KR20080004716A - Apparatus and method for reproducing recording meduim - Google Patents

Abstract

An optical recording/reproducing apparatus and a recording/reproducing method thereof are provided to maintain a sufficient gap between an SIL(Solid Immersion Lens) and a recording medium by having a servo unit about a skew of the recording medium, and to ensure accurate gap servo control of the recording medium by eliminating DC offset component included in a gap error signal. An optical recording/reproducing apparatus comprises an actuator(120), a first optical system, and a second optical system. The actuator is provided with an objective lens(121) to cause a first beam to be projected to a recording medium(123) and an SIL(Solid Immersion Lens,122). The first optical system comprises a first photo detector(113) as a first photoelectric unit which produces the first beam and detects a first serve signal from a signal reflected by the SIL, and a third photo detector(115) as a third photoelectric unit which detects an electric signal from an RF signal reflected to the recording medium. The second optical system comprises a second photo detector(133) as a second photoelectric unit which produces a second beam and detects a second servo signal from a signal reflected by the SIL. One of the first and second optical systems detects a servo signal for detecting tilting of the recording medium, while the other detects an error signal generated by movement of the objecting lens during the tilting servo operation.

Description

Apparatus and method for reproducing recording meduim

1 is a block diagram showing an optical system of an optical recording and reproducing apparatus.

2 is a diagram illustrating an optical system of a near field recording method.

3 is a view for explaining an optical recording and reproducing apparatus according to the embodiment of the present invention;

4 is a diagram comparing the tilt margin due to light emitted from the first laser diode and the tilt margin due to light emitted from the second laser diode.

5 is a view for explaining that light is incident on a recording medium on which a cover layer is not formed.

6 and 7 illustrate beam spots in a photo detector according to skew of a recording medium on which a cover layer is not formed.

8 is a view for explaining that light is incident on a recording medium on which a cover layer is formed.

9 and 10 illustrate beam spots in a photo detector according to skew of a recording medium having a cover layer formed thereon.

The present invention relates to an optical recording and reproducing apparatus, and more particularly, to an optical recording and reproducing apparatus and a recording and reproducing method, wherein a configuration for detecting a tilting error signal when detecting an error signal for recording or reproducing a signal is disclosed.

Recently, high-density rewritable optical recording media capable of recording and storing high-definition video data and high-quality audio data for a long time have been introduced. Blu-ray discs, for example.

As the standardization work for Blu-ray Disc proceeds rapidly, it is expected that related products will be developed and released and commercialized. Blu-ray discs can store as much as 25GB of data and, if built in dual layers, can store up to 50GB of data.

On the other hand, in order to increase the recording capacity of the optical recording medium, a method of shortening the wavelength of laser light or increasing the numerical aperture (NA) of the objective lens is used.

1 is a configuration diagram showing an optical system of an optical recording and reproducing apparatus.

Referring to FIG. 1, light generated by the laser diode 10 is converted into parallel light by the collimator lens 11, passes through the optical splitter 12, and then is recorded by the objective lens 13 by the recording medium 14. Condensed into a point at.

Light reflected from the recording medium 14 is reflected by the optical splitter 12 via the objective lens 13 and then collected by the lens 15 through the lens 15 to detect an electrical signal.

However, in the optical system as shown in FIG. 1, the method of shortening the wavelength to increase the recording capacity has almost reached the physical limit, and the method of increasing the objective lens numerical aperture is a conventional far-field recording method. Further big improvements are becoming difficult.

Accordingly, a near-field recording method using a solid immersion lens (SIL) has been studied. This is as shown in FIG.

As shown in Fig. 2, the near field recording method arranges the SIL 22 under the objective lens 21, and the SIL 22 is mounted as a hemispherical shape made of a medium having a refractive index n greater than one. . The SIL 22 makes the numerical aperture of the objective lens 21 equal to n * NA so that the recording capacity can be increased to 1 or more, thereby significantly increasing the recording capacity.

On the other hand, in the near field recording method, since the distance between the SIL 22 and the recording medium 23 is about several tens of nm, when skew is generated in the recording medium 23, the SIL 22 and the recording medium 23 are separated. If the gap GAP cannot be maintained accurately, the SIL 22 and the recording medium 23 collide with each other, resulting in a case where the SIL 22 is damaged.

In the related art, in the tracking servo operation for recording or reproducing data, a series of tracking servo operations are performed to move the objective lens 21 in the horizontal direction of the recording medium. The servo signal for measuring the tilting degree includes a signal caused by the movement of the objective lens, which makes it difficult to measure the tilting of the recording medium.

That is, when the objective lens is moved in accordance with the eccentricity of the recording medium by the tracking servo operation, the light is moved to the four-segment photodetector, which causes a DC offset.

Therefore, there is a problem in that the skew of the recording medium can not be detected more accurately due to the DC offset generated by the movement of the objective lens according to the gap servo control.

The present invention has been proposed to solve the above problems, and an object of the present invention is to propose an optical recording and reproducing apparatus and a recording / reproducing method equipped with a servo means for skew of the recording medium so as to properly maintain the gap between the SIL and the recording medium. It is done.

Another object of the present invention is to propose an optical recording / reproducing apparatus and a recording / reproducing method for efficiently removing a DC offset component included in a gap error signal in order to more accurately perform gap servo control of a recording medium.

An optical recording and reproducing apparatus according to an embodiment of the present invention comprises: an actuator having an objective lens for causing the first light to be incident on a recording medium and a solid immersion lens (SIL); First photoelectric means for generating the first light and detecting a first servo signal from the signal reflected by the SIL, and third photoelectric means for detecting an electrical signal from the RF signal reflected from the recording medium; A first optical system having; And a second optical system having second photoelectric means for generating a second light and detecting a second servo signal from the signal reflected by the SIL.

Hereinafter, an optical recording and reproducing apparatus according to the present invention will be described in detail with reference to the accompanying drawings.

First, in the embodiment of the present invention, the optical recording / reproducing apparatus includes a device capable of recording data on or reproducing data recorded on the recording medium, and also includes a device capable of recording and reproducing data.

3 is a view for explaining an optical recording and reproducing apparatus according to the embodiment of the present invention.

Referring to FIG. 3, an optical recording and reproducing apparatus according to an embodiment of the present invention includes a first optical system for recording or reproducing data on a recording medium 123, and a gap between the recording medium 123 and the SIL 122. Gap) a second optical system for detecting an error signal, a SIL 122 and an objective lens 121 having light incident on the recording medium 123 and incident light reflected from the recording medium 123 being formed Actuator 120 is included.

In detail, one of the first and second optical systems serves to detect a servo signal for measuring the tilting degree of the recording medium 123, and the other one moves the objective lens 121 during the tilting servo operation. It serves to detect the error signal generated by the.

That is, the tilting degree of the recording medium 123 and the movement amount of the objective lens 121 are measured by the photo detectors configured in each of the first and second optical systems.

The servo signal used below is used to include the amount of movement of the objective lens 121 or the actuator together with the tilting amount of the recording medium 123, each of which may be divided into a first servo signal and a second servo signal. have.

As the first optical system, the first laser diode 110 for emitting blue light of 405nm band, the first collimator lens 111 for converting the light emitted from the first laser diode 110 into parallel light, A first polarization beam splitter 112 and a third polarization beam splitter 114 for allowing incident light to be transmitted or reflected according to the polarization component of the incident light, and a first for adjusting the size of the light by controlling the divergence angle or convergence angle of the beam The expander 116, a first QWP (Quarter Wave Plate) 117 for changing the wavelength of the incident beam, and a beam splitter 118 are included.

The first optical system includes a third photo detector (third photoelectric means 115) for detecting an RF signal reflected from the recording medium 123 and incident through the third polarization beam splitter 114. A first photodetector (first photoelectric means) 113 is included for detecting a gap error signal reflected from the recording medium 123 and incident through the first polarization beam splitter 112.

For reference, it should be noted that the present invention is explained by exemplifying a photo detector as a photoelectric means.

As the second optical system, the second laser diode 130 for emitting red light of 650nm band, the second collimator lens 131 for converting the light emitted from the second laser diode 130 into parallel light, A second polarization beam splitter 132 for transmitting or reflecting the incident beam according to the polarization component of the incident beam, a second expander 113 for adjusting the size of the light by controlling the divergence angle or the convergence angle of the beam, and the incident light A second QWP 137 is included to cause the wavelength of to change.

The second optical system includes a second photo detector (second photoelectric means, 133) for detecting a gap error signal reflected from the recording medium 123 and incident through the second polarization beam splitter 132. do.

The actuator 120 includes an SIL 122 and an objective lens 121 for focusing the incident beam onto the recording medium 123.

The operation of the optical recording and reproducing apparatus configured as described above is as follows.

The first light emitted from the first laser diode 110 is converted into parallel light in the first collimated lens 111, and the first polarized beam splitter 112 and the third polarized beam splitter 114 The divergence angle or convergence angle is controlled by the expander 116 to change the size of the light.

In the first beam, linearly polarized light is converted into circularly polarized light in the first QWP 117 and is incident to the reflection mirror 119.

The first beam reflected by the reflection mirror 119 is incident on the recording medium 123 through the objective lens 121 and the SIL 122. At this time, the actuator 121 is formed with a coil and a magnetic circuit to perform a servo operation for gap error and tracking error.

Meanwhile, the light reflected from the recording medium 123 is converted into linearly polarized light at the first QWP 117. However, it is changed to the polarization direction perpendicular to the original polarization direction.

When the first light is used for reproducing the data recorded on the recording medium 123, the first light is not only reflected by the data recording / reproducing layer of the recording medium 123, but also a part thereof. Is totally reflected by the SIL 122 before being incident on the recording medium 123. Here, the surface where the light is totally reflected may be referred to as the reflection surface of the SIL 122, and the reflection surface becomes a flat surface of the SIL facing the recording medium 123.

In the near field optical recording / reproducing apparatus, a coupling is generated due to a correlation between the SIL 122 and the recording medium 123 and the refractive index of the SIL 122 and the recording medium 123 and air. Some of the light incident on the SIL 122 is totally reflected, and the other is incident on the recording medium 123.

Therefore, the light having the polarization component that can be reflected through the third polarization beam splitter 114 among the light reflected by the recording medium 123 is incident to the third photo deductor 115, and the third The signal incident on the photo detector 115 becomes an RF signal. The third photo detector 115 converts the RF signal into an electrical signal to reproduce data stored in the recording medium 123.

The light transmitted through the third polarization beam splitter 114 (more accurately, the light totally reflected in the SIL) among the light reflected by the recording medium 123 is reflected through the first polarization beam splitter 112. And the signal incident to the first photo detector 113, the signal incident to the first photo detector 113 may be a signal for detecting a tilting amount of the recording medium 123, or may be an objective lens 121 or an actuator 120. ) Is a signal for detecting the amount of movement.

In addition, the second photo detector, which will be described later, also serves to detect the tilting amount of the recording medium 123 or to detect the movement amount of the objective lens 121 or the actuator 120. .

On the other hand, the second beam emitted from the second laser diode 130 is converted into parallel light in the second collimator lens 131, and the second QWP 137 via the second polarization beam splitter 132 The polarized light is converted and incident on the reflection mirror 119.

The second beam reflected by the reflective mirror 119 is incident on the recording medium 123 through the objective lens 121 and the SIL 122.

In this case too, some of the second beams are totally reflected at the SIL 122. When the distance between the SIL 122 and the recording medium 123 is small, the amount of totally reflected light is small. When the distance between the SIL 122 and the recording medium 123 is large, the amount of totally reflected light is large.

This is due to the correlation between the refractive index of the air between the SIL 122, the recording medium 123, the SIL 122 and the recording medium 123, and the wavelength of the beam, and the SIL 122 and the recording medium 123. In the case where the distance between the beams is 100 nm or less, the gap between the SIL 122 and the recording medium 123 and the amount of beams totally reflected by the SIL 122 have a correlation, as described above.

The second beam reflected by the SIL 122 is reflected by the second polarization beam splitter 132 and is incident on the second photo detector 133. The second photo detector 133 extracts a servo signal from the second beam reflected by the SIL 122. The signal detected by the second photo detector 133 becomes a signal for detecting the tilting amount of the recording medium 123 or a signal for detecting the amount of movement of the objective lens 121 or the actuator 120. .

In the present invention, both the first beam and the second beam are used to detect the gap error signal, and in particular, the light totally reflected by the SIL 122 is used among the first beam and the second beam.

For the use of the first beam and the second beam for detecting the tilting error signal, see FIGS. 5 to 10 attached separately when the recording medium 123 has a cover layer (protective film) and when it does not. Let's look at it in more detail.

4 is a diagram comparing a tilt margin due to light emitted from a first laser diode and a tilt margin due to light emitted from a second laser diode.

The first light 140 emitted from the first laser diode 110 has a small light size in the SIL 122, and the tilt margin of the recording medium 123 that can be detected by the small light size is small.

That is, in the case of performing the gap servo by the first light 140, the tilting state of the recording medium 123 may be sensed when the recording medium 123 is in the first position 123b. Accordingly, the actuator 120 performs a control operation according to the gap servo to prevent collision between the SIL 122 and the recording medium 123 when the recording medium 123 is in the first position 123b.

On the other hand, the second light 141 emitted from the second laser diode 130 has a large light size in the SIL 122, the tilt margin of the recording medium 123 that can be detected as a large light size is It is larger than the first light 140.

That is, when performing the gap servo by the second light 141, the tilting state of the recording medium 123 may be sensed when the recording medium 123 is in the second position 123a.

Therefore, when the gap servo is performed by the second light 141, the movement of the recording medium 123 may be more sensitively sensed, and the control operation according to the more smooth gap servo may be performed.

In addition, since the second light 141 has a relatively large light size in the SIL 122, a signal more sensitive to the skew of the recording medium 123 can be obtained.

Hereinafter, a description will be given with reference to FIG. 3 described above, which will be divided into a case where the cover layer is formed on the recording medium 123 and a case where the cover layer is not.

In the near field recording medium, it is important to maintain the gap between the SIL and the surface of the recording medium. When the cover layer is formed on the recording medium, it is necessary to maintain the gap between the cover layer surface and the SIL. This is because the interval between the data recording / reproducing layer and the SIL needs to be maintained when is not formed.

FIG. 5 is a diagram illustrating light incident on a recording medium without a cover layer, and FIGS. 6 and 7 illustrate beam spots in a photo detector according to skew of a recording medium on which a cover layer is not formed. Drawing.

First, referring to FIG. 5, when the cover layer is not provided on the data recording / reproducing layer of the recording medium 123, the first light 140 may detect the RF signal and move the objective lens 121. The DC light 141 serves to detect the DC offset, and the second light 141 serves to measure the tilting amount of the recording medium.

That is, when the cover layer is not formed on the recording medium 123, the focus of the first light 140 is focused on the data recording and reproducing layer, and the optical size of the SIL 122 is the first. Light 140 is relatively larger than second light 141.

Therefore, as the size of light formed by the SIL 122 increases, the tilting amount (or skewing degree) of the recording medium 123 can be detected more accurately, so that the tilting amount of the second light 141 is recorded in the recording medium 123. It is used for the purpose of detecting.

In addition, the smaller the size of the light formed by the SIL 122, the more difficult it is to detect the tilting amount of the recording medium 123. Thus, the first photo detector may be used to detect the first light 140 in addition to the RF signal detection. 113 is used for detecting the movement amount (or DC offset) of the objective lens 121 or the actuator 120.

In this case, the photoelectrically converted signals observed through the first photo detector 113 and the second photo detector 133 are illustrated in FIGS. 6 and 7.

The first photo detector 113 is a photo detector divided into two, and the second photo detector 133 is a photo detector divided into four. That is, the first light 140 is used for detecting the DC offset due to the movement of the objective lens 121 in addition to the role of recording and reproducing data using the RF signal. Because the size of the first light 140 is smaller than that of the second light 141, it is difficult to detect the tilting amount of the recording medium 123 by the first light 140 as described above. Because it is the same.

The light spot photoelectrically converted through the first photo detector 113 among the light totally reflected by the SIL 122 is as shown in FIG. 6, and the DC offset according to the movement of the objective lens 121 is k × (EF). )

In addition, the light spot photoelectrically converted through the second photo detector 133 among the light totally reflected by the SIL 122 is as shown in FIG. 7, and the recording medium is detected by the second photo detector 133. The tilting amount of (123) becomes [(A + D)-(B + C)]. That is, the difference between the left and the right of the signal photoelectrically converted through the fourth divided photo detector 133 is a tilting amount.

Therefore, the tilting error signal TE of the recording medium measured according to the embodiment of the present invention becomes [(A + D)-(B + C)]-k × (EF), and the control signal by the detecting means Accordingly, the objective lens 121 performs a series of tilting servo operations in which the objective lens 121 is moved left and right in the horizontal direction of the recording medium 123 so that the tilting error signal TE is minimized.

Further, a detection means for detecting the tilting error signal of the recording medium through the first photo detector 113 and the third photo detector 133 should be further provided.

In addition, a case in which the cover layer is formed on the recording medium 123 will be described with reference to FIGS. 8 to 10.

In general, since the thickness of the cover layer is thicker than the distance between the SIL and the surface of the recording medium, the use of light for detecting the tilting error signal of the recording medium is different in the apparatus for recording or reproducing the recording medium with the cover layer.

That is, the recording or reproducing of data using the first light, which is blue light, may be the same as in the case where the cover layer is formed on the recording medium, but the distance between the data recording and reproducing layer and the SIL is formed on the recording medium. In this case, since the size is relatively larger, the size of light incident on the SIL is changed.

To illustrate this, FIGS. 8 to 10 are attached, and FIG. 8 is a view for explaining that light is incident on the recording medium on which the cover layer is formed, and FIGS. 9 and 10 are according to the tilting of the recording medium on which the cover layer is formed. It is a figure explaining the beam spot in a photo detector.

First, referring to FIG. 8, a recording and reproducing apparatus in a case in which a cover layer is formed on the data recording and reproducing layer of the recording medium 123, wherein the first light 140 is tilted of the recording medium together with the RF signal detection. Or skew), and the second light 141 serves to detect a DC offset caused by the movement of the objective lens 121 during the servo control operation.

That is, when the cover layer is formed on the recording medium 123, the size of the light formed on the SIL 122 is greater than the second light 141 because the first light 140 is larger than the second light 141. It is used for the purpose of detecting this DC offset.

In this case, the photoelectrically converted signals observed through the first photo detector 113 and the second photo detector 133 are illustrated in FIGS. 9 and 10.

The first photo detector 113 is a four-part photo detector, and the second photo detector 133 is a two-part photo detector.

The light spot photoelectrically converted through the first photo detector 113 among the totally reflected light from the SIL 122 is as shown in FIG. 9, and the recording medium 123 is detected through the first photo detector 113. ) Tilting amount is [(A + D)-(B + C)]. That is, the difference between the left and the right in the photoelectrically converted signal through the four-divided first photo detector 113 becomes the tilt detection amount of the recording medium.

The light spot photoelectrically converted through the second photo detector 133 among the light totally reflected by the SIL 122 is as shown in FIG. 10, and the objective lens detected by the second photo detector 133. The DC offset according to the movement of 121 becomes k × (EF).

Accordingly, the tilting error signal TE of the recording medium measured according to the embodiment of the present invention becomes [(A + D)-(B + C)]-k × (EF), and the object is detected by the detecting means. The lens 121 performs a series of tilting servo operations for moving the recording medium 123 in the horizontal direction such that the tilting error signal TE is minimized.

As described above, the optical recording and reproducing apparatus and the recording and reproducing method of the present invention can be performed by dividing into a case for recording or reproducing a recording medium having a cover layer and a case for recording or reproducing a recording medium without a cover layer. In addition, the tilting error signal from which the DC offset component is removed according to the movement of the objective lens during the servo control operation can be detected, so that a more accurate servo operation can be performed.

The optical recording / reproducing apparatus and the recording / reproducing method according to the present invention can maintain the distance between the SIL and the recording medium appropriately, thereby preventing damage to the SIL.

In addition, the optical recording / reproducing apparatus and the recording / reproducing method according to the present invention can respond sensitively to the tilt angle or skew of the recording medium.

In addition, the tilting error signal from which the DC offset component is removed can be detected, so that a more accurate servo operation can be performed.

Claims (10)

An actuator provided with an objective lens for causing the first light to enter the recording medium and the solid immersion lens (SIL); First photoelectric means for generating the first light and detecting a first servo signal from the signal reflected by the SIL, and third photoelectric means for detecting an electrical signal from the RF signal reflected from the recording medium; A first optical system having; And And a second optical system having second photoelectric means for generating a second light and detecting a second servo signal from the signal reflected by the SIL. The method of claim 1, And the first servo signal includes tilting information of the recording medium, and the second servo signal includes information about the amount of movement of the actuator. The method of claim 1, And the first servo signal includes information on the movement amount of the actuator, and the second servo signal includes tilting information of the recording medium. The method of claim 1, And detection means for measuring a tilting error signal of the recording medium by using servo signals detected by the first photoelectric means and the second photoelectric means. First photoelectric means provided in a first optical system for generating a first light for recording or reproducing data, and for detecting a first servo signal; Second photoelectric means provided in a second optical system for generating a second light, said second photoelectric means for detecting a second servo signal; Detecting means for detecting a tilting error signal of the recording medium by using the first servo signal and the second servo signal; And And an actuator for forming the objective lens and the SIL to allow the first light to enter the recording medium, and to be driven by a control signal according to the detection means. The method of claim 5, An optical recording / reproducing apparatus, wherein one of the first and second servo signals includes information on the tilting amount of the recording medium, and the other includes information about the moving amount of the objective lens. . Loading the recording medium; In a servo operation for recording or reproducing data, a first light is incident on the objective lens and the SIL, and a first servo signal is detected by the first photoelectric means from the first light reflected by the SIL; Detecting a second servo signal from a second light reflected by the SIL by a second photoelectric means; And And detecting a tilting error signal of the recording medium using the first servo signal and the second servo signal. The method of claim 7, wherein And the first servo signal or the second servo signal includes information on the amount of tilt of the recording medium. The method of claim 7, wherein And the first servo signal or the second servo signal includes information on the amount of movement of the objective lens according to the servo operation. In the servo control operation by the movement of the objective lens during recording or reproducing of data, Detecting the first servo signal by the first photoelectric means for detecting the tilting amount of the recording medium; Detecting a second servo signal by second photoelectric means for detecting the movement amount of the objective lens; And the movement amount information of the objective lens included in the tilt detection amount of the recording medium is removed using the first servo signal and the second servo signal.

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