KR0154200B1 - A compatible recording and reproducing optical pick up for cd/dvd disc - Google Patents

Abstract

The present invention relates to an optical pickup device, in order to solve the problem that a conventional high-density disc and a conventional CD cannot be played simultaneously, the thickness of the conventional optical pickup device by providing a light amount control means for adjusting the amount of light incident to the type of disc Can play data on different discs at the same time.

Description

Optical pickup device capable of recording / playing back CD / DVD series discs

1 is a block diagram of a conventional optical pickup device.

2 is a beam power distribution diagram on disks having different thicknesses.

3 (a) and 3 (b) are structural diagrams of a CD and a DVD, respectively.

4 (a) and (b) are diagrams of focus positions of CDs and DVDs according to incident beam sizes.

5 is a block diagram of an optical pickup apparatus capable of recording / reproducing a CD / DVD series disc compatible according to the present invention.

6 (a) and 6 (b) are embodiments of the light amount adjusting means shown in FIG.

7 is an embodiment of the light quantity control driving means shown in FIG.

FIG. 8 is a signal flowchart by the disk discriminating means shown in FIG.

* Explanation of symbols for main parts of the drawings

1: laser diode 2: diffraction grating

3: beam separation prism 4: collimating lens

5: objective lens 6: optical disc

6a: Compact Disc (CD) 6b: Digital Video Disc (DVD)

7: sensor lens 8: photodetector

9: light quantity adjusting means 10: disc discriminating means

11: light quantity control driving means 12: gain switching means

The present invention relates to an optical pickup apparatus, and more particularly, to an optical pickup apparatus for recording / reproducing two or more kinds of discs.

The structure of a general compact disk (hereinafter referred to as a CD) is shown in FIG. 3 (a). Pit information is spaced at intervals of 1.6 탆 on a transparent plastic substrate (disk) having a thickness of 1.2 mm. The CD 6a is constructed by recording the data.

A conventional optical pickup apparatus for recording / reproducing information using a laser beam on a CD configured as described above includes a laser diode (1) for scanning a laser beam (Beam), and the laser diode as shown in FIG. The diffraction grating 2 which makes the laser beam scanned in (1) into a main beam and two sub beams (three beams) for tracking servo, and the beam through the diffraction grating 2 is parallel light. A collimating lens 4 made of a light source, an objective lens 5 for condensing parallel light through the collimating lens 4 on the optical disk 6, and the information recorded on the optical disk 6 A beam splitting prism 4 for transmitting or reflecting a beam reflected according to the presence / absence and the incident beam through the diffraction grating 2 at a predetermined ratio, and for collecting the beams reflected through the beam splitting prism 4 The sensor lens 7 and the data signal of the beams through the sensor lens 7 for detecting It consists of the photodetector 8.

The following description will be given with reference to FIGS. 1 and 3 (a) attached to an operation of recording / reproducing information on a CD using a conventional optical pickup apparatus configured as described above.

First, the beam emitted from the laser diode 1 is converted into parallel light by the collimating lens 4 and then collected through the objective lens 5 to be reflected or diffracted by the information recorded on the surface of the optical disc 6.

The reflected beam is returned to the same path, and a part of the beams in the beam separation prism 3 reach the photodetector 8 via the sensor lens 7 and are converted into electrical signals.

It is well known that the diffraction grating 2 and the sensor lens 7 are used for conventional tracking and focusing servos.

On the other hand, in recent years, a high-density digital video disk (hereinafter referred to as a DVD), which has a recording density four times higher than the above-described CD series (CD, CD-ROM, Video-CD, etc.), has been developed. Both the method of adopting the thickness of the substrate (disk) of 1.2 mm equal to that of the CD and the method of adopting the thickness of 0.6 mm thinner than this are being considered.

However, since the optical aberration caused by the disc tilt becomes larger as the disk thickness becomes thicker, in order to reduce the influence of the optical aberration and increase the recording density, the disc thickness of the DVD is adopted as 0.6 mm thinner than the CD. The way to do this is emerging.

In the DVD structure, as shown in FIG. 3 (b), Pit information is recorded at a track pitch of 0.725 μm (or 0.8 to 0.9 μm) on a 0.6 mm thick transparent plastic substrate (disc). The DVD 6b is comprised.

In this case, the double-sided adhesive is generally used to improve the memory capacity and the flatness of the disk.

However, the following problems have arisen when attempting to reproduce information using the conventional optical pickup apparatus shown in FIG.

As described above, since the recording density of the DVD is increased by four times or more than that of the CD, the DVD can be reproduced only by a lens having a high numerical aperture of about 0.6 as the numerical aperture (NA) of the objective lens 5.

Therefore, when the objective lens 5 designed optimally with a numerical aperture NA of 0.6 according to the DVD 6b having a disk thickness of 0.6 mm is used and the laser beam is focused on the DVD 6b, the power distribution of the reproduction beam is reduced. It is shown as a graph with solid lines at 2 degrees.

By the way, when the objective lens 5 in which the numerical aperture NA is 0.6 in accordance with the DVD 6b is used and the laser beam is focused on the CD 6a having a thickness of 1.2 mm, the DVD 6b and the CD are used. Due to the thickness difference (6a), a positive spherical aberration is generated in proportion to the quadratic power of the light beam beam mirror, so that the power distribution of the reproduction beam is shown by a dotted line in FIG.

That is, not only the intensity of the signal lobe for reproducing the main lobe is significantly reduced, but also the intensity of the noise lobe, the side lobe, is relatively increased, thereby causing crosstalk from signals recorded in adjacent tracks. The crosstalk value is calculated worse than -20-.

Further, when the objective lens 5 designed with the numerical aperture NA of 0.6 according to the DVD 6b is used to reproduce the CD 6a having a thickness of 1.2 mm, the sensitivity to the disc tilt is too large. There was another problem.

For this reason, the conventional optical pickup apparatus shown in FIG. 1 cannot reproduce both the CD 6a having a disc thickness of 1.2 mm and the DVD 6b having a disc thickness of 0.6 mm.

Accordingly, the present invention has been proposed to solve the above-mentioned problems of the prior art, and is compatible with both the CD and DVD series by varying the numerical aperture (NA) of the objective lens according to the type of the CD and DVD discs. An object of the present invention is to provide an optical pickup apparatus capable of playing / reproducing.

The technical means of the present invention for achieving the above object is an optical pickup apparatus for recording / reproducing CD series and DVD series in a compatible manner, comprising: a light source for outputting a light beam for recording / reproducing one of two disks, and An optical system for forming an optical path of the light beam from the light source, an objective lens for condensing the light beam on the disk, numerical aperture adjusting means for varying the numerical aperture of the objective lens to record / reproduce the optical beam of the optical system in accordance with the standard of the disk; It consists of a control unit for controlling the numerical aperture adjusting means, the numerical aperture adjusting means is characterized in that the aperture means.

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

5 is a block diagram of an optical pickup apparatus capable of recording / reproducing CD / DVD-based discs according to the present invention, wherein the beam scanned by the laser diode 1 is diffracted through the diffraction grating 2 and then parallel light Collimating lens (4) made of light, an objective lens (5) for condensing parallel light through the collimating lens (4) on an optical disk (6)-CD (6a) or DVD (6b)-and the optical disk (6) A beam splitting prism 3 for transmitting or reflecting a reflected beam through the objective lens 5 and the collimating lens 4, and an incident beam through the beam splitting prism 3 through the sensor lens 7. Light amount control for shielding the light so as to accurately focus the light generated by the photodetector 8 and the laser diode 1 onto the optical disk 6 to form different CD reading beams or DVD reading beams. Means 9 and the focused beam are read by the photodetector 8 to A disk discriminating means 10 for discriminating the type of the disk 6 and a light quantity adjusting driving means 11 for driving the light quantity adjusting means 9 in accordance with the discrimination result by the disk discriminating means 10. have.

In the drawing, reference numeral 5a denotes an actuator for driving the objective lens 5 in the focus and track directions, and 12 denotes an electrical amplification of the loss of the amount of light reaching the optical disk 6 and the gain at this time. The selection is a gain switching means that is simply configured by the control line of the microcomputer and appropriately adjusts the gain of servo and high frequency signal processing (see FIG. 8).

The light quantity adjusting means 9 is implemented by a well-known circular aperture widely used in a camera or the like as shown in FIG. 6 (a), or as shown in FIG. It is implemented as a slide-in-out aperture consisting of two panels each having openings of different inner diameters for adjustment.

In the case of implementing the light amount adjusting means 9 with the circular aperture, the lens holder of the actuator 5a shown in FIG. 5 or not shown is installed in a fixed part (for example, an optical pickup body) to simplify the structure. And the light quantity adjusting means 9 interlocks with the objective lens 5.

The light quantity control driving means 11 can be implemented in a simple configuration requiring only two-valued driving such as a solenoid because only two different sizes of aperture opening diameters of the light quantity adjusting means 9 are used.

For example, as illustrated in FIG. 7, a gear train 14 constitutes a mechanism capable of driving the light quantity adjusting means 9 left and right, and the motor 13 is a gear train 14. Drive the light quantity adjusting means 9 is attached to an appropriate position of the optical pickup body (15).

The operation and effect of the optical pickup apparatus according to the present invention configured as described above will be described with reference to FIGS. 3 (b) to 8.

4 is a state diagram of focus positions on each disc for explaining the basic principle that the optical pickup apparatus of the present invention is compatible with both the CD 6a series and the DVD 6b series.

Spherical aberration is the criterion for performance evaluation in the optical pickup device. When the spherical aberration exceeds 0.07λ (λ is the laser wavelength), it is impossible to collect light due to the small spot due to the diffraction limit. I can't show it.

The present invention derives from the fact that such spherical aberration is proportional to the square of the beam beam mirror, so that the numerical aperture (NA) of the objective lens (5) is optimally designed in accordance with the DVD (6b). In the case of recording / reproducing a disc, the basic principle is that the amount of spherical aberration is significantly reduced if only the beam in the center region is used after shielding the outer diameter (edge) of a certain beam line without affecting the power of the reproduction beam.

First, when the numerical aperture NA of the objective lens 5 is designed to be 0.6 based on the DVD 6b having a thickness of 0.6 mm, the collimating lens 4 is used as shown in FIG. The laser beam converted into parallel light is condensed normally on the DVD 6b via the objective lens 5.

On the other hand, at the time of recording / reproducing of the CD 6a having a disc thickness of 1.2 mm, the effective numerical aperture NA of the objective lens 5 is adjusted by adjusting the diameter (beam beam diameter) of parallel light incident on the objective lens 5. Will be adjusted.

At this time, the relational expression is "a numerical aperture (NA) = SIN (theta) \ r", where (theta) is the angle which a focused light makes, and r is the radius of incident light. That is, the smaller the diameter of the incident light, the smaller the effective numerical aperture NA value.

Accordingly, when the numerical aperture NA of the objective lens 5 is reduced to 0.3 at the time of recording / reproducing of the CD 6a, the aberration is reduced while the power of the reproduction beam is not impaired. This is because spherical aberration satisfies the condition of 0.04λ (λ is a laser wavelength) in consideration of other margins when the numerical aperture NA is 0.3 to 0.4 as a result of the repetitive previous experiment.

Furthermore, when the CD 6a having a track pitch of 1.6 μm and a disc thickness of 1.2 mm is reproduced using an objective lens 5 having a numerical aperture NA of 0.3 with a laser having a wavelength λ of 635 nm, crosstalk is achieved. You can calculate that the level appears below -35㏈.

Accordingly, even if the optical pickup apparatus is designed in accordance with the DVD 6b having a disc thickness of 0.6 mm, the CD 6a can be adjusted by appropriately adjusting the beam beam diameter of the incident parallel light as described above during recording / reproducing of the CD 6a. Since recording / playback can be performed, compatibility with both the CD 6a series and the DVD 6b series is achieved.

Next, the overall operation of the optical pickup apparatus according to the present invention applying the above-described basic principles will be described.

First, the laser beam scanned by the laser diode 1 is diffracted and transmitted through the diffraction grating 2 and the beam splitting prism 3 to produce parallel light with the collimation lens 4.

Then, the parallel light incident through the collimating lens 4 is incident on an optical disk 6, that is, an unknown disk among the CD 6a and the DVD 6b, and the reflected beam is reflected through the beam separation prism 3. In other words, the sensor lens 7 condenses the reflected beam to the photodetector 8.

Accordingly, the photodetector 8 converts the optical information signal corresponding to the optical disk 6 into an electrical signal and outputs the electrical signal, and the disk discriminating means 10 converts the electrical signal (or the turn table) converted by the photodetector 8 into one. The type of the optical disk 6 is determined from the sensor attached to the unit, i.e., the CD 6a or the DVD 6b.

At this time, the disc discrimination means 10 calculates the track crossing signal frequency difference of the tracking error signal according to the embodiment to discriminate whether the type of the optical disc 6 is a CD 6a or a DVD 6b.

In this way, the disc type is determined by the disc discriminating means 10, and then the light quantity adjusting means 9 provided between the collimation lens 4 and the objective lens 5 is adjusted by the light quantity adjusting driving means 11, It has an opening diameter corresponding to the disk.

That is, the numerical aperture NA of the objective lens 5 is maintained at 0.6 in the case of the DVD 6b, and the numerical aperture NA of the objective lens 5 is adjusted to 0.3 at the CD 6a.

At this time, when the CD 6a is played back when the numerical aperture NA is 0.3, the amount of light reaching the disc is smaller than that when the numerical aperture NA is 0.6, and the numerical aperture NA of the collimating lens 4 is 0.17. At the same time, when the divergent light angle of the laser diode 1 is a general value, only 31% of the light reaches the disc in the case of CD 6a reproduction than in the case of DVD 6b.

The loss due to the unreasoning of the amount of light is electrically amplified by the gain switching means 12, and the gain selection at this time can be simply configured by the control line of the microcomputer to appropriately adjust the gain of the servo and the high frequency signal processing.

8 is a configuration in which a control signal is sent to the light amount control driving means 11 and the gain switching means 12 by using the block and the microcomputer of the disc discrimination means 10, and a high frequency (RF) used for the CD 6a series. The focus OK signal (signal indicating that the actuator operates normally after the disc is determined and the focus servo is on), the tracking error signal (TE signal), the level check signal, and the tracking error traversal Signal (TE signal indicating the track servo-off time) is used in the disc discrimination means 10.

Therefore, when the focus is turned on by operating in the DVD (6b) mode, the tracking error signal (the lens aberration is large because the lens aberration is large when the level is small and the disk thickness is large) and the frequency of the tracking error crossing signal is low. When it is detected (because of low density), the gain is converted to the CD 6a mode using the control line of the microcomputer and the light amount adjusting means 9 is adjusted by driving the motor 13 which is the light amount adjusting drive means 11 at the same time. It is.

As described above, the present invention can record and play both a CD series having a disc thickness of 1.2 mm and a DVD series having a disc thickness of 0.6 mm by a simple method of changing the aperture, and when reproducing a DVD series, other optical components (diffraction in hologram) Since there is no need to use an element or beam splitter) or an additional device, it is possible to use 100% of the light output from the laser diode and to maintain a high noise ratio during DVD series playback.

Claims (2)

An optical pickup apparatus for recording / reproducing a compact disc (CD) series and a digital video screen (DVD) series in a compatible manner, comprising: a light source for outputting a light beam for recording / reproducing any one of the CD and the DVD; An optical system for forming an optical path of a light beam, an objective lens for condensing the light beam on an unknown disk among the CD and DVD, and an optical lens for recording / reproducing the optical beam in accordance with the unknown disc standard. A CD / DVD-based disc compatible recording / playback apparatus comprising a numerical aperture adjusting means for varying the numerical aperture and a controller for controlling the numerical aperture adjusting means. The optical pickup apparatus of claim 1, wherein the numerical aperture adjusting means is an aperture means.