Patent ID: 8879375

Claim:
An optical pickup, comprising: a laser light source for emitting a laser beam; a laser beam divider that divides the laser beam emitted from the laser light source into signal light that is focused on a reflecting unit of an optical disk and reference light that is not focused on the optical disk; a reference light mirror that reflects the reference light; and an interference light detecting unit that detects interference light in which the signal light modulated by the reflecting unit of the optical disk and the reference light reflected off of the reference light mirror interfere with each other, wherein the laser light source, the laser beam divider, and the reference light mirror are arranged in such a manner as to satisfy the following expressions (1) to (3) simultaneously, [ Math . ⁢ 1 ] L sig + L BS ≠ s ⁢ ⁢ L ld m ⁢ ⁢ ( s ⁢ : ⁢ ⁢ positive ⁢ ⁢ integer , m ⁢ : ⁢ ⁢ positive ⁢ ⁢ integer ) ( 1 ) [ Math . ⁢ 2 ] L ref + L BS ≠ t ⁢ ⁢ L ld m ⁢ ⁢ ( t ⁢ : ⁢ ⁢ positive ⁢ ⁢ integer ) ( 2 ) [ Math . ⁢ 3 ] u ⁢ ⁢ L ld m - Δ ⁢ ⁢ L 2 ≤ L sig - L ref ≤ u ⁢ ⁢ L ld m + Δ ⁢ ⁢ L 2 ⁢ ⁢ ( u ⁢ : ⁢ ⁢ integer ) ( 3 ) where L ld represents an in-vacuum internal resonator length of the laser light source that is obtained as a product of an internal resonator length of the laser light source and an internal resonator refractive index of the laser light source, L BS represents an in-vacuum-converted optical path length of the laser beam between an emission end surface of the laser light source and the laser beam divider, L sig represents an in-vacuum-converted optical path length of the signal light between the laser beam divider and the reflecting unit of the optical disk, L ref represents an in-vacuum-converted optical path length of the reference light between the laser beam divider and the reference light mirror, and ΔL represents an interference permissible optical path length of the laser beam.