JPH01205734A - Optical head device - Google Patents

Abstract

PURPOSE:To minimize the off tracking of return light and to miniaturize the title device by providing a converging means to converge a converged laser beam on an optical disk recording face and detecting means to respectively detect quartered light flux. CONSTITUTION:The light reflected by an optical disk recording face 6 passes through a diaphragm lens 5 and 1/4 wavelength plate 4 again, reaches a polarizing beam splitter 3 and goes straight on through this. This return light 10 to go straight is narrowed down by a convex lens 7, passes through two parallel plates 8A and 8B and thus, it is level-divided into four. In this case, a difference occurs in the light quantity of the return light on light receiving elements 9C and 9D to the light quantity of the return light on light receiving elements 9A and 9B and a TE signal is generated. Consequently, by obtaining the difference signal of the outputs of adding amplifiers 11A and 11B by a differential amplifier 12A, a tracking error signal can be obtained. Thus, the return light is not deflected, a focus error signal and the tracking error signal can be detected by one photodetector and the title device is miniaturized.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical head device for recording or reproducing information on an optical disc.

2. Description of the Related Art The structure of a conventional optical head device will be described below with reference to the drawings. As shown in FIG. 12, the light emitted from the semiconductor laser l is focused by a condensing lens 2, and is directed onto an optical disk recording surface 6 on which a pregroup is formed by a polarizing beam splitter 3, a 174 wavelength plate 4, and an aperture lens 5. It's embedded. The light reflected from the optical disc recording surface 6 passes through the aperture lens 5 and the 174-wavelength plate 4 again, reaches the polarizing beam splitter 3, travels straight through this, is reflected by the convex lens 7, and is divided into three beams by the half mirror 19. separated. The light transmitted through the half mirror 19 is focused on a three-split photodetector 20 installed in front of the focal point, and the reflected light is focused on a three-split photodetector 21 installed behind the focal point.

FIG. 13 is an explanatory diagram showing the light distribution on the photodetector due to changes in the focal position.
Obtain the difference signal from 0C12IC, focus error signal F
E, and the light receiving elements 2OR, 21 are connected by the differential amplifier 23.
A tracking error signal TE is obtained from the difference between the sum of L and the sum of 2OL and 2IR. If the scanning light is just focused, the photodetector 20.2 as shown in FIG. 13(b)
The light distribution of the returned light in 1 is symmetrical, and the light receiving element 20
There is no difference in the amount of returned light between C and 2 ICs, and no FE multiplied signal is generated. When the scanning light becomes day focused, the photodetector 20.21 as shown in FIGS. 13(a) and (c)
Since the light distribution of the returned light is widened on one side and narrowed on the other, a difference occurs in the amount of returned light at the light receiving elements 20C and 2IC, and an FE multiplied signal is generated. In addition, the optical diametrical light of the returned light is diffracted and separated by the track that the scanning light is following and periodic reflections from other tracks around it, and the light becomes 0.
The distribution is such that the first-order diffracted light 24R and the first-order diffracted light 24L are superimposed on the second-order diffracted light 24C. When the scanning light deviates from the center of the track, a phase difference occurs between the first-order diffracted light 24R and the -first-order diffracted light 24L, and from this phase difference, the difference in the light L generated in the diffracted light superimposing section is amplified by the operational amplifier 23. A tracking error signal TE is generated.

Problems to be Solved by the Invention In the optical system of such a conventional optical head device, a half mirror separates the returned light into three beams with different optical axes, making it difficult to miniaturize the device.

In addition, two photodetectors were required, which hindered the cost reduction of the device. In view of this problem, the present invention provides an optical head device that detects a focus error signal and a tracking error signal with one photodetector without deflecting the returned light (that is, separating it into three beams with different optical paths). The purpose is to

Means for Solving the Problems The present invention provides a laser light source, a condensing means for condensing laser light from the laser light source into parallel light, and a converging means for converging the condensed laser light onto an optical disk recording surface. and a means for converging the return light from the converging means again and dividing the wavefront into four equal parts, and further focusing two light beams facing the optical axis among the four divided return lights at a focal position Fl. , divisional imaging means for forming an image of the other two opposing light beams at a focal point F2 on the same optical axis as the light beam, and a detection unit located between the focal positions Fl and F2 for detecting each of the four divided light beams. and the detection means includes at least four light-receiving elements D1, D2, D3, and D4 that respectively receive the quartered return light, and the detection means includes at least four light-receiving elements D1, D2, D3, and D4, each of which receives the quartered return light, and has a DI% D.
4, D2, and D3 are respectively disposed opposite to the optical axis, and between the light receiving elements D1, D2 and D3, D4, or between D1, D3 and D2, D4, or between DI, D2, and D3. and D4, a focus error signal is obtained by the difference between the sum signal of D1 and D4 and the sum signal of D2 and D3, and the difference between the sum signal of D1 and D2 and the sum signal of D3 and D4 is obtained. This is an optical head device characterized by obtaining a tracking error signal.

Effect: With the above-mentioned configuration, the return light is not deflected.
Embodiments The embodiments of the present invention will be described below with reference to FIGS. 1 to 11. Incidentally, in FIGS. 1 to 11, those having the same configuration as the conventional optical disk device (FIGS. 12 to 13) are designated by the same numbers, and detailed explanations thereof will be omitted.

FIG. 1 shows a configuration diagram of an optical head device in a first embodiment of the present invention. As shown in FIG. 1, the light emitted from the semiconductor laser 1 is condensed by a condensing lens 2 to become parallel light, and then a pre-group is formed by a polarizing beam splitter 3, a wavelength plate 4 and an aperture lens 5. The list was narrowed down to 6 types of optical disc recording. The light reflected from the optical disk recording surface 6 passes through the aperture lens 5 and the quarter-wave plate 4 again, reaches the polarizing beam splitter 3, and travels straight through it. This returning light lO that has traveled straight is reflected by the convex lens 7
The wavefront is divided into four equal parts by passing through two parallel flat plates 8A and 8B.

FIG. 2 is an explanatory diagram of the wavefront splitting light detecting section in the first embodiment, in which parallel flat plates 8A and 8B are installed to face the optical axis of the returned light lO. 8B
The wavefront of the returned light is divided into four equal parts. Of the four divided return lights, two light beams facing the optical axis (the sides that do not pass through the parallel plate) converge at the focal point Fl on the optical axis,
The other two opposing light fluxes (on the sides that pass through the parallel plate) converge at a focal point F2 on the optical axis. The returned light is at the focal position Fl
The light is received by a five-divided photodetector 9 installed between F2 and F2. The thickness of the parallel plates 8A and 8B is t, and the refractive index is n.
Then, as shown in FIG. 2(b), the focal positions F1 and F2 are
The difference between the two is t (1-1/n). The photodetector 9 is divided into light receiving elements 9A, 9B, 9C19D, and 9E, and sum signals of the light receiving elements 9A, 9B, sum signals of 9A, 9D,
A sum signal of 9B and 9C and a sum signal of 9C59D are obtained, and a difference signal between the outputs of the summing amplifier 11A and IID is obtained by the differential amplifier 12A, which is used as a tracking error signal TE, and the output of the summing amplifier 11B and IIC is obtained by the differential amplifier 12B. A difference signal is obtained and used as a focus error signal FE.

FIG. 3 is an explanatory diagram showing the light distribution on the photodetector with respect to changes in the focal position. If the scanning light on the optical disc recording surface -h is just in focus, the light will be The light distribution of the returned light at the detector 9 is the parallel plate transmitted light 1
0A, IOD and the parallel plate untransmitted light 10B, IOc are also symmetrical, and if the scanning light becomes day focus, (a),
As shown in (b), (d), and (e), the light distribution of the returned light at the photodetector 9 is one way (parallel plate transmitted light 10A,
10D or -, parallel plate untransmitted light 10B, 10C) widens, and the other (parallel plate untransmitted light 10B, IOc or parallel plate transmitted light 10A, 10D) narrows.

In addition, in (b), the focal point F2 is on the photodetector 9, and the parallel plate transmitted light 10A, IOD is narrowed down and fits into the light receiving element 9E, and in (d), the focal point Fl is on the photodetector 9, and the parallel plate transmitted light 10A is focused. The flat plate non-transmitted light 10B and IOC are reflected and fit into the light receiving element 9E.

FIG. 4(a) shows the summing amplifier 1 for the day focus amount.
These are the output signals of 1B and IIC, and day focus states A, B, C, D, and E are shown in Figure 3 (a).
), (b), (c), (d), and (e). 13B is the output signal 13 of the summing amplifier 11B
C is the output signal of the summing amplifier 11C. Output signal 13
The reason why B becomes zero in the day focus state B is because the parallel plate transmitted light beams 10A and 10D are focused and fit into the light receiving element 9E, and similarly, the output signal 13C becomes zero in the day focus state. is parallel plate untransmitted light lOB,
This is because the IOC is narrowed down and fits inside the light receiving element 9E. FIG. 4(b) is an explanatory diagram showing a focus error signal with respect to the day focus amount, and a figure-eight curve necessary for focus pull-in is obtained.

Figure 5(a) shows the optical distribution of the returned light just before wavefront division,
The light is diffracted and separated by the track on the optical disk recording surface that the scanning light is following and periodic reflections from other tracks around it, and the returned light IO is divided into 0th-order diffracted light 10C, 1st-order diffracted light 10L and 11 The distribution is such that the second-order diffraction light 10R is superimposed.

FIG. 5(b) shows the light distribution on the photodetector at just focus, and the region of the returned light 10 that does not pass through the parallel plates 8A, 8B is reversed with respect to the optical axis, but the parallel plates 8A, 8B are inverted with respect to the optical axis.
The area that transmits B is not inverted. Therefore, the 0th order diffracted light 1
A distribution in which the 1st-order diffracted light 10[, is superimposed on 0C appears on the light receiving elements 9A, 9B, and 9E, and a distribution in which -1st-order diffracted light 10R is superimposed on the 0th-order diffracted light 10C appears on the light-receiving elements 9C, 9D, and 9.
Appears on E. When the scanning light deviates from the center of the track, a phase difference occurs between the first-order diffracted light 10R and the first-order diffracted light 10L, and this phase difference causes a difference in light amount in the diffracted light superimposing section. That is, there is a difference in the amount of the returned light on the light receiving elements 9A and 9B in the tip of the returned light on 9C19D, and a TE multiplied signal is generated. Therefore, a tracking error signal can be obtained by obtaining a difference signal between the outputs of the summing amplifiers it IA and IID using the differential amplifier 12A. That is, according to this embodiment, the focus error signal and the tracking error signal can be detected with one photodetector without deflecting the returned light (separating it into three beams with different optical paths).

FIG. 6 is an explanatory diagram of a photodetector in a second embodiment of the present invention. The photodetector 9 includes light receiving elements 9A, 9B, and 9C19.
Divided into D, 9E, 9F, 9G and added tff
mW l I A, 11B, I IC, l ID are the sum signals of the light receiving elements 9A, 9B, 9A, 9, respectively.
D (7) Sum signal, 9B, 9C (7) Sum signal, 9c, 9D
The sum signal of summing amplifier 1 is obtained by differential amplifier 12B.
A difference signal between the outputs of 1B and IIC is obtained and used as a focus error signal FE. Summing amplifier 1 by differential amplifier 12A
1A, the difference signal 15 of the output of IID is obtained, and the differential amplifier 12
After a difference signal 16 between the light receiving elements 9F and 9G is obtained by C and passed through a high frequency filter 14, it is added to a difference signal I5 by a summing amplifier 12C to obtain a tracking error signal. Generally, the return light 1 is due to positional deviation due to adjustment error or temperature change.
0 is shifted from the center of the photodetector 9 in the X direction or in the X direction. In particular, an offset is added to the difference signal 15 due to the positional shift in the X direction. FIG. 7(a) shows a difference signal 15 when crossing the groove due to positional deviation in the X direction, and an offset of Vl is added. Therefore, if tracking control is performed using the difference signal I5 as a tracking error signal, off-tracking (track deviation) corresponding to the offset amount v1 will occur. 7th
Figure (b) shows the output signal 16 of the differential amplifier 12C when crossing the groove.
shows. In the light distribution of the light receiving elements 9F and 9G-H, the area where the ±1st-order diffracted light is superimposed on the O-order diffracted light is narrow, and most of this is an area containing only the O-order diffracted light, so the difference signal 16 is generated due to the positional shift in the X direction. The fluctuation component v3 at the time of groove crossing with respect to the offset component v2 is relatively small. FIG. 7(c) shows the signal after the high frequency filter 14, in which the fluctuating component v3 when crossing the groove is removed and only the offset component v2 remains. Figure 7(d)
indicates a tracking error signal, the offset component appearing in the difference signal 15 is removed, and off-tracking due to positional deviation of the returned light can be prevented.

FIG. 8 is an explanatory diagram of a photodetector in the third embodiment of the present invention. The detector 9 includes light receiving elements 9A, 9B, 9C, and 9D.
, 9F, 9G, and summing amplifiers 11A, IIB,
By IIC and IID, the sum signal of the light receiving elements 9A and 9B, the sum signal of 9A and 9D, the sum signal of 9B and 9C, and 9
A sum signal of C19D is obtained, and a difference signal of the outputs of the summing amplifier 11B and IIC is obtained by the differential amplifier 12B, which is used as a focus error signal FE. A difference signal 15 between the outputs of the summing amplifiers 11A and IID is obtained by the differential amplifier 12A, and a difference signal 16 between the light receiving elements 9F and 9G is obtained by the differential amplifier 12C, which is passed through the high frequency filter 14.
It is added to the difference signal 15 at 2C to obtain a tracking error signal. As in the second embodiment, the offset component appearing in the difference signal 15 is removed, and off-tracking due to positional deviation of the returned light can be prevented.

FIG. 9 is an explanatory diagram of a wavefront division section and a photodetection section in the fourth embodiment of the present invention. In order to provide a light shielding area of a constant width along the dividing line, the flat plate 17 and the parallel flat plates 8A and 8B are joined with the flat plate 17 in between. As a result, parallel plates 8A and 8B
It becomes easy to set the position. As a result of further sandwiching the flat plate 17,
In the light distribution on the photodetector 9, a gap of δ occurs in the y direction, and if the photodetector 9 has the shape described in the third embodiment, even if the light returns in the y direction and the position shifts, there will be no position shift. As long as δ/2 or less, no offset occurs in the difference signal 15, and the difference signal 15
Even if tracking control is performed using this as a tracking error signal, off-tracking will not occur.

FIG. 1O is an explanatory diagram of the wavefront dividing section in the fifth embodiment of the present invention, in which the returned light IO is divided into four equal parts by installing parallel plates 8A and 8B between the convex lens 7 and the concave lens 18. The wavefront is divided into In this case, by combining the convex lens 7 and the concave lens If, it is possible to converge the returned light without aberration and to reduce the thickness of the parallel plates 8A and 8B. Convergence of the returned light without aberration improves the focus control sensitivity and has the effect of reducing the amplitude of the focus error signal when crossing the groove.

FIG. 11 is an explanatory diagram of the wavefront dividing section in the sixth embodiment of the present invention, and shows the four-part convex lenses 7A and 7 having a focal length fl.
By combining D and the four-segment convex lenses 7B and 7C with a focal length of F2, the four-segment convex lens 7A with the same focal length can be created.
, 7B, 7C, and 7D can be combined with 7A, 7D shifted in the optical axis direction compared to 7B, 7C, the focal position Fl
It is possible to provide a difference between F2 and F2. Furthermore, by configuring the four-part convex lenses 7A, 7B, 7C, and 7D with Fresnel lenses, it is possible to provide a difference between the focal positions Fl and F2.

As a result of the invention, the optical head device of the present invention allows detection of a focus error signal and a tracking error signal with a single photodetector without deflecting the returned light, thereby preventing off-tracking due to positional deviation of the returned light. It is extremely effective in reducing the size and cost of devices.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of the main parts of an optical head device according to the first embodiment of the present invention, FIG. 2 is an explanatory diagram of the wavefront division section and photodetection section of the same device, and FIG. 3 is a focal point of the same device. Fig. 4 is a diagram of the distribution of light received by the photodetector due to changes in position; Fig. 4 is a diagram of the output signal wavelength of the summing amplifier with respect to the day focus amount of the same device; an explanatory diagram showing the focus error signal; Fig. 5(a) is the same A light distribution diagram of the returned light just before the wavefront division of the device, (b) is an explanatory diagram showing the light distribution on the photodetector at just focus, and FIG. 6 is a diagram showing the light detection in the second embodiment of the present invention. Explanatory diagram of the section, 7th
The figure is an explanatory diagram showing the signal output when crossing the groove of the same device, FIG. 8 is an explanatory diagram of the photodetection section in the third embodiment of the present invention, and FIG.
The figure is an explanatory diagram of the wavefront division section and the photodetection section in the fourth embodiment of the present invention, FIG. 1θ is an explanatory diagram of the wavefront division section in the fifth embodiment of the present invention, and FIG. An explanatory diagram of the wavefront splitting section in the sixth embodiment of the present invention, FIG. 12 is a configuration diagram of the main parts of a conventional optical head device, and FIG. 13 is a diagram showing the light received by the photodetector due to changes in the focal position of the same device. FIG. l... Semiconductor laser, 2... Condensing lens, 7...
Convex lens, 8A, 8B... Parallel plate, 9... Photodetector. /--Issute Dourin ν-Pu- Fig. 4 Fig. 5 (α) (b) /d-Ichitakatomo 3/Y filter 515, /ro Ichien 4 words Fig. 6 Fig. 7 (C1) Figure 8 1 Where/44 Figure 9/7-Chishiki

Claims (7)

[Claims] (1) A laser light source, a focusing means for condensing the laser light from the laser light source into parallel light, a converging means for converging the focused laser light onto the optical disk recording surface, and a converging means for converging the laser light from the converging means The returning light is converged again and the wavefront is divided into four equal parts, and two light beams facing the optical axis of the four divided return lights are imaged at the focal position F1,
divisional imaging means for forming an image of the other two opposing light beams at a focal position F2 on the same optical axis as the light beam, and the focal position F2;
1 and F2 for detecting each of the four divided light beams, and the detection means includes at least four light receiving elements D1, D2, D3, and D4 that respectively receive the four divided return lights. , D1 and D4 and D
2 and D3 are respectively disposed opposite to the optical axis, and between the light receiving elements D1, D2 and D3, D4, or between D1,
An optical head device characterized in that a gap is provided between D3, D2, and D4, or between D1 and D2, and D3 and D4. (2) In claim 1, the focus error signal is obtained by the difference between the sum signal of the light receiving elements D1 and D4 and the sum signal of D2 and D3, and the focus error signal is obtained by the difference between the sum signal of D1 and D2 and the sum signal of D3 and D4. An optical head device characterized by obtaining a tracking error signal. (3) In claim 1, the dividing image forming means is constituted by a convex lens and two transparent parallel flat plates facing the optical axis and arranged so as to divide the returned light into four parts, and the two light beams transmitted through the convex lens are An optical head device is characterized in that an image is formed at a focal position F1, and two light beams transmitted through the convex lens and a transparent parallel plate are imaged at a focal position F2. (4) In claim 1, the dividing image forming means is constituted by a convex lens, a concave lens, and two transparent parallel flat plates disposed between them to face the optical axis and divide the returned light into four parts, and the convex lens An optical head device characterized in that two light beams transmitted through a convex lens, a transparent parallel plate, and a concave lens are imaged at a focal position F1, and two light beams transmitted through the convex lens, a transparent parallel plate, and a concave lens are imaged at a focal position F2. (5) An optical head device according to claim 3 or 4, characterized in that the two transparent parallel flat plates are provided with a light-shielding area of a constant width along a dividing line that divides the returned light. (6) In claim 1, the divided imaging means is composed of four divided lenses, and two sets of convex lenses, a first and a second convex lens, are arranged to have the same focal length at positions opposite to the optical axis. The two light fluxes transmitted through the first convex lens are imaged at the focal position F1, and the two light fluxes transmitted through the second convex lens are imaged at the focal position F1.
An optical head device characterized by focusing two light beams on a focal position F2. (7) In claim 2, a light receiving element D5 is provided between the light receiving elements D1 and D2, a light receiving element D5 is provided between the light receiving elements D3 and D4,
An optical head device characterized in that an optical head device D6 is provided, and a difference signal between the light receiving elements D5 and D6 is subjected to high frequency filtering and added to a tracking error signal.