Diffraction optical elements with super-long-period grating film for laser beam forming.

Periodic structures called gratings cause the diffraction of light. In optics, this property is mainly used in spectroscopy, for example, to measure the emission and absorption of light. In this study, we propose a super-long-period (SLP) transmission grating that can change the beam shape without altering its spectral properties, and we analyze its characteristics. From the numerical simulations, as the grating period increases, the number of diffraction orders increases, and the diffraction efficiency takes on a pseudo-Gaussian shape. Therefore, the diffraction angle varies continuously, and the diffraction efficiency gradually changes near the zeroth order. These diffraction properties of the SLP grating allow for the transformation of a point laser beam into a line-shaped beam without spectral change. We fabricated a SLP grating film with a 100-µm-period rounded triangular shape and demonstrated its capability to transform a point source into a super-wide, ultra-fine, and uniform line beam at a desired distance. This beam shaping was achieved using a combination of the SLP grating film, a focusable lens, and a cylindrical lens. In addition, we successfully constructed a uniform two-dimensional array pattern beam using two orthogonal SLP gratings, as well as wide uniform illumination using a thin LiDAR light source with a VCSEL array. We expect that the SLP grating film will be suitable for various applications, such as LiDAR, security screening, and three-dimensional depth scanning systems.