KR20050027558A - Optical pick-up having device for compensating spherical aberration - Google Patents

Abstract

An optical pickup device having a spherical aberration compensation device is provided to compensate for spherical aberrations of a laser beam incident on an optical recording medium by being emitted from a light source and a laser beam re-incident by being reflected by the optical recording medium, thereby improving jitter characteristics. A 1/4 wave plate(142) rotates a phase of a parallel beam at about 90 degrees, which is incident by being polarized in vertical or horizontal direction to the propagated direction of a laser beam, and converts the rotated parallel beam into a left polarized beam or a right polarized beam. The 1/4 wave plate(142) rotates a phase of a circular polarized beam incident from an LCD plate(144) at about 90 degrees, converts the rotated circular polarized beam into a parallel beam, and emits the parallel beam. The LCD plate(144) controls phases of a laser beam incident on an optical disk(100a) through an objective lens(150) by being emitted from the 1/4 wave plate(142) and a laser beam re-incident by being reflected upon the optical disk(100a), and compensates for spherical aberrations of the laser beams.

Description

Optical pick-up having device for compensating spherical aberration

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup apparatus for a blue-ray disc, and more particularly, to spherical aberration generated in a process in which a laser beam emitted from a light source is incident on an optical recording medium and reflected from an optical disc. An optical pickup apparatus having a spherical aberration correcting apparatus capable of correcting spherical aberration.

Recently, as optical discs using laser diodes become more common, researches for improving recording capacity of optical discs have been conducted. Blu-ray Disc is an optical recording medium that can record a large amount of data.It records and plays back up to 27GB of data on one side of a 12cm disc by minimizing the track pitch to about half the size of a conventional CD or DVD (approximately 0.32㎛). It is possible. Blu-ray Disc adopts the structure of 405nm blue-violet semiconductor laser, objective lens with numerical aperture (NA) of 0.85 and disk with 0.1mm thickness of light transmitting protective layer.

The optical pickup device for a Blu-ray disc includes a light source for irradiating a 405 nm blue violet semiconductor laser, a half wave plate for converting a laser beam emitted from the light source into a parallel beam, and a parallel beam incident from the half wave plate. A beam splitter for reflecting and transmitting at a predetermined ratio, a collimator lens for converting a laser beam incident from the beam splitter into a parallel beam, a reflecting mirror for reflecting a laser beam emitted through the collimator lens at a predetermined angle, and incident from a reflecting mirror A quarter wave plate for rotating the direction of incident polarization of the laser beam in a predetermined direction, an objective lens for forming a laser beam incident through the quarter wave plate on the optical disc, an objective lens reflected from the optical disc, and a reflection mirror , Collimator lens, sensor lens for condensing the laser beam incident through the beam splitter, and sensor len It consists of a laser beam incident from a light detector for converting into an electric signal.

Referring to the operation of the optical pickup device configured as described above, the laser light emitted from the light source is incident on the optical disk through the half wave plate, the beam splitter, the collimator lens, the reflection mirror, the quarter wave plate and the objective lens. As a result, a beam spot is formed in the recording layer of the optical disc. In addition, the laser beam incident on the optical disk is reflected by the optical disk and is incident on the photodetector through the objective lens, the reflective mirror, the collimator lens, the beam splitter, and the sensor lens.

At this time, spherical aberration is generated in a process in which the laser beam emitted from the light source is incident on the optical disk and reflected in the optical disk. For example, spherical aberration caused by a difference in refractive index occurs when a laser beam emitted from a light source is incident on an optical disc via optical elements disposed on an optical path. In addition, when the laser beam incident on the optical disc is reflected by the optical disc, spherical aberration is generated due to the thickness error of the protective layer of the optical disc. In particular, the spherical aberration caused by the thickness error of the protective layer of the optical disk is generated in proportion to the third power of the numerical aperture (NA) of the objective lens. Therefore, as the numerical aperture of the objective lens becomes larger, the influence of the thickness error of the protective layer is increased. Receive.

Therefore, there is a need for a spherical aberration correction device for correcting spherical aberration generated in a process in which a laser beam is incident on an optical disk and a process in which a laser beam incident on an optical disk is reflected by the optical disk. If the laser beam is incident on the optical disk in the state where the spherical aberration is not corrected as described above, the beam spot formed on the recording layer of the optical disk is formed at a position deviating from the focusing position and the tracking position so that the optical The recording performance of the pickup apparatus is reduced. In particular, when spherical aberration caused by the thickness error of the protective layer is incident on the photodetector without correction, it is difficult to accurately track the track due to interference between adjacent signals, so that information is recorded on the wrong track. Or, you can erase the data already recorded on the surrounding tracks. This causes a problem that the jitter characteristic of the optical pickup device is lowered.

In order to solve the problems as described above, an object of the present invention, so as to correct the spherical aberration generated in the process of the laser beam emitted from the light source is incident on the optical recording medium and reflected from the optical recording medium. An optical pickup device having a spherical aberration correction device is provided.

In order to solve the above technical problem, the present invention employs a spherical aberration correction device consisting of a wave plate and a liquid crystal plate laser beam incident on the optical recording medium and a laser beam reflected by the optical recording medium and incident on the photodetector It is characterized in that the spherical aberration which this has can be corrected.

To this end, the present invention provides a spherical aberration correction device comprising a wave plate for converting the phase by rotating the incident beam by about 90 degrees, and a liquid crystal plate having a liquid crystal molecule structure capable of adjusting the phase for the circularly polarized beam.

Here, the liquid crystal plate is composed of a plurality of transparent substrates formed to face each other, the transparent electrode and the liquid crystal molecules arranged in a predetermined direction and a predetermined angle with respect to the transparent electrode and the transparent electrode surface is respectively installed inside the plurality of transparent substrate, It consists of a liquid crystal layer that transmits at different refractive indices according to the polarization direction of the incident beam upon application of voltage. In this case, it is preferable that the liquid crystal molecules of the liquid crystal layer are arranged to be inclined by about 45 ° in a predetermined direction so as to easily adjust the phase of the incident circularly polarized beam.

In the liquid crystal panel according to the present invention, the spherical aberration is corrected by adjusting the refractive index of the liquid crystal layer so as to generate an inverse spherical aberration corresponding to the spherical aberration of the incident laser beam.

In addition, the present invention is a liquid crystal plate having a liquid crystal molecule structure capable of adjusting the phase of the incident light beam is polarized in the vertical or horizontal direction with respect to the incident surface, and a wavelength plate for rotating the incident beam by 180 ° phase shift Implement the configured spherical aberration correction device.

In this case, the liquid crystal plate may include a plurality of transparent substrates formed to face each other, a transparent electrode provided inside each of the plurality of transparent substrates to which power is applied, and in one of a vertical direction and a vertical direction with respect to the surface of the transparent electrode. It consists of an array of liquid crystal molecules, a liquid crystal layer that transmits at different refractive indices according to the polarization direction of the beam incident upon application of voltage to the transparent electrode. By adopting such a spherical aberration correcting apparatus in the optical pickup apparatus, the spherical aberration of the laser beam incident on the optical recording medium and the laser beam reflected by the optical recording medium and incident on the photodetector is corrected, thereby recording and recording the optical pickup apparatus. Can improve regeneration ability.

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

1 is a view showing the configuration of an optical pickup apparatus having a spherical aberration correcting apparatus according to a first embodiment of the present invention.

In this embodiment, an optical pickup device for a Blu-ray disc will be described as an example of an optical pickup apparatus capable of irradiating a predetermined laser beam to an optical recording medium to record and reproduce data.

The optical pickup device 100 according to the present invention includes a blue laser diode 110, a half wave plate 115, a beam splitter 120, a front monitor 125, a collimator lens 130, and a reflection mirror 135. And a spherical aberration correcting device 140, an objective lens 150, a sensor lens 155, and a photodetector 160.

A blue laser diode (hereinafter referred to as "Blue-LD") 110 emits a blue violet semiconductor laser beam having a wavelength of 408 nm as a light source. At this time, the laser beam emitted from the Blue-LD 110 is a P-polarized beam that is polarized in the horizontal direction with respect to the incident surface or the S-polarized beam, the right-circular polarized beam and the left circular polarized beam polarized in the vertical direction with respect to the incident surface Can have characteristics.

The half-wave plate 115 transforms the direction of incident polarization by advancing and retarding the phase of the laser beam incident from the blue-LD 110 by about 180 °. That is, the half wave plate 115 converts and transmits the laser beam emitted from the Blue-LD 110 into a P-polarized beam or an S-polarized beam.

The beam splitter 120 reflects and transmits the laser beam incident through the 1/2 wave plate 115 at a predetermined ratio. Therefore, a part of the total amount of light of the laser beam incident from the half wave plate 115 is transmitted and is incident on the front monitor 125 to be described later, and the rest is reflected by the beam splitter 120 to collimator lens 130 Incident.

The front monitor (FPD) 125 detects the light amount of the laser beam incident from the beam splitter 120 and adjusts the light amount irradiated from the Blue-LD 110. The laser beam incident on the front monitor 125 is converted into an electrical signal and used for auto power control.

The collimator lens 130 converts the laser beam having a predetermined radiation angle into parallel light by the beam splitter 120 and transmits the parallel light.

The reflex mirror 135 reflects the laser beam emitted from the collimator lens 130 to be incident on the objective lens 150.

The spherical aberration correcting device 140 is installed between the reflective mirror 135 and the objective lens 150, the spherical aberration of the laser beam incident from the reflective mirror 135 and the laser beam reflected from the optical disk 100a Correct Aberration.

Spherical aberration correction device 140 is composed of a quarter wave plate (142) and a liquid crystal plate (Liquid Crystal Plate) (144).

The quarter wave plate 142 is rotated by 90 ° in the vertical or horizontal direction polarized in the vertical direction or the horizontal direction with respect to the laser beam travel direction to convert to a left circularly polarized beam or a right circularly polarized beam, and the liquid crystal The phase of the circularly polarized light beam incident from the plate 144 is rotated by about 90 degrees to be converted into a parallel beam and emitted. That is, the quarter wave plate 142 converts the P-polarized beam incident from the reflective mirror 135 into the right-side polarized beam and enters the liquid crystal plate 144. The left circle is reflected by the optical disk 100a and re-entered. The polarized beam is converted into the S-polarized beam and emitted to the reflecting mirror 135.

The liquid crystal plate 144 is a phase of a laser beam emitted from the quarter wave plate 142 and incident on the optical disk 100a through the objective lens 150 and reflected by the optical disk 100a and re-incident. To adjust the spherical aberration of the laser beam.

As shown in FIG. 2, the liquid crystal panel 144 is provided inside the plurality of transparent substrates 145a and 145b and the plurality of transparent substrates 145a and 145b which are formed to face each other. 146a and 146b and the transparent electrodes 146a and 146b, and are formed of a liquid crystal layer 147 that transmits at different refractive indices according to the polarization direction of the laser beam incident upon application of voltage.

The liquid crystal molecules formed on the liquid crystal layer 147 may be used to correct spherical aberration of the laser beam incident from the quarter wave plate 142 and the laser beam reflected from the optical disc 100a. The long axis direction of the liquid crystal molecules is inclined at a predetermined angle (for example, 45 °) with respect to the transparent substrates 145a and 145b so that the refractive index can be easily controlled. However, it is not necessarily limited thereto.

The liquid crystal molecules arranged in the liquid crystal layer 147 are rotated in a predetermined direction by voltages applied to the transparent electrodes 146a and 146b. The liquid crystal plate 144 is incident to correspond to the structure of the liquid crystal molecules changed by the applied voltage. The refractive index of the liquid crystal layer 147 is adjusted to change the phase of the laser beam. That is, the liquid crystal plate 144 adjusts the refractive index of the liquid crystal layer 147 to generate an inverse spherical aberration distribution corresponding to the spherical aberration distribution of the laser beam incident on the liquid crystal layer 147.

The object lens 150 forms a beam spot in the recording layer of the optical disc 100a and the laser beam emitted by spherical aberration correction by the liquid crystal plate 144. The objective lens 150 performs focusing servo and tracking servo by an actuator (not shown).

The sensor lens 155 is a type of concave lens, which is reflected from the optical disk 100a to be objective lens 150, quarter wave plate 142, reflecting mirror 135, collimator lens 130, and beam splitter 120. The laser beam incident through the light is focused into a circular or elliptical light according to a focusing state.

A photo detector is a kind of photodiode and converts a beam spot incident in a circular or elliptical form from the sensor lens 155 into an electrical signal. Since the detection operation of the photodetector 160 is already known, a detailed description thereof will be omitted.

Hereinafter, a control operation of an optical pickup device for a light control liquid crystal device capable of correcting spherical aberration will be described with reference to FIGS. 3 and 4. In the present embodiment, a case in which the laser beam emitted from the Blue-LD 110 is converted into a P-polarized beam by the 1/2 wave plate 115 and outputted is described as an example.

First, a laser beam of a predetermined wavelength (405 nm) emitted radially from the Blue-LD 110 is converted into a P-polarized beam by the half wave plate 115. The converted P-polarized beam is incident on the beam splitter 120 and then reflected and transmitted by the beam splitter 120 at a predetermined ratio. That is, some of the total amount of light of the P-polarized beam incident on the beam splitter 120 is transmitted and incident to the front monitor 125, and the rest is reflected and incident to the collimator lens 130.

The collimator lens 130 converts the P-polarized beam having a predetermined radiation angle into a parallel beam by the beam splitter 120 and transmits it. The P-polarized beam incident from the collimator lens 130 is reflected by the reflection mirror 135 by about 90 ° and is incident on the spherical aberration correcting unit 140.

3 is a view for explaining the operation of the spherical aberration correction device.

In FIG. 3, the x-axis denotes a traveling direction of the laser beam, the y-axis denotes a direction horizontal to the traveling direction of the laser beam, and the z-axis denotes a direction perpendicular to the traveling direction of the laser beam. Therefore, P polarization means a beam polarized in the y-axis direction, and S polarization means a beam polarized in the z-axis direction.

Referring to FIG. 3, the P-polarized beam incident on the spherical aberration correcting apparatus 140 is converted into a right circularly polarized beam by being 90 ° out of phase by the quarter wave plate 142. The beam converted into right circularly polarized light by the quarter wave plate 142 is corrected by spherical aberration by the liquid crystal plate 144. That is, the liquid crystal plate 144 adjusts the refractive index of the liquid crystal layer 147 to generate an inverse spherical aberration distribution corresponding to the spherical aberration distribution of the right circularly polarized beam incident on the optical disc 100a. Therefore, the right circularly polarized beam incident on the liquid crystal plate 144 is incident on the objective lens 150 after the spherical aberration is corrected by the liquid crystal plate 144.

The spherical aberration-polarized beam corrected by the liquid crystal plate 144 is focused by the objective lens 150 and then incident on the optical disk 100a. As a result, a beam spot is formed on the recording surface of the optical disc 100a.

Further, the beam spot formed on the recording layer of the optical disc 100a is reflected by the pit formed on the optical disc 100a, so that the objective lens 150, the liquid crystal plate 144, the quarter wave plate 142, and the reflection mirror ( 135, the collimator lens 130, the beam splitter 120, and the sensor lens 155 are incident to the photodetector 160. The laser beam reflected from the optical disc 100a changes in refractive index due to the difference in thickness of the protective layer of the optical disc 100a, resulting in spherical aberration. Spherical aberration caused by the difference in thickness of the protective layer of the optical disc 100a is corrected by the liquid crystal plate 144.

 4A and 4B are graphs for explaining a spherical aberration correction method of the laser beam incident on the cross section A in FIG.

Referring to FIGS. 4A and 4B, the left circularly polarized beam reflected by the optical disk 100a and re-incident to the cross section A is as shown in FIG. 4A due to the thickness of the optical disk 100a, the refractive index of the medium, and the numerical aperture of the objective lens. In the case of spherical aberration, the liquid crystal plate 144 adjusts the refractive index of the liquid crystal layer 147 to generate inverse spherical aberration as shown in FIG. 4B. That is, the spherical aberration of the left circularly polarized beam incident on the liquid crystal plate 144 is corrected by being attenuated by the inverse spherical aberration generated by the liquid crystal plate 144.

The spherical aberration corrected left circularly polarized beam is incident on the quarter wave plate 142. The left circularly polarized beam incident on the quarter wave plate 142 is transmitted by being phase-delayed by about 90 degrees by the quarter wave plate 142 and converted into the S polarized beam. The S-polarized beam incident from the quarter wave plate 142 is reflected by the reflection mirror 135 by about 90 ° and is incident on the collimator lens 130.

The S-polarized beam incident from the reflection mirror 135 is converted into a parallel beam by the collimator lens 130 and then incident to the beam splitter 120. The S-polarized beam incident on the beam splitter 120 is incident on the sensor lens 155, is collected by the sensor lens 155, and is incident on the photodetector 160. The S-polarized beam incident on the photodetector 160 is focused on a split sensor (eg, an 8 split sensor or a 12 split sensor) divided into predetermined regions. The detection operation of the photodetector 160 is well known in the art and a detailed description thereof will be omitted.

5 is a diagram showing the configuration of an optical pickup apparatus having a spherical aberration correction apparatus according to a second embodiment of the present invention. The optical pickup apparatus 200 according to the second embodiment of the present invention is a spherical aberration correction apparatus 240 having a different structure from the spherical aberration correction apparatus 140 employed in the optical pickup apparatus 100 according to the first embodiment. In the following description, only the parts related to the spherical aberration correcting apparatus 240 according to the present embodiment will be described, and detailed description of the remaining optical elements will be omitted.

The spherical aberration correcting apparatus 240 according to the present exemplary embodiment includes a liquid crystal plate 242 and a half wave plate 244.

The liquid crystal plate 242 corrects spherical aberration of the laser beam by adjusting phases of the laser beam incident through the reflection mirror 235 and the laser beam reflected from the optical disk 200a and re-incident.

The liquid crystal panel 242 includes a plurality of transparent substrates formed to face each other, a transparent electrode provided inside each of the plurality of transparent substrates to which power is applied, and a polarization direction of a laser beam that is formed between the transparent electrodes and is applied when a voltage is applied. It consists of a liquid crystal layer which transmits with different refractive index according to. The liquid crystal molecules formed on the liquid crystal layer are arranged in the vertical direction or the horizontal direction with respect to the transparent substrate surface. This is because the liquid crystal plate 242 according to the present embodiment is implemented to perform spherical aberration correction for the P-polarized beam.

The half wave plate 244 rotates the phase of the laser beam incident from the liquid crystal plate 242 by about 180 degrees to change the direction of incident polarization. In addition, the half wave plate 244 rotates the phase of the laser beam reflected by the optical disk 200a and reincident by about 180 ° to change the direction of incident polarization.

FIG. 6 is a view for explaining the operation of the spherical aberration correcting apparatus shown in FIG.

Referring to FIG. 6, the P-polarized beam, ie, the beam polarized in the y-axis direction, is incident on the liquid crystal plate 242 and transmitted after the spherical aberration is corrected. That is, the liquid crystal plate 242 adjusts the refractive index of the liquid crystal layer to generate inverse spherical aberration corresponding to the spherical aberration of the P-polarized beam incident on the optical disc 100a. Therefore, the P-polarized beam incident on the liquid crystal plate 242 is corrected on the spherical aberration by the liquid crystal plate 242 and then incident on the 1/2 wave plate 244. The P-polarized beam incident on the half wave plate 244 is converted into the S polarized beam by the half wave plate 244.

The S-polarized beam emitted from the half wave plate 244 is incident on the objective lens 250 and then collected by the objective lens 250 and incident on the optical disc 200a. As a result, a beam spot is formed in the recording layer of the optical disc 200a. The S-polarized beam incident on the optical disk 200a is reflected by the optical disk 200a and then incident again on the 1/2 wave plate 244. The S-polarized beam reflected by the optical disk 200 ㅁ and re-incident is converted into a P-polarized beam by the half wave plate 244 and then incident on the liquid crystal plate 240. The liquid crystal panel 240 corrects the spherical aberration of the P-polarized beam incident through the 1/2 wave plate 244 and then transmits it. Since the spherical aberration correction principle of the liquid crystal plate 242 according to the present embodiment is the same as the correction principle of the liquid crystal plate 144 according to the first embodiment, a detailed description thereof will be omitted.

As described so far, according to the optical pickup apparatus including the spherical aberration correcting apparatus according to the present invention, the process of the laser beam emitted from the light source is incident on the optical recording medium and the laser beam incident on the optical recording medium is the optical recording medium. By correcting the spherical aberration caused by the thickness difference of the optical disk, the refractive index, the numerical aperture of the objective lens, and the like in the process reflected by the optical disk, the recording and reproduction performance of the optical pickup apparatus can be improved.

In particular, since the spherical aberration of the laser beam reflected by the optical disk and incident on the photodetector is corrected, it is difficult to control the tracking servo due to interference between adjacent signals, thereby recording information on the wrong track or erasing data already recorded on the peripheral track. Problems can be eliminated. In addition, it is possible to improve the playback performance by preventing the focus offset caused by failing to set the correct focus position when recording data on the optical disc.

Although the present invention has been described in detail with reference to exemplary embodiments above, those skilled in the art to which the present invention pertains can make various modifications to the above-described embodiments without departing from the scope of the present invention. I will understand. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be defined by the claims below and equivalents thereof.

1 is a diagram showing the configuration of an optical pickup apparatus having a spherical aberration correcting apparatus according to a first embodiment of the present invention;

2 is a view showing a detailed configuration of the liquid crystal plate shown in FIG.

3 is a view for explaining the operation of the spherical aberration correction device shown in FIG.

4 is a graph illustrating a correction principle of the spherical aberration correction apparatus shown in FIG. 1;

5 is a diagram showing the configuration of an optical pickup apparatus having a spherical aberration correcting apparatus according to a second embodiment of the present invention;

FIG. 6 is a view for explaining the operation of the spherical aberration correcting apparatus shown in FIG.

Explanation of symbols on the main parts of the drawings

100, 200: optical pickup device 110, 210: blue laser diode

115, 215: 1/2 wave plate 120, 220: beam splitter

130, 230: collimator lens 135, 235: reflection mirror

140, 240: spherical aberration correction device 142: 1/4 wave plate

144, 242: liquid crystal plate 242: 1/2 wave plate

150, 250: objective lens

Claims (7)

An optical pickup apparatus for recording and reproducing data by irradiating a predetermined laser beam on an optical recording medium, The first parallel beam polarized in one of the vertical and horizontal directions with respect to the incident surface is converted into a first circularly polarized beam to be incident on the optical recording medium, and is reflected by the optical recording medium. A wave plate converting a second circularly polarized beam into a second parallel beam perpendicular to the first parallel beam; And And a liquid crystal plate disposed between the wavelength plate and the optical recording medium to adjust phases of the first circularly polarized beam and the second circularly polarized beam. The method of claim 1, The wavelength plate is a spherical aberration correction device, characterized in that the quarter wave plate for phase conversion by rotating the incident beam by 90 °. The method of claim 1, The liquid crystal plate, A plurality of transparent substrates formed to face each other; Transparent electrodes respectively installed inside the plurality of transparent substrates to which power is applied; And A liquid crystal layer comprising liquid crystal molecules arranged in a predetermined direction and at a predetermined angle with respect to the surface of the transparent electrode and transmitting at different refractive indices according to a polarization direction of a beam incident upon application of voltage to the transparent electrode; . The method of claim 3, wherein Spherical aberration correction device, characterized in that the predetermined angle is 45 °. An optical pickup apparatus for recording and reproducing data by irradiating a predetermined laser beam on an optical recording medium, The first parallel beam polarized in one of the vertical and horizontal directions with respect to the incident surface is converted into a second parallel beam perpendicular to the first parallel beam to enter the optical recording medium, and the optical recording medium A wave plate for converting the second parallel beam reflected by the second incident beam into the first parallel beam; And A liquid crystal plate disposed at a front end of the wavelength plate to adjust a phase of the first parallel beam incident on the optical recording medium and the first parallel beam reflected from the optical recording medium and re-incident through the wavelength plate; Spherical aberration correction device comprising a. The method of claim 5, The wavelength plate is a spherical aberration correction device, characterized in that the half-wave plate for converting the phase by rotating the incident beam by 180 °. The method of claim 5, The liquid crystal plate, A plurality of transparent substrates formed to face each other; Transparent electrodes respectively installed inside the plurality of transparent substrates to which power is applied; A liquid crystal layer comprising liquid crystal molecules arranged in one of a vertical direction and a vertical direction with respect to the surface of the transparent electrode and transmitting at different refractive indices according to a polarization direction of a beam incident upon application of voltage to the transparent electrode; Spherical aberration correction device.