Holographic Optical Elements: Advantages and Disadvantages for Efficient Lighting, Sun Protection, and Photovoltaic Power Supply of Buildings

The research of holographic optical elements (HOE) was carried out very intensively in the 1980s and 1990s. They provided great advantages in high-efficiency natural light, while at the same time providing effective sun protection and did not disturb the free view from the windows. The light-directing qualities of these devices made it possible to concentrate direct and scattered solar energy on photovoltaic batteries and solar collectors for hot water supply and solar heating. However, in recent years, research in this area has become less and less frequent without any explanation. The analysis of the research carried out in the framework of one of the latest projects carried out on behalf of the European Commission under the program “Energy, Environment, and Sustainable Development” (EU Contract Number: ENK6-CT‑2000–00327) with the participation of nine research organizations, higher schools, and universities is presented. The role of each of the participants in this interdisciplinary project was to attract experienced researchers in various fields of science and use their knowledge to obtain an objective result.

Optical See-through 2D/3D Compatible Display Using Variable-Focus Lens and Multiplexed Holographic Optical Elements

An optical see-through two-dimensional (2D)/three-dimensional (3D) compatible display using variable-focus lens and multiplexed holographic optical elements (MHOE) is presented. It mainly consists of a MHOE, a variable-focus lens and a projection display device. The customized MHOE, by using the angular multiplexing technology of volumetric holographic grating, records the scattering wavefront and spherical wavefront array required for 2D/3D compatible display. In particular, we proposed a feasible method to switch the 2D and 3D display modes by using a variable-focus lens in the reconstruction process. The proposed system solves the problem of bulky volume, and makes the MHOE more efficient to use. Based on the requirements of 2D and 3D displays, we calculated the liquid pumping volume of the variable-focus lens under two kinds of diopters.