Efficiency Simulation for Diamond-Turned Diffractive Lenses

Diffraction efficiencies of hybrid diffractive-refractive lenses fabricated by the diamond turning process are discussed. Since the tip of a diamond tool has a certain nose radius, the relief profiles are rounded by the diamond turning process. Consequently, fabricated lenses have different diffraction efficiencies from their design. A computer simulation software based on the scalar diffraction theory was developed to calculate the diffraction efficiency of diamond-turned hybrid lenses. Hybrid achromatic lenses for optical pickups are simulated and measured. For a 10 µm nose radius, simulation results showed a diffraction efficiency of 82%. The difference in diffraction efficiency between simulation results and measurement results was less than 2%. Dual focus object lenses for compact disk (CD) and digital versatile disk (DVD) compatible pickups were also simulated. The difference in diffraction efficiency for our developed relief profile was small enough even with a 50 µm process.