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 (1a), a second main surface (1b) and a bulk (1c) comprised between said opposed two main surfaces (1a, 1b), for which: ⋅ in the vicinity of the first main surface (1a), the liquid crystals (2a) are aligned along a main first direction, ⋅ in the vicinity of the second main surface (1b), the liquid crystals (2b) are aligned along a main second direction, different from the first direction, and in between, the bulk (1c) 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).