DETECTION OF FOCUS ERROR AND OPTICAL RECORDING MEDIUM

摘要

PURPOSE:To improve the quality of reproduction information signal by forming a 1st groove of lambda/8n depth and a 2nd groove of lambda/4n depth where the wavelength of the light to be projected for the purpose of reading is designated as lambda and the optical refractive index of an optical recording medium substrate as n. CONSTITUTION:The 1st groove 33 of lambda/8n depth and the 2nd groove 34 of lambda/4n depth are formed, where the wavelength of the light of a semiconductor laser 21 is designated as lambda and the optical refractive index of the optical recording medium substrate 31 as n. The recording medium 30 is irradiated with the light beam 40 emitted from the semiconductor laser 21 and the component of the difference between the detected light output on the surface of the optical recording medium 30 and the detected light output of the 2nd groove 34 is taken out with the detected light output of the 1st groove 33 as a reference and is used as a focus error signal. The need for wobbling frequencies is eliminated in this way and the quality of the reproduction signal is improved.