CONDENSING OPTICAL SYSTEM

摘要

A condensing optical system used for an optical pickup device that condenses a light flux having a wavelength lambda1 (350 nm<=lambda1<=450 nm) and a light flux having a wavelength lambda2 (650 nm<=lambda2<= 700 nm) to first and second optical information recording media respectively having protection substrate thicknesses t1 (0.5 mm<=t1<=0.7 mm) and t2 (0.5 mm<=t2<=0.7 mm). The condensing optical system comprises a single-lens objective optical element and a single-lens first optical element disposed immediately ahead of and opposite to the incident plane of this objective optical element, a phase difference affording structure being formed in at least one of these optical elements. The phase difference affording structure has a color correction function for correcting, to up to 0.03 lambda rms, aberration variations before and after wavelength changes at the same position in the optical axis direction when a wavelength changes 1 nm from lambda1.