JP2003217168A - Optical pickup device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent contamination of an objective lens of an optical pickup device existing within an optical disk device. <P>SOLUTION: A protective film consisting of a photocatalyst (TiO<SB>2</SB>of a rutile type) is formed on a surface of an objective lens 6 of the optical pickup device on the side opposite to an optical disk. <P>COPYRIGHT: (C)2003,JPO

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 recording and / or reproducing a signal on an optical disc, and particularly to prevent contamination of an objective lens.

[0002]

2. Description of the Related Art An optical disk has a feature of being resistant to dust, and since the disk and the optical pickup device are not in contact with each other, there is an advantage that the disk can be freely carried without being fixed to the device. For music, CDs (compact discs) and MDs (mini discs) are widely used. Also, for computer applications, it has become an indispensable existence by taking advantage of the characteristics of removable storage such as data exchange and distribution.

In recent years, the storage capacity required for removable media has been increasing year by year with the increase in the amount of information to be handled, and as a high definition digital video disk, a blue LD (laser diode) having a wavelength of about 405 nm and an NA are used.
A next-generation optical disc system that records and / or reproduces a signal using an optical pickup device using an objective lens having a (numerical aperture) of about 0.85 has been studied.

High-definition television sets have 525 to 1125 scanning lines and an aspect ratio of 4: 3, as compared with current televisions.
Therefore, the required amount of data is about 5 times. For example, in order to record a video for 2 hours, a capacity of about 23 GB (gigabyte), which is five times as large as that of a DVD, is required. Considering compatibility with the current DVD, the thickness of the cover layer of the optical disc is DVD. Same 0.6
It is preferably mm.

However, when the NA of the objective lens increases, the coma aberration and astigmatism caused by the tilt of the optical disk increase, and the spot quality deteriorates. In addition, coma increases crosstalk. In order to solve the problem caused by such disc tilt, it is necessary to make the cover layer thin.
A disc having a diameter of 12 cm and having a capacity of 23 GB on one side of the disk has been announced.

On the other hand, also in the optical pickup device, it is important to consider the contamination of the objective lens. Since the objective lens of the optical pickup device is usually inside the optical disk device and often cannot be directly touched by the user, it is considered that there are few stains such as scratches and fingerprints.
It is considered that dust, mold, cigarette tar, and ammonium sulfide that volatilizes from the circuit board in the optical disk device adheres.

Conventionally, as a technique for preventing the dirt of the objective lens in the optical pickup device, for example, one disclosed in Japanese Patent Laid-Open No. 5-258336 is known. In this publication, a protective coating film is formed on the surface of an objective lens of an optical pickup device, and the protective abdominal membrane is made of a phosphazene resin mixed with an antistatic material and a leveling material. The protective peritoneum makes it difficult for dirt such as dust and oil mist to adhere to the objective lens, and even if it adheres, dirt can be easily removed.

[0008]

However, as described above, the objective lens of the optical pickup device is often inside the optical disc device, and the user cannot easily clean the objective lens. If the user opens the housing of the device for cleaning, the objective lens may be accidentally scratched or damaged during cleaning (the objective lens can move in the tracking direction and the focus direction). Therefore, it may be broken if you apply violent force when wiping it with a cotton swab etc.), which is not preferable.

[0009]

In order to solve the above problems, according to the present invention, there is provided an optical pickup device for recording and / or reproducing a signal on an optical disk, which is a laser for generating a laser beam having a predetermined wavelength. A beam generating means, an objective lens for irradiating the optical disc with the laser beam generated by the laser beam generating means, and a protective film made of a photocatalyst formed on at least a surface of the objective lens facing the optical disc. It is characterized by

Further, in the optical pickup device of the present invention, the predetermined wavelength is 415 nm or less, and the protective film is TiO ₂ having a rutile type crystal structure. Further, in the optical pickup device of the present invention, the predetermined wavelength is 413 nm or less, and the protective film is SiC.

Further, in the optical pickup device of the present invention, the predetermined wavelength is 496 nm or less, and the protective film is CdS. In the optical pickup device of the present invention, the predetermined wavelength is 539n.
m or less, and the protective film is Fe ₂ O ₃ . Further, in the optical pickup device of the present invention,
The predetermined wavelength is 551 nm or less, and the protective film is GaP.

Further, in the optical pickup device of the present invention, the predetermined wavelength is 730 nm or less, and the protective film is CdSe.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a schematic diagram showing an optical system of the optical pickup device of the present invention. In the figure, 1 is a laser diode, 2 is a half mirror, 3 is a collimator lens, 4 is a rising mirror, 5 is a quarter wavelength plate, and 6 is an objective lens. The laser beam generated by the laser diode 1 is reflected by the half mirror 2, converted into parallel light by the collimator lens 3, changed in direction by the rising mirror 4, and further passed through the quarter wavelength plate 5 and then by the objective lens 6. The light is focused on the recording layer of the optical disc (not shown). Further, the reflected light from the recording layer of the optical disc travels in the route opposite to the above, and is transmitted through the half mirror 2 to be detected by the optical sensor 7. The present invention is characterized in that a protective film 8 made of a photocatalyst is formed on the surface of the objective lens 6 facing the optical disc.

The photocatalyst used in the present invention will now be described. First, the photocatalyst is a catalyst that accelerates the reaction or increases the progress rate by irradiating light. As a typical example, titanium dioxide (hereinafter referred to as TiO ₂ ) which is a semiconductor catalyst has been put into practical use and has characteristics such as redox reaction and superhydrophilicity. 1) Redox reaction Electrons and holes are generated by light irradiation, and remain for a while without recombination. The electrons that have diffused to the film surface react with oxygen to generate superoxide ions, and the holes react with water to generate hydroxy radicals. Many compounds are oxidatively decomposed by the action of these two active oxygens. 2) Due to the holes generated by superhydrophilic light irradiation, TiO ₂ also has oxygen defects in the crystal, and water is adsorbed in the oxygen defects in the form of hydroxyl groups to form hydrophilic domains. By further continuing the light irradiation, the surface becomes uniformly hydrophilic. Superhydrophilic means that the contact angle with water is 10 degrees or less, preferably 5 degrees or less.

Further, TiO ₂ has three types of crystal structures of anatase type, rutile type and brookite type. Anatase-type TiO ₂ commonly used as a photocatalyst
Has a bandgap of 3.23 eV and a wavelength of 385 n
Photoexcitation is possible only with ultraviolet light of m or less. Therefore, in the present invention, rutile type TiO ₂ is used. Since this material has a weaker decomposing power than anatase type TiO ₂ , it has hardly been used as a photocatalyst until now, but it has a band gap of 3.0 eV and is known to be photoexcited at a wavelength of 415 nm or less. . Therefore, a protective film made of rutile type TiO ₂ was formed on the surface of the objective lens 6 shown in FIG.

Next, a method of forming the protective film will be described. Generally, a vacuum deposition method and a sputtering method are known as a method for forming a thin film. In the case of the vacuum deposition method, TiO ₂
Since is a high melting point, it is general to carry out reactive vapor deposition of titanium or titanium oxide in an oxygen atmosphere. Further, a TiO ₂ film can be formed also by the sputtering method. However, these film forming methods cannot be used when plastic is used as the material of the objective lens, because the film is converted to the anatase type by heating the substrate at 300 ° C. or higher and a higher temperature is required for the conversion to the rutile type. . In that case, a method of adding fine particles of TiO ₂ to a silica-based inorganic binder or a fluororesin binder and fixing the fine particles on the surface of the objective lens is preferable for forming the protective film. The absorption coefficient of a 15 wt% solution of rutile type TiO ₂ powder is about 8 × 10 ⁴ m ⁻¹ , and the film thickness of TiO _{2 having} an absorption of 0.1 to 1.0% is calculated from this value to be 13
~ 130 nm, which is several tens of n if spin coating is used.
It is possible to form a film with a film thickness of m. When the glass lens is used, the vacuum deposition method or the sputtering method may be used.

Further, as described above, rutile type TiO ₂
Since the protective film made of is photoexcited at a wavelength of 415 nm or less, the wavelength of the laser beam generated by the laser diode 1 in FIG. 1 must be 415 nm or less,
In the present invention, a laser diode that outputs a blue laser having a wavelength of 405 nm is used. The NA of the objective lens was 0.85. As described above, by providing a protective layer made of a photocatalyst on the surface of the objective lens, 1) irradiation of the laser beam decomposes a small amount of dirt adhering to the surface of the objective lens and always maintains a clean state. In addition, it is also effective for secondary pollution in which dust adheres to dirt such as oil.

2) The irradiation of the laser beam makes the surface of the objective lens superhydrophilic, prevents the formation of water droplets due to dew condensation, and can withstand use in a humid environment. 3) Since it is a catalytic reaction, its effect lasts semipermanently and is suitable for long-term use. 4) Since a laser beam for recording / reproducing is used as a light source, it is not necessary to separately provide a light source. That is, it is possible to realize a maintenance-free optical pickup device having a self-cleaning function in an environment such as the inside of an optical disk device where external light such as sunlight or fluorescent light does not reach. And so on.

The photocatalytic decomposition reaction is a two-dimensional reaction on the surface of the film, and it is premised that light reaches the surface of the film and that an object is in contact with it. It is known that photocatalysts can strongly decompose dirt from cigarette smoke and E. coli, but it takes a long time for decomposition when relatively large dirt such as fingerprints is attached, but it is not suitable for optical pickup devices. There is almost no problem in a structure which is inside the optical disk device and in which the user cannot directly touch the objective lens.

The fact that the protective film acts as a photocatalyst by the laser beam means that it absorbs light of that wavelength. If the light absorption of the protective layer is large, the light intensity of the laser beam will change. Therefore, it is necessary to consider the optimum light intensity of the laser beam for signal recording / reproduction. Is small and has little effect.

Further, in the above description, TiO ₂ was mainly explained, but other than this, a photocatalyst as shown in the following table can also be used.

[0022]

[Table 1] The above materials can be used properly according to the wavelength of the laser used.

[0023]

As described above in detail, according to the present invention, a laser beam generating means for generating a laser beam of a predetermined wavelength is provided in an optical pickup device for recording and / or reproducing a signal on an optical disc. Since the objective lens for irradiating the optical disc with the laser beam generated by the laser beam generating means and the protective film made of a photocatalyst formed on at least the surface of the objective lens facing the optical disc are provided, the objective lens The protective layer decomposes the dirt adhering to the surface of, and can always maintain a clean state. In addition, the surface of the objective lens becomes superhydrophilic by the protective layer, and it is possible to prevent the generation of water droplets due to dew condensation.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an optical system of an optical pickup device of the present invention.

[Explanation of symbols]

1 laser diode 2 half mirror 3 Collimator lens 4 launch mirror 5 1/4 wave plate 6 Objective lens 7 sensors 8 protective film

Continued front page    F-term (reference) 2K009 CC03 EE05                 5D119 AA43 BA01 DA01 DA05 FA05                       JA44                 5D789 AA43 BA01 DA01 DA05 FA05                       JA44

Claims (7)

[Claims] 1. An optical pickup device for recording and / or reproducing a signal on an optical disc, comprising: a laser beam generating means for generating a laser beam having a predetermined wavelength; and a laser beam generated by the laser beam generating means. An optical pickup device comprising: an objective lens for irradiating an optical disc onto the optical disc; and a protective film made of a photocatalyst formed on at least a surface of the objective lens facing the optical disc. 2. The predetermined wavelength is 415 nm or less, and the protective film is TiO ₂ having a rutile type crystal structure.
The optical pickup device according to claim 1, wherein 3. The optical pickup device according to claim 1, wherein the predetermined wavelength is 413 nm or less, and the protective film is SiC. 4. The optical pickup device according to claim 1, wherein the predetermined wavelength is 496 nm or less, and the protective film is CdS. 5. The predetermined wavelength is 539 nm or less.
And the protective film is Fe ₂O₃Claims characterized by
Item 1. The optical pickup device according to item 1. 6. The optical pickup device according to claim 1, wherein the predetermined wavelength is 551 nm or less, and the protective film is GaP. 7. The optical pickup device according to claim 1, wherein the predetermined wavelength is 730 nm or less, and the protective film is CdSe.