KR20060126800A - Optical device for recording and reproducing - Google Patents

Abstract

The invention relates to an optical scanning device for scanning an information carrier (12) comprising tracks. The optical scanning device comprises a fixed part (10) with a radiation source (101) and means for compensating for spherical aberration (104), and a movable part (11) comprising a folding mirror (111) and an objective lens (112). The optical scanning device comprises first moving means for moving the movable part (11) in a cross track direction in a track selection mode, and second moving means for moving the objective lens (112) in a cross track direction in a fine tracking mode and for moving the folding mirror (111) in the fine tracking mode such that the folding mirror (111) substantially follows the objective lens (112).

Description

Optical device for recording and playback {OPTICAL DEVICE FOR RECORDING AND REPRODUCING}

The present invention relates to an optical scanning device having means for scanning an information carrier with tracks and for compensating spherical aberration.

The present invention is particularly suitable for optical disc devices, such as CD, DVD and / or Blu-ray Disc (BD) recorders and players, which record and read to optical discs.

Many optical scanning devices require a means to compensate for spherical aberration. In practice, the information carrier is often scanned by the optical scanning device through the transparent layer protecting the information layer. Small variations in the thickness of the transparent layer cause a significant change in spherical aberration due to the high aperture radiation beam passing through the transparent layer. Spherical aberration compensation is also necessary for scanning multilayer information carriers, as the spacer layer between the two layers generates spherical aberration when jumping from one layer to another. In addition, spherical aberration compensation is also required for scanning various kinds of information carriers having various cover layer thicknesses.

Various spherical aberration compensation means are known. The first example is a liquid crystal cell disposed in the light path. Spherical aberration is introduced into the radiation beam in that the refractive index of the liquid crystal cell is locally changed by applying a voltage across the liquid crystal cell. A second example is a compensating plate placed between two lenses. When it is necessary to introduce spherical aberration to the radiation beam, a compensation plate is placed in the optical path, while when spherical aberration is not necessary, the compensation plate is mechanically removed from the optical path. Other examples such as birefringent replicated polymer phase plates are also known.

Moreover, many optical scanning devices often require the use of split optics. The optical scanning device using the splitting optical device includes, in particular, a fixing part including a radiation source, and a movable part including a folding mirror and an objective lens. The use of split optics simplifies optical scanning and increases radiation source life as heat sinks can be placed in the vicinity of the radiation source when the radiation source is fixed.

An optical scanning device which implements a split optical device and includes means for compensating spherical aberration, has a fixing part having a radiation source and spherical aberration compensating means, and a movable part including a folding mirror and an objective lens. The optical scanning device further includes means for moving the movable portion in the track crossing direction to achieve track selection. In addition, the optical scanning device further provides a means for achieving fine tracking by moving the objective lens in the track crossing direction to ensure that the radiation beam remains focused on the track regardless of the eccentricity of the information carrier. Equipped.

However, the applicant has found that in such an optical device, a large amount of coma aberration occurs during tracking.

After all, it is an object of the present invention to provide an optical scanning device having a splitting optic and a means for compensating spherical aberration, which can reduce the amount of coma aberration during tracking.

To achieve the above object, the present invention provides an optical scanning device for scanning an information carrier including tracks, comprising: a fixing unit having a radiation source and spherical aberration compensation means, and a movable unit including a folding mirror and an objective lens. First moving means for moving the movable part in a track crossing direction in a track selection mode, and moving the objective lens in a track crossing direction in a fine tracking mode and the folding mirror to follow the objective lens in the fine tracking mode. An optical scanning device having a second moving means for moving a folding mirror is provided.

Applicants have found that coma aberration occurs during tracking due to the fact that the center of the means for compensating spherical aberration does not remain aligned with the center of the objective lens in the optical path. According to the present invention, the radial position of the folding mirror with respect to the radial position of the objective lens is always kept the same. The radial position is the position in the track cross direction. According to this, the center of the spherical aberration compensating means is maintained in alignment with the center of the objective lens. Thus, coma aberration is eliminated during tracking.

In the first embodiment, the second moving means is configured to move the movable portion in the fine tracking mode. According to this embodiment, no radial actuator is used to move the folding mirror or the objective lens. The movable part itself moves during tracking. Therefore, the optical scanning device is relatively simple.

In a second embodiment, the second moving means includes a first actuator for moving the objective lens and a second actuator for moving the folding mirror. This embodiment is preferred when the movable portion cannot move during tracking, which may be the case when the weight supported by the movable portion is too large.

Preferably, the optical scanning device further comprises means for detecting the position of the objective lens and means for transmitting a signal indicating the position to the second actuator. Such a configuration makes it possible to control the radial position of the folding mirror with respect to the radial position of the objective lens with relatively high precision.

Preferably, the first and second actuators are controlled by the same tracking signal. In this case, since the means for detecting the position of the objective lens is not necessary, the optical scanning value is simplified.

The above and other inventions of the present invention will become more apparent with reference to the following examples.

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

1 shows an optical scanning device according to the prior art,

FIG. 2 shows a part of the optical scanning device shown in FIG. 1 during tracking;

3 shows an optical scanning device according to a first embodiment of the present invention,

4 shows an optical scanning device according to a second embodiment of the present invention.

The optical scanning device according to the prior art is illustrated in FIG. 1. This optical scanning device includes a fixed portion 10 and a movable portion 11. The fixing unit 10 includes a radiation source 101, a beam splitter 102, a collimating lens 103, a spherical aberration compensating unit 104, a servo lens 105, and a detecting unit 106. The movable portion 11 includes a folding mirror 111 and an objective lens 112. This optical device is intended to scan the information carrier 12.

During the scanning operation, which may be a writing operation or a reading operation, the information layer 12 is scanned by the radiation beam generated by the radiation source 101. The collimating lens 103 and the objective lens 112 focus the radiation beam on the information layer of the information carrier 12. In response to an error in positioning of the radiation beam on the information layer, a focus error signal may be detected. Such a focus error signal is detected by the detection means 106 and used to correct the axial position of the objective lens 112 to compensate for the focus error of the radiation beam. For this purpose, the controller drives the actuator to move the objective lens 112 in the axial direction, i.e., in the amount of movement indicated by F perpendicular to the information carrier.

The information carrier comprises tracks on which data is recorded. In order to scan a constant track, a radiation beam must be focused on the constant track. For this purpose, the movable portion 11 moves in the track crossing direction with the movement amount indicated by S, so that the radiation beam reaches the desired track. This corresponds to a track selection mode in which the movable portion moves in the track crossing direction until the radiation beam is focused on the desired track. Once the radiation beam is in focus on the desired track, the radiation beam must remain focused on the track during rotation of the information carrier 12. However, the information carrier is eccentric. Thus, the objective lens 12 moves so that the radiation beam remains in focus on the track. This corresponds to a tracking mode in which the objective lens moves in the track crossing direction with the movement amount indicated by T so that the radiation beam remains focused on the desired track.

The movable part is moved using a normal linear motor in track selection mode, while the objective lens is moved using a normal actuator in tracking mode. The actuator is controlled by a tracking signal that indicates the difference between the position of the radiation beam and the center of the track. Track selection and tracking are known to those skilled in the art and will not be described in further detail.

2 shows a part of an optical scanning device according to the prior art in a tracking mode. As shown in FIG. 2, the displacement of the objective lens 112 during tracking leads to the fact that the center of the spherical aberration compensating means 104 in the optical path does not remain aligned with the center of the objective lens 12. . This would not occur without the spherical aberration compensation means 104. In practice, the generation of coma aberration is due to the introduction of wavefront aberration inside the radiation beam by the spherical aberration compensation means 104 and the combination of the center shift of the objective lens 112 with respect to the spherical aberration compensation means 104. .

The optical scanning device according to the first embodiment of the present invention is illustrated in FIG. 3. In the drawings, the same reference numerals as the reference numerals of FIG. 1 mean the same components. According to this first embodiment, the folding mirror 111 and the objective lens 112 are attached to the movable part 11, so that radial displacement between the eastern part 11 and the objective lens 112 is not possible. This means that, as compared to the conventional optical scanning device, the optical scanning device of Fig. 3 does not have a radial actuator for moving the objective lens in the track crossing direction during tracking. Instead, the moving unit 11 is moved in the track crossing direction by the movement amount T using the moving means during tracking. This moving means may be the moving means used to move the movable part 11 in the track crossing direction in the track selection mode. For example, the linear motor used to move the movable part 11 in the track selection mode may be used in the tracking mode. Such a linear motor must have a relatively large stroke for moving the movable part 11 during track selection and a relatively high bandwidth for moving the movable part 11 in the tracking mode. Alternatively, the moving means used to move the movable part 11 in the tracking mode may be provided with a one-dimensional radial actuator. Examples of suitable one-dimensional actuators include linear electromagnetic actuators and piezoelectric ceramic actuators well known to those skilled in the art. Such a one-dimensional radial actuator should have a relatively high bandwidth for moving the movable part 11 in the tracking mode. This is possible in an optical scanning device using a splitting optical device in which the total weight of the movable portion is relatively low compared to the total weight of the trolley of the optical device not using the splitting optical device.

According to the first embodiment, since only the objective lens 112 and the folding mirror 111 can move in the radial direction together with the movable part 11, the radial position of the folding mirror 11 is the radius of the objective lens 112. It always stays the same for the position of the direction. Therefore, in the optical scanning device according to the first embodiment of the present invention, the center shift that occurs during tracking in the prior art as shown in FIG. 2 no longer occurs. As a result, according to the first embodiment of the present invention, coma aberration does not occur during tracking.

At this time, it should be noted that the optical scanning device according to the first embodiment of the present invention is simpler than the optical scanning device according to the prior art. In the optical scanning device of the prior art, a two-dimensional actuator is attached to the movable portion 11 to move the objective lens 112 in respective movement amounts F and T. In the optical scanning device according to the first embodiment, one-dimensional An actuator is attached to the movable portion 11 to move the objective lens to the moving amount F. FIG. One-dimensional actuators are simpler, smaller in volume and less expensive than two-dimensional actuators.

The optical scanning device according to the second embodiment of the present invention is illustrated in FIG. In this figure, the same reference numerals as those of Fig. 1 denote the same components. According to a second embodiment, the movable portion 11 has first and second actuators not shown in FIG. 4. The first actuator is designed to move the objective lens 112 in the track crossing direction with the movement amount T1 in the tracking mode, and the second actuator is designed to move the folding mirror 111 in the track crossing direction with the movement amount T2 in the tracking mode. Alternatively, another one-dimensional actuator may be used to move the objective lens 112 to the movement amount F. FIG.

According to a second embodiment of the invention, the movements T1 and T2 are almost identical. Therefore, the radial position of the folding mirror 111 always remains almost the same with respect to the radial position of the objective lens 112. In the prior art, the center shift that occurs during tracking does not occur or affect the optical scanning device according to the second embodiment of the present invention. As a result, according to the second embodiment of the present invention, coma aberration does not occur during tracking.

In order to ensure that the movement amount T2 is about the same as the movement amount T1, that is, the folding mirror 11 follows the radial movement of the objective lens during tracking, the first method is to determine the radial position of the objective lens 112 during tracking. It consists of measuring steps. According to the measured position relative to the position of the folding mirror 111, a signal is transmitted to the actuator to move the folding mirror 111 until the folding mirror reaches the same radial position as the objective lens 112. The folding mirror moves.

The second method consists in controlling the second actuator using the same signal as the signal controlling the first actuator. As described in FIG. 1, a conventional optical scanning device has means for generating a tracking signal, which is sent to an actuator to move the objective lens during tracking by moving the objective lens. This tracking signal indicates the difference between the position of the radiation beam and the center of the track. This tracking signal is obtained using the so-called three-spot push-pull tracking method, for example. When the actuator for moving the folding mirror 111 is controlled by the same signal as the actuator for moving the objective lens 112, the folding mirror 111 has the same amount of movement as the objective lens 112.

Reference signs in the appended claims should not be construed as limiting the claim. It is obvious that the use of the verbs "comprise", "comprises" and their conjugations does not exclude the presence of components other than those described in the claims. The word "a" or "an" in front of a component does not exclude the presence of such a plurality of components.

Claims (5)

An optical scanning device for scanning an information carrier (12) comprising tracks, comprising: a fixed portion (10) having a radiation source (10) and spherical aberration compensation means (104), a folding mirror (111), and an objective lens (112) And a first moving means for moving the movable part 11 in a track crossing direction in a track selection mode, and moving the objective lens 112 in a track crossing direction in a fine tracking mode. And a second moving means for moving the folding mirror (111) in the fine tracking mode so that the folding mirror (111) follows the objective lens (112). The method of claim 1, And the second moving means is configured to move the movable part (11) in the fine tracking mode. The method of claim 1, And said second moving means comprises a first actuator for moving said objective lens and a second actuator for moving said folding mirror. The method of claim 3, wherein Means for detecting the position of the objective lens (112) and means for transmitting a signal indicating the position to the second actuator. The method of claim 3, wherein And the first and second actuators are controlled by the same tracking signal.

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