In parallel to the work on FBG Fibre Optic thermo hygrometers an R&D activity on sensor derived from a different grating technique is on-going in collaboration with a pool of university laboratories: sensors produced through the Long Period Grating (LPG) technique are coated with Titanium dioxide (100 nm thick layer) to obtain a new generation of RH FOS with improved sensitivity, long-time stability and intrinsic high radiation hardness. Preliminary results are extremely promising. Different qualities of gratings and different techniques of oxide deposition are being presently explored.