| 摘要 |
PROBLEM TO BE SOLVED: To hold excellent image forming performance as a proximity field optical system with simple constitution by constituting an objective lens of a single lens, making the surface of the lens on an object side a curved surface, especially, an aspherical surface and engraving the zonal band of a diffraction lens on the curved surface. SOLUTION: In the proximity field optical disk optical system; the objective lens is composed of the single lens, its surface on the object side is made the curved surface and the zonal band of the diffraction lens is engraved on the curved surface. Namely, a refraction surface being the aspherical surface on the object side is set as a base surface, where the diffraction lens having the zonal band symmetric with respect to an optical axis is formed. Thus, a light beam is formed into an image without aberration on a plane side surface on an image side. Though the objective lens is the single piano-convex lens as a whole, the proximity field optical disk optical system distributes the action of turning the incident light into converged light to diffractive power as well as refractive power, so that the curvature of the convex surface is made moderate, a sine condition is improved, and the excellent image forming performance is obtained not only on an optical axis but also for a light beam whose angle of view is about ±1 deg.. |
