KR20030071069A - Apparatus for optical pick-up - Google Patents

Abstract

PURPOSE: An optical pick-up is provided to correctly record and reproduce data in spite of an error in an optical path caused by a minute variation in the position of a laser diode and photo-diode. CONSTITUTION: An optical pick-up that records and reproduces data using a laser beam includes the first and second detectors(50,60). The first detector detects a laser beam that is reflected from an optical disk(45) in order to record/reproduce data. The second detector detects a beam transmitted according to a life edge mode from the reflected beam received by the first detector. The cell size of a photo-diode used for the second detector is larger than the cell size of a photo-diode used for the first detector.

Description

Optical pickup device {APPARATUS FOR OPTICAL PICK-UP}

The present invention relates to an optical pickup device, and more particularly, to arrange two detectors among optical systems for recording / reproducing data on an optical disc, thereby separating the tracking operation and the focusing operation so that the optical system is accurate despite the slight error of the optical systems. An optical pickup apparatus capable of recording / reproducing data.

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 showing a conventional pickup type optical pickup structure according to the prior art.

As shown in Fig. 1, a laser diode 1 for generating a laser light source, a collimator lens 3 for converting a laser light source generated from the laser diode 1 into parallel light, and The shaping prism 5 which controls the direction of parallel light incident at an arbitrary angle through the collimator lens 3, and the laser beam passing through the shaping prism 5, or the laser reflected from the optical disk 15 A beam splitter 7 for refracting light at right angles, a λ / 4 plate 9 for converting linearly polarized laser light into circularly polarized laser light, and a laser light passing through the λ / 4 plate 9 A grating 10 for decomposing the beam into three beams to detect more accurate data, a reflection mirror 11 for reflecting the laser light passing through the grating 10 toward the objective lens 13 disposed on the actuator, The reflector The objective lens 13 for refracting the laser light reflected from the (11) to form a light spot, the optical disc 15 for recording / reproducing data by irradiating the light spot generated by the objective lens 13, It consists of a detector 20 for detecting data contained in the laser light reflected from the optical disk 15.

In addition, a non-point lens 17 is disposed in front of the detector 20 to cause the reflected light refracted from the beam splitter 7 to propagate to the detector 20, and is generated from the laser diode 1. The front monitor 19 which arranges to measure a laser beam quantity and to generate stable laser beam is arrange | positioned.

The optical pickup apparatus having the optical system structure as described above operates as follows to detect data.

First, when laser light is generated in the laser diode 1 to record / reproduce data on the optical disc 15, the laser light is incident on the collimator lens 3 and converted into parallel laser light. Next, it is incident on the orthopedic prism 5. The orthopedic prism 5 serves to refract the laser light incident at an arbitrary angle into a horizontal laser light that can travel in a predetermined direction. The laser light passing through the orthopedic prism 5 passes through the beam splitter 7 without refracting and then proceeds horizontally. The inclined surface of the beam splitter 7 is coated with a polarization beam splitter (PBS) to allow light incident horizontally to the inclined surface to pass through, and to direct 90 degrees of light traveling in the opposite direction to the inclined surface.

Since the laser light passing through the beam splitter 7 is light propagating from the laser diode 1 and is linearly polarized, the laser light passes through the λ / 4 plate 9 to convert it into circularly polarized light. The circularly polarized laser light passing through the λ / 4 plate 9 is decomposed into three lights in the grating 10 in order to apply a three beam method for detecting more accurate data. The three laser lights decomposed by the grating 10 are reflected by the reflection mirror 11 and then incident on the objective lens 13 disposed on the actuator. The laser light incident on the objective lens 13 is refracted to form a light spot, and three laser lights are irradiated onto the data track of the optical disk 15.

The three laser lights are composed of a main laser light and two sub laser lights, the main laser light being used for recording or reproducing data on a data track of the optical disc 15, the sub laser light being a track. It is irradiated to the areas protruding to the left and right mountains and used for accurate tracking servo.

Then, the light reflected from the optical disk 15 is converted into linearly polarized laser light while passing through the reflective mirror 11, the grating 10, and the λ / 4 plate 9, and the beam split 7 After refracting the light beam through the non-point lens 17 and irradiates the detector 20.

2 is a view showing the structure of a detector in a conventional type optical pickup according to the prior art.

As shown in FIG. 2, the 4-division photodiode system is shown as a structure of the photodiode generally used. That is, an astigmatism method is used in which four photodiodes A, B, C, and D are arranged to analyze the difference of the reflected laser light to correct focusing and tracking errors. In the astigmatism method, when the focal length is changed by the vertical movement of the optical disc, the left and right sizes of the beam irradiated to the detector are changed so that the output values of the four photodiodes are changed to detect the focus error.

In general, it is expressed by the formula of focus error = (A + C)-(B + D).

Here, A, B, C, and D represent output values of the photodiodes in the detector.

In addition, the tracking error detection method of the optical pickup decomposes the laser light that has passed through the beam splitter into three beams by grating, irradiates it onto the data track of the optical disc, and detects the reflected value to correct the error.

In general, a tracking error = E-F is expressed, and the E and F photodiodes are arranged in the detector 20 to represent photodiodes for detecting tracking errors.

Therefore, in general, a three-beam method using a grating and a four-segment photodiode are arranged in a detector to detect tracking errors and focusing errors, thereby accurately recording / reproducing data.

However, although the optical pickup device having the conventional conventional structure is cheaper than the hologram structure, the photodiode and the radar diode disposed in the detector are increased by the high temperature of the laser light or the external low temperature as time goes by. There is a disadvantage that the deformation is rapidly lowered reliability.

Therefore, in order to prevent the above problems, the bonding is performed using a bond and an epoxy to fix the laser diode and the photodiode, but the deformation of the adhesive occurs due to heat, thereby causing the problem of changing the position of the laser diode and the photodiode. Occurs.

In recent years, since the precision is increased with the development of the high storage optical disk, even if the laser diode and the photodiode move several micrometers, the error rate of the laser light for recording / reproducing data is greatly generated.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and by disposing a first detector and a second detector in a detection area for detecting laser light reflected from an optical disk, a minute position change of the laser diode and the photodiode It is an object of the present invention to provide an optical pickup apparatus capable of recording / reproducing accurate data despite errors in optical paths caused by the optical path.

1 is a view showing a conventional type of optical pickup structure according to the prior art.

2 is a diagram showing the structure of a detector in a conventional type optical pickup according to the prior art;

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

4 shows a cell structure of detectors according to the invention.

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

31: laser diode 33: collimator lens

35: orthopedic prism 37: beam splitter

40: grating 41: reflection mirror

43: objective lens 45: optical disk

47: non-point lens 50: first detector

60: second detector

In order to achieve the above object, the optical pickup device according to the present invention,

An optical pickup apparatus for recording / reproducing data by using laser light,

A first detector arranged to detect laser light reflected from the optical disc for recording / reproducing data, and a light detector arranged to detect light transmitted by a known life edge method among the reflected light received on the first detector; And a second detector.

Here, the cell size of the photodiode used for the second detector is larger than the cell size of the photodiode used for the first detector, and the reflected light received by the second detector has a boiling point using a known life edge method. It is characterized in that a reflected light having a large diameter, which is not formed, is formed.

According to the present invention, two detectors are arranged in a detection area used for an optical pickup so that focusing error detection and tracking error detection can be separated, and the size of the second detector is increased so that the laser diode or the photodiode This results in accurate signal detection even when the strain is slightly deformed or the adhesive is melted.

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

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

As shown in FIG. 3, a laser diode 31 for generating laser light, a collimator lens 33 for converting a laser light source generated from the laser diode 31 into parallel light, and the collimator lens ( 33 and an orthogonal prism 35 that adjusts the direction of parallel light incident at an arbitrary angle, and passes through the laser light passing through the orthogonal prism 35 without refracting, or reflects the laser light reflected from the optical disk 45. A beam splitter 37 for refracting at right angles, a λ / 4 plate 39 for converting the linearly polarized laser light into a circularly polarized laser light, and a 3 beam of laser light passing through the λ / 4 plate 39 A grating 40 decomposed into a light source, a reflecting mirror 41 reflecting a laser beam decomposed into a 3-beam form from the grating 40 in the direction of the optical disk 45, and a reflecting mirror 41 reflected from the reflecting mirror 41 Refracting laser light An objective lens 43 for forming an optical spot, and a first detector 50 for irradiating the data track of the optical disk 45 with the light spot generated by the objective lens 43 and detecting the reflected laser light. And a second detector 60 for detecting the reflected light transmitted from the reflected light received by the first detector 50.

In addition, it is generated from the non-point lens 47 and the laser diode 31 that reflects the reflected light refracted from the beam splitter 37 and propagates on the first detector 50 after being reflected from the optical disk 45. A front monitor detector 49 is arranged in the optical pickup optical system that measures the amount of laser light to be adjusted to generate stable laser light.

The optical pickup apparatus having the optical system structure as described above operates as follows to detect data.

First, the laser light generated by the laser diode 31 to regenerate data on the optical disk 45 is incident from the collimator lens 33 is adjusted to the parallel laser light. Subsequently, parallel light from the collimator lens 33 is incident on the orthopedic prism 35, and the orthopedic prism 35 is incident on the inclined plane at an angle along the inclined plane. In parallel in the direction indicated. The laser light refracted in parallel in the orthopedic prism 35 passes through the beam splitter 37 without refracting and then proceeds horizontally. The inclined surface of the beam splitter 37 is coated with PBS (Polarization Beam Splitter), and the PBS passes light incident on the inclined surface of the beam splitter 37 as it is, and the light incident in the other direction of the inclined surface is 90 It has a property of refraction.

Since the laser light passing through the beam splitter 37 is light propagating from the laser diode 31, the laser light is linearly polarized. The laser beam is disposed together with the beam splitter 37 to convert the laser light into circularly polarized laser light. Pass the λ / 4 plate 39. The circularly polarized laser light passing through the λ / 4 plate 39 is decomposed into three lights in the grating 40 in order to apply a three beam method for detecting more accurate data. The light decomposed into three in the grating 40 is reflected by the reflection mirror 41 and then enters the objective lens 43 disposed in the actuator. Three laser lights incident on the objective lens 43 are refracted to form a light spot, and three laser lights are irradiated onto the data track of the optical disk 45.

The three laser lights are composed of a main laser light and two sub laser lights, the main laser light is irradiated to the data track groove of the optical disc 45, and the remaining sub laser light is irradiated to an adjacent protruding mountain track. Tracking errors are detected.

Then, the laser light reflected from the optical disk 45 is converted into linearly polarized laser light while passing through the reflective mirror 41, the grating 40, and the λ / 4 plate 39, and the beam split 37 After 90 ° refraction at), it proceeds to the first detector 50.

Reflected light is collected on the first detector 50 by the non-point lens 47 disposed in front of the first detector 50. In this case, the first detector is known by a known edge method. A portion of the reflected light received at 50 is passed to form the second detector 60 while the reflected light does not form a boiling point.

Accordingly, although the boiling point of the reflected light in the first detector 50 is formed by the boiling point lens 47, the boiling point does not occur in the second detector 60, and rather large reflected light is formed. Thus, a focusing error is detected using the reflected light received by the first detector 50, and a tracking error is detected using the light received by the second detector 60.

4 is a diagram illustrating a cell structure of detectors according to the present invention.

As shown in FIG. 4, the structure of the first detector 50 and the second detector 60 used in the present invention uses a quadrant photodiode system generally used as it is, but the first detector 50 is used. The cell of the photodiode of the second detector 60 is made larger than the size of the photodiode cell.

The amount of light in the beam is detected from the reflected laser light, and RF uses an amplifier to determine the beam shape.

It is detected through the equation RF = A + B + C + D.

An error in the focusing direction of the objective lens is detected through the first detector 50, which is given by focusing error detection (FES) = (A '+ B' + F)-(C '+ D' + E). The detection values of the A ', B', C ', and D' photodiodes for detecting the reflected light of the main laser light and the detection values of the E and F photodiodes for detecting the reflected light of the sub laser light among the light spots irradiated to the optical disc data track. Error in the focusing direction of the objective lens is detected.

An error in the tracking direction of the objective lens is detected using reflected light having a large diameter such that the boiling point does not occur in the second detector 60 by a life edge method. Tracking error detection (DPD) = Phase (A + C) It is given by -Phase (B + D).

The phase difference of the laser light reflected by the groove formed in the data track of the optical disc is used to determine whether the light spot is accurately irradiated onto the data track.

In addition, the tracking error is detected by removing the amount of offset generated in the main laser light of the three laser beams by sub laser light, and the formula used to detect the tracking error is DPP (Defferential Push Pull) = [(A + D)-(B + C)]-k [(G + I)-(H + J)].

A ', B', C ', D', E and F shown above represent values detected in the photodiode of the first detector 50, and A, B, C, D, G, H, I and J represents a value detected in the photodiode of the second detector 60.

Therefore, in the present invention, the laser light reflected from the optical disk is detected separately from the first detector 50 and the second detector 60, and then the first detector 50 performs a focusing servo, and the second detector In 60, the diameter of the photodiode was increased to enable tracking servo.

As described in detail above, the present invention arranges two detectors for detecting reflected light among optical systems used in an optical pickup, and increases the diameter of the photodiode used in one of the detectors. The change in position also has the effect of detecting accurate data.

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 (3)

An optical pickup apparatus for recording / reproducing data by using laser light, A first detector arranged to detect laser light reflected from the optical disc for recording / reproducing data, and a light detector arranged to detect light transmitted by a known life edge method among the reflected light received on the first detector; And a second detector. The method of claim 1, The cell size of the photodiode used for the second detector is larger than the cell size of the photodiode used for the first detector. The method of claim 1, The reflected light received by the second detector is a light pick-up device, characterized in that to form a reflected light having a large diameter, the boiling point is not formed using a known life edge method.