JPS63161543A - Optical head device - Google Patents

Abstract

PURPOSE:To miniaturize the titled optical disk by devising a grating lens such that it diffracts a reflected light from a recording medium via a polarized beam splitter at each region and leads it to a photodetector including the 0-th diffracted light. CONSTITUTION:The radiated light 2 from a light source 1 transmits through a polarized beam splitter 5, is converted into a collimated light 4 by a collimating lens 3, converted into a circularly polarized light by a 1/4 wavelength plate 6, reflected totally in the total reflection prism 7 and the optical path is folded by 90 deg. and the light is converged into an optical disk face 9 by a converging lens 8. The reflected light from the optical disk face is returned to the 1/4 wavelength plate 6 through the inverted path, converted into a linearly polarized light orthogonal to the polarized path, converted into a converged light by the collimating lens 3, reflected in the polarized beam splitter 5, the reflected light is diffracted by a grating lens 21 and incident in a 6-split photodetector 23. The 0-th diffracted light is made incident in the photodetector 22. Thus, only the grating lens 21 is enough for the optical component of the photodetection system component and the entire device is miniaturized.

Description

Detailed Description of the Invention (Field of Industrial Application) This invention is applicable to so-called write-on (DRAW), rewritable (E-DRAW) optical discs, video discs, digital audio discs, etc. (hereinafter collectively referred to as optical discs). The present invention relates to an optical head device used for recording and reproduction.

(Prior Art) A conventional optical head device for an optical disc is shown in FIG. Emitted light 2 from a semiconductor laser 1 as a light source is converted into collimated light 4 by a collimating lens 3, transmitted through a polarizing beam splitter 5, converted into circularly polarized light by a quarter-wave plate 6, and then passed through a total reflection prism 7. The light is totally reflected by the light beam, bending the optical path by 90', and converging onto the optical disk surface 9 by the converging lens 8.

The reflected light from the optical disk surface returns to the quarter-wave plate 6 in the opposite path, is converted into linearly polarized light orthogonal to the polarization of the path, and is reflected by the polarizing beam splitter 5.

The reflected light is converted into convergent light by a lens 10 and split into transmitted light and reflected light by a beam splitter 11. The transmitted light 19 enters the two-split photodetector 14 and the photodetector element 12
A track error signal by the push-pull method is obtained using the difference signal between and 13, and an RF multiplied signal is obtained from the sum signal of the photodetecting elements 12 and 13. On the other hand, half of the reflected light 20 is blocked by the knife 15, and the remaining light enters the two-split photodetector 18, and a focus error signal based on the Foucault method is obtained from the difference signal between the photodetectors 16 and 17.

(Problems to be Solved by the Invention) The above-mentioned conventional optical head devices, even those in practical use, have a size of approximately 40 x 40 x 30 mm2 or more, and are therefore heavy, which is an obstacle to reducing the size and weight of the entire optical disk. It became.

In addition, since the push-pull method is adopted for tracking error detection, the converging lens 8
When the is moved in a direction perpendicular to the optical axis by an actuator (not shown), the optical axis of the converging lens and the dividing line of the two-split photodetector for tracking error detection become misaligned, and the photodetecting elements 12 and 13 The amount of incident light becomes unbalanced.

As a result, a direct current offset occurs in the tracking error signal, resulting in a disadvantage that the control range of tracking error control becomes narrow. Furthermore, the above-mentioned conventional optical head has the drawback that it uses a large number of optical parts that require optical polishing, which makes adjustment difficult and increases costs.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks and provide a compact and low-cost optical head device.

(Means for Solving the Problems) An optical head device of the present invention includes a light source, a quarter wavelength plate, and an imaging lens that focuses light from the light source onto a recording medium.
The grating lens is composed of a polarizing beam splitter that extracts the reflected light from the recording medium from the optical path of the recording medium irradiation light, a grating lens consisting of a plurality of areas with different characteristics, and a photodetector having a light receiving surface divided into a plurality of parts. The optical head device is characterized in that the reflected light from the recording medium that has passed through the polarizing beam splitter is diffracted in each of the regions and guided to the photodetector including the 0th order diffracted light. .

(Operation) The operation and principle of the present invention are as follows. In the optical head device of the present invention, a grating lens is used to make the received light optical system composed of the lens 10, the beam splitter 11, and the knife 15 into a single element. There is an O-th order light that directly passes through. Then, this 0th order diffracted light is received to obtain an RF multiplied signal. Furthermore, in the present invention, in order to extract a focus error signal using the first-order diffracted light, the grating lens grating directions are made to differ from each other along a line that intersects the optical axis of the imaging lens. It acts equivalent to the knife 15 in the device and converts it into a light beam almost equivalent to the Foucault single method (more specifically, the double knife method).

Furthermore, in order to extract the tracking error signal, two regions with different grating directions are formed on the grating lens, which are slightly apart from each other around the point where the optical axis of the imaging lens intersects with the grating lens. By comparing the diffracted light intensities from the two regions, a tracking error signal can be obtained using the push-pull principle.

That is, the grating lens has a beam splitter function that splits the beam into RF signal light, focus error detection light, and tracking error detection light.

(Example) Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a perspective view showing the basic configuration of a first embodiment of the present invention. The emitted light 2 from the light source 1 is transmitted through a polarizing beam splitter 5
The collimated light 4 is transmitted through the collimating lens 3.
The light is converted into circularly polarized light by the 174 wavelength plate 6, totally reflected by the total reflection prism 7, bending the optical path by 90', and converged onto the optical disk surface 9 by the converging lens 8. The reflected light from the optical disk surface returns to the 1/4 wave length plate 6 in the opposite path,
It is converted into linearly polarized light perpendicular to the polarization of the path, converted into convergent light by the collimating lens 3, and reflected by the polarizing beam splitter 5. The reflected light passes through the grating lens 21
The light is diffracted by the light beam and enters the 6-split photodetector 23. The 0th order diffracted light enters the photodetector 22.

Figure 3 shows the grating lens 21 and 6-split photodetector 2 in Figure 1.
3 is a partial perspective view for explaining the relationship between the photodetector 3 and the photodetector 22. FIG. In FIG. 3, the converging lens 8 and the disk surface 9 are shown simultaneously through omitted lines 28 to show the directional relationship between the divided areas in the grating lens and the tracks.

The grating lens 21 consists of four grating lens regions, an A region grating lens (first region) 36 and a B region grating having different focal lengths and diffraction directions with respect to a line 35 intersecting the optical axis of the collimating lens 3. The lens (second area) 37 is further divided into an A area lattice lens 36 on the dividing line 35.
, and a C-area grating lens (third area) 38 and a D-area grating lens (fourth area) 39 having different focal lengths and diffraction directions from the B-area grating lens 37, respectively.

The A-region grating lens 36 has a grating pattern corresponding to interference fringes between a spherical wave diverging from the photodetector 22 and a spherical wave divergent from a point 40 on the division line of the 6-split photodetector 23. The B-region grating lens 37 has a grating pattern corresponding to interference fringes between the spherical wave diverging from the photodetector 22 and the spherical wave divergent from the point 41 on the division line of the 6-split photodetector 23. The C-region grating lens 38 has a pattern corresponding to interference fringes between the spherical wave emanating from the photodetector 22 and the spherical wave emanating from the point 42 on the photodetector element 30 of the 6-split photodetector. The D region grating lens 39 is the semiconductor laser 1
The spherical wave diverging from and the photodetecting element 2 of the 6-split photodetector
9 has a pattern corresponding to interference fringes with a spherical wave diverging from point 43 on point 9.

In Figure 3, the grid pitch is drawn larger than it actually is to make the arrangement easier to understand.

Since such a grating lens 21 is used, the light incident on the reflection 12 grating lens from the disk surface 8 is diffracted light 24,
Point 40 on the 6-split photodetector as 25, 26 and 27,
Convergence is reached at 41°, 42 and 43, respectively. Further, the 0th order light that has not undergone diffraction converges and reaches the photodetector G22.

FIG. 5 is a diagram for explaining the state of diffracted light on the 4-split photodetector element in the center of the 6-split photodetector 23. FIG. 5(a) is a diagram showing a focused state in which the light beam is converged on the disk surface 9, and shows the diffracted light 2 from the A-area grating lens 36.
The diffracted light 25 from the 4 and B area grating lens 37 is on the first dividing line 44 of the 6-divided photodetector 23, and on the second dividing line 45.
Each converges between the two. Figure 5(b) shows the disk surface 9.
8 is a diagram illustrating diffracted light in a defocused state that has been displaced and moved away from the converging lens 8. FIG. The diffracted light 24.25 enters the photodetecting element 33 and the photodetecting element 32 of the 6-split photodetector 23, and the diffracted light 24.25 enters the photodetecting element 31 and the photodetecting element 34, respectively.
is not incident on .

FIG. 5(C) is a diagram showing diffracted light in a defocused state when the disk surface 9 is displaced and approaches the converging lens 8. The diffracted light 24.25 is detected by the photodetecting element 31 of the 6-split photodetector 23.
and the photodetecting element 34, respectively, but not the photodetecting element 33 and the photodetecting element 32. Therefore, the four photodetecting elements 31, 32, 33°3 in the center of the 6-divided photodetector 23
The output of 4 is 81. S2. S3,84, the focus error signal is obtained from (S1+84)-(S2+83).

On the other hand, the tracking error signal utilizes the fact that when the focus spot on the disk surface 9 shifts from the center of the track, the intensity distribution of the returning light becomes unbalanced. A line connecting the center of the C area grating lens 38 of the grating lens 21 and the center of the D area grating lens 39 includes a point where the optical axis of the convergent lens intersects the grating lens, and.

Make sure that it is parallel to the direction of the tracking error of the disk. When a tracking error occurs, the C area grating lens 3
A difference occurs between the amount of light incident on the D area grating lens 39 and the amount of light incident on the D area grating lens 39. This light amount difference is determined by the two photodetectors 29.
It can be detected as an output difference of 30 degrees, and the direction of the tracking error can also be detected depending on the sign of this signal.

A reproduction signal from the disc can be obtained from the signal output of the photodetector 22.

In focus error detection and tracking error detection using a grating lens, which is a diffraction element, when the wavelength of the semiconductor laser changes, the diffraction angle changes, causing a positional shift of the diffracted light on the photodetector. It is necessary to take measures against fluctuations in the oscillation wavelength, and the present invention takes the following solution to this problem. On the 6-divided photodetector 23, two directions, a direction parallel to the first dividing line 44 and a direction perpendicular to it, will be considered. There is no problem with positional fluctuation in the direction parallel to the first dividing line 44 as long as it does not exceed the second dividing line 45 or deviate from the photodetector. Regarding the positional fluctuation in the direction perpendicular to the first dividing line, the four photodetecting elements 31, 32, 33°3 in the center of the 6-divided photodetector 23
However, since the grating lenses A and B regions of the present invention have almost no spatial frequency in this direction, the positional fluctuation of the diffracted light in this direction can be ignored.

In addition, a photodetector 29°30 detects the tracking error.
Regarding this, since the diffracted light can be made to enter the center of each photodetector, there is no problem even if the wavelength of the semiconductor laser varies.

In the method that adopts the push-pull method as the tracking error detection method and moves the convergence lens to correct the error,
A misalignment occurs between the optical axis of the optical system on the error detection side and the optical axis on the lens side, and a difference in the amount of light incident on the tracking error detection photodetector occurs, causing an offset in the error signal. In order to solve this problem, the present invention takes the following measures.

The grating lenses 38 and 39 in the C area and the D area are symmetrical about the optical axis and are arranged so as to detect light incident on an equal area. Therefore, even if the optical axis of the converging lens deviates from the optical axis of the error detection system in the direction perpendicular to the track,
There is no change in the amount of light incident on the grating lenses 38 and 39 in the D area, and the occurrence of tracking error offset is suppressed.

FIG. 4 is a perspective view showing a second embodiment of the invention.

In the first embodiment, the first dividing line 44 of the six-divided photodetector 23
is perpendicular to the disk track direction, but in this embodiment, the first dividing line 44 of the six-segment photodetector 23 is arranged parallel to the disk track direction, so that the C area, C area grating lens 38, 39 is the dividing line 35 of the grating lens 46
They are placed on both sides of the board. Further, in the first embodiment, the photodetectors 29 and 30 for tracking error detection are arranged on the extension line of the first dividing line 44 of the six-divided photodetector 23, but in this embodiment, the second It is arranged on an extension of the dividing line 45. The other configurations are the same as in the first embodiment.

The arrangement of the 6-split photodetector 23 is changed from the arrangement shown in the first embodiment or the second embodiment to the dividing line 35 of the grating lens 22, with the optical axis of the light incident on the grating lens as the center. Of course, it is also possible to arrange it by rotating it by an arbitrary angle. Furthermore, the arrangement of the photodetectors 29 and 30 for tracking error detection may be arbitrary as long as the diffracted light 24 from the C-area grating lens 38 and the diffracted light 25 from the C-area grating lens 39 can be separated and independently detected. I can do it.

FIG. 6 shows a grating lens 5 used in the third embodiment of the present invention.
It is a figure showing 4. The configuration of the optical system is the same as that shown in FIG. 1 (details are shown in FIG. 3) and will therefore be omitted. The grating lens 54 is
It is divided into four areas by two boundary lines 51 and 52, and the areas corresponding to areas A, B, C, and D of the first embodiment are 47.48 and 49.50, respectively. Therefore, by setting in the track direction and in the direction of the arrow 53 shown in the figure, the same operation as in the first embodiment can be obtained.

(Effects of the Invention) The optical head device of the present invention requires only a grating lens as the optical component of the light receiving system, and it is possible to significantly reduce the number of parts in the optical head device, which conventionally used a large number of parts. It becomes possible to reduce the size of the optical head, which has hitherto been a bottleneck in downsizing the entire optical disk device. Furthermore, since the lattice lens used in the present invention is an element with a convex-convex surface, a replica can be easily obtained by a heat press method or a 7-otopolymer method after making a mold, so it can be mass-produced at low cost. . Further, according to the present invention, by producing a photodetector and a 6-split photodetector on the same pellet, it is possible to realize an optical head that is highly mass-producible and highly reliable.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing a first embodiment of the present invention, FIG. 2 is a perspective view showing an example of a conventional optical head device, and FIGS. 3 and 4 show the first and second embodiments. FIG. 5 is a diagram for explaining the state of diffracted light on the 6-split photodetector,
FIG. 6 is a diagram showing a grating lens used in a third embodiment of the present invention. 1... Semiconductor laser, 2... Radiation beam, 399.
Collimating lens, 4... collimated beam,
5.1. Polarizing beam splitter, 6... 1/4 wavelength plate, 7... Reflection prism 1.8... Converging lens, 9...
... Disk surface, 10... Luns, 11... Beam splitter, 12, 13, 16, 17, 29, 30, 31
, 32, 33° 34... photodetection element, 14.18...
・Two-split photodetector, 15... Naifetsuji, 19...
・Transmitted beam, 20...Reflected beam, 21°36.3
7, 38, 39, 46, 47, 48, 49, 50.54
... Lattice lens, 2210. Photodetector, 23...6
Split photodetector, 24, 25, 26, 27... diffracted light,
28...Omitted line, 35,51.52...Border line, 4
0,41,42.43...Convergence point, 44...First dividing line, 45...Second dividing line, 53...Figure 1, Figure 2] 8. Yamamasu Figure 3 Figure 4

Claims (1)

[Claims] 1. A light source, a quarter wavelength plate, an imaging lens that focuses the light from the light source onto a recording medium, and a polarizing beam splitter that separates the reflected light from the recording medium from the recording medium irradiation optical path and takes it out. , a grating lens consisting of a plurality of regions with different characteristics, and a photodetector having a light-receiving surface divided into a plurality of regions, the grating lens directing the reflected light from the recording medium that has passed through the polarizing beam splitter to the regions. 1. An optical head device characterized in that the optical head device is configured to diffract each of the 0th-order diffracted lights and guide the 0th-order diffracted light to the photodetector.