KR100349028B1 - Optical Pick-up Apparatus and Optical Record and Reproduction Apparatus using the same - Google Patents

Abstract

PURPOSE: An optical pickup device and an apparatus for writing and reading light using the same are provided to access different kinds of optical disks with the appropriate size of an optical beam, thereby simplifying a configuration of the optical pickup device. CONSTITUTION: A first light source(14) generates a first optical beam. A second light source generates a second optical beam having a wavelength longer than that of the first optical beam. An optical system selectively irradiates the first optical beam or the second optical beam according to an optical disk to be accessed, and has a liquid crystal plate and a polarizing plate controlling the number of apertures to have a first value and a second value smaller than the first value. An optical detector(24) detects a reflected optical beam reflected from the optical disk for converting the reflected optical beam into electric signals, so that the first optical beam is irradiated having the first value of the apertures in the case of a first optical disk(10a), the second optical beam is irradiated having the first value of the apertures in the case of a second optical disk(10b), and the second optical beam is irradiated having the second value of the apertures in the case of a third optical disk(10c).

Description

Optical Pick-up Apparatus and Optical Record and Reproduction Apparatus using the same}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording and reproducing apparatus, and more particularly, to an optical pickup apparatus capable of responding to a plurality of types of optical discs having different layout conditions such as recording density and light transmitting layer thickness, and an optical recording and reproducing apparatus using the same. will be.

In general, an optical recording and reproducing apparatus (i.e., an optical disc driver) for driving a conventional disc-shaped medium such as a compact disc such as a compact disc (CD) or the like may generate a laser beam while rotating the disc. The recording surface is irradiated to record or reproduce the data. To this end, the optical recording and reproducing apparatus has an optical pickup for irradiating the recording surface of the optical disk with the laser beam generated from the semiconductor laser which is the light source using the optical system elements.

Recently, a DVD (Digital Versatile Disc) type optical disc capable of recording a larger amount of information than a conventional CD type optical disc is commercially available. As described above, as the DVD has a high recording density, the size of the light beam irradiated to the recording surface in the form of spots should be smaller than that of the CD. The spot-shaped light beam size d is usually proportional to the wavelength? Of the light beam, as shown in the following equation (1), but inversely proportional to the numerical aperture NA of the objective lens that focuses the light beam on the recording surface.

Where d is a light beam size, k is a constant, λ is a wavelength, and NA is a numerical aperture of an objective lens. It can be seen from Equation 1 that the wavelength λ of the light beam can be reduced or the numerical aperture NA can be increased in order to reduce the light beam size d. Accordingly, the optical pickup for accessing the DVD is designed to have a shorter light beam wavelength lambda and a larger objective lens numerical aperture NA than the CD series optical pickup. Specifically, the CD-based optical pickup is designed to have a light beam wavelength λ of 780 nm and an objective numerical aperture (NA) of 0.45, while the DVD-based optical pickup has a light beam wavelength of 650 nm and 0.6 It is designed to have an objective lens numerical aperture NA.

As described above, as the objective lens numerical aperture NA of the DVD-based optical pickup increases, the characteristic of the light beam becomes sensitive to the thickness of the disk, so that the depth of the recording surface of the DVD, that is, the thickness of the light transmitting layer is set smaller than that of the CD. . This is due to the fact that irradiating a light beam to the recording surface of the CD with an objective lens having a numerical aperture of 0.6 increases aberration, which increases the noise component of the light beam, thereby making it impossible to properly record or reproduce data. In fact, the light transmissive layer of the CD has a thickness of 1.2 mm, while the light transmissive layer of the DVD has a thickness of 0.6 mm, which is half thereof. This means that the distance between the objective lens and the recording surface of the DVD should be set smaller than the distance between the objective lens and the recording surface of the CD.

As a result, the optical pickup for accessing the CD series and the DVD series optical discs in one optical recording and reproducing apparatus had to include two light sources generating light beams of different wavelengths and two objective lenses having different numerical apertures. . However, when two light sources and an objective lens are respectively provided in the optical pickup, the size of the optical pickup is not only large, but the structure is complicated and the manufacturing cost is increased. In order to solve this problem, studies on optical pickups that can access CDs and DVDs by using one light source and appropriately adjusting the numerical aperture of the objective lens according to the corresponding disks have been actively conducted.

For example, the optical pickup disclosed in Japanese Patent Application Laid-Open No. 9-185839 provides a liquid crystal filter and a polarization filter to access two kinds of optical disks having different thicknesses of the light transmitting layer by adjusting the numerical aperture of the objective lens. This optical pickup is to change the polarization characteristics of the light beam generated from the light source by the liquid crystal filter is turned on (on) / off (Off) according to the application of voltage, and according to the polarization characteristics of the light beam changed by the liquid crystal filter in the polarization filter By selectively blocking part of the light beam, the numerical aperture of the objective lens is adjusted in two ways.

In addition, the optical pickup disclosed in Japanese Patent Application Laid-Open No. 9-198704 is a twin-lens driving method in which two objective lenses are configured on one lens support, and the lenses are switched according to the rotation of the support. By adjusting the numerical aperture, two types of optical discs are accessed.

On the other hand, recently, as a blue laser which generates a light beam having a significantly lower wavelength than that of conventional laser beams is realized, a recording medium that can further increase the recording density by using it has been studied. By the way, the next-generation optical disk (hereinafter referred to as a blue laser disk) using this blue laser eventually requires an objective lens having a different numerical aperture along with light sources of different wavelengths. In other words, as the blue laser disk can be further densified by the short wavelength of the blue laser, the size d of the light beam irradiated to the recording surface must be smaller than that of the DVD. For this purpose, the numerical aperture of the objective lens must be further increased than in the case of DVD.

In detail, the optical beam wavelength lambda and the objective numerical aperture NA of the optical pickup for accessing the CD and DVD-based optical discs and the blue laser optical disc have a relationship as shown in Equation 2 below.

Here, lambda 1, lambda 2, and lambda 3 represent first to third wavelengths and are sequentially wavelengths of light beams corresponding to the blue laser disk, DVD, and CD. NA1, NA2, and NA3 represent the first to third numerical apertures, and are sequentially numerical apertures of the objective lens corresponding to the blue laser disk, DVD, and CD. Accordingly, the size d of the light beams irradiated to the three types of optical discs has a relationship as shown in Equation 3 below.

Here, each of d1, d2, and d3 represents the size of the light beam irradiated on the blue laser disk and the DVD and the CD.

As described above, when three types of optical discs require different sizes of light beams, the optical pickup that can access the optical discs in a compatible manner requires three light sources and three objective lenses. . However, when the optical pickup is configured as described above, the structure becomes complicated, which results in a problem that the manufacturing cost is increased while being reversed to the development direction of the optical pickup which is in the light weight. Accordingly, there is a demand for an optical pickup apparatus that can access a plurality of types of optical discs and has a minimum light source and an objective lens.

Accordingly, it is an object of the present invention to provide an optical pickup apparatus capable of accessing a plurality of types of optical disks having different recording densities, thicknesses of light transmitting layers, and the like.

Another object of the present invention is to provide an optical recording and reproducing apparatus using an optical pickup apparatus capable of accessing a plurality of types of optical disks in a minimal configuration.

1 is a view showing an optical system configuration of an optical pickup apparatus according to a first embodiment of the present invention.

2 is a diagram illustrating an optical system configuration of an optical pickup apparatus according to a second exemplary embodiment of the present invention.

3 is a plan view showing the configuration of the polarizing plate shown in FIG.

4 is a diagram illustrating an optical system configuration of an optical pickup apparatus according to a third exemplary embodiment of the present invention.

<Brief description of symbols for the main parts of the drawings>

10a, 10b, 10c: first to third optical disks 12: first light source

14, 32: second light source 16: collimating lens

18, 19: first and second beam splitter 20: twin objective lens

22 sensor lens 24 photodetector

26: liquid crystal plate 28, 34: polarizing plate

28a, 34a: non-polarization area 28b, 34b: polarization area

In order to achieve the above object, the optical pickup apparatus according to the present invention comprises: an optical pickup apparatus for accessing first to third optical disks having a gradually decreasing density, comprising: a first light source for generating a first light beam; The second light source generates a second light beam having a wavelength longer than that of the first light beam, and according to the optical disk to be accessed, selectively irradiates any one of the first and second light beams to the optical disk and reduces the numerical aperture of the light beam. An optical system including a numerical aperture adjusting means for adjusting one value and a second value smaller than the first value; A light detecting means for detecting the reflected light beam reflected from the optical disk to be accessed and converting the light beam into an electrical signal; When the optical disc to be accessed is the first optical disc, causing the first light beam to be irradiated with a first value of the numerical aperture; When the optical disc to be accessed is the second optical disc, causing the second light beam to be irradiated with the first value of the numerical aperture; When the optical disc to be accessed is a third optical disc, the second light beam is irradiated with the second value of the numerical aperture.

The optical recording and reproducing apparatus according to the present invention is characterized by including the optical pickup apparatus.

In addition, the optical pickup apparatus according to the present invention comprises: an optical pickup apparatus for accessing first to third optical disks having a gradually decreasing density, comprising: a first light source for generating a first light beam; A second light source for generating a second light beam having a wavelength longer than the first light beam; Depending on the optical disc to be accessed, the optical disc is selectively irradiated with any one of the first and second light beams, and the numerical aperture of the light beam is one of the first value and the second value smaller than the first value. An optical system including a numerical aperture adjusting means for adjusting to have; A light detecting means for detecting the reflected light beam reflected from the optical disk to be accessed and converting the light beam into an electrical signal; When the optical disc to be accessed is the first optical disc, causing the first light beam to be irradiated with a first value of the numerical aperture; When the optical disc to be accessed is the second optical disc, causing the first light beam to be irradiated with the second value of the numerical aperture; When the optical disc to be accessed is the third optical disc, the second light beam is irradiated with the second value of the numerical aperture.

The optical recording and reproducing apparatus according to the present invention is characterized by including the optical pickup apparatus.

Other objects and advantages of the present invention in addition to the above object will become apparent from the description of the preferred embodiment of the present invention with reference to the accompanying drawings.

The present invention includes a blue laser disk using a blue laser having a significantly lower wavelength than a conventional laser beam, and is compatible with a plurality of types, that is, three types of optical disks having different recording densities and light transmitting layers. Accessing three types of optical disks by appropriately combining the wavelength of the light beam and the numerical aperture of the objective lens using two light sources for generating light beams of different wavelengths λ and an optical system controlled in two numerical aperture (NA) modes. will be.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to FIGS. 1 to 4.

1 is a view schematically showing an optical system configuration of an optical pickup apparatus according to a first embodiment of the present invention.

The optical pickup apparatus shown in FIG. 1 includes a first light source 12 for generating the aforementioned first wavelength lambda 1 light beam, a second light source 14 for generating the aforementioned third wavelength lambda 3 light beam, The first to third optical disks 10a, 10b, and 10c are accessed by using the twin objective lens 20 having the first numerical aperture NA1 mode and the third numerical aperture NA3 mode. In other words, when the optical pickup apparatus accesses the first optical disk 10a (that is, the blue laser optical disk), the optical pickup device uses the light beam of the first wavelength λ1 and the first numerical aperture NA1, and the second optical disk. When accessing 10b (i.e., DVD), the light beam of the third wavelength lambda 3 and the first numerical aperture NA1 are used for the mode. When the third optical disc 10c (ie, CD) is accessed, the light beam of the third wavelength lambda 3 and the third numerical aperture NA3 are used for the mode. As a result, the sizes d1, d2, d3 of the first to third light beams irradiated onto the recording surfaces of the first to third optical discs 10a, 10b, and 10c can be expressed by the following equation.

Referring to FIG. 1, an optical pickup apparatus may include first and second light sources 12 and 14 and light beams generated from the first and second light sources 12 and 14 to generate light beams having different wavelengths. A twin objective lens 20 for focusing on the recording surface of the third optical disk 10a, 10b, 10c, and a photodetector 24 for converting the light beam reflected from the optical disk 10a, 10b, 10c into an electrical signal. do. The optical pickup apparatus shown in FIG. 1 includes a first beam splitter 18 and a first beam splitter 18 positioned in a path of light beams from the first and second light sources 12 and 14. And a second beam splitter 19 disposed between the twin objective lens 20 and the photodetector 24, and a collimation lens 16 disposed between the first light source 12 and the first beam splitter 18. And a sensor lens 22 disposed between the photodetector 24 and the second beam splitter 19.

In the optical pickup apparatus of FIG. 1, the first optical disk 10a corresponds to a blue laser optical disk having a relatively higher recording density and a thinner thickness, corresponding to the blue laser, and the second optical disk 10b corresponds to the first optical disk ( The DVD having a light transmission layer thickness thicker than 10a) and the third optical disk 10c correspond to a CD having a light transmission layer thicker than DVD. The first light source 12 generates a light beam having the above-described first wavelength? 1, that is, 400 nm, using a blue laser, and the second light source 14 generates the above-described third wavelength? 3, Generate a light beam with a wavelength of 780 nm. The collimating lens 16 converts the divergent light beam traveling from the first light source 12 toward the first beam splitter 18 into a parallel light beam to prevent leakage of the light beam. The first beam splitter 18 passes the light beam from the collimating lens 16 toward the second beam splitter 19 or reflects the light beam from the second light source 14 toward the second beam splitter 19. . The second beam splitter 18 passes the light beam from the first beam splitter 18 toward the twin objective lens 20 and is reflected from the recording surfaces of the optical discs 10a, 10b, and 10c so that the twin objective lens 20 can be reflected. The reflected light beam propagates through the sensor lens 22 is reflected toward the photodetector 24. As the first and second beam splitters 18 and 19, a dichroic polarizer beam splitter (DPBS) is usually used. The sensor lens 22 focuses a parallel light beam traveling from the second beam splitter 19 toward the photodetector 24 on the surface of the photodetector 24 to prevent leakage of the light beam. The photodetector 24 is reflected by the recording surfaces of the optical discs 10a, 10b, and 10c and receives an reflected light beam incident through the twin objective lens 20, the second beam splitter 19, and the sensor lens 22 as an electrical signal. Convert to This electrical signal includes a servo signal and an information signal.

The twin objective lens 20 includes first and second objective lenses 20a and 20b having different numerical apertures NA. The first and second objective lenses 20a and 20b are mounted on one lens support, and the lens supports are rotated according to the corresponding optical disk, thereby selectively changing the positions of the first and second objective lenses 20a and 20b. . The lens support is driven by an actuator, and the actuator is usually driven in an axial perturbation manner such that the lens support is pivoted about a rotation axis. Here, the first objective lens 20a is set to have a first numerical aperture NA1, that is, a numerical aperture of 0.7, and the second objective lens 20b has a third numerical aperture NA3, that is, a numerical aperture of 0.45. . Hereinafter, a case in which the first to third optical disks are accessed by combining the wavelength and the numerical aperture of the above-described light beam will be described in detail.

First, when the first optical disk 10a is accessed, the light beam of the first wavelength λ1 generated by the first light source 12 passes through the collimating lens 16, the first and second beam splitters 18 and 19. Incident on the first objective lens 20a. The incident light beam is focused by the first objective lens 20a having the first numerical aperture NA1 to irradiate the recording surface of the first optical disk 10a with the size d1 of the first light beam.

On the contrary, when the second optical disk 10b is accessed, the light beam of the third wavelength λ3 generated from the second light source 14 is reflected by the first beam splitter 18 at right angles to the second beam splitter 19. The light is incident on the first objective lens 20a via. The incident light beam is focused by the first objective lens 20a having the first numerical aperture NA1 to irradiate the recording surface of the second optical disk 10b with the size d2 of the second light beam.

In addition, when the third optical disk 10c is accessed, the support of the twin objective lens 20 is pivoted by driving the actuator so that the second objective lens 20b having the third numerical aperture NA3 is positioned in the optical path. do. Accordingly, the light beam of the third wavelength λ3 generated from the second light source 14 is reflected by the first beam splitter 18 at right angles to the second objective lens 20b via the second beam splitter 19. Incident. The incident light beam is focused by the second objective lens 20b having the third numerical aperture NA3 and irradiated to the recording surface of the third optical disk 10c at the size d3 of the third light beam.

Here, specific numerical values of the wavelength of the light beam and the numerical aperture of the objective lens corresponding to the first to third optical discs 10a, 10b, and 10c may be expressed as shown in Table 1 below.

2 is a diagram schematically illustrating an optical system configuration of an optical pickup apparatus according to a second exemplary embodiment of the present invention.

The optical pickup device shown in FIG. 2 includes two light sources 12 and 14, one objective lens 30, and a numerical aperture mode of the light beam incident on the objective lens 30 to generate light beams having different wavelengths. The first to third optical disks 10a, 10b, and 10c are accessed by combining the wavelength and the numerical aperture by providing a numerical aperture adjusting means for adjusting the numerical value, that is, the liquid crystal plate 26 and the polarizing plate 28. Here, the numerical aperture mode corresponding to the light beam of the third wavelength [lambda] 3 generated from the second light source 14 by being disposed on the side of the second light source 14 is the liquid crystal plate 26 and the polarizing plate 28. Will be controlled by In other words, when accessing the first optical disk 10a (that is, the blue laser optical disk), the light beam of the first wavelength λ1 and the first numerical aperture NA1 are used as the mode, and the second optical disk 10b ( That is, when the DVD is accessed, the light beam of the third wavelength λ3 and the first numerical aperture NA1 are used as the mode. When the third optical disc 10c (ie, CD) is accessed, the light beam of the third wavelength lambda 3 and the third numerical aperture NA3 are used for the mode. As a result, the sizes d1, d2, and d3 of the first to third light beams irradiated onto the recording surfaces of the first to third optical discs 10a, 10b, and 10c may be expressed as in Equation 4 above. Hereinafter, detailed descriptions of components overlapping with the optical pickup apparatus of FIG. 1 will be omitted.

The first light source 12 generates a light beam of a first wavelength λ1 of 400 nm, and the second light source 14 generates a light beam of a third wavelength λ3 of 780 nm. The light sources 12 and 14 typically generate vertically polarized beams (called TE waves, called S waves) having polarization characteristics flowing in an axial direction with respect to an ellipse, or horizontally having polarization characteristics flowing in an axial direction with respect to an ellipse. A polarization beam (TM wave called P wave) is generated. In the present invention, it is assumed for convenience that the light beams generated by the first and second light sources 12 and 14 are vertically polarized beams.

The numerical aperture adjusting means includes a liquid crystal plate 26 disposed between the second light source 14 and the first beam splitter 18, and a polarizing plate 28 disposed between the second beam splitter 19 and the objective lens 30. ) Is configured. The liquid crystal plate 26 serves to vary the polarization characteristics of the light beam depending on whether a voltage is applied, and the polarizing plate 28 selectively blocks a part of the light beam according to the polarization characteristics of the incident light beam. The liquid crystal panel 26 selectively rotates the vertically polarized beam traveling from the second light source 14 toward the first beam splitter 18 by 90 ° depending on whether voltage is applied. For example, the liquid crystal plate 26 allows the vertical polarization beam generated from the second light source 14 to pass through while maintaining the original polarization characteristic when a voltage is applied to access the second optical disk 10b, that is, the DVD. . On the other hand, if no voltage is applied to access the third optical disk 10c, that is, the CD, the liquid crystal panel 26 converts the vertically polarized beam generated from the second light source 14 into a horizontally polarized beam by rotating it by 90 degrees. do. On the contrary, when the horizontal polarization beam is generated by the second light source 14, the liquid crystal plate 26 selectively converts the polarization characteristics of the light beam by turning the horizontal polarization beam on / off according to the voltage opposite to the above.

The polarizing plate 28 includes a circular non-polarization area 28a and a polarization area 28b formed around the non-polarization area 28a as shown in FIG. 3. The non-polarization area 28a positioned at the center of the polarizing plate 28 passes the light beam toward the objective lens 30 regardless of the polarization characteristic of the incident light beam. The polarization region 28a passes when the polarization direction of the light beam is the same as its polarization direction, while blocking the polarization region 28a when the polarization direction of the light beam is different from its polarization direction. In other words, when the incident light beam is a vertically polarized beam, that is, when the first or second optical disks 10a and 10b are accessed, the polarized region 28b of the polarizing plate 28 causes the vertically polarized beam to be a non-polarized region 28b. Pass toward the objective lens 30 as shown in FIG. On the other hand, when the incident light beam is a horizontally polarized beam, that is, when accessing the third optical disk 10c, the polarization region 28b blocks the horizontal polarization beam and passes only to the non-polarization region 28b. Here, the non-polarization area 28a has an area corresponding to the third numerical aperture NA3 of the objective lens 30. Accordingly, the objective lens 30 is designed to have a first numerical aperture NA1 of 0.7, but the light beam incident on the objective lens 30 corresponds to the non-polarization region 28b of the flat plate 28 described above. The numerical aperture, that is, the third numerical aperture NA3 can be varied. As a result, the beam diameters of the light beams incident on the objective lens 30 by the liquid crystal plate 26 and the polarizing plate 28 are adjusted so that the objective lens has two numerical aperture modes, namely, the first numerical aperture NA1 and the third numerical aperture. It has a numerical aperture NA3.

Hereinafter, the case of accessing the first to third optical disks will be described in detail.

First, when the first optical disk 10a is accessed, the vertically polarized beam of the first wavelength λ1 generated from the first light source 12 may be collimated lenses 16, first and second beam splitters 18 and 19. The light enters the objective lens 30 through the polarizing plate 28. The incident light beam is focused by the objective lens 30 having the first numerical aperture NA1 to irradiate the recording surface of the first optical disk 10a with the size d1 of the first light beam.

On the contrary, when the second optical disk 10b is accessed, the liquid crystal plate 26 is turned on. Accordingly, the vertically polarized beam of the third wavelength λ3 generated from the second light source 14 is reflected at right angles by the first beamsplitter 18 via the turned-on liquid crystal plate 26 to thereby form the second beamsplitter. It enters into the polarizing plate 28 via (19). The vertically polarized beam incident on the polarizing plate 28 passes through the polarizing plate 28 as it is and is focused by the objective lens 30 having the first numerical aperture NA1 so that the second light beam is recorded on the recording surface of the second optical disk 10b. The size d2 is to be irradiated.

In addition, when the third optical disk 10c is accessed, the liquid crystal plate 26 is turned off. Accordingly, the vertically polarized beam of the third wavelength [lambda] 3 generated from the second light source 14 is converted into a horizontally polarized beam by the turned-off liquid crystal plate 26 and reflected at right angles by the beam splitter 18. The light is incident on the polarizer 28 via the second beam splitter 19. The horizontally polarized beam incident on the polarizer 28 is blocked in the outer polarized region 28b and passed through the non-polarized region 28a to be incident on the objective lens 30 with the beam diameter reduced. As a result, the light beam incident on the objective lens 30 is converted into the third numerical aperture NA3 corresponding to the area of the non-polarization region 28a of the polarizing plate 28. The incident light beam of the third numerical aperture NA3 is focused by the objective lens 30 so that the recording surface of the third optical disk 10c is irradiated with the size d3 of the third light beam.

As a result, the sizes d1, d2, and d3 of the light beams irradiated to the first to third optical discs 10a, 10b, and 10c may be expressed by Equation 4 above. Here, numerical values of wavelengths and numerical apertures of the light beams corresponding to the first to third optical discs 10a, 10b, and 10c are also shown in Table 1 above.

4 is a diagram schematically illustrating an optical system configuration of an optical pickup apparatus according to a third exemplary embodiment of the present invention.

In contrast to the optical pickup device illustrated in FIG. 2, the optical pickup device illustrated in FIG. 4 uses a second light source 32 that generates a second wavelength λ2 instead of the third wavelength λ3 light beam and uses a liquid crystal plate. (26) is disposed between the first light source 12 and the collimation lens 16, and the non-polarization region 34a of the polarizing plate 34 is smaller than the third numerical aperture NA3 (hereinafter, referred to as a fourth). It is set to have an area corresponding to the numerical aperture NA4). In other words, when accessing the first optical disk 10a (that is, the blue laser optical disk), the light beam of the first wavelength λ1 and the first numerical aperture NA1 are used as the mode, and the second optical disk 10b ( In other words, when the DVD is accessed, the light beam of the first wavelength λ1 and the fourth numerical aperture NA4 are used for the mode. When the third optical disc 10c (ie, CD) is accessed, the light beam of the second wavelength lambda 2 and the fourth numerical aperture NA4 are used for the mode. As a result, the sizes d1, d2, d3 of the first to third light beams irradiated onto the recording surfaces of the first to third optical discs 10a, 10b, and 10c can be expressed by the following equation.

In the optical pickup device shown in FIG. 4, the 400 nm first wavelength λ1 light beam generated by the first light source 12 is formed by the liquid crystal plate 26 and the polarizing plate 34. It selectively corresponds to the four numerical apertures NA4. Here, the first light source 12 generates a horizontal polarized beam or a vertical polarized beam. For convenience, the light beam generated by the first light source 12 is assumed to be a vertically polarized beam. However, the light beam diameter of the second wavelength λ2 light beam generated by the second light source 32 should be reduced by the polarizing plate 34 to correspond to the fourth numerical aperture NA4. For this reason, the second light source 32 must generate a horizontally polarized beam.

The liquid crystal plate 26 disposed between the first light source 12 and the collimating lens 16 selectively rotates the vertically polarized light beam generated from the first light source 12 by 90 ° depending on whether a voltage is applied. In detail, the liquid crystal panel 26 allows the vertical polarization beam generated from the first light source 12 to maintain the original polarization direction when a voltage is applied to access the first optical disk 10a, that is, the blue laser optical disk. On the other hand, when no voltage is applied to access the second optical disk 10b, that is, the DVD, the liquid crystal plate 26 converts the vertically polarized beam generated from the first light source 12 into a horizontally polarized beam by rotating it by 90 degrees. . On the contrary, when the horizontal polarization beam is generated from the first light source 14, the liquid crystal panel 26 selectively converts the polarization characteristics of the light beam by turning the horizontal polarization beam on / off according to the voltage opposite to the above.

The polarizing plate 34 disposed between the second beam splitter 19 and the objective lens 30 has a circular non-polarization region 34a and polarization formed around the non-polarization region 34a as shown in FIG. 3. A region 34b is provided, and a part of the light beam is selectively blocked according to the polarization characteristic of the incident light beam. The non-polarization region 34a passes the light beam toward the objective lens 30 regardless of the polarization characteristic of the incident light beam. The polarization region 34b passes when the polarization direction of the light beam is the same as its polarization direction, while blocking the polarization region 34b when the polarization direction of the light beam is different from its polarization direction. In other words, when the incident light beam is a vertically polarized beam, that is, when the first optical disk 10a is accessed, the polarization region 34b of the polarizing plate 34 uses the vertical polarization beam like the non-polarization region 34b. Pass it toward (30). On the other hand, when the incident light beam is a horizontally polarized beam, that is, when the second and third optical disks 10b and 10c are accessed, the polarized region 34b blocks the horizontal polarized beam and the non-polarized region 34a passes through. do. Here, the non-polarization region 34a of the polarizing plate 34 has an area corresponding to the fourth numerical aperture NA4 of the objective lens 30. Accordingly, the objective lens 30 is designed to have a first numerical aperture NA1 of 0.7, but the light beam incident on the objective lens 30 corresponds to the aperture corresponding to the non-polarization region 34b of the polarizing plate 34 described above. The number, that is, the fourth numerical aperture NA4, can be varied. As a result, the beam diameters of the light beams incident on the objective lens 30 by the liquid crystal plate 26 and the polarizing plate 34 are adjusted so that the two numerical aperture modes, namely, the first numerical aperture NA1 and the fourth numerical aperture ( NA4).

Hereinafter, the case of accessing the first to third optical disks will be described in detail.

First, when the first optical disk 10a is accessed, the liquid crystal plate 26 is turned on. Accordingly, the vertically polarized beam of the first wavelength λ1 generated from the first light source 12 is turned on as it is, the collimating lens 16, the first and second beam splitters 18, 19) and enters the objective lens 30 via the polarizing plate 34. The incident light beam is focused by the objective lens 30 having the first numerical aperture NA1 to irradiate the recording surface of the first optical disk 10a with the size d1 of the first light beam.

On the contrary, the liquid crystal plate 26 is turned off when the second optical disc 10b is accessed. Accordingly, the vertically polarized beam of the first wavelength λ1 generated from the first light source 12 is converted into a horizontally polarized beam by the turned-off liquid crystal plate 26, so that the first and second beam splitters 18, It enters into the polarizing plate 34 via 19). The horizontally polarized beams incident on the polarizer 34 are blocked in the outer polarized region 34b and passed through the non-polarized region 34a to be incident on the objective lens 30 with the beam diameter reduced. As a result, the light beam incident on the objective lens 30 is converted into the fourth numerical aperture NA4 corresponding to the area of the non-polarization region 34a of the polarizing plate 34. The incident light beam of the fourth numerical aperture NA4 is focused by the objective lens 30 so that the recording surface of the second optical disk 10b is irradiated with the size d2 of the second light beam.

Lastly, when the third optical disk 10c is accessed, the horizontally polarized beam of the second wavelength λ2 generated from the second light source 32 is reflected by the first beam splitter 18 at right angles so that the second beam splitter ( It enters into the polarizing plate 34 via 19). The horizontally polarized beams incident on the polarizer 34 are blocked in the outer polarized region 34b and passed through the non-polarized region 34a to be incident on the objective lens 30 with the beam diameter reduced. As a result, the light beam incident on the objective lens 30 is converted into the fourth numerical aperture NA4 corresponding to the area of the non-polarization region 34a of the polarizing plate 34. The incident light beam of the fourth numerical aperture NA4 is focused by the objective lens 30 so that the recording surface of the third optical disk 10c is irradiated with the size d3 of the third light beam.

Here, numerical values of wavelengths and numerical apertures of the light beams corresponding to the first to third optical discs 10a, 10b, and 10c may be expressed as shown in Table 2 below.

As described above, the optical pickup apparatus according to the present invention employs two light sources for generating light beams having different wavelengths and an optical system controlled in two numerical aperture modes, so that three types of recording density and light transmitting layer are different. Access to the size of the light beam respectively suitable for the optical disc. Accordingly, not only the configuration of the optical pickup that is compatible with the plurality of types of optical discs can be simplified, but also the manufacturing cost can be reduced. Furthermore, the optical pickup apparatus according to the present invention can implement an optical disk driver capable of accurately accessing the plurality of types of optical disks.

Those skilled in the art will appreciate that various changes and modifications can be made without departing from the technical spirit of the present invention. Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification but should be defined by the claims.

Claims (15)

An optical pickup apparatus for accessing first to third optical disks having a gradually decreasing density, A first light source for generating a first light beam, A second light source generating a second light beam having a wavelength longer than that of the first light beam; Depending on the optical disc to be accessed, one of the first and second light beams is selectively irradiated to the optical disc, and the numerical aperture of the light beam is any one of a first value and a second value smaller than the first value. Optical system including a numerical aperture adjusting means for adjusting to have a; And a light detecting means for detecting the reflected light beam reflected from the optical disk to be accessed and converting the light beam into an electrical signal. When the optical disk to be accessed is the first optical disk, causing the first light beam to be irradiated with a first value of the numerical aperture; The second optical beam is irradiated with the first value of the numerical aperture when the optical disc to be accessed is the second optical disc, And the second optical beam is irradiated with a second value of the numerical aperture when the optical disc to be accessed is the third optical disc. The method of claim 1, The numerical aperture adjusting means A twin objective lens having different numerical apertures and focusing the light beam on an optical disk to be accessed by changing its position according to the optical disk to be accessed; A support for supporting the twin objective lens; And a drive means for pivotally driving the support. The method of claim 1, The numerical aperture adjusting means An objective lens for focusing the light beam on the optical disk to be accessed; Polarization conversion means for selectively converting the polarization characteristics of the light beam depending on whether a voltage is applied; And a polarization selecting means integrated with the objective lens to selectively block a part of the light beam incident from the polarization converting means according to a polarization characteristic. The method according to any one of claims 2 and 3, The optical system A first beam splitter for advancing the light beam generated by any one of the first and second light sources toward the optical disc to be accessed; A second beam splitter for advancing the light beam incident from the first beam splitter toward the optical disc to be accessed, and for advancing the reflected light beam reflected from the optical disc to be accessed toward the light detecting means; A collimating lens for traveling a light beam generated by any one of the first and second light sources in parallel toward the first beam splitter; And a sensor lens for collecting the reflected light beam incident from the second beam splitter toward the light detecting means. The method of claim 3, wherein The polarization converting means And an optical pick-up device arranged on one of the first and second light sources. The method of claim 3, wherein The polarization selection means A non-polarization region formed in the center to transmit the incident light beam irrespective of the polarization characteristic; And a polarization region formed around the non-polarization region and selectively transmitting an incident light beam in accordance with polarization characteristics. The method according to any one of claims 1 and 2 and 3 to 6, And an optical pickup device. An optical pickup apparatus for accessing first to third optical disks having a gradually decreasing density, A first light source for generating a first light beam, A second light source generating a second light beam having a wavelength longer than that of the first light beam; Depending on the optical disk to be accessed, the optical disk is selectively irradiated with any one of the first and second light beams to the optical disk, so that the numerical aperture of the light beam is one of a first value and a second value smaller than the first value. An optical system including a numerical aperture adjusting means for adjusting to have a value; And a light detecting means for detecting the reflected light beam reflected from the optical disk to be accessed and converting the light beam into an electrical signal. When the optical disk to be accessed is the first optical disk, causing the first light beam to be irradiated with a first value of the numerical aperture; If the optical disc to be accessed is the second optical disc, cause the first light beam to be irradiated with a second value of the numerical aperture; And the second optical beam is irradiated with a second value of the numerical aperture when the optical disc to be accessed is the third optical disc. The method of claim 8, The numerical aperture adjusting means An objective lens for focusing the light beam on the optical disk to be accessed; Polarization conversion means for selectively converting the polarization characteristics of the light beam depending on whether a voltage is applied; And a polarization selecting means integrated with the objective lens to selectively block a part of the light beam incident from the polarization converting means according to a polarization characteristic. The method of claim 9, The optical system A first beam splitter for advancing the light beam generated by any one of the first and second light sources toward the optical disc to be accessed; A second beam splitter for advancing the light beam incident from the first beam splitter toward the optical disc to be accessed, and for advancing the reflected light beam reflected from the optical disc to be accessed toward the light detecting means; A collimating lens for traveling a light beam generated by any one of the first and second light sources in parallel toward the first beam splitter; And a sensor lens for collecting the reflected light beam incident from the second beam splitter toward the light detecting means. The method of claim 9, The polarization converting means And an optical pick-up device arranged on one of the first and second light sources. The method of claim 9, The polarization selection means A non-polarization region formed in the center to transmit the incident light beam irrespective of the polarization characteristic; And a polarization region formed around the non-polarization region and selectively transmitting an incident light beam in accordance with polarization characteristics. The method according to any one of claims 8 to 12, And an optical pickup device. The method of claim 1, The first light source generates a light beam of about 400nm wavelength band, The second light source generates a light beam of about 780nm wavelength band, And wherein the first value of the numerical aperture is about 0.7 and the second value is about 0.45. The method of claim 8, The first light source generates a light beam of about 400nm wavelength band, The second light source generates a light beam of about 650nm wavelength band, And wherein the first value of the numerical aperture is about 0.7 and the second value is about 0.37.