  We present a theoretical study of electron wave functions in ballistic
circular n-p junctions of bilayer graphene. Similarly to the case of a circular
n-p junction of monolayer graphene, we find that (i) the wave functions form
caustics inside the circular region, and (ii) the shape of these caustics are
well described by a geometrical optics model using the concept of a negative
refractive index. In contrast to the monolayer case, we show that the strong
focusing effect is absent in the bilayer. We explain these findings in terms of
the angular dependence of Klein tunneling at a planar n-p junction.
