KR100556692B1 - Reproductive Apparatus For Optical Disc - Google Patents

Abstract

The present invention relates to an information reproducing apparatus adapted for reproducing a high density optical recording medium.

The optical disc reproducing apparatus of the present invention includes a condensing optical system for irradiating at least two light beams so that a part of each beam is irradiated to a target track of the optical disc, and two for detecting two-split reflected light in the track direction corresponding to the two light beams reflected from the optical disc. And a means for detecting a reproduction signal based on the split reflection light corresponding to the target track in the two light detection units.

With this arrangement, the optical disc reproducing apparatus according to the present invention can reproduce the information recorded on the high density optical disc using only a part of the optical spot in reproducing the information.

Description

Optical Disc Playback Device {Reproductive Apparatus For Optical Disc}

The present invention relates to an apparatus for reproducing an optical recording medium, and more particularly to an information reproducing apparatus suitable for reproducing an optical recording medium of high density.

CDs are already common in optical recording media, and recently, DVD-RAMs having data of up to 4.7 GB are being developed. Generally, in the optical recording medium, as shown in FIG. 1, pits 12 are formed along a track running from the inner circumference to the outer circumference in a spiral or concentric manner. The reproduction of the information is done by detecting the amount of light reflected by irradiating a light beam onto the pits 12 in the form of a light spot 14. Here, the reflected light reflected from the mirror area where the pit 12 is not formed is detected as "light", while the reflected light reflected from the pit 12 is detected as "dark". That is, the light beam irradiated to the mirror area is almost totally reflected and the reflected light amount is large, while the light beam irradiated to the pit 12 is diffusely reflected to reduce the reflectance. The reflected light beam detected by light and dark is converted into an electrical signal by a photodetector and reproduced.

Recently, studies on the high density of optical recording media have been actively conducted to accommodate a large amount of information. As the optical recording medium becomes higher, the pit size is reduced and the track pitch TP, which is a track interval, is narrow. In addition, although the light spot 14 should be made smaller in correspondence with the high density structure, the size of the light spot 14 is so-called "diffraction limit value" proportional to λ / NA depending on the wavelength λ of the light source and the numerical aperture NA of the objective lens. It cannot be made smaller than. Accordingly, in the reproducing apparatus of the optical recording medium, in order to shorten the oscillation wavelength? Generated by the light source, a short wavelength light source such as a blue laser and a method of increasing the numerical aperture NA of the objective lens have been attempted. It is true that it is difficult to realize a light spot below the diffraction limit because there is a limit to the high aperture of the lens and the objective lens.

Accordingly, when the track pitch TP is narrowed, the light spot 14 becomes relatively large, so that not only the track desired by the light (hereinafter referred to as the "target track") but also the peripheral track adjacent to the target track (hereinafter referred to as "adjacent track"). Is also investigated. The light irradiated from the adjacent tracks appears as a noise component with respect to the reproduction signal reproduced by the light irradiated to the target track. Crosstalk, which appears as described above, is emerging as a problem of inhibiting densification in the three-beam reproducing method as well as the one-beam reproducing method.

It is therefore an object of the present invention to provide an optical disc reproducing apparatus which can increase the recording density.

In order to achieve the above object, the optical disc reproducing apparatus of the present invention comprises a condensing optical system for irradiating at least two light beams so that a part of each beam is irradiated to a target track of the optical disc, and a track direction corresponding to the two light beams reflected from the optical disc. And a light receiving optical system including two photodetectors for detecting two-split reflected light, and means for detecting a reproduced signal based on the split reflected light corresponding to the target track in the two photodetectors.

The optical disc reproducing apparatus of the present invention detects two-split reflected light in the track direction corresponding to two light beams reflected from the optical disc, and a condensing optical system that irradiates at least two light beams to irradiate a portion of each beam to adjacent tracks of the optical disc. And a means for detecting a tracking error signal based on the split optical light corresponding to the adjacent tracks in the two photodetectors.

The optical disc reproducing apparatus of the present invention includes at least two light beams so that each beam is irradiated simultaneously to the first light beam overlapping the target track and the first adjacent track of the optical disc, and the second light beams overlapping the target track and the second adjacent track. A light-receiving optical system including a condensing optical system for irradiating the light, a two-light detecting unit for detecting two-split reflected light in the track direction in response to the two light beams reflected from the optical disk, and a split reflected light corresponding to the target track in the two light detecting units. Signal detection means for detecting a reproduction signal on the basis of the detection signal and detecting the reproduction signal based on the split reflection light corresponding to the adjacent tracks.

Other objects and features of the present invention in addition to the above objects will become apparent from the description of the embodiments with reference to the accompanying drawings.

Hereinafter, exemplary embodiments of the present invention will be described with reference to FIGS. 2 to 5.

Referring to FIG. 2, each of the optical recording media 20 in which the pits 22 are formed along the tracks n-1, n, n + 1 running spirally or concentrically from the inner circumference to the outer circumference is formed. First and second light spots 24 and 25 are shown in which only 1/2 is irradiated to the target track. In the case of reproducing the information recorded in the nth track n, the first light spot 24 is irradiated to the nth track n, 1/2 of which is the destination track, and the other half is adjacent to the outer circumference side from the destination track. The n + 1th track n + 1 is irradiated. The second light spot 25 passes through the same point after a predetermined time difference Δt passes, 1/2 is irradiated to the nth track n, which is the target track, and the other 1/2 is n-1th adjacent to the inner circumferential side from the target track. The track n-1 is irradiated. The information recorded in the n-th track n is photoelectrically converted by the photodetector from the reflected light of the first and second light spots 25 to the n-th track n, respectively. The signal is added and reproduced by detecting as a high frequency signal RF. The tracking error signal for the tracking servo is an optical component and an n-1th track irradiated to the n + 1th track (n + 1) in the reflected light of the first and second light spots 25 by a photo detector, respectively. After the light component irradiated to (n-1) is photoelectrically converted, these signals are detected by subtracting.

As described above, in the present invention, since the light spot irradiates only 1/2 of the target track to reproduce the information, it is assumed that the light spot size is the same as before, so that only half of the light spot size is used to reduce the pit size and track pitch. It can accommodate a large amount of information.

3 shows an optical pickup for condensing the first and second light spots 24, 25 on the optical recording medium 20. As shown in FIG.

In the configuration of FIG. 3, the optical pickup according to the embodiment of the present invention includes a light source 32 for generating a light beam, and an objective lens for focusing the light beam generated from the light source 32 on the recording surface of the optical recording medium 20. 42, and a photodetector 46 for converting the light beam reflected from the optical recording medium 20 into an electrical signal, and a polarization disposed between the light source 32 and the objective lens 42 and the photodetector 46. The diffraction grating 34 disposed between the beam splitter 38, the light source 32, and the polarization beam splitter 38, and the collimation lens 36 disposed between the diffraction grating 34 and the polarization beam splitter 38. And a λ / 4 plate 40 disposed between the polarizing beam splitter 38 and the objective lens 42, and a sensor lens 44 disposed between the polarizing beam splitter 38 and the photodetector 46. do. The light beam generated from the light source 32 is split into two light beams by the diffraction grating 34 to be transmitted toward the collimating lens 36. Here, the diffraction grating 34 serves to divide the incident light into two light beams, thereby suppressing the zeroth order diffraction component and transmitting the ± first order diffraction component toward the collimating lens 36. The diffraction grating 34 may be replaced by a prism that refracts incident light in different directions and divides the light into two parts. The collimating lens 36 converts the light incident on the collimated light into a parallel beam and transmits the light toward the polarization beam splitter 38. The polarizing beam splitter 38 transmits the light beam incident from the collimating lens 36 toward the objective lens 42 and reflects the reflected light beam reflected from the recording surface of the optical recording medium 20 toward the sensor lens 44. . Here, the light beam incident from the collimating lens 36 and transmitted through the polarization beam splitter 38 is incident on the λ / 4 plate 40 as horizontally polarized light (hereinafter referred to as "P wave"). The λ / 4 plate 40 converts the P-waves incident from the polarization beam splitter 38 into circularly polarized light and transmits them toward the objective lens 42. The circularly polarized light reflected from the recording surface of the optical recording medium 20 is incident. It is converted into vertical linearly polarized light (hereinafter referred to as "S wave") and transmitted to the polarization beam splitter 38. The polarization beam splitter 38 and the λ / 4 plate 40 are used to minimize light loss. The objective lens 42 serves to focus the two light beams incident from the polarization beam splitter 38 on the recording surface of the optical recording medium 20 as first and second light spots 24 and 25, respectively. The first and second light spots 24 and 25 focused from the objective lens 42 are focused on the target track and the adjacent track as shown in FIG. 2, and then reflected to back the optical path. The light beam traveling back from the optical recording medium 20 to the optical path is sequentially detected by the sensor lens 44 by the sensor lens 44 via the objective lens 42, the λ / 4 plate 40 and the polarizing beam splitter 38. Is condensed on. The photodetector 46 can be either a two or four split photodetector, but in the embodiment two two split photodetectors are used.

As illustrated in FIG. 4, the photodetector 46 includes a first photodetector 47 for detecting the reflected light 24 ′ of the first light spot 24 and a reflected light 25 ′ of the second light spot 25. And a second photodetector 48 for detection. The first photodetector 47 is composed of first and second photodetector pieces PDa1 and PDb1 in the track direction. The first and second photodetectors PDa1 and PDb1 of the first photodetector 47 respectively have an n + 1th track (n + 1) component and a target in the reflected light 24 'of the first light spot 24. The nth track n component, which is a track, is collected. The second photodetector 48 is composed of first and second photodetection pieces PDa2 and PDb2 in the track direction. The first and second photodetectors PDa2 and PDb2 of the second photodetector 48 respectively have an n-th track n component and n− which are the target tracks in the reflected light 25 'of the second optical spot 25. The first track (n + 1) component is condensed. Reflected lights 24 'and 25' of the first and second light spots 24 and 25, which are collected by the first and second photodetectors 47 and 48, are converted into electrical signals and supplied to a signal detector, which will be described later. do.

Referring to FIG. 5, first and second retarders 52 and 54 connected to output terminals of the first and second photodetector pieces PDa1 and PDb1 of the first photodetector 47, respectively, An output terminal of the second delay unit 54 and a differential amplifier 56 commonly connected to the output terminal of the delay unit 52 and the output terminal of the second photodetector piece PDb2 of the second photodetector 48. And a signal detector having an adder amplifier 58 commonly connected to the output terminal of the first photodetector piece PDa2 of the second photodetector 48.

In the first photodetector 47, the output signal Sn + 1 of the first photodetector piece PDa1 and the output signal Sn of the second photodetector piece PDb1 are respectively preceded by the first light spot 24. The reflected light 24 'corresponds to the n + 1th track (n + 1) signal as an adjacent track and the nth track (n) signal as a target track. In the second photodetector 48, the output signal Sn 'of the first photodetector piece PDa2 and the output signal Sn-1 of the second photodetector piece PDb2 are respectively formed in the second light spot 25. The reflected light 25 'corresponds to the n-th track n signal, which is the target track, and the n-1th track n-1 signal, which is the adjacent track.

The first retarder 52 delays the output signal Sn + 1 of the first photodetector PDa1 by a delay value corresponding to a predetermined time difference Δt in the first photodetector 47 so as to delay the differential amplifier 56. Supply to non-inverting input terminal. The second delayer 54 delays the output signal Sn of the second photodetector PDb1 by the delay value corresponding to a predetermined time difference Δt in the first photodetector 47 so as to input one side of the adder amplifier 58. Supply to the terminal. Here, the delay values of the first and second retarders 52 and 54 are equal to a predetermined time difference Δt = X / V (where X is the distance between the first and second light spots and V is the linear velocity at the disc rotation).

The output signal Sn-1 of the second photodetector piece PDb2 is supplied from the second photodetector 47 to the inverting input terminal of the differential amplifier 56. The differential amplifier 56 amplifies the difference between the output signal ΔtSn + 1 of the first retarder 52 and the output signal Sn-1 of the second photodetector PDb2 in the second photodetector 48. The tracking error signal Te is detected.

On the other hand, in the first photodetector 47, the output signal Sn + 1 of the first photodetector piece 47 and the output signal? TSn-1 of the second retarder 54 are adjacent track signals to the reproduction signal. It can be used to remove the included crosstalk component.

The adder amplifier 58 adds the output signal ΔtSn of the second retarder 54 and the output signal Sn 'of the first photodetector PDb2 by the second photodetector 48 to generate a high frequency signal RF. ) Will be detected. The high frequency signal RF includes information recorded in the nth track n as the target track.

On the other hand, in the present invention, since the target track is reproduced by two light beams, the target track signal detected by the first light spot 24 and the target track signal detected by the second light spot 25 are also compared. Can be used.

As described above, the optical disc reproducing apparatus according to the present invention can reproduce the information recorded on the high density optical disc using only a part of the optical spot in reproducing the information. Furthermore, in the present invention, the crosstalk caused by the adjacent tracks can be eliminated by detecting the crosstalk component included in the reproduction signal by irradiating adjacent tracks by using a portion of the light spots, and the two light spots on the same track can be eliminated. By examining the data, we can effectively verify the data.

Those skilled in the art will appreciate that various changes and modifications can be made without departing from the technical spirit of the present invention. Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification but should be defined by the claims.

1 schematically shows a conventional optical recording medium.

2 is a view showing an optical spot in the optical disk reproducing apparatus according to the embodiment of the present invention.

3 is a diagram showing an optical pickup in the optical disc reproducing apparatus according to the embodiment of the present invention.

4 is a detailed view of the photodetector shown in FIG.

Fig. 5 is a block diagram showing a signal detector in the optical disc reproducing apparatus according to the embodiment of the present invention.

           <Description of the code | symbol about the principal part of drawing>

10,20: optical recording medium 12,22: feet

14,24,25: light spot 32: light source

34 diffraction grating 36 collimation lens

38 polarization beam splitter 40 λ / 4 plate

42: objective lens 44: sensor lens

46,47,48: photodetector 52,54: retarder

56: differential amplifier 58: addition amplifier

Claims (8)

A condensing optical system for irradiating at least two light beams so that a part of each beam is irradiated to a target track of the optical disc; A light receiving optical system including two light detectors for detecting reflected light in response to the two light beams reflected from the optical disk; Delay means for delaying a signal corresponding to the target track from the following light beam signal by keeping a phase difference with respect to the preceding light beam among the two light beams for a predetermined time; And a reproducing signal detecting means for detecting a reproducing signal by adding a signal corresponding to the object track and an output signal of the delaying means to the preceding light beam signal. The method of claim 1, The condensing optical system A light source for generating a light beam, A diffraction grating for dividing the light beam into two light beams, And an objective lens for condensing the two light beams on the optical disk. The method of claim 2, The diffraction grating is characterized in that the 0th order diffracted light of incident light is suppressed and transmits ± 1st diffracted light. The method of claim 2, And the diffraction grating is a prism for refracting the incident light in different directions to divide the light into two directions. The method of claim 1, The light-receiving optical system includes two photodetectors for photoelectrically converting two-split reflected light in a track direction corresponding to two light beams reflected from the optical disk; And a sensor lens for condensing each of the two light beams onto each of the two photodetecting elements. The method according to claim 2 or 5, And a beam splitter for guiding the light beam incident from the light source toward the objective lens and for guiding the light beam incident from the objective lens toward the photodetecting device. The method of claim 1, The two light beams are respectively irradiated to left and right adjacent tracks, and further comprising means for detecting a tracking error signal based on the split reflected light corresponding to the adjacent tracks in the two light detectors. Optical disc player. The method of claim 7, wherein The means for detecting the tracking error signal includes: delay means for delaying a signal corresponding to the adjacent track from the following light beam signal, which maintains a phase difference with respect to a preceding light beam, of the two light beams for a predetermined time; And detecting means for differentially amplifying a signal corresponding to an adjacent track located on the opposite side of the adjacent trap from the preceding light beam signal and an output signal of the delay means based on a target track to detect a tracking error signal. Optical disc player.