KR20030078215A - Opticak pickup - Google Patents

Abstract

PURPOSE: An optical pickup is provided to erase astigmatism due to the structure of a semiconductor layer by installing an astigmatism correcting element, thereby detecting a reproduction signal having an excellent jitter characteristic. CONSTITUTION: A first semiconductor laser(11) and a second semiconductor laser(12) emit first beams(11a) and second beams(12a) having a wavelength respectively appropriate for a first optical disk(10a) and a second optical disk(10b) different in thickness. An objective lens(18) focuses the beams to be formed at an optical spot on recording surfaces of the optical disks. A photo detector(20) receives and detects the beams reflected from the recording surfaces of the optical disks. An astigmatism correcting element(15) erases astigmatism due to at least one of the first and second semiconductor lasers.

Description

Optical pickup {Opticak pickup}

The present invention relates to an optical pickup, and more particularly, to an optical pickup capable of removing astigmatism of a semiconductor laser.

In general, jitter during information signal reproduction of an optical disc becomes smaller as the aberration of light focused on the optical disc becomes smaller. When jitter is irradiated with light to read pits (or marks) formed along tracks on the optical disc, jitter increases when the pits are not properly formed or the shape of the irradiated light spot is asymmetric. Say.

The aberration included in the optical spot irradiated on the optical disk has a great influence on this jitter. As the aberration increases, light is focused asymmetrically when light spots are formed on the optical disc. If this asymmetric light spot reads through the pit of an optical disc, the jitter becomes very bad.

Therefore, it is common to design an optical pickup in which optical spots are formed on the optical disc, and the light reflected from the optical disc is detected and used to reproduce the information signal of the optical disc so that the aberration is included as little as possible in the optical spot formed on the optical disc. For example, the objective lens is designed such that the aberration generated when the parallel light is incident as small as possible.

By the way, even though the optical elements constituting the optical pickup are optimally designed for aberration, a semiconductor laser (edge emitting semiconductor laser) having a general structure as a light source (FIG. 1 is a structure of a general semiconductor laser) is used. In the case of employing the jitter, jitter increases due to astigmatism caused by the light source structure itself, which becomes relatively more difficult than when there is no aberration at the time of detecting the reproduction signal. Here, the jitter signal is better the smaller the aberration.

Referring to FIG. 1, in general, the shape of the laser light emitted from the active layer 3 of the semiconductor laser 1 maintains an elliptical shape. In other words, the semiconductor laser 1 emits a laser light beam having an elliptical cross section. This is because the thickness (vertical direction size) and the width (horizontal direction size) of the active layer 3 are different from each other.

Due to the structural characteristics of the active layer 3, the vertical and horizontal diffraction angles of the light emitted from the semiconductor laser 1 are different from each other, so that the spreading angles of the light in the horizontal direction and the light in the vertical direction are different from each other. The light in the direction appears to be emitted at a position entered by ΔZ relative to the light in the vertical direction. The distance difference ΔZ between the starting point of the light in the vertical direction and the light in the horizontal direction according to the spreading degree is defined as a non-point difference.

Generally, the light emitted from the semiconductor laser 1 due to the above astigmatism includes astigmatism of 5 to 10 mu m.

1 is the spreading angle in the horizontal direction, and? Is the spreading angle in the vertical direction.

This astigmatism caused by the structural characteristics of the semiconductor laser 1 increases jitter and makes the reproduction signal detection worse.

The present invention has been made to solve the problems described above, and has an optical configuration capable of canceling astigmatism caused by the structure of a semiconductor laser, and provides an optical pickup that can improve jitter signals as compared with the prior art. Its purpose is to.

1 is a perspective view schematically showing a semiconductor laser emitting laser light to the side surface,

2 is a view schematically showing an example of an optical configuration of an optical pickup according to a first embodiment of the present invention;

3 is a view schematically showing an example of an optical configuration of an optical pickup according to a second embodiment of the present invention;

4 is a view for explaining a principle of eliminating astigmatism by a semiconductor laser, having a plate-shaped beam splitter used as an astigmatism correction element in an optical pickup according to the present invention;

Fig. 5 is a graph showing a change in astigmatism amount according to the inclination? Of a plate-shaped beam splitter having a thickness t = 0.7 mm made of an optical medium (glass material) having a refractive index n = 1.5111 with respect to a wavelength of 780 nm.

<Description of Symbols for Main Parts of Drawings>

10,30 ... optical disk 10a ... DVD-based optical disc

10b ... CD series optical discs 11,12 ... first and second semiconductor lasers

11a, 12a ... first and second light 14, 34 ... optical path conversion device

15,35 ... astigmatism correction element 18, 38 ... objective lens

20.Photodetector

According to an aspect of the present invention, there is provided an optical pickup comprising: first and second semiconductor lasers emitting first and second light having wavelengths suitable for first and second optical disks having different thicknesses; An objective lens for condensing the light emitted from the first and second semiconductor lasers to form an optical spot on the recording surface of the optical disk; A photodetector for receiving and detecting the light reflected from the recording surface of the optical disk; And astigmatism correction elements for canceling astigmatism caused by at least one of the first and second semiconductor lasers.

Here, one of the first and second optical discs is preferably a DVD-based optical disc, and the other is a CD-based optical disc.

The astigmatism correcting element is used as a first optical path conversion device to cancel astigmatism caused by the second semiconductor laser and to convert a traveling path of the first light emitted from the first semiconductor laser, and the second semiconductor laser And a second optical path changing device for converting a traveling path of the second light emitted from the second optical path.

The first light emitted from the first semiconductor laser is reflected by the astigmatism correcting element and travels toward the objective lens, and the second light emitted by the second semiconductor laser is reflected by the second optical path conversion device. And an optical arrangement passing through the astigmatism correction element and traveling toward the objective lens.

Preferably, the astigmatism correcting element is a plate-shaped beam splitter arranged to cancel astigmatism included in the second light transmitted therethrough.

Alternatively, the astigmatism correcting element may be arranged to cancel astigmatism included in the light while transmitting at least one of the first and second light emitted from the first and second semiconductor lasers. It is preferable that it is a type | mold beam splitter.

In order to achieve the above object, the present invention provides an optical pickup for irradiating light emitted from a semiconductor laser to an optical disc, detecting light reflected from the recording surface of the optical disc, and reproducing information recorded on the optical disc. It characterized in that it comprises a; astigmatism correction element for canceling astigmatism by.

Here, the astigmatism correcting element is preferably a plate-shaped beam splitter arranged to cancel astigmatism while transmitting light incident from the semiconductor laser.

It is preferable that the optical disc is any one of a DVD-based optical disc and a CD-based optical disc.

Hereinafter, with reference to the accompanying drawings, a preferred embodiment of the optical pickup according to the present invention will be described in detail.

2 is a view schematically showing an optical configuration of an optical pickup according to a first embodiment of the present invention.

Referring to the drawings, in the optical pickup according to the first embodiment of the present invention, the first and second optical disks 10a and 10b having different thicknesses can be used interchangeably, and the first and second optical disks ( First and second semiconductor lasers 11 and 12 that emit first and second light 11a and 12a of wavelengths suitable for 10a and 10b, respectively, and the first and second semiconductor lasers 11 An objective lens 18 for focusing the first and second lights 11a and 12a emitted from the 12) to form an optical spot on the recording surface of the optical disk 10, and on the recording surface of the optical disk 10. A photodetector 20 for receiving and detecting the reflected light and astigmatism correcting element 15 for canceling astigmatism by at least one of the first and second semiconductor lasers 11 and 12; It is composed.

The first optical disk 10a is, for example, a DVD-based optical disk having a relatively thin thickness, and the second optical disk 10b is, for example, a CD-based optical disk having a relatively thick thickness. In this case, the first semiconductor laser 11 may include a semiconductor laser that emits the first light 11a having a wavelength suitable for the first optical disk 10a, for example, a 650 nm wavelength, and emits laser light to the side. have. In addition, the second semiconductor laser 12 may include a semiconductor laser that emits a second light 12a having a wavelength of 780 nm suitable for the second optical disk 10b and emits laser light to the side.

FIG. 2 includes an optical path changing device 14 for converting a traveling path of the second light 12a emitted from the second semiconductor laser 12 to the optical pickup according to the first embodiment of the present invention. The score difference correcting element 15 cancels astigmatism caused by the second semiconductor laser 12 and shows an example used as an optical path changing device for converting a traveling path of the light emitted from the first semiconductor laser 11.

That is, in the optical pickup according to the first embodiment of the present invention, as shown in FIG. 2, the second light 12a emitted from the second semiconductor laser 12 is incident on the optical path conversion device 14. The first light 11a that is reflected, passes through the astigmatism correcting element 15 and proceeds toward the objective lens 18, and is emitted from the first semiconductor laser 11 and is incident on the astigmatism correcting element 15. ) And may have an optical arrangement that is reflected toward the objective lens 18.

As described above, astigmatism that functions as an optical path conversion device with respect to the first light 11a emitted from the first semiconductor laser 11 and also eliminates astigmatism by the second semiconductor laser 12 The correction element 15 includes a plate-shaped beam splitter disposed inclined with respect to the optical axis so as to generate astigmatism opposite to astigmatism included in the second light 12a incident from the second semiconductor laser 12. Can be. Since the plate-shaped beam splitter is arranged inclined with respect to the optical axis, it causes astigmatism in the transmitted light.

On the other hand, it is also possible to include a plate type beam splitter as the optical path changing device 14 for converting the traveling path of the second light 12a.

As described above, when the astigmatism correction element 15 functions to cancel astigmatism caused by the structure of the second semiconductor laser 12, the second optical disc 10b, for example, when playing a CD-based optical disc, Compared with the jitter, a reproduction signal with better jitter can be detected.

On the other hand, as described above, when the plate-type beam splitter is provided with at least one of the optical path conversion device 14 and the astigmatism correction element 15, including the astigmatism correction element 15, the optical disk 10 of the The first and second lights 11a and 12a, which are reflected on the recording surface and via the objective lens 18, generate astigmatism while passing through the optical path changing device 14 and the astigmatism correcting element 15. 20 is received. This is because, as mentioned above, the plate-shaped beam splitter causes astigmatism in the transmitted light.

Therefore, when the plate-type beam splitter is included in at least one of the optical path conversion device 14 and the astigmatism correction element 15 including the astigmatism correction element 15, the focus error signal by the astigmatism method is applied. There is an advantage that it is not necessary to have a separate optical element for causing astigmatism in the light received toward the photodetector 20 to detect.

Here, in the optical pickup according to the first embodiment of the present invention, the astigmatism correction element 15 functions to cancel the astigmatism by the first semiconductor laser 11 and at the same time the second semiconductor laser 12 It is used as an optical path conversion device for converting the traveling path of the second light 12a emitted from the optical path, the optical path conversion device 14 is the travel of the first light (11a) emitted from the first semiconductor laser 11 It may also be an optical arrangement for converting paths.

In addition, the optical pickup according to the first embodiment of the present invention, the first and second light (11a) emitted from the first and second semiconductor laser (11) 12, apart from the astigmatism correction device (15) And optical path changing devices for converting the traveling path of 12a), and the astigmatism correcting element 15 cancels both astigmatisms by the first and second semiconductor lasers 11 and 12. In this case, the erase amount may be different).

In addition, in the optical pickup according to the first embodiment of the present invention, the first and second optical discs 10a and 10b having different thicknesses may be interchangeably employed, and the astigmatism correction element 15 may be used as the first and second optical discs 10a and 10b. While having an optical configuration that functions to cancel astigmatism by at least one of the second semiconductor lasers 11 and 12, the overall optical configuration can be variously modified.

On the other hand, the optical pickup according to the first embodiment of the present invention is the first and second semiconductor laser 11, 12 (12) on the optical path between the first and second semiconductor laser (11) 12 and the objective lens 18 It may further include a collimating lens 17 for converting the divergent light emitted from the radiation angle with approximately parallel light. When the structure having the collimating lens 17 as shown in Figure 2, the objective lens 18 includes an objective lens designed for parallel incident light.

Further, the optical pickup according to the first embodiment of the present invention is different from the second semiconductor laser 12 so that the tracking error signal can be detected by the 3-beam method during recording / reproducing of the CD-based second optical disc 10b. A grating 13 may be further provided between the score difference correcting elements 15 to branch the incident light into the 0th order and the ± 1th order. Here, the tracking error signal during recording / reproducing of the DVD-based first optical disc 10a uses a differential phase detection (DPD) method, as is well known in the art.

In addition, the optical pickup according to the first embodiment of the present invention preferably further includes a concave lens 19 coupled with the collimating lens 17 to enlarge the size of the light spot received by the photodetector 20. Do. This concave lens 19 is commonly referred to as a Yo-lens, and as shown in Fig. 2, when the optical path changing device 14 is provided with a plate type beam splitter, the plate type beam splitter is inclined. In order to remove the coma aberration caused by the it is preferable that the inclined opposite to the plate-shaped beam splitter.

In FIG. 2, reference numeral 16 denotes a reflection mirror.

The optical pickup according to the first embodiment of the present invention as described above is capable of adopting a plurality of types of optical disks having different thicknesses, and canceling astigmatism caused by a semiconductor laser used as a light source. 15, it is possible to detect a reproduction signal having a smaller jitter than the conventional one for the first and / or second optical discs 10a and 10b.

3 shows an optical configuration of an optical pickup according to a second embodiment of the present invention, which is characterized in that it comprises a single semiconductor laser 31 and an astigmatism correcting element 15. In FIG. 3, the same reference numerals as used in FIG. 2 denote members having substantially the same or similar functions, and thus detailed description thereof will be omitted.

Referring to FIG. 3, an optical pickup according to a second exemplary embodiment of the present invention includes a single semiconductor laser 31 for emitting laser light to a side surface and an optical path for converting a propagation path of light emitted from the semiconductor laser 31. The conversion device 34, the objective lens 38 for condensing the light emitted from the semiconductor laser 31 to form an optical spot on the recording surface of the optical disk 30, and the reflection surface reflected from the recording surface of the optical disk 30. And a photodetector 20 for receiving and detecting light, and an astigmatism correcting element 35 for canceling astigmatism by the semiconductor laser 31.

The semiconductor laser 31 may include, for example, a semiconductor laser 31 that emits light having a wavelength of 650 nm or 780 nm.

When the optical pickup according to the second embodiment of the present invention is a DVD-based optical disc playable type (including a CD-based optical disc compatible type), the semiconductor laser 31 is approximately 650 nm (or 635 nm or 480 nm (blue laser)). It is preferable to be able to emit light of a wavelength.

When the optical pickup according to the second embodiment of the present invention is for an optical disc of CD series, the semiconductor laser 31 preferably emits light having a wavelength of about 780 nm.

The astigmatism correcting element 35 is arranged to cancel astigmatism included in the light while transmitting the light emitted from the semiconductor laser 31. The astigmatism correcting element 35 may be provided with a plate-like beam splitter as in the previous embodiment.

In addition, the optical path changing device 34 may include a plate type beam splitter.

As in the second embodiment of the present invention shown in FIG. 3, the plate-type beam splitter is connected to at least one of the astigmatism correcting element 35 and the optical path changing device 34 including the astigmatism correcting element 35. In the case of adopting the same method, the astigmatism is generated in the light reflected and incident on the recording surface of the optical disk 30, so that the focus error signal by the astigmatism method can be obtained without an optical element generating the astigmatism. There is an advantage that can be detected.

Here, in the optical pickup according to the second embodiment of the present invention, the light emitted from the semiconductor laser 31 passes through the astigmatism correcting element 35 toward the optical disk 30, and on the recording surface of the optical disk 30, The reflected light may have an optical configuration in which the reflected light is reflected by the astigmatism correcting element 35 and received by the photodetector 20. In this case, the astigmatism correcting element 35 can function as an optical path changing device for canceling astigmatism by the semiconductor laser 31 and at the same time converting a traveling path of the light emitted from the semiconductor laser 31. have. Therefore, in this case, the optical pickup according to the second embodiment of the present invention is an astigmatism correcting element 35 instead of the configuration including the optical path changing device 34 and astigmatism correcting element 35 shown in FIG. It may have an optical configuration having only). In this case, however, light reflected from the recording surface of the optical disc 30 and incident on the astigmatism correcting element 35 is reflected by the astigmatism correcting element 35 and directed toward the photodetector 20, thereby correcting the astigmatism. Since the element 35 does not generate astigmatism for detecting the focus error signal by the astigmatism method, for example, when the focus error signal is to be detected by the astigmatism method, astigmatism is generated separately. It is preferable to further include an astigmatism lens (not shown) or to detect the focus error signal using a beam-size measurement method.

On the other hand, when the optical pickup according to the second embodiment of the present invention is a CD-based optical disc recording and / or reproducing type, the tracking error signal can be detected by the three-beam method so that the semiconductor laser 31 and the optical path conversion can be detected. On the light path between the devices 34, it is desirable to further include gratings (not shown).

As described above, the optical pickup according to the second embodiment of the present invention includes a single semiconductor laser 31 and an astigmatism correction device 35 having a function of canceling astigmatism by the semiconductor laser 31. With the configuration provided, the overall optical configuration can be variously modified.

In the optical pickup according to the embodiments of the present invention as described above, the astigmatism correction device is provided with a plate-shaped beam splitter to cancel astigmatism.

Referring to FIG. 4, the astigmatism amount generated by the plate-shaped beam splitter 50 when the plate-shaped beam splitter 50 used as the astigmatism correcting element is inclined by θ with respect to the optical axis c of the incident light. ΔA can be represented as in Equation 1.

In Equation 1, t is the thickness of the plate-shaped beam splitter 50, n is the refractive index of the optical medium constituting the plate-shaped beam splitter 50.

For example, when the plate-shaped beam splitter 50 having a thickness t = 0.7 mm made of an optical medium (glass material) having a refractive index n = 1.5111 for a wavelength 780 nm is inclined with respect to the optical axis c by θ = 18.5 °, The score difference ΔA = −28 μm can be obtained. 5 is a graph showing a change in astigmatism amount according to the inclination θ of the plate-shaped beam splitter 50 having a thickness t = 0.7 mm as described above. The graph of FIG. 5 is obtained using Equation 1.

As can be seen from the description with reference to equations (1), (4) and (5), changing the inclination and / or thickness (t) with respect to the optical axis (c) of the plate-shaped beam splitter 50, the plate-like The astigmatism amount generated in the light passing through the beam splitter 50 can be changed.

Therefore, due to the structure of the semiconductor laser employed as the light source in the optical pickup according to the present invention, the plate type functions as an astigmatism correction element on the optical path so as to cancel the astigmatism contained in the light emitted from the semiconductor laser. When the beam splitter 50 is arranged to generate astigmatism in a direction opposite to that caused by the semiconductor laser, it is possible to detect a reproduction signal having excellent jitter.

Since the optical pickup according to the present invention as described above includes an astigmatism correcting element, it is possible to cancel astigmatism due to the structure of the semiconductor laser, so that a reproduction signal having excellent jitter characteristics can be detected.

Claims (9)

First and second semiconductor lasers emitting first and second light having wavelengths suitable for the first and second optical disks having different thicknesses, respectively; An objective lens for condensing the light emitted from the first and second semiconductor lasers to form an optical spot on the recording surface of the optical disk; A photodetector for receiving and detecting the light reflected from the recording surface of the optical disk; And an astigmatism correction device for canceling astigmatism caused by at least one of the first and second semiconductor lasers. The optical pickup of claim 1, wherein one of the first and second optical discs is a DVD-based optical disc, and the other is a CD-based optical disc. The first optical path conversion device according to claim 1 or 2, wherein the astigmatism correcting element cancels astigmatism caused by the second semiconductor laser and converts a traveling path of the first light emitted from the first semiconductor laser. Used as a device, And a second optical path changing device for converting a traveling path of the second light emitted from the second semiconductor laser. The method of claim 3, wherein the first light emitted from the first semiconductor laser and incident is reflected by the astigmatism correcting element and travels toward the objective lens, and the second light emitted from the second semiconductor laser is incident to the objective lens. 2. An optical pickup having an optical arrangement reflected from a two-path conversion device and passing through the astigmatism correcting element toward the objective lens. The optical pickup according to claim 4, wherein the astigmatism correcting element is a plate-shaped beam splitter arranged to cancel astigmatism included in the transmitted second light. The astigmatism correction device according to claim 1 or 2, wherein the astigmatism correction element transmits at least one of the first and second light emitted from the first and second semiconductor lasers and is included in the light. And a plate-shaped beamsplitter arranged to cancel the score difference. In an optical pickup in which light emitted from a semiconductor laser is irradiated to an optical disc, the light reflected from the recording surface of the optical disc is detected, and information recorded on the optical disc is reproduced. And astigmatism correction elements for canceling astigmatism caused by the semiconductor laser. The optical pickup according to claim 7, wherein the astigmatism correcting element is a plate-shaped beam splitter arranged to cancel astigmatism while transmitting light incident from the semiconductor laser. The optical pickup of claim 7 or 8, wherein the optical disc is any one of a DVD-based optical disc and a CD-based optical disc.