KR100570858B1 - Optical pick-up apparatus for dvd - Google Patents

Abstract

The present invention provides a DVD finite element including an objective lens having a magnification of 1/5 to 1/10 to obtain the same optical distance and the same performance as an infinite optical system without using a collimator lens. A DVD optical pickup apparatus constituting an optical system, the DVD optical pickup apparatus according to the present invention comprises: a two-wavelength light source module for selectively generating light beams of two different wavelengths; A diffraction grating for dividing the light beam into a main beam which is 0th order light and a sub beam of ± 1 order or more; A beam splitter installed on an optical path to reflect and transmit a light beam incident from the two wavelength light source module; A mirror for changing a path of light reflected by the beam splitter; The objective lens for condensing the light beam reflected from the mirror to one point of the optical disk; And an optical detector that detects and converts the reflected light beam into an electrical signal by hitting the signal track of the optical disk.

2-wavelength light source module, diffraction grating, beam splitter, mirror, objective lens, light detector

Description

DVD Optical Pickup Device {OPTICAL PICK-UP APPARATUS FOR DVD}

1 is a configuration diagram schematically showing a conventional optical pickup device.

2 is a configuration diagram schematically showing the optical pickup device according to the present invention.

Figure 3 is a schematic diagram for explaining the optical system magnification in the present invention.

Figure 4a is a graph showing the performance test results for the DVD according to the present invention.

Figure 4b is a graph showing the performance test results for the CD according to the present invention.

◎ Explanation of symbols for main part of drawing

1, 11: light source module 2, 12: diffraction grating

3, 13: beam splitter 4, 14: mirror

5: collimator lens 6, 16: objective lens

7, 17: optical disk 8, 18: optical detector

The present invention relates to an optical pickup device for recording and reproducing information on a recording medium such as an optical disk, and more particularly, to apply a finite optical system that does not use a collimator lens in constructing a DVD optical system. A DVD optical pickup apparatus using an objective lens having a magnification of 1/5 to 1/10.

In general, an optical pickup device is a device for reproducing signals recorded on various optical disks or recording signals on optical disks. An optical pickup device with an increased storage capacity and a faster processing speed has been developed. Products are widely used.

Of course, although DVD products have high capacity technology, most people are relatively inexpensive and are more accustomed to the widespread use of CD products. Cannot survive, and for this reason, all DVD products on the market are designed to read CD discs together.

In the optical system of such a DVD product, two light source modules having different wavelengths are used in the related art. For example, a CD product stores 650 MB of information using a light beam of 780 nm wavelength, and a DVD product stores 4.7 GB of information using a light beam of 650 nm wavelength. However, in recent years, in order to reduce the number of components of the optical system, one light source module having two wavelengths embedded in two semiconductor chips is used.

In addition, in order to increase the density of the optical recording medium, the spot size of the optical pickup apparatus for recording and reproducing information is reduced. Since the diameter of the light spot is proportional to the wavelength used and inversely proportional to the numerical aperture, the method of reducing the size of the light spot greatly reduces the wavelength of the light source and the method of increasing the numerical aperture of the objective lens system. The development of laser diodes that generate short wavelengths by reducing the wavelength of the light source is in progress, and the development of objective lenses is constantly progressing by increasing the numerical aperture of the objective lens system used in the optical pickup device.

As described above, in the optical pickup device, a method of reducing the size of the optical spot while reducing the optical component has been studied.

1 schematically shows the configuration of an optical pickup device composed of an infinite optical system which is a conventional DVD optical system.

Referring to this, the conventional optical pickup device is a two-wavelength light source module (1) for selectively generating two light beams having different wavelengths, that is, the wavelength of 650nm of DVD series and 780nm of CD series, and the two wavelength light source The diffraction grating 2 which splits the light beam emitted from the module 1 by using the diffraction effect of the light, and the light beam branched by the diffraction grating 2 are reflected in the direction of the optical disc 7 A main beam splitter (3), a mirror (4) for changing the path of the reflected light beam, and a light beam reflected by the mirror (4) to convert into parallel light A collimator lens 5, an objective lens 6 for condensing the light beam passing through the collimator lens 5 at one point of the optical disk 7, and the light reflected from the optical disk 7 again. A light detector 8 through which the beam penetrates the beam splitter 3 and detects this light beam and converts it into an electrical signal. It consists of).

Briefly describing the operation of the optical pickup device configured as described above, the light beam generated from the two-wavelength light source module 1 is incident on the diffraction grating 2 and branched into a main beam that is zero-order light and a sub-beam of ± 1 order or more. The light beam is reflected by the coated beam splitter 3, and the light path is changed again by the inserted mirror 4 to adjust the height of the optical pickup device and is incident on the collimator lens 5. The light beam incident on the collimator lens 5 is converted into parallel light. When the optical distance from the two wavelength light source module 1 to the collimator lens 5 is designed to be equal to the focal length of the collimator lens 5, the parallel light You will be able to create The parallel light is collected by the objective lens 6 and then reflected by hitting the signal track of the optical disc 7. At this time, the Pit, which is an information recording unit on the disc, is read.

The beam reflected by the optical disc 7 is returned to the same path and then changed by passing through the beam splitter 3, and the light beam is collected and converted into an electrical signal by the photo detector 8.

As described above, an infinite optical system is used as a conventional DVD optical system in which a collimator lens 5 is used to make a light beam into parallel light and focuses on the objective lens 6.

However, since the collimator lens 5 has to be used additionally to make the light beam generated from the light source module 1 into parallel light, there is a problem that the configuration of the optical pickup device is complicated and enlarged. There is a difficulty in aligning the optical element to the optical axis because it uses.

The present invention is to overcome the above-mentioned conventional problems, an object of the present invention is to use an objective lens having a magnification of 1/5 to 1/10 without using a collimator lens in configuring a DVD optical system The DVD optical pickup device constituting the finite optical system that can achieve the same performance as the optical system is implemented.

In addition, an object of the present invention is to provide a DVD optical pickup apparatus capable of high-density recording and reproduction that can be easily produced and used by removing a collimator lens as an optical element.

As a means for achieving the above object, the DVD optical pickup apparatus applying the finite optical system to the DVD according to the present invention, the light source module for generating a light beam of a predetermined wavelength; A diffraction grating for branching the light beam; A beam splitter installed on an optical path to reflect and transmit a light beam incident from the two wavelength light source module; A mirror for changing a path of light reflected by the beam splitter; An objective lens for condensing the light beam reflected from the mirror to one point of the optical disk; And an optical detector that detects and converts the reflected light beam into an electrical signal by hitting the signal track of the optical disk, wherein the objective lens has a magnification of 1/5 to 1/10.

Here, the light source module is preferably a two-wavelength light source module for selectively generating light beams of two different wavelengths.

In addition, the light beam generated by the two-wavelength light source module is a light beam of 655nm, 785nm wavelength.

Here, the diffraction grating splits a single light beam into a main beam that is 0th order light and a sub beam of ± 1 order or more.

In addition, the tracking error signal of the CD is detected by using the light beam branched through the diffraction grating.

The beam splitter may be coated to reflect and transmit a light beam, and to generate astigmatism to detect focus error signals of CDs and DVDs.

Here, the mirror is coated with a reflectance of 95% or more, characterized in that for adjusting the height of the optical pickup.

In addition, the objective lens is characterized in that the aspherical lens.

In the optical pickup design, it is first necessary to select whether the optical system is an infinite optical system or a finite optical system. Infinite optical system refers to a case where the light incident on the objective lens is parallel light, which uses a collimator lens to make the light beam into parallel light. When the light incident on the objective lens is divergent light (or converged light) instead of parallel light, it is called a finite optical system. In this case, no collimator lens is used. In general, in the case of a high number of openings (DVD), such as DVD, most of them adopt an infinite optical system, and in the case of a relatively low number of openings (CD), such a finite optical system.

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

2, the configuration of the DVD optical pickup apparatus according to the present invention is schematically shown.

Referring to this, in the DVD optical pickup apparatus according to the present invention for reproducing signals recorded on various optical disks or recording signals on optical disks, the light beam generated by the light source module 11 is branched by the diffraction grating 12. , The light beam is reflected by the beam splitter 13, and the light beam is changed again by the inserted mirror 14 to adjust the height of the optical pickup device. 16, the optical disk 17 is condensed.

Then, the light beam reflected by the optical disk 17 is configured to be reflected by the mirror 14 again and transmitted through the beam splitter 13 to be converted into an electrical signal by the photo detector 18.

Here, the light source module 11 uses one two-wavelength light source module 11 for selectively projecting light beams of different wavelengths. The two-wavelength light source module 11 is provided with two semiconductor chips at predetermined intervals inside, one of the two semiconductor chips emits a light beam having a wavelength of 650 nm of the DVD series, and the other is a CD. The light beam having a wavelength of 780 nm of the series is emitted.

Each light beam projected by the same wavelength path through the two-wavelength light source module 11 is branched through the diffraction grating 12 into a main beam that is zero order light and a sub beam of ± 1 order or more. Here, the tracking error signal of the CD is detected using the light beam branched through the diffraction grating 12.

The light beam branched through the diffraction grating 12 is reflected by the beam splitter 13 which reflects the optical path in the direction of the optical disk 17 and then again by the mirror 14.

Here, the beam splitter 13 is coated on its surface to reflect and transmit the light beam, and generates astigmatism by the beam splitter 13 to detect focus error signals of CD and DVD.

In addition, the mirror 14 is coated so that the reflectivity of the light beam is 95% or more to change the path of the light beam, by changing the path of the light beam in this way can adjust the height of the optical pickup device have.

In the DVD optical pickup apparatus according to the present invention, the light beam reflected through the mirror 14 is directly focused on the objective lens 16.

In the optical system configuration of the DVD optical pickup apparatus, as shown in FIG. 1, conventionally the light beam reflected by the mirror 4 using the collimator lens 5 between the mirror 4 and the objective lens 6. Is converted into parallel light through the collimator lens 5 to focus on the objective lens 6, but unlike the infinite optical system using the collimator lens 5 as in the related art, the present invention is shown in FIG. Then, the collimator lens is removed and a finite optical system for focusing the light beam generated by the light source module 11 on the objective lens 16 of high magnification. In this case, the implementation of the optical system having the desired optical distance is determined by the objective lens.

3 is for explaining an optical system magnification, and may be represented as follows.

Optical magnification (m) = S2 / S1 = (2nd principal point (H2) of the focal point to the objective lens on the optical disk) / (1st main point (H1) of the light source to the objective lens)

In the case of reproducing the information stored in the conventional endless optical system DVD, the optical magnification required for the condensing optical system of the optical pickup device is required to be about 1/6 to 1/7, whereas the information is recorded or reproduced on the CD However, the optical magnification required for the condensing optical system is required to be about 1/4 to secure more light.

However, in order to apply the DVD finite optical system to obtain the same performance while having the same optical distance as the infinite optical system without using the collimator lens, the optical pickup device uses an objective lens having a magnification of 1/5 to 1/10. .

Data of the design parameters for the objective lens according to the embodiment of the present invention are shown in the following [Table 1].

 Wavelength λ (nm) 655 (DVD) 785 (CD)  Focal Length f (mm) 2.98 2.99  Numerical aperture NA 0.60 0.47  Optical magnification 0.125 (= 1/8)  Working distance W.D. (mm) 1.78 1.41  I / O distance (mm) 31.32 31.92  Disk side protective board (mm) 0.6 1.2  Light source side protection board (mm) 0.95  Center thickness t (mm) 2.3

Here, the objective lens of this embodiment is composed of an aspherical lens.

In the data of Table 1, the numerical aperture of an objective lens having a wavelength of 655 nm and a 2.98 mm focal length in a DVD is 0.60, and the numerical aperture of an objective lens having a 785 nm wavelength and a 2.99 mm focal length in a CD is 0.47. . Here, Numerical Aperture (NA) is a determinant of resolution, which indicates the ability to focus light in an optical system, and when an optical system with a high numerical aperture is used, a brighter image may have better resolution. You can get it. Resolution is the ability to distinguish an isolated thin line into an image through an optical system, expressed in lp / mm (Line pairs per millimeter).

The working distance (W.D.) refers to the distance from the object to be measured to the lowest mechanical part of the optical system, and is usually the distance between the object and the outermost optical part. In this embodiment, the DVD is 1.78 mm and the CD is 1.41 mm, which is the distance between the objective lens and the optical disk surface. The working distance affects the convenience of operation of the measurement object.

In addition, I / O distance means the total distance from a light source (object) to an optical disk (image), DVD is 31.32 mm and CD is 31.92 mm.

The thickness of the protective substrate (transparent substrate) provided on the information recording surface side of the optical disk, which is an optical information recording medium, is 0.6 mm in DVD, 1.2 mm in CD, and the thickness of the protective substrate provided in the light source module side in DVD and CD. 0.95 mm.

Again, as shown in FIG. 2, the objective lens 16 designed by [Table 1] focuses the light beam that is reflected by the mirror 14 and is incident on the optical disk 17 to focus.

This light beam is subsequently reflected by hitting the signal track of the optical disc 17, at which time it reads the Pit, an information recording unit on the disc.

The pit of the optical disk is made up of grooves and lands, and the reflectance at each part is different, so that there is a difference in the intensity of the beam reflected back from the disk.

The reflected beam is returned to the same path again and passes through the beam splitter 13 to change the path, and the light beam is focused on the photo detector 18.

The photo detector 18 detects the difference in intensity of the light beam and converts the electrical signal into an electrical signal. The converted electrical signal is demodulated and reproduced by the control circuit, not shown.

4A and 4B are graphs of wavefront aberrations for showing performance test results of the design data of Table 1 according to the present invention, and FIG. 4A is a graph of DVD and FIG. 4B is a CD.

Aberration refers to a difference between an actual image and an ideal image for an object in optical imaging, and includes spherical aberration, coma aberration, and astigmatism. The RMS value of each of these aberrations is called wavefront aberration. In general, the direction of travel of the light beam moves perpendicular to the wavefront, which represents the aberration as the difference between the ideal reference plane and the actual wavefront.

Although there are various items for evaluating the performance of the optical pickup device, they can be represented as jitter. Jitter is a standard deviation with respect to the measurement time of the pits 3T to 11T during optical disc signal reproduction. The smaller the jitter value, the better the optical pickup performance.

However, wavefront aberration is a major factor influencing such jitter. When aberration occurs in the reproduction optical system, distortion occurs in the reproduction waveform, resulting in problems such as disc recognition error. In addition, light beam noise, circuit noise, and disc temporal variation also influence jitter.

Therefore, the experimental results for the wavefront aberration of the DVD optical pickup apparatus according to the present invention is shown in Figure 4a and 4b, the CD and DVD to which the conventional infinite optical system and the finite optical system from which the collimator lens is removed according to the present invention It can be seen that the performance results of the used CD and DVD are almost the same.

On the other hand, the above-described DVD optical pickup apparatus according to the present invention can be applied to various types of optical recording and reproducing apparatuses.

What has been described above is only an embodiment for implementing a DVD optical pickup device applying a finite optical system to a DVD according to the present invention, and the scope of the present invention is not limited to the above-described embodiment, and the interpretation of the claims Extends to the limit defined by

According to the present invention, a DVD optical pickup device can be made smaller and lighter by implementing a finite optical system DVD using an objective lens having a magnification of 1/5 to 1/10 without using a collimator lens. It can be done.

In addition, by omitting the collimator lens in the configuration of the optical pickup device, it is possible to induce improved productivity by reducing the material cost and simplifying the manufacturing process.

Claims (8)

A two-wavelength light source module for generating two light beams having different wavelengths; A grating for branching the light beam; A beam splitter installed on an optical path to reflect and transmit a light beam incident from the two wavelength light source module; A mirror for changing a path of light reflected by the beam splitter; an objective lens for condensing the light beam reflected by the mirror to a point of an optical disk; And A light detector which detects and converts the reflected light beam into an electrical signal by hitting the signal track of the optical disc, And the objective lens has a magnification of 1/5 to 1/10 and the light beam is divergent light. delete According to claim 1, And a light beam generated by the two wavelength light source module is a light beam having a wavelength of 655 nm and a 785 nm. According to claim 1, And the diffraction grating splits a single light beam into a main beam that is zero order light and a sub beam of ± 1 order or more. According to claim 1, And a tracking error signal of the CD using a light beam branched through the diffraction grating. According to claim 1, The beam splitter is coated to reflect and transmit a light beam, and to generate astigmatism to detect focus error signals of CDs and DVDs. According to claim 1, And the mirror is coated with a reflectance of 95% or more and adjusts the height of the optical pickup. According to claim 1, And the objective lens is an aspherical lens, the numerical aperture of the light beam of one wavelength is 0.6 and the numerical aperture of the light beam of the other wavelength is 0.47.

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