JP2719421B2 - Optical pickup device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Industrial application field The present invention relates to reading information from a recording medium on which information is recorded optically readable, or new information on this recording medium. The present invention relates to an optical pickup device for additional writing or rewriting, and can be used for an optical document file device, various CD players, and the like.

(B) Prior art FIG. 6 is a schematic configuration diagram of a conventional optical pickup device. In this conventional device, 61 is a laser light source such as a semiconductor laser that outputs laser light, 62 is a light output unit that irradiates the recording medium 60 with a laser beam from this laser light source, and 63 branches the reflected light from the recording medium 60. A branching unit 64 is a first photodetector for inputting the reflected light from the branching unit 63 through a first optical path 65, and a reference numeral 66 is a second photodetector for inputting the reflected light from the branching unit 63 through a second optical path 67. is there.
The second optical path 67 is provided with a cylindrical lens 68 which is an optical element having a lens effect, and the axis A of the lens 68 has a fixed angle (for example, 45 °) with respect to the track direction B of the recording medium 60. (See FIG. 7). The first photodetector 64 includes four photodiodes a, b, c, and d, and the second photodetector 65 includes four photodiodes a, b, c, and d.
The divided photodiodes a ', b', c ',
d '. Each diode is arranged as shown in FIG. 8 when viewing each diode from the back. The outputs of these diodes are calculated to obtain a focus error signal FE based on the astigmatism method and a tracking error signal TE based on the push-pull method. See Sanyo Electric Technical Report Vol. 17 No. 2

(C) Problems to be Solved by the Invention In the above-mentioned conventional apparatus, the shape of the spot on the diode at the time of focusing is as shown in FIG. As a result, the intensity of the oblique line in the figure changes. The state of change becomes asymmetric depending on the depth and shape of the groove, and noise N is generated in the focus error signal FE due to the effect that the division line of the photodiode does not completely coincide with the track direction (No. 9). (Figure b). Since the objective lens is shaken by the noise, the stability of the servo at the time of access is deteriorated.

In addition, in the detection of the track shift, as shown in FIG. 10A, the beam moves on the photodiode when the objective lens moves, so that a DC offset (FIG. 10B) occurs in the tracking error signal TE. The lens is moved and servo stability is degraded.

(D) Means for Solving the Problems The present invention is to solve the above two problems at the same time, and comprises a laser light source, a light output unit for irradiating a laser beam from the laser light source to a recording medium, A light receiving unit that receives the reflected light from the recording medium, a branching unit provided in the light receiving unit to branch the reflected light, a first photodetector that inputs the reflected light from the branching unit through a first optical path,
An optical pickup device comprising: a second photodetector for inputting reflected light from the branching unit through a second optical path, wherein the first optical path and the second optical path each include an optical element having a lens effect, The optical element is characterized in that axes having a lens effect are arranged in the same direction with respect to the track direction of the recording medium.

(E) Function Since the present invention is configured as described above, the first,
The shape of the spot on the photodiode of each of the second detectors is as shown in FIGS.
It changes at the time of in-focus (b) and at the time of near focus (c). By appropriately calculating these, it is possible to accurately perform focus control and tracking control without having the FE and TE of the conventional device. Can be made.

(F) Examples The present invention will be described in detail based on examples. Figure 1
FIG. 1 is a schematic configuration diagram showing one embodiment of an optical pickup device of the present invention. FIGS. 2A, 2B and 3C and FIGS. 3A and 3B are waveform diagrams of spots on the first and second detectors for explaining the operation of the present embodiment.

In FIG. 1, 1 is a laser light source, 2 is a light output unit,
3 is a light receiving section, 4 is a branching means, 5 is a first light detector, 6 is a first light path, 7 is a second light detector, 8 is a second light path, 9 is an optical element in the first light path, 10 is An optical element in the second optical path. Reference numeral 11 denotes a recording medium.

The laser light source 1 includes a semiconductor laser that generates a laser beam, and generates a laser beam for irradiating the recording medium 11. The laser light from the laser light source 1 is applied to the track of the recording medium 11 via the light output unit 2 including the collimator lens 12, the beam splitter 13, the prism mirror 14, and the objective lens 15. Then, the reflected light from the recording medium 11 is input to the light receiving unit 3 including the objective lens 15, the prism mirror 14, and the beam splitter 13. In the present embodiment, a condensing lens 16 that receives a light beam from a beam splitter 13 that is used for both the light output unit 2 and the light receiving unit 3 and a beam splitter 17 are used as the branching unit 4. . The light beam from this branching means 4 (beam splitter 17)
On the one hand, it is supplied to the first photodetector 5 via the first optical path 6 and on the other hand to the second detector 7 via the second optical path 8.

An optical element 9 (cylindrical lens) having a lens effect in which the optical axis C has a fixed angle (for example, 45 °) with respect to the track direction B of the recording medium 11 is provided in the first optical path 6. Is provided with an optical element 10 (cylindrical lens) having a lens effect in which the optical axis D has the same fixed angle (for example, 45 °) with respect to the track direction B (see FIGS. 4A and 4B). As another embodiment of the optical element,
Instead of the above-described cylindrical lens, a parallel flat plate that is obliquely arranged with respect to the incident light beam may be used.

The first photodetector 5 includes photodiodes a, b, c, and d divided into four, and the second photodetector 7 includes:
Photodiodes a ', b', c 'divided into four parts,
d '. Each diode is arranged as shown in FIG. 5 when viewing each diode from the back.

Therefore, the light beam from the branching means 4 is transmitted to the first photodetector 5 according to the position of the pickup with respect to the recording medium 11.
Then, an image is formed on each diode of the second photodetector 7 as shown in FIG. FIG. 2B shows a case where the positions of the recording medium and the pickup are in a focused state, and FIG. 2 shows a case where A and C are far from or close to the focused position, respectively. When the light beam applied to the recording medium is applied off the track, the light beam is applied to the first photodetector 5 or the second photodetector 7 as shown in FIG. The light beam applied to the diode changes from a broken line state to a solid line state in the figure.

Therefore, the focus error signal FE and the tracking error signal TE are each converted into noise by using the output of both the first photodetector 5 and the second photodetector 7, that is, by appropriately calculating the output. It can output accurately without being disturbed. The above operations may be performed as follows.

FE = (a + c + b '+ d')-(a '+ c' + b + d)... TE = (b + c + a '+ d')-(a + d + c '+ b') The above calculation cancels the track diffraction pattern appearing on the diode. Also, by calculation,
The DC offset due to the movement of the objective lens is canceled.

(G) Effects of the Invention As described above, the present invention includes optical elements each having a lens effect in the first and second optical paths from the branching unit to the first and second photodetectors, respectively. Since the axes having the lens effect are respectively arranged in the same direction with respect to the track direction of the recording medium, the calculation of the output of each of the detectors reduces the noise in the focus error signal and the DC offset in the tracking error signal, respectively. Therefore, the servo stability can be improved. Then, the recording and reproduction characteristics of the pickup can be improved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the apparatus of the present invention. FIGS. 2A, 2B and 2C show three spots on the first detector (left) and the second detector (right) for explaining the present embodiment.
FIG. 6 shows two different waveform diagrams. FIGS. 3A and 3B are waveform diagrams of spots on the first and second detectors for explaining the operation of the present embodiment. FIGS. 4A and 4B show the relationship between the direction of the axis of the optical element having a lens effect and the track direction. FIG. 5A and FIG. 5B are diagrams showing the arrangement of the diodes of the first and second photodetectors. FIG. 6 is a schematic configuration diagram of a conventional optical pickup device. FIG. 7 is an explanatory diagram of characteristics of a conventional optical element. FIG. 8A and FIG. 8B are arrangement diagrams of diodes of the photodetector of the conventional device. Fig. 9
FIGS. 10A and 10B are explanatory diagrams for explaining the problems of the conventional device. DESCRIPTION OF SYMBOLS 1 ... Laser light source, 2 ... Optical output part, 3 ... Light receiving part, 4, 17 ... Division means (beam splitter), 5 ... First photodetector, 6 ... First optical path, 7 ...
Second photodetector, 8... Second optical path, 9, 10... Optical element (cylindrical lens), 11.

Claims (1)

(57) [Claims] 1. A laser light source, a light output unit for irradiating a laser beam from the laser light source to a recording medium, a light receiving unit for receiving reflected light from the recording medium, and branching the reflected light provided in the light receiving unit A first light detector for inputting reflected light from the first branch through a first optical path;
An optical pickup device comprising: a second photodetector for inputting reflected light from the branching unit through a second optical path, wherein the first optical path and the second optical path each include an optical element having a lens effect, An optical pickup device, wherein the optical element has axes having a lens effect arranged in the same direction as the track direction of the recording medium.