KR20070060603A - Optical pick-up apparatus - Google Patents

Abstract

An optical pickup device is provided to allow a valid area of an objective lens to selectively transmit or block a beam according to two wavelengths. An objective lens(113) includes the first area(113a) and the second area(113b). The first area(113a) transmits all incident optical beams of inter-different wavelengths. The second area(113b) is coated for blocking only a beam of a CD(Compact Disc) series among the incident optical beams of the inter-different wavelengths. The first area(113a) is located in an internal area of the objective lens(113). The second area(113b) is located in an external area of the objective lens(113).

Description

Optical pick-up apparatus

1 is a block diagram of an optical pickup device according to the present invention.

2 is a detailed block diagram of an objective lens according to an embodiment of the present invention.

<Description of the symbols for the main parts of the drawings>

Laser diodes 103,118 ... Grating elements

103 Compensation lens 106,107 Beam splitter

111 ... collimator lens 113 ... objective lens

113a ... inner area 113b ... outer area

113c ... coating side 115 ... disc

119 sensor lens 121 photodetector

123 ... monitor light detector

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup apparatus, in particular, having an compatible objective lens for irradiating different types of optical beams of different wavelengths.

Today, the storage medium is changing from tape to disk due to digitalization, large capacity, and the like, and the storage capacity of the disk is increased by increasing the recording density for storing data on the disk. Therefore, in a compact disc (CD) having a laser diode used as a light source having a wavelength of 780 nm, discs suitable for wavelengths of 650 nm and 400 nm have recently been developed for the purpose of large capacity. Accordingly, optical pickup apparatuses for recording and reproducing information on the discs have been variously developed to simultaneously apply to discs having different storage densities in terms of backward compatibility.

In addition, DVD (Digital Video Disk) has a higher recording density (i.e., track density) than CD, and has a shorter distance from the surface of the disk to the information recording surface. Because of this, it is difficult for the optical pickup device for DVD to record / reproduce information on a CD, which is spherical aberration due to a change in the distance between the surface and the information recording surface on the optical disc, and coma aberration and decoupling due to tilting of the optical disc. This is caused by astigmatism or the like caused by focus.

Spherical aberration causes the intensity of the main lobe of the light beam by the area of the information recording medium to become relatively large compared to the intensity of the side lobe by the area other than the information recording medium, thereby causing interference between information tracks. Coma aberration and astigmatism destabilize the optical system and degrade the optical characteristics. Such spherical aberration (SA), coma aberration (CA) and astigmatism (DA) are the change in the distance between the surface and the information recording surface on the optical disk, the refractive index, the numerical aperture (NA) of the objective lens, the amount of defocus, the degree of tilt of the optical disk Depend on

However, the optical pickup apparatus can access both the CD and the DVD when the numerical aperture NA adjusts the diameter of the light beam from the light source using different objective lenses.

In other words, in order to access a compact disc, only one wavelength of light and a cover glass thickness of 1.2 mm were supported. However, in order to cope with two cover classes (DVD 0.6 mm and CD 1.2 mm), a DVD object was used. The lens and the objective for CD were used separately. However, currently only one objective lens that is CD / DVD compatible is used.

Therefore, although two kinds of objective lenses having different numerical apertures can be used, an optical pickup apparatus capable of accessing both CD and DVD using one compatible objective lens has been proposed. The prior art of such an optical pick-up apparatus is described in Korean Patent Application No. 10-2001-0056464, and is configured to record / reproduce heterogeneous recording media having different recording densities with one compatible lens.

In addition, the focal length is slightly different when used as a DVD and CD in a CD / DVD compatible lens, but the numerical aperture is smaller than that of a DVD. In other words, DVD playback is about 0.60 to 0.63NA, CD playback is about 0.45NA, DVD recording is about 0.65NA and CD recording is about 0.51 to 0.53 NA. Conventional CD / DVD compatible objectives use a diffraction method or an annular mask to reduce the numerical aperture.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problem, and an object of the present invention is to provide an optical pickup apparatus having an objective lens compatible for accessing a heterogeneous recording medium.

The present invention provides an optical pickup apparatus in which an effective area of an objective lens can be selectively transmitted or blocked according to two wavelengths.

An object of the present invention is to provide an optical pickup apparatus in which an internal or external region of an effective region of an objective lens can selectively block any wavelength.

An object of the present invention is to provide an optical pickup apparatus which coats an inner or an outer region of an effective region of an objective lens to selectively coat any wavelength.

Optical pickup device according to the present invention for achieving the above object,

An optical pickup apparatus for accessing a heterogeneous optical recording medium,

And an objective lens including a first region for transmitting all incident light beams and a second region coated to block only the CD-based beams among the incident light beams having different wavelengths. do.

Preferably, the first region is located in the inner region of the objective lens, and the second region is located in the outer region of the objective lens.

Preferably, the first region is an effective diameter through which the CD-based wavelength or a DVD-based wavelength passes, and the second region is an effective diameter through which only the DVD-based wavelength passes.

Preferably, the coating surface in the second region of the objective lens is an entrance surface and / or an exit surface of the objective lens.

Hereinafter, with reference to the accompanying drawings as follows.

1 is a block diagram showing an optical pickup device according to an embodiment of the present invention.

Referring to FIG. 1, first and second laser diodes 101 and 102 generating beams having different wavelengths, and first and second grading elements 105 and 118 provided on the emission side of each laser diode 101 and 102. And a compensation lens 103 provided on the output side of the first laser diode 101 to compensate for aberration, and first and second beam splitters 107 and 117 which transmit or reflect the generated beam according to the incident direction. And a reflection mirror 109 for converting the beam emitted from the first beam splitter 107 in a disc direction; The collimator lens 111 for paralleling the beam emitted from the reflecting mirror 109, the objective lens 113 for irradiating the parallelized beam to the disk 115, and the beam reflected from the disk in the reverse path It comprises a sensor lens 119 for condensing on the photodetector 119 and a monitor photodetector 123.

Here, the objective lens 113 is divided into two regions, and one of the two regions is a region in which all different wavelengths are transmitted, and the other region is one of two wavelengths, and only one wavelength is transmitted. The wavelength is 100% blocking.

Referring to the accompanying drawings, the optical pickup device according to an embodiment of the present invention configured as described above is as follows.

Referring to FIG. 1, the first laser diode 101 or the second laser diode 102 respectively generate different wavelengths, and each of the disks, which are heterogeneous recording media, is accessed by a light source generated according to the type of the inserted disk. To occur. Here, the first laser diode 101 may be a CD LD, and the second laser diode 102 may be a DVD LD.

Grating elements 105 and 118 are disposed on the exit sides of the first and second laser diodes 101 and 102, and are divided into several (eg, three) beams by using the diffraction phenomenon of the incident beam.

In addition, a compensation lens 103 is disposed between the first laser diode 102 and the grating element 103, and the compensation lens 103 corrects the aberration of the beam generated from the first laser diode 101. . An aberration compensation lens such as a toric lens or a cylinder lens is installed on one surface of the compensation lens 102.

The first light source generated from the first laser diode (eg, CD LD) 101 is converted to a direction of linear polarization through a correction lens (CD lens) 103 and a grating lens 105 to thereby split the beam splitter 107. Is incident on.

The beam splitter 107 transmits or reflects the incident beam according to the polarization direction, and the reflected beam is reflected in the direction of the objective lens in the reflection mirror 109 and is converted into a parallel beam by the collimator lens 111. It is made and condensed at a point on the disk (not shown) through the objective lens 113. Here, when the first laser diode is CD LD, the first light beam is focused on the CD disk 115a by the objective lens.

The first light beam reflected from the disk is focused on the photodetector 121 through the objective lens 113, the collimator lens 111, the reflective mirror 109, the beam splitters 107 and 117, and the sensor lenses 119. It is detected as an electrical signal. The detected signal is used to output servo and RF control signals. Here, the sensor lens 119 is not a uniform curvature of the lens surface, but differently configured in the vertical direction and the horizontal direction to generate astigmatism. Here, the beam splitter may use a cubic prism or a polarizing beam splitter as the optical path switching means for transmitting or reflecting an incident beam according to the polarization direction, and the position of each other may be changed, or a beam splitter of the same type may be used.

On the other hand, the second light beam generated from the second laser diode (eg, DVD LD) 102 is incident on the beam splitter 117 via the grating element 118, and the beam splitter 117 receives the second light beam. The light is reflected and collected at a point on the disk through the beam splitter 107, the reflection mirror 1109, the collimator lens 111, and the objective lens 113. Here, if the second laser diode is DVD LD, the second light beam is focused on the DVD disc 115b.

Then, the second light beam generated from the second laser diode 102 is reflected from the disk, and the reflected second light beam is detected as an electrical signal to the photo detector 121 through the reverse path, so as to serve as servo and RF signals. Is output.

In this way, two light beams having different wavelengths are recorded or reproduced on heterogeneous recording media having different recording densities by using one compatible objective lens.

To this end, as shown in FIGS. 1 and 2, the objective lens 113 is divided into two regions 113a and 113b, and one region 113a is a region in which all different wavelengths are transmitted. The other region 113b transmits only a specific wavelength, for example, a relatively short wavelength.

In addition, two regions formed in the objective lens 113 are divided into inner and outer regions 113a and 113b, and the inner region 113a transmits only a CD / DVD wavelength, for example, and the outer region 113b. ) Transmits only the DVD wavelength (about 650 nm) and the CD wavelength (about 780 nm) is blocked. As another example, when the wavelength for DVD / HD is used, the external region of the objective lens may be blocked or transmitted to different wavelengths to selectively enter, and the optical system for this may be correspondingly configured.

If the objective lens 113 is to be used as a CD / DVD compatible lens, the inner region 113a of the objective lens 113 is the CD effective diameter R1, and the inner region 113a and the outer region 113b. The whole is used as the DVD effective diameter R2.

To this end, the outer region 113b of the objective lens 113 is coated to transmit only a light beam of a specific wavelength. The coating surface is formed on the incident surface 113c of the objective lens. As the coating material of the incident surface, SiO 2, TiO 2, etc. may be used as a material allowing only the DVD wavelength to pass. As another example, the coating surface may be the exit surface of the objective lens, or may be both the entrance surface and the exit surface of the objective lens.

In other words, when used as a DVD and a CD in the objective lens 113, the focal length is slightly different, but the numerical aperture is smaller than the DVD. DVD playback is 0.60 to 0.63NA, CD playback is about 0.45NA, DVD recording is about 0.65NA, and CD recording is about 0.51 to 0.53 NA. Since the CD numerical aperture is smaller than the DVD numerical aperture NA in this manner, the CD effective diameter can be defined as the area inside the objective lens. That is, the light source having a relatively long wavelength uses the internal region of the objective lens.

The numerical aperture and the effective diameter are established as in Equation (1).

NA = φ / 2f

Where? Is the objective lens effective diameter and f is the objective lens focal length. Reducing the effective diameter of the objective lens in Equation 1 can reduce NA.

As shown in FIG. 2, the inner region 113a of the objective lens 113 is an effective diameter R1 through which both wavelengths are transmitted, and only one wavelength is transmitted through the outer region 113b. Accordingly, one wavelength transmits both the inner region and the outer region, and the other wavelength transmits only the inner region. For example, when used as a CD / DVD compatible lens, the inner region is a CD effective mirror, and the inner / outer region is used as a DVD effective mirror.

If the objective lens is used as a DVD / HD compatible lens, an inner region of the objective lens becomes a DVD effective diameter, and an inner / outer region of the objective lens becomes an HD effective diameter. In addition, the incidence surface and / or the emission surface of the outer region of the objective lens is formed with a coating that blocks the DVD wavelength and transmits only the HD wavelength. In this way, it can also be used as a DVD / BD compatible objective.

As described above, the objective lens of the present invention focuses on one wavelength and does not scatter other wavelengths, and selectively transmits or blocks each wavelength, thereby allowing a relatively long wavelength to enter the external region of the objective lens. It blocks 100% of the light beams of the CD-based wavelengths so that all of the CD / DVD discs can be accessed. In addition, by blocking the light beam of the CD-based wavelength can reduce the NA for the CD by that area.

So far, the present invention has been described with reference to the preferred embodiments, and those skilled in the art to which the present invention pertains to the detailed description of the present invention and other forms of embodiments within the essential technical scope of the present invention. Could be implemented. Here, the essential technical scope of the present invention is shown in the claims, and all differences within the equivalent range will be construed as being included in the present invention.

According to the optical pickup device according to the present invention as described above, by providing an objective lens that selectively blocks or transmits the wavelength to each other in the optical pickup device using different wavelengths, heterogeneous light by using light sources of different wavelengths There is an effect that recording or reproduction can be performed on the recording medium.

The objective lens of the present invention has the effect of eliminating the problem caused by scattering by coating to have a characteristic that converges or blocks 100%, rather than converge or scatter for different wavelengths.

Claims (4)

An optical pickup apparatus for accessing a heterogeneous optical recording medium, And an objective lens including a first region transmitting all the light beams having different wavelengths incident thereto, and a second region coated to block only the CD-based beams among the light beams having different wavelengths incident thereto. Optical pickup device. The method of claim 1, The first region is located in the inner region of the objective lens, And the second region is located at an outer region of the objective lens. The method of claim 1, The first region is an effective diameter through which the CD-based wavelength or the DVD-based wavelength passes, and the second region is an effective diameter through which only the DVD-based wavelength passes. The method of claim 1, And the coating surface of the second region of the objective lens is an incident surface and / or an exit surface of the objective lens.

Images