Patent ID: 7149174

Claim:
An optical pickup comprising: a light source for emitting S-polarized light intended for writing, reading or erasing information; a beam splitter for reflecting and transmitting said S-polarized light incident at an incident plane thereof from said light source in accordance with a predetermined first reflectance and first transmittance, thereby outputting a first reflected light and a first transmitted light; a quarter-wavelength plate for causing said first reflected light to pass through and to be output toward an information recording medium; detecting means for detecting said first transmitted light to exercise a feedback control on emission power of said light source based on a result of detection; and light receiving means for receiving light reflected back from said information recording medium, passing through said quarter-wavelength plate again, and transmitted through said beam splitter, as said first reflected light is incident on said information recording medium through said quarter-wavelength plate, wherein said beam splitter has said first transmittance and a predetermined second transmittance to the light reflected back from said information recording medium, the respective transmittances being determined in accordance with a condition given by: Tpc (λ c )/ Tp (λ)= K ×( Tsc (λ c )/ Ts (λ)), where Ts(λ) is a transmittance to light of predetermined wavelength λ emitted from said light source, Tsc(λc) is a transmittance to light of wavelength λc emitted when said light source varies in wavelength characteristic, Tp(λ) is a transmittance to the light reflected back from said information recording medium through said quarter wavelength plate when the light of predetermined wavelength λ is emitted from said light source, Tpc(λc) is a transmittance to the light reflected back from said information recording medium through said quarter wavelength plate when the light of wavelength λc is emitted from said light source varying in wavelength characteristic, and K is a predetermined variable which is either 1 or a value of (1−Ts(λ))/(1−Tsc(λc)), or a value falling within a range of 1 and (1−Ts(λ))/(1−Tsc(λc)).