Optical head assembly having compatibility with a digital versatile disk (DVD) and a recordable compact disk (CD-R) for obtaining a high-speed access time

Abstract: An optical head assembly having compatibility with a recordable compact disk (CD-R) and a digital video disk (DVD) comprises a stationary first optical unit (200) and a second optical unit (300) which moves to a target sector travelling between an inner circumference and an outer circumference of a disk. The first optical unit (200) directs an emitted first light beam having a wavelength of 635nm for a DVD' to the second optical unit (300) and detects information contained in the first light beam redirected from the second optical unit (300). Meanwhile, the second optical unit (300) focuses both the first light beam incident from the first optical unit (300) and an emitted second light beam having a wavelength of 780nm for a CD-R on an information recording surface of the loaded optical disk transmits the first light beam reflected by the optical disk to the first optical unit (200), and detects information from the second light beam reflected by the optical disk (8, 9).

Description: The present invention relates to an optical head assembly for use in an optical disk driver using light having wavelengths different from each other for at least two optical disks, and more particularly, to an optical head assembly for use in an optical disk driver which is compatible with a digital versatile disk (DVD) and a recordable compact disk (CD-R). In the optical disk apparatus being a recording medium for storing a large quantity of information, a compact disk (CD) and a digital versatile disk (DVD) have been widely used. Recently, a recordable compact disk (CD-R) and a digital versatile disk - random access memory (DVD-RAM) have been known. When reproducing information, laser light having a wavelength of 780nm is used for a CD-R, laser light having a wavelength of 650nm or 635nm is used for a DVD-RAM. Accordingly, an optical disk driver which can record information on and reproduce information from these optical disks, includes at least two light sources for emitting laser light having different wavelengths from each other. Referring to Figure 1, an optical system of an optical head for an optical disk driver which is compatible with a conventional DVD and a CD-R is described as follows. Figure 1 shows a conventional optical head assembly for use in an optical disk driver for a digital versatile disk (DVD) and a recordable compact disk (CD-R). The optical head assembly includes a first light source 1 for emitting a first light beam having a wavelength of 635nm for recording and reproducing information with respect to a digital versatile disk (DVD) 8, a second light source 11 for emitting a second light beam having a wavelength of 780nm for recording and reproducing information with respect to a recordable compact disk (CD-R) 9, and an objective lens 7 for focusing the first and second light beams emitted from the first and second light sources 1 and 11 on an information recording surface of the DVD 8 and that of the CD-R 9, respectively. The first light beam emitted from the first light source 1 is collimated in the form of a parallel beam by a first collimating lens 2 and then is transmitted to a first beam splitter 3. The first beam splitter 3 directs the first light beam incident from the first collimating lens 2 to an interference filtering prism 4, and transmits the first light beam returned from the interference filtering prism 4 to a first photodetector 10. In more detail, the first beam splitter 3 directs the first light beam which is P polarization beam incident from the first collimating lens 2 to the interference filtering prism 4, and transmits the first light beam which is S polarization beam incident from the interference filter prism 4 to the first photodetector 10. A variable aperture 6 having a thin film structure transmits the first light beam being a parallel light beam incident from a quarter-wave plate 5 to the objective lens 7. The objective lens 7 focuses the first light beam passed through the variable aperture 6 on an information recording surface of the DVD 8 having a thickness of 0.6mm. Therefore, the first light beam is focused on the information recording surface of the DVD 8 by the objective lens 7, and the focused first light beam reflected from the information recording surface of the DVD 8 contains the information to be recorded at a position on which the first light beam is focused. The reflected first light beam passes through the objective lens 7, the variable aperture 6, the quarter-wave plate 5, the interference filter prism 4 and the first beam splitter 3, in sequence, and then is received by the first photodetector 10. The first photodetector 10 detects information from the first light beam incident from the first beam splitter 3. The second light beam of the 780nm wavelength which is emitted from the second light source 11 passes through a second collimating lens 12 and a second beam splitter 13, and then is incident to a convergent lens 14. The convergent lens 14 converges the second light beam incident from the beam splitter 13 to then transmit the converged second light beam to the interference filter prism 4. The interference filter prism 4, which totally transmits or reflects incident light according to a wavelength, totally transmits the first light beam for the DVD having a wavelength of 635nm and totally reflects the second light beam having a wavelength of 780nm incident from the convergent lens 14. The interference filter prism 4 reflects the second light beam incident from the convergent lens 14 to the quarter-wave plate 5 in the form of a divergent beam. The quarter-wave plate 5 transmits the second light beam incident from the interference filter prism 4 to the variable aperture 6. The variable aperture 6 passes only part of the second light beam of the 780nm wavelength incident in the form of a divergent beam. The objective lens 7 focuses the second light beam incident from the variable aperture 6 on the information recording surface of the CD-R 9 having a thickness of 1.2mm. Thus, the second light beam is focused on the information recording surface of the CD-R 9 by the objective lens 7, and the second light beam reflected by the information recording surface contains information recorded at a position on which the second light beam is focused. The second beam splitter 13 of Figure 1 makes the second light beam incident from the convergent lens 14 proceed to a second photodetector 15. In more detail, the second beam splitter 13 totally transmits the second light beam incident from the second collimating lens 12 to the convergent lens 14, and totally reflects the second light beam incident from the convergent lens 14 to the second photodetector 15. The second photodetector 15 receives the second light beam from the second beam splitter 13 and detects information from the second light beam. Figure 2 shows in detail a variable aperture shown in Figure 1 having a thin film structure. The variable aperture having a thin film structure, as shown in Figure 2, can selectively transmit the rays of the light incident to the region not more than the numerical aperture (NA) of 0.6. Among two regions, a first region 1 has the numerical aperture (NA) of 0.45 or below and transmits both 780nm and 635nm wavelength lights. A second region 2 shown is made by coating a dielectric thin film and has the numerical aperture (NA) of 0.45 or more, and totally transmits the 635nm wavelength light and totally reflects the 780nm wavelength light. The region 1 is comprised of a quartz (SiO 2 ) thin film in order to remove any optical aberration generated by the dielectric thin film coated region 2. By using the variable aperture 6, the 780nm wavelength light passing through the region 1 having the 0.45 NA or below forms a beam spot appropriate to the CD-R on the signal recording surface thereof. The 635nm wavelength light transmitting the regions 1 and 2 having the 0.6 NA or below forms a beam spot appropriate to the DVD on the signal recording surface thereof. As shown, the optical head system of Figure 1 can perform recording and reproduction operation with respect to both DVD and CD-R. In the above optical head system, all optical systems for compatibility with the DVD and the CD-R are constructed as a single unit, and thus an actuator carrying the unit is imposed under more load. Accordingly, a data access time and a target sector seek time increase. With a view to solve or reduce the problems, an aim of embodiments of the present invention is to provide an optical head assembly reducing the load of an actuator by carrying only one of two optical units, which comprises an optical unit for recording and reproducing a digital versatile disk (DVD) and another optical unit for recording and reproducing a recordable compact disk (CD-R). Other prior Art document, such as US 5 555 539 or US 527 8813 have both optical units on the movable part. The following description of the invention concerns only GREAT BRITAIN which has not been validly designated by EP 0 831 466 disclosing the same subject-matter and being part of the prior Art according to Art. 543, EPC. For Germany, the invention concerns an optical head assembly according to claim 1 of the set of claims for Germany. According to a first aspect of the present invention, there is provided an optical head assembly for use in an optical disk driver using different wavelengths from each other for at least two optical disks, the optical head assembly comprising: a first optical unit mounted fixedly in the optical head assembly; and a second optical unit mounted movably with respect to an optical disk loaded in the disk driver, wherein the first optical unit emits a first light beam to the second optical unit and detects. information from the first light beam received from the second optical unit, and the second optical unit focuses the first light beam incident from the first optical unit on an information recording surface of the loaded optical disk and transmits the first light beam reflected from the optical disk to the first optical unit, and generates a second light beam, focuses the generated second light beam on an information recording surface of the loaded optical disk and detects information from the second light beam reflected from the optical disk the assembly being characterised in that said first optical unit further comprises a beam forming optical element for beam-forming the first light beam emitted from said first light source and transmitting the beam-formed first light beam to said polarizing beam splitter. Preferably, said first optical unit transmits the first light beam in the form of a parallel light beam to said second optical unit. Preferably, said first optical unit comprises: a first light source emitting the first light beam; a first photodetector for detecting information from the first light beam; first optical path alteration means for transmitting the first light beam emitted from said first light source toward said second optical unit, and transmitting the first light beam emitted from said second optical unit toward said first photodetector; and a collimating lens for collimating the first light beam emitted from said first optical path alteration means to a parallel light beam and transmitting the collimated light beam to said second optical unit. Preferably, said first optical path alteration means comprises: a polarizing beam splitter for transmitting the first light beam emitted from said first light source to the collimating lens, and transmitting the first light beam incident from the collimating lens to said first photodetector; and a phase plate positioned between said polarizing beam splitter and said collimating lens. Preferably, said second optical unit travels along the direction parallel to the first light beam emitted from said first optical unit. Said second optical unit preferably comprises: a second light source emitting the second light beam; a second photodetector for detecting information from the second light beam; an objective lens for focusing the first light beam transmitted from said first optical unit and the second light beam emitted from said second light source on the information recording surface of the loaded optical disk; and second optical path alteration means for transmitting the first light beam emitted from said first optical unit and the second light beam emitted from said second light source to said objective lens, the first light beam incident from said objective lens to said first optical unit, and the second light beam incident from said objective lens to said second photodetector respectively. Preferably, said second optical path alteration means comprises a beam splitter for transmitting the first light beam incident from said first optical unit and reflecting the second light beam emitted from said second light source. The assembly preferably further comprises a variable aperture, positioned between said second optical path alteration means and said objective lens, for defining the first light beam and the second light beam to different numerical apertures (NA). Preferably, said second optical path alteration means further comprise reflecting means, intermediate said beam splitter and said objective lens, to reflect the light beam so that the light beam emitted from said beam splitter proceeds to said objective lens. Said reflecting means preferably reflects incident laser light to an approximately right angle. The assembly is preferably arranged to record and pickup information from a DVD-RAM and a CD-R. For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example, to the accompanying diagrammatic drawings, in which: Figure 1 is a view illustrating a conventional optical head assembly for use in an optical disk driver for a digital versatile disk (DVD) and a recordable compact disk (CD-R) ; Figure 2 is a view explaining a variable aperture having a thin film structure used in a conventional optical head assembly; Figure 3 is a view showing a mechanical construction of an optical head assembly for use in an optical disk driver for a DVD and a CD-R according to an embodiment of the present invention; and Figure 4 is a view illustrating an optical head assembly for use in an optical disk driver for a DVD and a CD-R according to an embodiment of the present invention. Preferred embodiments of the present invention will be described below in more detail with reference to the accompanying drawings. Figure 3 is a view showing a mechanical construction of an optical head assembly for a DVD and a CD-R according to a preferred embodiment of the present invention. The optical head assembly shown in Figure 3 comprises a first stationary optical unit 200 and a second movable optical unit 300. The first optical unit 200 is fixedly mounted considering a location of the second movable optical unit 300 so that the second movable optical unit 300 can receive a first light beam for a DVD emitted from the first optical unit 200. The second optical unit 300 moves at a high speed on a guide rail which is installed along the diameter direction of an optical disk 8 or 9 loaded within an optical disk driver (not shown), and focuses the first and second light beams on the information surface of the optical disk. Figure 4 shows an optical system of an optical head assembly shown in Figure 3. The first optical unit 200 comprises a first light source 1 for emitting a first light beam having a wavelength of 635nm for the DVD, a beam forming prism 22 for transmitting the first beam to the second optical unit 300, a third beam splitter 23, a phase plate 24, a third collimating lens 25, a photodetection lens 26 for detecting information from the first light beam incident from the second optical unit 300, and a third photodetector 27. The first light source 1 emits the first light beam which is a linearly polarized beam having a wavelength of 635nm. For the convenience of description, the first light beam emitted from the first light source 1 defines a P polarization beam. The beam forming prism 22 performs beam-formation so that the first light beam incident from the first light source 1 has a desired beam section. The third beam splitter 23 and phase plate 24 direct the first light beam emitted from the beam forming prism 22 to the second optical unit 300, and makes the first light beam returned from the second optical unit 300 proceed to the third photodetector 27. In more detail, the third beam splitter 23, including a reflection surface 231 which totally reflects the first light beam which is changed into an S polarization beam by the phase plate 24 before being incident and totally transmits the first light beam which is a P polarization beam incident from the beam forming prism 22, splits the light beam to form another optical path according to a polarization state of the first light beam. The phase plate 24 changes the first light beam incident from the second optical unit 300 into an S polarization beam. The third collimating lens 25 collimates the first light beam incident from the phase plate 24 and transmits the collimated light beam to the second optical unit 300. The first light beam proceeding from the first optical unit 200 to the second optical unit 300 by such a third collimating lens 25 does not produce an optical aberration, even when there occurs a relative difference in distance between the first optical unit 200 and the second optical unit 300. The second optical unit 300 which is an optical unit for recording and reproducing the CD-R, comprises a light source and photodetector 31 in which a light source 31a and a photodetector 31b are integrated, a holographic beam splitter 32, a fourth beam splitter 33, a reflecting means such as a reflective prism or mirror 34, a holographic variable aperture 35 and an objective lens 36. The light source 31a generates a second light beam having a wavelength of 780nm for recording and reproduction of the CD-R, and the photodetector 31b detects information from the second light beam incident from the holographic beam splitter 32. The fourth beam splitter 33 transmits the first light beam incident from the first optical unit 200 to the reflective prism 34, directs the first light beam returned from the reflective prism 34 to the first optical unit 200, transmits the second light beam incident from the holographic beam splitter 32 to the reflective prism 34, and transmits the second light beam returned from the reflective prism 34 to the holographic beam splitter 32. The reflective prism 34 reflects the light beam incident from the fourth beam splitter 33 to the variable aperture 35 and the light beam incident from the variable aperture 35 transmits the fourth beam splitter 33. The variable aperture 35 transmits the first light beam of the 635nm wavelength incident from the reflective prism 34 to the objective lens 36, and transmits only part of the second light beam of the 780nm wavelength incident from the reflective prism 34 to the objective lens 36. Further specifically, the variable aperture 35 totally transmits the first light beam incident from the reflective prism 34 and passes the transmitted first light beam to the objective lens 36, and transmits only the second light beam incident to the region having the NA of 0.45 or below among the second light beam incident from the reflective prism 34 and passes the transmitted second light beam to the objective lens 36. The objective lens 36 focuses the first light beam incident from the variable aperture 35 on the information recording surface of the DVD 8 having a thickness of 0.6mm, and the second light beam incident from the variable aperture 35 on that of the CD-R 9 having a thickness of 1.2mm. Accordingly, when the DVD 8 is loaded on the optical disk driver, the first optical unit 200 performs photoemission and/or photo-detection operation with regard to the first light beam of the 635nm wavelength, and the second optical unit 300 focuses the first light beam at a desired location of the DVD 8, travelling on the guide rail 100. Meanwhile, when the CD-R 9 is loaded on the optical disk driver, the second optical unit 300 performs photoemission and/or photo-detection operation with regard to the CD-R 9 using the second light beam of the 780nm wavelength, travelling on the guide rail 100. The optical head assembly described above comprises separately a first optical unit 200 for recording an reproduction of a DVD and a second optical unit 300 for recording and reproduction of a CD-R. The movable second optical unit 300 performs recording and reproduction with respect to the loaded disk 8 or 9, travelling on a guide rail 100. Accordingly, the optical head assembly can reduce the load of an actuator, thereby providing an effect of a data access time and a target sector seek time.

Claims: Claim for the following Contracting State : DE An optical head assembly for use in an optical disk driver using different wavelengths from each other for at least two optical disks, the optical head assembly comprising: a first optical unit (200) mounted fixedly in the optical head assembly; and a second optical unit (300) mounted movably with respect to an optical disk (8, 9) loaded in the disk driver, wherein said first optical unit (200) emits a first light beam to said second optical unit (300) and detects information from the first light beam received from said second optical unit (300), and said second optical unit (300) focuses the first light beam incident from said first optical unit (200) on an information recording surface of the loaded optical disk (8, 9) and transmits the first light beam reflected from the optical disk (8, 9) to said first optical unit (200), and generates a second light beam, focuses the generated second light beam on an information recording surface of the loaded optical disk (8, 9) and detects information from the second light beam reflected from the optical disk (8, 9) the assembly being characterised in that said first optical unit (200) further comprises a beam forming optical element (22) for beam-forming the first light beam emitted from said first light source (1) and transmitting the beam-formed first light beam to said polarizing beam splitter (23). The optical head assembly according to claim 1, wherein said first optical unit (200) transmits the first light beam in the form of a parallel light beam to said second optical unit (300). The optical head assembly according to claim 1 or 2, wherein said first optical unit comprises: a first light source (1) emitting the first light beam; a first photodetector (27) for detecting information from the first light beam; first optical path alteration means (23) for transmitting the first light beam emitted from said first light source (1) toward said second optical unit (300), and transmitting the first light beam emitted from said second optical unit (300) toward said first photodetector (27); and a collimating lens (25) for collimating the first light beam emitted from said first optical path alteration means (23) to a parallel light beam and transmitting the collimated light beam to said second optical unit (300). The optical head assembly according to claim 3, wherein said first optical path alteration means (23) comprises: a polarizing beam splitter (23) for transmitting the first light beam emitted from said first light source (1) to the collimating lens (25), and transmitting the first light beam incident from the collimating lens (25) to said first photodetector (27); and a phase plate (24) positioned between said polarizing beam splitter (23) and said collimating lens (25). The optical head assembly according to any of the preceding claims, wherein said second optical unit (300) travels along the direction parallel to the first light beam emitted from said first optical unit (200). The optical head assembly according to any of the preceding claims, wherein said second optical unit (300) comprises: a second light source (31a) emitting the second light beam; a second photodetector (31b) for detecting information from the second light beam; an objective lens (36) for focusing the first light beam transmitted from said first optical unit (200) and the second light beam emitted from said second light source (300) on the information recording surface of the loaded optical disk (8, 9); and second optical path alteration means (33, 34) for transmitting the first light beam emitted from said first optical unit (200) and the second light beam emitted from said second light source (31a) to said objective lens (36), the first light beam incident from said objective lens (36) to said first optical unit (200), and the second light beam incident from said objective lens (36) to said second photodetector (31b) respectively. The optical head assembly according to claim 6, wherein said second optical path alteration means comprises a beam splitter (33) for transmitting the first light beam incident from said first optical unit (200) and reflecting the second light beam emitted from said second light source (31a). The optical head assembly according to claim 6, further comprising a variable aperture (35), positioned between said second optical path alteration means (33, 34) and said objective lens (36), for defining the first light beam and the second light beam to different numerical apertures (NA). The optical head assembly according to claim 7, wherein said second optical path alteration means further comprises reflecting means (34), intermediate said beam splitter (33) and said objective lens (36), to reflect the light beam so that the light beam emitted from said beam splitter (33) proceeds to said objective lens (36). The optical head assembly according to claim 9, wherein said reflecting means (34) reflects incident laser light to an approximately right angle. The optical head assembly according to claim 1 in which information is recorded on and picked up from a DVD-RAM and a CD-R. Claim for the following Contracting State : GB An optical head assembly for use in an optical disk driver using different wavelengths from each other for at least two optical disks, the optical head assembly comprising: a first optical unit (200) mounted fixedly in the optical head assembly; and a second optical unit (300) mounted movably with respect to an optical disk (8, 9) loaded in the disk driver, wherein said first optical unit (200) emits a first light beam to said second optical unit (300) and detects information from the first light beam received from said second optical unit (300), and said second optical unit (300) focuses the first light beam incident from said first optical unit (200) on an information recording surface of the loaded optical disk (8, 9) and transmits the first light beam reflected from the optical disk (8, 9) to said first optical unit (200), characterized in that said second optical unit generates a second light beam, focuses the generated second light beam on an information recording surface of the loaded optical disk (8, 9) and detects information from the second light beam reflected from the optical disk (8, 9). The optical head assembly according to claim 1, wherein said first optical unit (200) transmits the first light beam in the form of a parallel light beam to said second optical unit (300). The optical head assembly according to claim 1 or 2, wherein said first optical unit comprises: a first light source (1) emitting the first light beam; a first photodetector (27) for detecting information from the first light beam; first optical path alteration means (23) for transmitting the first light beam emitted from said first light source (1) toward said second optical unit (300), and transmitting the first light beam emitted from said second optical unit (300) toward said first photodetector (27); and a collimating lens (25) for collimating the first light beam emitted from said first optical path alteration means (23) to a parallel light beam and transmitting the collimated light beam to said second optical unit (300). The optical head assembly according to claim 3, wherein said first optical path alteration means (23) comprises: a polarizing beam splitter (23) for transmitting the first light beam emitted from said first light source (1) to the collimating lens (25), and transmitting the first light beam incident from the collimating lens (25) to said first photodetector (27); and a phase plate (24) positioned between said polarizing beam splitter (23) and said collimating lens (25). The optical head assembly according to any of the preceding claims, further comprising a beam forming optical element (22) for beam-forming the first light beam emitted from said first light source (1) and transmitting the beam-formed first light beam to said polarizing beam splitter (23). The optical head assembly according to any of the preceding claims, wherein said second optical unit (300) travels along the direction parallel to the first light beam emitted from said first optical unit (200). The optical head assembly according to any of the preceding claims, wherein said second optical unit (300) comprises: a second light source (31a) emitting the second light beam; a second photodetector (31b) for detecting information from the second light beam; an objective lens (36) for focusing the first light beam transmitted from said first optical unit (200) and the second light beam emitted from said second light source (300) on the information recording surface of the loaded optical disk (8, 9); and second optical path alteration means (33, 34) for transmitting the first light beam emitted from said first optical unit (200) and the second light beam emitted from said second light source (31a) to said objective lens (36), the first light beam incident from said objective lens (36) to said first optical unit (200), and the second light beam incident from said objective lens (36) to said second photodetector (31b) respectively. The optical head assembly according to claim 7, wherein said second optical path alteration means comprises a beam splitter (33) for transmitting the first light beam incident from said first optical unit (200) and reflecting the second light beam emitted from said second light source (31a). The optical head assembly according to claim 7, further comprising a variable aperture (35), positioned between said second optical path alteration means (33, 34) and said objective lens (36), for defining the first light beam and the second light beam to different numerical apertures (NA). The optical head assembly according to claim 8, wherein said second optical path alteration means further comprises reflecting means (34), intermediate said beam splitter (33) and said objective lens (36), to reflect the light beam so that the light beam emitted from said beam splitter (33) proceeds to said objective lens (36). The optical head assembly according to claim 10, wherein said reflecting means (34) reflects incident laser light to an approximately right angle. The optical head assembly according to claim 1 in which information is recorded on and picked up from a DVD-RAM and a CD-R.

Inventors: LEE CHUL-WOO, YOO JANG-HOON, LEE, CHUL-WOO, YOO, JANG-HOON
Applicants: SAMSUNG ELECTRONICS CO LTD, SAMSUNG ELECTRONICS CO., LTD.
Application year: 1998
Main classification: G11B7
IPC codes: G11B7