Much interest has been drawn in Photonic crystal, which are novel nanostructure of light. In the present paper, we present how the emerging technology of Photonic crystal can be suitably exploited to design and make a nano sized tunable optical falter. A novel theory to design tunable optical filter using one dimensional nano photonic structure is proposed in this present paper far ultraviolet and visible region of wavelength. A periodic structure of different dielectric and semiconductor materials (i.e. air and GaAs, air and Ge) are used. This idea is based on the Kronig -Penny model in the band theory of solids.