JPS61271630A - Optical system head device - Google Patents

Abstract

PURPOSE:To detect the focus error of the astigmatism system with a simple optical system where astigmatism is caused in a reflected luminous flux and no cylindrical lens used by forming a luminous flux separating face of a beam splitter as a curved face so as to separate the reflected luminous flux from an irradiated luminous flux. CONSTITUTION:The luminous flux separating face 18 of the beam splitter 6 separating the irradiated luminous flux 2 from a light source 1 an the reflected luminous flux from a focused spot on an optical disc 4 is formed as a cylindrical face. Thus, the splitter 6 acts like a parallel flat plate to the luminous flux 2 but uses its split face 18 as a cylindrical mirror to the luminous flux 5, which is separated from the luminous flux 2 and converted into the astigmatism luminous flux at the same time. Thus, the automatic focus adjusting mechanism of the astigmatism system is realized by a simple optical system while not employing a cylindrical lens, the number of components is decreased to simplify the head device.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical head device for a device that reads or writes information to a medium such as an optical digital disk, and particularly relates to an optical head device of an astigmatic type. This invention relates to automatic focus adjustment (focus servo) using a focus error detection system.

[Conventional technology]

2. Description of the Related Art In recent years, optical disc devices that reproduce information optically recorded on an information recording disc using a head using a laser beam, or conversely record information, have become popular.

This type of optical head device requires a focus servo to always accurately focus and irradiate a focused laser beam onto the information recording track of the disk, which is the information recording medium, in order to accurately record and reproduce information. As such an automatic focus adjustment device, a method is known in which information detection and focus position detection are performed using an astigmatism optical system.

Figure 4 is an optical path diagram schematically showing an automatic focus adjustment system for an optical disk head using this conventional astigmatism optical system.
The figure is a schematic diagram showing the servo mechanism below the photodetector.

In FIGS. 4 and 5, (1) is a light source such as a semiconductor laser, (2) is the emitted light flux emitted from the light source (1), and (
3) is an objective lens, (4) is an optical disk which is an information recording medium placed near the focal point position of the objective lens, and (5) is an optical disc that is an information recording medium placed near the focal point position of the objective lens.
(6) is a beam splitter that separates the output beam (2) and the reflected beam, (7) is the reflected beam (5).
A cylindrical lens is an optical element that gives astigmatism to ), and its cylindrical axis direction is X (perpendicular to the plane of the paper), and the direction perpendicular to this within the lens plane is y. (8) is 1?7 direction and 45°
With the dividing line having an angle of (8a) (8b) (8c)
The photodetector is divided into four parts (8+1), (9) is the reflected light spot due to the reflected light flux (7) projected onto it, (lO
) is a focus error detection circuit consisting of an adder (11), (12) and a differential amplifier (13), (14) is an information detection circuit consisting of an adder, and (15) is a focus error detection circuit consisting of an adder (11), (12) and a differential amplifier (13), and (15) is an information detection circuit consisting of an adder. The focus actuator (16) energizes the focus actuator (15) to drive the objective lens. The lens drive circuit (17) is an information reproducing circuit (not shown).

Next, its operation will be explained. The laser beam (2) emitted from the light source (1) is converged by the objective lens (3),
A focused spot is formed on the information track of the disk (4). The reflected beam (5) containing information read from the information track on the disk (4) from this focused spot is separated from the output beam (2) by a beam splitter (6),
The cylindrical lens (7)K focuses the light in only one direction and converts it into an astigmatic light beam.

In other words, there is no lens action in the plane that includes the cylindrical axis Plane(
In the plane of the drawing, the light is focused on point q by the convergence effect of the cylindrical lens (7). Therefore, the light distribution shape of the reflected light beam subjected to astigmatism is a long line in the X direction at point q, and a y line at point P.
The shape is a long line in the direction, and the part between them is an oval or circle whose major axis is in either the x or y direction.

A 4-split photodetector is installed at a position where the light distribution shape of the reflected light flux that has undergone astigmatism becomes circular when the disk (4) is at the focused position of the objective lens (3) (hereinafter referred to as "in-focus"). (8)
is placed. Therefore, the shape of the reflected light spot (9) on the photodetector (8) becomes circular when focused, and the optical disc (
4) approaches the objective lens (3) when in focus (if the reflected light spot (9) is displaced, the shape of the reflected light spot (9) becomes an elongated oval in the X direction, and when it is displaced in the direction away from the objective lens (3) during focus, it becomes elongated in the y direction. It becomes an oval shape.

And each light receiving area when the reflected light spot (9) is circular (
The light receiving areas according to 8a) (8b) (8c) and (8d) are equal, and when the major axis of the reflected light spot (9) is in the X direction, the light receiving area (sa) (sc) is the same as the reflected light spot (9).
When the long axis of is in the y direction, the light receiving area (8b) (8d) is
Each area has a larger light receiving area than other areas.

Therefore, the output of the adder (11) that calculates the sum of the light receiving outputs of the light receiving area (8a) C80) and the light receiving area (8m) X8i1
), the difference between the output of the adder (12) and the output of the adder (12), which calculates the sum of the received light outputs of the When the reflected light spot (9) is circular, it is zero, and the optical disc (4)
) becomes closer than when in focus, and the reflected light spot (9) becomes elongated in the The output is approximately proportional to the deviation from the in-focus position.

Therefore, the output Kf of this focus error detection circuit (10) controls the lens drive circuit (16), energizes the focus actuator (15), and moves the objective lens (3) in the optical axis direction. The focus is adjusted accordingly. Further, the read information from the optical disk (4) included in the reflected light beam (5) is extracted by an information detection circuit (14) that calculates the sum of the light reception outputs of each light reception area, and is sent to a reproduction circuit (17).
guided by.

[Problem that the invention seeks to solve]

As mentioned above, in the conventional optical head device, an independent dedicated optical system is used as an astigmatism optical system that causes a change in the shape of the reflected light spot (9) on the photodetector (8) corresponding to the focus error. A cylindrical lens (7) is used. Since this cylindrical lens (7) is required, and an adjustment mechanism is required to adjust the mutual position of the cylindrical axis and the dividing line of the photodetector (8), and adjust the inclination with the optical axis,
There were problems such as high cost due to the large number of parts.

This invention was made in view of the above-mentioned conventional problems, and its purpose is to provide an optical head device capable of detecting focus errors using an astigmatism method using a simple optical system. It is in.

[Means for solving problems]

In the optical head device according to the present invention, in a beam splitter that separates a light beam emitted to an objective lens and a light beam reflected from an information recording medium, the shape of the beam separation surface is a curved surface that causes astigmatism in the reflected light beam. , the reflected light beam is separated in a direction different from the emitted light beam.

[Effect]

In the apparatus of the present invention, in addition to the reflected light beam being separated from the incident light beam by the beam splitter, astigmatism occurs in the separated reflected light beam. Focus errors can be detected using the astigmatism method.

[Embodiments of the invention]

FIG. 1 shows the main structure of an optical head device according to an embodiment of the present invention.

This device consists of a light source (1) such as a semiconductor laser, and an objective lens (1) that focuses the emitted light beam (2) from the light source (1) onto a track of an optical disk (4) that is an information recording medium.
3), a reflected light beam (5) that is reflected from a condensed spot on the optical disk (4) and passes through the objective lens (3) in the opposite direction, and an emitted light beam (2) from the light source (1). A beam splitter (6) and a photodetector (6) that is disposed at a position to receive the reflected light beam (5) separated by the beam splitter (6) and that produces different detection outputs depending on the shape of the received reflected light spot. 8) and a focus error detection circuit (not shown) which extracts a signal corresponding to the error from the focused position of the objective lens (3) of the optical disc (4) from the output of the photodetector (8). , the objective lens (3) is displaced in the optical axis direction by the output of this detection circuit to correct the focus error.

(18) is a beam splitting surface of the beam splitter (6), which is a cylindrical surface in this embodiment. Let the cylindrical axis direction of this cylindrical beam separation surface (18) be X, and the direction perpendicular to X and the optical axis trap be y. The photodetector (8) is divided by two mutually orthogonal separating lines forming an angle of 45° in the Xm F direction, and its shape may be the same as that shown in FIG. Further, the configuration of the focus error detection circuit may be the same as that shown in FIG.

The beam splitter (6) is made of glass or plastic, and while conventionally it was made up of two triangular prisms glued together, in this embodiment, the beam splitter is the glued surface of the two triangular prisms. The surface (18) is formed into a cylindrical curved surface.

Therefore, the beam splitter (6) acts as a parallel plate for the light beam (2) emitted from the light source (1), but
The beam separation surface (18) acts as a cylindrical mirror for the reflected beam (5) K, and the reflected beam (5) is separated from the output beam (2) and simultaneously converted into an astigmatic beam.

The reflected light beam (5) in a plane including the cylindrical axis direction X of the beam separation surface (18) and the optical axis has no lens action, and is converged at a point P by the objective lens (3).

Also, the reflected light flux (
5) is subjected to a lens action by the cylindrical surface of the beam separation surface (18), and is focused on point q. A photodetector (8) is installed at a focused position between points P and Q.

Therefore, the shape of the reflected light spot on the photodetector (8) changes as shown in FIG. The position of (3) is corrected by the actuator (15). This operation is the same as the conventional one.

In the above embodiment, the beam splitting surface (18) of the beam splitter (6) is a -axial cylindrical surface, but the present invention is not limited thereto.

For example, as shown in FIG. 2, the beam splitting surface (18) may be a biaxially curved surface having different curvatures in two orthogonal directions, that is, a so-called toric surface. In this case, the size of the spot at the focal point position can be set arbitrarily.

Further, even if the beam separation surface (18) is either -axial or biaxial, its curved surface can be made an aspherical surface to improve the detection accuracy of focus errors.

Further, as shown in FIG. 3, the beam separating surface (18) may be formed into a curved surface that is convex with respect to the reflected beam. In this case, the position of the PtQ point in FIG. 1 is reversed, but it is different from the above. Focus errors can be detected in the same way.

〔Effect of the invention〕

As described above, according to the present invention, since the beam splitting surface of the beam splitter is curved to cause astigmatism in the reflected beam, an astigmatism-based automatic focus adjustment mechanism can be used without using a conventional cylindrical lens. can be realized with a simple optical system, reducing the number of parts and lowering costs.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an optical head device according to an embodiment of the present invention, FIGS. 2 and 3 are diagrams showing the shape of a beam splitting surface according to another embodiment of the invention, and FIGS. 4 and 5 The figure is a configuration diagram of a conventional device. (1) is a light source, (3) is an objective lens, (4) is an optical disk, (5) is a reflected light beam, (6) is a beam splitter, (
8) is a photodetector, and (18) is a beam separation surface. Note that the same reference numerals in each figure indicate the same or corresponding parts. Agent: Patent Attorney Masuo Oiwa (and 2 others) Figure 1: 8: Yusokea Kuzu 15; Figure 2, Figure 3, Figure 4; lit. b' Figure 5 Procedural amendment (voluntary) 2. Name of the invention Optical head device 3, Person making the amendment 5, Subject of the amendment 3, Contents of the amendment Claims (1) Light source and light source from this light source an optical means for condensing an emitted light beam onto a track of an information recording medium, and separating a reflected light beam that is reflected from a condensed spot on the recording medium and passes through the optical means in reverse and an emitted light beam from the light source. *
+m+i and this (1) photodetector which is disposed at a position to receive the reflected light beam separated by the separation means and produces different detection outputs depending on the shape change of the received reflected light spot, and the above-mentioned record from the output of this photodetector. A focus error detection circuit is provided for extracting a signal corresponding to the error from the focused position of the medium 11LL, and the output of this detection circuit
An optical head device configured to correct the focus error by displacing L in the optical axis direction, the astigmatism causing a shape change of the reflected light spot corresponding to the focus error on the photodetector. An optical head device characterized in that, as an aberration optical system, a light beam separation surface of the optical separation hand l is curved. (2) The optical head device according to claim 1, wherein the light beam separating surface is a cylindrical surface. (3) The optical head device according to claim 1, wherein the light beam separating surface is a uniaxial aspherical surface. (4) The optical head device according to claim 1, wherein the light beam separating surface is a two-wheeled spherical surface having different curvatures along two orthogonal axes. (5) The optical head device according to claim 1, wherein the light beam separating surface is a biaxial aspherical surface.

Claims (5)

[Claims] (1) A light source, an objective lens that focuses the light beam emitted from the light source onto a track of an information recording medium, and a reflected light beam that is reflected from the focused spot on the recording medium and passes through the objective lens in reverse. A beam splitter that separates the emitted light beam from the light source, and a beam disposed at a position to receive the reflected light beam separated by the beam splitter, and a beam that produces different detection outputs depending on the shape of the received reflected light spot. A detector, and a focus error detection circuit that extracts a signal corresponding to an error from the focal point position of the objective lens on the recording medium from the output of the photodetector, and the output of the detection circuit moves the objective lens to the optical axis. An optical head device configured to correct the focus error by displacement in the direction, the astigmatism optical system causing a shape change of the reflected light spot corresponding to the focus error on the photodetector. An optical head device characterized in that the beam splitting surface of the beam splitter is curved. (2) The optical head device according to claim 1, wherein the light beam separating surface is a cylindrical surface. (3) The optical head device according to claim 1, wherein the light beam separating surface is a uniaxial aspherical surface. (4) The optical head device according to claim 1, wherein the light beam separating surface is a biaxial spherical surface having different curvatures along two orthogonal axes. (5) The optical head device according to claim 1, wherein the light beam separating surface is a biaxial aspherical surface.