JPH06274932A - Optical pickup device - Google Patents

Abstract

PURPOSE:To eliminate the need of excess optical power in the case of erasing without lowering the resolution of an information bit at the time of reproduction even though a light spot has astigmatism by making the light spot on a recording medium an elliptic spot respectively having a major axis or a minor axis in the track direction at the time of erasing and reproducing a record. CONSTITUTION:A light beam projected from a light source 1 passes through a collimator lens 2, is circularly shaped by a shaping prism 7 in terms of a beam cross-sectional shape, passes through a beam spliter 3, is bent by a deflecting prism 4 in terms of an optical path, and forms the light spot on the surface of the recording medium through an objective lens 5. The reflected light reversely advances so as to be reflected by the beam spliter, and is made incident on a detecting optical system, so that an information signal, a track error signal, a focusing signal, and a focusing error, signal, etc., can be obtained. As to the light spot having the astigmatism; the spot on the medium 6 is controlled to become the elliptic spot having the major axis or the minor axis in the track direction in the case of erasing or reproducing the information. Thus, the excess light is not required to irradiate an adjacent track in the case of erasing and the resolution of the information bit is improved in the case of reproducing.

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 using a semiconductor laser as a light source.

[0002]

2. Description of the Related Art As shown in FIG. 10, an optical pickup device for writing and reading information on a storage medium collimates a light beam from a light source 1 by a collimating lens 2, collimates the beam, and forms a beam splitter 3 and a deflection prism 4. , And the recording medium 6 through the objective lens 5. A semiconductor laser is generally used as a light source in this case.

A semiconductor laser S as such a light source 1
As for L, as shown in FIG. 11, the divergence angle of the light beam emitted is different between the vertical direction θ ₁ and the horizontal direction θ ₂ with respect to the joint portion, and the vertical direction θ ₁ is the long axis and the horizontal direction. θ ₂ becomes a short-axis elliptical beam. Therefore, this light beam is
When condensed by a general optical pickup device as shown in 0, the light spot on the recording medium 6 also becomes an elliptical spot.

When the major axis of the elliptical spot coincides with the track direction of the recording medium 6, the resolution of the information pits is lowered and the information cannot be read accurately. If the minor axis of the elliptical spot coincides with the track direction, for example, when data is recorded on the Nth track as shown in FIG. 12, the light spot reaches the (N−1) th track or the (N + 1) th track and the rack. , The light beam is emitted to the N−1th track and the N + 1th track, which are not related to recording, and extra optical power is required.

Therefore, in order to avoid this, in general, beam shaping for shaping an elliptical beam into a circular beam is performed. An example thereof is shown in FIG. FIG. 13A shows the shaping of the light beam in the horizontal direction, and FIG. 13B shows the shaping in the vertical direction. The horizontal direction θ ₂ of the light beam is (a) in FIG.
As shown in (1), the light beam obtained from the light source 1 through the collimating lens 2 is expanded by the two prisms 7A and 7B from the diameter a of the parallel light beam to the diameter b. At this time, the beam shaping magnification is A = b / a. On the other hand, as shown in FIG. 13B, the parallel light beams in the vertical direction are reflected by the prisms 7C and 7D.
And the diameter c of the parallel light beam does not change before and after the prisms 7C and 7D. The beam shaping magnification is determined so that b = c. In this way, the surface spot on the recording medium 6 of the optical system that has undergone beam shaping can be obtained as a circular spot if the adjustment is appropriate.

[0006]

However, if the adjustment at the time of beam shaping is misaligned, the following problems will occur. Now, assuming that the beam shaping magnification is A, the focal length fc of the collimator lens 2 is equivalent to the horizontal focal length becoming A * fc. The vertical focal length remains fc. Therefore, when the distance between the light source 1 and the collimator lens 2 deviates from an appropriate value, astigmatism occurs as shown in FIG. 14, and astigmatism occurs in the light spot. Here, the astigmatic difference refers to the distance between the most narrowed position in the x direction and the most narrowed position in the y direction. Table 1 shows values of astigmatism of the light spot on the upper surface of the recording medium 6 with respect to the displacement between the light source 1 and the collimator lens 2. This table shows the case where the focal length of the collimator lens 2 is 8 mm, the beam shaping magnification is 2.3 times, and the focal length of the objective lens is 4 mm.

[0007]

[Table 1]

As can be seen from the above, the recording medium 6 can be obtained by only shifting the distance between the light source 1 and the collimating lens 2 by several μm.
An astigmatic difference of 0.5 to 1.5 μm occurs on the top. That is, if the distance between the light source 1 and the collimator lens 2 is shifted,
Astigmatism is generated in the light spot on the recording medium 6, and the generation direction thereof is the track direction, so that the resolution of the information pits is lowered and it becomes impossible to read the information accurately. The gap between the light source 1 and the collimator lens 2 always occurs due to a change with time or a change in environmental temperature.

Therefore, it is an object of the present invention that the resolution of the information pit does not decrease when reproducing information even if the light spot on the surface of the recording medium has astigmatism, and an extra optical power is required when erasing the recording. The present invention provides an optical pickup device that does not operate.

[0010]

SUMMARY OF THE INVENTION An optical pickup device of the present invention includes a beam shaping means for shaping a light beam from a light source, and a light beam passing through the beam shaping means for condensing the rewritable recording medium. A condensing optical system, a light separating unit that separates the reflected light from the recording medium that receives the light beam from the condensing optical system and the light beam from the light source, and performs recording based on the separated reflected light. A detection optical system for detecting the information recorded on the medium and a control so that the light spot on the recording medium becomes an elliptical spot having a major axis in the track direction when recording or erasing the information on the recording medium. When reproducing information on the medium, there is provided focus control means for controlling the light spot on the recording medium to be an elliptical spot having a minor axis in the track direction.

[0011]

In the optical pickup device of the present invention, the light spot on the recording medium has a long axis in the track direction so that the optical power from the light source can be effectively used when recording and erasing information on the recording medium. Control so that it becomes an elliptical spot,
On the other hand, when reproducing information on the recording medium, the light spot on the recording medium is controlled to be an elliptical spot having a short axis in the track direction in order to improve the accuracy of the read data. As a result, even if there is astigmatism on the surface of the recording medium, the resolution of the information pit does not decrease when reading information, and an extra light source output is not needed when recording and erasing, so efficient data recording, Playback and deletion are performed.

[0012]

EXAMPLE An example of the present invention will be described below. Figure 1
FIG. 4 shows a configuration diagram of an optical pickup device of the present invention. First, the light beam emitted from the light source 1 is collimated by the collimator lens 2. The light beam, which is considered as parallel light,
The beam shaping prism 7, which is a beam shaping unit, shapes the parallel beam cross-section into a circular shape. Then, the light passes through the beam splitter 3 which is the light separating means and is input to the deflection prism 4 of the condensing optical system. The deflecting prism 4 bends the optical path substantially at a right angle, and the objective lens 5 irradiates the recording surface of the rewritable recording medium 6 with the light. The diameter is about 1 on the surface of the recording medium 6.
A light spot is formed so as to form a circle of μm.

The light beam reflected by the recording medium 6 passes through the objective lens 5 to become parallel light again, is reflected by the deflecting prism 4 and is reflected by the beam splitter 3 to obtain an information signal,
A detection optical system for a track error signal, a focus signal, a focus error signal, etc. is reached. That is, the reflected light from the recording medium 6 and the light beam from the light source 1 are separated by the beam splitter 3 which is the light separating means, and reflected from the recording medium 6 by the detection optical system which detects the information stored in the recording medium. Enter the light.

Here, in the optical system using beam shaping,
As described above, the gap between the light source 1 and the collimator lens 2 always occurs due to the change with time or the environmental temperature. Therefore, in the present invention, the influence of the astigmatism on the spot on the medium 6 due to the gap is prevented. Therefore, the focus control means performs the following control.

With respect to a light spot having astigmatism, when recording and erasing information on the recording medium 6, as shown in FIG.
The light spot on the recording medium 6 is controlled to be an elliptical spot having a major axis in the track direction. By doing so, when recording and erasing data on the recording medium 6, no extra light is emitted to the adjacent tracks, and the light beam from the light source 1 can be efficiently used.

Next, FIG. 3 shows the relationship between the light spot having astigmatism and the track 6A of the recording medium 6.
3A shows the case where the long axis of the light spot is located in the track direction, and FIG. 3B shows the case where the long axis and the short axis of the light spot are located slightly displaced from the track direction.
<C> indicates the case where the minor axis of the light spot is located in the track direction. Then, as shown in FIG.
<B><c> indicates the magnitude of the amplitude of the track error signal corresponding to each light spot position of <a><b><c> in FIG. As can be seen from FIGS. 3 and 4, the amplitude of the track error signal becomes maximum when the light spot is most narrowed in the track orthogonal direction, that is, when the major axis of the elliptical spot is in the track direction.

Therefore, before recording and erasing information on the recording medium 6, the tracking error signal is monitored while offsetting the focusing error signal, and the offset value of the focusing error signal is held at the maximum amplitude of the tracking error signal. Then, the recording is erased in the focused state. In this case, the relationship between the recording medium 6, the objective lens 5, the track orthogonal direction beam 8 and the track direction beam 9 is shown in FIG.

On the other hand, when reproducing information on the recording medium 6 for a light spot having astigmatism, as shown in FIG.
The light spot on the recording medium 6 is controlled to be an elliptical spot having a short axis in the track direction. By doing so, when the information on the recording medium 6 is reproduced, the resolution of the information pit is improved and the information can be reproduced with high accuracy.

Next, FIG. 7 <a><b><c> is shown in FIG.
<a><b><c> shows the magnitude of the amplitude of the pre-pit signal corresponding to the respective astigmatic light spots,
Similarly, FIG. 8 <a><b><c> is similar to FIG. 3 <a><b>.
The magnitude of the amplitude of the data signal corresponding to each light spot having astigmatism in <c> is shown.

As can be seen from these figures, the amplitude of the prepit signal or the data signal becomes maximum when the light spot is most narrowed down in the track direction, that is, when the minor axis of the elliptical spot is in the track direction.

Therefore, before recording and erasing information on the recording medium 6, the pre-pit signal and the data signal are monitored while offsetting the focus error signal, and when the amplitude of the pre-pit signal and the data signal is maximum, the focus error signal The offset value is held, and recording / reproduction is performed in that focus state. In this case, the relationship between the recording medium 6, the objective lens 5, the beam 8 in the track orthogonal direction, and the beam 9 in the track direction is as shown in FIG.

Further, when the objective lens 5 is moved to the track to be recorded / reproduced on the recording medium 6, that is, at the time of direct seek of the condensing optical system, the light spot on the recording medium 6 is an ellipse having a major axis in the track direction. Control so that it becomes a spot. Before doing a direct seek,
The track error signal is monitored while offsetting the focus error signal, the offset value of the focus error signal is held when the amplitude of the track error signal is maximum, and track counting is performed. As a result, the accuracy of track counting is significantly improved.

[0023]

As described above, according to the present invention, even if the light spot on the surface of the recording medium has astigmatism, the light spot on the recording medium has a short axis in the track direction when reading information. So that it becomes an elliptical spot with
Since the resolution of the information pit does not decrease and the light spot on the recording medium is an elliptical spot having a long axis in the track direction during recording and erasing, an optical pickup device that does not require extra optical power is provided. Can be provided.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an optical pickup device of the present invention.

FIG. 2 is an explanatory diagram when a long axis of an astigmatism light spot is located in a track direction of a recording medium.

FIG. 3 is an explanatory diagram showing a positional relationship between a light spot having astigmatism and a track of a recording medium.

FIG. 4 is an explanatory diagram showing the magnitude of the track error signal amplitude in the respective positional relationships of FIG.

FIG. 5 is an explanatory diagram showing a relationship between a recording medium 6, an objective lens 5, a track orthogonal direction beam 8 and a track direction beam 9 when recording and erasing information.

FIG. 6 is an explanatory diagram when a short axis of an astigmatism light spot is located in a track direction of a recording medium.

7 is an explanatory diagram showing the magnitude of pre-pit signal amplitude in the case of the respective positional relationships of FIG. 3. FIG.

FIG. 8 is an explanatory diagram showing the magnitude of the data signal amplitude in the respective positional relationships of FIG.

FIG. 9 is an explanatory diagram showing a relationship between a recording medium 6, an objective lens 5, a track orthogonal direction beam 8 and a track direction beam 9 at the time of recording / reproducing information.

FIG. 10 is a configuration diagram of a conventional optical pickup device having no beam shaping means.

FIG. 11 is an explanatory diagram of a light beam when the light source is a semiconductor laser.

FIG. 12 is an explanatory diagram at the time of recording information when the short axis of the astigmatism light spot is located in the track direction of the recording medium.

FIG. 13 is an explanatory diagram of a beam shaping unit.

FIG. 14 is an explanatory diagram of astigmatism.

[Explanation of symbols]

 1 light source 2 collimator lens 3 beam splitter 4 deflection rhythm 5 objective lens 6 recording medium 7 prism 8 track orthogonal direction beam 9 track direction beam

Claims (4)

[Claims] 1. A beam shaping means for shaping a light beam from a light source, a condensing optical system for condensing the light beam passing through the beam shaping means onto a rewritable storage medium, and the condensing optical system. Light separating means for separating the reflected light on the recording medium that received the light beam from the light beam from the light source, and detecting the information recorded on the storage medium based on the separated reflected light. When detecting and erasing the information on the recording medium and the recording medium, the light spot on the recording medium is controlled so as to be an elliptical spot having a major axis in the track direction, and at the time of reproducing the information on the recording medium. An optical pickup device comprising: a focus control unit that controls the light spot on the recording medium to be an elliptical spot having a short axis in the track direction. 2. The focus control means controls the focus so that the amplitude of the track error signal is maximized when the information is erased from the recording medium, and the focus control means when the information is reproduced on the recording medium. 2. The optical pickup device according to claim 1, wherein focus control is performed so that the amplitude of the pre-pit signal or the data signal is maximized. 3. A beam shaping means for shaping a light beam from a light source, a condensing optical system for condensing the light beam passed through the beam shaping means onto a rewritable recording medium, and from this condensing optical system. Of light reflected by the recording medium and the light beam from the light source that have received the light beam, and information recorded on the recording medium is detected based on the reflected light separated here. A light comprising a detection optical system and focus control means for controlling the light spot on the recording medium to be an elliptical spot having a major axis in the track direction during direct seek of the condensing optical system. Pickup device. 4. The optical pickup device according to claim 3, wherein the focus control means controls the focus so that the amplitude of the track error signal is maximized.