Revisited Figure 3 of [32]: the phase-birefringence dispersion dB/dλ is very high, and it has a positive slope; this yields a group birefringence B_g with an opposite sign. This figure shows the interest of the geometrical construction with the tangent, that allows one to visualize simply the relationship between phase and group birefringences. The insert shows the shape of the micro-structured solid-core PM fiber described in [32].