KR19990031138A - Multi-wavelength optical pickup device - Google Patents

Abstract

The present invention relates to a multi-wavelength optical pickup device, wherein the laser diode 30 can emit a multi-wavelength beam so that the wavelength, light output, etc. can be selected according to the type of disk used as the light source, and for each wavelength With a different light emitting point, the biaxial actuator 8 moves the objective lens 6 in the axial direction of the disk 7 to position the beam focused from the objective lens 6 in the center of the recording surface track of the disk 7. And the light detector 40 changes the combination of cells used to detect a required signal according to the position of the light emitting point of the beam reflected from the disk 7 and transmitted through the beam splitter 4. It is composed of a plurality of cells so as to convert the beam transmitted through the beam splitter 4 into an electrical signal.

According to the multi-wavelength optical pickup apparatus of the present invention, the structure of the optical pickup that requires several wavelengths can be simplified to reduce the number of parts, to facilitate the manufacture, and to increase the compatibility with other types of disks.

Description

Multi-wavelength optical pickup device

The present invention relates to a multi-wavelength optical pickup apparatus, and more particularly, to an optical pickup apparatus capable of selecting a wavelength of a light source according to the type of an optical disk when recording / reproducing an optical disk so that various types of optical disks can be used interchangeably. will be.

As is well known, optical disc devices include LDP (Laser Disc Player), which was commercialized in 1978, and the most popular compact disc player (CDP), CD-ROM, and magneto-optic disc drive. , Digital Versatile Disc Player (DVDP), DVD-ROM, and the most recent DVD-RAM.

1 is a view showing the structure of an optical system and a light receiving cell of a conventional optical pickup device, as shown in the laser diode (1) (laser diode) in which the wavelength, light output, etc. are selected according to the type of disk used as a light source And a grating for dividing the beam emitted from the laser diode 1 into a number so as to use a three beam as a means for detecting a tracking error signal, and a laser diode ( A beam splitter 4 and a laser diode 1 which partially reflect the beam emitted from 1) toward the disk 7 and transmit a portion of the beam reflected from the disk 7 and incident again. A collimator lens 5 for converting the beam emitted from the light into parallel light, an objective lens 6 for focusing the beam on the recording / reproducing layer of the disk 7, and a recording surface track of the disk 7. With objective lens (6) in the center Biaxial actuator 8 for moving the objective lens 6 in the axial and radial directions of the disk 7 to position the focused beam, and light for converting the beam reflected from the disk 7 into an electrical signal It consists of a detector (photodetector). The grating 2 is not used when a tracking error signal detecting means other than the three beam method is used, and the beam splitter 4 uses a cube shape depending on the configuration of the optical pickup, so there is a difference in transmission / reflectance. .

The collimator lens 5 may not be used depending on the purpose of the optical pickup, and the objective lens 6 has a different NA (numerical aperture) depending on the type of disk. Also, the photodetector 3 differs in structure and size of the cell according to the data signal detection method of the disc and the focus / tracking error signal detection method. In FIG. 1, when a current sum (A + B + C + D) generated in a cell is used to detect a data signal recorded on a disk, and astigmatism is used to detect a focus error signal, the difference in the diagonal direction sum [( When A + C)-(B + D)] is used as the focus error signal and the 3-beam method is used for the detection of the tracking error signal, (E-F) is used as the tracking error signal.

The various types of optical disc devices described above were in the form of recording / reproducing only one type of disc. However, with the demand for large capacity and high speed optical disk devices, the emergence of new optical disks has increased the demand for recording / reproducing various types of optical disks in one optical disk device. In particular, the DVD, which was developed to meet the demand of a large capacity among the new optical discs, is a high density optical disc having a recording capacity of 7 times that of a conventional CD, and in order to increase the density of the optical disc, the focus beam size of the optical pickup apparatus is used. For this purpose, the wavelength of the light source should be shortened and the NA of the objective lens should be increased for this purpose, but if the NA of the objective lens is increased, the tolerance of the optical pickup device will be worsened. Since the thickness needs to be made thinner, the substrate thickness of the CD is 1.2 mm, whereas the DVD uses a 0.6 mm disc whose substrate thickness is 1/2 of the CD. As such, the compatibility of existing optical discs such as CDs in DVD devices has become a big challenge.

To maintain this compatibility, one must first consider the wavelength of the light source and the NA of the objective lens, i.e., the DVD has a 650 nm wavelength compared to the CD with an 780 nm wavelength light source and an NA 0.45 objective lens. It is necessary to take into account the use of a light source with an objective lens of NA 0.6. Second, when using optical disks with different physical constants of the disk, signal detection problems caused by different wavelengths of the light source as compatibility factors. The problem of spherical aberration compensation due to the difference of

For example, in the case of a general reproducible CD disc, in the case of a signal detection problem in which the wavelength of the light source is different, since the depth of the pit used for recording data is produced at about 1/6 of the wavelength used, the optical disc for DVD is used. Even when the 650 nm wavelength of the pickup apparatus is used, the CD disk can be reproduced because the peak depth of the CD disk is about 1/5 of the wavelength. However, when the NA of the objective lens is 0.6, the tolerance of the substrate thickness of the disc is only about 30-40 μm, so that the spherical aberration caused by the difference in substrate thickness is required for the DVD optical disc device to reproduce the CD disc. ), A DVD optical disk device uses a hologram lens, a twin lens method, an LCD shutter method, and the like, thereby maintaining compatibility with the CD. .

On the other hand, in the case of a CD-R disc, which has recently been expanded in use, unlike a disc for exclusive use of reproduction, data is detected by the difference in reflectance between pits and lands. Most CD-R discs are manufactured for a wavelength of 780 nm. When a light source having a wavelength of 630-650 nm is used, the reflectance decreases due to an increase in the absorptivity of the disc recording material, thereby making it difficult to reproduce the disc. Accordingly, in order for the DVD optical disc device to be compatible with the CD-R disc, a light source having a separate 780 nm wavelength for reproducing the CD-R disc or the high density optical disc is required in addition to the light source having the 650 nm wavelength. ) And a CD-R disc were reproduced with an optical pickup device developed by mounting the optical system 20 for DVD.

In addition, in the case of a high-density optical disk device using a 400 nm light source under development, the wavelength of the CD disk corresponds to about half of the wavelength of the CD disk, so the pit depth of the CD disk corresponds to about 1/2 of the wavelength used. Since this is impossible, for this purpose, as shown in FIG. 3, it is necessary to reproduce a high density optical disc with an optical pickup apparatus developed to use two light sources of 400 nm and 650 nm or 780 nm wavelengths via the beam splitter 9.

However, the optical pickup device as shown in FIGS. 2 and 3 has a problem in that the number of parts increases and the total volume increases, the assembly process is complicated, and the price is increased.

Accordingly, the present invention has been made in view of the above-mentioned problems and necessities, and an object thereof is to provide a wavelength for reproducing different types of optical discs, thereby increasing compatibility with other types of discs. It is to provide an optical pickup device.

The multi-wavelength optical pickup device of the present invention for achieving the above object can emit a multi-wavelength beam, so that the wavelength, light output, etc. can be selected according to the type of disk used as a light source, and different light emission for each wavelength A laser diode having a dot, a grating for dividing the beam emitted from the laser diode into several parts so as to use a three-beam method as a means for detecting a tracking error signal, and partially reflecting the beam emitted from the laser diode in a disc direction A beam splitter for transmitting a part of the beam reflected from the disk and incident again, a collimator lens for converting the beam emitted from the laser diode into parallel light, and a beam emitted from the laser diode for recording / recording of the disk. An objective lens focused on a reproduction layer, and a recording surface track of the disc A biaxial actuator for moving the objective lens in the axial and radial directions of the disk to position the beam focused from the objective lens at the center, and the position of the light emitting point of the beam reflected from the disk and transmitted through the beam splitter It consists of a plurality of cells to change the combination of cells used to detect the required signal according to the, characterized in that consisting of a photodetector for converting the transmitted beam into an electrical signal.

According to the multi-wavelength optical pickup device of the present invention, the wavelength can be selected according to the disk used, and the NA of the objective lens can be converted according to the selected wavelength, thereby improving the compatibility of the optical disk device.

1 is a view showing a cell structure of an optical system and a photodetector of a conventional optical pickup device,

2 is a view showing a conventional optical pickup apparatus using the optical system for a CD and the optical system for a DVD so as to be compatible with a CD-R disc.

3 is a view showing a conventional optical pickup device using two light sources for the same purpose as FIG.

4 is a view showing the tilt of the optical axis of the optical pickup device generated when there are a plurality of light emitting points in the light source,

FIG. 5 is a view showing an optical pickup apparatus using independent light receiving cells for each wavelength by using two wavelengths according to an embodiment of the present invention.

FIG. 6 is a diagram illustrating an optical pickup apparatus using two wavelengths according to another embodiment of the present invention, and commonly using a part of a cell adjacent to a light receiving cell structure for each wavelength.

FIG. 7 is a diagram illustrating an optical pickup apparatus using three wavelengths according to another embodiment of the present invention, and commonly using a part of a cell adjacent to a light receiving cell structure for each wavelength.

8 illustrates a case where a plurality of light emitting points exist in an optical pickup apparatus using a finite optical system according to another embodiment of the present invention. FIG. 8A illustrates a case where a light emitting point without tilting is used. 8B illustrates an optical axis tilt generated when using a light emitting point different from that of FIG. 8A, and FIG. 8C illustrates a case where the optical axis tilt generated by using a light emitting point different from that of FIG. 8A is canceled.

<Description of Symbols for Major Parts of Drawings>

One ; Laser diode 2; Grating

3; Photodetector 4; Beam splitter

5; Collimator lens 6; objective

7; Optical disk 8; 2-axis actuator

10; CD optical system 20; DVD optical system

30; Laser diode 40; Photodetector

The above and other objects and various advantages of the present invention will become more apparent to those skilled in the art from the preferred embodiments of the invention described below with reference to the accompanying drawings. In the drawings, the same reference numerals are given to the same components as in the related art.

FIG. 5 illustrates an optical pickup device using independent light-receiving cells for each wavelength using two wavelengths according to an embodiment of the present invention, which uses astigmatism for detecting a focus error signal and detects a tracking error signal. The 3-beam method was used for this purpose.

The laser diode 30 as a light source of the multi-wavelength optical pickup apparatus shown in FIG. 5 can selectively emit λ1 and λ2 wavelengths depending on the type of disk used, and for each wavelength. It has a different light emitting point.

On the other hand, the photodetector 40 selects (ON) λ 1 by using a selection switch (not shown) of the laser diode 30 as a light source and turns it on to use a wavelength of λ 1, where A, B, C, D, E, When a signal is detected using the F light receiving cell, and λ2 is selected and turned on to use a wavelength of λ2, the signal is detected using the light receiving cells A ', B', C'D ', E, F. That is, when λ1 is used, (A + B + C + D) is used to detect the data signal recorded on the disc 7, and [(A + C)-(B) to detect the focus error signal. + D)] signal, and the (E-F) signal to detect the tracking error signal. In addition, when λ2 is used, (A '+ B' + C '+ D') is used to detect the data signal recorded on the disc, and [(A '+ C')-( B '+ D')] and (E-F) to detect the tracking error signal. At this time, the objective lens 6 can use both wavelengths λ1 and λ2, or select the objective lens 6 by using a device capable of converting the NA of the objective lens as in a DVD. As a result, an appropriate wavelength is selected among the two wavelengths to increase disk compatibility of the optical disk device.

In the optical pickup apparatus, in order to secure the performance of the optical pickup, the aberration of the optical system of the optical pickup should be reduced, and in particular, off-axis aberration, especially coma aberration, generated during the assembly of the optical pickup. In order to reduce), the coma aberration caused by the tilt of the optical axis of the optical pickup and the tilt of the objective lens should be minimized.For this purpose, the coma aberration by the optical axis tilt was compensated by adjusting the tilt of the objective lens in the manufacturing process of the optical pickup. As shown in FIG. 4, when the light emitting point for λ 1 and the light emitting point for λ 2 are different from each other in the light source, since two optical axes exist, it is difficult to compensate for coma aberration for the two optical axes. It is necessary to minimize this.

FIG. 6 illustrates an optical pickup apparatus using two wavelengths according to another embodiment of the present invention, and commonly using a part of a cell adjacent to a light receiving cell structure for each wavelength. As shown in FIG. 5 is identical to FIG. 5 except that 40 uses two cells in common.

In the case of using the lambda 1 wavelength of the two wavelengths, the data signals recorded on the disk 7 are converted into (A + B + C + D) using the A, B, C, D, E, and F cells of the photodetector 40. ), The focus error signal and the tracking error signal are detected from [(A + C)-(B + D)] and (E-F), respectively. In the case of using the λ2 wavelength, data signals, focus error signals, and tracking error signals recorded on the disc 7 using A ', B', C, D, E, and F cells of the photodetector 40 are (A '+ B' + C + D), [(A '+ C)-(B' + D)], and (E-F) respectively.

As such, when two cells are commonly used for two light emitting points, the distance between the two light emitting points can be reduced, thereby reducing the angle between the two optical axes.

On the other hand, as mentioned with reference to Figure 4, the coma aberration caused by the tilt, disk tilt, optical axis tilt of the objective lens greatly degrades the performance of the optical pickup device, in particular, the tilt direction is the scanning direction of the disk This further degrades the performance than when the tilt direction is radial. When the tilt is generated, the beam size increases in the direction in which the tilt is generated. Since the distance between the marks is usually shorter than the track pitch, the tilt in the scanning direction further increases the inter-signal interference. Due to this fact, as in the case of FIG. 6, when two light emitting points are provided in the light source to use two wavelengths, it is the signal of the optical axis tilt that the alignment direction of the two light emitting points is radial when viewed from a disk. Can be minimized.

In addition, when three wavelengths are required, as another embodiment of the present invention, as shown in FIG. 7, a part of a cell adjacent to the light receiving cell structure for each wavelength is commonly used. In Fig. 7, the laser diode 30 is provided with three light emitting points as a light source.

Of the three wavelengths, the A, B, C, D, E, and F cells of the photodetector 40 are used, and when the wavelength of λ 2 is used, A ', In the case of using cells B ', C, D, E, and F, and then using a wavelength of λ 3, cells A, B, C', D ', E, and F of the photodetector 40 are used. As described above, the signal recorded on the disk, the focus error signal, and the tracking error signal are detected. At this time, the objective lens 6 may use all of the wavelengths λ1, λ2, and λ3, or select the objective lens 6 using a device capable of converting the NA between the objective lenses as in DVD. By selecting an appropriate wavelength among three wavelengths according to the type of the optical disk apparatus capable of recording / reproducing multi-wavelengths.

8 is for explaining the prevention of the tilt generation of the optical axis when there are a plurality of light emitting points in the optical pickup device using a finite optical system according to another embodiment of the present invention, Figure 8a is a light emission without tilting 8B shows an optical axis tilt generated when using other light emitting points separated by Δ, and FIG. 8C shows an offset of the optical axis tilt generated by using other light emitting points separated by 8A and Δ. The case is shown. In the case of a finite optical system in which the optical pickup apparatus does not use the collimator lens 5, when the light emitting point in which the tilt adjustment of the objective lens 6 is adjusted in the several optical axes is used as shown in FIG. 8A, the tilt of the objective lens is shown. Using a light emitting point that has not been adjusted, it is shown as in Fig. 8B. Thus, in order to offset this, offset is made to the biaxial actuator 8 which moves the objective lens 6 in the vertical and radial directions of the disk 7 so that the beam collected from the objective lens 6 is located at the track center of the recording surface. When the biaxial actuator 8 is viewed from the disc 7 by applying a voltage, the center of the objective lens 6 is moved in the radial direction by the distance between the two emitting points, with the light emitting points aligned in the radial direction. This prevents the generation of the optical axis tilt due to the positional movement of the light emitting point.

The embodiments disclosed above are merely illustrative and have been described with two or three wavelengths as examples, but the present invention is not limited to these wavelengths, and all modifications having equivalent meanings to the claims are also described. Will be included in the category of.

As described above, the multi-wavelength optical pick-up apparatus of the present invention has an effect of simplifying the structure of the optical pickup requiring multiple wavelengths, reducing the number of parts, and facilitating manufacturing, while increasing compatibility with other types of disks. Has

Claims (4)

In the multi-wavelength optical pickup device, A laser diode 30 capable of emitting a multi-wavelength beam so as to select a wavelength, light output, etc. according to the type of disk used as a light source, and having a different light emitting point for each wavelength; A grating 2 for dividing the beam emitted from the laser diode 30 into a number so as to use a three-beam method as a means for detecting a tracking error signal, A beam splitter 4 for partially reflecting the beam emitted from the laser diode 30 in the direction of the disc 7 and transmitting a part of the beam reflected from the disc 7 and incident again; A collimator lens 5 for converting the beam emitted from the laser diode 30 into parallel light; An objective lens 6 for focusing the beam emitted from the laser diode 30 on the recording / reproducing layer of the disc 7; Biaxial actuator 8 for moving the objective lens 6 in the axial and radial directions of the disk 7 to position the beam condensed from the objective lens 6 in the center of the recording surface track of the disk 7. Wow, It is composed of a plurality of cells so that the combination of cells used to detect a required signal according to the position of the light emitting point of the beam reflected from the disk 7 and transmitted through the beam splitter 4 can be changed. Multi-wavelength optical pickup device, characterized in that consisting of a photodetector 40 for converting the beam into an electrical signal. The method of claim 1, When using a light emitting point in which an optical axis tilt is generated due to a position difference between light emitting points, a part of the cells of the photodetector 40 is commonly used when using adjacent light emitting points to determine a distance between cells corresponding to each light emitting point. Multi-wavelength optical pickup device, characterized in that to minimize the tilt angle to minimize the occurrence of axle. The method of claim 1, Multi-wavelength optical pickup device, characterized in that the emitting point is aligned in the radial direction when viewed from the disk (7). The method of claim 3, wherein In the case of a finite optical system that does not use the collimator lens 5, the objective lens 6 is applied by applying an offset voltage to the radial direction of the biaxial actuator 8 in a direction to cancel the optical axis tilt by the position difference of the light emitter. Multi-wavelength optical pickup device, characterized in that for moving the center of the radial direction.