Design and fabrication of infrared holographic optical elements with both beam splitting and convergence functions

Holographic optical element (HOE) are widely used due to their lightweight, miniaturization, and multifunctional characteristics. However, making HOE that can be applied in the infrared band is a challenging task, especially when HOE has multiple function. This paper proposes a design and fabrication method for a near-infrared multifunctional HOE that can be recorded using visible light. The three recording beams of this multifunctional HOE include a plane beam and two spherical beams. Therefore, on the basis of achieving beam redirection, it can also achieve beam splitting and the convergence of each split beam. To solve the problem of wavelength mismatch while achieving multiple functions of HOE. The decrease in diffraction efficiency caused by wavelength shift is compensated by the angle shift of recording light. The wavefront aberration caused by wavelength mismatch is compensated by introducing a cylindrical lens in the recording optical path. The multifunctional HOE has the potential to be used in infrared optical systems to achieve system miniaturization, and this paper provides an application example for laser Doppler velocimeter (LDV). The designed HOE successfully achieved two sets of stripes with opposite slopes in the measurement volume of LDV at different working wavelengths, proving the feasibility of the design and fabrication methods. Furthermore, the method proposed in this paper can provide reference for the design and fabrication of other HOEs working in the near-infrared band.