The invention concerns a transparent thin liquid crystal alignment film (1) including liquid crystals (2) within a polymerised liquid crystal composition, the film (1) comprising a first main surface (la), a second main surface (lb) and a bulk (lc) comprised between said opposed two main surfaces (la, lb), for which: in the vicinity of the first main surface (la), the liquid crystals (2a) are aligned along a main first direction, in the vicinity of the second main surface (lb), the liquid crystals (2b) are aligned along a main second direction, different from the first direction, and in between, the bulk (lc) comprises liquid crystals (2c) maintained in an isotropic orientation. The invention concerns also a process of manufacturing such a liquid crystal alignment film (1) and a polarization-independent spatial phase modulator including such a liquid crystal alignment film (1).