JP2818405B2 - Optical pickup device equipped with a wave plate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup device capable of reducing the effective size of an optical spot irradiated on an optical recording medium, and more particularly to a method using a plurality of wave plates having different optical axis directions. Linear polarization (linear polal
optical pickup device for reducing the size of a spot that has been subjected to ization).

[0002]

2. Description of the Related Art In general, long-wavelength light having a wavelength of 780 nm or 830 nm has been mainly used as a light source of an optical pickup device. The size of the light spot irradiated on the optical disc needs to be further reduced.

The diameter of the light spot becomes smaller as the wavelength of the light source becomes shorter, and the numerical aperture (numerical aperture) of the objective lens becomes smaller.
ture), the larger the diameter. Therefore,
In order to increase the resolution of the reproduction signal, a method of blocking the center light of the objective lens is used, but at this time, a large amount of light is lost, and the servo signal is weakened.

FIG. 1 is a schematic diagram showing a conventional optical pickup device. The structure, function and problems of the conventional optical pickup device will be described below with reference to this drawing.

An optical pickup device is a light source 1 for generating incident light having a short wavelength of about 530 nm in order to reduce the size of a light spot irradiated on an optical disk 7 as an optical recording / reproducing medium.
An objective lens 6 for converging the light emitted from the light source 1 onto the optical disc 7; and a photodetector 9 for receiving the light reflected from the optical disc 7 and passing through the objective lens 6 to detect recording information and an error signal. And a collimating lens (collimating lens) that converts the light generated by the light source 1 into parallel light.
z) 4, a polarization beam splitter 2 for making the path of light reflected from the optical disk 7 different from the path of incident light,
A diffraction grating 3 for diffracting light to detect a tracking error signal and an astigmatism lens 8 for detecting a focus error signal on an optical path between the polarization beam splitter 2 and the photodetector 9 are provided. .

The diameter of the light spot formed on the optical disk 7 converged by the objective lens 6 is set between the collimating lens 4 and the objective lens 6.
The diaphragm 5 is provided for fine adjustment according to the recording density. The focus error signal and the track error signal detected by the photodetector 9 are transmitted to a focus / track servo (not shown) to adjust the distance between the objective lens 6 and the optical disk 7 and compensate for the off-track of the objective lens 6. Is done.

In such a conventional optical pickup device, the size of the spot can be adjusted according to the recording density of the optical disk 7, and the light amount loss due to the stop 5 can be measured by a light amount measuring device (not shown).
, The signal can be detected with a relatively constant light amount. However, there is a disadvantage in that the size of the light spot must be adjusted using the stop 5, and a driving device (not shown) for driving the stop 5 is required. Further, since the amount of light reaching the optical disk is reduced by the stop 5, there is a problem that the output drive range of the light source 1 must be widened. Further, there is a problem that the first-order diffracted light of the spot is large and jitter due to mutual interference is generated.

[0008]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an optical pickup device which improves the efficiency of using the amount of light emitted from a light source by using different wave plates in the optical axis direction without using a stop. Is to do.

[0009]

According to the present invention, there is provided an optical pickup device for irradiating a light spot on an optical medium with light generated from a light source to write a signal on the medium or to write a signal on the medium. An optical pickup device for reading a signal from a light source, the objective lens focusing the light on the surface of the medium or focusing the light reflected from the surface of the medium, and the light between the light source and the objective lens. Consists of multiple concentric circles with different radii located on the path
The effective aperture smaller than the effective aperture of the objective lens.
At least three or more wave plates having
The first wave plate made up of the smallest concentric circles of the plate is linearly polarized.
Optical axis direction so that the emitted beam component is completely cut off
And the second wave plate composed of the largest concentric circle is linear
The optical axis is oriented so that the polarized beam components are completely transmitted.
Adjusting the direction, the second wavelength being larger than the first wavelength plate.
At least composed of concentric circles with a smaller radius than the plate
And one other wave plate has a linearly polarized beam component
The optical axis direction is adjusted so as to be partially blocked .

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an optical pickup device according to the present invention will be described in detail with reference to the accompanying drawings.

FIG. 2 is a schematic view showing an optical pickup apparatus according to the present invention, wherein the size of a linearly polarized light component of a spot can be adjusted using a plurality of wave plates having different optical axis directions. The optical pickup device includes a light source 1 that diverges light, an objective lens 6 that focuses light generated from the light source 1 on an optical disk 7 of an optical recording medium, and a light beam that is reflected from the optical disk 7 and focused through the objective lens 6. And a photodetector 9 for detecting a reproduction signal from the reflected light. The light source 1 emits light of a short wavelength to reproduce and erase information on an optical disk on which information is written at a high density, and is used to write information on the optical disk.

On the optical path between the light source 1 and the objective lens 6, a collimating lens 4 for converting divergent light incident from the light source 1 into parallel light, and light reflected from the optical disk 7 travels to a photodetector 9. In such a manner as to change the optical path of the reflected light. The beam diverged from the light source 1 passes through the quarter-wave plate 20 having a smaller aperture than the effective aperture of the objective lens 6 via the collimating lens 4, and then becomes a linearly polarized beam and a circularly polarized beam. Separated. At this time, if the quarter-wave plate 20 is provided at the center of the optical axis direction, the center of the spot on the optical disk 7 is constituted by a purely linearly polarized beam, and the periphery of the spot is constituted by a circularly polarized beam. Is done. Thus, resolution is increased because the effective spot (ie, linearly polarized beam) at which a signal can be detected from the disk is reduced.

FIG. 3 is a graph showing the degree of circular polarization (Ellipticity) according to the size of the spot, and shows that only a linearly polarized component exists at the center C of the spot. In FIG. 3, when the circularly polarized light component is 0 °, the light is linearly polarized light, and when the circularly polarized light component is 45 °, the light is circularly polarized light.

FIG. 4 shows a comparison between the size 4a of the spot of the conventional optical pickup device and the size 4b of the spot of the optical pickup device according to the present invention. It can be seen that the spot is smaller than the spot 4a of the optical pickup device.

FIG. 5 is a graph showing an optical transfer function value indicating the resolution of the optical system. In a high frequency region, the transfer function value 5b of the optical pickup device according to the present invention is higher than the conventional transfer function value 5a. Recognize.

FIG. 6 and FIG. 7 show one having different optical axis directions.
FIG. 6 shows an embodiment of a quarter-wave plate, and FIG. 6 shows ring-shaped quarter-wave plates (A, B, C,
It is sectional drawing of D), and FIG. 7 is its perspective view. FIGS. 8 and 9 show another embodiment of a quarter-wave plate having different optical axis directions, in which four quarter-wave plates (A, B) having different optical axis directions are shown. , C, and D) are a cross-sectional view and a perspective view of a concentric wave plate composed of respective substrates.

For example, the optical axis directions of A, B, and C are set so as to be 45 °, 60 °, and 90 ° with the incident optical axis, respectively, and the optical axis direction of D is set so as to coincide with the incident optical axis. Then, the size of the first-order diffracted light of the spot focused on the optical disk 7 is reduced.

Therefore, by adjusting the radius of the central portion A and the peripheral portions B, C, and D of the quarter-wave plate and the direction of the optical axis thereof, the size of the spot can be appropriately adjusted according to recording / reproduction. Further, the polarization component of the spot focused on the optical disc 7 can be constituted by a linear or circular polarization component, and the size of the first-order diffracted light of the spot having linear polarization can be reduced.

FIG. 10 is a diagram showing the magnitude of the spot and the intensity distribution of the beam, wherein a, b, c and d are each 1/4.
E indicates the magnitude of the spot and the beam intensity by the wave plates A, B, C, and D, and e indicates the magnitude of the spot and the beam intensity indicated by the wave plates. It can be seen that according to the present invention, the size of the spot and the size of the first-order diffracted light are reduced.

FIGS. 11 and 12 show the size of the spot and the beam intensity distribution of the optical pickup device when two and four wave plates having different optical axis directions are used, respectively. Compared to FIG. 11, it can be seen that the size of the spot is relatively small, but the first-order diffracted light is greatly reduced and hardly shown. Therefore, by adjusting the size of the quarter-wave plate and the direction of the optical axis, the spot can be enlarged when data is recorded on the optical disk and the spot can be adjusted small when reproducing data from the optical disk.

[0021]

As described above, the optical pickup device according to the present invention uses different quarter-wavelength plates in the optical axis direction between the light source and the disc in order to adjust the size of the spot. And the first-order diffracted light can be reduced, and the size of the spot can be adjusted by the recording / reproducing mode.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a conventional optical pickup device.

FIG. 2 is a schematic view showing an optical pickup device according to the present invention.

FIG. 3 is a view illustrating a circularly polarized light component of a spot in the optical pickup device according to the present invention.

FIG. 4 is a diagram illustrating the size of spots of a conventional optical pickup device and an optical pickup device according to the present invention.

FIG. 5 is a diagram showing optical modulation values of a conventional optical pickup device and an optical pickup device of the present invention.

FIG. 6 is a view illustrating an embodiment of the wave plate illustrated in FIG. 2;

FIG. 7 is a view showing another embodiment of the wave plate shown in FIG. 2;

FIG. 8 is a view showing another embodiment of the wave plate shown in FIG. 2;

FIG. 9 is a view showing another embodiment of the wave plate shown in FIG. 2;

FIG. 10 is a diagram illustrating the magnitude of a spot and the intensity distribution of a beam in the optical pickup device according to the present invention.

FIG. 11 is a diagram showing the size of a spot and the intensity distribution of a beam of an optical pickup device when two wavelength plates are used.

FIG. 12 is a drawing showing the size of a spot and the beam intensity distribution of an optical pickup device when four wavelength plates are used.

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Claims (3)

(57) [Claims] 1. An optical pickup device for irradiating a light spot on an optical medium with light generated from a light source to write a signal on the medium or read a signal from the medium, wherein the light is applied to a surface of the medium. An objective lens for converging light on and reflecting light reflected from the surface of the medium, and located on an optical path between the light source and the objective lens.
A plurality of concentric circles having different radii,
Less effective aperture than lens effective aperture
A first wave plate comprising at least three wave plates, and a minimum concentric circle among the wave plates
Make sure that the linearly polarized beam components are completely blocked
The second wavelength composed of the largest concentric circle
The plate ensures that the linearly polarized beam components are completely transmitted.
The optical axis direction is adjusted so that it is larger than the first wave plate.
It is composed of concentric circles having a smaller radius than the second wave plate.
The at least one other wave plate is a linearly polarized
Adjust the optical axis direction so that the
Optical pickup device, characterized in that that. 2. The wave plate, wherein the first wave plate, the at least one other wave plate, and
The second wave plate is sequentially multiplied so that its center coincides with the order of the second wave plate.
Waves composed of concentric circles, each layer having a different radius
2. The optical pickup device according to claim 1, wherein the optical axis direction is adjusted by making the thicknesses of the long plates different . 3. An optical axis direction of the first wavelength plate corresponds to the light of the light.
45 degrees from the axial direction, the optical axis direction of the second wave plate is
The optical axis direction and 0 degree, and the first wave plate and the second wave plate
The optical axis direction of the other two wave plates existing between
Configured to be 60 degrees and 90 degrees with the axial direction respectively
The optical pickup device according to claim 1, wherein the optical pickup device is used.