Optical Performance of Aspheric Singlets for Compact Disc Use

We reported the diffracton-limited plastic aspheric singlet for CD(Compact Disc) use last year,1,2 and it is now under mass-production. We investigated the off-axis performance of bi-aspheric singlets as well as mono-aspheric singlets, and achievable size of image field from a point of view of optical design. In this study, the specifications of singlets are f=4.5mm, 4mm, NA 0.45 and NA 0.6. Optical performance is evaluated by the value of max-imum image field defined by the area of which the rms wave front error is less than 0.07X (Marechal Criterion). The performance of the design results of bi-aspheric singlets and mono-aspheric singlets under several conditions are investigated. From these results, we concluded that bi-aspheric singlets are most suitable for not only CD but also general optical disc use maintaining enough back focal length and image field.