JP3374000B2 - Optical pickup device and mark forming method - Google Patents

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 which forms a mark on an information recording medium by utilizing both a main lobe and a side lobe formed by a super-resolution effect.

[0002]

2. Description of the Related Art In recent years, the demand for increasing the storage capacity of information storage media using laser light, which is a light beam, has generally been met by increasing the storage density.

The storage density depends on the number of marks that can be formed on the information recording medium. Therefore, it is necessary to reduce the spot diameter of the laser beam formed on the information recording medium.

That is, an optical pickup device used for a compact disc or the like condenses laser light emitted from a semiconductor laser with an objective lens to form a spot on an information recording medium, thereby writing / reading information. / Erasure is performed. At this time, the diameter of the spot formed on the information recording medium determines the recording density.

The spot diameter is inversely proportional to the numerical aperture of a condenser lens for forming the spot, and is also proportional to the wavelength of laser light. Therefore, a condenser lens having a numerical aperture as large as possible and a laser beam having a short wavelength are used. However, since laser light is generally generated by a semiconductor laser, its wavelength is also limited.

For this reason, the super-resolution effect (M. Borna
nd E. Wolf: Principles of O
ptics "Principles of Optics" P. A technology using 628 Tokai University Press is disclosed (Japanese Patent Laid-Open No. 2-12).
622).

According to the super-resolution effect, the central portion of the laser light incident on the objective lens is blocked and condensed,
The light intensity distribution of the formed main lobe becomes sharp, and the spot diameter of the main lobe can be made smaller than that in the case where light is not shielded. At this time, the light intensity of the side lobes formed on both sides of the main lobe also has a characteristic of being larger than that in the case where the super-resolution effect does not occur.

In the above-mentioned publication, the laser light emitted from the semiconductor laser is split symmetrically, and the split laser light is made incident on the condenser lens so that the laser light does not enter the central portion of the objective lens. The spot size is reduced by producing the super-resolution effect.

[0009]

However, when the super-resolution effect is generated as described above, the light intensity of the side lobes becomes large, which causes the following problems.

When the recording layer in the information recording medium uses phase transition, there is a problem that even if the information is written in the main lobe, the written information changes due to the side lobes.

That is, in the information recording medium utilizing the phase transition, when the recording layer is heated at the spot and then rapidly cooled, the heated portion becomes amorphous, and when gradually cooled, it becomes crystallized. Since the crystalline state and the non-crystalline state have greatly different light reflectances, information can be reproduced from the amount of the reflected light.

However, even if the recording layer is heated by the main lobe to be cooled rapidly, it is reheated by the side lobe passing therethrough, and the side lobe is heated though its light quantity is smaller than that of the main lobe. Since it has heat that does not rapidly cool the part, as a result, it is gradually cooled and becomes a crystalline state. Therefore, a situation may occur in which wrong information is written.

In this case, it is necessary to reduce the light quantity of the side lobes, but if the light quantity of the side lobes is reduced without decreasing the light quantity of the main lobe, the super-resolution effect becomes small. There is a problem that the minimum value of is determined by the allowable light amount of the side lobe.

Since the writing / reading / erasing of information is performed by the main lobe, the side lobe is not used and the light quantity of the side lobe becomes a loss.

Therefore, it is necessary to allow for the loss due to the side lobes to emit light, but for this purpose, a semiconductor laser that emits a large amount of light must be used.

However, since there is a limit to the high-power semiconductor laser, it is necessary to give the spot a quantity of light necessary for information recording by beam shaping or the like, but the beam shaping mechanism has poor assembling ability and is weak against changes over time. For this reason, there are problems that the cost of the optical pickup device increases and the reliability decreases.

Further, when reproducing information, since the reproduced signal by the two side lobes is mixed with the reproduced signal by the main lobe, there is a problem that the signal processing becomes complicated.

Therefore, in the present invention, the main lobe is sharpened by the super-resolution effect to form a fine spot, which enables high-density recording and also the side lobe to be used, and the emitted laser light is effectively used. An object of the present invention is to provide a pickup device that can be used and that has low cost and high reliability.

[0019]

In order to solve the above-mentioned problems, the invention according to claim 1 contemplates a light beam from a light source being condensed by a condenser lens, and a main lobe of the light beam on an information recording medium. By writing / erasing a mark on the information recording medium by forming a spot by two side lobes formed in the mark forming direction of the information recording medium sandwiching the spot by the main lobe and the spot by the main lobe, In the optical pickup device for reading the mark written in the information recording medium by receiving the reflected light from the light receiving element through the condenser lens, the spot formed by the two side lobes comes first in the mark forming portion. An asymmetric beam generating means for making the light intensity distribution of the arriving spot larger than the light intensity distribution of the arriving spot And wherein the digit.

The invention according to claim 2 is characterized in that the asymmetric beam generating means is a light shielding plate which asymmetrically shields the laser light with respect to the optical axis of the condenser lens.

The invention according to claim 3 is characterized in that the asymmetric beam generating means is a phase plate for making the phase of the laser light asymmetric with respect to the optical axis of the condenser lens.

The invention according to claim 4 is characterized in that the asymmetric beam generating means is an optical path changing means for making the optical path of the laser light asymmetric with respect to the optical axis of the condenser lens.

According to the fifth aspect of the present invention, the amount of heat given to the information recording medium by the spot by the side lobe having a large light intensity is Q1, the amount of heat given by the spot by the main lobe to the information recording medium is Q2, and the mark is put on the information recording medium. When the amount of heat required for formation is Q3, the light source satisfies the relations of Q1 + Q2 ≧ Q3 and Q2 <Q3 at the time of mark formation.

In the invention according to claim 6, the light source is faster than the mark is written on the information recording medium.
It is characterized in that the relationship of 1 + Q2 ≧ Q3 and Q2 <Q3 is satisfied.

According to a seventh aspect of the present invention, the light beam from the light source is condensed by a condenser lens, and the information recording medium is sandwiched between the spot by the main lobe and the spot by the main lobe of the light beam. In a mark forming method of writing a mark on an information recording medium by forming a spot by two side lobes formed in the mark forming direction, the light intensity distribution of the spot by the two side lobes is formed asymmetrically. When a mark is formed on the recording medium, the mark forming portion is preheated by a spot having a large light intensity distribution among spots formed by the two side lobes.

[0026]

BEST MODE FOR CARRYING OUT THE INVENTION A first embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a schematic configuration of an optical system (incident system) in the pickup device according to the present embodiment.

In the following description, of the two side lobes, a side lobe having a high light intensity is called a large side lobe and a side lobe having a low light intensity is called a small side lobe, and a main lobe, a large side lobe and a small side lobe. The spots formed by are referred to as a main spot, a large side spot, and a small side spot, respectively.

The optical pickup device 1 comprises a semiconductor laser 1
1, a collimator lens 12 and an objective lens 15. Between the collimator lens 12 and the objective lens 15, a light shielding plate 14 as an asymmetric beam generating means is provided asymmetrically with respect to these optical axes.

In the above structure, the laser light emitted from the semiconductor laser 11 as the light source is collimated by the collimator lens 12.
As a result, parallel light 13 (hereinafter appropriately referred to as laser light) is made incident on the objective lens 15. At this time, since the light blocking plate 14 is disposed between the collimator lens 12 and the objective lens 15, a part of the laser light 13 entering the objective lens 15 is blocked and enters the objective lens 15. After that, the laser light 13 incident on the objective lens 15 is condensed and forms a spot 18 on the recording layer 17 of the disk 16.

The diameter of the spot 18 is determined by the numerical aperture of the objective lens 15. Since the laser light 13 entering the objective lens 15 is blocked by the light blocking plate 14, the pupil function changes and the super-resolution effect is obtained. Occurs, which reduces the main spot.

FIG. 2A shows a case where the light shield plate 14 is arranged asymmetrically with respect to the optical axis (the light shield plate 1 according to the present embodiment.
4) and FIG. 2B show a case where the light shield plate 14 is arranged symmetrically with respect to the optical axis (arrangement of the light shield plate 14 according to the prior art), and FIG. It shows the case where it is not arranged. In addition, the light intensity distribution and spot shape of the spot in this state are also shown. In addition,
The arrow shown in the figure showing the spot shape indicates the moving direction of the recording medium, and the hatched area indicates the mark where information is recorded or the mark position where information is recorded.

As can be seen from FIG. 2B, when the light shielding plate 14 is arranged symmetrically with respect to the optical axis of the objective lens 15, side lobes Ib2 and Ib3 having a large light intensity are generated symmetrically and the main The light intensity distribution of the lobe Ib1 becomes sharp.

Therefore, the diameter of the main spot Sb1 can be made smaller than in the case of FIG. 2C in which the light shielding plate is not arranged, but the side lobes Ib2, Ib of high light intensity are obtained.
Since b3 is generated, a total of three spots Sb including the main lobe Ib1 and the two side lobes Ib2 and Ib3.
1, Sb2, Sb3 are formed on the recording layer 17 of the disc 16.

On the other hand, in the case of FIG. 2 (a) in which the light shielding plate 14 is arranged asymmetrically with respect to the optical axis of the objective lens 15, FIG.
Although the diameter of the main spot Sa1 can be made smaller than in the case of (c), the light intensity of the side lobes Sa2, Sa3 is asymmetrical.

Next, a method of recording information on the recording layer 17 using the spot 18 having such a spot shape will be described. FIG. 3 shows a temperature change when attention is paid to a certain point (mark forming portion) of the recording layer 17.

At time t ₀ , the large side spot Sa2 becomes
When the mark forming portion is approached, the large side spot S
When heated by a2, the temperature of the mark forming portion rises.
After that, at time t ₁ , the peak (the maximum light intensity portion) of the large side spot Sa2 reaches this mark forming portion and the temperature of the mark forming portion becomes the first peak P ₁ .

[0037] and, away from the large side spot Sa2 the mark forming portion, the temperature is lowered gradually, the time t ₂
Then, the main spot Sa1 approaches the mark forming portion, and the temperature of the mark forming portion starts to rise again.

After that, at time t ₃ , the main spot Sa1
Reaches the mark forming portion, and the temperature of the mark forming portion reaches the second peak P ₂ . The peak P ₂ is a value higher than the melting point of the recording layer 17.

After that, when the emission power of the semiconductor laser 11 is lowered to the erasing power, the mark forming portion is rapidly cooled, and from time t ₄ , the main spot Sa1 at the erasing power is reached.
It cools down along the skirt of and reaches room temperature at time t ₅ .

By the way, in the conventional example shown in FIG. 2B, since the side spot Sb3 passes through the mark forming portion after being rapidly cooled and reaching time t ₄ , it is heated again and finally cooled gradually. In this state, the information recording on the non-crystal becomes unstable.

However, in the present invention, the main spot Sa1
After passing through, the small side spot Sa3 passes through, but since the light intensity is small, the recording layer 17 is hardly heated, and stable amorphous / crystalline information recording is possible.

Next, the amount of light for forming marks will be described. Large side spot Sa during mark formation
2 is Q1, the amount of heat applied to the recording layer 17, and the main spot S
Assuming that the heat quantity a1 applies to the recording layer 17 is Q2 and the heat quantity required for mark formation is Q3, the emission power of the semiconductor laser 11 satisfies the following relationship: Q1 + Q2 ≧ Q3 (Equation 1) Q2 <Q3 (Equation 2) To set. That is, the large side spot Sa2 is the recording layer 17
Is heated in advance (as indicated by the dotted line in FIG. 3), and then the main spot Sa1 heats the recording layer 17.

As shown in equation 1, the large side spot S
Since the sum of the heat quantity Q1 applied to the recording layer 17 by a2 and the heat quantity Q2 applied by the main spot Sa1 to the recording layer 17 is larger than the heat quantity Q3 necessary for forming the mark, a mark can be formed.

Further, as shown in the equation 2, the heat quantity Q2 applied to the recording layer 17 by the main spot Sa1 is smaller than the heat quantity Q3 necessary for mark formation, so that the light emission quantity of the semiconductor laser 11 is particularly increased. There is no need.

Next, the timing of setting the light emission amount of the semiconductor laser 11 to the recording power will be described with reference to FIG. The time during which the semiconductor laser 11 is in the recording power state is set so that the moving distance of the recording layer 17 is longer than the length of the mark formed on the recording layer 17 during the time. That is, the semiconductor laser 11 has a recording power faster than writing a mark on the recording layer 17.

FIG. 4A shows the moment when the light emission amount of the semiconductor laser 11 is raised to the recording power, and the main spot Sa
1 heats the recording layer 17, the large side spot Sa2
Does not preheat the part that forms the mark,
The recording layer 17 does not rise to the temperature required for recording, and the mark corresponding to the amorphous state is not formed. That is, only Expression 2 is satisfied and Expression 1 is not satisfied.

After that, a little time elapses from FIG. 4 (a) and the state shown in FIG. 4 (b) is reached, whereby the main spot Sa1 moves by a distance corresponding to the time (moves to the right in the drawing). ing).

In this state, the recording layer 17 on which the main spot Sa1 is heated is already on the large side spot Sa2.
Since it is heated by, the condition of the expression 1 is satisfied, and the recording layer 17 is in a molten state.

As described above, in the period from FIG. 4A to FIG. 4B, the recording layer 17 is not heated until the mark is formed, but during this period, the semiconductor laser 11 emits light at a recording power. is doing.

Further, when a predetermined time elapses from FIG. 4B, the result becomes FIG. 4C, and the main spot Sa1 moves by a predetermined amount. After that, the amount of light emitted from the semiconductor laser 11 is reduced to the erasing power to form the mark.

As described above, according to the present embodiment, the light-shielding plate is provided asymmetrically with respect to the optical axis, so that the super-resolution effect can be brought about, thereby reducing the diameter of the main spot and recording. In addition to increasing the density, a large side lobe with high light intensity and a small side lobe with low light intensity are formed, and the mark formation part is preheated by the large side spot. It has become possible to effectively use the laser light.

Next, a second embodiment according to the present invention will be described with reference to FIG. The same components as those in the first embodiment are designated by the same reference numerals and the description thereof will be omitted.

In the optical pickup device 2 according to the present embodiment, a parallel plate 50 made of a transparent member is provided between the collimator lens 12 and the objective lens 15. A phase plate 51 is vapor-deposited on half of the surface of the parallel plate 50.

With the above structure, the laser light 13 incident on the objective lens does not pass through the phase plate 51.
And the transmitted laser beam 13b is incident.

At this time, the phase of the wavefront of the laser beam 13b lags the phase of the wavefront of the laser beam 13a, so that a phase difference occurs asymmetrically with respect to the optical axis, which changes the pupil function,
The diameter of the main spot Sa1 becomes smaller.

Further, the light intensity of side lobes formed on the left and right is also asymmetrical, and large side spots and small side spots are formed.

Therefore, it is possible to obtain the same effect as that of the first embodiment. In addition, in this embodiment, since the laser light incident on the objective lens is not shielded, the light amount loss due to the shielding is eliminated. The parallel plate 50 may be a wave plate.

Next, a third embodiment according to the present invention will be described with reference to FIG. The same components as those of the above-described embodiment are designated by the same reference numerals and the description thereof will be omitted.

The optical pickup device 3 according to the present embodiment has a parallel plate 60 which is an optical path changing means between the collimator lens 12 and the objective lens 15, and the parallel plate 6 is provided.
0 is provided so that it is inclined with respect to the optical axis and half of the laser light 13 is incident.

With the above structure, a part of the laser light 13 is refracted when it enters the parallel plate 60 and is transmitted, and is displaced in the direction orthogonal to the optical axis. Therefore, the laser light 13 entering the objective lens 15 has a light intensity distribution that is asymmetric with respect to the optical axis, the pupil function changes, and the main spot Sa due to the super-resolution effect.
The diameter of 1 becomes smaller. Further, the light intensity of side lobes formed on the left and right is also asymmetrical, and a large side spot and a small side spot are formed. Therefore, it is possible to obtain the same effect as that of the first embodiment. In addition, in this embodiment, since the laser light incident on the objective lens is not shielded, the light amount loss due to the shielding is eliminated.

[0061]

According to the first aspect of the invention, the asymmetrical beam generating means is provided to make the light intensity of the light beam incident on the condenser lens asymmetrical with respect to the optical axis of the condenser lens. It is possible to generate a main lobe, a side lobe with a high light intensity, and a side lobe with a low light intensity, and it is possible to reduce the spot diameter by the main lobe and increase the recording density.

According to the second aspect of the present invention, since the asymmetrical beam generating means is the light shielding plate which shields light asymmetrically with respect to the optical axis of the condenser lens, the main lobe, the side lobe having a large light intensity, and the light intensity having a small light intensity. Side lobes can be generated, the spot diameter due to the main lobe can be reduced, and the recording density can be increased.

According to the third aspect of the invention, since the asymmetric beam generating means is the phase plate which makes the phase asymmetric with respect to the optical axis of the condenser lens, the main lobe, the side lobe having a large light intensity, and the light intensity are high. A small side lobe can be generated, the spot diameter of the main lobe can be reduced, and the recording density can be increased. In addition, since the light beam is not blocked, it is possible to effectively use the light beam.

According to the fourth aspect of the present invention, the asymmetrical beam generating means is the optical path changing means for making the optical path asymmetric with respect to the optical axis of the condenser lens. Therefore, the main lobe, the side lobe having a large light intensity, and the light intensity. It is possible to generate a small side lobe and a small spot diameter due to the main lobe, and it is possible to increase the recording density. In addition, since the light beam is not blocked, it is possible to effectively use the light beam.

According to the fifth aspect of the invention, the amount of heat given to the information recording medium by the spot due to the side lobe having a large light intensity is Q1, the amount of heat given to the information recording medium by the spot due to the main lobe is Q2, and the information recording medium is marked. When the amount of heat required to form the layer is Q3, the light source is designed to satisfy the relationship of Q1 + Q2 ≧ Q3 and Q2 <Q3 at the time of forming the mark. Marks can be formed by the main lob, and the recording density can be improved while effectively utilizing the emitted laser light without using a light source with a large emission amount.

According to the sixth aspect of the invention, Q1 + Q2 ≧ Q1 + Q2
Since the relationship of Q3 and Q2 <Q3 is satisfied, the recording layer can be preheated by the side lobes, and then the mark can be formed by the main lobe, and light is emitted without using a light source with a large light emission amount. It is possible to improve the recording density while effectively using the laser light.

According to the seventh aspect of the invention, the light beam from the light source is condensed by the condensing lens, and the information recording medium is sandwiched between the spot by the main lobe and the spot by the main lobe. In a mark forming method for writing a mark on an information recording medium by forming a spot by two side lobes formed in a mark forming direction of a recording medium, a light intensity distribution of the spot by the two side lobes is formed asymmetrically. When the mark is formed on the information recording medium, the mark forming portion is preheated by the spot having the larger light intensity distribution among the spots by the two side lobes. Therefore, the recording layer is preheated by the side lobe. , After that, it became possible to form marks by the main lobe, and use a light source with a large amount of light emission. Ku, it is possible to improve the recording density while effectively utilizing the emitted laser beam.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an optical system of an optical pickup device applied to the description of the first embodiment.

FIG. 2 is a diagram comparing a light intensity distribution and a shape of a spot with respect to an arrangement position of a light shielding plate.

FIG. 3 is a diagram showing a temperature change at a mark formation point.

4A and 4B are schematic diagrams temporally showing a situation in which a mark is formed, where FIG. 4A is immediately before the recording power is set, FIG. 4B is where the mark starts to be formed, and FIG. FIG.

FIG. 5 is a schematic configuration diagram of an optical system of an optical pickup device applied to the description of the second embodiment.

FIG. 6 is a schematic configuration diagram of an optical system of an optical pickup device applied to the description of the third embodiment.

[Explanation of symbols]

1, 2, 3 optical pickup device 11 Semiconductor laser 12 Collimating lens 14 Light shield 15 Objective lens 16 discs 17 recording layers 18 spots Ia1 main robe Ia2 large side lobe Ia3 small sidelobe Sa1 Spot by main lobe Sa2 Large side lobe spot Sa3 Spot by small side lobe 51 Phase plate 60 parallel plates

Claims (7)

(57) [Claims] 1. A mark forming direction of the information recording medium, wherein a light beam from a light source is condensed by a condenser lens, and a spot due to the main lobe of the light beam and a spot due to the main lobe are sandwiched on the information recording medium. Formed on 2
By writing / erasing marks on the information recording medium by forming spots by two side lobes,
In an optical pickup device for reading a mark written in the information recording medium by receiving reflected light from the information recording medium by a light receiving element via the condenser lens, An optical pickup device comprising an asymmetric beam generating means for making the light intensity distribution of a spot arriving first at the mark forming portion larger than the light intensity distribution of a spot arriving later. 2. The optical pickup device according to claim 1, wherein the asymmetric beam generating means is a light shielding plate that asymmetrically shields the laser light with respect to the optical axis of the condenser lens. 3. The optical pickup device according to claim 1, wherein the asymmetric beam generating means is a phase plate that makes the phase of the laser light asymmetric with respect to the optical axis of the condenser lens. 4. The optical pickup device according to claim 1, wherein the asymmetric beam generating means is an optical path changing means for making the optical path of the laser light asymmetric with respect to the optical axis of the condenser lens. 5. A mark is formed on the information recording medium by the amount of heat given to the information recording medium by the spot by the side lobe having a high light intensity being Q1, the amount of heat given by the spot by the main lobe on the information recording medium by Q2. The optical pickup according to any one of claims 1 to 4, wherein when the amount of heat required for this purpose is Q3, the light source satisfies the relationship of Q1 + Q2 ≧ Q3 and Q2 <Q3 when the mark is formed. apparatus. 6. The light source sets Q1 + Q2 ≧ Q3 and Q2 earlier than writing a mark on the information recording medium.
The optical pickup device according to claim 5, wherein the relationship of <Q3 is satisfied. 7. A mark forming direction of the information recording medium, wherein a light beam from a light source is condensed by a condenser lens and a spot due to the main lobe of the light beam and a spot due to the main lobe are sandwiched on the information recording medium. Formed on 2
A mark forming method for writing a mark on the information recording medium by forming a spot by two side lobes, wherein a light intensity distribution of the spot by the two side lobes is formed asymmetrically to form a mark on the information recording medium. In this case, the mark forming portion is preheated with a spot having a large light intensity distribution among spots formed by the two side lobes.