KR20080046463A - Optical pick-up apparatus - Google Patents

Abstract

An optical pickup apparatus is provided to reduce the number of components forming an optical path and minimize assembly clearance of relative displacement of each component since each component has multiple functions. An optical pickup apparatus comprises a light source(20), a diffraction-type polariscope(22), a collimator lens(26), a circular polarizer(28), an objective lens(30), a photodetector(36), a beam splitter(24), and a sensor lens(34). The light source generates light of different wavelengths. The diffraction-type polariscope diffracts the light from the light source to split the light, and selectively shifts polarization direction. The collimator lens makes the light from the polariscope into parallel light. The circular polarizer makes the light from the collimator lens polarized in circle. The objective lens receives the circularly polarized light and illuminates the light on a recording medium. The photodetector receives the light reflected from the recording medium to reproduce a signal recorded on the recording medium. The beam splitter is installed between the diffraction-type polariscope and the collimator lens for splitting incident light and transmitting toward the recording medium and photodetector. The sensor lens condenses the light transmitted by a disk(32) onto a photodetector in the form of a spot.

Description

Optical pick-up apparatus

1 is a block diagram showing a configuration of an optical pickup apparatus according to the prior art.

Figure 2 is a block diagram showing the configuration of a preferred embodiment of the optical pickup apparatus according to the present invention.

Figure 3 is a schematic perspective view showing the configuration of an embodiment of the present invention.

Explanation of symbols on the main parts of the drawings

20: light source 22: diffractive polarizer

24: Optical separator 26: Collimator lens

28: phase delay total mirror 30: objective lens

32: disc 34: sensor lens

36: photodetector

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 capable of generating digital light of different wavelengths and recording digital data on a different type of recording medium and reproducing the recorded data.

An optical pickup apparatus generates light from a light source to form pit information on a surface of a disk, which is a recording medium, or reproduces recorded data using light reflected from the formed pit information.

In this case, there are various types of recording media used, and CDs and DVDs are most commonly used. Meanwhile, an optical pickup that can record and play back both the CD and the DVD is provided so that both the CD and the DVD can be used as one disc drive. In order to use both CD and DVD in one disk drive, two light sources generating light of different wavelengths are used.

1 is a block diagram of a conventional optical pickup apparatus having a light source for generating light having different wavelengths.

A first light source 1 and a second light source 2 for generating light of different wavelengths are provided. The first light source 1 generates CD light, for example, and the second light source 2 generates DVD light.

On the path through which the light from the light sources 1 and 2 travel, polarization half wave plates 3 are respectively provided. The polarization half wave plate 3 separates the light into three to enable the tracking operation and generates a 180 degree phase difference with respect to the vertical and horizontal polarization to rotate in the polarization direction of the incident light.

The light from the light sources 1 and 2 passes through the polarization half wave plate 3 and is then transmitted to the prism 5. The prism 5 transmits the light from the first light source 1 and reflects the light from the second light source 2 to match the path of the light from each of the light sources 1 and 2.

Light exiting the prism 5 is reflected by the optical splitter 7. The optical separator 7 serves to transmit the light reflected from the disk 17 to be described below to the photodetector 19 and to reflect the light from the light sources 1 and 2.

The collimating lens 9 converts the light from the light sources 1 and 2 into parallel light so that the recording of the signal on the disk 17 and the reproduction of the recorded signal are performed well. In other words, the scattered light is made into parallel light.

The circularly polarizing plate 11 improves recording characteristics or noise characteristics by making linearly polarized light into circularly polarized light. The circularly polarizing plate 11 serves to make circularly polarized light that has passed through the collimating lens 9.

The total mirror 13 changes the path of the light so that the light can be transmitted to the objective lens 15. The total mirror 13 reflects the light to change the path of the light exiting the circular polarizer 11 to be transmitted to the objective lens 15.

The objective lens 15 is installed in the bobbin (not shown) of the actuator in the optical pickup device to condense the light onto the disk 17. The objective lens 15 also receives the light reflected from the disk 17 and transmits the light through the reverse path.

Light reflected from the disk 17 passes through the optical separator 7 and is transmitted to the sensor lens 18. The sensor lens 18 causes the light detector 19 to collect light in a spot shape. The photodetector 19 detects the light reflected from the disk 17 and plays a role of reproducing the signal recorded on the disk 17.

However, the optical pickup apparatus according to the related art as described above has the following problems.

First, the prior art uses the first and second light sources 1 and 2 to generate light of different wavelengths in one optical pickup device. Therefore, each light source 1, 2 should be installed in the optical pickup device, and since the polarization half-wave plate 3 is required, respectively, there is a problem that the number of parts is increased as a whole and the size of the optical pickup device is increased.

In addition, components each having a specific function must be used separately, and their relative positions must be adjusted so as to form an optical path. Therefore, when a large number of parts are installed while forming an optical path, there is a problem that the operation reliability of the optical pickup device is deteriorated while the cumulative tolerance such as relative position values between the parts increases.

Accordingly, it is an object of the present invention to provide an optical pickup apparatus which minimizes the number of components to solve the problems of the prior art as described above.

Another object of the present invention is to provide an optical pickup apparatus which minimizes a cumulative tolerance according to a relative position between components in an optical pickup apparatus.

According to a feature of the present invention for achieving the above object, the present invention is a light source for providing light of different wavelengths, and diffraction to separate the light by diffracting the light from the light source and to selectively change the polarization direction And a collimating lens for converting the light passing through the diffractive polarizer into parallel light, a circular polarizing plate for circularly polarizing the light passing through the collimating lens, and irradiating the recording medium with the circularly polarized light. And an optical detector for receiving the light reflected from the recording medium and reproducing the signal recorded on the recording medium.

An optical splitter is further provided between the diffractive polarizer and the collimator lens to separate and transmit incident light to the recording medium and the photodetector.

A sensor lens for condensing the light reflected from the disk and transmitted to the photodetector in a spot form is further provided.

The diffractive polarizer comprises a grating for diffraction selectively according to the type of light and a broadband half-wave plate for generating a 180 degree phase difference with respect to the incident vertical and horizontal polarization directions to change the polarization angle of the light.

According to another feature of the invention, the present invention is a light source for providing light of different wavelengths, a diffractive polarizer for diffracting the light from the light source to separate the light and to selectively change the polarization direction, the diffractive polarizer A collimating lens for converting light passing through the light into parallel light, a phase delay total mirror for circularly polarizing the light passing through the collimating lens and changing the optical path, and the light passing through the phase delay total mirror to the recording medium. An objective lens to be irradiated and a photodetector which receives the light reflected from the recording medium and reproduces the signal recorded on the recording medium.

The phase delay total mirror is formed by forming a coating layer such that the phase difference occurs at a predetermined angle with respect to the horizontal and vertical polarization in the total mirror for changing the path of light by reflection.

An optical splitter is further provided between the diffractive polarizer and the collimator lens to separate and transmit incident light to the recording medium and the photodetector.

A sensor lens for condensing the light reflected from the disk and transmitted to the photodetector in a spot form is further provided.

The diffractive polarizer comprises a grating for diffraction selectively according to the type of light and a broadband half-wave plate for generating a 180 degree phase difference with respect to the incident vertical and horizontal polarization directions to change the polarization angle of the light.

According to the present invention having such a configuration, the number of components is minimized, so that the optical pickup apparatus can be miniaturized, and since the components having a plurality of functions are used, the operation reliability is improved while the accumulated tolerance according to the relative position is minimized.

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

Fig. 2 shows the construction of a preferred embodiment of the optical pickup apparatus according to the present invention, and Fig. 3 shows the construction of the embodiment of the present invention in a schematic perspective view.

As shown in these figures, the light source 20 generates light for recording and reproducing data. In particular, the light source 20 selectively generates light having different wavelengths for recording and reproducing on the CD and DVD, respectively. The wavelength of the light is about 780 nm for CD and about 650 nm for DVD.

The diffractive polarizer 22 is installed on the path along which the light from the light source 20 travels. The diffractive polarizer 22 performs a function of selectively diffracting the light emitted from the light source 20 and a function of rotating a polarization direction of the light by generating a phase difference with respect to the vertical and horizontal polarization directions.

To this end, the diffractive polarizer 22 may be composed of two wavelength-selective gratings that serve to diffract light. One of the gratings diffracts only the light for the DVD and the other grating diffracts only the light for the CD. As such, the light is diffracted to separate the light from the light source 20 into three to enable the tracking operation.

In addition, a half wave plate is used for the diffractive polarizer 22. The half-wave plate generates a phase difference of 180 degrees with respect to the incident vertical and horizontal polarization directions, and rotates the polarization direction of light incident at an angle of -2a, for example. In particular, the half-wave plate in the present invention uses a broadband half-wave plate. This results in the same performance over a wide wavelength range (a wavelength range in which both CD and DVD light).

Light exiting the diffractive polarizer 22 is transmitted to the optical separator 24. In the optical separator 24, the light emitted from the light source 20 is reflected to change the optical path. The optical separator 24 also performs a function of transmitting the light reflected from the disk 32, which is a recording medium, to be transmitted to the photodetector 36, which will be described below.

Light from the optical separator 24 passes through a collimator lens 26. Since the collimating lens 26 is a light emitted from the light source 20 is a scattered light, it serves to convert it into parallel light. By making the light emitted from the light source 20 into parallel light in this way, the recording of the signal on the disk 32 is made better.

The light passing through the collimation lens 26 is reflected by the phase delay total mirror 28. The phase delay total mirror 28 has a function of generating a phase difference at 90 degrees or 270 degrees with respect to the vertical and horizontal polarization when light is incident at a specific angle. The phase delay total mirror 28 generates a phase delay by forming a coating layer on the surface of the total mirror that changes the path of light. For example, when light polarized in the 45 degree direction is incident, the light is converted into circularly polarized light. When light is made circularly polarized in this manner, recording characteristics and noise characteristics are relatively improved.

The light reflected by the phase delay total mirror 28 is transmitted to the objective lens 30. The objective lens 30 is installed in a bobbin (not shown) constituting an actuator of the optical pickup device. As the bobbin is moved for tracking and focusing operation, the objective lens 30 irradiates light to a position moved from the disk 32.

The sensor lens 34 is installed on a path through which the light reflected from the disk 32 and passed through the optical separator 24 is transmitted. The sensor lens 34 collects light in a spot form on the photodetector 36 to be described below.

The photodetector 36 detects light reflected from the disk, and a photodiode may be used. The photodetector 40 is provided with a plurality of cells to detect the light collected by the sensor lens 34.

Hereinafter, the operation of the optical pickup apparatus according to the present invention having the configuration as described above will be described in detail.

First, the operation of the optical pickup apparatus of the present invention will be described schematically. The light emitted from the light source 20 is diffracted while passing through the diffractive polarizer 22 to split the light into three. In this way, when splitting the light by diffraction, the grating of the diffractive polarizer 22 diffracts the light of each wavelength. The broadband half-wave plate generates a 180 degree phase difference with respect to the incident vertical and horizontal polarization directions.

Next, the light passing through the diffractive polarizer 22 is transmitted to the optical splitter 24. The light is reflected by the optical separator 24 and transmitted to the collimating lens 26. As the light passes through the collimating lens 26, light is changed from scattered light to parallel light.

The light that passes through the collimating lens 26 and becomes parallel light is circularly polarized by the phase delay total mirror 28 to be transmitted to the objective lens 30. In the phase delay total mirror 28, when light is incident at a specific angle, a phase difference is generated at 90 degrees or 270 degrees with respect to the vertical and horizontal polarization. For example, when the light polarized in the 45 degree direction is incident, circularly polarized light is generated. The reflection is reflected by the objective lens 30.

Light transmitted to the objective lens 30 is irradiated onto the signal recording surface of the disk 32 as the bobbin moves. Light condensed on the disk 32 through the objective lens 30 records a signal on the disk 32 or reproduces the recorded signal. The light writes a signal to the disk 32 because the light irradiated to the disk 32 forms pit information on the signal recording surface of the disk 32. And, the reproduction of the signal recorded by the light on the disk 32 is accomplished by being reflected in the pit information and transmitted to the photodetector 36 through the path described below.

The light reflected from the disk 32 passes through the objective lens 30, the phase delay total mirror 28, the collimation lens 26, and the optical separator 24 and is transmitted to the sensor lens 34. The sensor lens 34 condenses the light in the form of spots in the cells of the photodetector 36. The photodetector 36 receiving the light reproduces the signal recorded on the disk 32 through the reflected light.

The scope of the present invention is not limited to the embodiments described above, but is defined by the claims, and various changes and modifications can be made by those skilled in the art within the scope of the claims. It is self evident.

For example, the optical pickup apparatus of the present invention does not need to include all the various components shown in FIG. 2, and may be configured by selectively using the components according to design conditions. As a specific example, if there is no problem in forming the optical path, the optical separator 36 or the like may not be used. In the case of the sensor lens 34, light may be formed in the spot of the photodetector 36 without the sensor lens 34.

In addition, any one component having a plurality of functions may be used among the components shown in the illustrated embodiment, and the remaining components may each use one component having one function. For example, a diffractive polarizer 22 may be used, and a general total mirror and a circular polarizer may be used instead of the phase delay total mirror 28.

In the optical pickup apparatus according to the present invention as described in detail above, the following effects can be obtained.

In the present invention, a component having a plurality of functions, such as a diffractive polarizer for diffraction and polarization, and a phase delay total mirror for forming a circularly polarized light, using a single light source for providing light having two different wavelengths use. Therefore, the total number of parts constituting the optical pickup device is reduced, thereby minimizing the space required for installing the optical pickup device and miniaturizing the optical pickup device.

In the present invention, since there are many parts having a plurality of functions, the cumulative tolerance according to the relative position between each part can be minimized. Therefore, the operation reliability of the optical pickup device can be improved.

Claims (9)

A light source providing light of different wavelengths, A diffractive polarizer for diffracting the light emitted from the light source to separate the light and selectively changing the polarization direction; A collimating lens for converting the light passing through the diffractive polarizer into parallel light; A circular polarizer for circularly polarizing light passing through the collimating lens; An objective lens for receiving the circularly polarized light and irradiating the recording medium; And an optical detector for receiving the light reflected from the recording medium and reproducing the signal recorded on the recording medium. The optical pickup apparatus of claim 1, further comprising an optical splitter between the diffractive polarizer and the collimating lens to separate and transmit incident light to the recording medium and the photodetector. The optical pickup apparatus of claim 1 or 2, further comprising a sensor lens for condensing the light reflected from the disk and transmitted to the photodetector in a spot shape. 4. The optical waveguide according to claim 3, wherein the diffractive polarizer comprises a grating for diffraction selectively according to the type of light and a broadband half-wave plate for generating a 180 degree retardation with respect to the incident vertical and horizontal polarization directions to change the polarization angle of the light. Optical pickup device. A light source providing light of different wavelengths, A diffractive polarizer for diffracting the light emitted from the light source to separate the light and selectively changing the polarization direction; A collimating lens for converting the light passing through the diffractive polarizer into parallel light; A phase delay total mirror which circularly polarizes the light passing through the collimating lens and changes the optical path; An objective lens for receiving light passing through the phase delay total mirror and irradiating the recording medium; And an optical detector for receiving the light reflected from the recording medium and reproducing the signal recorded on the recording medium. The optical pickup apparatus of claim 5, wherein the phase delay total mirror is formed by forming a coating layer such that the phase difference occurs at a predetermined angle with respect to the vertical and horizontal polarizations in the total mirror for changing the path of light by reflection. The optical pickup apparatus of claim 6, further comprising an optical separator for separating and transmitting the incident light to the recording medium side and the photodetector side between the diffractive polarizer and the collimating lens. The optical pickup apparatus of any one of claims 5 to 7, further comprising a sensor lens for condensing the light reflected from the disk and transmitted to the photodetector in a spot shape. 9. The method of claim 8, wherein the diffractive polarizer comprises a grating for diffraction according to the type of light and a broadband half-wave plate for generating a 180 degree retardation with respect to the incident vertical and horizontal polarization directions to change the polarization angle of the light. Optical pickup device.

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