where $s \in (0,1)$. We obtain sharp energy estimates for stable solutions when 0<s<1/2 and rough estimates when 1/2 \le s <1. These lead to a different proof from literature of the fact that when d=2,0<s<1, entire stable solutions to the fractional Allen Cahn equation are 1-D solutions. This is a joint work with Professor Changfeng Gui.