JPH06150360A - Optical pickup device - Google Patents

Abstract

PURPOSE:To provide an optical pickup device having high efficiency of utilization of a laser light source. CONSTITUTION:An aperture 3a for limiting the passage of light 2 radiated from a semiconductor laser light source 1 is made elliptical. The major axial direction of the aperture 3a is made parallel to the horizontal direction of the light source 1 and the angle of estimate of the aperture 3a to the light source 1 is made large while keeping a converged light spot 9 circular.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup device for optically recording / reproducing information.

[0002]

2. Description of the Related Art FIG. 4A shows the structure of a conventional optical pickup device. In the figure, 1 is a semiconductor laser light source, 2 is
Is a radiated light from the semiconductor laser light source 1, 3 is a circular opening for limiting the passage of the radiated light 2 as shown in FIG.
4 is an objective lens for converging the radiated light 2 on the recording medium 5,
6 is the reflected light from the recording medium 5, 7 is the emitted light 2 and the reflected light 6
Is a beam splitter that separates the reflected light, 8 is a photodetector that receives the reflected light 6, and 9 is a focused spot.

Next, the operation will be described. The emitted light 2 from the semiconductor laser light source 1 has an elliptical emission intensity distribution. That is, the intensity distribution of the radiated light 2 can be represented as an ellipse by connecting points that are ½ of the peak intensity. That is, the intensity of the emitted light 2 continuously decreases as it deviates from the optical axis of the semiconductor laser light source 1, but the attenuation in the minor axis direction is greater than that in the major axis direction of the ellipse. Generally, the direction in which the emitted light 2 is greatly attenuated, that is, the minor axis direction of the ellipse is called the horizontal direction of the laser, and the direction perpendicular to this is called the vertical direction.

The emitted light 2 from the semiconductor laser light source 1 is limited by the circular opening 3 and is focused on the recording medium 5 by the objective lens 4. After this, it is modulated by the recorded information on the recording medium 5 and reflected. The reflected light 6 reflected by the recording medium 5 is separated from the emitted light 2 by the beam splitter 7, converted into an electric signal by the photodetector 8 and used as digital data or the like.

By the way, in order to make the recording density as high as possible, the shape of the focused spot 9 on the recording medium 5 needs to be circular. The shape of the focused spot 9 depends on the variation in the intensity of the peripheral portion of the opening 3, and tends to become longer in the direction in which the intensity of the radiated light 2 around the aperture 3 decreases. Therefore, the diameter of the opening 3 is such that the angle of view of the opening 3 as viewed from the semiconductor laser light source 1 is 1 with respect to the peak intensity of the emitted light 2 in the horizontal direction.
The angle is set to be smaller than the angle that gives the intensity of / 2, ie, the full-width half-maximum angle in the horizontal direction, and the fluctuation of the radiated light 2 at the periphery of the opening 3 is generally set to 1: 2 or less. Target.

[0006]

The conventional optical pickup device is constructed as described above, and the prospective angle of the opening 3 must be less than or equal to the full-width half-maximum angle of the semiconductor laser light source 1 in order to utilize the luminous flux. There was a problem of inefficiency.

The present invention has been made to solve the above problems, and an object of the present invention is to obtain an optical pickup device having a high utilization efficiency of laser light.

[0008]

According to a first aspect of the present invention, there is provided an optical pickup device in which an opening for restricting passage of radiated light has an elliptical shape, and its major axis direction is parallel to the horizontal direction of a laser light source. Is.

In the optical pickup device according to a second aspect of the present invention, the major axis direction of the opening is parallel to the track direction of the recording medium.

[0010]

According to the first aspect of the present invention, the major axis of the elliptical opening is parallel to the horizontal direction of the laser light source, the horizontal numerical aperture of the laser light source is increased, and the radiant light intensity around the opening is increased. The shape of the focused spot on the recording medium is kept circular even if the intensity is less than 1/2 of the intensity at the center, and the prospective angle of the aperture can be set to be larger than the full-width half-maximum angle of the laser light source. The utilization efficiency of is improved.

According to a second aspect of the present invention, the long axis direction of the opening, the horizontal direction of the laser light source and the track direction of the recording medium are parallel to each other, the rim strength in the track direction is low, and the ring spot of the focused spot is formed in the track direction. This does not occur and the ring zone does not hang on the adjacent pit of the track, and the reproduction characteristic is stabilized.

[0012]

【Example】

First Embodiment Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a front view of the opening 3a according to the first embodiment.
Has an elliptical shape and limits the spread of the emitted light 2, and corresponds to the opening 3 in FIG. Other configurations are shown in FIG.
Is the same as.

Next, the operation will be described. The major axis direction of the elliptical opening 3a is parallel to the horizontal direction of the semiconductor laser light source 1. Also, the opening 3 viewed from the semiconductor laser light source 1
The prospective angle of a is set to be larger than the full-width half-value angle of the emitted light 2 in the horizontal direction. Here, the radius d of the focused spot 9 on the recording medium 5 is roughly given by d = K (λ / NA) (1). NA is the numerical aperture, λ is the wavelength of the semiconductor laser light source 1, and K is a coefficient determined by the ratio of the intensity of the peripheral portion of the aperture 3a to the peak intensity of the luminous flux within the aperture 3a. This strength ratio is called rim strength, and K decreases as rim strength decreases.

In the first embodiment, the elliptical opening 3a is used, the axis of the emitted light 2 in the minor axis direction and the major axis direction of the opening 3a are parallel, and the numerical aperture of the semiconductor laser light source 1 in the horizontal direction increases. . Therefore, even if the horizontal rim strength of the semiconductor laser light source 1 decreases and the coefficient K increases, the numerical aperture NA also increases and the diameter of the horizontal focused spot 9 of the semiconductor laser light source 1 does not increase. The condensing spot 9 is maintained in a circular shape, and an optical pickup device with high utilization efficiency of the emitted light 2 of the semiconductor laser light source 1 can be obtained.

Second Embodiment In the first embodiment, the major axis direction of the elliptical opening 3a is parallel to the horizontal direction of the semiconductor laser light source 1, but in the second embodiment, the major axis direction of the opening 3a is as shown in FIG. And parallel to the track direction of the recording medium 5. As shown in FIG. 3, the focused spot 9 is formed of a central portion 9a and an annular zone 9b around the central portion 9a, and the intensity of the annular zone 9b decreases as the rim strength decreases. Generally, the track on the recording medium 5 is formed by rows of regions called pits having different complex reflectances,
The information is recorded on the track on the recording medium 9 in the pit arrangement state. When the pits on the same track are close to each other, the ring zone 9b of the focused spot 9 is applied to the adjacent pits, and the pit state cannot be correctly reproduced. In the second embodiment, the major axis direction of the opening 3a is parallel to the horizontal direction of the semiconductor laser light source 1 and the track direction, the rim strength in the track direction becomes low, and the ring zone 9b does not occur in the track direction, so that they are adjacent to each other. Ring 9b in the pit
It is possible to obtain stable reproduction characteristics without being affected.

[0016]

As described above, according to the first aspect of the present invention, since the opening has an elliptical shape and its major axis direction is parallel to the horizontal direction of the laser light source, the shape of the focused spot on the recording medium is formed. The angle of view of the aperture with respect to the laser light source can be increased while maintaining a circular shape, and an optical pickup device with good utilization efficiency of the emitted light from the laser light source can be obtained.
Further, according to claim 2, the long axis direction of the opening, the horizontal direction of the laser light source, and the track direction of the recording medium are parallel to each other, the rim strength in the track direction is weakened, and an annular zone of a focused spot is formed in the track direction. This does not occur, the ring zone does not cover the adjacent pits of the track, and the reproduction characteristics can be stabilized.

[Brief description of drawings]

FIG. 1 is a front view of an opening of an optical pickup device according to a first embodiment.

FIG. 2 is a front view of an opening of an optical pickup device according to a second embodiment.

FIG. 3 is an intensity distribution diagram of a focused spot of the optical pickup device according to the second embodiment.

FIG. 4 is a configuration diagram of a conventional device.

[Explanation of symbols]

 1 semiconductor laser light source 2 radiated light 3a aperture 4 objective lens 5 recording medium 6 reflected light 8 photodetector 9 focused spot

Claims (2)

[Claims] 1. A laser light source that emits elliptical radiation having different divergence angles in the horizontal direction and the vertical direction, an opening that limits passage of the radiation, and radiation that passes through the opening is converged on a recording medium. In an optical pickup device equipped with an optical system and a detection system for detecting reflected light from a recording medium, the opening is elliptical, and its major axis direction is parallel to the horizontal direction of the laser light source. Pickup device. 2. The optical pickup device according to claim 1, wherein the major axis direction of the opening is parallel to the track direction of the recording medium.