Comparative assessment of optical performance for the optical design of HD-DVD micro objective lens with NA 0.65 using aspheric and freeform surfaces

A micro objective lens for HD-DVD with the Numerical Aperture (NA) of 0.65 at blue laser wavelength with clear aperture diameter of 1.5 mm has been designed on acrylic material using freeform surfacing method. Optical performance evaluation parameters have been compared with bi-aspheric surfaces based objective lens design. Freeform surface based design has higher degrees of freedom compare to conventional aspheric surfaces that can reduce aberrations significantly. Maximum RMS error is 0.003λ at 0.4° and maximum RMS radius is 0.027 μm while airy disk radius is 0.3803 μm for freeform surface based design. Hence single freeform surface based design can reduce the fabrication complexity and tooling time, at the same instance provides comparable performance with bi-aspheric surfaces based design.