Patent attributes
The present invention relates to a phase retardation plate including a thin organic film with a phase retardation function due to birefringence and a fixed substrate bonded to at least one surface of the thin organic film using an adhesive, and to an optical pickup device having the phase retardation plate. In the phase retardation plate and the optical pickup device using the same, a liner thermal expansion coefficient (L1) of the thin organic film, a liner thermal expansion coefficient (L2) of the adhesive and a liner thermal expansion coefficient (L3) of the fixed substrate satisfy a relationship of L1>L2>L3; and the thin organic film retards the phase of incident light with a wavelength in a range of 400 to 800 nm by π/2 or π, the thin organic film having a phase retardation value between 0 and π. Accordingly, there is provided a phase retardation plate and an optical pickup device using the same, wherein fixation between materials is securely kept against a change in temperature over a long period of time, thereby improving reliability of products and obtaining a desired amount of phase retardation for incident light of a wide wavelength band.
