KR100447149B1 - Optical pickup device for different kinds of optical disks, especially related to forming a beam spot on an information recording surface of an optical disk without tracking and focusing errors - Google Patents

Abstract

PURPOSE: An optical pickup device for different kinds of optical disks is provided to configure another light sources having different wavelengths, and to integrate a beam splitter with an objective lens as one spherical lens, thereby enabling recording/reproducing compatibility between optical disks having different wavelengths. CONSTITUTION: The first light source(31) generates an optical beam for DVD. The second light source(33) generates an optical beam for CD-R. A beam splitting integration-type objective lens(34) transmits or reflects the optical beams generated according to wavelengths created from the first and second light sources(31,33), and condenses the transmitted or reflected optical beams into one point on a surface of an optical disk(30) by controlling an opening ratio.

Description

Optical pickup device for different optical discs

The present invention relates to an optical pickup apparatus for heterogeneous optical disks having different substrate thicknesses and wavelengths, and in particular, a compact disk in the same optical pickup apparatus using a dichroic mirror-coated beam split integrated spherical objective lens and two light sources. An optical pickup apparatus for fish species optical discs that enables recording / playback of not only (Compact Disc; CD) and Digital Versatile Disc (DVD) but also recordable CDs, that is, CD-R (Compact Disc Recordable). will be.

1 is a schematic diagram of an optical system of a conventional optical pickup device, which includes a light source 11 generating white light, a spherical mirror prism 12 that refracts a light beam generated by the light source 11 in a vertical direction, and the spherical mirror prism And an objective lens 13 for condensing the beam refracted from 12 at one point on the surface of the optical disk 10.

In this case, it is assumed that the light detector is integrally formed in the light source to reduce the volume.

According to FIG. 1 configured as described above, the beam generated from the light source 11 is reflected at the vertical angle on the curved surface of the spherical mirror prism 12 and is incident on the objective lens 13.

The objective lens 13 focuses the light beam incident upon the vertical refraction onto the information recording surface of the optical disk 10 so as to record information on the disk 10 or to access the recorded information.

However, FIG. 1 described above shows that when the light source 11 is fixed so that the objective lens accesses the information of the disc 10, that is, when the objective lens rises by focusing and tracking, the spot point shows a certain height from the upper side. DC offset occurs as in FIG.

Since this is a position deviating from the reference axis a1 of the basic design, there is a problem that a high aberration beam spot is caused, resulting in deterioration of beam quality.

That is, no spot enters the photo detector in the light source at the design position, and signal detection becomes impossible.

Therefore, if the light source and the objective lens are implemented as an integral driving type to solve this problem, the problem of generation of height can be solved, but the weight is increased and the length is long, so that the thin and high speed pickup cannot be achieved.

On the other hand, the light source used for the optical pickup for DVD has a wavelength of 635 to 650 nm (visible light, red), and a light source having a wavelength of 780 nm (infrared light) is required to simultaneously read a CD-R disc in the same player. .

In other words, in the case of CD-R, the medium of the disc uses cyanine (blue pigment) dye, which has a property of having a reflectance only at 780 nm.

Therefore, since a light source of 780 nm is necessarily required, it cannot be used as a DVD light source.

At this time, the CD can be read at both 780 nm and 635 to 650 nm wavelengths.

As a result, in order to use the CD-R as a combined use, a light source for the CD-R and a light source for the DVD are respectively required.

In addition, in order to read a CD or CD-R in a DVD player, it is necessary to adjust the aperture ratio NA of the objective lens.

That is, in the case of the combined CD / DVD, a light source having the same wavelength may be used, but since the thickness of the disk is different (for example, 1.2 μm for a CD and 0.6 μm for a DVD), spherical aberration is changed, and it is necessary to correct this.

For example, the aperture ratio NA1 of the objective lens required for CD should be smaller than the aperture ratio NA2 required for DVD (NA2 > NA1).

Therefore, conventionally, a twin-lens method using two light sources separately for such a CDR / CD / DVD combined use, and separately using an DVD objective lens and a CD objective lens to adjust the aperture ratio has been proposed.

However, in the twin lens method, two objective lenses and a separate optical device for driving the respective lenses must be added, so that the product is heavy and complicated, so that the light and small is difficult and the price increases.

The present invention is to solve the above problems, an object of the present invention is to separately configure a light source having a different wavelength and to focus the light beam at a point on the disk and a beam splitter for transmitting or reflecting the beam according to the wavelength difference By integrating an objective lens into one spherical lens, it is possible to provide an optical pickup device for a heterogeneous optical disc that enables recording / playback compatibility of optical discs having different wavelengths while preventing image generation.

It is another object of the present invention to design an optical separation integrated objective lens to selectively transmit all or a part of the beam depending on the wavelength, so that the aperture ratio of the objective lens can be easily adjusted to record / record optical discs having different thicknesses and recording densities. An optical pickup device for heterogeneous optical discs capable of playback compatibility.

A feature of the optical pickup device for heterogeneous optical disks according to the present invention for achieving the above object is a first light source for emitting a beam of a first wavelength, and a beam of a second wavelength different from the first wavelength A second light source, beam separation means for transmitting or reflecting an incident beam according to the wavelength of the beam generated from the first or second light source, and focusing means for condensing the light beam on a corresponding surface of an optical disk having a different wavelength and thickness, etc. It is configured to include a beam separation unitary objective lens that is integrally formed in the lens of.

1 is a configuration diagram of an optical system of a conventional optical pickup device

FIG. 2 is a block diagram of an optical system of an optical pickup apparatus showing an example of occurrence of an incident during focusing in FIG.

3 is a configuration diagram of an optical system of an optical pickup apparatus for heterogeneous optical disks according to the present invention;

FIG. 4 is a plan view illustrating an example in which an optical coating of a predetermined portion of the beam splitting region is performed to adjust the aperture ratio in FIG. 3.

5 is a view showing a reflection path by parallel light and non-parallel light in FIG.

FIG. 6 is a cross-sectional view illustrating an example in which the light source and the photo detector are integrally formed in a light source package in FIG. 3.

Explanation of symbols for the main parts of the drawings

30: optical disc

30a: first information recording surface 30b: second information recording surface

31: first light source 32: collimator lens

33 second light source 34 beam-integrated objective lens

34a: beam separation surface 34b: objective lens surface

34c: optical coating area 34d: uncoated area

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

3 is an optical system configuration diagram of an optical pickup device for heterogeneous optical disks according to the present invention, wherein the first light source 31 generates a DVD light beam, the second light source 33 generates a CD-R light beam, The first and second light sources 31 and 33 are composed of a beam-separated integrated objective lens 34 which transmits or reflects a light beam generated according to a wavelength generated by the second light source 31 and 33 to adjust the aperture ratio to focus at a point on the surface of the optical disk 30. do.

At this time, between the first light source 31 and the beam split integrated lens 34, a collimator lens for traveling the beam generated by the first light source 31 in parallel to the beam split integrated lens 34 ( 32) is installed to eliminate the occurrence of the image caused by the DVD light beam.

The beam separation integrated objective lens 34 is a spherical lens, and the spherical surface is divided into a beam separation surface 34a and an objective lens surface 34b.

That is, the surface on which the beam generated by the first or second light sources 31 and 33 is incident is the beam separation surface 34a, and the surface on which the light reflected by the mirror surface 34e is incident is the objective lens surface 34b. )to be.

In this case, the objective lens curved surface 34b is designed so that the light beam is focused on one point of the disk 30, and the mirror surface 34e is a polarizing beam splitter for transmitting or reflecting the beam according to the direction of polarization. Assume that it is coated.

Then, the beams generated by the first light source 31 and the second light source 33 are incident on the disk 30 through the same path, and the direction of linearly polarized light on the beam separation surface 34a to adjust the aperture ratio of the incident beam. A λ / 2 plate is attached to the film, and an optical coating for reflecting the wavelength for the CD-R is reflected on a predetermined portion of the λ / 2 plate.

That is, the optical wavelength for reflecting the specific wavelength, for example, the CO-R wavelength, is formed in the portion 34c corresponding to the CD aperture ratio (NA = 0.45) as shown in FIG. Since both the optical coating region 34c and the uncoated region 34d of the C-R are transmitted and the wavelength of the CD-R is controlled by the optical coating layer, the spherical aberration is not large even when the CD-based optical disc is reproduced. Proper playback is possible.

In an embodiment of the invention it is assumed that the optical coating is coated with a dichroic mirror that transmits or reflects the beam depending on the wavelength.

That is, when the CD series uses a wavelength of 780 nm, the DVD series uses a wavelength of 635-650 nm, the NA required for the CD series is NA1 = 0.45, and the NA required for the DVD series is NA2 = 0.6.

At this time, when the focal length is F, the incident light of the CD series requires D1 = 2 · NA1 · F, the incident light of the DVD requires D2 = 2 · NA2 · F, and D2> D1.

Therefore, as shown in FIG. 4, the dichroic mirror reflecting the CD-R wavelength beam without transmitting it is coated on the region 34c of the incident mirror D1 corresponding to the case where the NA for CD is 0.45.

3, the first information recording surface 30a of the optical disc 30 is an information recording surface of a DVD, the second information recording surface 30b is an information recording surface of a CD, and the second information recording surface 30b is a first information. It is located 0.6 mm further from the surface of the optical disc 30 than the recording surface 30a.

On the other hand, after focusing on the first information recording surface 30a or the second information recording surface 30b of the optical disk 30, the reflected beam is incident to each photodetector via the opposite path.

In this case, it is assumed that the photo detector is integrally formed in the light source package as shown in FIG. 6.

That is, the laser diode 61 and the photodetector 62 are disposed side by side in the package of the light source, and the beam incident into the light source package is diffracted toward the photodetector 62 using the hologram 63.

In the present invention configured as described above, the wavelength of a wide range generated by the first light source 31 is 635-650 nm used for the DVD-based optical disc, and the wavelength of the light beam generated by the second light source 33 is used for the CD-based optical disc. Assume that it is 780nm.

In addition, linearly polarized light of beams having different wavelengths emitted from the first and second light sources 31 and 33 is fixed to P waves, and the mirror surface 34e of the beam splitting integral objective lens 34 transmits P waves. Assume that it is PBS coated to reflect S waves.

Further, the beam separation surface 34a of the beam separation unit objective lens 34 has a? / 2 plate attached thereto, and a dike for transmitting or reflecting the beam according to the wavelength to the? / 2 plate to which the light beam of the wavelength for CD-R is incident. It is assumed that the roic mirror is coated, and the dichroic mirror is coated to reflect light at 780 nm wavelength and reflect light at 635-650 nm wavelength.

Here, 780 nm is a wavelength for CD-R, and 635-650 nm is a wavelength for DVD.

At this time, the CD can be read in both 780nm or 635-650nm, but in the present invention uses 780nm for CD-R / CD / DVD combined use.

Hereinafter, the recording / reproducing of the DVD-based optical disc and the recording / reproducing of the CD-based optical disc will be described separately.

i) DVD series optical disc

A light beam of P-wave having a wavelength of 635-650 nm from the first light source 31 becomes parallel light by the collimator lens 32 and is incident on the beam separation surface 34a of the beam separation integrated objective lens 34.

At this time, since the optical coating region 34c of the beam separation surface 34a transmits the light beam having a wavelength of 635-650 nm due to the dichroic coating property, the light beam having the wavelength for DVD incident on the beam separation surface 34a is uncoated region. Both 34d and optical coating area 34c are transmitted.

Since the linearly polarized light of the DVD light beam passing through both the optically coated region 34c and the uncoated region 34d is P wave, it is converted into S wave by the λ / 2 plate and is incident on the mirror surface 34e.

Since the linearly polarized light of the light beam incident on the mirror surface 34e is an S wave, it is reflected from the mirror surface 34e and is incident on the objective lens surface 34b.

Thus, the beam diameter of the light beam is not reduced, so the original numerical aperture (i.e., 0.6) is maintained.

Therefore, the objective lens surface 34b accurately transmits a light beam passing through both the uncoated region 34d and the optical coating region 34c to the first information recording surface 30a of the optical disk 30, that is, the information recording surface of the DVD. The light is collected to record information on the DVD or to access the recorded information.

Here, the beam of the wavelength for DVD is parallel-beamed by the collimator lens 32, and an image height does not generate | occur | produce.

Therefore, aberration-free beam spots can be formed on the first information recording surface 30a of the optical disc 30 during focusing and tracking.

On the other hand, the light beam reflected from the first information recording surface 30a is incident to the light source 31 through the beam separation integrated objective lens 34. The light source 31 has a laser diode 61 and a photo detector as shown in FIG. 6. Since 62 is disposed side by side, the beam incident on the light source 61 is diffracted by the hologram 63 and is incident on the photodetector 62.

The photo detector 62 converts the incident light beam into an electrical signal to obtain a high frequency signal, a focus error signal, and a tracking error signal.

ii) CD series optical disc

A light beam of P waves having a wavelength of 780 nm is generated from the second light source 33 and is incident on the mirror surface 34e of the beam separation integrated objective lens 34.

Here, since the polarization of the beam incident on the mirror surface 34e is a P wave, it is incident on the beam separation surface 34a after passing through the mirror surface 34e, and at the optical coating area 34c of the beam separation surface 34a. After being reflected by the dichroic coating characteristic, it is converted into S-waves by the λ / 2 plate and is incident again on the mirror surface 34e.

In this case, since the linearly polarized light of the light beam incident on the mirror surface 34e is converted into S-waves, it is reflected by the mirror surface 34e and is incident on the objective lens surface 34b.

That is, the beam for the CD-R incident on the objective lens surface 34b is reflected by the dichroic coating characteristic in the optical coating region 34c, thereby reducing the beam diameter of the light beam.

When the beam diameter of the light beam is reduced, the numerical aperture is reduced to the CD numerical aperture (i.e., 0.45), so that the light beam reflecting the optical coating region 34c is passed through the objective lens surface 34b to the second information recording surface of the optical disc 30 ( 30b) That is, the information is condensed accurately on the information recording surface of the CD, and hence the information can be recorded on the CD series optical disk or the recorded information can be accessed.

On the other hand, the light beam reflected from the second information recording surface 30b is also incident on the light source 33 through the beam separation integrated objective lens 34, and the beam incident on the light source 33 is diffracted by the hologram 63. Incident to the photodetector 62.

The photo detector 62 converts the incident light beam into an electrical signal to obtain a high frequency signal, a focus error signal, and a tracking error signal.

At this time, when the beam generated from the second light source 33 is parallel light as shown in a of FIG. 5, the beam reflected from the concave beam separation surface 34a is collected at the point f, and is incident at a predetermined angle as shown in b. If the beam becomes a beam, the beam reflected from the beam splitting surface 34a is collected at point p.

Here, the point p is always located at one point between the point f and the point R on the light side, and the point f is half of R of the concave diameter.

Therefore, even if the beam split-integrated objective lens 34 moves up and down by a focusing operation or the like, the p point is always positioned on the optical axis, so that no image height occurs.

As described above, according to the optical pickup apparatus for heterogeneous optical disks according to the present invention, a plurality of light sources generating different wavelengths are separately formed, and a beam splitter and a beam splitter for transmitting or reflecting beams according to the wavelengths generated by the light sources. CD-based optical discs that use different wavelengths with the same optical pickup at high speed and thinness, because the objective lens for condensing the reflected beam on the information recording surface of the optical disc is integrally formed in one spherical lens. Recording / playback compatibility of / DVD series optical discs can be achieved.

Further, by selectively transmitting the whole or part of the beam according to the wavelength of the beam to adjust the numerical aperture of the objective lens, the numerical aperture can be easily adjusted without the need for a separate optical component, thereby making it easy to reduce the thickness of the optical pickup device.

In addition, the light beam for DVD is made into parallel light by the collimator lens to eliminate the occurrence of image height, and the point where the beams reflected from the dichroic mirror and the dichroic mirror on the beam separation surface are always kept constant. Even with respect to the CD-R light beam generated with no image generation, a beam spot free from aberration during tracking and focusing can be formed on the corresponding information recording surface of the optical disc.

Claims (9)

An optical pickup apparatus for heterogeneous optical disks for condensing a light beam on a corresponding surface of an optical disk having a different wavelength and thickness, First light emitting means for emitting a first wavelength beam, Second light emitting means for emitting a beam of a second wavelength different from the first wavelength; And a mirror surface and a spherical surface which are optically coated to transmit or reflect the incident beam according to the polarization direction, wherein the sphere is transmitted from the first and second light emitting means again according to the wavelength of the incident beam. And a beam splitting-integrated objective lens which is divided into a beam splitting surface for reflecting and an objective lens surface for focusing the beam reflected from the mirror surface on a corresponding surface of the optical disk. The method of claim 1, The beam generated by the first light emitting means passes through the beam separation surface of the beam splitting integral objective lens and enters the mirror surface, and the beam reflected from the mirror surface travels through the optical lens surface to the optical disk. Optical pickup device for heterogeneous optical disk, characterized in that. The method of claim 1, The beam generated by the second light emitting means passes through the mirror plane of the beam splitting integral objective lens, enters the beam splitting plane, and then is reflected to the mirror plane. An optical pickup apparatus for heterogeneous optical disks, characterized in that it proceeds to the optical path emitted. The beam splitting surface of the beam splitting integral objective lens further includes a λ / 2 plate for changing the direction of linearly polarized light, and polarized light incident by forming an optical coating film on a predetermined region of the λ / 2 plate. The optical pickup apparatus for heterogeneous optical disks, characterized in that for converting and reflecting or transmitting a beam incident to the optical coating film according to the wavelength of the incident beam. The method of claim 4, wherein the optical coating film Optical pickup device for heterogeneous optical disk, characterized in that the dichroic mirror is coated. The method of claim 4, wherein the region where the optical coating film is formed An optical pickup apparatus for heterogeneous optical disks, characterized in that the region corresponds to the aperture ratio for CD. The method of claim 1, wherein the mirror surface of the beam splitting integral objective lens An optical pickup device for heterogeneous optical disks, characterized in that it is optically coated to transmit or reflect the incident beam according to the polarization direction. The method of claim 1, The method of claim 1, wherein the first and second light emitting means An optical pickup apparatus for heterogeneous optical disks, characterized in that the optical detection means is integrally formed. The method of claim 8, wherein the first and second light emitting means An optical pickup apparatus for a heterogeneous optical disc, characterized in that the beam reflected from the optical disc is diffracted by the hologram element and incident to the optical detection means.