JPH04123331A - Optical pickup - Google Patents

Abstract

PURPOSE:To simultaneously reproduce plural tracks on an optical disk with a relatively simple constitution by providing an illuminating optical system, an image forming optical system which forms the image of a spot, and plural light receiving elements which photoelectrically convert parts corresponding to plural tracks of the image of the spot. CONSTITUTION:A light emitting element 28 and illuminating optical systems 40 and 42 which converge the output light of this element 28 to a spot 44 traversing plural tracks 36, 37, and 38 on an optical disk 35 are provided. An image forming optical system 42 which an image 44I of the spot and plural light receiving photo diodes A1, B1, and C1 which photoelectrically convert parts corresponding to plural tracks of the image of the spot are provided. The output signal of each of plural light receiving elements correspond to the reproduced signal of one of plural tracks 36, 37, and 38 on the optical disk 35. Thus, plural tracks are simultaneously reproduced by the simple constitution where the light emitting element, illuminating optical systems, and the image forming optical system are shared.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is an optical disc playback device that is highly effective when applied to an optical disc playback device that plays back an optical disc on which a signal with a large amount of information, such as a high-definition signal, is recorded. Regarding pickup.

[Summary of the Invention] The present invention relates to an optical pickup that is highly effective when applied to an optical disc playback device that plays back an optical disc on which a signal with a large amount of information, such as a high-definition signal, is recorded.
a light emitting element; an illumination optical system that focuses output light of the light emitting element onto a spot across a plurality of tracks of the optical disk;
By having an imaging optical system that forms an image of the spot, and a plurality of light receiving elements that photoelectrically convert portions of the image of the spot that correspond to the plurality of tracks,
This allows one optical pickup to read information from multiple tracks at the same time.

[Prior Art] Optical disk devices such as optical video disk playback devices, compact disk playback devices, and magneto-optical disk recording and playback devices use optical pickups for recording or playing back information signals.

Fig. 5 shows an optical pickup of a conventional optical disc playback device. In Fig. 5, (1) is a base, (2)
) and (3) are the side walls of the base (1), respectively, and the bushes (4A) and (4B) are attached to the coaxial through holes of these side walls (2) and (3), respectively.
A guide shaft (5) extending in the radial direction of the optical disk is inserted through 4A) and (4B), and the side wall (2) and the side wall (3)
A tilt sensor (7) is attached between the guide shaft (5) and the L-shaped fitting (6). Further, a U-shaped guide portion (8) is provided on the base (1) so as to be located on the opposite side of the side walls (2) and (3). The rotation axis of the optical disc is located approximately on the extension of the guide shaft (5), and the optical pickup is moved in the radial direction (R direction) of the optical disc along the guide shaft (5) by a drive mechanism (not shown). be able to.

(9) is first mounted on a plate, and a pair of U-shaped yokes (10) and (13) are mounted on the base (1) so as to face each other through the plate (9). (
Magnetized bodies (11) and (10) and (13) are respectively placed on the inner surfaces of
14) and close the magnetic paths of these yokes (10) and (13) by installing small inverted U-shaped yokes (12).
) and (15). The base (1) and mounting are on the board (
A through hole for passing the laser beam is provided in the portion between the yoke (10) and the yoke (13) of 9).

(16) is a U-shaped second mounting plate, and its first
For the second installation, place the plate (16) on the plate (9) so that one yoke (13) is sandwiched between them, and for these installations, the plates (9) and (16) should be placed on the plate (17) so that one yoke (13) is sandwiched between them. ) on the base (1), and for this second installation, one end of the leaf spring (19) consisting of four parallel plates is attached to the relay member (18) which is attached by bending one end of the plate (16). Attach. A bobbin (20) is attached to the free end of this leaf spring (19) via a stopper (21), and a focus (Fo) coil (22) for focusing and a tracking (T) for tracking are attached to this bobbin (20). r ) Coil (2
3), these coils (22) and (23) are installed.
) are both located in front of the magnetized body (11) and in front of the magnetized body (14).

A through hole is bored in the focusing direction of the bobbin (20), an objective lens (24) is attached to one end of the through hole, and a protective cover is provided to prevent the objective lens (24) from directly colliding with the optical disc. Cover with (25). The bobbin (20) and the objective lens (24) are connected to the leaf spring (
The action of coils (22) and (23) allows the optical disc to swing freely in the radial direction (R direction) and axial direction (two directions, see Figure 6), and the action of coils (22) and (23) allows it to swing freely in the R direction and Z direction. can be positioned at desired coordinates. That is, this constitutes a two-axis actuator.

(26) is a storage member for optical components, (27) is a light receiving board attached to one end of this storage member (26), and this storage member (26) is attached to the lower surface of the base (1).

FIG. 6 shows the configuration of the optical system of the optical pickup of the example shown in FIG. 5. In this FIG. 29), plate-shaped half mirror (30),
It is guided to an optical disk (33) through a collimator lens (31), a prism (32) for converting the optical path to a right angle, and an objective lens (24). The reflected light from this optical disk (33) travels in the opposite direction to the optical path of the incident light and passes through the half mirror (33).
0) is reached. A light-receiving substrate (27) is arranged approximately symmetrically with the semiconductor laser light source (28) with respect to this half mirror (30), and the light that has passed through this half mirror (30) among the reflected light from the optical disk (33) is collected. The light is guided to the light receiving substrate (27) via a concave lens (34) or the like. This light receiving board (27
) are arranged with 6 photodiodes consisting of 4 photodiodes in the center shape and 2 photodiodes at the top and bottom.

In this example, the output light of the semiconductor laser light source (28) is divided into three light beams by the diffraction grating (29), and these three light beams are each split into one light beam along one track of the optical disk (33). Focused on a spot. Images of those three spots are then formed on the light receiving substrate (27). Then, focusing servo is performed using the astigmatism method, for example, using the output signals of the four Ta-shaped photodiodes based on the center spot, and the output signals of the two upper and lower photodiodes based on the two upper and lower spots are using 3
Tracking servo is applied using the beam method. Further, the sum of the output signals of the four central photodiodes is used as a reproduction signal containing reproduction information.

As mentioned above, conventionally, three spots are formed along one track of an optical disk to apply tracking servo, but only the signal of one track is reproduced. Even with this, there was no problem in reproducing normal NTSC video signals.

[Problems to be Solved by the Invention] However, since the video signal of the high-definition system, which is being developed in recent years, has a large amount of information, for example, the video signal of one field or one frame is transmitted over 360 degrees of one track of an optical disc. It becomes difficult to record in the section. Therefore, if a video signal of 1 field or 1 frame is to be recorded in a 360' section of three adjacent tracks on an optical disc, in order to reproduce the video signal, three
An optical pickup that can play multiple tracks simultaneously is required. Such an optical pickup can be constructed, for example, by arranging three sets of optical systems in the example shown in FIG. 6 in parallel, but this structure is complicated and large and is not practical.

In view of the above, an object of the present invention is to provide an optical pickup capable of simultaneously reproducing a plurality of tracks of an optical disc with a relatively simple configuration.

[Means for Solving the Problems] As shown in FIGS. 1 and 2, the optical pickup according to the present invention includes a light emitting element (28) and a plurality of optical discs (35) that output light from the light emitting element (28). Truck (36
, 37, 38), and an illumination optical system (40, 42) that focuses on a spot (44) that crosses the
), and a plurality of light receiving elements (photodiodes^1.B) that photoelectrically convert portions of the spot image corresponding to the plurality of tracks.
1. CI).

[Function] According to the present invention, the output signal of each of the plurality of light receiving elements is a reproduction signal of a different one of the plurality of tracks (36, 37, 38) of the optical disc (35). corresponds to Therefore, a plurality of tracks can be simultaneously reproduced with a simple configuration in which a light emitting element, an illumination optical system, and an imaging optical system are shared.

[Embodiment] Hereinafter, an embodiment of the present invention will be explained with reference to FIGS. The present invention is applied to an optical disc playback device for playing back optical discs.

FIG. 1 shows the configuration of an optical system such as an optical pickup in this example. In FIG. 1, (35) is an optical disk, (
36) to (38) are the center axes of a series of tracks in this optical disk (35), and video signals are recorded in the form of pings (39) along the center axes of these tracks, respectively. The pitch of the center axes (36) to (38) of these tracks in the radial direction (R direction) of the optical disc (35) is approximately 1
．． It is 6μkaku.

(40) shows a cylindrical lens with a curvature of about 2000 mm, (41) shows a prismatic beam splitter with a structure of two prisms bonded together, and a semiconductor laser light source (
28) to a beam splitter (41) via a cylindrical lens (40), and a mirror (32a) and an objective lens (42) for bending the optical path of the light transmitted through the beam splitter (41) at right angles. The laser beam is focused to form a spot (44) on the pit (39) formation surface of the optical disk (35) via the laser beam. In this case, in this example, the spot (44) of the laser beam is extended in the radial direction of the optical disk (35) by the cylindrical lens (40), so the spot (44) is called an elliptical spot. A combination of a collimator lens and an objective lens may be used instead of the objective lens (42).

The shape of the elliptical disc) (44> is the shape of the optical disc (
35) is set so that the width W in the circumferential direction is about 1.3 μm, and the length in the radial direction (R direction) is about 5 to 6 μm. That is, the length L of the oval spot (44) is set to such a length that it crosses a series of three tracks (for example, the tracks whose central axis is (36) to (38)) of the optical disc (35). .

(43) shows a light receiving substrate arranged approximately symmetrically with the semiconductor laser light source (28) with respect to the semi-transparent surface of the beam splitter (41), and the reflected light from the oblong spora) <44) is reflected from the objective lens ( 42) and a mirror (32a) to the beam splitter (41).
The light reflected by the semi-transparent surface of 41) is transferred to the light-receiving substrate (43).
). An image (441) of an oblong spora (44) in the optical disk (35) is formed on this light-receiving substrate (43). If the magnification of the image formed by the objective lens (42) is, for example, 20 times, the image (441)
The width is about 26 μm, and the length is about 100 to 120 μm.

Figure 2 shows the light receiving board (43) and its signal processing circuit of this example.
photodiodes A1. A2. B1. B2. CI,
Form C2. On this light-receiving board (43) are the three track center axes (36) to (38) of the optical disc (35).
If the images of these track center axes are (36I) to (381), respectively, then the pitch IP of these center axis images (361) to (381) is the same as that of the optical disc (35). Objective lens (4
2) is the value multiplied by the imaging magnification. In this example, the width of each photodiode A1 to C2 is set to be smaller than IP/2, and a pair of photodiodes A1 and A2 are arranged on the left and right of the central axis image (381) at one end, and A pair of photodiodes B1 and B2 are arranged on the left and right sides of the central axis image (371), and a pair of photodiodes C1 and C2 are arranged on the left and right sides of the central axis image (36n) at the other end.

The length of these photodiodes is elliptical spora) (44
) is made smaller than the width of the image (441).

(45) to (50) each indicate a current/voltage converter, and the output currents of the photodiodes A1 and A2 are connected to a common adder (45) and (46), respectively.
51) and a subtracter (52). Adder (51)
A first sum signal AA, which is the sum of the outputs of the photodiodes AI and A2, is output from the subtracter (52), and a first difference signal SA, which is the difference between the outputs of the photodiodes AI and A2, is output from the subtracter (52). Ru.

Similarly, the adder (53) outputs a second sum signal AB, which is the sum of the outputs of photodiodes B1 and B2, and the subtracter (54) outputs a second sum signal AB, which is the difference between the outputs of photodiodes 81 and B2. A difference signal SB is output.

Further, the adder (55) outputs a third sum signal AC, which is the sum of the outputs of photodiodes C1 and C2, and the subtracter (56) outputs a third sum signal AC, which is the difference between the outputs of photodiodes C1 and C2. A difference signal SC is output.

The above-mentioned first sum signal AA to third sum signal AC are reproduction signals of a series of tracks (38) to (36) of the optical disc (35), respectively, and these sum signals AA-AC are respectively connected to the connection terminal (57). ) to (59) to a reproduction circuit (not shown). This reproducing circuit sequentially reproduces one field or one frame of video signals from the three supplied reciprocating signals.

(60) shows a focus error signal generation circuit, (62) shows a tracking error signal generation circuit, and the former focus error signal generation circuit (60) receives three sum signals AA.
, AB and AC, and the latter tracking error signal generation circuit (62) receives three difference signals SA, SB and S.
Supply C. Focus error signal generation circuit (60)
generates a focus error signal FE that can be expressed, for example, by the following equation.

FE= (AA+AC)-2AB...(1)
This focus error signal FE is supplied to a focus servo circuit (not shown) via a connection terminal (61). For example, the focus coil (22) is adjusted so that the absolute value of the focus error signal FE in equation (1) is small, that is, the oval spot (44) in FIG. 1 evenly crosses a series of three tracks. The focus servo operates by supplying current to (see FIG. 5).

Note that it is also possible to apply focus servo using a wobbling method. In this case, for example, a periodic disturbance signal is mixed into the focus coil (22) to vibrate the objective lens (42) in the focus direction (Z direction in FIG. 1). Then, for example, three sum signals AA-A
The position where the low frequency signal of the signal obtained by adding C is the maximum is the in-focus position.

Further, the tracking error signal generation circuit (62) adds the three difference signals SA to SC to obtain the tracking error signal TE (TE=SA+SB+SC), and sends this tracking error signal TE via the connection terminal (63). The signal is supplied to a tracking servo circuit (not shown). The position of the oval spot (44) on the pit-forming surface of the optical disc (35) is displaced in the radial direction (R direction) of the optical disc (35), for example, as shown by the broken line near the light receiving board (43) in FIG. As shown, when the image (381) of the center line of the track deviates from the boundary between the photodiodes AI and 42, the first
The absolute value of the difference signal SA becomes larger.

Similarly, the absolute values of the difference signals SB and SC also increase, so
As a result, the absolute value of the tracking error signal TH increases. Therefore, for example, the tracking coil (2
3) By energizing (see FIG. 5), the image of the center axis of each track is set at the boundary between each pair of photodiodes.

This activates the tracking servo. Note that the wobbling method can also be used for tracking servo, but in this case, the number of photodiodes on the light receiving substrate (43) may be one for each I track.

FIG. 3 shows the state of the tracks of the optical disc (35) of this example. As shown in FIG. Form the entire track in a spiral. Then, the 360° section of those three tracks (for example, position R1 in Figure 3)
to position R2), one field or one frame of video signals (and also audio signals) is recorded as a whole. In this example, a series of three tracks are played back simultaneously, so for example, if the oval spot for reading is at position (44A) at this point, if the optical disc (35) rotates 360 degrees from that point on, tracking will occur. The position of the oval spot is changed by the operation of the servo (
44A) radially three tracks away from (
44B).

As described above, according to the optical pickup of this example, the optical disc (35) is
An oval spot that crosses three tracks (44)
At the same time, an image (4) of this oval spot (44) is formed.
41) is a light-receiving board with six photodiodes (
43) It is made to form on the top.

Therefore, there is an advantage that the information of three parallel tracks can be simultaneously reproduced with a simple configuration in which the semiconductor laser light source (28) and optical system are shared.

In addition, in this example, since six photodiodes A1 to C2 are formed on the light receiving substrate (43), it is possible to easily generate a focus error signal for focus servo and a tracking error signal for tracking servo. There is profit.

Next, another embodiment of the present invention will be described with reference to FIG. FIG. 4 shows the optical system of the optical pickup of this embodiment. In FIG. 4, parts corresponding to those in FIG.
(65) is an objective lens with aspherical surfaces on both sides. In this example, astigmatism is actively generated in the plate-shaped beam splitter (64), and the cylindrical lens in The function of (40) and the function of beam splitter (41) are combined.

That is, as shown in FIG. 4, an objective lens (65) is arranged on the lower surface of the optical disk (35), and a beam splitter (64) and a semiconductor laser light source (28) are arranged in sequence on the lower surface of this objective lens (65). A light-receiving substrate (43) on which six photodiodes are formed is arranged at a position approximately symmetrical to the semiconductor laser light source (28) with respect to the half mirror surface (64a) of the beam splitter (64). Assuming that among the output light of the semiconductor laser light source (28), the light ray perpendicular to the paper surface of FIG. 4 is focused on the smallest spot on the pit-forming surface of the optical disk (35), Rays parallel to the plane of the paper in FIG. 4 (indicated by solid lines) are stretched on the pit-forming surface by the action of the beam splitter (64).

Correspondingly, the reflected light (indicated by a broken line) of the elongated spot parallel to the plane of the paper in FIG. ) and then imaged.

Therefore, as in the example of FIG. 1, information on a plurality of tracks can be reproduced simultaneously.

It goes without saying that the present invention is not limited to the above-mentioned embodiments, and that various configurations can be adopted without departing from the gist of the present invention.

[Effects of the Invention] According to the present invention, since the output light of the light emitting element is focused on a spot that crosses a plurality of tracks on an optical disk, it is possible to simultaneously read information on a plurality of tracks with one optical pickup. There are profits that can be made.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing the configuration of an optical system of an optical pickup according to an embodiment of the present invention, FIG. 2 is a configuration diagram showing a signal processing circuit for an optical pickup according to the embodiment, and FIG. FIG. 4 is a plan view of an optical disc according to one embodiment, FIG. 4 is a partially sectional side view showing the optical system of an optical pickup according to another embodiment, and FIG. 5 is a diagram showing the configuration of a conventional optical pickup. 6 is a perspective view showing the configuration of the optical system of the example shown in FIG. 5. FIG. (28) is a semiconductor laser light source, (35) is an optical disk,
(36) to (38) are track center axes, (40) is a cylindrical lens, (41) is a beam splitter,
(42) is the objective lens, (43) is the light receiving board, (44)
is an oval spot, (64) is a plate-shaped beam splitter,
Al, Bl. C1 is a photodiode, respectively. Agent Hidemori Matsukuma - 11 photos of the optical system of the Jitsukata example Fig. 1 Jijigo of the Jitsukata Hiku °j! Rotation division Figure 2 - Practical optical building test 3rd page I Tomoe's implementation 'J's honor system 4th section Conventional optical bilquature Figure 5 Ji! +5 Figure 6.

Claims (1)

[Scope of Claims] A light-emitting element, an illumination optical system that focuses output light of the light-emitting element onto a spot that crosses a plurality of tracks on an optical disk, an imaging optical system that forms an image of the spot, and an image of the spot. an optical pickup having a plurality of light receiving elements that respectively photoelectrically convert portions of the plurality of tracks corresponding to the plurality of tracks.