JPH07287858A - Optical pickup device - Google Patents

Abstract

PURPOSE:To form a thin and light in weight optical pickup device capable of always performing stable control. CONSTITUTION:This device is provided with an objective lens driving mechanism 21 comprising an objective lens holder 14 holding an objective lens 9, a holder supporting member 17 for supporting the objective lens holder 14, capable of freely displacing, and a lens driving means. On the lower part of the objective lens 9 in the objective lens driving mechanism 21, the exit plane 7d to which a 1/4 wavelength plate 8 is stuck of a deflection prism 7 is arranged and an extending part 7a extended in the exit direction of the deflection prism 7 is fixed on a housing 20. Consequently, the objective lens driving mechanism 21 as a movable part A is made light in weight and the vertical thickness of the movable part A is formed to be thin.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup device for performing focus control and tracking control by an objective lens driving mechanism.

[0002]

2. Description of the Related Art A conventional optical pickup device will be described by taking a separation type device as shown in FIG. 7 as an example. This apparatus is divided into a fixed optical system 1 and a movable optical system 2. First, linearly polarized emitted light a emitted from a semiconductor laser 3 as a laser light source in the fixed optical system 1 is collimated by a collimator lens 4. It becomes light, passes through the polarization beam splitter 5, exits from the fixed optical system 1, and advances to the movable optical system 2. The outgoing light a that has entered the movable optical system 2 is reflected upward by the deflecting prism 7 provided on the base 6, becomes circularly polarized by the quarter-wave plate 8, and becomes the objective lens 9
Optical disc 1 as an optical information recording medium after being condensed by
A minute light spot of about 1 μm is formed on the 0 surface, and information recording or erasing is performed by this. Further, the reflected light b from the optical disk 10 follows a path opposite to the incident light path, becomes linearly polarized light (S polarized light) by the quarter-wave plate 8, is reflected by the deflection prism 7, and is again fixed optical system. Guided within 1. Then, the S-polarized reflected light b is reflected by the polarization beam splitter 5 this time, is condensed by the condenser lens 11, passes through the cylindrical lens 12, and is guided to the light receiving element 13. As a result, information is reproduced, a focus error signal is detected by using the well-known astigmatism method, and a track error signal is detected by using the well-known push-pull method. In this case, the objective lens 9 is held by the objective lens holder 14, and is moved up and down in the lens optical axis direction (Z direction) by the focus coil 15 arranged around the objective lens holder 14 for focusing. Further, by disposing a tracking coil (not shown) around the objective lens holder 14,
It is possible to finely adjust the tracking in the disk radial direction (X direction).

[0003]

In the above-mentioned separation type optical pickup device (not only in this separation type but also in the case of an integral type optical pickup device), the objective lens holder 14 for holding the objective lens 9 is used. Since the quarter-wave plate 8 is attached below the
Also, the weight of the movable part A including the actuator bobbin such as the focus coil 15 and the like increases, and high-speed operation cannot be performed. Further, since the quarter-wave plate 8 is located below the objective lens 9 and the deflection prism 7 is located below this quarter-wave plate 8, the vertical thickness D of the movable portion A is D.
(That is, the distance from the upper surface of the objective lens 9 to the bottom surface of the deflection prism 7) becomes thicker, and it is not possible to reduce the thickness.

[0004] Japanese Patent Application No. 5-320261 discloses a "objective lens driving mechanism" filed by the present applicant. As shown in FIG. 8A, this is because the objective lens 9 is attached to the protruding portion of the upper portion of the objective lens holder 14.
Is held, and the deflection prism 7
Is provided. The deflecting prism 7 is movable as shown in FIG. 8 (b) by supporting such a movable portion A with the fixed portion 18 using the upper and lower two leaf springs 17 in total. The portion A is completely accommodated within the range of the vertical thickness d (the distance from the upper surface of the objective lens 9 to the bottom surface of the deflecting prism 7), which allows the above-described conventional example (see FIG. 7). It can be made thinner than the thickness D (d <D). However, when the position of the center of gravity G of the movable portion A is lowered to almost the same position as the deflecting prism 7 to support the deflecting prism 7 in order to reduce the thickness, the 1/4 wavelength plate 8 is used as the deflecting prism. In order to mount the movable portion A between the objective lens 9 and the objective lens 9 at a position above the center of gravity G, it is necessary to attach a similar weight to the position below the center of gravity G, and the weight becomes even heavier. .

Moreover, when the optical axis of the objective lens 9 does not pass through the center of gravity G as shown in FIG. 8, the objective lens 9 is not located at the center of the movable portion A, so that the focusing (focus direction Fo, that is, Z) of FIG. 9A is performed. Direction) and the tracking of FIG. 10A (tracking direction Tr, that is, X direction),
As shown in FIGS. 9B and 10B, when a resonance 19 rotating around the center of gravity G other than the point P occurs, the displacement of the objective lens 9 becomes large, and as a result, focusing and tracking control are performed. There is a problem that is likely to become unstable.

[0006]

According to the first aspect of the present invention, information is recorded by converging light emitted from a laser light source by an objective lens and irradiating it onto the surface of an optical information recording medium. In an optical pickup device that separates the reflected light from the optical information recording medium from the emitted light by a polarization beam splitter and guides it to a light receiving element to reproduce information, an objective lens holder that holds the objective lens,
An objective lens driving mechanism having a holder supporting member for movably supporting the objective lens holder and a lens driving means for displacing the objective lens holder in the focus direction and the tracking direction is provided, and the objective in the objective lens driving mechanism is provided. An emission surface located below the lens and having a quarter-wave plate attached thereto, a reflection surface located below the emission surface, and a part of the reflection surface extending in the emission direction of the laser light source to the housing. A deflection prism having a fixed extension and an entrance surface formed at one end of the extension is provided.

According to a second aspect of the invention, in the invention of the first aspect, the exit surface of the deflection prism to which the quarter-wave plate is attached is formed to be inclined with respect to the lens optical axis of the objective lens.

According to a third aspect of the invention, in the first aspect of the invention, a polarization beam splitter is integrally attached to the incident surface of the deflection prism.

According to a fourth aspect of the invention, in the first aspect of the invention, the objective lens holder holds the objective lens so that the optical axis of the lens passes through the center of gravity.

[0010]

According to the first aspect of the present invention, the light emitted from the laser light source enters from the incident surface of the deflecting prism, travels through the extending portion, and is reflected by the reflecting surface located in the objective lens driving mechanism. The light is reflected upward and emitted from the emission surface, passes through the quarter-wave plate attached to the emission surface, is condensed by the objective lens, and is irradiated onto the surface of the optical information recording medium. As a result, the quarter-wave plate is mounted on the deflecting prism side instead of being mounted on the objective lens driving mechanism side as in the conventional case, so that the weight of the movable objective lens holder can be reduced. Further, the deflection prism is fixed to the housing by the extending portion extending to the outside of the objective lens drive mechanism, so that the deflection prism is not arranged in the vertical direction of the objective lens drive mechanism unlike the prior art. Therefore, it becomes possible to reduce the thickness.

According to the second aspect of the present invention, it is possible to prevent the flare light reflected on the surface of the quarter-wave plate from entering the light receiving element.

According to the third aspect of the present invention, since the deflection prism and the polarization beam splitter are integrated, it is possible to reduce the number of light transmitting surfaces that require precise polishing and reduce the number of parts.

According to the fourth aspect of the invention, since the lens optical axis passes through the center of gravity of the objective lens holder, it is possible to reduce the influence of resonance rotating around the center of gravity.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described with reference to FIGS. 1 to 5, 9 and 10. The description of the same parts as in the conventional example is omitted, and the same parts are denoted by the same reference numerals. 1 to 3 show the structure of an integrated optical pickup device. First, the configuration of the objective lens driving mechanism 21 will be described. The objective lens 9 is held at the upper center of the objective lens holder 14. in this case,
The lens optical axis L of the objective lens 9 is set so as to pass through the center of gravity G of the objective lens holder 14. Focus coils 15a and 15b are arranged on the side surface of the objective lens holder 14 in the Y direction (direction orthogonal to the traveling direction of the emitted light a), and the magnet 2 is spaced apart from these coils by a predetermined distance.
2a and 22b and back yokes 23a and 23b are fixed to the housing 20 side. Further, tracking coils 16a and 16b are arranged on the side surface of the objective lens holder 14 in the X direction (the traveling direction of the emitted light a). This constitutes lens driving means. The objective lens holder 14 surrounded by the lens driving means is supported by one end of a leaf spring 17 as a holder support member composed of two upper and lower two in total by the protrusion 24. In this way, the leaf spring 17 that supports the objective lens holder 14
Is fixed to the fixed portion 18 to form a movable portion A.

Next, the structure of the deflecting prism 7 will be described. The deflecting prism 7 is provided with a linear extending portion 7a arranged in the X direction, one end of the extending portion 7a is formed with an incident surface 7b on which the emitted light a is incident, and the other end thereof is formed. The reflecting surface 7c is formed, and the emitting surface 7d is formed on the reflecting surface 7c. This exit surface 7d has 1
A quarter wave plate 8 is attached. The deflecting prism 7 is fixed and held by the partition 20a of the housing 20 at the extension 7a. The extending portion 7a of the deflecting prism 7 located in the housing on the objective lens 9 side is inserted through the hole 25 formed in the side surface of the objective lens holder 14 which is the movable portion A, and the exit surface 7d thereof is of the objective lens 9. It is located below. Further, on the incident surface 7b of the deflecting prism 7 located inside the housing on the semiconductor laser 3 side,
The polarization beam splitter 5 is attached integrally.

In such a structure, the objective lens holder 14 is supported by four parallel leaf springs 17 and is displaceable. Then, as shown in FIG. 4, the focus coils 15a and 15b and the tracking coil 16 are
By passing an electric current through a and 16b, the objective lens holder 14 which is the movable portion A is displaced in the focus direction Fo and the tracking direction Tr by the electric current and the magnetic field generated by the magnets 22a and 22b, and the surface shake of the optical disc 10 It can be made to follow track shake. At this time,
The optical axis L of the objective lens 9 is the objective lens holder 1
Since it is held so as to pass through the center of gravity G at the center of 4,
Even if resonance that rotates around the center of gravity G occurs, the objective lens 9 is hardly affected by the resonance,
As a result, stable control can always be performed. This is similar to the objective lens holder 14 shown in FIGS. 9A and 10A. Since the center of gravity G is located at the point Q which is the center of the holder, resonance that rotates around the center of gravity G occurs. Even so, the gain-frequency characteristics shown in FIGS. 9C and 10C are obtained, and as a result, the resonance 19 as in the conventional case is generated.
Does not occur, and stable control can always be performed.

Further, since the quarter-wave plate 8 is mounted on the side of the deflection prism 7 instead of being mounted on the side of the objective lens driving mechanism 21 as in the conventional case, the objective lens holder 14 which is the movable portion A is light in weight. Can be converted. Further, the deflection prism 7 has an extending portion 7 extending outside the objective lens driving mechanism 21.
Since a is fixed by the partition 20a of the housing 20,
The deflection prism 7 has the objective lens driving mechanism 21 as in the past.
The vertical thickness d can be reduced and the vertical thickness d can be made thinner than the conventional thickness D. Therefore, because of this, it is possible to provide an optical pickup device that can always operate at high speed in a stable state. Further, since the deflection prism 7 and the polarization beam splitter 5 are integrally provided, the number of light transmitting surfaces that require precise polishing can be reduced, the number of components can be reduced, and the cost of the device can be reduced. be able to. Moreover, by integrating in this way, the deflection prism 7 can be provided without increasing the assembling accuracy of the housing 20.
It is possible to improve the relative positional accuracy between the polarization beam splitter 5 and the polarization beam splitter 5. Further, here, since the extending portion 7a of the deflection prism 7 is inserted into the hole 25 on the side surface of the objective lens holder 14, the vertical thickness of the optical pickup device can be thinned.

Next, a modification of the deflecting prism 7 will be described with reference to FIG. Here, the exit surface 7d of the deflecting prism 7 to which the quarter-wave plate 8 is attached is formed so as to be inclined by a certain angle with respect to the lens optical axis L of the objective lens 9. Now, the inclination angle of the emission surface 7d and the quarter-wave plate 8 from the horizontal direction is θ, the inclination angle of the reflected light b with respect to the normal line of the emission surface 7d and the quarter-wave plate 8 is θ ′, and the refractive index of the glass is Is n, then sin θ ′ = sin θ / n. As a result, the tilt angle of the reflected light b with respect to the lens optical axis L becomes θ−θ ′, and in order to reflect the outgoing light a traveling horizontally in the prism by θ−θ ′ with respect to the vertical direction, The reflecting surface 7c set at 45 ° is (θ-
Inclination from 45 ° by θ ′) / 2. For example, θ = 2
When set to °, the inclination ψ of the reflecting surface 7c is ψ = 45− (θ−θ ′) / 2≈44.333 °, (n =
1.5). With such a configuration, it is possible to prevent the flare light 26 reflected on the surface of the quarter-wave plate 8 from entering the light-receiving element 13, and thereby accurately including the noise and the like. Signal detection can be performed.

Next, a second embodiment of the present invention will be described with reference to FIG. The description of the same parts as those in the first embodiment described above will be omitted, and the same reference numerals will be used for the same parts. Although the optical pickup device is provided as an integrated type in the above-described first embodiment, it is configured as a separate type here. In the movable optical system 2, one end of the deflection prism 7 is fixed in a hole 27 provided in the housing 29. The exit surface 7d of the deflecting prism 7 to which the quarter-wave plate 8 is attached is located below the objective lens 9. The lens optical axis L of the objective lens 9 passes through the center of gravity G of the objective lens holder 14. On the other hand, in the fixed optical system 1, a semiconductor laser 3, a collimator lens 4, a polarization beam splitter 5, etc. are fixed to a housing 30, respectively, and emitted light a is emitted through a hole 28 provided in the housing 30 and deflected. Incident surface 7a of prism 7
Be led to.

In such a structure, by moving only the movable optical system 2 in parallel (X direction) at the time of access, a high speed access can be realized as compared with the first embodiment described above. In addition, the incident surface 7b of the deflection prism 7
Since the hole 7b of the housing 29 is closed by, it is possible to prevent dust and the like from entering the housing 29 when the movable optical system 2 moves in the access direction. This allows
Since the reflecting surface 7c and the emitting surface 7d of the deflecting prism 7 in the housing 29 are not contaminated, the performance can be maintained for a long time. Further, since the incident surface 7b of the deflecting prism 7 is located outside the housing 29, dirt attached to the incident surface 7b can be removed by simple cleaning. Therefore, by adopting such a separation type device, it is possible to provide an optical pickup device which can realize high-speed access while being thin and lightweight, and which can maintain high performance for a long period of time. .

[0021]

According to the first aspect of the present invention, the light emitted from the laser light source is condensed by the objective lens and irradiated onto the surface of the optical information recording medium to record information.
In an optical pickup device that separates the reflected light from the optical information recording medium from the emitted light by a polarization beam splitter and guides it to a light receiving element to reproduce information, etc., an objective lens holder that holds the objective lens and the objective lens. An objective lens driving mechanism having a holder supporting member for movably supporting a holder and a lens driving means for displacing the objective lens holder in a focus direction and a tracking direction is provided, and the objective lens driving mechanism is provided below the objective lens. An emission surface on which a quarter-wave plate is attached, a reflection surface located below the emission surface, and a part of the reflection surface extended in the emission direction of the laser light source and fixed to the housing. By providing the deflecting prism having the extending portion and the incident surface formed at one end of the extending portion, the objective lens serving as the movable portion is provided. The drive mechanism side can reduce the weight of the movable part for not include a quarter-wave plate, also,
Since the extension of the deflection prism is inserted from the side surface of the objective lens holder and one end of the extension is fixed to the housing, the vertical thickness of the optical pickup device can be reduced. As a result, it is possible to provide a compact and lightweight optical pickup device that can be accessed at high speed.

According to a second aspect of the invention, in the first aspect of the invention, the emission surface of the deflection prism to which the quarter-wave plate is attached is formed to be inclined with respect to the lens optical axis of the objective lens. , Flare light generated by reflection on the quarter-wave plate does not enter the light receiving element, whereby accurate signal detection can be performed without including noise and the like.

According to a third aspect of the present invention, in the first aspect of the present invention, since the polarization beam splitter is integrally attached to the incident surface of the deflection prism, the number of light transmitting surfaces that require precise polishing is reduced and the number of parts is reduced. It is possible to reduce the cost, realize the cost reduction, and increase the relative positional accuracy between the deflection prism and the polarization beam splitter by easy manufacturing.

According to a fourth aspect of the present invention, in the first aspect of the invention, the objective lens holder holds the objective lens so that the optical axis of the lens passes through the center of gravity, so that the objective lens holder is affected by resonance rotating about the center of gravity. The focus control and tracking control can always be performed in a stable state.

[Brief description of drawings]

FIG. 1 is an exploded perspective view showing an integrated optical pickup device according to a first embodiment of the present invention.

FIG. 2 is a plan view of an optical pickup device.

FIG. 3 is a vertical sectional front view showing a cross section taken along the line AA of FIG.

FIG. 4 is a perspective view showing a configuration of a timing circuit.

FIG. 5 is a front view showing a modified example of the deflection prism.

FIG. 6 is a vertical sectional front view showing a separation type optical pickup device which is a second embodiment of the present invention.

FIG. 7 is a front view showing a conventional separation type optical pickup device.

8A is a perspective view showing a conventional objective lens driving mechanism, and FIG. 8B is a front view thereof.

9A is a front view showing a displacement state of a conventional objective lens holder during focusing, and FIG. 9B is a characteristic showing open loop frequency characteristics when resonance occurs in the conventional objective lens holder. FIG. 6C is a characteristic diagram showing an open loop frequency characteristic when the center of gravity Q of the objective lens holder of the present invention is replaced with the conventional objective lens holder of FIG.

FIG. 10A is a plan view showing a displacement state during tracking in a conventional objective lens holder, and FIG. 10B is a characteristic showing open loop frequency characteristics when resonance occurs in the conventional objective lens holder. FIG. 6C is a characteristic diagram showing an open loop frequency characteristic when the center of gravity Q of the objective lens holder of the present invention is replaced with the conventional objective lens holder of FIG.

[Explanation of symbols]

 3 Laser Light Source 5 Polarizing Beam Splitter 7 Deflection Prism 7a Extending Part 7b Incident Surface 7c Reflecting Surface 7d Emitting Surface 8 1/4 Wave Plate 9 Objective Lens 10 Optical Information Recording Medium 14 Objective Lens Holder 17 Holder Supporting Member 20, 29, 30 Housing 21 Objective lens drive mechanism L Lens optical axis G Center of gravity

Claims (4)

[Claims] 1. Information is recorded by condensing light emitted from a laser light source by an objective lens and irradiating the light onto the surface of an optical information recording medium, and the reflected light from the optical information recording medium is polarized. In an optical pickup device that separates the emitted light by a beam splitter and guides it to a light receiving element to reproduce information, an objective lens holder that holds the objective lens, and a holder support member that displaceably supports the objective lens holder. An objective lens drive mechanism having a lens drive means for displacing the objective lens holder in the focus direction and the tracking direction is provided, and a ¼ wavelength plate is attached below the objective lens in the objective lens drive mechanism. Emission surface, a reflection surface located below the emission surface, and a part of the reflection surface that extends in the emission direction of the laser light source from the reflection surface. An optical pickup device comprising: a deflection prism having an extending portion fixed to the housing and an incident surface formed at one end of the extending portion. 2. The optical pickup device according to claim 1, wherein the emission surface of the deflection prism to which the quarter-wave plate is attached is formed to be inclined with respect to the lens optical axis of the objective lens. 3. The optical pickup device according to claim 1, wherein a polarization beam splitter is integrally attached to the incident surface of the deflection prism. 4. The optical pickup device according to claim 1, wherein the objective lens holder holds the objective lens so that the optical axis of the lens passes through the center of gravity.