  We have built a frequency chain which enables to measure the absolute
frequency of a laser emitting in the 28-31 THz frequency range and stabilized
onto a molecular absorption line. The set-up uses an optical frequency comb and
an ultrastable 1.55 $\mu$m frequency reference signal, transferred from
LNE-SYRTE to LPL through an optical link. We are now progressing towards the
stabilization of the mid-IR laser via the frequency comb and the extension of
this technique to quantum cascade lasers. Such a development is very
challenging for ultrahigh resolution molecular spectroscopy and fundamental
tests of physics with molecules.
