KR100684340B1 - Optical pick-up device comprising a polka dot beam splitter - Google Patents

Abstract

An optical pickup device including a PBS(Polka dot Beam Splitter) is provided to supply the beam splitter which is irrelevant to a polarized direction of a beam, therefore a separate half-wave plate is not required. A laser source(210) generates a beam. A PBS(220) reflects the beam passing through a GR(Grating)(212') at predetermined angle. A CL(Collimate Lens)(214) changes the reflected beam into a parallel beam. An MR(Mirror)(230) receives the parallel beam to convert a direction of the beam toward an optical disk(260). An OL(Objective Lens)(240) is interposed between the disk(260) and the MR(230), and focuses the beam on a surface of the disk(260). A PDIC(Photo Detector with Integrated Circuit)(250) receives the beam reflected from the disk(260) via the OL(240), the MR(230), the CL(214), and the PBS(220).

Description

Optical pick-up device comprising a polka dot beam splitter}

1 is a block diagram showing an optical pickup apparatus having a conventional optical system;

2 is a block diagram showing an example in which a conventional polka dot beam splitter is used;

3 is a block diagram showing an optical pickup device having an optical system according to an embodiment of the present invention;

4 is a schematic diagram illustrating an example in which the polka dot beam splitter of the present invention reflects / transmits light;

5a and 5b exemplarily show the form of a polka dot beam splitter of the present invention; And

6 is a block diagram showing an optical pickup device having an optical system according to another embodiment of the present invention.

<Description of Symbols for Main Parts of Drawings>

100, 200, 200 ': Optical pickup device

10, 210: laser light source 12, 212, 212 ': diffraction grating

14, 214: collimated lens 16: 1/4 wave plate

20: polarized beam splitter (PBS) 30, 230, 230 ': reflective mirror

32: front light detector (FPD) 40, 240: objective lens

50, 250: photodetector (PDIC) 52: sensor lens (SL)

54: hologram optical element (HOE) 60, 260: optical disc

220: Polka dot beam splitter 222: Polka dot

A: direction of light incidence B: direction of light reflection

C: light transmission direction

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup apparatus, and more particularly, to an optical pickup apparatus including a polka dot beam splitter having a reflectance independent of the polarization direction in an optical system using a laser diode having polarization characteristics as a light source. .

In general, an optical pickup device is a device used to read information recorded on the surface of an optical disk or to record information on the surface of the optical disk, and basically a light source, a mirror (MR), and a light source. An objective lens (OL) for focusing on the surface of the optical disk, a detector for receiving and detecting light reflected from the surface of the optical disk (PDIC), and interposed between these light sources, the objective lens and the detector It consists of an optical system including a plurality of optical lenses (optical lens).

Various types of optical lenses may be used according to the configuration of the optical system. Representative optical lenses include a collimate lens (CL) for converting light into parallel light, a diffraction grating for diffracting light, A beam splitter (BS) for selectively transmitting / reflecting light, a holographic optical element (HOE) for coupling different optical axes, and a sensor lens (SL) for detecting a focus error signal And the like can be used.

The present invention describes a beam splitter (BS), which is responsible for receiving light from a light source and reflecting the light to the optical disk side, and transmitting the light reflected from the optical disk to the detector. Specifically, a specific beam splitter, for example, An optical system (or an optical pickup device) including a polka dot beam splitter will be discussed.

1 is a block diagram illustrating an optical pickup device 100 according to a conventional optical system. Referring to Figure 1, a conventional optical system is described as follows.

Conventional optical systems are configured based on heterogeneous laser light sources, such as CD and DVD, and are described as heterogeneous laser light sources integrally formed in FIG. 1 for convenience of description. For reference, a pair of optical paths indicated by solid and dashed lines in FIG. 1 indicate paths of light having different polarization directions (eg, light emitted from light sources for CD and DVD).

According to FIG. 1, a conventional optical pickup apparatus 100 includes a laser light source 10 (or laser diode) generating light, a diffraction grating 12 diffracting light from a light source, and light passing through the diffraction grating. A beam splitter 20 (BS) reflecting at a predetermined angle, a collimate lens (CL) 14 for converting light reflected from the beam splitter into parallel light, and receiving parallel light to the optical disk 60 side Reflecting mirror 30 (MR) for changing the direction, the objective lens 40 (OL) interposed between the optical disk and the reflecting mirror to focus light on the surface of the optical disk and the light reflected from the optical disk, the objective lens, reflective mirror, collimated And a photo detector with integrated circuit (PDIC) for receiving light through a lens, beam splitter, and the like.

In addition, the conventional optical pickup apparatus 100 includes a hologram optical element 54 (HOE) coupled with different optical axes in front of the photodetector 50, and a sensor lens 52 (SL) for detecting a focus error signal. More).

In addition, since the laser light source 10 emits linearly polarized light (P wave polarization or S wave polarization) light, a quarter wave plate 16 (QWP; quarter wave plate) for converting it into circularly polarized light is added, The apparatus further includes a front monitor photo detector (FPD) 32 for controlling the intensity of light focused on the surface of the optical disk.

The beam splitter 20 used in the conventional optical pickup device 100 is a polarized beam splitter (PBS), which has a characteristic that its reflection / transmittance varies according to the polarization direction of light emitted from the laser light source. . For example, when compared based on S-wave polarization and P-wave polarization, light of P-wave polarization is formed to have a reflectance of about 10 &gt; lower in the polarization beam splitter. Specifically, in the polarization beam splitter applied to the conventional optical pickup apparatus, the reflectance Rs of the S-wave polarization may be approximately 95%, and the reflectance Rp of the P-wave polarization may be formed to approximately 80%.

As described above, since the reflectance of P-wave polarized light in the conventional polarization beam splitter PBS is lower than that of S-wave polarized light, the light of P-wave polarized light is converted to S-wave polarized light when P-polarized light is used. It is common to use a half wave plate (HWP) for the purpose of conversion.

For example, in the conventional optical pickup device 100, a structure in which a half wave plate is formed on the surface of the diffraction grating 12 is illustrated. As such, the half wave plate may be provided coupled to any component in the optical system or may be provided separately as an independent component.

However, since the cost associated with such a half wave plate is a large part in the optical pickup device, the use of the half wave plate itself results in an increase in the overall price of the conventional optical pickup device, and also 1 When the conversion efficiency through the / 2 wavelength plate is lowered, there is a problem that the desired degree of efficiency cannot be expected even in an optical system to which a relatively expensive 1/2 wave plate is applied.

The present invention is to provide an optical pickup device comprising a beam splitter having a reflection / transmittance independent of the polarization direction of light.

The present invention is to provide an optical pickup apparatus in which a separate half wave plate is not required by providing a beam splitter independent of the polarization direction of light.

In order to achieve this object, the present invention is a laser light source; A polka dot beam splitter for selectively transmitting / reflecting light from the laser light source; A reflection mirror for redirecting the light reflected from the polka dot beam splitter to the optical disk side; An objective lens interposed between the reflective mirror and the optical disc to focus light onto the surface of the optical disc; And a photodetector that is reflected from the surface of the optical disc and sequentially receives and detects light passing through the polka dot beam splitter through an objective lens and a reflecting mirror, wherein the polka dot beam splitter is related to the polarization direction of the light of the laser light source. An optical pickup apparatus comprising a polka dot beam splitter characterized by having a constant reflection / transmittance without.

In the present invention, the polka dot beam splitter includes a plate-shaped body and a coating coated in an array of dots on the surface of the body, wherein the transmission / reflectance of the polka dot beam splitter is the remaining portion of the body surface of the polka dot beam splitter. It is set based on the area ratio of a part (uncoated part), It is characterized by the above-mentioned.

Further, in the present invention, the coating portion of the polka dot beam splitter is an polka dot array made of aluminum, the body is characterized in that the transparent substrate of silica material.

In the present invention, the angle of incidence of the polka dot beam splitter is 0 to 45 degrees.

In the present invention, the diffraction grating is interposed between the laser light source and the polka dot beam splitter.

Further, in the present invention, a quarter wave plate for converting light of the laser light source into circularly polarized light is interposed during the optical path between the laser light source and the objective lens, and the quarter wave plate is provided in combination with a reflecting mirror or a diffraction grating. It is characterized in that provided in combination with.

EMBODIMENT OF THE INVENTION Hereinafter, preferred embodiment of this invention is described with reference to an accompanying drawing.

Prior to describing a preferred embodiment of the present invention, US Pat. No. 6,774,368 will be described briefly with regard to polka dot beam splitters.

FIG. 2 is a view illustrating an example in which a conventional polka dot beam splitter is used, and in FIG. 2, the polka dot beam splitter 120 reflects light emitted from the slit 112 of the spectrometer 110 with a predetermined reflectance. It transmits to the reference detector 150 and at a predetermined transmittance, and branches to the sample detector 140 via the sample cell 130.

Also shown in FIG. 2 are collimated lens 126 and lenses 122 and 124 that focus light onto each detector.

The light emitted from the spectrometer has different polarizations for each wavelength, and a polka dot beam splitter having a predetermined reflection / transmittance is used regardless of polarization characteristics. As such, the polka dot beam splitter is an optical element having a predetermined reflection / transmittance irrespective of polarization characteristics, and details thereof will be described below.

3 is a block diagram illustrating an optical pickup apparatus 200 having an optical system according to an exemplary embodiment of the present invention. Referring to Figure 3 describes an optical pickup device according to the present invention.

The optical system according to an embodiment of the present invention is configured based on a heterogeneous laser light source, such as a CD and a DVD. For reference, a pair of optical paths represented by a solid line and a dotted line in FIG. 3 are respectively as in the case of FIG. 1. A path of light having different polarization directions (eg, light from light sources for CD and DVD) is shown.

According to FIG. 3, the optical pickup device 200 according to the present invention includes a laser light source 210 for generating light, a diffraction grating 212 ′ (GR) for diffracting light emitted from the laser light source, and light passing through the diffraction grating. Polka dot beam splitter 220 for reflecting at an angle of PBS (polka dot beam splitter), collimating lens 214 (CL) for converting light reflected from the polka dot beam splitter into parallel light, and receiving optical light 260 Reflecting mirror 230 (MR) to change the direction toward the side, the objective lens 240 (OL) interposed between the optical disk and the reflective mirror to focus light on the surface of the optical disk and the light reflected from the optical disk objective lens, reflective mirror, And a photodetector 250 (PDIC) that receives light via a collimated lens, a polka dot beam splitter, and the like.

In addition, the optical pickup device 200 of the present invention further includes a hologram optical element 254 (HOE) that couples different optical axes in front of the photodetector 250 and a sensor lens 252 (SL) for detecting a focus error signal. It may include.

In addition, since the laser light source 210 emits light of linearly polarized light (P wave polarization or S wave polarization), a quarter wave plate (QWP) for converting it into circularly polarized light may be added. In Fig. 1, the quarter wave plate is provided in a state coupled with the diffraction grating 212 '.

In such an optical system, since the polka dot beam splitter has a constant reflection / transmittance regardless of the polarization direction, a half wave plate (HWP) for changing the polarization direction of light from, for example, P-wave polarization to S-wave polarization unlike the conventional art. It can be seen that this is not used.

That is, while the conventional polarizing beam splitter is configured with a different reflectance according to the polarization direction, the polka dot beam splitter of the present invention has a constant reflection / transmittance regardless of the polarization direction (for example, P wave polarization and S wave polarization). Since it can be provided, it is not necessary to change the light of the low-reflection P-wave polarization into the light of the high-reflection S-wave polarization, thereby eliminating the 1/2 wave plate responsible for changing the polarization direction of the light. It is possible to provide a simplified optical system.

As such, an optical pickup device having a simplified optical system excluding a half wave plate can be supported by using a polka dot beam splitter, and thus the features of the present invention can be summarized by applying a polka dot beam splitter.

Details of the polka dot beam splitter will be described with reference to FIGS. 4 and 5.

As shown in Fig. 4, the polka dot beam splitter 220 of the present invention has light incident at a predetermined angle, for example, preferably at 45 ° (see arrow A), and at the incident angle at a predetermined reflectance on its surface. It is configured to reflect at a corresponding angle (eg 45 °) (see arrow B) and to transmit at a predetermined transmittance (see arrow C).

As shown in FIGS. 5A and 5B, the polka dot beam splitters 220 and 220 ′ are dots formed by being arranged in the form of polka dots on the body S and S ′ of a transparent substrate and on a surface thereof. 222), wherein the polka dot beam splitter has a reflectance determined based on a ratio between the area of the coated portion coated with dots and the area of the remaining portion (uncoated portion) except the coated portion of the body.

The shape of the dot may be a rectangular shape, and the dot coated in the predetermined area S is arranged in a predetermined pattern, whereby the area ratio between the coating part in the predetermined area S and the uncoated part which is the remaining part thereof may be determined. Can be.

In addition, in the present invention, the coating of the polka dot beam splitter is formed of an aluminum coating, and the body is preferably formed of a transparent substrate made of silica. More preferably, "B270 glass" or "UV fused silica" may be used as the transparent substrate.

In addition, it is preferable that the reference | standard of the polka dot beam splitter applied to this invention is a reflectance about 90% +/- 2% or more. That is, in the conventional polarizing beam splitter, it is preferable to have a value close to the relatively high reflectance of the reflectance Rs for light of S-wave polarization and the reflectance Rp for light of P-wave polarization.

As such, since the reflectance of the incident light is determined based on the area ratio between the coated portion and the uncoated portion, the polka dot beam splitter of the present invention has a polarization direction in the optical pickup device using the light of the laser light source having the polarization characteristic. It is possible to reflect light irrespective of each other, thereby fundamentally preventing the demand of the 1/2 wave plate for forcibly changing the polarization direction of the incident light as described above.

In addition, unlike the conventional case in which the diffraction grating and the half wave plate are coupled, in the present invention, the diffraction grating and the quarter wave plate are combined, so that a separate quarter wave plate is not required and thus an optical system is constructed. The number of elements can be radically reduced. Further, since the quarter wave plate is configured before the polka dot beam splitter, light of circular polarization can be incident on the polka dot beam splitter, and the quarter wave plate can be made smaller in effective diameter.

Next, FIG. 6 is a block diagram illustrating an optical pickup device 200 ′ having an optical system according to another embodiment of the present invention. 6 is basically similar to the optical system of FIG. 3 except that the quarter wave plate QWP is formed by being coupled to the reflection mirror. Therefore, detailed description of the similar components will be omitted.

As described above, the present invention is characterized by an optical system using a polka dot beam splitter having a constant reflectance irrespective of the polarization direction in place of the conventional polarizing beam splitter, and by providing an optical pickup device according to such an optical system The / 2 wavelength plate (HWP) can be excluded from the optical system to reduce the manufacturing process and the number of components required for the configuration. In addition, the shortening of the manufacturing process can result in improved product reliability.

In addition, by eliminating the 1/2 wave plate, it is possible to reduce the number of parts, thereby improving the production yield by reducing the manufacturing cost and shortening the process.

The optical pickup apparatus including the polka dot beam splitter according to the present invention is characterized by applying a polka dot beam splitter in place of the conventional polarizing beam splitter, thereby changing the light of the P wave polarization into the light of the S wave polarization. It is possible to exclude components such as a half wave plate to make, to reduce the number of components constituting the optical system and to shorten the manufacturing process can improve the reliability of the product.

Claims (9)

Laser light source; A polka dot beam splitter for selectively transmitting / reflecting light from the laser light source; A reflection mirror for redirecting light reflected from the polka dot beam splitter to an optical disk; An objective lens interposed between the reflective mirror and the optical disk to focus light onto the surface of the optical disk; And A photodetector that is reflected from a surface of the optical disk and sequentially receives light passing through the objective lens and a reflection mirror to pass through the polka dot beam splitter; Wherein the polka dot beam splitter has a constant reflection / transmittance regardless of the polarization direction of light of the laser light source. The polka dot beam splitter of claim 1, wherein the polka dot beam splitter includes a flat body and a coating coated on the surface of the body in a dot array, and the transmission / reflectance of the polka dot beam splitter is coated on the surface of the body. An optical pickup apparatus characterized in that it is set based on the area ratio of the remaining portion (uncoated portion) that is not. The optical pickup apparatus of claim 2, wherein the coating part of the polka dot beam splitter is an polka dot array made of aluminum. The optical pickup apparatus of claim 2, wherein the body of the polka dot beam splitter is a transparent substrate made of silica. The optical pickup apparatus of claim 1, wherein an incident angle of the polka dot beam splitter is 0 to 45 degrees. The optical pickup apparatus of claim 1, wherein a diffraction grating is interposed between the laser light source and the polka dot beam splitter. An optical pickup apparatus according to claim 1, wherein a quarter wave plate for converting light of the laser light source into circularly polarized light is interposed during the optical path between the laser light source and the objective lens. 8. The optical pickup apparatus of claim 7, wherein the quarter wave plate is provided in combination with the reflective mirror. 8. The optical pickup apparatus of claim 7, wherein the quarter wave plate is provided in combination with the diffraction grating.

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