OPTICAL FILTER

PURPOSE:To provide an optical filter by which absorption edge of an absorption spectrum can be precisely controlled. CONSTITUTION:An optical filter is formed by using porous silicon produced by an anodization method. When an anodization method is applied on monocrystal/polycrystal silicon and the porous silicon is produced on the monocrystal/polycrystal silicon, an absorption edge of an absorption spectrum of the porous silicon can be controlled by controlling the wave length of the light radiated on the monocrystal/polycrystal silicon, by varying a specific electric resistance of monocrystal/polycrystal silicon to be used, or by controlling a current density of the current let flow in the monocrystal/polycrystal silicon.