JPS62289933A - Optical head device - Google Patents

Abstract

PURPOSE:To decrease the number of optical components greatly and to reduce the size of the device by providing a photodetector which is divided into four by parallel dividing lines and a diffraction lens consisting of a right and a left lens which differ in convergence length about a line crossing an otpical axis. CONSTITUTION:Light 2 from a semiconductor 1 is image-formed on a disk 6, its reflected light is diffracted by the grating lens 3, and diffracted light beams 8 and 10 converged on points 9 and 11 are guided to the four-division detector 28. A lens 3 consists of the left and right lenses 29 and 30 which differ in convergence length about the line crossing the optical axis to detect the diffracted light 8 by photodetecting elements 32 and 33 and the diffracted light 10 by elements 34 and 35 respectively. The direction and quantity of defocusing on the disk are detected from the large-small relations between the detection outputs 32 and 35, and 33 and 34 of the elements and an off-track direction is detected from the large-small relation of the difference between the sum of the outputs 32 and 33 and the sum of the outputs 34 and 35. Thus, only the image forming lens 4 and diffraction lens 3 are provided, so the number of components is decreased greatly and the device is reducible in size.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention [Field of Industrial Application] The present invention relates to an optical head device used for recording and reproducing so-called optical discs, digital audio discs, video discs, and the like.

[Conventional technology]

Conventional optical head devices for video discs, digital audio discs, and optical discs (hereinafter collectively referred to as optical discs) collimate a semiconductor laser 1 as a light source and emitted light 15 of the semiconductor laser 1, as shown in FIG. In addition to a collimating lens 17 that converts light into light 16, a converging lens 18, and a beam splinter prism 19, it is configured to include focus error detection means and tracking error detection means.

There are various methods for focusing error detection means, but the wedge prism method is the method most closely related to the method of the present invention. The wedge prism type focus error detection means uses a wedge prism 20 as shown in FIG.
and 21, a two-split photodetector consisting of photodetecting elements 22 and 23, and a two-split photodetector consisting of photodetecting elements 24 and 25. When the convergent beam 5 is just focused on the disk surface 6, the light beams 26 and 27 from the wedge prisms 20 and 21 are directed between the photodetecting elements 22 and 23 and between the photodetecting elements 24 and 21, respectively. 25
However, when the convergent beam 5 is defocused with respect to the disk surface 6, the light beams 26 and 27 are defocused in the direction away from each other or in the direction toward each other, so that optical detection is not possible. A focus error signal can be obtained by taking the differential outputs of the elements 22 and 23 or the differential outputs of the photodetecting elements 24 and 25.

There are various methods for tracking error detection means, but the push-pull method is the most closely related to the method of the present invention. The push-pull method uses a two-split photodetector to detect the reflected light from the disk surface. A tracking error signal can be obtained by taking the difference from the sum of . The conventional optical head device shown in Fig. 2 was published by Philips Technical Review.
40 (published in 1982), No. 6, pages 151 to 156.

[Problem that the invention seeks to solve]

The above-mentioned conventional optical head devices, even those that have been put into practical use, have a size of about 40 x 40 x 3 (hm3) and are therefore heavy, so it is necessary to downsize the entire optical disk device.

This is an obstacle to reducing weight or realizing stacked large-capacity optical discs. One of the reasons for this is that the optical axis of the reflected light from the optical disk is bent by 906 degrees using a half prism or a polarizing beam splitter prism to separate it from the light source, and a photodetector is placed behind it. Therefore, it is difficult to make the optical system uniaxial.

To solve this problem, a compact optical head has been proposed that utilizes the so-called 5-coop effect, in which the oscillation output increases due to the self-coupling effect when light is returned to the light emitting part of the semiconductor laser light source.

However, it has been pointed out that the self-coupling effect is an instability of the oscillation phenomenon of semiconductor lasers, and in digital audio discs, video discs, etc. that have been put into practical use within the past few years, it is used as a noise that leaks into the playback signal 1 positioning signal. On the contrary, techniques to suppress this self-binding effect are being developed. The self-coupling effect of a semiconductor laser must be considered in terms of a resonator made up of three mirrors, in which a reflective surface called an optical disk is added to the resonator of the semiconductor laser itself. While the disc is rotating, due to the fluttering of the disc in the optical axis direction,
Even when focus servo is applied, the distance between the semiconductor laser and the optical disk fluctuates by a width of about 1 μm, resulting in an extremely unstable resonator configuration. Therefore, due to such a 5COOP effect, it is difficult to reproduce signals on an optical disk.

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical head device capable of solving the above-mentioned drawbacks and realizing a compact optical head.

[Means for solving problems]

The optical head device of the present invention includes a semiconductor laser light source, an imaging lens that focuses an image of the light source onto a recording medium, and a light receiving surface that is placed beside the light source and is divided into four parts by dividing lines parallel to each other. a photodetector, provided between the light source and the imaging lens, having different convergence distances with respect to a boundary line parallel to the dividing line that intersects with the optical axis of the imaging lens; The present invention is characterized by comprising a grating lens that divides the reflected light from the recording medium that has passed through the lens along the boundary line and guides the light onto the left and right dividing lines of the photodetector.

[Effect]

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 guide reflected light from the optical disk surface to a photodetector in order to achieve a uniaxial optical system. In addition to the desired +1st-order diffracted light, the grating lens has 0th-order directed light.

The 0th-order finger light is light directly transmitted through the grating lens.

Therefore, if this grating lens is placed between the semiconductor laser light source and the imaging lens, and the 0th order diffracted light is used for the light going from the semiconductor laser to the disc surface, it is simply equal to the thickness of the substrate of the grating lens. It will be the same as if a transparent plate was inserted.

On the other hand, for the light reflected from the disk surface, the desired
Next time, if the jR light is used, the information light can be extracted off the optical axis without using a half prism or a polarizing beam splitter prism. In other words, the grating lens will act as a heel splinter. As a result, small size,
A lightweight optical head device can be constructed.

Furthermore, in the present invention, in order to extract not only a signal but also a focus error signal and a tracking error signal from the information light extracted outside the optical axis, the convergence distance of the grating lens is set at four points with a line intersecting the optical axis of the imaging lens. By making the second
The conventional light shown in the figure is given an effect equivalent to that of a wedge prism at a 7FW position, and converted into a light beam almost equivalent to that of the wedge prism system.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a front sectional view showing the basic configuration of an embodiment of the present invention. The emitted light 2 of the semiconductor laser l passes through the grating lens 3
passes through as zero-order diffracted light, and is converged by the imaging lens 4 onto a point 7 on the disk surface 6.

The reflected light from the disk surface 6 is converged by the imaging lens 4 and diffracted by the grating lens 3, and is transmitted as diffracted light 8 and diffracted light 10 to a photodetector element 32 located beside the semiconductor laser.
．． It reaches a four-part photodetector 28 consisting of 33.34.35.

FIG. 3 shows a right side view of the first optical head device. As shown in FIG. 3, the grating lens 3 is an off-axis lens having convergence points 11 and 9, respectively, and directs the return light from the disk surface 6 to a four-part photodetector 28 placed off-axis.

FIG. 4 does not schematically show the arrangement of the grating when the grating lens 3 is viewed from the direction of the semiconductor laser l.

The pitch and direction of the grating lenses are drawn larger than they actually are to make the arrangement easier to understand. The grating lens 3 is composed of a left grating lens 29 and a right grating lens 30, which have different convergence distances with respect to a line intersecting the optical axis of the imaging lens 4. The +1st-order diffracted light of the left grating lens 29 converges at a point 9 shown in FIGS. 1 and 3. On the other hand, the +1st-order diffracted light of the right grating lens 30 is at point 1 shown in FIGS. 1 and 3.
Converges to 1.

Therefore, the photodetecting elements 32, 33° 34, 35 of the 4-split photodetector 28 are arranged as shown in FIG. 35, and in a focused state where the light beam 5 is converged on the disk surface 6, by arranging it so that the spot diameters of both times on the 4-split photodetector 28 are equal, the next As explained, a focus error signal, a tracking error signal, and a reproduction signal can be obtained.

FIG. 5 is a diagram for explaining the state of diffracted light on the four-split photodetector 28. FIG. 5 (al is a diagram showing a focused state in which the optical beam 5 is converged on the disk surface 6; the left side diffracted light 8 and the right side diffracted light 10 have the same spot diameter, and the 4-split photodetector 28 FIG. 5 (bl is a diagram showing the diffracted light in a defocused state that has approached the imaging lens 4 due to the surface wobbling of the disk surface 6. Diffracted light 8 Since the convergence points of 1) and 10 are farther from the grating lens 3 than when in focus, in the 4-split photodetector 28-L, the left side 1) 1 light 8
The spot diameter of the right-side diffracted light IO becomes larger, and the spot diameter of the right-side diffracted light IO becomes smaller. However, the position of the boundary line 31 of the semicircular spot corresponding to the boundary line of the grating lens does not change.

Therefore, the outputs of the photodetecting elements 32 and 35 increase,
The outputs of photodetecting elements 33 and 34 decrease. On the other hand, when the disk surface 6 moves away from the imaging lens, the convergence point of the diffracted lights 8 and 10 will be closer to the grating lens 3 than when they are focused, so that On the split photodetector, the spot diameter of the left side diffracted light 8 becomes small, and the spot diameter of the right side diffracted light 10 becomes large. In this case as well, the position of the boundary line 31 of the semicircular spot does not change. Therefore, the outputs of the photodetecting elements 32 and 35 decrease, and the outputs of the photodetecting elements 33 and 34 increase.

Based on the above considerations, the photodetector element 32.33.34.35
The output voltages of V(32L, V(33), V(34
), V(35), the reconnaissance point error signal is V(3
2) +V (35) -V (33) -V (34
), and the direction and amount of defocus of the disc can be detected.

On the other hand, the tracking deviation signal utilizes the fact that when the focused spot of the emitted light 2 from the semiconductor laser 1 on the disk deviates from the track position, an imbalance occurs in the intensity distribution of the returned light. If the arrangement is such that the tracks extend in the direction perpendicular to the plane of the paper in FIG. The sum of the output signals,
A difference occurs between the sum of the output signals of the photodetecting elements 34 and 35. Therefore, the tracking signal is v (32) 10V (
33) -v (34) -V (35) The direction of the track deviation can also be detected based on the sign of this difference signal.

The signal from the disk is the sum of the light amounts of the four-division photodetector 28 V (32) + V (33) + V (34)
It can be detected by taking 10V (35).

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 of a semiconductor laser, and the present invention provides the following solution to this problem.

Now, the positional shift due to the diffraction angle will be considered separately on the photodetector 28 in two directions: a direction parallel to the dividing line and a direction perpendicular to the dividing line. There is no problem with positional fluctuations in the direction parallel to the dividing line, as shown by dotted lines in FIG. 6, since they do not affect the signal strength at all. Regarding the positional fluctuation in the direction perpendicular to the dividing line as shown by the dotted line in FIG.
5 will change, so care must be taken. The tracking error signal is v (32) + V (33) −V
(34) −V (35) and the information signal is V (3
2) + V (33) 10v (34) ±V (35
), so no change will occur. Regarding the focus error signal, in the present invention, the focus error signal is first
As shown in the figure, the 4-split photodetector 28 is arranged on one side of a plane containing the boundary line of the grating lens 3 and the optical axis of the imaging lens 4, and the diffracted lights 8 and 10 on the 4-split photodetector 28 are By making the interval equal to the interval between the left and right dividing lines of the 4-split photodetector, focus errors are prevented from occurring due to wavelength fluctuations, as described below. FIG. 8 shows the output of each of the photodetecting elements 32 to 35 when such an arrangement is adopted. Curves 36 and 37 in FIG. 8(a) indicate the output voltage v = V (34) to V (
35), curves 38 and 39 are V −V (32) −V
(33) is shown. The dotted line and solid line correspond to the case of the solid line and dotted line in FIG. Thus, V (34) −V
(35) or v (32) −v (33) generates an offset voltage as shown in FIG. The error signal is expressed as v (32) + V (3
5) -V (33) -V (34) Therefore, as shown by curves 40 and 41 in FIG. 8(b), almost no offset occurs even if the position of the diffracted light changes.

In FIG. 8 fbl, Δ2 is a focus error, VF is a focus error signal, and a dotted line 41 and a solid line 4o correspond to the solid and dotted lines in FIG.

〔Effect of the invention〕

In the optical head device of the present invention, the optical components include an imaging lens;
Only a grating lens is required, and it is possible to significantly reduce the number of parts used in optical head devices that used to have many parts. This makes it possible to reduce the size of the optical head.

Further, according to the present invention, by hybridly fabricating a semiconductor laser and a 4-split photodetector in the same package, it is possible to realize an optical head device that is highly reliable in mass production.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the basic configuration of an embodiment of the present invention, FIG. 2 is a sectional view showing an example of a conventional optical head device, and FIG. 3 is a right side view of the embodiment shown in FIG. Figure 4 is the first
A plan view showing the configuration of the grating lens of the example shown in the figure, Figures 5, 6 and 7 are diagrams for explaining the state of diffracted light on the 4-split photodetector, Figure 8 is the focus FIG. 3 is a diagram for explaining a change in a focus error signal with respect to an error. 1... Semiconductor laser beam 2.15... Radiation laser beam 3... Grating lens 4... Imaging lens 5... Converging beam 6... Disk surface 7.9.11... Converging Point 8.10... Diffracted light 22.23, 24, 25, 32, 33.34.35...
・Photodetection element 16...Collimated light 17...Collimating lens 18...Convergent lens 19...Beam splinter prism 20.21...Wedge prism 26.27...Split light beam 28 ...Four-split photodetector 29...Left grating lens 30...Right grating lens 31...Boundary line of semicircular spot 36, 37, 38, 39...Difference signal 40 of photodetector element
．． 41...Focus error signal Representative Patent Attorney Yoshi Iwasa Yukihiro R 吋L'l ■ Haku, )' Figure 3 Figure 4 Figure 6 Figure 7 (a) (b) (C) Figure 5 (a) (b) Figure 8

Claims (2)

[Claims] (1) a semiconductor laser light source, an imaging lens that focuses the image of the light source onto a recording medium, and a photodetector that is placed beside the light source and whose light-receiving surface is divided into four by parallel dividing lines; The light source is provided between the light source and the imaging lens, and has different convergence distances with respect to a boundary line parallel to the dividing line that intersects with the optical axis of the imaging lens. An optical head device comprising: a grating lens that divides the reflected light from the recording medium along the boundary line and guides the light onto the left and right dividing lines of the photodetector. (2) The photodetector is arranged on one side of a plane including the boundary line and the optical axis, and the interval between the reflected light on the photodetector and the interval between the two left and right dividing lines are The optical head device according to claim 1, wherein the optical head device is made equal to each other.