WO1998054704A1

WO1998054704A1 - Optical pickup system for recording/reading different types of optical disks

Info

Publication number: WO1998054704A1
Application number: PCT/KR1998/000134
Authority: WO
Inventors: Yang Oh Choi
Original assignee: Daewoo Electronics Co., Ltd.
Priority date: 1997-05-31
Filing date: 1998-05-29
Publication date: 1998-12-03
Also published as: JPH10340472A

Abstract

An optical pickup system for recording/reading optical disks which are selectively loaded on a disk tray, wherein the optical disks have different thicknesses and/or recording surfaces, is provided with a first and a second light sources for generating a first or a second light beam depending on the thickness of the loaded optical disk, each of the first and a second light beams having a different wavelength from each other, μ1, μ2, a lens holder having a first and a second objective lenses, a beam splitter having a first and a second reflection surfaces and a detector. In the above system, if the loaded optical disk is a recordable compact disk having a thickness of 1.2 mm and a recordable reflection surface, the second light source is turned on and the second objective lens is utilized for recording/reading the loaded optical disk. If the loaded optical disk is a digital video disk having a thickness of 0.6 mm and a read-only reflection surface, the first light source is turned on and the first objective lens is utilized for recording/reading the loaded optical disk.

Description

OPTICAL PICKUP SYSTEM FOR RECORDING/READING DIFFERENT TYPES OF OPTICAL DISKS

TECHNICAL FIELD OF THE INVENTION

The present invention relates to an optical pickup system; and, more particularly, to an improved optical pickup system capable of recording/reading optical disks which are selectively loaded on a disk tray, wherein the optical disks have different thicknesses and/or recording surfaces .

BACKGROUND ART

As is well known, a short wavelength light source and a large numerical aperture (NA) are important optical factors in optical pickup systems for realizing high density optical storage. However, a large NA lens, e.g., 0.6, is preferably used with a thin optical disk of thickness of, e.g., 0.6mm, and if an optical head for reading the thin optical disk is used to read a conventional 1.2mm disk, the spherical aberration caused by the disk thickness difference must be corrected. A twin lenses optical pickup system with an actuator assembly provided with a pair of objective lenses has been introduced to solve the problem.

In Fig. 1, there is shown the twin lenses optical pickup system 100 for reproducing information signals stored on a thin or a thick optical disk loaded on a disk tray alternately, wherein each of the optical disks has a corresponding recording surface, which is described in Masahisa et al . , "Twin Lenses Optical Pickup System for Use in DVD", OPTRONICS (1996) No. 12. The twin lenses optical pickup system 100 comprises a light source 110, a beam splitter 120, a collimate lens 130, a mirror 140, an actuator assembly 150 provided with a first and a second objective lenses 152, 154 and a detector 160.

In the system 100, if a thin, e.g., 0.6mm, optical disk is loaded on the disk tray, the actuator assembly 150 rotates in such a way that the first objective lens 152 is aligned with a position on which a light beam emitted from the light source 110 impinges. In this case, the light beam emitted from the light source 110, e.g., a laser diode, enters the first objective lens 152 via the beam splitter 120 for partially reflecting by the surface thereof, the collimate lens 130 for making the light beam from the beam splitter 120 to be parallel and the mirror 140. The first objective lens 152 focuses the light beam impinged thereon on the recording surface of the thin optical disk as a focused light beam. The focused light beam is reflected by the recording surface of the thin optical disk, and then converged by the first objective lens 152 on the detector 160 via the mirror 140, the collimate lens 130 and the beam splitter 120.

On the other hand, when the thick, e.g., 1.2mm, optical disk is loaded on the disk tray, the actuator assembly 150 rotates in such a way that the second objective lens 154 is aligned with a position on which a light beam emitted from the light source 110 impinges. It should be noted that the functions and structures of the optical components except the second objective lens 154 for the thick optical disk in the optical pickup system 100 be similar to those for the thin optical disk. Therefore, the twin lenses optical pickup system 100 is capable of reproducing information signals stored on a thin or a thick optical disk loaded on a disk tray selectively.

There is a number of problems associated with the above-described twin lenses optical pickup system 100, however. First of all, if the light source 110 is designed for the thin optical disk, e.g., a digital video disk (DVD), the light source 110 has a wavelength range of 635 to 655 nm to obtain an optimum focused light beam on the recording surface of the DVD. On the other hand, if the thick optical disk loaded on the disk tray is a recordable compact disk (CD-R), the wavelength of the light source 110 must be about 785 nm so as to obtain reflectivity higher than 70% since the CD-R has a recording surface made of an organic dye material. That is, it is impossible that the light source 110 be designed to be used with both of the DVD and the CD-R, compatibly.

DISCLOSURE OF THE INVENTION

It is, therefore, a primary object of the present invention to provide an improved optical pickup system capable of recording/reading optical disks which are selectively loaded on a disk tray, wherein each of the optical disks has a different thickness and/or a recording surface.

In accordance with the present invention, there is provided an optical pickup system for recording/reading optical disks which are selectively loaded on a disk tray, wherein each of the optical disks has a different type of thickness and/or a recording surface, the optical pickup system comprising: a first and a second light sources for generating light beams, each of the light beams having a different wavelength from each other, wherein a corresponding light source is selected based on the type of the recording surface of the loaded optical disk; a beam splitter for partially reflecting the light beam generated from the corresponding light source to the recording surface of the loaded optical disk; a lens holder for focusing the light beam reflected from the beam splitter on the recording surface of the loaded optical disk, wherein the lens holder includes a first and a second objective lenses, being selected based on the thickness type of the loaded optical disk; and a detector, being placed opposite the loaded optical disk with respect to the reflecting means, provided with a plurality of reception surfaces, each of the reception surfaces being capable of measuring a light beam intensity and generating a corresponding output signal.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention together with the above and other objects and advantages will become apparent from the following description of preferred embodiments given in conjunction with the accompanying drawings, wherein:

Fig. 1 represents a schematic side view of a prior art optical pickup incorporated therein an actuator assembly having a twin objective lenses;

Fig. 2 illustrates a schematic side view of an optical pickup system in accordance with the present invention, when a thin and read only type optical disk is loaded on a disk tray;

Fig. 3 depicts a schematic side view of an optical pickup system in accordance with the present invention, when a thick and recordable optical disk is loaded on the disk tray; and

Figs. 4A and 4B present a flow chart illustrating the sequence of driving the optical pickup according to the present invention.

MODES OF CARRYING OUT THE INVENTION

There are illustrated in Figs. 2 to 4 various views of the inventive optical pickup system in accordance with a preferred embodiment of the present invention.

As shown in Fig. 2, the optical pickup system 200 in accordance with the present invention comprises a first and a second light sources 210, 212, e.g., a semiconductor laser, for generating a first or a second light beam, selectively, each of the first and the second light beams having a different wavelength from each other, a first wavelength λ. , and a second wavelength λ₂, a beam splitter 220 provided with a transparent base 222, a first and a second reflection surfaces 224, 226, a lens holder 230 including a first and a second objective lenses 234, 232 and a detector 250_

In the system 200, if an optical disk 240, e.g., a digital video disk (DVD) having a thickness of 0.6mm and a read-only recording surface, is selected among various optical disks to be loaded on a disk tray, the first light source 210 is selected between the light sources 210, 212 and turned on to generate a first light beam having a wavelength range about 630-650nm, whereas the second light source 212 is turned off. The light beam emitted from the first light source 210 impinges onto the first surface 224 of the beam splitter 220. The first reflection surface 224 of the beam splitter 220 is arranged in such a way that it is inclined at a predetermined angle with respect to an optical axis formed by a central point of the detector 250 and the focal point of the first light beam transmitted through the first objective lens 234 on the recording surface 242 of the loaded DVD 240. It is preferable that the predetermined angle be 45 degrees. In this case, the beam splitter 220 includes a transparent base 222 transparent to the light beams emitted from the light sources 210, 212, the first and the second reflection surfaces 224, 226, wherein the first reflection surface 224 is coated with a first dielectric film capable of partially reflecting only the first light beam having the first wavelength λ₁ and totally transmitting the second light beam, whereas the second reflection surface 226 is coated with a second dielectric film capable of partially reflecting only the second light beam having the second wavelength λ₂, but totally transmitting the all the other light beams impinging thereon. It should be noted that each of the dielectric films may be made of a stack of layers, wherein the stack of layers can be made by stacking high refraction index layers and low refraction index layers alternately and the thickness of each layer is 1/4 of the wavelength.

A portion of the first light beam is reflected by the first reflection surface 224 of the beam splitter 220 to the recording surface 242 of the loaded DVD 240 through the first objective lens 234 of the lens holder 230, wherein the first objective lens 234 is selected based on the thickness of the loaded DVD 240. The first objective lens 234 focuses the portion of the first light beam transmitted therethrough on the recording surface 242 of the DVD disk 240. In this case, the numerical aperture (NA) of the first objective lens 234 is larger than that of the second objective lens 232. The portion of the first light beam reflected from the recording surface 242 of the loaded DVD 240 impinges onto the detector 250 through the first objective lens 234 and the beam splitter 220.

Alternatively, in Fig. 3, there is shown a schematic side view of an optical pickup system 200 in accordance with the present invention, when a thick and recordable optical disk, e.g., a recordable compact disk (CD-R) which has a thickness of 1.2mm and a recording surface made of an organic dye material, is loaded on the disk tray.

In recording information signals on the recording surface 246 of the loaded CD-R 244, the second light source 212 selected between the light sources 210, 212 is turned on to generate a second light beam having a wavelength λ₂, whereas the first light source 210 is turned off. In order to record the information signals on the recording surface 246 of the loaded CD-R 244 in the form of pits, the second light source 212 has a high power enough to cause a physical or a chemical change of the organic dye material on the recording surface 246. In this regards, the wavelength λ₂ of the second light source 212 must be about 770-830nm. The light beam emitted from the second light source 212 impinges onto the second surface 226 passing through the first surface 224 of the beam splitter 220, wherein the first surface 224 is capable of totally transmitting the second light beam and the second surface 226 is capable of partially reflecting the second light beam. A portion of the second light beam is reflected by the second reflection surface 226 of the beam splitter 220 to the recording surface 246 of the loaded CD-R 244 through the second objective lens 232 of the lens holder 230, wherein the second objective lens 232 is designed for the thick, e.g., 1.2mm, optical disk. The second objective lens 232 focuses the portion of the second light beam transmitted therethrough on the recording surface 246 of the loaded CD-R 244. The portion of the second light beam reflected from the recording surface 246 of the loaded CD-R 244 impinges onto the detector 250 through the second objective lens 232 and the beam splitter 220.

With reference to Figs. 4A and 4B, the method for checking the disk type loaded on the disk tray and for driving the optical pickup in accordance with the present invention will now be described in detail. When a user loads an optical disk on the disk tray, the inventive checking method starts at step S100.

At step S110, a controller (not shown) turns on the first light source (1st LS) for generating the first light beam and turns off the second light source (2nd LS) . At step S120, the controller starts to rotate the lens holder 230 for aligning the first objective lens (1st OL) with a line which is formed by connecting the center point of the detector 250 to the center point of the first light beam impinged on the first reflection surface 224 of the beam splitter 220. At step S130, the lens holder 230 is moved up and down m times (m=l, 2, 3...) within its range of focus adjustment, thereby obtaining a disk type signal (Sdt) from the detector 250, wherein the Sdt represents an average intensity value for the first light beam impinged thereon. The magnitudes of the detected Sdt are different depending on the types, e.g, readonly/recordable and/or thickness, of the loaded optical disk. If the detected Sdt is less than a first predetermined reference signal (RF.) , the controller regards the loaded optical disk as a type 1, e.g., a CD-R which has a thickness of 1.2mm and a recordable reflection surface, and the process goes to step S150, and if not, goes to step S144. At step 150, the controller turns off the 1st LS 210 and turns on the 2nd LS 212. And then, the process goes to step S160 to rotate the lens holder 230 for aligning the second objective lens (2nd OL) 232 with a line which is formed by connecting the center point of the detector 250 to the center point of the second light beam impinged on the second reflection surface 226 of the beam splitter 220. Thereafter, the optical pickup system 200 detects a focusing error signal (FES) and a tracking error signal (TES) for the loaded optical disk.

At step 144, the controller compares the detected Sdt with a second predetermined reference signal (RF₂) being larger than the RF₁. If the detected Sdt is less than the RF₂, the controller regards the loaded optical disk as a type 2, e.g., an optical disk which has a thickness of 1.2mm and a read-only reflection surface, and the process goes to step S160, and if not, goes to step S146.

At step 146, the controller compares the detected Sdt with a third predetermined reference signal (RF,) being larger than the RF₂. If the detected Sdt is less than the RF-., the controller regards the loaded optical disk as a type 3, e.g., an optical disk which has a thickness of 0.6mm and a recordable type reflection surface, and the process goes to step S180, and if not, goes to step S148. At step 180, the controller turns off the 1st LS 210 and turns on the 2nd LS 212. Thereafter, the process goes to step S170.

At step 148, the controller compares the detected Sdt with a fourth predetermined reference signal (RF₄) being larger than the RF₃. If the detected Sdt is less than the RF₄, the controller regards the loaded optical disk as a type 4, e.g., a DVD which has a thickness of 0.6mm and a read-only reflection surface, and the process goes to step S170, and if not, goes to step S190. At step 190, the controller displays an error message on a key matrix panel (not shown) and ends the whole process.

In addition, the detections of FES and TES may be achieved by utilizing a beam size and a push-pull methods, respectively. In comparison with the prior art twin lenses optical pickup system 100, the inventive optical pickup system 200 further includes a function for selectively recording/reading optical disks loaded on a disk tray, wherein the optical disks have different thicknesses and/or recording surfaces. This is achieved by incorporating therein a first and a second light sources for generating a first and a second light beams, and a beam splitter having a first and a second reflection surfaces, wherein the first reflection surface is capable of partially reflecting the first light beam and totally transmitting the second light beam, whereas the second reflection surface is capable of partially reflecting the second light beam and totally transmitting the first light beam.

While the present invention has been described with respect to the preferred embodiments, other modifications and variations may be made without departing from the spirit and scope of the present invention as set forth in the following claims.

Claims

What is claimed is:

1. An optical pickup system for recording/reading optical disks which are selectively loaded on a disk tray, wherein each of the optical disks has a different type of thickness and/or a recording surface, the optical pickup system comprising: a first and a second light sources for generating light beams, each of the light beams having a different wavelength from each other, wherein a corresponding light source is selected based on the type of the recording surface of the loaded optical disk; means for partially reflecting the light beam generated from the corresponding light source to the recording surface of the loaded optical disk; and means for focusing the light beam reflected from the reflecting means on the recording surface of the loaded optical disk.

2. The optical pickup system of claim 1, further comprising a detector, being placed opposite the loaded optical disk with respect to the reflecting means, provided with a plurality of reception surfaces, each of the reception surfaces being capable of measuring a light beam intensity and generating a corresponding output signal .

3. The optical pickup system of claim 2, wherein the other light source is turned off.

4. The optical pickup system of claim 3, wherein the reflecting means includes a first and a second reflection surfaces, wherein the first reflection surface is capable of partially reflecting a light beam emitted from the first light source and totally transmitting a light beam emitted from the second light source, whereas the second reflection surface is capable of partially reflecting the light beam emitted from the second light source and totally transmitting the light beam emitted from the first light source.

5. The optical pickup system of claim 4, wherein the focusing means includes a first and a second objective lenses .

6. The optical pickup system of claim 5, wherein if the loaded optical disk is a thin optical disk, the first objective lens is used for focusing the light beam from the corresponding light source on the recording surface of the loaded optical disk, and if the loaded optical disk is a thick optical disk, the second objective lens is used for focusing the light beam from the corresponding light source on the recording surface of the loaded optical disk.

7. The optical pickup system of claim 6, wherein the reflecting means is disposed between the focusing means and the detector.

8. The optical pickup system of claim 7, wherein one of the optical disk has a recording surface made of metal.

9. The optical pickup system of claim 8, wherein the other optical disk has a recording surface made of an organic dye material .

10. The optical pickup system of claim 8, wherein the first light source is capable of generating a light beam having a wavelength range of 635-655nm for use with the optical disk having the recording surface made of the metal.

11. The optical pickup system of claim 9, wherein the second light source is capable of generating a light beam having a wavelength range of 770-830nm for use with the optical disk having the recording surface made of the organic metal .

12. The optical pickup system of claim 5, wherein the reflecting means is arranged in such a way that it is inclined at a predetermined angle with respect to an optical axis formed by a central point of the detector and the central point of the light beam impinged onto the beam splitter.

13. The optical pickup system of claim 11, wherein the predetermined angle is 45 degrees.

14. The optical pickup system of the claim 13, wherein a tracking error signal is detected by applying a push- pull method.

15. A method for recording/reading optical disks which are selectively loaded on a disk tray and have different types of thicknesses and/or recording surfaces, wherein the optical pickup system includes a first and a second light sources and a lens holder having a first and a second objective lenses, the method comprising the steps of:

(a) moving the lens holder up and down N times to generate a disk type signal;

(b) comparing a magnitude of the disk type signal with a predetermined number of threshold values and deciding the type of the loaded optical disk based on the comparison result;

(c) selectively rotating the lens holder to select one of the two objective lenses based on the thickness type of the loaded disk; and

(d) selectively turning one of the two light sources based on the recording surface type of the loaded disk.

16. The method according to claim 15, wherein the predetermined number of threshold values has a first, a second, a third and a fourth threshold values, when the disk type signal is less than the first threshold value, the first disk type signal represents the loaded optical disk as a recordable compact disk which has a thickness of 1.2mm and a recordable reflection surface, and when the disk type signal is less than the fourth threshold value and larger than the third threshold value, the disk type signal represents the loaded optical disk as a digital video disk which has a thickness of 0.6mm and a read-only reflection surface.

17. The method according to claim 16, wherein if the disk type signal is less than the first threshold value, the second light source is turned on and the second objective lens is utilized for recording/reading the loaded optical disk.

18. The method according to claim 17, wherein if the disk type signal is less than the fourth threshold value and larger than the third threshold, the first light source is turned on and the first objective lens is utilized for recording/reading the loaded optical disk.