JPH0675298B2 - Optical information reproducing device - Google Patents

Description

Description: (1) Technical Field of the Invention The present invention relates to an optical information reproducing apparatus for optically reading information on a recording medium, and particularly, to improve a vibration method of a light beam for obtaining a control signal. .

(2) Background of the Technology In an optical information reproducing apparatus that reads information such as sound and images from an optical recording medium called an optical disk, the positional relationship between the information reading light flux and the information track becomes a problem. The eccentricity of the recording medium that is rotationally driven is one of the factors that cause the deviation of the light flux with respect to the information track (tracking deviation). Therefore, in general, a tracking control signal is obtained so that the information reading light flux is made to follow the deviation of the information track.

(3) Prior Art and Problems FIG. 1 shows an example of an optical system for obtaining a tracking control signal in a conventional optical information reproducing apparatus. In the figure, 1 is a semiconductor laser as a light source, 2 is a collimator lens, 3 is a polarization beam splitter, 4 is a λ / 4 plate, 5 is a convex lens, and 6
Is a two-division light receiving element, 7 is a rotating mirror (galvano mirror), 8 is a focusing lens, and 11 is a recording medium. recoding media
Reference numeral 11 shows a part of the cross section, which rotates in the direction of arrow A. 11a is the information track. The light flux L _O emitted from the laser 1 is incident on the rotating mirror 7 through the lens 2, the beam splitter 3, and the λ / 4 plate 4, and is reflected here and then is irradiated onto the recording medium 11 through the focusing lens 8 (focused). As luminous flux L _1. ) On the other hand, since the reflected light L _{2 from} the recording medium 11 returns through the lens 8 and the rotating mirror 7 and is incident on the λ / 4 plate 4 again, a delay of round trip λ / 2 occurs here. As a result, the light is separated by the beam splitter 3 toward the lens 5 side,
Incident on.

With this optical system, the turning mirror 7 is moved to a voice coil motor (VC
When rotated about the axis 7a by M) or the like, the light beam L ₁ incident on the recording medium 11 vibrates in the direction B orthogonal to the track 11a. Generally, due to the eccentricity of the rotation axis of the recording medium,
If the rotation speed at that time is 1800 rpm, 11a vibrates at a frequency resulting from the rotation speed, that is, at an integral multiple of 30 Hz. The vibration is about several tens to several hundreds of μm. Therefore, the rotating mirror 7 is rotated in accordance with this vibration so that the light beam L ₁ follows the track 11a. Further, as one of methods for obtaining the tracking control signal, there is a method called a wobbling method. This is to detect the off-track by vibrating the light beam L ₁ in the direction of arrow B with an amplitude of zero μm, and its vibration frequency is as high as several 10 KHZ. Since the rotating mirror 7 is rotated at a high speed around the shaft 7a as described above, the mechanical bearing accuracy of the shaft 7a becomes a problem in the vibration method of FIG. 1 and the stability is lacking. Since the mirror 7 needs to be set at the bending point of the optical axis, the optical axis from the laser 1 to the lens 8 is L.
There is a drawback that it becomes a letter shape, and the use efficiency of the space is reduced (the device configuration is enlarged).

(4) Object of the Invention An object of the present invention is to provide an optical information reproducing apparatus which is capable of vibrating a light flux stably and surely without using a turning mirror and which is advantageous for miniaturization.

(5) Structure of the Invention According to the present invention, when the focal positions of the two lenses are aligned on the optical axis and one of the lenses is moved in the direction perpendicular to the optical axis in this state, the light passing through the combined lens is transmitted. Is made by paying attention to the characteristic that the direction of light is changed while keeping the parallel bundle. In an optical information reproducing apparatus that optically scans a recording medium to read information, a concave lens, a convex lens or a convex lens is used. Combining lenses made up of the same lens are arranged so that the focal positions of the respective lenses coincide with each other on a light beam for obtaining a control signal, and one of the combination lenses is moved in a direction orthogonal to the light beam so that the light beam end is the optical axis. It is characterized in that it is configured to move in an orthogonal direction to perform tracking.

(6) Examples of the Invention Hereinafter, the present invention will be described in detail with reference to the illustrated examples. FIG. 2 is an explanatory view of essential parts showing an embodiment of the present invention, and FIG. 3 is an overall view. In this example, instead of the rotating mirror 7 of FIG. 1, a combination lens 10 composed of a concave lens 10a and a convex lens 10b is arranged between the λ / 4 plate 4 and the focusing lens 8,
(Both lenses 10a and 10b may be convex lenses.) One of them (convex lens 10b in this example) is reciprocated in the direction orthogonal to the optical axis 13. The means for reciprocating the convex lens 10b is
A single-layer or multi-layer piezoelectric element 9 is preferable at high frequencies,
VCM may be used at low frequencies. When the convex lens 10b is on the laser 1 side and the concave lens 10a is on the medium 11 side, the focal length b of the former is made longer than the focal length a of the latter (b> a), and the focal positions f of both are matched. Under this condition convex lens 10b
If the center 12 of the concave lens 10a coincides with the optical axis 13 of the concave lens 10a (solid line position in FIG. 2), the parallel luminous flux L ₁₁ incident on the convex lens 10b side is emitted as the luminous flux L _{12 also} parallel to the optical axis 13. .
In this case, the diameter of the light flux L ₁₂ is such that the closer the focal length b is to a, the light flux L
It approaches the diameter of ₁₁ .

On the other hand, the convex lens 10b is moved in the direction B'that is orthogonal to the optical axis 13.
When the light beam L ₁₂ is moved in parallel with, the light beam L ₁₂ is emitted in the direction inclined by the angle θ from the optical axis 13 without changing the diameter (the state of the broken line in FIG. 2). Therefore, the convex lens 10b is attached to the optical axis 13 by the piezoelectric element 9.
By vibrating around, the light flux L ₁ incident on the medium 11 vibrates in the direction of arrow B. Since the other structures are the same as those in FIG. 1, the same reference numerals are given and detailed description thereof will be omitted. Also, the concave lens 10a and the convex lens 10b may be arranged in the opposite way or the lenses 10a, 10
b Similar effects can be obtained by using convex lenses for both.

FIG. 4 shows an explanatory view when both the lenses 10a and 10b are convex lenses. Since the focal positions f of both lenses are made to coincide with each other, if the incident light is a parallel bundle, the emitted light is also a parallel bundle. The refraction of the emitted light is performed by vibrating one lens in a direction perpendicular to the optical axis.

(7) Effects of the Invention As described above, according to the present invention, the light flux irradiating the surface of the recording medium is vibrated at a high speed only by vibrating one of the concave-convex combination lens or the convex-combination lens combination in the direction orthogonal to the optical axis. Therefore, stable and highly accurate operation can be expected as compared with the rotary drive system. Further, since it is not necessary to bend the optical axis from the light source to the recording medium, there is an advantage that the space can be effectively utilized and the device configuration can be downsized.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an optical system in a conventional optical information reproducing apparatus using a rotating mirror, FIGS. 2 and 3 are main part explanatory views and an overall view showing one embodiment of the present invention, and FIG. The figure is an explanatory view in the case of convex lenses. In the figure, 1 is a light source (semiconductor laser), 9 is a piezoelectric element, 10 is a concavo-convex combined lens, 11 is a recording medium, and 13 is an optical axis.

Claims (1)

[Claims] 1. An optical information reproducing apparatus for optically scanning a recording medium to read information, wherein a concave lens, a convex lens or a combination lens composed of convex lenses is provided on a light beam whose focal position is a control signal. Are arranged so as to coincide with each other, and one of the combined lenses is moved in a direction orthogonal to the light beam to move a light beam end in a direction orthogonal to the optical axis to perform tracking. Expression information reproducing device.