Experimental characterization of a switchable wedge-shaped holographic grating involved as a tunable phase retarder is reported. The structure is made of polymer slices alternated to films of well aligned Liquid Crystals (POLICRYPS). The sample shows a birefringence that depends on the anisotropy of the composite liquid crystalline material and on the geometrical cell parameters. The phase retardation introduced by the structure on the impinging probe light can be finely tuned by varying the amplitude of the externally applied electric field or by spatially shifting the probed area on the sample. The quarter wave plate condition for a He-Ne laser probe has been obtained confirming the possible application of the structure as an achromatic phase retarder.