KR20040081640A - Aberration less detecting hologram optical element for optical pick-up system - Google Patents

Abstract

PURPOSE: A hologram element for detecting a spherical aberration of an optical pickup system is provided to configure at least more than one mixed pattern area where different hologram patterns are overlapped to detect an amount of a spherical aberration with optical information from an optical detector, thereby compensating for the aberration while enabling an AF(Automatic Focusing) control. CONSTITUTION: A collimating lens(21) converts an optical beam generated from a light source(20) into a parallel light. An objective lens(22) condenses the parallel light into an optical disk(10). A beam splitter(23) separates an incident light from a reflected light. Coupling lenses(24) condense the separated reflected light. A hologram element(25) is formed with hologram patterns. An optical detector(26) detects optical information and spherical aberration information stored in the optical disk(10) through an interference waveform mapped by the hologram element(25).

Description

Hologram element for detecting spherical aberration of optical pick-up system {ABERRATION LESS DETECTING HOLOGRAM OPTICAL ELEMENT FOR OPTICAL PICK-UP SYSTEM}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup system of an optical recorder / player, and more particularly, feeds back spherical aberration information detected by an optical detector to an interference waveform generated by mapping reflected light reflected from an optical disk toward an optical detector. The present invention relates to a hologram element for detecting spherical aberration of an optical pickup system for controlling spherical aberration compensation.

In general, the Digital Video Disk (DVD) drive currently being developed defines a numerical aperture of 0.85 in order to reduce the size of spots formed on the optical disk using a blue laser. The structure of the optical disk is also to have two data recording surfaces on one sheet in the form of a double recording layer.

In addition, for the protective layer thickness of 100um of optical disc, the deviation within the optical disc is +/- 1.5um and the deviation between each optical disc is +/- 5um, and the distance between the first recording surface and the second recording surface is It is prescribed about 20-30um.

The deviation range caused by this protective layer thickness is much larger than the deviation range for keeping the spot of the light beam focused on the recording surface to a minimum size, and the amount of spherical aberration caused by the deviation with respect to the protective layer thickness of the optical disk. Is investigated using Zeidel coefficients, +/- 0.0403 lambda rms are already generated only by the deviation occurring in the optical disk.

In addition, in order to realize the theoretical beam size determined by the numerical aperture given on the optical disk recording surface, the total amount of aberrations of the beam reaching the entire optical disk recording surface is 0.07 lambda rms or less when expressed as wavefront aberration. Considering that should be done, it can be seen that more than 50% of the total aberration changes only by the variation of the optical disk thickness.

Therefore, when developing an optical pickup system of a digital video optical disc drive, the amount of spherical aberration generated from the optical disc is detected, and the detected signal is fed back to compensate for spherical aberration, auto focusing and tracking. In order to control, an optical device capable of detecting spherical aberration generated from an optical disk must be implemented.

Hereinafter, a spherical aberration detection hologram element of a conventional optical pickup system will be described with reference to the accompanying drawings. FIG. 1 is a diagram illustrating an optical pickup system generally used in the prior art, and FIG. 2 illustrates a hologram element for detecting spherical aberration of a conventional optical pickup system.

Conventionally used optical pickup systems, as shown in Figure 1, the light source 120, the collimating lens 121 for converting the light beam generated from the light source 120 into parallel light, and the parallel light An objective lens 122 for condensing light on the optical disk 110, a beam splitter 123 positioned between the collimating lens 121 and the object lens 122 to separate incident light and reflected light; A coupling lens 124 for condensing the reflected light vertically separated from the beam splitter 123, a hologram element 125 having a hologram pattern formed to map the light beam collected at the coupling lens 124 into an interference waveform, and And an optical detector 126 for detecting optical information and spherical aberration information stored in the optical disk through the interference waveform mapped by the hologram element 125.

In addition, an AF / TR servo circuit for controlling the actuator 129 to be automatically focused and tracked by the signal detected by the photo detector 126, and is located between the beam splitter 123 and the objective lens 122, spherical aberration The servo (Servo) 127 which consists of the spherical aberration detection circuit which controls the compensation plate 128, and the RF circuit which detects a reproduction data signal is comprised.

As illustrated in FIG. 2, the hologram element 125 has a regular linear curved pattern for hologram patterns for mapping the interference waveform toward the photodetector with the reflected light collected through the coupling lens 124.

As shown in FIG. 3, the hologram pattern synthesizes two patterns of the 1D hologram I and the hologram II so as to form a 2D hologram III pattern.

Therefore, the two-dimensional hologram obtained by synthesizing two hologram elements having each one-dimensional hologram described above cannot control diffraction efficiency, and more accurate spherical aberration amount with the interference waveform mapped by the hologram element. Cannot be detected by the photo detector 126.

As the spherical aberration compensation control is not made more precisely for the reasons described above, the optical disk 110 must be manufactured precisely to have a smaller deviation range, and a problem arises in that the user bears the cost increase.

According to the present invention devised to solve the above problems, the present invention provides a hologram element for detecting spherical aberration of an optical pickup system, which detects spherical aberration generated in the optical pickup system more precisely, thereby enabling spherical aberration compensation and focusing compensation control. For that purpose.

1 is a block diagram of a conventional optical pickup system.

2 is a diagram illustrating a typical hologram pattern of a conventional hologram element for detecting spherical aberration;

3 is a view illustrating a synthesis process of a conventional hologram element for detecting spherical aberration;

4 is a view showing a hologram pattern synthesis process of the spherical aberration detection hologram element used in the present invention,

5 is a block diagram of an optical pickup system of the present invention.

6 is a perspective view illustrating a spherical aberration detection process using a hologram element according to an embodiment of the present invention;

7 is a front view of a hologram device according to an embodiment of the present invention;

8 is a view showing an arrangement of the photo detector of FIG.

9 is a diagram schematically showing a process of generating spherical aberration when the protective layer of the optical disk is thin;

10 is a view showing a spherical aberration detection signal in the state of FIG. 8;

11 is a diagram schematically showing a process of generating spherical aberration when the protective layer of the optical disk is thick;

12 illustrates a spherical aberration detection signal in the state of FIG. 10;

13 is a view showing a light detection state using a general rotational grating and diffractive optical element;

14 is a diagram illustrating a hologram pattern of a spherical aberration detection hologram element according to another embodiment of the present invention.

* Description of the main parts of the drawings *

10: optical disc 20: light source

21: collimating lens 22: objective lens

23: beam splitter 24: coupling lens

25, 50: hologram element 25a, 25b: single pattern region

25c, 25d: Mixed pattern region 26: photo detector

27: Servo 28: Spherical Aberration Compensation Plate

29: actuator 30: diffraction grating

40: optical element lens

In order to achieve the above object, the present invention focuses a light beam generated from a light source through an objective lens on a recording layer of an optical disk, and interferes a light beam reflected from the recording layer of the optical disk according to a hologram pattern of a hologram element. In the optical pickup system for detecting the optical information by the optical detector by mapping to the optical sensor, at least one mixed pattern region formed by overlapping different hologram patterns to detect the spherical aberration amount together with the optical information in the optical detector It is achieved by a hologram element for detecting spherical aberration of the optical pickup system, characterized in that it is configured to include.

Here, the mixed pattern region is preferably overlapped with the hologram pattern of the single pattern region adjacent to the outer peripheral surface of at least one single pattern region formed inside the center circle of the hologram element.

First, referring to the technical background from which the technical idea of the present invention is derived, as shown in FIG. 4, by dividing the hologram pattern of the hologram I into the hologram pattern of the hologram II, the phase value in each region is periodically adjusted to the hologram III. Let's get a holographic pattern of. In the hologram pattern of hologram III, Δ can be adjusted according to a given phase value and the diffraction efficiency of hologram II can be determined by the difference of the patterns. In addition, the hologram II may be used not only at the 2 phase level but also at the 4 phase level and the 8 phase level.

Hereinafter, the configuration and operation of the hologram element for detecting the optical pickup system of the present invention will be described in detail as follows.

4 is a diagram illustrating a hologram pattern synthesizing process of a spherical aberration detection hologram element used in the present invention, FIG. 5 is a configuration diagram of an optical pickup system of the present invention, and FIG. 6 is according to an embodiment of the present invention. FIG. 7 is a perspective view illustrating a process of detecting spherical aberration using a hologram element, FIG. 7 is a front view of a hologram element according to an exemplary embodiment, and FIG. 8 is a view illustrating an arrangement state of the photo detector of FIG.

9 is a diagram schematically illustrating a process of generating spherical aberration when the protective layer of the optical disk is thin, FIG. 10 is a diagram illustrating a spherical aberration detection signal in the state of FIG. 8, and FIG. FIG. 12 is a diagram illustrating a process of generating spherical aberration when the protective layer is thick, and FIG. 12 is a diagram illustrating a spherical aberration detection signal in FIG. 10.

As shown in FIG. 5 or FIG. 6, an optical pickup system to which a spherical aberration detection hologram element according to an exemplary embodiment of the present invention is applied, parallels a light source 20 and a light beam generated from the light source 20. Collimating lens 21 for converting the light, the objective lens 22 for condensing the parallel light on the optical disk 10, and between the collimating lens 21 and the objective lens 22, incident light and reflected light A beam splitter 23 for separating the light, a coupling lens 24 for condensing the reflected light vertically separated from the beam splitter 23, and an optical beam focused at the coupling lens 24. A hologram element 25 in which a hologram pattern is formed to map into a waveform, and an optical detector 26 for detecting optical information and spherical aberration information stored in an optical disk through interference waveforms mapped by the hologram element 25. .

Then, the AF / TR servo circuit for controlling the actuator 29 to be automatically focused and tracked by the signal detected by the photodetector 26, and located between the beam splitter 23 and the objective lens 22, spherical aberration And a servo (Servo) 27 composed of a spherical aberration detection circuit for controlling the compensation plate 28 and an RF circuit for detecting the reproduction data signal.

As shown in FIG. 6, the hologram element 25 includes four pattern regions 25a, 25b, 25c, which are designed in consideration of the focal length, diffraction angle and aberration of the objective lens according to the purpose of using the hologram pattern. 25d), which will be described in more detail. Two single pattern regions 25a and 25b in which different hologram patterns are formed on the center circle based on the central axis, and the hologram pattern of the single pattern region adjacent to the outer circumferential surface thereof. It consists of two mixed pattern regions 25c and 25d having different hologram patterns overlapping with each other.

As shown in FIG. 8, the photo detector 26 is composed of four photodiodes A, B, C and D for detecting the interference waveform mapped by the hologram element 25. In addition, the photodiode is divided into three cells (subscripts ₁ , ₂ , and _{3 shown} ) in which the output signal is adjusted to 0 at the reference position.

By such a configuration, the operation and effect of the spherical aberration detection hologram element of the optical pickup system according to an embodiment of the present invention will be described.

First, referring to a schematic operation of the optical pickup system, the light beam generated from the light source 20 passes through the beam splitter 23 in a parallel light state through the collimation lens 21 and is transmitted by the objective lens 22 to the optical disk ( 10) The light beam spot is formed in this recording layer. Then, the light beam reflected from the recording layer of the optical disk 10 is separated in the vertical direction in the beam splitter 23 and passes through the coupling lens 24 and then passes through the four pattern regions of the hologram element 25. While being mapped to an interference waveform, the interference waveform mapped through two mixed pattern regions 25c and 25d of the spherical aberration is detected at each photodiode of each photodetector.

On the other hand, when the recording surface of the optical disk 10 is at the focal position of the objective lens 22, the interference waveform of the light beam mapped by the hologram element forms a difference behind the photodiodes A and C of the photodetector 26, Images form in front of photodiodes B and D.

Therefore, as the distance between the recording layer of the optical disk 10 and the objective lens 22 increases, the size of the image mapped to the photodiodes A and C becomes smaller, and the size of the light beams of the photodiodes C and D becomes larger. On the contrary, when the distance between the recording layer of the optical disc 10 and the objective lens 22 becomes closer, the distance becomes larger for each photodide A and C and smaller for the photodiodes B and D.

As such, the distance between the recording layer of the optical disk 10 and the objective lens, that is, the distance generated as the protective layer of the optical disk becomes thicker or thinner than the standard value, is increased by the spherical aberration generated by the spherical aberration. A focusing error signal (FES) is detected through each photodiode of the photodetector.

The focusing error signal FES is obtained by adding or subtracting values obtained by each cell of the photodiode of each photodetector according to Equations 1 and 2 as follows.

Then, the positions of the optical disks through which the S curves obtained by the respective focusing error signals FES1 and FES2 cross the zero value are different from each other, which feeds back to the optical pickup system so that the values become zero at the same time.

For example, as shown in FIG. 9, when the protective layer thickness of the optical disc 10 becomes thin, the focusing error signal FES is detected in the form of an S curve as shown in FIG. 10, wherein the focusing air The S curve of signal FES1 shifts toward the S curve of FES2 so that both S curves simultaneously control the positive compensation of passing zero values.

On the contrary, as shown in FIG. 11, when the protective layer thickness of the optical disc 10 is thick, the focusing error signal FES is detected in the form of an S curve as shown in FIG. 12, and in this case, the focusing air signal FES2 is detected. Move the S curve of FES1 to the S curve of FES1 so that both S curves can control negative compensation at the same time.

At this time, the compensation control of (±) is controlled by controlling the spherical aberration compensation plate 28 through the servo spherical aberration detection circuit and simultaneously driving the actuator 29 supporting the objective lens through the AF / TR servo circuit. Focusing and tracking control.

Therefore, by using the hologram element 25 of the present invention to detect more diverse and accurate information on the amount of spherical aberration caused by the deviation range of the optical disk to compensate and control in the optical pickup system to widen the deviation range of the optical disk An inexpensive optical disc 10 can be supplied to the consumer.

In addition, a feedback circuit is independently used by auto focusing using a part of the light beam returned from the objective lens 22 and by using a part of light outside thereof to detect spherical aberration amount. This can simplify the circuit design of the servo 27.

The spherical aberration detection hologram element of the optical pickup system according to another embodiment of the present invention will be described in detail with reference to the accompanying drawings. The description will be avoided.

12 is a diagram illustrating a light detection state using a general rotating grating and a diffractive optical element, and FIG. 13 is a diagram schematically illustrating a hologram pattern of a spherical aberration detection hologram element according to another exemplary embodiment of the present invention.

As shown in FIG. 12, in general, in the optical pickup system, the reflected light separated by the beam splitter 23 is split at a predetermined angle while passing through the diffraction grating 30 according to each polarization state, Is configured to detect the reflected light beam with a detector using a diffraction optical element lens (DOM) 40.

However, as shown in FIG. 13, the hologram device 50 proposed in another embodiment of the present invention simultaneously performs the functions of the diffraction grating 30 and the diffractive optical element lens 40. It is formed to have a hologram pattern.

By such a configuration, in another embodiment of the present invention, the spherical aberration detection hologram element can simplify a system that can use the diffraction grating 30 and the diffraction optical element lens 40 as one hologram element. This paper proposes a new type of hologram device capable of performing various functions that cannot be realized in a single hologram pattern.

As described above, according to the present invention, the spherical aberration compensation and the automatic focusing control are possible by the various detection signals detected by having the pattern overlapping section in which each hologram pattern overlaps the hologram element.

In addition, the more accurate spherical aberration compensation control is possible, the wider the deviation range of the optical disk can be supplied to the consumer at a lower price of the optical disk.

In addition, since part of the light beam returned from the objective lens is used for auto focusing and some external light is detected to detect spherical aberration, the feedback circuit can be brought independently so that the circuit design of the servo can be obtained. Becomes simpler.

In addition, the diffraction grating and the diffraction optical element may be implemented as one hologram element.

Claims (3)

The light beam generated from the light source is focused onto the recording layer of the optical disk through the objective lens, and the optical beam is reflected by the optical detector by mapping the light beam reflected from the recording layer of the optical disk according to the hologram pattern of the hologram element. In the optical pickup system, The hologram element is configured to include at least one mixed pattern region formed by overlapping different hologram patterns so as to detect the spherical aberration amount together with the optical information in the photo detector, hologram for detecting the spherical aberration of the optical pickup system device. The method of claim 1, And the mixed pattern region overlaps with a hologram pattern of the single pattern region adjacent to at least one single pattern region outer circumferential surface formed inside the center circle of the hologram element. The light beam generated from the light source is focused onto the recording layer of the optical disk through the objective lens, and the light beam reflected from the recording layer of the optical disk is divided by a diffraction element, and then condensed by a diffraction optical element lens, and the light is detected by the optical detector. In the optical pickup system for detecting information, And a diffraction grating and a diffractive optical element are integrated into a hologram element having an overlapping hologram pattern for simultaneously performing diffraction and condensing.