JPS62145545A - Pickup device - Google Patents

Abstract

PURPOSE:To obtain a device which has symmetry property, is small-sized, lightweight and high in the performance by providing the diffraction grating having the brazing characteristic between a light source and a convergent lens, dividing the return light from the recording support with the diffraction grating, guiding it to a photodetector and obtaining a photodetecting signal. CONSTITUTION:A diffraction grating 3' is constituted to have a brazing characteristic, the light generated from the arranging point D of a semiconductor laser 7 is diffracted by the diffraction grating 3', and the optical spot is formed only at two points A and B on a recording support 1. Out of these, the reproducing signal by the light modulated in the point A of the recording support 1 is a correct signal, and the reflecting light is diffracted by the diffraction grating 3', and arrives at the position F of a detector 6 and the arranging point D of the semiconductor laser 7. On the other hand, the light, which is not diffracted by a diffracted grating 3 due to the return light modulated in the point B (on the other track) of the position a little separated from a correct spot position A, arrives at a position E not provided with the detector 6 and the arranging point D of the semiconductor laser 7. Consequently, only the return light from a correct spot position A arrives at the detector 6.

Description

[Detailed description of the invention] <Industrial application field> What has yet to be invented is the so-called compact disc player.

The present invention relates to a pickup device suitable for use in an optical disc device such as a video disc player.

BACKGROUND TECHNOLOGY Conventionally, optical disk devices perform recording by providing minute holes spirally or concentrically in a disc-shaped record carrier, or by creating magnetic changes, and the data is concentrated in this recording area. A spot light beam is emitted, and reflected light or transmitted light is extracted as reproduced information.

FIG. 4 is a cross-sectional view showing the structure of a conventionally proposed optical information reading optical amplifier device that can be incorporated into an optical disk device. In the figure, the optical system includes a collimating lens 4 and a beam splitter 10 in a housing 5.
Laser light from the semiconductor laser 7 is condensed and irradiated onto the record carrier l via the collimating lens 4, beam splitter 10, and objective lens 2. After this irradiated light undergoes a change in the recorded information portion on the record carrier l, it is split by a beam splitter lO via an objective lens 2, and one of the beams is detected as a light via a detection system convex lens 8 and a cylindrical lens 9. The light enters the vessel 6c.

In the optical information reading pickup having the optical system 2 described above, in order to correctly record or reproduce information on the record carrier l, it is necessary to record the recorded information part (information recording track) in which the focused light spot is recorded spirally or concentrically. ), it is necessary to control the correct tracking of the light spot, and at the same time control the focusing of the light spot.

Furthermore, in actual use, since the disc is affected by eccentricity, wobbling, external vibration, etc., a mechanism is required to extract these deviations as error signals and automatically correct them. For this purpose, focus control and tracking control are usually performed using an electromagnetic drive device consisting of a magnetic circuit and a coil force. In order to control up to a high frequency range during this tracking drive, it is desirable that the drive part be small and light.

From this point of view, some systems drive only the objective lens 2 separately from the pickup housing 5, but with this structure, an axis misalignment occurs between the optical axis of the pickup and the optical axis of the objective range.
Degradation of signal quality of pickup control signal? wake up,
It is necessary to deal with this. Furthermore, in order to avoid deterioration of signals recorded on and reproduced from the disk, a driving device having sufficiently high force and precision is required so that the optical axis of the objective lens 2 is not tilted when the objective lens 2 is driven.

On the other hand, in a pickup that drives the entire pickup as shown in FIG. 4, the housing is not configured axially symmetrically, so crosstalk between tracking control and focus control is likely to occur. That is, when the pickup is driven in a direction perpendicular to the recording surface of the disk-shaped record carrier 1 for focus control, if all assumptions are made, there is a phenomenon in which the optical axis deviates from the direction perpendicular to the recording surface in a pickup that is not axially symmetrical. is unavoidable.

In view of these problems, the present inventors have already considered the configuration shown in FIG. 5 (filed on November 11, 1985). FIG. 5 shows a sectional view showing the structure of the optical information reading pickup device, and parts corresponding to the structure in FIG. 4 are given the same reference numerals.

In the figure, inside a housing 5 extending in a direction perpendicular to the recording surface 1a of the record carrier 1, an objective lens 29, a diffraction grating 3, and a collimating lens 4 are arranged in order in the direction away from the record carrier 1.
．． A laser diode 7 and photodetectors 6a and 6b are arranged.

In this pickup device, the light emitted from the semiconductor laser 7 is collimated by the collimating lens 4, and after passing through the diffraction grating 3, the zero-order light travels in a direction perpendicular to the recording surface 1a of the record carrier 1, and passes through the objective lens. 2 and irradiates the recording surface 1aK. This emitted light is
The objective lens 2 receives the modulation in the recorded information portion on the record carrier 1.
After the light is focused by the diffraction grating 3, it is diffracted by the diffraction grating 3. The light diffracted by this diffraction grating 3 is transmitted to a collimating lens 4
As a result, the light is focused on the detectors 6a and 6b, and the information on the record carrier 1 can be reproduced.

In this way, by using the diffraction grating 3 as the leading edge splitting element, it is not only possible to realize the symmetry of the pickup, but also to realize smaller size, lighter weight, and lower cost.

However, in a pickup configured as shown in Figure 5,
Crosstalk issues may occur. That is, the sixth
As shown in the figure, when the light emitted from the semiconductor laser 7 passes through the entire diffraction grating 3, in addition to the zero-order light A, ±1st-order light B and Ci are generated.As a result, three light beams are formed on the record carrier. A light spot is formed. Reproduction signals from the return lights of these three light spots enter the detectors 6a, 6bVc. At this time, the diffraction signals caused by the ±1st-order lights B and C cause crosstalk. FIG. 7 is a diagram schematically showing this state only by focusing on the zero-order light A and the principal rays of ±1 dimensions B and C. In the figure, light emitted from a semiconductor laser 7, which is a light source, is diffracted by a diffraction grating 3 to form light spots at three points A, B, and C on a recording carrier l. Among these signals, the signal generated by the light modulated at point A of the record carrier 1 is a correction signal, and its reflected light is diffracted by the diffraction grating 3 and reaches positions E and F of the detectors 6a and 6b.

On the other hand, the light that is not diffracted by the diffraction grating 3 due to the modulated return light at point B (on another track) located slightly away from the upper spot position KA is detected by the detector 6b.
The beam reaches position E, and is not diffracted by the diffraction grating 3 due to the modulated return light at VC at six points (on other tracks) located slightly away from the top b spot position A. One light reaches position F of the detector 6a. If crosstalk occurs due to the signals returned from points B and 6, it is natural that good signal reproduction will not be possible.
In order to reduce the phenomenon described above, it is possible to defocus the spot light at points B and 6 using the objective lens 2 with a large curvature of field, but it is not possible to obtain a sufficient effect. .

Purpose The present invention has been made to solve the above problems, and its main purpose is to suppress crosstalk by imparting blaze characteristics to the diffraction direction of a diffraction grating.

<Embodiment> Hereinafter, an embodiment of a pickup device according to the invention will be described in detail with reference to the drawings.

FIG. 1 shows a sectional view of an embodiment of a pickup device according to the present invention. Moreover, FIGS. 2 and 3 are simplified diagrams thereof.

In FIG. 1, the same parts as in FIG. 5 are designated by the same reference numerals.

In FIG. 1, an objective lens 21, a diffraction grating 3', a collimating lens 4, and a collimating lens 4 are shown in order in the direction away from the record carrier l, inside the housing tube 5 extending in the direction perpendicular to the recording surface 1a of the record carrier 1. .A laser diode 7 and a photodetector 6 are arranged.

In this pickup device, the light emitted from the semiconductor laser 7 is collimated by the collimating lens 4, and after passing through the diffraction grating 3', the zero-order light travels in a direction perpendicular to the recording surface 1a of the record carrier l, and is directed to the objective. The light is focused by the lens 2 and irradiated onto the recording surface 13. The irradiated light is modulated by the recorded information portion on the record carrier 1, focused by the objective lens 2, and then diffracted by the diffraction grating 3'.

The light diffracted by this diffraction grating 3' is focused onto a detector 6 by a collimating lens 4, and the information on the record carrier 1 is reproduced.

The major difference between the pickup device shown in FIG. 1 and the pickup device shown in FIG. 5 lies in the structure of the diffraction grating. That is, in FIG. 1, the diffraction grating 8' has a blaze characteristic. Is the configuration of the diffraction grating 3' with blaze characteristics shown in Figures 2 and 3? show.

One surface of the diffraction grating 3' shown in FIG. 2 is gradually shaped into a diagonal shape. FIG. 8 shows an enlarged view of the diffraction grating 3' of FIG. 2. Here, in order to blaze the light that has passed through the diffraction grating 3', the direction of the refracted light due to the shape matches the direction of the diffracted light, and the energy is concentrated in the direction of diffraction. refractive index kn of grating 3'
Assuming that light is perpendicularly incident on the plane side of the diffraction grating 3', n s in α=sinβ d sinβ2λ ? Set it up to satisfy you.

(However, d nigerating pitch λ: previous wavelength) Also, the diffraction grating 3' shown in FIG.・The refractive index and absorption coefficient distribution are formed using Figure 9 (al shows the diffraction grating 3' of Figure 3)
Figure 9 (bl) shows the refractive index distribution in the A-A' cross-sectional view. In order to blaze the light that has passed through the diffraction grating 3', The direction of the reflected light and the direction of the diffracted light due to the vertical surface force and the inclination of are made to match, and the energy is concentrated in the direction of diffraction.
1n(2α);λ/4? Set it up to satisfy you.

(However, dnigelating, λ: previous wavelength) By using the above-described diffraction grating 3', as shown in FIGS. 2 and 3, light emitted from the point where the semiconductor laser 7 is arranged is diffracted by the diffraction grating 3', forming light spots only at two points A and B on the recording carrier l. Among these, the reproduced signal by the light modulated at point A of the record carrier L is a correct signal, and the reflected light is diffracted by the diffraction grating 3' and is reflected at the position F of the detector 6 and the arrangement point of the semiconductor laser 7. reach. On the other hand, the light that was not diffracted by the diffraction grating 3 due to the modulated return light at point B (on another track), which is a little distant from the above-mentioned upper spot position A, is at position E where there is no detector 6. The location of the semiconductor laser 7 is reached. Therefore, since only the returned light from the correct b spot position A75- reaches the detector 6Q, there is no influence of crosstalk.
Moreover, a pickup device having good characteristic 2 with high light utilization efficiency is obtained.

<Effects> According to the present invention described above, it is possible to realize a pickup device that has symmetry, is small, lightweight, and has good scrap performance.

[Brief explanation of drawings]

Fig. 1 is a sectional view of an embodiment of the pickup device according to the great invention, Figs. 2 and 3 are simplified views thereof, Fig. 4 is a sectional view of a conventional pickup device, and Figs. 5 and 6 are 7 is a simplified diagram thereof, FIG. 8 is a partial perspective view of the diffraction grating, and FIG. 9 [al is a partial perspective view of the diffraction grating; Its refractive index distribution diagram 2
show. In the figure, l: record carrier, 2: objective lens, 3a':
Diffraction grating, 4: Collimator lens, 5: Housing tube, 6
: Photodetector, 7: Semiconductor laser, 8: Detector convex lens, 9 Nijilintorical lens, lO two beam spur
Ivy. Agent Patent attorney Aihiko Fukushi (and 2 others) OE Figure 4 fib 7 f;a Figure 5

Claims (1)

[Claims] 1 In a pickup device that records and reproduces information by irradiating a light beam focused by a lens onto a record carrier, a diffraction grating with blaze characteristics is placed between the light source and the condensing lens, and the recording A pickup device characterized in that the return light from the carrier is split by the diffraction grating and guided to a photodetector to obtain a photodetection signal.