Design of an Aberration-Free Spherical Micro Lens with a Diffractive Relief Grating Film on a Refractive Spherical Glass Substrate

A combined micro-objective lens for optical disc use has been developed. The lens consists of a thin relief diffraction grating film and a planoconvex glass substrate. The combined lens, which is called the spherical grating lens (SGL), is inherently a spherical lens, but has some interesting features such as high numerical aperture and “spherical aberration”-free. The aberration in the refractive substrate is canceled by a thin diffraction grating film. This paper shows the ray tracing design of the SGL and the calculation results, and finally, the experimental results show that the SGL can he used as a low-cost objective lens in the optical disc head if it is appropriately designed.