Reduced wavelength-dependent quarter-wave plate fabricated by a multilayered subwavelength structure.

We developed a novel fabrication method of a reduced wavelength-dependent quarter-wave plate (QWP) based on form birefringence of a multilayered subwavelength structure. The multilayered structure was constructed by depositing a high-refractive-index thin film on a subwavelength-structured substrate with a low refractive index. The surface structure of the substrate was shallow enough to be formed by a mass replication technology. A high-refractive-index subwavelength grating was formed on ridges of the substrate by sputtering Zn2SnO4 (refractive index of 2.03 at a wavelength of 633 nm). Moreover, since the grooves of the high-refractive-index grating were very deep and narrow, the dispersion of form birefringence suppressed the dependency of phase retardance on the wavelength of light in a limited spectral region. The phase retardance of the fabricated QWP was 89 degrees at a 633 nm wavelength and 79 degrees at a 785 nm wavelength.