PURPOSE: To minimize the loss of light energy and to improve a Kerr enhancement effect by forming a 1st protective layer to have the refractive index approximately equal to the refractive index of a transparent substrate and smaller than the refractive index of a 2nd protective layer.
CONSTITUTION: The 1st protective layer 2 to be formed on the transparent substrate 1 is formed to have the refractive index approximately equal to the refractive index of the transparent substrate 1 and smaller than the transparent substrate of the 2nd protective layer 3. The 1st protective layer 2 is made optically equiv. to the transparent substrate 1 if the material to be used for the 1st protective layer 2 and the material to be used for the transparent substrate 1 are combined and selected in such a manner that the material to be used for the 2nd protective layer 3 has the refractive index larger than the refractive index of the material to be used for the 1st protective layer and the refractive index of the transparent substrate 1. Since the 2nd protective layer 3 functions independently as an antireflection layer, the Kerr enhancement effect is improved while the loss of the light energy is minimized.
UETAKE ATSUSHI
MIYAMOTO KAZUAKI
