Polarized diffractive filter and layered polarized diffractive filter

A polarized diffractive filter, comprising:

• two transparent substrates;
• cyclic concave/convex portions formed as a diffractive grating on or in at least one of said two transparent substrates;
• and
• each substrate comprising a transparent conductive film which is present a) on said diffractive grating, or b) below said diffractive grating or c) on said substrate if no diffractive grating is present;
• wherein the concave portions are filled with an optical material;
• wherein the concave/convex portions comprise an isotropic material;
• and
• wherein the optical material filled in the concave portions comprises a liquid crystal material;
• wherein said polarized diffractive filter is capable of receiving light having at least two different peak wavelengths and changing a wavelength to be diffracted by applying a voltage across the transparent conductive films to change a wavelength to be transmitted;
• wherein said polarized diffractive filter is capable of changing a wavelength having a phase difference φ of 2π or 4π according to an applied voltage,
• wherein the diffractive grating has the phase difference φ changing from φ=2π·(ne−ns)·d/λ in a non-voltage application time to φ=2π·(no−ns)·d/λ in a voltage application time,
• wherein the cyclic concave/convex portions of the diffractive grating have a depth d, the liquid crystal material has an extraordinary refractive index ne and an ordinary refractive index no, and the light has a wavelength λ.