JPH029028A - Optical pickup device - Google Patents

Abstract

PURPOSE:To realize high density recording in a state that recording power is necessary by forming a light beam spot to a prescribed shape by using a collimator lens and a beam shaping prism. CONSTITUTION:A divergent elliptical laser beam from a semiconductor laser 1 is corrected to elliptical parallel beams by using a collimator lens having such a numerical aperture as an elliptical major axis shaded by the collimator lens. Subsequently, when the elliptical minor axis diameter of this beam is enlarged to the aperture of an objective lens 4 by using a beam shaping prism 3, and the beam is converged by an objective lens 5 onto a recording medium 4 such as a disk, a light beam spot on the medium 4 becomes an elliptical shape by which the rotating direction of the disk becomes a minor axis, and in a state that recording power is comparatively necessary, high density recording can be realized.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to an optical pickup device included in an optical information recording apparatus that performs recording, reproduction, and erasure on a disk-shaped recording medium using a semiconductor laser.

[Prior Art] A conventional optical pickup device is shown in FIG. 4(a), for example.
The devices shown in FIG. 5(b) and FIGS. 5(a) and 5(b) are known. In the example shown in FIGS. 4(a) and (b),
The beam emitted from the semiconductor laser 1 is corrected into a parallel beam using a collimator lens 2 having a numerical aperture that almost eliminates kicking by the lens, and a beam shaping prism 3 is inserted so that the beam shape becomes circular. The light was then focused on the recording medium 4 using the objective lens 5 to form a minute circular spot for recording and reproduction.

Furthermore, in the example shown in FIGS. 5(a) and 5(b), a lens 2 having a numerical aperture such that the beam emitted from the semiconductor laser 1 is deflected by the collimator lens has a major axis diameter of the ellipse.
is used to correct the beam to a parallel beam, insert a beam shaping prism 3 so that the intensity distribution of the beam becomes circular, and converge it onto the recording medium 4 with an objective lens 5 to form a minute circular spot for recording and reproduction. It was like that.

[The problem that the invention aims to solve] In such a conventional system, FIG. 4(a).

In the example shown in (b), the beam diameter and intensity distribution converged on the recording medium are circular, and the beam is hardly kicked by the lens, so the light from the semiconductor laser light source can be used efficiently. increases the recording density on the medium
Therefore, in order to reduce the beam diameter, it is necessary to increase the numerical aperture of the objective lens or shorten the oscillation wavelength of the semiconductor laser. However, both methods cannot be used at the current state of the art.

On the other hand, in the examples shown in FIGS. 5(a) and 5(b), the beam is kicked more by the objective lens and the collimator lens, resulting in poor light utilization efficiency, and in situations where a large amount of recording power is required, The drawback was that it could not be used.

[Means for Solving the Problems] The optical pickup device of the present invention uses a lens having a numerical aperture such that a diverging elliptical beam emitted from a semiconductor laser is deflected by a collimator lens. The beam is adjusted to an elliptical parallel beam, the short axis diameter of the ellipse of the corrected beam is expanded to the diameter of the objective lens, and the beam is focused on the disk-shaped recording medium by the objective lens, so that the shape of the minute spot for recording and reproduction is made into an ellipse. It is something. Further, the arrangement is such that the radial direction of the disk-shaped recording medium is the long axis of the elliptical minute spot.

[Embodiments] Next, embodiments of the present invention will be shown and explained with reference to the drawings.

In FIGS. 1(a) and (b), a semiconductor laser 1
A diverging elliptical beam emitted from the elliptical beam is corrected into an elliptical parallel beam using a lens 2 having a numerical aperture such that the major axis diameter of the ellipse is offset by the collimator lens 2. next,
The corrected elliptical minor axis diameter of the beam is expanded to the diameter of an objective lens 40 using a beam shaping prism 3, and the beam is focused onto a recording medium 4 by an objective lens 5. At this time, the direction expanded and corrected by the beam shaping prism 3 becomes the long axis of the ellipse, and by kicking with the collimator lens 2, the beam diameter in the direction in which the beam intensity distribution shape approaches a uniform distribution from a Gaussian distribution becomes the short axis of the ellipse. This results in a converging elliptical beam shape.

As shown in FIG. 2, this elliptical beam is arranged so that the radial direction of the disk-shaped recording medium is the long axis of the convergent elliptical beam. FIG. 3 shows the reproduction characteristics when the optical pickup device of this embodiment is applied to a magneto-optical disk device and a single frequency is recorded.

When determining the beam spot diameter in the disk circumferential direction on the disk in this state, the optical pickup device of the present invention is approximately 12% smaller than the conventional one.

[Effects of the Invention] As explained above, the present invention provides a light beam spot on a disk-shaped recording medium having an elliptical shape with the short axis in the direction of the rotation axis of the disk. This has the effect of allowing high-density recording.

[Brief explanation of the drawing]

1(a) and 1(b) are layout diagrams showing the configuration of an embodiment of the present invention, FIG. 2 is a plan view showing a beam on a recording medium of one embodiment, and FIG. 3 is a diagram showing the signal amplitude ratio. A graph showing the relationship with recording frequency, FIG. 4(a). 5(b), FIGS. 5(a) and 5(b) are layout diagrams showing conventional examples, respectively. 1...Semiconductor laser 2...Collimator lens, 3...Beam shaping prism, 4...Recording medium, objective lens, beam splitter, elliptical minute spot, elliptical minute spot elliptical type.

Claims (2)

[Claims] (1) In an optical pickup device that uses a semiconductor laser to perform recording and reproduction on a disk-shaped recording medium, a diverging elliptical beam emitted from the semiconductor laser is placed in a collimator lens at a position where the major axis diameter of the ellipse is larger than the collimator lens aperture. corrected into a parallel ellipse using a lens having a numerical aperture such that the beam is mounted, and a shaping means capable of expanding the short axis diameter of the ellipse to the objective lens aperture;
An optical pickup device characterized in that a minute spot converged by an objective lens on a disk-shaped recording medium for recording and reproduction is an ellipse. (2) The optical pickup device according to claim 1, wherein the radial direction of the disk-shaped recording medium is the long axis of the elliptical minute spot.