Make a parallel plane ABCD intersect OO' at G point,

So? G=√2/4，

According to Pythagorean theorem, we can get

OO^'=√( 1-〖O^'？ C〗^2？ )=√2/2,

∴OG=√2/4，

∫OS = 1。 ? ∴〖SG〗^2= 1- 1/8=7/8，

∴SO^'=√(〖O^'？ G〗^2+〖SG〗^2？ )=√( 1/8+7/8)= 1