JP2966612B2 - Information playback device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an information reproducing apparatus for reproducing information by irradiating a recording medium with a light beam.

[0002]

2. Description of the Related Art In an optical system of an optical disk drive such as a CD (compact disk) drive, an elliptical laser beam emitted from a semiconductor laser is converted into a circular light beam by a shaping prism, and then converted into an optical disk by an objective lens. As a light spot on the track. Return light from the optical disc is collected by the objective lens,
The light enters the light receiving element via the cylindrical lens.

The light receiving element has a four-divided light receiving part,
The division direction is set to be 45 degrees with respect to the generatrix direction of the cylindrical lens (the cylindrical axis direction of the cylindrical lens).

As a result, a reproduction signal is obtained by the light receiving element, and a focus error signal and a tracking error signal are obtained by the astigmatism method and the push-pull method, respectively.

[0005]

However, in the above-mentioned conventional configuration, if the oscillation wavelength of the semiconductor laser changes due to a change in the ambient temperature, an offset occurs in the tracking error signal, so that accurate tracking cannot be performed. have.

That is, when the wavelength of the laser beam changes, the beam direction of the light beam deviates from the optical axis of the optical system due to the wavelength dispersion of the refractive index of the material used for the shaping prism. At this time, even if the light spot shifts in the tangential direction of the track, the light intensity distribution of the return light on the light receiving element changes as if the light spot shifted in the direction orthogonal to the track.

The reason will be described with reference to FIGS.

It is assumed that the return light from the optical disk is shifted by S in the tangential direction on the main surface of the cylindrical lens as shown in FIG. X indicates a direction perpendicular to the generatrix direction of the cylindrical lens, and Y indicates the generatrix direction.

Since the cylindrical lens acts as a lens for the X component of S, as shown in FIG. 6, the return light is focused before the light receiving element. For this reason, the intensity distribution of the light spot is switched left and right. On the other hand, since it does not work as a lens with respect to the Y-direction component of S, as shown in FIG.

In FIGS. 6 and 7, P and Q are the main surface of the cylindrical lens and the light receiving surface of the light receiving element, respectively, and L and M are the optical axis of the optical system and the central axis of the return light, respectively.

The shift (S ') of the return light on the light receiving element due to the operation of the cylindrical lens is as shown in FIG. 5, but the intensity distribution of the light spot is in the direction (S) orthogonal to the track. ). Therefore, an offset occurs in the tracking error signal, so that accurate tracking cannot be performed.

[0012]

[0013]

According to a first aspect of the present invention, there is provided an information reproducing apparatus, comprising: a light source;
The emitted divergent beam is shaped into a circular optical beam by a shaping prism.
And irradiates the light onto a track of a recording medium, converges return light from the recording medium through a cylindrical lens to a light receiving element, and obtains a reproduction signal and a tracking error signal from an output of the light receiving element. A cooling device that cools the light source so as to keep the wavelength of the light beam constant, and a track offset detection circuit that obtains a track offset from a tracking error signal, and operates the cooling device according to the track offset. It is characterized by:

[0014]

[0015]

According to the structure of the first aspect, the light emitted from the light source is emitted.
Convert divergent beam into circular light beam by shaping prism
And irradiates the light on the track of the recording medium, the return light from the recording medium converges on the light receiving element through the cylindrical lens, and an information reproducing apparatus that obtains a reproduction signal and a tracking error signal from the output of the light receiving element. a cooling device for cooling the light source so as to keep the wavelength constant, and the track offset detecting circuit for obtaining the track offset from the tracking error signal is provided with, so to actuate the cooling device in accordance with the track offset, shaping prism And using a cylindrical lens
In the configuration to obtain the raw signal and the tracking error signal
Avoid track offset due to temperature rise
Can be. Thereby, accurate tracking can be performed. In addition, since the cooling device operates as needed, power consumption can be reduced.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS.

As shown in FIG. 1, the optical disk drive (information reproducing apparatus) of this embodiment comprises an optical pickup 2, an amplifier circuit 3 for tracking error signal, an actuator drive circuit 4 for tracking, and a track offset detecting circuit. 5 and a cooling device 6.

The optical pickup 2 is, as shown in FIG.
A semiconductor laser 14 (light source), a collimating lens 20 for converting a divergent beam emitted from the semiconductor laser 14 into a parallel beam, a shaping prism 15 for converting the parallel beam into a circular light beam, and a light beam from the shaping prism 15 Prism 16 for transmitting light from the optical disk 1 (recording medium) to the light receiving element 19, a mirror 11 for reflecting a light beam transmitted through the composite prism 16 toward the optical disk 1, and a light from the mirror 11. An objective lens 7 for converging a beam on the optical disc 1 as a light spot is provided.

The optical pickup 2 also includes a light receiving element 19 for detecting return light from the compound prism 16, a spot lens 17 for converging the return light on the light reception element 19, and a light source between the spot lens 17 and the light reception element 19. It has a cylindrical lens 18 provided.

The light receiving element 19 has a four-part light receiving part (not shown), and the dividing direction is set to be 45 degrees with respect to the generatrix direction of the cylindrical lens 18. Thus, not only a reproduction signal can be obtained by the light receiving element 19, but also a focus error signal and a tracking error signal can be obtained.

The optical pickup 2 further includes a tracking coil 8 (FIG. 1) and a magnetic circuit (not shown) for driving the objective lens 7 in the tracking direction.

The track offset detection circuit 5 is configured to obtain a track offset from a tracking error signal from the optical pickup 2 and output a signal for activating the cooling device 6 according to the magnitude of the track offset.

Here, a method of obtaining the track offset will be described with reference to FIG.

When the light spot moves in the radial direction of the optical disk 1, the tracking error signal output from the optical pickup 2 becomes a curve that changes in an S shape as shown in FIG.

For the sake of simplicity, the substrate 1 of the optical disc 1
As shown in FIG. 2B, it is assumed that grooves 1b are formed in a spiral shape (or concentrically), and the grooves 1b or the lands 1c between the grooves 1b are used as tracks. It is said that.

When there is no track offset, the zero level of the tracking error signal is located at the center of the amplitude.
If there is a track offset, the 0 level will be shifted from the center of the amplitude.

The track offset is T, the tracking error signal from level 0 to the maximum level is A, the level from the 0 level to the minimum level is B, and the track pitch is 1.6.
If μm, T = (A−B) / 2 (A + B) × (1.6 / π) (1)

Here, the tracking error signal is assumed to be a sin curve, and the zero level of the tracking error signal is approximated to be on a tangent passing through the origin of the sin curve.

The track offset detection circuit 5 includes, for example, a microcomputer, and calculates the track offset using the above equation (1).

The cooling device 6 operates in accordance with the track offset obtained by the track offset detection circuit 5, and cools the semiconductor laser 14 so that the track offset becomes zero. .

As the cooling device 6, specifically, for example, a Peltier element arranged in close contact with the semiconductor laser 14 is used. Further, the cooling fins may be arranged in close contact with the semiconductor laser 14, or an air cooling fan may be arranged near the semiconductor laser 14. Furthermore, water cooling or cooling using a CFC-based refrigerant may be used.

In the above configuration, the optical pickup 2
The light beam from FIG. 1 is irradiated as a light spot on the track of the optical disc 1, and the return light from the optical disc 1 is transmitted to the spot lens 17 of the optical pickup 2 and the cylinder.
The light is converged on the light receiving element through the cull lens 18 and detected. As a result, a reproduction signal, a tracking error signal, and a focus error signal are obtained.

After the tracking error signal is amplified by the amplifier circuit 3, it is input to the actuator drive circuit 4. The actuator drive circuit 4 controls the tracking coil 8 so that the tracking error signal becomes zero.
, And drives the objective lens 7 in the tracking direction. Thus, the light spot follows the track.

The track offset detection circuit 5 calculates a track offset based on the tracking error signal from the optical pickup 2. The cooling device 6
It operates according to the track offset, and cools the semiconductor laser 14 so that the track offset becomes zero.

As a result, the semiconductor laser 14 is maintained at a predetermined temperature, so that the oscillation wavelength (wavelength of laser light) of the semiconductor laser 14 becomes constant. Therefore, accurate tracking can be performed, and information can be accurately reproduced.

In the above embodiment, specific examples of the optical disk 1 include a CD and a magneto-optical disk, but any type may be used as long as it reproduces information by irradiating a light beam.

In addition to the disk-shaped optical disk 1,
The present invention is also applicable to an information reproducing apparatus for reproducing a card-shaped or tape-shaped recording medium. Furthermore, the present invention can be applied to an information recording / reproducing apparatus that performs not only information reproduction but also information recording.

[0038]

[0039]

According to the first aspect of the present invention, there is provided an information reproducing apparatus comprising:
As described above, the divergent beam emitted from the light source
The light beam is converted into a circular light beam by a rhythm and irradiated onto a track of a recording medium. The return light from the recording medium is converged on a light receiving element through a cylindrical lens, and a reproduction signal and a tracking error signal are obtained from the output of the light receiving element. In the information reproducing apparatus, a cooling device for cooling the light source so as to keep the wavelength of the light beam constant, and a track offset detecting circuit for obtaining a track offset from a tracking error signal are provided, and cooling is performed according to the track offset. Since the device operates, the shaping prism and
The playback signal and tracking error are
Error caused by the rise in temperature
Rack offset can be prevented. Thus, accurate tracking can be performed, so that information can be accurately reproduced. In addition, since the cooling device operates as needed, there is an effect that power consumption can be reduced.

[Brief description of the drawings]

FIG. 1, showing an embodiment of the present invention, is a block diagram illustrating a schematic configuration of an optical disk drive.

FIG. 2 is a perspective view showing a schematic configuration of the optical pickup of FIG. 1;

FIG. 3 is an explanatory diagram showing a method of obtaining a track offset in the track offset detection circuit of FIG.

FIG. 4 shows a conventional example, and is an explanatory diagram showing a shift of a light spot on a main surface of a cylindrical lens.

FIG. 5 is an explanatory diagram showing a shift of a light spot on a light receiving element.

FIG. 6 is an explanatory diagram showing a shift component of a spot in a direction perpendicular to a generating line of a cylindrical lens.

FIG. 7 is an explanatory diagram showing a shift component of a spot in a generatrix direction of a cylindrical lens.

[Explanation of symbols]

 Reference Signs List 1 optical disk (recording medium) 2 optical pickup 5 track offset detection circuit 6 cooling device 14 semiconductor laser (light source)

Claims (1)

(57) [Claims] A divergent beam emitted from a light source is shaped by a shaping processor.
The light beam is converted into a circular light beam by a rhythm and irradiated onto a track of a recording medium. The return light from the recording medium is converged on a light receiving element through a cylindrical lens, and a reproduction signal and a tracking error signal are obtained from the output of the light receiving element. The information reproducing apparatus is provided with a cooling device for cooling the light source so as to keep the wavelength of the light beam constant, and a track offset detection circuit for obtaining a track offset from a tracking error signal. An information reproducing apparatus characterized by operating the apparatus.