Patent ID: 6967776

Claim:
A polarizing filter having a laminate structure, comprising: a first group of dielectric thin film materials; a second group of dielectric thin film materials; and a third layer of dielectric thin film material, wherein a plurality of dielectric materials different from one another in refractive index with respect to a wavelength of incident light are classified into said first group and said second group so that a maximum value among the refractive indices of the dielectric materials belonging to said first group is lower than a minimum value among the refractive indices of the dielectric materials belonging to said second group; wherein at least one layer of dielectric thin film selected from the dielectric materials belonging to said first group and at least one layer of dielectric thin film selected from the dielectric materials belonging to said second group are alternately laminated to form said laminate structure, said laminate structure being mounted on a transparent flat substrate beginning with a first layer adjacent to said transparent flat substrate; wherein said third layer of dielectric thin film has a refractive index which is higher than the maximum value selected from said refractive indices of the dielectric materials belonging to said first group and which is lower than the minimum value selected from said refractive indices of the dielectric materials belonging to said second group and is laminated on an outermost surface of said laminate structure, said laminate structure being between said third layer and said transparent flat substrate; wherein said first layer includes the dielectric thin film selected from the dielectric materials belonging to said second group; and wherein said polarizing filter polarizes non-polarized light into polarized light having an s-polarized light component and a p-polarized light component, the transmittance ratio of the s-polarized light component to the p-polarized light component being in the range of 0.2 to 1.0, said transmittance ratio of said polarizing filter being controllable to obtain a desired intensity ratio of the s-polarized light component to the p-polarized light component of said non-polarized light.