KR19990020934A - Optical pickup device - Google Patents

Abstract

An optical pickup apparatus is described. The optical pickup apparatus described includes: a laser light source; A first reflective optical element provided between the objective lens and the laser light source to circularly polarize the first polarization in the first direction toward the disk, and convert the circularly polarized light reflected from the disk into the second polarization in the second direction Wow; A second reflection type optical element provided between the first reflection type optical element and a laser light source to split and reflect the second polarized light in the second direction with a plurality of photodetectors; Equipped. Such an optical pickup device is capable of miniaturization and light weight since a small number of optical parts is applied, and a manufacturing cost is low because no expensive optical parts are used.

Description

Optical pickup device

The present invention relates to an optical pickup device, and more particularly, to a miniaturized optical pickup device.

Optical pickup records and reproduces information such as an image, sound, or data on a recording medium with high density. Recording media include discs, cards, tapes, and the like, and discs form a large variety of recording media. The disk has a substrate made of plastic or glass of constant thickness through which light is transmitted and a recording layer on which information is recorded on the back of the substrate. The disc has a standardized size, and the amount of information that can be recorded is limited. Therefore, in order to store more information on a disc of standardized size, it is necessary to increase the information recording density of the recording layer. In order to increase the recording density, the size of the beam spot formed in the recording layer should be reduced. The size of the beam spot is closely related to the size of the numerical apature of the objective lens and the wavelength of the beam. That is, the larger the numerical aperture of the objective lens and the shorter the wavelength of the beam, the smaller the beam spot size.

Digital versatile disks (DVDs), which have been recently developed and used, are examples of high capacity disks in which information is recorded at high density. DVD is a high-capacity and recordable and reproducible, so the digital versatile disk drive (DVDP) has recently emerged as a replacement for the video tape recorder (VTR), and ongoing research is ongoing.

DVDP uses a high power laser diode as a light source. The power of a light source of about 1 mW is required for reproduction, and a high power of 10 mW or more is required for recording. Therefore, it is urgent to increase the optical light utilization efficiency for recording and reproducing more effective information. In order to increase the light utilization efficiency, a wave plate is generally used together with a polarization splitting element. Due to the use of such optical components, optical pickup for DVD for recording and reproduction is heavier as a result than conventional optical pickup for CD playback. This heavy optical pickup is disadvantageous for accessing and recording information on the recording layer of the disc.

1 is a schematic configuration diagram of a conventional optical pickup apparatus.

Referring to Fig. 1, photodetectors 8 are provided on both sides of a laser diode 1 for generating a laser beam to receive light reflected from the disk 7. The laser beam emitted from the laser diode 1 passes through the collimating lens 2 and then is reflected by the reflecting plate 3 and then proceeds toward the disc 7. On the optical propagation axis between the reflecting plate 3 and the disc 7, a polarization hologram element 4, a quarter wave plate 5 and an objective lens 6 are provided in the optical propagation direction. The laser beam emitted from the laser diode 1 is linearly polarized and circularly polarized while passing through the quarter wave plate 5. Then, the light reflected from the disk 7 passes through the quarter-wave plate 5 again and changes to linearly polarized light rotated 90 degrees in the initial polarization direction. The polarization hologram element 4 diffracts the linearly polarized light rotated 90 degrees by the quarter wave plate 5 into ± 1 light. The diffracted light is reflected by the reflecting plate 3 and then passes through the collimating lens 2 to reach the photo detector 8 provided on both sides of the laser diode 1.

The polarization hologram element 4 has a diffraction grating 41 for diffracting polarized light as shown in FIG. In general, the polarization hologram element 4 is made of LiNbO ₃ , which is a birefringent material, and has a proton exchanged region 42 and a dielectric film 43 of the diffraction grating 41. The proton exchange region is filled with protons of similar refractive index as those of ordinary ray. In addition, the quarter-wave plate is made of quartz of a predetermined optical thickness (D, D = (2m + 1/4) λ, m: arbitrary integer, λ: wavelength of the laser beam).

The conventional optical pickup apparatus as described above can be miniaturized to some extent by applying a polarizing hologram element, but is disadvantageous in terms of cost because of the use of a polarizing hologram element made of an expensive birefringent material.

SUMMARY OF THE INVENTION An object of the present invention is to provide a compact, lightweight optical pickup.

It is also an object of the present invention to provide a low-cost optical pickup.

1 is a schematic configuration diagram of a conventional optical pickup device;

2 is an enlarged view of a portion A of FIG. 1;

3 is a schematic structural diagram of an optical pickup apparatus according to the present invention;

4 is an exploded perspective view of the main parts of the optical pickup device according to the present invention shown in FIG.

5 is a view showing first and second embodiments of a diffraction grating formed on a reflecting surface of a first reflective optical element of the optical pickup device according to the present invention;

6 is a schematic structural diagram of a third embodiment of an optical pickup apparatus according to the present invention;

FIG. 7 is a view showing an incidence direction of first polarized light on a reflective surface of a first reflective optical element of the optical pickup device shown in FIG. 6; and

FIG. 8 is a view schematically showing a light traveling path with respect to a reflective surface of the first reflective optical element of the optical pickup device shown in FIG. 6.

According to the present invention for achieving the above object, a laser light source; An objective lens for condensing a laser beam on the disk, the laser beam generating linearly polarized light from the light source; A plurality of photodetectors for detecting the light reflected from the disk; A first reflection optical element provided between the objective lens and the laser light source to circularly polarize the polarization in the first direction toward the disk, and convert the circularly polarized light reflected from the disk into linearly polarized light in the second direction; A second reflection type optical element provided between the first reflection type optical element and a laser light source to split and reflect the linearly polarized light in the second direction with the plurality of photodetectors; There is provided an optical pickup device provided.

In the present invention, the first reflective optical element has two light passing surfaces and one light reflecting surface, and converts the first linearly polarized light into circularly polarized light and the circularly polarized light into second linearly polarized light on the light reflective surface. It is desirable to apply a prism in which a diffraction grating can be formed. In addition, the second reflecting optical element is a flat reflector or a first reflecting optical element having a reflecting surface on which a diffraction grating is formed to divide the second linearly polarized light into two paths by a birefringence action by diffraction of light. It is preferable to apply a prism having two light passing surfaces and one reflecting surface as shown in FIG.

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

Examples 1 and 2

3 and 4, a photodetector 800 for receiving light reflected from the disk 700 on both sides of the laser beam vibrating in the first direction, that is, the laser diode 100 generating the first polarization. ) Is installed. Between the disk 700 and the laser diode 100, the collimating lens 200, the second reflective optical element 400, the first reflective optical element 500 in the light traveling direction from the laser diode 100. And an objective lens 600 is provided. The first and second optical devices 500 and 400 are formed with two light passing surfaces 501 and 502, 401 and 402 and light reflection surfaces 503 and 403 like a prism. The light reflection surface of the second optical element has a diffraction grating 404 having a vector component 405 parallel to an imaginary plane, ie, an incident surface, on which a traveling path of incident light and a traveling path of reflection are located. . The vector component 405 is perpendicular to the longitudinal direction of the diffraction grating. On the light reflection surface 503 of the first optical device 500, a first polarized light incident from a laser diode is rotated 90 degrees with respect to the first polarized light and circularly polarized light reflected from the disk 100. A diffraction grating 504 is formed to convert to polarized light. The diffraction grating 504 is arranged to maintain an angle of 45 degrees with respect to the first and second polarizations. As shown in FIGS. 5A and 5B, a diffraction grating 504 may be formed on the reflective surface 503, at which time the direction of the diffraction grating 504 is 45 degrees with respect to the first polarized light. The first reflective optical device 500 is disposed to maintain. The diffraction grating 404 is also formed on the reflective surface of the second reflective optical element 400. The diffraction grating 404 of the second reflective optical element 400 is formed such that a birefringence effect occurs on the second polarized light. The diffraction grating 404 is engraved on the reflective surface 403 of the second reflective second optical element 400, and a metal or dielectric thin film is deposited thereon. The pitch of the diffraction grating 404 has a value smaller than the wavelength of light, and its direction is parallel to the second polarization. This is to use the birefringence phenomenon that appears when the period of the diffraction grating is smaller than the light wavelength. The diffraction efficiency is different depending on the direction of polarization with respect to the grating direction.

Example 3

Referring to FIG. 6, photodetectors 800 are installed on both sides of the laser beam oscillating in the first direction, ie, the laser diode 100 generating the first polarized light. It is. Between the disk 700 and the laser diode 100, the collimating lens 200, the second reflective optical element 400, the first reflective optical element 500 in the light traveling direction from the laser diode 100. And an objective lens 600 is provided. The first and second optical devices 500 and 400 are formed with two light passing surfaces 501 and 502, 401 and 402 and light reflection surfaces 503 and 403 like a prism. The light reflection surface of the second optical element has a diffraction grating 404 having a vector component 405 parallel to an imaginary plane, ie, an incident surface, on which a traveling path of incident light and a traveling path of reflection are located. . On the light reflection surface 503 of the first optical device 500, a first polarized light incident from a laser diode is rotated 90 degrees with respect to the first polarized light and circularly polarized light reflected from the disk 100. A diffraction grating 504 is formed to convert to polarized light. The diffraction grating 504 is arranged to maintain an angle of 45 degrees with respect to the first and second polarizations. Meanwhile, the light passing surface 501 of the second optical device 500 is rotated with respect to the first optical device 400. At this time, the first polarized light incident to the second optical element 500 in FIG. 7 is rotated so as to be incident at an inclination of 45 ° with respect to the diffraction grating 504 of the light reflection surface 503. Meanwhile, referring to FIG. 8, an imaginary plane, that is, an incident surface 600, in which a traveling path i of light incident to the second optical device 500 and a traveling path o of reflected light are located. It is perpendicular to this light reflection surface 503. In FIG. 8, x, y, and z are three-dimensional coordinate lines shown to show the relative positions of the incident surface 600 and the reflective surface 503.

Looking at the optical operation of the optical pickup of the three embodiments having the above structure as follows.

The laser diode 100 generates a first polarized beam having a vibration axis in a first direction by a physical structure therein. In practice, the laser beam generated from the laser diode 100 is an elliptical polarization, of which the first polarization beam component vibrating strongly in the first direction constitutes most of the laser beam. The beam passing the first polarized beam through the collimating lens 200 is converted into parallel light and incident to the second reflective optical element 500, and then reflected without diffraction at the reflective surface 503, and then reflected on the first reflection. It enters into the type optical element 400. The first polarized light is diffracted on the reflective surface 403 of the first reflective optical element 400 and converted into a circular polarized light, ie, natural light oscillating in all directions, and then the disk 100 is rotated by the objective lens 200. Focus on. The light reflected by the disk 100 passes through the objective lens 200 and then enters the first reflective optical element 300. At this time, the light is converted to the second polarized light in the direction rotated by 90 degrees with respect to the first polarized light. The second polarized light is incident on the second reflective optical element 400 and is birefringent at the reflective surface 403 of the second reflective optical element 400 to be spectroscopically. The second polarized light is incident on the photodetectors 800 provided at both sides of the laser diode 100.

As described in the above embodiments, the optical pickup according to the present invention has a simple structure and is light in weight because less optical components are used than in the conventional optical pickup. In addition, since expensive optical components are not used, the manufacturing cost is low.

Claims (8)

A laser light source; An objective lens for condensing a laser beam on the disk, the laser beam generating a first polarization in a first direction from the light source; A plurality of photodetectors for detecting the light reflected from the disk; A first reflection type optical element provided between the objective lens and the laser light source to circularly polarize the first polarized light directed toward the disk, and convert the circularly polarized light reflected from the disk into a second polarized light in a second direction; A second reflective optical element provided between the first reflective optical element and a laser light source for dividing and reflecting the second polarized light into the plurality of photodetectors; Optical pickup device characterized in that it comprises. The optical pickup apparatus of claim 1, wherein at least one of the first reflective optical element and the second reflective optical element is a prism type having two light passing surfaces and one reflecting surface. The optical pickup apparatus of claim 2, wherein the first reflective optical element has a reflective surface on which a diffraction grating inclined at 45 degrees with respect to the first polarized light is formed. The optical pickup apparatus of claim 2, wherein the second reflective optical element has a reflecting surface formed with a diffraction grating in a direction parallel to the second polarized light. The optical pickup apparatus of claim 1, wherein the first reflective optical element has a reflective surface on which a diffraction grating inclined at 45 degrees with respect to the first polarized light is formed. The optical pickup apparatus of claim 1, wherein the second reflective optical element has a reflecting surface formed with a diffraction grating in a direction parallel to the second polarized light. The optical pickup apparatus of claim 1, wherein the diffraction grating of the second reflective optical element has a vector component parallel to an incident surface of light incident on the second reflective optical element. . The diffraction grating of the first reflective optical element has a vector component perpendicular to an incident surface of light incident on the first reflective optical element. Optical pickup device.