KR100339345B1 - Optical pickup device - Google Patents

Abstract

PURPOSE: An optical pickup device is provided to minimize the optical system by using small-sized hologram/photodetector modules, simplify the alignment of an optical pickup, and minimize the diffraction loss by minimizing the numerals for the RF detection of 0th beams and using both +1th and -1th refracted beams. CONSTITUTION: An optical pickup device includes a laser diode for radiating beams to a surface of an optical disc via an objective lens, a grating for applying the laser diode beams for generating tracking error signals, a convex lens(16) for focussing the beams reflected from the optical disc surface, an HOE(Holographic Optical Element,17-1) for determining to diffract the beams focussed by the convex lens, a focus error photodetector cell(17-2-2,17-2-3) disposed on focus surfaces of +1th and -1th diffracted beams in the HOB for detecting the +1th and -1th diffracted beams, comparator for comparing a focussing distances of the detected +1th and -1th diffracted beams for generating a focus error signal, an RF photodetector cell(17-2-1) disposed on a focus surface of 0th beam transmitted without any diffraction in the HOE for generating RF signals, and a tracking error detecting photodetector cell(17-2-4,17-2-5) for detecting the beams reflected from the optical disc surface via the grating to generate tracking error signals.

Description

Optical pickup device

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-density optical pick-up device, and more particularly, to a high-density optical sensor that detects signals from RF signals and servos using a small hologram / photodetector module, and is suitable for high-density recording / reproducing of an optical disk. An optical pickup apparatus.

Hereinafter, a conventional optical pickup apparatus will be described with reference to the accompanying drawings.

1 shows a first optical pickup configuration according to the prior art.

As shown in FIG. 1, the beam emitted from the laser diode LD 1 is condensed on the optical disk surface by the objective lens 6 through various processes.

It is also possible to produce parallel light with a collimator 2 depending on the way of picking up, or to use a grading 4 for the purpose of a 3-beam tracking servo. It may also go through an orthopedic prism (3) to shape the beam.

The beam reflected or rotated on the disk again reaches the photo detector 9 via the objective lens 6 and the mirror.

The photodetector 9 is composed of a pattern which not only reads a signal recorded on the disk but also generates a signal for implementing a servo in the focus direction and the track direction.

FIG. 1 shows that the focus error signal is generated by the collimator and cylindrical lenses 7 and 8 and the three-beam tracking error signal is generated by the grating 4. It was.

And, a typical divided surface of the photo detector 9 will be described with reference to FIG.

2 shows a divided configuration diagram of a conventional photodetector 9 according to FIG.

First, the RFD signal and the focus error signal of the recording signal are detected by the ABCD 4-split photodetector in the center, and the tracking error signal is detected by the E and F photodetectors.

However, the prior art described in FIGS. 1 and 2 has a problem in that a crosstalk component is mixed in an RF signal.

Thus, another solution of the prior art will be described with reference to the attached third and fourth drawings as follows.

3 is a block diagram illustrating a conventional second optical pickup.

3 is substantially the same as the configuration of FIG. 1, and a second second photodetector 11 is placed at a confocal position of the optical system to improve the quality of the RF signal.

The first photodetector 10 is similar to the photodetector 9 of FIG. 1 and detects a servo error signal.

Also, the half mirror 15 is used to detect the astigmatism focus error signal by the lenses 12, 13, and 14 and to distribute the light of the first and second photo detectors 10 and 11.

The type of the second photodetector 11 will be described with reference to FIG. 4 as follows.

4 is a view for explaining the type of a conventional photodetector.

As shown in FIG. 4, the photodetectors in (a) and (b) are slits and are arranged parallel or perpendicular to the radial direction of the disc so that intersymbol noise or adjacent tracks are arranged. The crosstalk in (track) is reduced and the photodetector in (c) is composed of squares (or circles) to reduce crosstalk and intersymbol noise in both radial and tangential directions.

Then, it is determined by the magnification of d = track pitch × confocal optical system, which is the length of one side of the slits or squares.

The conventional optical pickup apparatus described above has the following problems.

1. In FIG. 1, the quality of a detection signal is deteriorated because there are many crosstalk components in the detected RF signal.

2. In FIG. 3, in the recording / reproducing of the optical disc, a first and a second photodetector and a half miller for distributing the light of the first and second photodetectors are required so that the total volume is increased, and the optical alignment ( hard to align)

The present invention provides a high-density optical pickup device that improves the quality of the RF signal, miniaturizes the optical system, and facilitates alignment of the optical pickup by using a small hologram / photodetector module to solve the above problems. The purpose is to provide.

The high-density optical pickup device of the present invention for achieving the above object is a laser diode that the optical disk surface scans the beam through the objective lens, the grating to apply the laser diode beam for the tracking error signal generation, and the optical disk surface A convex lens for converging the beam reflected by the convex lens, a HOE for determining a diffraction edge of the beam condensed on the convex lens, a focus error photodetector cell for applying a -first and +1 order diffraction beam of the HOE, and Focus error A comparator for generating a focus error signal by comparing the focal lengths of the -1st, + 1st, and diffraction beams applied to the photodetector cell, and applying the focused beam without diffraction in the HOE to generate an RF signal. A photodetector cell for RF and a tracking error photodetector cell for generating a tracking error signal by applying a beam reflected from the optical disc surface through the grating. It characterized.

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

5 shows an optical pickup configuration of the present invention.

As shown in FIG. 5, the focusing optical system for condensing the laser diode to the disk uses the conventional technology as it is.

In other words, the beam from the laser diode is focused on the optical disk surface by the objective lens.

Also, depending on the method of pickup, the collimator can produce parallel light, and use grating or shaping the beam shape for the purpose of 3-beam tracking servro. It may go through a prism.

The beam reflected or diffracted in the disk then reaches the hologram / photodetector module 17 by the objective lens and the convex lens 16 shown.

In addition, the convex lens 16 may be described as the lens 12 described in FIG. 3, and in the case of a finite optical system, may be described as the mirror 5 and the lens 12.

In addition, the hologram / photodetector module 17 includes a holographic optical element 17-1 and a photo detector cell 17-2 in the same package, and the convex lens The beam condensed from (16) forms an image on the photodetector cell 17-2 by the operation of the H0E 17-1, thereby detecting the RF signal and the servo error signal.

The photodetector cell 17-2 for detecting the RF signal and the servo error signal is again subjected to the RF photodetector cell 17-2-1 and the focus error photodetector cell 17-2-2, 17. -2-3) and tracking error photodetector cells 17-2-4 and 17-2-5, respectively.

The HOE 17-1 has two types of pattern shapes, an amplitude modulation type and a surface relief type, and both types can be used. In particular, the surface relief type has high efficiency and good productivity. This is excellent.

The position of the tracking error photodetector cells 17-2-4 and 17-2-5 is a focus error photodetector cell centered around the RF photodetector cell 17-2-1 as indicated in an abbreviated form. 17-2-2, 17-2-3) and tracking error photodetector cells 17-2-4, 17-2-5 are located in a rhombus shape, respectively.

6 shows an operation explanatory diagram of the hologram / photodetector module according to the first embodiment of the present invention.

In FIG. 6, the RF photodetector cell 17-2-1 and the focus error photodetector cells 17-2-2, 17-2-3 are arranged at the same position as in FIG. That is, the RF photodetector cell 17-2-1 is placed on the focal plane of the convex lens 16, and the focus error photodetector cell 17 is positioned on the focal planes of the + 1st and -1st diffraction beams, respectively. -2-2, 17-2-3).

Accordingly, the zero-order beam transmitted without diffraction in the HOE 17-1 is formed in the RF photodetector cell 17-2-1 located in the focal plane of the convex lens 16, and the confocal described in FIG. The configuration for confocal optics allows for high-density disc playback.

In addition, since the -first-order diffraction beam has the effect of passing through the convex lens 16, the focus is formed past the focus error photodetector cell 17-2-2, and the + 1st-order diffraction beam has the effect of passing through the concave lens. Therefore, focus is achieved before reaching the focus error photodetector cell 17-2-3.

At this time, focus error signal detection will be described with reference to FIG.

7 is an operation explanatory diagram of the focus error photodetector cell of the present invention. As shown, a focus error signal is detected based on the difference between a + 1st diffraction beam and a -1st diffraction beam.

That is, (a) shows the focus error photodetector cell 17-2-3, and (b) shows that the beams detected by the focus error photodetector cell 17-2-2 are close to when the disk and the objective lens are far from the focal point. (C) shows that a focus error signal is obtained by the difference between (a) and (b).

In addition, the tracking error signal described in FIG. 5 is applied to a device such as the grating 4 described in FIG. 3 on the tracking error photodetector cells 17-2-4 and 17-2-5. Servo-beams generated by reflection are obtained by reflecting back to the disk and forming.

The size of the RF photodetector cell 17-2-1 of the present invention described above is d = track pitch x magnification of a confocal optical system, that is, track pitch as shown in FIG. Is 0.8 µm and the magnification is 6 d 5㎛ is because the size of the RF picture detector cell (17-2-1) for can be obtained by d ^2.

In the case of the focus error photodetector cells 17-2-2 and 17-2-3, the focus error photodetector cells 17-2-2 and 17-2-3 are installed outside the focus portion as described in FIG. It is large and its size changes depending on the position of the focusing portion.

Usually, the photodetector cell for RF (17-2-1) is d In the case of 5 mu m, the focus error photodetector cells 17-2-2 and 17-2-3 are designed in the range of 10 mu m <d <100 mu m.

In this case, the distance between the focus error photodetector cell and the RF photodetector cell may be designed to be 1.5 times lower than that of the RF photodetector cell.

8 shows an operation explanatory diagram of the hologram / photodetector module according to the second embodiment of the present invention, in which the RF photodetector cell 17-2 is focused on the focus of a + 1st diffraction beam having a convex lens function. -1) and focus error photodetector cells 17-2-2 and 17-2-3 on the focal plane of the 0th order beam and the -1st order diffraction beam, respectively. By using the difference, the focus error signal is obtained.

In the same manner, the RF photodetector cell 17-2-1 is positioned at the focal point of the -l order diffraction beam, and the focus error photodetector cells 17-2-2 and 17-2-3 are respectively 0th order beams. It is also possible to obtain a focus error signal by using the difference between the 0th order beam and the + 1st order diffraction beam by positioning the focal plane of the + 1st order diffraction beam.

9 is a diagram illustrating the operation of the hologram / photodetector module according to the third embodiment of the present invention, wherein the H0E 17-1 is used as a winch lens pattern, and RF is focused on the zeroth order beam. The photodetector cell 17-2-1 is located and the servo detector 18 is positioned at the position of the + 1st diffraction beam or the -1st diffraction beam. Then, the + 1st order diffraction beam or the -1st order diffraction beam is formed on the servo detector 10, so that the servo error signal can be obtained by the astigmatism method.

The optical pickup device of the present invention described above achieves miniaturization of the optical system by using a small hologram / photodetector module, and minimizes numerical values for the ease of alignment of the optical pickup and the use of the zero-order beam for RF detection. There is an effect of minimizing the diffraction loss by using both the first and -first diffraction beams.

1 is a first optical pickup configuration according to the prior art

2 is a block diagram of a photodetector according to the related art.

3 is a second optical pickup configuration according to the prior art

4 is a diagram illustrating the type of photodetector according to the prior art.

5 is a schematic diagram of an optical pickup according to the present invention

6 is an operation explanatory diagram of a hologram / photodetector module according to the first embodiment of the present invention.

7 is an explanatory diagram of generation of a focus error signal according to the present invention;

8 is an explanatory view of the operation of the hologram / photodetector module showing the second embodiment according to the present invention.

9 is an explanatory view of the operation of the hologram / photodetector module showing the third embodiment according to the present invention.

Explanation of symbols for the main parts of the drawings

17: hologram / photodetector module 17-1: HOE

17-2: Photo detector cell 17-2-1: Photo detector cell for RF

17-2-2, 17-2-3: Focus error photodetector cell

17-2-4, 17-2-5: Tracking error photo detector cell

18: Servo detector

Claims (5)

A laser diode for irradiating a beam through an objective lens on an optical disk surface; A grating for applying the laser diode beam to generate a tracking error signal; A convex lens for converging the beam reflected on the surface of the optical disk; HOE for determining whether to diffract the beam converged on the convex lens, A focus error photodetector cell disposed on a focal plane of the + 1st and -1st diffraction beams diffracted by the HOB to detect the -1st and + 1st diffraction beams of the HOE; A comparator for generating a focus error signal by comparing the focal lengths of the -l and + l diffraction beams detected by the singer focus error photodetector cell; An RF photodetector cell disposed on a focal plane of a zero-order beam that is transmitted without being diffracted in the HOE, for detecting a beam that is not diffracted in the HOE and generating an RF signal; And a tracking error photodetector cell which detects the beam reflected from the optical disk surface through the grating and generates a tracking error signal. The method of claim 1, The RF photodetector cell is disposed on the focal plane of the + 1st diffraction beam to generate an RF signal, and the focus error photodetector cell is disposed on the focal plane of the -primary diffraction beam and the 0 th order beam, respectively, and the comparator And a focus error signal is generated by comparing the focal lengths of the -first-order diffraction beam detected by the focus-error photodetector cell and the non-diffraction zero-order beam. The method of claim 1, The RF photodetector cell is disposed on the focal plane of the -first-order diffraction beam to generate an RF signal, and the focus error photodetector cell is disposed on the focal plane of the + 1-order diffraction beam and the 0th order beam, respectively, and the comparator And a focus error signal is generated by comparing the focal lengths of the + 1st diffraction beam detected by the focus error photodetector cell and the non-diffraction 0th order beam. The method of claim 1, The HOE is defined as a cylindrical lens pattern, and the RF photodetector cell is disposed on a focal plane of a zeroth order beam that is not diffracted in the HOE to generate an RF signal, and a focus of a + 1st order diffraction beam or a -first order diffraction beam. A servo detector is disposed on a surface, and the servo detector detects a -1st or + 1st diffraction beam and generates each servo error signal by astigmatism. The method of claim 1, And the distance between the focus error photodetector cell and the RF photodetector cell is 1.5 times the track pitch.