'>

A further important point should be noted is that Eq. (26) can be obtained from Eq. (24) 

