KR20030072029A - Method for control grating - Google Patents

Abstract

PURPOSE: A method for adjusting gratings is provided to remove an error generated in three laser beams disassembled in the gratings by rotating or moving the grating used in an optical pickup. CONSTITUTION: A beam emitted from a first laser diode(31) or a second laser diode(33) is dissembled into a main laser beam and two sub-laser beams by using a first grating(32a) or a second grating(32b). The disassembled beams pass through optical systems used in an optical pickup. A reflective beam reflected from an optical disk(50) is formed on a photo diode of a detector(39). The gratings are rotated or moved forward and backward following an optical axis to focus the main laser beam and the two sub-laser beams reflected from the optical disk to a center four-division photo diode, and upper and lower four-division photo diodes arranged on the detector.

Description

How to adjust grating {METHOD FOR CONTROL GRATING}

The present invention relates to an optical pickup, and more particularly, by moving the grating used in the optical pickup along a rotation or optical axis, not only to eliminate the error of the reflected light received by the detector, but also to perform a stable servo operation. It relates to a grating adjustment method.

Today, the storage medium is changing from tape to disk due to the digitalization and large capacity of data, and the disk storage capacity is increased by increasing the recording density for storing data on the disk. Doing. Therefore, in a compact disk (CD) in which a laser diode used as a light source has a wavelength of 780 nm, in recent years, disks suitable for wavelengths of 650 nm and 400 nm have been developed for the purpose of large capacity. Accordingly, the optical pickup apparatus for recording and reproducing information on the disk constitutes a plurality of optical systems for a plurality of light sources having different wavelengths so that they can be simultaneously applied to disks having different storage densities in terms of backward compatibility.

In addition, a compact disk (CD), which is widely known as a recording medium, has a substrate thickness of 1.2 mm and has a reflecting surface on which light reflects as a recording layer and is a combination of pits formed concave on the reflecting surface. It stores information such as sound, text and graphics. In addition, digital video disks (DVDs) having a high-density storage of a large amount of video information and having a substrate thickness of 0.6 mm have also emerged. Unlike CD, optical pickup for DVD uses a short wavelength light source and focuses light with an objective lens having a large numerical aperture (NA) to form a micro spot for high density reproduction.

On the other hand, in recent years, a phase change disk (CD-R) has been put into practical use as a recording medium that can only be recorded once and then reproduced. The substrate thickness is the same as that of the above-described CD, and only the pit of the CD is used as the recording layer. Unlike), it is made of a phase change material in which the reflectances of the recording wavelength and the reproduction wavelength in the specific wavelength band are changed. Such a CD-R is recordable and reproduced in the same optical pickup environment as that of a CD.

As a result of the appearance of discs of different thicknesses or recording materials, a compatible optical pickup of such discs is required from the user's point of view. In accordance with such a requirement, a conventional optical pickup compatible with DVD and CD has been provided. Conventionally known DVD and CD compatible optical pickups generally use one short wavelength (650 nm) light source and have a means for adjusting the numerical aperture of the objective lens according to the thickness of the disc to be reproduced.

That is, a small spot is formed by using all the apertures (NA: 0.6) of the objective lens during DVD playback, and in the case of CD playback, the beam diameter of the light incident from the light source to the objective lens is limited or a small numerical aperture in the objective lens, for example, The above-described spherical aberration is corrected by adjusting the aperture to 0.45, such as using the paraxial region. As described above, in the disk compatible optical pickup, recently, a surface emitting laser diode (SEL) is used as a light source and a hologram optical pickup apparatus is used as a means for adjusting the aperture of the objective lens.

1 is a view schematically showing an optical pickup structure according to the prior art.

As shown in FIG. 1, the first laser diode 1 and the second laser diode 3 generating the laser light source and the laser light source generated from the first laser diode 1 are decomposed into three laser lights. The first grating 2a and the second grating 2b for converting the laser light source generated from the second laser diode 3 into parallel light, and the first grating 3a and the second grating 2b. The first beam splitter 5 and the first beam splitter 5 for adjusting the direction of the parallel light incident at an arbitrary angle and passing the laser light or refracting the laser light reflected from the optical disk 15 at a right angle. The second beam splitter 7 for refracting or passing the laser light in a predetermined direction and the collimator lens 11 for converting the laser light emitted from the second beam splitter 7 into parallel light. ), And A reflection mirror 13 for reflecting parallel light generated from the collimator lens 11 in the direction in which the optical disc 15 is located, and a laser beam reflected from the reflection mirror 13 to refract a light spot. The objective lens 15 and the detector 9 which detects the light reflected by the optical spot 15 which generate | occur | produced in the said objective lens 15 are comprised.

The optical pickup device in which the optical system is arranged in the above structure operates as follows to detect data.

Recently, a plurality of laser diodes are often arranged in one optical pickup device, for example, a DVD and a CD are integrated. When the optical pickup device having two functions is integrated into one, many laser diodes generate a laser light source, but it is common to place fewer detectors than the number of laser diodes.

As shown in Fig. 1, a laser light source is generated in the first laser diode 1 and the second laser diode 3, and their functions are different. For example, if the first laser diode 1 is a diode for DVD (Digital Video Di) or the second laser diode (3) is a diode for CD, laser light is generated from two laser diodes, respectively. It is used to record / play back data.

First, the laser light generated by the first laser diode 1 is decomposed into main laser light and two sub laser light while passing through the first grating 2a, and proceeds without refraction in the first beam splitter 5. Then, after passing through the second beam splitter 7 continues in the direction in which the optical disk 15 is located. The laser light passing through the second beam splitter 7 is converted into parallel light in the collimator lens 11 and then reflected by the reflecting mirror 13 and then incident on the objective lens 15.

After the three beams incident on the objective lens 15 are refracted, the main laser light is irradiated onto the data track groove of the optical disc 15 to record / reproduce data, and the sub laser light is left and right on the track groove. The track mountains of are irradiated and used for tracking error detection.

When the laser light is also generated in the second laser diode 3 in the same manner as described above, the second grating 2b is decomposed into a main laser light and two sub laser lights, and is perpendicular to the first beam splitter 5. After refraction, the flow proceeds to the second beam splitter 7. The second beam splitter 7 proceeds without refracting and is incident on the collimator lens 11, and the collimator lens 11 converts three laser beams into parallel beams, and then the reflection mirror 13 Reflected by the light incident on the objective lens 15.

The laser light generated by the first laser diode 1 and the second laser diode 3 passes through optical spectra used in the optical pickup, is reflected by the optical disk 20 and then received by the detector 9. In this case, the two laser diodes are used, and the detector which receives the reflected light through one detector is composed of four-segment photodiodes up and down around the four-segment photodiode for tracking error detection and focusing error detection.

2 is a view for explaining a position adjustment method of the laser laser light by the grating rotation used in the optical pickup according to the prior art.

As shown in FIG. 2, the grating that decomposes the laser light generated from the laser diode into the main laser light and the two sub laser lights is a lattice structure having an uneven shape. Of the three beams generated in the grating, the main laser light is irradiated on the groove of the data track of the optical disc, and the remaining two sub laser lights are irradiated on the mountains protruding to the left and right of the data track to detect a tracking error. .

Therefore, when the main laser light is reflected and formed on the detector, the error is corrected by rotation about a vertical center axis when the grating pitch error occurs. Rotation of the grating when the laser light generated from the laser diode is decomposed into three lights, but the three beams on the detector are not accurately focused on the divided photodiode when detected by being reflected on the optical disc. By correcting the error.

However, in the optical pickup apparatus for recording / reproducing data by using the laser light generated from two or more laser diodes as described above, since the number of detectors is usually smaller than the number of the laser diodes, tracking error detection and focusing are performed. Three photodiodes divided by four are arranged so that error detection can be performed by one detector.

In order to ensure that the reflected light received by the detector having the structure as described above is exactly formed at the center of the photodiode, an error cannot be eliminated only by adjusting the rotation of the grating.

3 is a view showing a pattern pitch error of the grating according to the prior art appeared on the detector.

As illustrated in FIG. 3, a quadrant divided photodiode is disposed at the center of the detector, and a photodiode which is somewhat larger in diameter is arranged in a quadrant form. The quadrant photodiode disposed at the center of the detector receives the reflected light of the main light decomposed in the grating and detects the tracking and focusing errors.

Four-quadrant photodiodes disposed above and below the detector are used to detect tracking errors by receiving reflected light of sub-laser lights decomposed by grating among three beams of laser light generated from two laser diodes.

However, since the photodiode of the detector that receives the reflected light of the sub laser light is also divided into four, the beam (d is the distance between the centers of the four-divided photodiodes) should be formed at the center, but an up and down error occurs (Δd). At this time, there is a problem that the pitch error of the grating cannot be corrected only by the operation of rotating the grating as in the conventional optical pickup.

That is, although the reflected light of the main laser light is exactly centered on the center quadrant photodiode of the detector, the reflected light of the remaining sub laser light does not form on the center of the quadrant photodiode disposed above and below the detector.

The present invention has been made to solve the above problems of the prior art, it is possible to eliminate the error of the sub-laser light in the detector due to the grating pitch error by the rotation of the grating to generate the three beams in the optical pickup and the movement in the optical axis direction. It is an object of the present invention to provide a grating adjustment method.

1 is a view schematically showing an optical pickup structure according to the prior art.

2 is a view for explaining a position adjustment method of the laser light by the grating rotation used in the optical pickup according to the prior art.

3 is a view showing a pattern pitch error of the grating according to the prior art appeared in the detector.

4 schematically illustrates an optical pickup structure according to the present invention;

5 is a view for explaining the position adjustment barrier of the laser light by the grating adjustment used in the optical pickup according to the present invention.

6 is a view showing a state in which a pattern pitch error of the grating according to the present invention is removed and shown in the detector.

* Description of the symbols for the main parts of the drawings *

31: first laser diode 33: second laser diode

32a: first grating 32b: second grating

35: first beam splitter 37: second beam splitter

39: detector 41: collimator lens

43: reflection mirror 45: objective lens

50: optical disc

In order to achieve the above object, the grating adjustment method according to the present invention,

Decomposing the light generated from the laser diode into a main laser light and two sub laser lights using grating;

Passing the light decomposed into three laser lights in the grating through the optical systems used in the optical pickup and then condensing the reflected light reflected from the optical disk onto the photodiode of the detector; And

Rotating the grating back and forth along the optical axis to focus the May laser light and the two sub-laser lights reflected from the optical disk onto a centered quadrant photodiode arranged in the detector and a quadrant photodiode arranged up and down. It features.

According to the present invention, in the optical pickup device using a plurality of laser diodes and one detector, the grating is rotated as well as the optical axis direction in order to eliminate an error caused when the reflected light of the sub laser lights decomposed in the grating is formed on the detector. It can move back and forth.

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

4 is a view schematically showing an optical pickup structure according to the present invention.

As shown in FIG. 4, the first laser diode 31 and the second laser diode 33 generating the laser light source and the laser light source generated from the first laser diode 31 are decomposed into three laser lights. And a first collimator lens 32a capable of moving back and forth along the traveling direction of the laser light and rotating along a vertical central axis, and three laser light sources generated from the second laser diode 33. A second grating 32b and a first grating 31a and a second grating 32b, which may be decomposed into laser light, and may move back and forth along the advancing direction of the laser light, and may rotate along a vertical central axis. The laser beam passing through the first beam splitter 35 and the second beam splitter 37 and the second beam splitter 37 for passing or refracting the laser light incident therefrom are converted into parallel light. The collimating lens 41, the reflecting mirror 43 reflecting parallel laser light passing through the collimating lens 41 toward the optical disk 50, and the laser reflecting from the reflecting mirror 43. An objective lens 45 for refracting light to form a light spot, and a detector 39 for detecting reflected light after the light spot generated from the objective lens 45 is irradiated to the optical disc 50. .

The optical pickup device in which the optical system is arranged in the above structure operates as follows to detect data.

Laser light is generated in two laser diodes arranged for CD or DVD. The laser light generated by the first laser diode 31 or the second laser diode 33 is decomposed into main laser light and two sub laser light while passing through the first grating 32a and the second grating 32b. .

The laser lights decomposed by the gratings 32a and 32b are incident on the collimator lens 37 while sequentially traveling through the first and second beam splitters 35 and 37. Since the laser light passing through the beam splitters 35 and 37 is a radiation type light, the collimator lens 41 converts the laser light into parallel light in which a light spot can be formed well. The laser light that is changed in parallel in the collimator lens 41 is reflected by the reflection mirror 43, and then the optical disk 50 is positioned. The laser light reflected by the reflective mirror 43 is incident on the objective lens 45 to form a light spot, and irradiates the data track of the optical disk 50.

The light spots irradiated onto the optical disc 50 are three laser beams decomposed by the first or second gratings 32a and 32b. The main laser light decomposed by the gratings 32a and 32b is irradiated and reflected on the data track groove of the optical disc 50, and the sub laser light is scattered to the left and right of the data track groove of the optical disc 50. Is irradiated and reflected. The light reflected by the optical disk 50 is detected by the detector 39 while passing through the objective lens 45, the reflective mirror 43, the collimator lens 41, and the second beam splitter 37.

As described above, two laser diodes are disposed, and the detector 39 which detects the reflected light through one detector has a four-part photodiode at the center, and a four-part photodiode with a somewhat larger diameter at the top and bottom. have. Accordingly, the reflected main laser light is condensed on the quadrant photodiode at the center, and the two reflected sub laser beams are condensed on the four split photodiodes arranged up and down from the center.

In general, the structure of the detector is divided into two upper and lower photodiodes around a four-sided photodiode, but the structure of the detector that detects the reflected light using two laser diodes and one detector is vertically A photodivided photodiode is placed, and the sub laser light reflected is detected.

Accordingly, the reflected sub laser light should have a beam formed at the center of the photodiode divided into four vertical parts. Particularly, even when the main laser light formed on the center 4-divided photodiode is formed at the center, the sub laser light does not form at the center in the vertical 4-divided photodiode.

When the grating pattern pitch error occurs as described above, the error cannot be corrected by rotation as in the prior art, and must be moved by focusing in the optical axis direction.

Therefore, when a grating pattern error occurs in the detector 39, the error can be corrected by rotating the first and second gratings 32a and 32b or moving back and forth along the optical axis.

5 is a view for explaining a position adjustment method of the laser light by the grating adjustment used in the optical pickup according to the present invention.

As shown in FIG. 5, the grating that decomposes the laser light generated from the laser diode into the main laser light and the two sub-laser lights has a shape in which the groove portion and the mountain portion are bent alternately like a concave-convex shape. The transmittance of the laser light decomposed varies with the distance from the groove to the mountain.

Of the three beams generated in the grating, the main laser light is irradiated on the groove of the data track of the optical disc, and the remaining two sub laser lights are irradiated on the mountains protruding to the left and right of the data track to detect a tracking error. .

Therefore, when the reflected light is not accurately formed on the detector, that is, the grating pattern error occurs, the grating disposed in front of the laser diode is moved back and forth along the optical axis or rotated along the vertical center axis to correct the error. .

6 is a view showing a state in which the pattern pitch error of the grating according to the present invention is removed and shown in the detector.

As shown in FIG. 6, a quadrant divided photodiode is disposed at the center of the detector, and a photodiode which is somewhat larger in diameter is arranged in a quadrant form. The 4-divided photodiode disposed at the center of the detector has a reflected main laser light at the center, and the sub-laser light reflected by the rotation and movement of the grating is also divided up and down 4-divided photodiode centers (distance between centers of the 4-divided photodiodes). d) to eliminate grating pattern errors.

Tracking error detection and focusing error detection are performed using laser light received from a detector having the above structure.

As described in detail above, the present invention allows the grating used in the optical pickup to move back and forth along the optical axis as well as to rotate the grating used in the optical pickup, thereby correcting the error occurring in the three laser lights decomposed in the grating. have.

In addition, since the reflected light formed on the detector can be moved up, down, left and right, there is an advantage that stable servo can be performed even using two laser diodes.

The present invention is not limited to the above-described embodiments, and various changes can be made by those skilled in the art without departing from the gist of the present invention as claimed in the following claims.

Claims (1)

Decomposing the light generated from the laser diode into a main laser light and two sub laser lights using grating; Passing the light decomposed into three laser lights in the grating through the optical systems used in the optical pickup, and then condensing the reflected light reflected from the optical disk onto the photodiode of the detector; And Rotating the grating back and forth along the optical axis to focus the May laser light and the two sub-laser lights reflected from the optical disk onto a centered quadrant photodiode arranged in the detector and a quadrant photodiode arranged up and down. A grating adjustment method characterized by the above-mentioned.