In an optical device such as an optical pickup or the like, the number of optical assemblies may be reduced, an alignment required when the optical assemblies are disposed may be simplified, the whole of the device may be simplified and miniaturized, a tracking signal such as a tracking error signal or the like may be stably obtained relative to optical recording media having various pit depths, and the optical device may be manufactured with ease by the semiconductor process.
An optical device (10) includes an irradiated portion (2) formed of an optical recording medium in which a pit (P) is formed on a reflection surface, a semiconductor unit (7) in which a semiconductor laser (LD), a semiconductor structure (4) and a photo-detection element (PD) are formed on the same semiconductor substrate (1), and a converging means (3) for converging a light (LF) emitted from the semiconductor laser (LD) and irradiating the same on the irradiated portion (2) and further converging a returned light (LR) reflected from the irradiated portion (2). The semiconductor structure (4) is formed near the confocal of the converging means (3) and includes at least three reflection surfaces (M 1 , M 2 , M 3 ). The photo-detection element (PD) includes a first detection element (PD R ) for receiving a returned light LR reflected on the second reflection surface (M2) and a second detection element (PD L ) for receiving the returned light (LR) reflected on the third reflection surface (M3), wherein a first detection signal which results from detecting a diffracted light from one pit edge of the pit (P) by the first detection element (PD R ) and a second detection signal which results from detecting the diffracted light from one pit edge of the pit by the second detection element (PD L ) are obtained, and the first and second detection signals are computed to generate a tracking error signal (TE).