A optical device comprises at least one group of following structure 1) phase modulation layer (31), 2) a partially reflective layer (38) and 3) a phase compensation layer (36). When incident lights (30) pass through the phase modulation layer (31), partially reflective layer (38) reflects and scatters the light back to the viewers (42). The direction and profile of the reflected light (32) are determined by the phase modulation profile. On the other hand, when light passes through both the first phase modulation layer (31) and the second phase compensation layer (36), its phase modulation is compensated to substantially small level, Therefore, the transparent light passes through the optical device just like passing through a parallel transparent substrate without any disturbing. A transparent display is achieved.