JPS62139146A - Optical head device - Google Patents

Abstract

PURPOSE:To attain miniaturization by providing a diffraction grating which bisects reflected light from a recording medium through an image forming lens with a boundary line, and leads it to a photodetector. CONSTITUTION:The titled device is so constructed to have a light source 1, the image forming lens 18 stopping the image of the light source 1 on the recording medium, plural photodetectors 19 and 20 which are arranged on both sides of the light source 1 and bisected independently, and the diffraction grating 17, which has different grating pitches with the boundary line intersecting with the optical axis of the image forming lens 18 installed between the light source 1 and the image forming lens 18 as a reference, bisects the reflected light from a recording medium 13 through the image forming lens 18 with the boundary line and leads it to the photodetectors 19 and 20. In terms of the diffraction grating 17, the + or - primary diffraction light of a diffraction grating at right 21 converges at points 23 and 26 on the plane the same as the bisecting photodetector 20. Thus the overall optical disk device is scaled down, and the size of the optical head can be reduced.

Description

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.

(Prior Art) Conventional optical head devices for video discs, digital audio discs, and optical discs (hereinafter collectively referred to as optical discs) have a semiconductor laser 1 as a light source and a semiconductor laser 1 as shown in FIG. In addition to a collimating lens 4 that converts the emitted light 2 into collimated light 3, a converging lens 5, and a beam splitter prism 6, it also includes 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. As shown in FIG. 2, the wedge prism type focus error detection means has a two-split photodetector consisting of wedge prisms 7 and 8, photodetectors 9 and 10, and a two-split light beam consisting of photodetectors 11 and 12. It consists of a detector. Convergent beam 1 to disk surface 13
4 is just focused, the light beams 15 and 16 from the wedge prism are converged between photodetectors 9 and 10 and between photodetectors 11 and 12, respectively, but the convergent beam When the light beams 14 are defocused with respect to the disk surface 13, the light beams 15 and 16 are defocused in the direction away from each other or in the direction toward each other, so that the differential outputs of the photodetectors 9 and 10, Or photodetectors 11 and 12
By taking the differential output of , a focus error signal can be obtained.

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, and the sum of the outputs of photodetectors 9 and 10 shown in FIG.
By taking the difference between the sum of the outputs of photodetectors 11 and 12,
A tracking error signal is obtained. The conventional optical head device shown in FIG. 2 is manufactured by Philips Technical Rev.
evi-ew) Volume 40 (published in 1982), No. 6, pages 151 to 156.

(Problems to be Solved by the Invention) The above-mentioned conventional optical head devices, even those that have been put into practical use, have a size of about 40×40×30 am and are therefore heavy. Otherwise, it is an obstacle to realizing stacked large-capacity optical disks. One of the reasons for this is that the optical axis of the reflected light from the optical disk is bent 90 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 has been put into practical use within the past few years, such as in digital audio discs and video discs, where the self-coupling effect is used to correct signals.

On the contrary, techniques for suppressing this self-coupling effect as noise leaking into the positioning signal are being developed. The self-coupling effect of a semiconductor laser must be considered in terms of a resonator consisting of three mirrors, which is a resonator of the semiconductor laser itself, in addition to a reflective surface called an optical disk. Because the disk fluctuates in the optical axis direction while the disk is rotating, the distance between the semiconductor laser and the optical disk is approximately 1 μm even when the focus servo is applied.
This results in an extremely unstable resonator configuration. Therefore, this more than 5 COOP
Due to the effect, reproducing the signal on the optical disc has too many difficult challenges.

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

(Means for Solving the Problems) The optical head device of the present invention includes a light source, an imaging lens that focuses an image of the light source onto a recording medium, and an imaging lens arranged on both sides of the light source, each of which is divided into two parts. and a plurality of photodetectors provided between the light source and the imaging lens, each having a grating pitch that is different from the other with respect to a boundary line that intersects with the optical axis of the imaging lens. and a diffraction grating that divides the reflected light from the recording medium into two parts along the boundary line and guides the light onto the photodetector.

(Operation) The operation and principle of the present invention are as follows. In the optical head device of the present invention, a diffraction grating is used to guide reflected light from the optical disk surface to a photodetector in order to achieve a uniaxial optical system. The diffraction grating contains +1st-order diffracted light and -1st-order diffracted light, excluding higher-order diffracted light.

There are three diffracted lights of the 0th order new party. The 0th order new light is the light that directly passes through the diffraction grating. Therefore, if this diffraction grating is placed between the semiconductor laser light source and the imaging lens, and a 0th-order beam is used for the light traveling from the semiconductor laser to the disk surface, it is possible to simply create a transparent material with a thickness equal to the thickness of the substrate of the diffraction grating. It will be the same as the board was made so.

On the other hand, with respect to the reflected light from the disk surface, if the ±1st-order diffracted light is used, the information light can be extracted off the optical axis without using a half prism or a polarizing beam splitter prism. That is, the diffraction grating will act as a beam splitter. As a result, a small and lightweight optical head device can be constructed.

Furthermore, in the present invention, in order to generate a focus error signal and a tracking error signal as well as a signal from two information beams as ±1st-order diffracted beams taken out off the optical axis, the pitch of the diffraction grating is adjusted to the beam of the imaging lens. By making the lines that intersect with the axis different from each other, the beam prisms have an effect equivalent to that of the wedge prism in the conventional optical head device shown in FIG. 2, and are converted into a light beam equivalent to the wedge prism system.

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

FIG. 1 is a sectional view showing the basic configuration of a first embodiment of the present invention. The emitted light 2 of the semiconductor laser 1 is transmitted through the diffraction grating 17.
passes through as a 0th-order new beam, and is focused on the disk surface 13 by the imaging lens 18. The reflected light from the disk surface 13 is converged by the imaging lens 8, diffracted by the diffraction grating 17, and transmitted as diffracted light 15 and diffracted light 16 to two-split photodetectors 19 and 2o on both sides of the semiconductor laser. reach. The two-split photodetectors 19 and 20 are photodetectors 9°1
0 and a photodetector 11.12.

FIG. 3 schematically shows the grating arrangement when the diffraction grating 17 is viewed from the direction of the semiconductor laser 1.

The pitch of the grid is drawn larger than it actually is to make the arrangement easier to understand. The diffraction grating 17 is connected to the imaging lens 18
It is composed of a left-hand diffraction grating 21 and a right-hand diffraction grating 22, which have different grating pitches with respect to a line that intersects with the optical axis. The ±1st-order diffracted light of the left diffraction grating 21 is transmitted to a two-split photodetector 19.
converges to points 24 and 25 on the same plane. On the other hand, the ±1st-order diffracted light of the right diffraction grating 22 is transmitted to the two-split photodetector 20.
converges to points 23 and 26 on the same plane. Therefore,
With the light beam converging on the disk surface 13 and the two-split photodetectors 19 and 2o in the focused position, the convergence points 25 and 26 of the diffracted light are divided into the photodetectors 9 and 10 as shown in FIG. By arranging them in alignment with the line and the dividing line of the photodetectors 11 and 12, it is possible to obtain a focus error signal, a tracking error signal, and a reproduction signal, as described below.

2 each for vertical vibration (defocus) of an optical disc.
Since the amount of light received by the photodetectors 9 to 12 of the split photodetector 19 and 20 varies, a difference signal indicating the difference in the amount of light received by the photodetectors 9 and 10 and the difference in the amount of light received by the photodetectors 11 and 12 is generated. Let this be the focus error signal. That is, at the in-focus position, the difference signal becomes zero because the diffracted lights 15 and 16 converge on the dividing line of the two-split photodetector 19, 20 as described above. When the disk surface 13 is shifted away from the imaging lens 18, the convergence point of the diffracted lights 15 and 16 is
Shift from above the two-split photodetector 19 and 20 toward the diffraction grating 17. At this time, since the light beam enters the center of the diffraction grating 17, that is, the optical axis of the imaging lens 18, and does not move, the convergence point of the diffracted light is blurred by the photodetectors inside each of the two-split photodetectors 19 and 20. 10 and 11 and photodetector 10
and the amount of light coming to 11 increases. Conversely, when the disk approaches the imaging lens 18, the convergence point of the diffracted lights 15 and 16 shifts in the direction away from the diffraction grating 17.

In this case, the light intensity of the outer photodetectors 9 and 12 of each of the two-split photodetectors 19 and 20 increases, and a difference signal is generated.

Based on the above idea, the output voltages of the photodetectors 9, 10, 11 and 12 are set to V(9), Vα4. va force, ■(2), the focus error signal is ■αO+Vα1− (V(9
)+■(b)), and the direction and amount of focus shift 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 light. If the arrangement is such that the tracks extend in the direction perpendicular to the plane of the paper in FIG. arise. Therefore, the tracking signal R1V(9)+lO-(V(11)+
VU) K! ! l) It is possible to detect the direction of track misalignment based on the positive or negative sign of this difference signal.

The signal from the disk can be detected by taking the sum of the light amounts of the two-split photodetectors 19 and 20: V(9)+V(10+Vα+V(6)).

In the embodiments shown in FIGS. 1 and 3 above, the diffracted light converging on points 23 and 24 in FIG. 3 is not used, so 1/2 of the information light is lost. Next, another embodiment of the present invention that also utilizes this light will be described.

FIG. 4 shows a second embodiment of the present invention, in which two-split photodetectors 31 and 32 are also used to reach the convergence points 23 and 24 of the diffracted light.
are placed. Added two-split photodetectors 31 and 32
The output voltages of the photodetectors 27.28°29.30 that constitute the are V@, V2, and (c), respectively.

If ■(to), the one focus error signal is VQO+V(1 or +■(5)+■(to)-
(V (9) 10 ■ (B) 10 ■ (C) + Vl, tracking error signal C, V (9) + VCIce + V @ + VC
[-[VQ1 + VQa + VW + V (c)] The reproduced signal from the Jijibuis is transmitted to four 2-split photodetectors 19.20
, 31.32 light JHDtlV(9)+Va(e+11
)+V(L1+V@+V#+■(c)+■(7) υ
Can be detected.

(Effects of the Invention) The optical head device of the present invention requires only the imaging lens and the diffraction grating as optical components, and it is possible to significantly reduce the number of parts used in the optical head device, which conventionally used many parts. Until now, there has been a reduction in the size of the entire optical disk device, or
It becomes possible to reduce the size of the optical head, which has been a bottleneck in stacked optical disk devices. Further, according to the present invention, by hybridly fabricating a semiconductor laser and a two-split photodetector in the same package, it is possible to realize an optical head that is highly reliable in mass production.

[Brief explanation of drawings]

Fig. 1 is a sectional view showing the basic configuration of the first 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 diffraction grating of the embodiment shown in Fig. 1. FIG. 4 shows the diffraction grating 17 and the two-split photodetectors 19, 20, 3 of the second embodiment of the present invention.
It is a figure showing 1.32. 1... Semiconductor laser, 2... Radiation beam, 3... Collimated light, 4... Collimating lens, 5... Convergence lens, 6.
...Beam splitter prism, 7.8...
... Wedge prism, 9, 10, 11° 12.27,
28,29.30...Photodetector, 13...
...Disc surface, 14... Convergent beam, 15.
16...Divided light beam, 17...Diffraction grating, 18...Imaging lens, 19, 20, 31
．． 32...Two-split photodetector, 21...
Left side diffraction grating, 22...Right side diffraction grating, 23,
24,25.26...Convergence point of diffracted light. Oak 1 button 2 times

Claims (1)

[Claims] a light source, an imaging lens that focuses an image of the light source onto a recording medium, a plurality of photodetectors arranged on both sides of the light source and each divided into two, and between the light source and the imaging lens. The reflected light from the recording medium that has passed through the imaging lens is divided into two parts using the boundary line that intersects with the optical axis of the imaging lens. An optical head device comprising: a diffraction grating guided onto the photodetector.