Fabrication of half-wave plates with subwavelength structures

Various optical elements with subwavelength structures are currently being developed. Because phase plates require a deep grating structure in which the line width is narrow and the aspect ratio is high, it has been difficult to develop half-wave plates. We have designed and developed lambda/2 plates, and evaluated their optical characteristics. The fabricated phase plates have subwavelength gratings the depth of which is 1170 nm with a period of 260 nm. The phase plates achieved a phase retardation of 180 deg. at a wavelength of approximately 850 nm, and 90 deg. at the optical communication wavelength of approximately 1550nm. The transmittance was approximately 70% around 850nm and approximately 80% around 1550nm.