KR100894321B1 - Grating device and optical pickup apparatus using the same - Google Patents

Abstract

A diffraction grating and an optical pickup device using the same are provided to minimize the components of optical pickup device by generating main beam and sub beam appropriate for various wavelengths of lights while using a general diffraction grating not a wavelength-selective diffraction grating. A diffraction grating comprises a transparent substrate, and a first grating layer(22b) and a second grating layer(22c) formed on both sides of the transparent substrate. The first grating layer generates main beam and sub beam by diffracting the light of first wave length, and the second grating layer generates main beam and sub beam by diffracting the light of second wave length.

Description

Grating device and Optical pickup apparatus using the same

The present invention relates to a diffraction grating and an optical pickup apparatus using the same, and more particularly, diffraction grating and wavelength selective diffraction for diffracting at least two different wavelengths of light to form a main beam and a sub beam for each light. The present invention relates to an optical pickup apparatus that is compatible with various types of optical recording media while using a general diffraction grating rather than a grating.

An optical pickup apparatus is an apparatus that provides light to an optical recording medium and extracts data signals and focusing / tracking error signals by detecting light reflected from the optical recording medium. In order to extract the focusing and tracking error signal in such an optical pickup apparatus, as is well known, the light emitted from the light source is diffracted using a diffraction grating, and the number of diffracted to the zero-order diffracted main beam by ± 1st order or more. To form a sub-beam. The main beam and the sub-beams thus formed are reflected by the optical recording medium and then detected by the multisegment photodetector. In this case, a data signal, a tracking error signal, a focusing error signal, and the like may be extracted according to a differential push-pull (DPP) method based on the output from the multi-segment photodetector.

Meanwhile, with the recent diversification of standards such as CD / DVD / BD / HD-DVD, there is a demand for an optical pickup apparatus compatible with various standards. It is necessary to use a common optical system to minimize the size and lower the cost of the optical pickup device compatible with these various specifications. However, since the diffraction characteristics of the diffraction gratings vary depending on the wavelength of incident light, a separate diffraction grating suitable for each standard is required. For example, an infrared laser light source having a wavelength of about 780 nm is used for a CD, and a red laser light source having a wavelength of about 650 nm is used for a DVD, and a blue laser light source having a wavelength of about 405 nm is used for an HD-DVD or a BD. A diffraction grating suitable for the wavelength shall be used in the optical system.

Accordingly, as shown in FIGS. 1A and 1B, the use of a wavelength selective diffraction grating that diffracts incident light of a specific wavelength and passes incident light of another wavelength is proposed. 1A and 1B show twin diffraction gratings in which two wavelength selective diffraction gratings 11 and 12 are bonded to each other. Here, the first diffraction grating layer 11 diffracts only the CD light as the CD diffraction grating, for example, and the second diffraction grating layer 12 can diffract only the DVD light as the DVD diffraction grating. have. In this case, the CD light is diffracted in the first diffraction grating layer 11 and then passes through the second diffraction grating layer 12 without diffraction. In addition, the light for DVD passes through the first diffraction grating layer 12 without diffraction, and is then diffracted by the second diffraction grating layer 12. Therefore, a main beam and a sub beam suitable for both CD light and DVD light can be obtained. However, the above-mentioned wavelength selective diffraction grating has a disadvantage in that the price burden is large.

If the first and second diffraction grating layers 11 and 12 are general diffraction gratings instead of the wavelength selective diffraction gratings, the light for CD and the light for DVD are applied to the first and second diffraction grating layers 11 and 12. Are all diffracted. Accordingly, diffraction beams other than the necessary beams are generated, and data signals, tracking error signals, focusing error signals, and the like cannot be efficiently extracted.

SUMMARY OF THE INVENTION An object of the present invention is to provide optical recording media of various specifications while using diffraction gratings and diffraction gratings that diffract at least two different wavelengths of light, respectively, to form a main beam and a subbeam for each light, and a general diffraction grating rather than a wavelength selective diffraction grating. It is to provide a compatible optical pickup device for.

According to one type of the invention, there is provided a diffraction grating which diffracts at least two different wavelengths of light, respectively, to form a main beam and a subbeam for each light, said diffraction grating having at least two diffraction grating layers. And at least one of the at least two diffraction grating layers has a depth optimized for light of any one of the at least two different wavelengths of light.

According to the invention, the depth of each diffraction grating layer is two out of a plurality of depths to satisfy a predetermined ratio of main beam and sub beam to light of a corresponding wavelength among the light of the at least two different wavelengths. The depth above the first cycle can be selected.

For example, the depth of each diffraction grating layer may be such that the intensity of the zero-order diffracted beam is greater than or equal to 90% of the total intensity of the remaining light for the remaining light other than the light of the corresponding wavelength among the light of the at least two different wavelengths. May be selected.

On the other hand, an optical pickup apparatus according to another type of the present invention, a multi-light source for emitting light of at least two different wavelengths; A diffraction grating diffracting the at least two different wavelengths of light, respectively, to form a main beam and a subbeam for each light; A beam splitter that transmits the light traveling from the multi light source to the optical recording medium and reflects the light reflected from the optical recording medium; An objective lens for focusing light emitted from the multi light source onto an optical recording medium; And a photodetector for detecting light reflected from the beamsplitter, wherein the diffraction grating includes at least two diffraction grating layers, and at least one of the at least two diffraction grating layers is light emitted from the multi light source. It has a depth that is optimized for light of any one of the wavelengths.

According to the present invention, the depth of the diffraction grating layer is greater than or equal to a second cycle among a plurality of depths to satisfy a predetermined ratio of the main beam and the sub beam to the light of the corresponding wavelength among the light emitted from the multi light sources. Depth can be selected.

For example, the multi light source emits light of a first wavelength and a second wavelength different from each other, and the diffraction grating diffracts the light of the first diffraction grating layer and the second wavelength to diffract the light of the first wavelength. The second diffraction grating layer may be provided.

In this case, the depth of the first diffraction grating layer may be selected as the depth of the second cycle or more from a plurality of depths to satisfy a predetermined ratio of the main beam and the sub-beam to the light of the first wavelength.

For example, the depth of the first diffraction grating layer may be selected such that the intensity of light of the second wavelength diffracted by the first diffraction grating layer is 90% or more of the total intensity of the light of the second wavelength.

In addition, the depth of the second diffraction grating layer may be selected from a plurality of depths of more than a second cycle to satisfy a predetermined ratio of the main beam and the sub-beams to the light of the second wavelength.

For example, the depth of the second diffraction grating layer may be selected such that the intensity of light of the first wavelength diffracted by the second diffraction grating layer is 90% or more of the total intensity of the light of the first wavelength.

In addition, the multi light source may emit light of different first to third wavelengths, and the diffraction grating may include first to third diffraction grating layers for diffracting light of the first to third wavelengths, respectively. have.

In this case, the depths of the first to third diffraction grating layers each have a depth greater than or equal to a second cycle among a plurality of depths to satisfy a predetermined ratio of the main beam and the sub beam to the light of the first to third wavelengths. Can be selected.

For example, the depth of the first diffraction grating layer is selected such that the intensity of light of the second and third wavelengths diffracted by the first diffraction grating layer is 90% or more of the total intensity of the light of the second and third wavelengths, respectively. The depth of the second diffraction grating layer is selected such that the intensity of light of the first and third wavelengths diffracted by the second diffraction grating layer is 90% or more of the total intensity of the light of the first and third wavelengths, respectively. And select a depth of the third diffraction grating layer such that the intensity of light of the first and second wavelengths diffracted by the third diffraction grating layer is 90% or more of the total intensity of the light of the first and second wavelengths, respectively. Can be.

According to the present invention, a plurality of diffraction gratings can be used to form appropriate main and sub beams for each of light of various wavelengths. Therefore, the number of parts of the optical pickup device may be reduced, thereby minimizing the size of the optical pickup device and reducing the weight.

Furthermore, according to the present invention, it is possible to form an appropriate main beam and sub beam for each of various wavelengths of light while using a general diffraction grating rather than a wavelength selective diffraction grating, thereby greatly reducing the manufacturing cost of the optical pickup apparatus. Can be.

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

2 shows a schematic configuration of an optical pickup apparatus according to the preferred embodiment of the present invention. Referring to FIG. 2, the optical pickup apparatus 20 according to the present invention includes a light source 21 emitting light having a predetermined wavelength, a diffraction grating 22 diffracting light to form a main beam and a sub beam, and the light source. A beam splitter 23 for transmitting the light traveling from the optical source 21 to the optical recording medium D and reflecting the light reflected from the optical recording medium D, and a collie for making the light emitted from the light source 21 into a parallel beam A mating lens 24, a mirror 25 that reflects light onto the optical recording medium D, an objective lens 26 that focuses the light to form a spot on the optical recording medium D, and the beam splitter 23 It includes a photodetector 27 for detecting the light reflected from. Here, the position of the collimating lens 24 may vary depending on the embodiment. For example, the collimating lens 24 may be disposed between the light source 21 and the diffraction grating 22 or between the diffraction grating 22 and the beam splitter 23. In addition, in some embodiments, the mirror 25 may not be used.

As is known, in the structure of the optical pickup device 20 described above, the light emitted from the light source 21 is diffracted by the diffraction grating 22 and divided into a main beam and a plurality of sub beams, and then a beam splitter ( 23) pass. Then, each main beam and subbeam are converted into parallel beams by the collimating lens 24 and then reflected by the mirror 25. The reflected main and sub beams are respectively focused on the recording track of the optical recording medium D by the objective lens 26. Then, the light reflected and diffracted in the recording track of the optical recording medium D is reflected by the beam splitter 23 and enters the photodetector 27. In this case, the beam splitter 23 may be, for example, a polarizing beam splitter that transmits or reflects light according to the polarization direction of the incident light. In this case, for example, a quarter wave plate (not shown) may be further disposed in the optical path between the beam splitter 23 and the objective lens 26 to change the polarization direction of the incident light. On the other hand, the output of the light detected by the photodetector 27 is converted into an electrical signal and then provided to a control circuit not shown. The control circuit extracts a data signal, a tracking error signal and a focusing error signal according to the DPP method based on the input optical output. To this end, the photodetector 27 may be a multi-segment photodetector.

According to the present invention, the light source 21 may be a twin light source emitting two light having different wavelengths from each other. For example, the light source 21 may emit light for a CD having a wavelength of 780 nm and light for a DVD having a wavelength of 650 nm, or light having a wavelength of 405 nm and a light for DVD having a wavelength of 650 nm. It may emit light for HD-DVD or BD. Alternatively, the light source 21 may be a multi light source that emits three or more lights having different wavelengths. For example, the light source 21 may be a multi-light source that emits both light for CD having a wavelength of 780 nm, light for DVD having a wavelength of 650 nm, and light for HD-DVD or BD having a wavelength of 405 nm.

Further, according to the present invention, the diffraction grating 22 is a twin diffraction grating configured to form a main beam and a sub beam, respectively, for two light having different wavelengths. Alternatively, according to the present invention, the diffraction grating 22 may be a multi diffraction grating capable of forming a main beam and a sub beam for at least three lights having different wavelengths. In particular, the diffraction grating 22 according to the present invention may be configured using a general diffraction grating, not a wavelength selective diffraction grating.

For example, FIG. 3 schematically shows a configuration of a twin diffraction grating 22 constructed by joining two general diffraction gratings together. Referring to FIG. 3, first diffraction grating layers 22b and second diffraction grating layers 22c having different depths are formed on both surfaces of the transparent substrate 22a. The first and second diffraction grating layers 22b and 22c may be formed, for example, by arranging glass or plastic at a predetermined pitch and depth. Here, the first diffraction grating layer 22b may be, for example, a CD diffraction grating and the second diffraction grating layer 22c may be a diffraction grating for DVD. On the contrary, the first diffraction grating layer 22b may be a DVD diffraction grating, and the second diffraction grating layer 22c may be a CD diffraction grating. According to the embodiment, the first diffraction grating layer 22b may be used as the diffraction grating for DVD, and the second diffraction grating layer 22c may be used as the diffraction grating for BD or HD-DVD.

If the first diffraction grating layer 22b is for CD and the second diffraction grating layer 22c is for DVD, the first diffraction grating layer 22b hardly diffracts the DVD light and the second diffraction grating layer 22c ) Should hardly diffract light for CD. In the conventional case, when a general diffraction grating other than the wavelength selective diffraction grating is used, diffraction occurs in both diffraction gratings. The present invention can solve this problem by using the fact that the diffraction characteristics of the diffraction grating change with the depth of the diffraction grating. That is, according to the present invention, the depth of the first diffraction grating layer 22b is appropriately selected so as to minimize the influence on the light for DVD while achieving an optimal ratio of main beam to sub beam to the light for CD, The depth of the second diffraction grating layer 22c is appropriately selected so as to minimize the effect on the light for the CD while achieving an optimal ratio of main beam to sub beam to light. The optimal thickness of these first and second diffraction grating layers 22b and 22c can be found, for example, by simulation.

For example, FIG. 4 shows that the DVD light is the first diffraction grating layer 22b and the second diffraction grating layer 22c when the first diffraction grating layer 22b is for CD and the second diffraction grating layer 22c is for DVD. The form diffracted by) is shown by way of example. As shown in Fig. 4, the light for DVD is diffracted once by the first diffraction grating layer 22b and then diffracted by the second diffraction grating layer 22c again. In this case, for focusing and tracking servo, when one main beam is diffracted and two sub beams are diffracted by ± 1st order, the intensity of light indicated by 1-3 and 7-9 in FIG. Should be minimized.

Simulation was performed to confirm the thickness of the first diffraction grating layer 22b to satisfy this. At this time, the depth of the second diffraction grating layer 22c is fixed at 1600 ,, and the refractive indices of the materials of the first diffraction grating layer 22b and the second diffraction grating layer 22c are respectively n = 1.514 at a wavelength of 661 nm, It is assumed that n = 1.511 at a wavelength of 785 nm. 5 is a simulation result showing the intensity change of the zero-order diffracted main beam with respect to the CD light and the DVD light according to the depth change of the first diffraction grating layer 22b. In the simulation result of FIG. 5, the curves marked with '-▲-' are for the light for CD, and the curves marked with '-◆'-are for the light for DVD.

Here, it is assumed that the optimal ratio of the first sub-beam: main beam: second sub-beam to the light for CD is about 1: 16.5: 1. Then, as shown in FIG. 5, the depth of the first diffraction grating layer 22b such that the ratio of the first subbeam: main beam: second subbeam to the light for CD satisfies about 1: 16.5: 1 d1 and d2 are present. In addition, although not further illustrated in FIG. 5, the depth of the first diffraction grating layer 22b satisfying the ratio of the first sub-beam: main beam: second sub-beam is equal to the zero-order diffraction beam shown in FIG. 5. There is one for each cycle of the change curve for. In the following description, only d1 and d2 are considered.

First, when the depth of the first diffraction grating layer 22b is d1, the ratio of the first sub-beam: main beam: second sub-beam of DVD light diffracted by the first diffraction grating layer 22b is about 1. It's about 8: 1. Therefore, while the light for DVD is diffracted again in the second diffraction grating layer 22c, the intensity of the light of Nos. 1-3 and 7-9 shown in FIG. On the other hand, when the depth of the first diffraction grating layer 22b is d2, the ratio of the first sub-beam: main beam: second sub-beam of DVD light diffracted by the first diffraction grating layer 22b is about 1. : 98: 1 or so. In this case, the intensities of the lights 1-3 and 7-9 shown in Fig. 4 become negligible. Therefore, when the depth of the first diffraction grating layer 22b is d2, the diffraction effect on the light for DVD is almost influenced only by the second diffraction grating layer 22c, and the focusing and tracking servo for the DVD Can be performed normally.

Table 1 below shows the intensity of light 1-9 shown in FIG. 4 for the case where the depth of the first diffraction grating layer 22b is d1 and the case of d2. As can be seen from Table 1 below, when the depth of the first diffraction grating layer 22b is d2, the light for DVD is hardly affected by the first diffraction grating layer 22b. Thus, by selecting a depth that does not affect the light for the DVD most among the depths of the first diffraction grating layer 22b that satisfies the proper ratio of the main beam and the sub-beam to the light for the CD, the wavelength according to the present invention It is possible to use a general diffraction grating rather than a selective diffraction grating. For example, the depth of the first diffraction grating layer 22b can be selected so that the intensity of DVD light diffracted by the first diffraction grating layer 22b is 90% or more of the total light intensity for DVD. In particular, it is appropriate to select the depth in the second or more cycles in the change curve for the zeroth order diffraction beam shown in FIG. 5.

In the same manner as described above, the depth of the second diffraction grating layer 22c may also be appropriately selected. However, even though the CD light has a small diffraction and a large tolerance range, it is relatively easy to extract a data signal, a tracking error signal, and a focusing error signal. Therefore, when the first diffraction grating layer 22b is for CD, the diffraction of the light for CD may not be considered in selecting the depth of the second diffraction grating layer 22c.

In the above, the case where the first diffraction grating layer 22b is used for the CD and the second diffraction grating layer 22c is used as an example has been described. However, the principle of the present invention is that the first diffraction grating layer 22b is used for the DVD. The same applies to the case where the second diffraction grating layer 22c is for BD or HD-DVD. In addition, the case of diffraction of light having two different wavelengths by using two diffraction grating layers has been exemplarily described, but in the case of diffraction of light having three or more different wavelengths using three or more diffraction grating layers, respectively The principles of the present invention can be equally applied.

To date, exemplary embodiments have been described and illustrated in the accompanying drawings in order to facilitate understanding of the present invention. However, it should be understood that such embodiments are merely illustrative of the invention and do not limit it. And it is to be understood that the invention is not limited to the illustrated and described description. This is because various other modifications may occur to those skilled in the art.

1A and 1B schematically show a twin diffraction grating constructed by bonding two wavelength selective diffraction gratings together.

2 shows a schematic configuration of an optical pickup apparatus according to the present invention.

FIG. 3 schematically illustrates a configuration of a twin diffraction grating formed by bonding two general diffraction gratings having different depths according to the present invention.

FIG. 4 exemplarily shows light diffracted by the twin diffraction grating shown in FIG. 3.

FIG. 5 illustrates the intensity change of the zero-order diffraction beam for two light having different wavelengths according to the depth change of the twin diffraction grating shown in FIG. 3.

<Description of Symbols for Main Parts of Drawings>

20 ..... optical pickup device 21 ..... light source

22 .... Diffraction Grid 23 ..... Beam Splitter

24 ..... collimating lens 25 ..... mirror

26 .... Objective

Claims (13)

In order to extract a focusing and tracking error signal in an optical pickup device using two different wavelengths of light, a diffraction grating diffracts the two different wavelengths of light to form a main beam and a sub beam for each light. , Transparent substrate; And a first diffraction grating layer and a second diffraction grating layer respectively formed on both surfaces of the transparent substrate, The first diffraction grating layer diffracts light of a first wavelength to form a main beam and a sub beam, and the second diffraction grating layer diffracts light of a second wavelength to form a main beam and a sub beam, The depth of the first diffraction grating layer is obtained by calculating an intensity change curve of a zeroth order diffraction beam for light of a first wavelength according to the depth of the first diffraction grating layer, and at least a second of the periodic cycles of the change curve. From the depth of the first diffraction grating layer corresponding to the cycle, the depth having the least influence on the light of the second wavelength is selected, The depth of the second diffraction grating layer is obtained by calculating a change curve of a zero-order diffraction beam for light of a second wavelength according to the depth of the second diffraction grating layer, and at least a second cycle among the periodic cycles of the change curve. The depth of the second diffraction grating layer corresponding to the diffraction grating, characterized in that the depth of the least influence on the light of the first wavelength is selected. The method of claim 1, The depth of the first diffraction grating layer is selected such that the intensity of the zero-order diffracted beam for light of the second wavelength is at least 90% of the light intensity of the entire second wavelength, and the depth of the second diffraction grating layer is And wherein the intensity of the zero-order diffracted beam for light of one wavelength is selected to be at least 90% of the light intensity of the entire first wavelength. delete A multi light source for emitting light of two different first and second wavelengths; A diffraction grating diffracting the two different first and second wavelengths, respectively, to form a main beam and a subbeam for each light; A beam splitter that transmits the light traveling from the multi light source to the optical recording medium and reflects the light reflected from the optical recording medium; An objective lens for focusing light emitted from the multi light source onto an optical recording medium; And It includes a photo detector for detecting the light reflected from the beam splitter, The diffraction grating is a transparent substrate; And a first diffraction grating layer and a second diffraction grating layer respectively formed on both surfaces of the transparent substrate, The first diffraction grating layer diffracts light of a first wavelength to form a main beam and a sub beam, and the second diffraction grating layer diffracts light of a second wavelength to form a main beam and a sub beam, The depth of the first diffraction grating layer is obtained by calculating an intensity change curve of a zeroth order diffraction beam for light of a first wavelength according to the depth of the first diffraction grating layer, and at least a second of the periodic cycles of the change curve. From the depth of the first diffraction grating layer corresponding to the cycle, a depth at which the influence on the light of the second wavelength is minimal is selected, The depth of the second diffraction grating layer is obtained by calculating a change curve of a zero-order diffraction beam for light of a second wavelength according to the depth of the second diffraction grating layer, and at least a second cycle among the periodic cycles of the change curve. The depth of the second diffraction grating layer corresponding to the optical pick-up device, characterized in that the depth of the least influence on the light of the first wavelength is selected. delete delete delete The method of claim 4, wherein The depth of the first diffraction grating layer is selected such that the intensity of the zero-order diffracted beam for light of the second wavelength is at least 90% of the light intensity of the entire second wavelength, and the depth of the second diffraction grating layer is And wherein the intensity of the zeroth order diffracted beam for light of one wavelength is selected to be at least 90% of the light intensity of the entire first wavelength. delete delete delete delete delete

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