The design of multi-wavelength confocal diffractive optical element based on set operation

A method suitable for the design of large aperture multi-wavelength confocal diffractive optical element (DOE) was proposed. The method is based on set operation for microstructures. As examples, different multi-wavelength confocal DOEs with aperture of 20 mm were designed. The results of the numerical simulations show that the confocal DOEs achieved diffraction-limited focusing performance at all design wavelengths, but the diffraction efficiencies were lower than the ideal DOEs. For experimental verification, one three-wavelength confocal DOE with focal length of 200 mm was fabricated and tested. The optimum full width at half maximum (FWHM) is preferably 1.067 times of the diffraction limit and the highest optical imaging solution reaches 94.6% of the diffraction limit. Both the simulation results and the experimental results verify the validity of this method for designing multi-wavelength confocal DOE. The presented work may find applications in large-aperture multi-wavelength laser communication, wide-spectrum diffractive telescopes, and high-precision multi-wavelength Computer generated holography (CGH).