Optical pickup apparatus

The present invention relates to an optical pickup apparatus enabling to reproduce/record data of different kinds of disks in different thicknesses, using one single optical pickup. The optical pickup apparatus includes two objective lens, in which one objective lens has an incident plane and an outgoing plant formed of a flat plane at a designated radius domain from an optical axis, thereby preventing spherical aberration caused by the difference of the thickness between different kinds of disks.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical pickup apparatus. In particular, the present invention relates to an optical pickup apparatus, which enables to reproduce/record data for different kinds of discs with different thicknesses, using an optical pickup.

2. Description of the Related Art

To keep abreast of a recent trend in data digitalization and high capacity data storage, a recording medium also has been changed from a magnetic tape to a disc. Now, the storage capacity of the disc is even enlarged by increasing recording density for recording data in the disk.

As a result of long, untiring efforts for increasing the recording capacity, a digital video disk (hereinafter, it is abbreviated to DVD) having high recording capacity was first developed from the existing compact disk (hereinafter, it is abbreviated to CD). Before long, a high density (hereinafter, it is abbreviated to HD) disk was introduced. Amazingly, the HD disk could record and reproduce the data at a very high density (i.e., twice of CD), using the existing CD. The emitting wavelength from a laser diode light source is also different for each disk. For example, in case of the CD, the wavelength is equal to 780 nm, and in case of the DVD and the HD, the wavelengths are equal to 650 nm and 405 nm, respectively.

The numerical aperture (NA) of a typically used objective lens in an optical pickup apparatus for reproducing HD is equal to 0.85 and the thickness of its disk is equal to 0.1t. Meanwhile, the numerical aperture of the objective lens in an optical pickup apparatus for reproducing DVD is equal to 0.6 and the thickness of its disk is 0.6t.

As aforementioned, the numerical aperture of the HD use objective lens is 0.85, which is larger than the numerical aperture of the DVD use objective lens, 0.6. Therefore, when the HD use optical pickup apparatus is employed, one realizes that one objective lens is not just sufficient to satisfy the numerical aperture requirement. For this reason, two objective lenses are used instead of one, as shown inFIG. 1, to make the numerical aperture 0.85.

FIG. 1is a schematic diagram showing a configuration of a HD use optical system in the prior art. As depicted in the drawing, the HD use optical system includes a first objective lens110, whose incident plane112and outgoing plane114are aspheric, and a second objective lens120, whose incident plane122is spherical but the outgoing plane124is flat. Alternatively, the optical system can be configured by making the incident plane112and the outgoing plane114of the first objective lens110, and the incident plane122of the second objective lens120all aspheric, while making the outgoing plane124of the second objective lens120flat.

Still as another option, the optical system can be configured by making the incident plane112of the first objective lens110and the incident plane122of the second objective lens120aspheric, and making the outgoing plane114of the first objective lens110and the outgoing plane of the second objective lens120flat. Here, the reference numeral130can be either HD or DVD.

In short, the HD use optical system can have a variety of configurations by alternating the shape of the first objective lens110and the second objective lens120.

However, if one intends to reproduce DVD using two objective lenses appropriate for the HD use optical system, the difference in thickness between HD and DVD, that is, 0.1 t for HD and 0.6 t for DVD, causes spherical aberration, and as the result thereof, signal degradation occurs.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide an optical pickup apparatus, which enables to reproduce/record data for different kinds of disks with different thicknesses.

Another object of the present invention is to provide an optical system for use of the optical pickup apparatus.

To achieve the above objects, there is provided an optical system for use of optical pickup apparatus including: two objective lenses, wherein one objective lens has an incident plane and outgoing plane with a flat radius zone from an optical axis.

The coated domain transmits digital video disk (DVD) light beams only by coating the flat domain.

Also, a domain other than the flat domain is formed of an aspheric plane.

The flat domain is mounted with a diffraction element by diffracting high density (HD) use light beams.

In another aspect of the present invention, there is provided an optical system for use of optical pickup apparatus includes a first objective lens, of which incident plane and outgoing plane for light beams are formed of a coated flat plane at a designated radius domain from an optical axis; and a second objective lens, which focuses incident light beams transmitted the coated flat plane of the first objective lens on an arbitrary spot on a disk.

In yet another aspect of the present invention, there is provided an optical system for use of optical pickup apparatus, the system includes a first objective lens, of which incident plane and outgoing plane for light beams are formed at a designated radius domain from an optical axis, being mounted with a diffraction element; and a second objective lens, which focuses incident light beams transmitted the diffraction element of the first objective lens on an arbitrary spot on a disk.

In further another aspect of the present invention, there is provided an optical pickup apparatus includes a light source for emitting light beams separately; a light splitter for transmitting or reflecting the light beams emitted from the light source; a collimator lens for making the light beams progressed from the light splitter into parallel light beams; a reflecting mirror for reflecting the parallel light beams transmitted the collimator lens and alternating an optical path thereof and two objective lens, in which one objective lens has an incident plane and an outgoing plane that form a flat plane at a designate radius domain after being coated, and focuses the alternated light beams at the reflection mirror on an arbitrary spot on a disk.

The coated flat domain transmits digital video disk (DVD) use light beams only, and other uncoated domain except for the coated flat domain transmits high density (HD) use light beams only.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A preferred embodiment of the present invention will now be described with reference to the accompanying drawings. In the following description, same drawing reference numerals are used for the same elements even in different drawings. The matters defined in the description focus on those that will assist in a comprehensive understanding of the invention. Thus, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail.

In general, an optical pickup apparatus includes a hologram pickup module (HPM) for outputting laser beams for use of compact disk (CD), digital video disk (DVD), or high density (HD), a beam splitter for transmitting or reflecting the light beams outputted from the HPM, a collimator lens for making the light beams from the beam splitter to parallel light beams, a reflecting mirror for alternating an optical path of the parallel light beams that passed through the collimator lens; and an objective lens for focusing the alternated light beams by the reflecting mirror and forming a beam spot on a disk.

As already explained in the prior art, the HD use optical pickup apparatus can focus light beams on a HD use disk by combining two objective lenses.

The present invention also introduces an optical system, in which two objective lenses are used to focus light beams on an arbitrary spot on the disk, in order to make the optical pickup apparatus applicable not only to HD but also to DVD.

FIG. 2is a schematic diagram showing a configuration of an optical system for use of an optical pickup apparatus in accordance with the present invention. Referring toFIG. 2, the optical system for use of the optical pickup apparatus of the present invention includes; a first objective lens210, in which an incident plane and an outgoing plane form flat radius domains (hereinafter, it is referred to flat domain)212and214from an optical axis, and the rest of domain except for the flat domains212and214forms aspheric domains211and213; and a second objective lens220, which focuses the incident light beams transmitted through the first objective lens210to an optical system use disk230. Preferably, the optical use disk230is a DVD use disk or RD use disk. As long as the primary object or gist of the present invention is not changed, the flat domains212and214can be formed on either the incident plane or the outgoing plane of the first objective lens210. More preferably, however, the flat domains212and214are formed on both the incident plane and the outgoing plane. Therefore, the DVD use light beam is transmitted through the flat domains212and214of the first objective lens210, and is focused on the DVD use disk via the second objective lens220. On the other hand, the RD use light beam is transmitted through the aspheric domains211and213, and is focused on the HD use disk via the second objective lens220.

More details are provided with reference toFIG. 3andFIG. 4.

FIG. 3is a diagram showing an optical path particularly of the DVD use optical system in the optical system for use of the optical pickup apparatus in accordance with the present invention. According to the optical path of the DVD use optical system shown in the drawing, the DVD use light beam is incident upon the flat domain212on the incident plane of the first objective lens210. The light beam incident upon the flat on the outgoing plane of the first objective lens210, and is incident upon the second objective lens220. The DVD use light beam is incident upon the second objective lens220is focused on the DVD use disk240with a thickness of 0.6 t. Here, the second objective lens220can be designed especially for the DVD use disk240in order to focus the incident light beam upon the second objective lens220on the DVD use disk240.

In the meantime, the flat domains212and214of the first objective lens210are coated to transmit the DVD light beam only (wavelength: 650 nm). In this manner, when the HD use light beam (wavelength: 405 nm) incidents upon the first objective lens210, it cannot transmit the coated domains212and214, but transmits the non-coated aspheric domains211and213instead. domain212of the incident plane then transmits through the flat domain212.

FIG. 4is a diagram showing an optical path particularly of the HD use optical system in the optical system for use of the optical pickup apparatus in accordance with the present invention. Typically, to increase the numerical aperture, the HD use light beam can be incident more broadly than the DVD use light beam. According to the optical system for use of the optical pickup apparatus ofFIG. 4, the HD use light beam with a large optical width is incident very broadly to be able to cover the coated domains216and218of the first objective lens210. The HD use light beam, at this time, cannot pass through the coated domains216and218. Instead, it transmits through the non-coated aspheric domains211and213, and is incident upon the second objective lens220. When the light beam is incident upon the second objective lens220after passing through the aspheric domains211and213, it focuses on the HD use disk250with a thickness of 0.1 t. More desirably, to focus the incident light beam upon the second objective lens220on the HD use disk250, it is preferred that the non-coated domains211and213be aspheric.

In short, in case of the DVD use disk240, the second objective lens220should be designed suitable for the DVD use disk, while in case of the HD use disk250, the non-coated domains211and213of the first objective lens210should preferably be aspheric in order to focus the light beam incident upon the second objective lens220on the optical system disks240and250.

In such manner, that is, by designing the first objective lens and the second objective lens in an optimal manner, the light beam can be focused on the DVD disk or the HD disk at the same time.

To this end, the second objective lens220is preferably a DVD exclusive lens, and the non-coated domains211and213of the first objective lens210should be aspheric.

Thusly configured optical system secures compatibility of the HD use optical system and the DVD use optical system. Although, in case of the HD use optical system, part of lights (or the intensity of the light) could be lost as the central portion of the light beam is blocked, the system can prevent any aberration caused by the differences in thickness of two different kinds of disks. Besides, the HD use optical system yields super resolution effect, which effect in turn resolves problems with light beams for recording/reproducing the HD disk. Further, by selecting appropriate material for the first objective lens and the second lens, the chromatic aberration, a typical problem caused by wavelength change of the laser used as a light source, can be successfully removed.

On the other hand, the comparability of the HD use optical system and the DVD use optical system, while preventing any loss of lights, can be obtained by using a diffraction element.FIG. 5andFIG. 6are schematic diagrams of an optical system of the optical pickup apparatus according to different embodiments of the present invention. That is to say, the light loss in the HD use optical system can be prevented by forming the diffraction element like hologram optical element (HOE) on a certain portion of the flat domain of the first objective lens shown inFIG. 2. Particularly,FIG. 5illustrates a case in which the diffraction element is formed on the flat domain of the incident plane of the first objective lens, andFIG. 6illustrates a case in which the diffraction element is formed on the flat domain of the outgoing plane of the first objective lens.

For example, when the HD use light beam (wavelength 405 nm) incidents upon the first objective lens310and410, the light beam is diffracted by the diffraction element on the incident plane or the diffraction element on the outgoing plane, and then the diffracted light beam incidents upon the second objective lens320and420. On the other hand, the HD use light beam, which incidents upon the aspheric domain311,313,411and413except for the diffraction containing domain312and414, refracts while transmitting the outgoing plane, and incidents upon the second objective lens320and420. Therefore, the diffracted light beam and the refracted light beam are focused on the optical system use disk330and430by the second objective lens320and420.

In short the HD use light beam that could not transmit through the coated domain of the first objective lens inFIG. 4could be transmitted through the diffraction element of the first objective lens310and410as depicted inFIG. 5andFIG. 6, and is focused on the optical system use disk330and430, without losing the lights as much as possible.

Meanwhile, the diffraction element is preferably designed in such manner that no phase shift occurs when the DVD use light beam (wavelength: 650 nm) passes through the first objective lens310and410.

In this manner, the incident DVD use light beam upon the first objective lens310and410can transmit the outgoing plane without experiencing the phase shift, and be focused on the optical system use disk330and430via the second objective lens320and420.

So far, the explanation of the optical pickup apparatus of the present invention has been limited to only the configuration of the objective lens for better compatibility (or interchangeability) of the DVD use optical system and the HD use optical system. However, it is always possible to design a versatile objective lens that can be used not only for the DVD use optical system/HD use optical system but also for the CD optical system, simply by changing the shape and material of the objective lens.

In conclusion, the optical pickup apparatus according to the present invention enables to reproduce/record data for different kinds of disks in different thicknessses by using one single optical pickup, which consequently prevents spherical aberration due to the difference of the thickness between different kinds of disks and compensates the light loss.

While the invention has been described in conjunction with various embodiments, they are illustrative only. Accordingly, many alternative, modifications and variations will be apparent to persons skilled in the art in light of the foregoing detailed description. The foregoing description is intended to embrace all such alternatives and variations falling with the spirit and broad scope of the appended claims.