JPH06290480A - Optical head device - Google Patents

Abstract

PURPOSE:To realize a small optical system capable of making the enlarging ratio of a beam transmitted from a light source large in an optical head device. CONSTITUTION:A transmitted light beam of a laser light source 1 is enlarged by means of an optical system composed of curved surface mirrors 2 and 3 and made incident on an objective lens 4. When the diameter of a light shielding part in the diameter of the incident beam on the objective lens 4 generated by the optical system is made smaller than a half of the beam diameter, the influence of the side lobe of a converged light spot is little.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head device for recording / reproducing information on / from a recording medium.

[0002]

2. Description of the Related Art One of the features of an optical disk device is that recording / reproduction of recording pits of the order of microns (μm) is possible at a position separated by 1 to 2 mm or more from a recording medium. In order to form a recording pit having a minute spot from such a distant position, the incident beam diameter to the objective lens of the optical head device needs to be 3 to 4 mm or more. This is because the diameter of the focused spot formed by the objective lens is proportional to the lens focal length and inversely proportional to the lens aperture. Therefore, as the distance from the recording medium increases, a lens with a large aperture is required to obtain the same minute spot.

When the laser light source used in the optical head device is a gas laser or a solid-state laser, the emitted beam diameter is 1 mm or less, and the emission angle is often as small as 1 degree or less. Therefore, in order to secure the incident beam diameter (several mm) to the objective lens, a distance of several tens of cm or more is required between the light source and the objective lens, and the size of the device becomes large.

In order to avoid the size increase of such a device, in the conventional optical head device, as shown in FIG. 4, a magnifying lens 10 such as a concave lens is installed between the laser light source 1 and the objective lens 4. By expanding the radiation angle of the beam, the distance between the light source 1 and the objective lens 4 is reduced.

[0005]

However, in such a conventional optical head device, the expansion amount of the radiation angle that can be realized by the magnifying lens 10 is limited, and it is difficult to realize a sufficient reduction in distance. This is because it is difficult to obtain a lens having a short focal length of several mm or less with the refractive magnifying lens 10.

It is an object of the present invention to provide an optical head device having an optical system which can solve such problems and realize miniaturization.

[0007]

The optical head device of the present invention is an optical head device having an optical system for guiding light emitted from a laser light source to an objective lens and condensing it as a minute spot on a recording medium. A system reflects a light emitted from the laser light source in front of the objective lens to expand the beam diameter, and a reflected beam of the first curved mirror to return to the objective lens. Second
And a curved mirror.

[0008]

The present invention is characterized in that the magnifying optical system is constituted by the reflection type lenses (curved surface mirrors 2 and 3) as shown in FIG. In the reflective lens, it is possible to easily form a lens having the same radius of curvature and a short focal length as compared with the refractive lens. Therefore, it is easy to increase the expansion ratio of the radiation angle, and since the optical axis is folded back in the reflection type optical system, the effective optical path length can be lengthened in a small space, and the device can be downsized. Is easy.

Incidentally, in such a reflection type magnifying optical system, a part of the incident light to the objective lens 4 is shielded as shown by a broken line in FIG. When such a beam is focused by the objective lens, side lobes are generated. Figure 3
FIG. 4 is a characteristic diagram showing the ratio of the side lobe intensity to the main lobe intensity when the ratio of the light blocking diameter to the beam diameter changes. If the light blocking diameter ratio is 50% or less, the side lobe intensity is It can be seen that
Therefore, if the diameter of the curved mirror 2 is set to be half the diameter of the beam incident on the objective lens 4 or less, the influence of side lobes can be suppressed.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings.

FIG. 1 is a side view of an embodiment of the present invention in a partially sectional state. The light emitted from the laser light source 1 passes through the hole in the center of the curved mirror 3, is reflected by the curved mirror 2 in front of the objective lens 4, and is returned to the reflecting surface of the curved mirror 3. The light beam reflected and expanded by the curved mirror 3 is returned to the objective lens 4 and is condensed on the recording medium 6 by the objective lens 4.

FIG. 2 is a side view showing another embodiment of the present invention. The light emitted from the laser light source 1 has its optical path bent at a right angle by the reflection mirror 5, and is returned to the curved mirror 13 by the curved mirror 2 in front of the objective lens 4. The light beam reflected and expanded by the curved mirror 13 is focused on the recording medium 6 by the objective lens 4. In this embodiment, the curved mirror 13 does not need to be provided with a hole for passing light, which facilitates its manufacture.

[0013]

As described above, according to the present invention, it is possible to easily realize a small-sized optical head device even if a laser light source having a small beam diameter or a small emission angle is used.

[Brief description of drawings]

FIG. 1 is a side view of an embodiment of the present invention.

FIG. 2 is a side view of another embodiment of the present invention.

FIG. 3 is a characteristic diagram for explaining the operation of the present invention.

FIG. 4 is a side view of a conventional device.

[Explanation of symbols]

 1 Laser Light Source 2, 3, 13 Curved Mirror 4 Objective Lens 5 Reflection Mirror 6 Recording Medium

Claims (3)

[Claims] 1. An optical head device having an optical system for guiding light emitted from a laser light source to an objective lens and condensing it as a minute spot on a recording medium, wherein the optical system emits light emitted from the laser light source to the objective. A first curved mirror for reflecting the beam in front of the lens and expanding the beam diameter; and a second curved mirror for reflecting the reflected beam of the first curved mirror back toward the objective lens. Optical head device. 2. The first curved mirror is arranged within a range of a diameter of a reflected beam from the second curved mirror, and the diameter of the first curved mirror is larger than that of the second curved mirror. The optical head device according to claim 1, wherein the diameter is equal to or less than half the diameter of the reflected beam. 3. The optical system has a reflection mirror for changing the emitted light of the laser light source to the direction of the optical axis shared by the first and second curved mirrors and the objective lens. The optical head device described.