APPARATUS FOR DETECTING TRACKING ERROR OF OPTICAL HEAD

An apparatus for detecting a tracking error of an optical head by introducing a laser beam from a semiconductor laser element (1) into a diffraction grating (3), introducing a zero order beam and positive and negative primary beams, which leave the diffraction grating (3), into an object lens (5) through a beam splitter (4), reflecting on an optical recording medium (6) the focused beams, which are introduced from the object lens (5) thereinto, to pass these reflected beams, which consist of the zero order beam and positive and negative primary beams, through the object lens (5), reflect the resultant beams on the reflecting surface of the beam splitter (4) and thereafter introduce the reflected beams into an optical detector (7), obtaining from this optical detector (7) a pair of outputs representative of optically detected data and corresponding to the positive and negative primary beams, and obtaining on the basis of a difference between the levels of the outputs from the optical detector (7) a tracking error signal which is in accordance with the tracking condition of the zero order beam on the optical recording medium (6). A pair of specular lenses (9), (10), and a light-shielding member (11), which is set between these specular lenses (9), (10), and which is adapted to pass therethrough only the center beam out of the center beam and beams on both sides thereof, which three beams are reflected on the optical recording medium (6), passing through the object lens (5), beam splitter (4) and diffracting grating (3) and advancing to the semiconductor laser element (1), and to intercept the two side beams, are provided between the semiconductor laser element (1) and diffraction grating (3). This enables obtaining a tracking error signal which is is free from the possibility that this signal varies due to variations in the tangential skew angle of the zero order beam in an optical head OH with respect to the optical recording medium (6). Ce dispositif permet de détecter une erreur de suivi de piste d'une tête optique en introduisant un faisceau laser produit par un élément laser à semi-conducteur (1) dans un grillage de diffraction (3), en introduisant un faisceau d'ordre zéro et des faisceaux primaires positif et négatif, quittant le grillage de diffraction (3), dans un objectif (5) à travers un diviseur de faisceaux (4), en réfléchissant sur un support d'enregistrement optique (6) les faisceaux focalisés, qui y sont introduits depuis l'objectif (5), pour