KR100294886B1 - Compatible optical pickup device - Google Patents

Abstract

PURPOSE: A compatible optical pickup device is provided to realize compact structure and reduce size by optically modeling an optical element having integrated hologram elements and grating and a 10-split or 12-split main photo detector and to enhance light utilization efficiency by controlling transmission and diffraction employing a polarization hologram element. CONSTITUTION: A compatible optical pickup device comprises a first and a second light sources(50,60) placed on a substrate(41) near to each other to exit a first and a second lights(L1,L2) having difference wavelengths, an objective lens(83) to focus the first and second lights on the recording surface of a recording medium(10), a main photo detector(45) placed on the substrate to detect an information signal and an error signal by receiving the first and second lights reflected onto the recording medium, and an optical element(70) placed on light paths between the light sources and the objective lens and composed of a first and a second transparent members(71,72) and a first and a second hologram elements(74,75) installed on the surfaces of the first and second transparent members to diffract and transmit the first and second lights toward the photo detector.

Description

Compatible Optical Pickup Device

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a compatible optical pickup apparatus, and more particularly, to a compatible optical pickup apparatus in which compatible recording media having different formats can be used.

In general, an optical pickup device is employed in a compact disc player (CDP), a digital multifunction disc player (DVDP), a CD-ROM driver, a DVD-ROM driver, or the like to perform recording / reproducing of information on a recording medium in a non-contact manner.

DVDP and DVD-ROM are attracting attention in the video / audio field as devices capable of high-density recording / playback. The optical pickup device employed in this DVDP employs not only digital video discs (DVDs) but also compact discs (CDs), CD-Rs (Recordables), CD-Is, and CD-Gs as recording media for compatibility. Even if so, it should be possible to record and / or reproduce information.

However, the thickness of the DVD has been standardized to a different specification from the thickness of the CD family due to mechanical disc tilt tolerance and objective lens numerical aperture. That is, the thickness of the existing CD family is 1.2mm while the DVD is 0.6mm. As such, when the CD family and the DVD have different thicknesses, spherical aberration due to the difference in thickness occurs when the optical pickup apparatus for DVD is applied to the CD family. This spherical aberration causes a problem of failing to obtain sufficient light intensity for recording the information signal or deterioration of the signal during reproduction.

Also, in the wavelength of the reproduction light source, DVD has been standardized into a wavelength range different from that of the CD family. That is, while the reproduction light source wavelength for the existing CD family is approximately 780 nm, the reproduction light source wavelength for DVD is approximately 650 nm.

Due to this difference in standardization, since information recorded on a DVD cannot be reproduced by a normal CDP, development of an optical pickup device for a DVD is required. At this time, the optical pickup device for DVD should be compatible with the existing CD family.

As described above, the conventional compatible optical pickup apparatus in consideration of the point, the first light source 21 and the first photodetector 27 to emit light of 780nm wavelength and to receive incident light as shown in FIG. ) Converts a traveling path of light irradiated from the optical module 20 formed integrally with each other, the second light source 31 emitting light having a wavelength of 650 nm, and the first and second light sources 21 and 31, respectively. First and second polarization beam splitters 25 and 33 for reflection, objective lens 17 for focusing incident light onto the disk 10, and reflected from the disk 10 and the first and second polarization beam splitters. And a second photodetector 37 for receiving the incident light through (25) and (33). Here, the first light source 21 is for a relatively thick disk 10b, for example the CD family, and the second light source 31 is for a relatively thin disk 10a, for example, DVD.

The optical module 20 includes a substrate 22 on which a first light source 21, a first light detector 27, the first light source 21 and the first light detector 27 are installed, and the first light source 21. A housing 24 provided to surround the first light source 21 and the first photodetector 27, and a hologram element 23 that changes the traveling path according to the traveling direction of the light transmitted through the housing 24; It is configured to include.

The first and second polarization beam splitters 25 and 33 have mirror surfaces adapted to selectively transmit or reflect incident light according to the polarization direction, and may be integrally formed as shown in the optical configuration. .

The light irradiated from the first light source 21 is reflected by the first polarized beam splitter 25 toward the disk 10, and the light irradiated from the second light source 31 is the second polarized beam splitter. After being reflected at 33, it passes through the first polarizing beam splitter 25 and is directed toward the disk 10.

A λ / 4-wavelength plate for converting light of linearly polarized light into circularly polarized light and circularly polarized light into linearly polarized light on the side of the objective lens 17 side of the first polarization beam splitter 25. 11 is disposed. In addition, on the optical path between the λ / 4 wavelength plate 11 and the objective lens 17, a reflecting mirror 13 reflecting incident light in consideration of optical arrangement and a collimating lens 15 focusing the incident light Is placed.

The light irradiated from the first light source 21 is reflected by the disk 10b having a relatively thick thickness, and is reflected by the first polarization beam splitter 25. Thereafter, the light is diffracted by the hologram element 23 and then received by the first photodetector 27.

On the other hand, the light irradiated from the second light source 31 is reflected by the disk 10a having a relatively thin thickness, and passes through the first and second polarization beam splitters 25 and 33. This light passes through the detection lens 35 causing astigmatism and is received by the second photodetector 37.

As described above, the conventional compatible optical pickup apparatus constructed is complicated in its configuration and has a large number of parts. As a result, the manufacturing cost is high, and the weight of the optical pickup device is large, so that an access time of the disk drive employing the optical pickup device is large.

The present invention has been made in view of the above-described disadvantages, and an object thereof is to provide a compatible optical pickup apparatus having a structure of simplifying an optical configuration and reducing a number of components.

1 is a schematic view showing an optical arrangement of a conventional compatible optical pickup device.

2 is a schematic view showing an optical arrangement of a compatible optical pickup device according to an embodiment of the present invention.

3 is a schematic view showing a first hologram device of FIG. 2;

4 is a graph showing transmission / diffraction efficiency different from the temperature of the first hologram element shown in FIG. 3;

FIG. 5 is a schematic configuration diagram illustrating an embodiment of the photodetector illustrated in FIG. 2;

FIG. 6 is a schematic configuration diagram illustrating another embodiment of the photodetector shown in FIG. 2.

<Description of Symbols for Main Parts of Drawings>

10.Recording medium 40.Light source

41 ... substrate 42 ... housing

43.Photodetector for monitors 45 ... Main photodetector

50, 60 first and second surface optical lasers 70 optical elements

71,72 ... 1st and 2nd transparent member 73 ... Grating

74 First hologram element 74a, 74d Transparent substrate

74b ... liquid crystal polymer 74c ... phase delay plate

75 second hologram element 77 reflective member

83.Objective lens

A compatible optical pickup device according to the present invention for achieving the above object, the substrate; First and second light sources disposed adjacent to each other on the substrate and emitting first and second light having different wavelengths; An objective lens for focusing the first and second light emitted from the light source onto a recording surface of a recording medium; A main photodetector disposed on the substrate, the main photodetector receiving first and second light reflected from the recording medium to detect an information signal and an error signal; The objective lens is disposed on an optical path between the light source and the objective lens, and is disposed on a surface of the first and second transparent members having a predetermined thickness toward the objective lens of the first and second transparent members. And an optical element having first and second hologram elements for diffracting and transmitting each of the first and second light incident from the side toward the photodetector.

Here, the first or second hologram element is preferably a polarization hologram element that varies the transmission efficiency and diffraction efficiency according to the polarization state of the incident light.

Here, the main photodetector may include eight first split plates each having a 2 × 4 array structure independently photoelectrically converted to detect focus error signals and information signals for recording media having different thicknesses; Two second partition plates having a 2 × 1 array structure provided on one side of the first partition plate and a 2 × 1 array structure provided on the other side of the first partition plate so as to detect a track error signal for a recording medium. It is preferred to include two third partition plate having.

On the other hand, the main photodetector, six first split plate having a 2 × 3 array structure that each independently photoelectric conversion so as to detect the focus error signal and the information signal for the recording medium of different thickness, and the Two second partition plates having a 2 × 1 array structure provided on one side of the first partition plate and a 2 × 1 array structure provided on the other side of the first partition plate so as to detect a track error signal for a recording medium. It may include two third partition plate having.

On the other hand, the reflection member is provided on a part of the surface of the first transparent member facing the light source, reflecting a portion of the light irradiated from the light source; And a monitor photodetector provided on the substrate around the light source to receive the light reflected from the reflective member to detect the amount of light emitted from the light source.

Hereinafter, exemplary embodiments of a compatible optical pickup apparatus according to the present invention will be described in detail with reference to the accompanying drawings.

Referring to FIG. 2, a compatible optical pickup apparatus according to an exemplary embodiment of the present invention includes a substrate 41, a light source 40 installed on the substrate 41, and light emitted from the light source 40. An objective lens 83 focused on the recording surface of the recording medium 10, an optical element 70 disposed on an optical path between the light source 40 and the objective lens 83, and on the substrate 41. And a main photodetector 45 arranged to receive light reflected from the recording medium 10 to detect an information signal and an error signal. Here, the substrate 41, the light source 40, the main photodetector 45 and the optical element 70 is preferably installed in the housing 42, as shown in the integral optical module.

The substrate 41 is installed in the housing 42 and is electrically connected to the light source 40 and the main photodetector 45 and electrically coupled to the outside through the lead frame 49.

The light source 40 is disposed adjacent to each other on the substrate 41 and emits first and second light sources 50 and 60 that emit first and second lights L1 and L2 having different wavelengths. Equipped. The first and second light sources 50 and 60 preferably include surface light lasers 50 and 60. In this case, the first and second surface light laser (50, 60) is the size of the window (not shown) that the light is emitted so that the emission angle of the first and second light (L1) (L2) is different from each other It is preferable to vary. In general, the surface light laser emits light in the stacking direction of the semiconductor material layer, thereby facilitating a structural arrangement. In addition, since the size of the first and second surface light laser (50, 60) is within a few tens of micrometers (㎛), the aberration caused by the light emitted from different positions is not a big problem.

The first surface light laser 50 emits red light having a wavelength of approximately 635 to 650 nm so as to be suitable for a relatively thin disk 10a such as DVD, DVD-ROM, DVD-RAM, and the like. Then, the second surface light laser 60 emits infrared light having a wavelength of approximately 780 nm so as to be suitable for the CD family, for example, CD-R, which is a relatively thick disk 10b. Here, the first light L1 emitted from the first surface light laser 50 has a larger radiation angle than the second light L2 emitted from the second surface light laser 60.

The objective lens 83 is mounted and driven in an actuator (not shown) to correct focus error and track error. By the spherical aberration, the objective lens 83 focuses the incident light so that the focal position of the light incident on the paraxial region and the focal position of the light incident on the circular axis region are different. Therefore, the first light L1 having a large emission angle emitted from the first surface light laser 50 passes through the optical element 70 and is focused while passing through the circular axis region of the objective lens 83 to have a thickness. It forms on the relatively thin disk 10a. On the other hand, the second light L2 having a small emission angle emitted from the second surface light laser 60 passes through the optical element 70 and is focused while passing through the paraxial region of the objective lens 83 to have a thickness. It forms on the relatively thick disk 10b.

Here, the collimating lens 81 may be further provided between the optical element 70 and the objective lens 83 so that the light irradiated from the light source 40 is incident on the objective lens 83 in parallel.

The optical element 70 is disposed on an optical path between the light source 40 and the collimating lens 81, and has first and second transparent members 71 having a predetermined thickness from the light source 40. 72 and the first and second light beams L1 and L2 respectively provided on the objective lens 83 side of the transparent members 71 and 72 and incident from the objective lens 83 side, respectively. Gratings formed on the first and second hologram elements 74 and 75 for diffraction transmission toward the main photodetector 45 and on a surface of the first transparent member 71 opposite to the light source 40. 73).

The first and second transparent members 71 and 72 are installed in the housing 42 to be spaced apart from the light source 40 by a predetermined interval and transmit incident light. The first and second hologram elements 74 and 75 are provided on the surfaces of the first and second transparent members 71 and 72 facing the objective lens 83, respectively. The first and second transparent members 71 and 72 are preferably installed in close proximity to each other, that is, bonded with an adhesive. At this time, the thickness of the first transparent member 71 is designed in consideration of the optical width between the first hologram element 74 and the grating 73.

The first hologram element 74 is preferably a polarization hologram element that varies the transmission efficiency and the diffraction efficiency according to the polarization state of the incident light. As shown in FIG. 3, the first hologram element 74 includes a pair of transparent substrates 74a and 74d, a liquid crystal polymer 74b positioned between the transparent substrates 74a and 74d, and And a phase delay plate 74c positioned between the liquid crystal polymer 74b and the transparent substrate 74d toward the objective lens 83 to change the polarization of incident light. In addition, a hologram pattern (not shown) is formed on one surface of the transparent substrate 74d, for example, the light incident from the light source 40 passes straight through and the light incident from the disk 10 is diffracted. Here, the hologram pattern of the first hologram element 74 is formed in consideration of the diffraction angle of the first light L1.

On the other hand, the first hologram element 74 diffracted transmits incident light into a 0th order beam and a 1st order beam, and when the 0th order beam is S-polarized, the primary beam becomes P-polarized light, and when the 0th order beam is P-polarized light, the primary beam Is the S polarization.

FIG. 4 is a graph showing diffraction efficiency and transmittance for P-polarized light and S-polarized light according to temperature in the polarization hologram device shown in FIG. 3.

As shown, the light of P polarization in the range of approximately 0 ° C. to 60 ° C. has a transmittance of about 90% or more and a diffraction efficiency of less than about 5%. The light of S-polarized light has a diffraction efficiency of about 70% and a transmittance of about 5%.

Therefore, when considering the characteristics of the polarizing hologram element and the transmission / diffraction efficiency according to the polarization, the main photodetector by suppressing the loss of the light irradiated from the light source 40, that is, the first surface light laser 50 to the maximum The amount of light received at 45 can be increased. The main photodetector 45 is disposed on the substrate 41 to receive light diffracted by the first hologram element 74.

The second hologram element 75 is a conventional hologram element and is disposed on a surface of the second transparent member 72 facing the objective lens 83. The second hologram element 75 may be formed by etching a portion of the surface to form a hologram pattern, and the light incident from the light source 40 passes straight through and is incident from the disk 10 side. The light to be selectively diffracted is transmitted. That is, among the light incident from the disk 10 side, the first light L1 is transmitted through the straight line, and the second light L2 is diffracted and transmitted to the main photodetector 45. Here, the hologram pattern of the second hologram element 75 is formed in consideration of the diffraction angle of the second light L2.

The grating 73 diffracts and transmits the light irradiated to the light source 40 with a 0 th order beam, a ± 1 st order beam, ..., so that the track error signal can be detected by the 3-beam method.

On the other hand, a part of the surface of the first transparent member 71 facing the light source 40 reflects a part of the light irradiated from the light source 40 toward the monitor photodetector 43 to be described later It is preferable that 77 is further provided. The reflective member 77 may be formed by coating on the first transparent member 71.

The monitor photodetector 43 is installed on the substrate 41 around the light source 40, and receives the light reflected from the reflective member 77 to detect the amount of light emitted from the light source 40. do.

The main photodetector 45 receives the light reflected from the recording medium 10 and diffracted through the hologram element 75 to receive the focus error signal for each of the two disks 10a and 10b having different thicknesses, The track error signal and the information signal (RF signal) are detected. For this purpose, the main photodetector 45 preferably has a structure as shown in FIGS. 5 and 6, respectively.

As shown in Fig. 5, the main photodetector 45 is divided into 12 parts. Here, reference numeral 46 denotes a photodetector structure having an arrangement of a 2x4 structure, and reference numerals 47 and 48 each represent a 2x provided around the photodetector structure having the 2x4 arrangement to detect a track error signal. It shows a photodetector structure having an array of one structure.

When a relatively thin disk 10a is employed as the recording medium, the light irradiated from the first surface light laser 50 is used as the effective light. At this time, the 0th order beams capable of detecting the information signal and the error signal are received by the split plates A, B, C, and D of the main photodetector 45.

Accordingly, in the case of the disk 10a, the focus error signal FES, the track error signal TES, and the information signal RFS may be represented by Equation 1 below. Here, the track error signal uses the DPD method. In this case, the ± first order beams received on the dividers I and J and the dividers K and L, respectively, are not used.

FES = (A + C)-(B + D)

TES = (A + C)-(B + D)

RFS = A + B + C + D

In addition, when the disk 10a is a DVD-RAM, the track error signal uses a differential push-pull (DPP) method.

On the other hand, when the relatively thick disk 10b is employed as the recording medium, the light irradiated from the second surface light laser 60 is used as the effective light. At this time, the 0th order beams for detecting the information signal and the focus error signal are received on the partition plates E, F, G, and H of the main photodetector 45, and the track errors are applied to the partition plates I, J, K, and L, respectively. The ± 1st order beam which can detect a signal is received. Here, the ± first order beam received by the divider is received at a position different from the ± first order beam of the disk 10a having the above thickness.

In this case, the focus error signal FES ', the track error signal TES', and the information signal RFS 'may be represented by Equation 2. Here, the track error signal is based on the three beam method.

FES '= (E + G)-(F + H)

TES '= (I + J)-(K + L)

RFS = E + F + G + H

In addition, the main photodetector 45 may be divided into 10, as shown in FIG. Here, reference numeral 46 'denotes a photodetector structure having an array of 2x3 structures.

When a relatively thin disk 10a is employed as the recording medium, the light irradiated from the first surface light laser 50 is used as the effective light. At this time, the 0th order beams are received by the split plates A, B, E, and F of the main photodetector 45, and the ± 1st order beams are received by the split plates I, J, K, and L, respectively.

Therefore, in the case of the disk 10a, the focus error signal FES, the track error signal TES, and the information signal RFS may be represented by Equation 3 below. Here, the track error signal is based on the DPD method.

FES = (A + E)-(B + F)

TES = (A + E)-(B + F)

RFS = A + B + E + F

When the DVD-RAM is adopted as the disk 10a, the track error signal uses a differential push pull method.

On the other hand, when the relatively thick disk 10b is employed as the recording medium, the light irradiated from the second surface light laser 60 is used as the effective light. At this time, the 0th order beams for detecting the information signal and the focus error signal are received by the dividers B, C, D, and E of the main photodetector 45, and the track errors are applied to the dividers I, J, K, and L, respectively. The ± 1st order beam which can detect a signal is received.

In this case, the focus error signal FES ', the track error signal TES', and the information signal RFS 'may be represented by Equation 4.

FES '= (B + D)-(C + E)

TES '= (I + J)-(K + L)

RFS = B + C + D + E

In this way, the partitions 10 and 10 share the partitions B and E for two disks having different thicknesses.

Hereinafter, an operation of a compatible optical pickup apparatus according to an exemplary embodiment of the present invention will be described with reference to FIG. 2.

When a relatively thin disk 10a such as a DVD is used as the recording medium, the light irradiated from the first surface light laser 50 is used as the effective light. For example, the light irradiated from the first surface light laser 50 is mostly P-polarized light, and the first hologram element 74 is polarized light having polarization transmission / diffraction efficiency according to temperature as shown in FIG. 4. In the case of a hologram element, the 0th order light by the polarization hologram element is light of P polarization, and the 1st order light is light of S polarization. Therefore, one of the first light L1 incident on the first surface light laser 50 side, for example, P-polarized light passes straight through the first hologram element 74 and is focused by the objective lens 83 to be disc. It is concluded at (10a). Thereafter, the light reflected from the disk 10a passes through the objective lens 83 and is re-entered into the first hologram element 74. Of the re-incident first light L1, for example, light of S-polarized light is diffracted through the first hologram element 74 and directed to the main photodetector 45.

The main photodetector 45 is composed of 12 divisions or 10 divisions, and independently converts light received at each partition plate. On the other hand, the light irradiated from the first surface light laser 50 and reflected from the reflective member 77 is received by the monitor photodetector 43 provided on the substrate 1. Since the output light amount of the first surface light laser 50 can be known from the received light signal, the light output of the first surface light laser 50 can be controlled based on this.

On the other hand, when the disk 10b having a relatively thick thickness is employed as the recording medium, the light emitted from the second surface light laser 60 is used as the effective light. The second light L2 emitted from the second surface light laser 60 passes straight through the second hologram element 75 and is focused by the objective lens 83 to be formed on the disk 10b. Thereafter, the light reflected from the disk 10b passes through the objective lens 83 and is re-incident to the second hologram element 75. The second incident light L2 is diffracted and transmitted through the second hologram element 75 to the main photodetector 45 and is received by another splitter plate of the main photodetector 45.

As described above, the compatible optical pickup apparatus according to the present invention employs two surface optical lasers that emit light having different wavelengths as a light source, an optical element in which first and second hologram elements and gratings are integrally installed; By adopting a 10- or 12-divided main photodetector and optically modularizing it, it is possible to realize the reduction of the number of parts, the simplification of the structure, and the miniaturization.

In addition, since the polarization hologram element is provided as the first hologram element, transmission / diffraction is controlled, so that light utilization efficiency is high.

Claims (9)

A substrate; First and second light sources disposed adjacent to each other on the substrate and emitting first and second light having different wavelengths; An objective lens for focusing the first and second light emitted from the light source onto a recording surface of a recording medium; A main photodetector disposed on the substrate, the main photodetector receiving first and second light reflected from the recording medium to detect an information signal and an error signal; The objective lens is disposed on an optical path between the light source and the objective lens, and is disposed on a surface of the first and second transparent members having a predetermined thickness toward the objective lens of the first and second transparent members. And an optical element having first and second hologram elements for diffracting and transmitting each of the first and second light incident from the side toward the photodetector. The compatible optical pickup apparatus of claim 1, wherein the first or second hologram element is a polarization hologram element having different transmission efficiency and diffraction efficiency according to the polarization state of incident light. The method of claim 2, wherein the polarization hologram element, A pair of transparent substrates; A liquid crystal polymer positioned between the transparent substrates and varying transmission efficiency according to the polarization state of incident light; And a phase delay plate positioned between the liquid crystal polymer and the transparent substrate toward the objective lens to change the polarization of the incident light. The compatible optical pickup apparatus of claim 1, wherein each of the first and second light sources is a surface light laser that generates and emits light in a stacking direction of the semiconductor material layer. The method of claim 1, wherein the main photodetector, Eight first split plates each having a 2 × 4 array structure for photoelectric conversion independently so as to detect focus error signals and information signals for recording media having different thicknesses; Two second split plates having a 2 × 1 array structure provided on one side of the first partition plate and a 2 × 1 array provided on the other side of the first partition plate so as to detect a track error signal for the recording medium. Compatible optical pickup device characterized in that it comprises two third partition plate having a structure. The method of claim 1, wherein the main photodetector, Six first split plates each having a 2 x 3 array structure for photoelectric conversion independently so as to detect focus error signals and information signals for recording media having different thicknesses; Two second split plates having a 2 × 1 array structure provided on one side of the first partition plate and a 2 × 1 array provided on the other side of the first partition plate so as to detect a track error signal for the recording medium. Compatible optical pickup device characterized in that it comprises two third partition plate having a structure. The method of claim 1, wherein the optical element, And a grating formed on a surface of the first transparent member facing the light source to diffract and transmit incident light. The light emitting device of claim 1, further comprising: a reflection member disposed on a portion of the surface of the first transparent member that faces the light source; And a monitor photodetector mounted on the substrate around the light source to receive the light reflected from the reflective member and detect the amount of light emitted from the light source. The compatible optical pickup apparatus of claim 8, wherein the reflective member is a reflective coating film formed on a portion of the surface of the first transparent member facing the light source.