JPH09120577A - Optical head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately perform focusing control and tracking control by integrally molding a diffraction grating to be disposed in an optical path and an optical element having a lens function out of the same material into optical elements. SOLUTION: An integrally molded body 50 of transparent plastic is formed with a fitting surface to be fitted with a laser diode 20, and a surface opposite to an emitting surface of this laser diode 20 is recessed, and its bottom surface is provided with a groove part 50b in a fashion of a large number of fine lines to form a collimator lens. Then, a surface on which a light beam reflected by a recording medium and then reflected by a hald mirror surface 23a of a beam splitter 23 is incident is provided with a concave spherical surface to form a concave lens surface as a 2nd optical surface, and its emitting surface is formed with a cylindrical surface 50d to form a cylindrical lens. An opaque coated layer 51 is provided over the whole surface of the integrally molded body 50 except every optical surface of the integrally molded body and the fitting surface of the beam splitter 23.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head for recording and reproducing information on an optical recording medium such as an optical disc such as a compact disc or a video disc or an optical disc such as a magneto-optical disc or a magneto-optical disc. It is about.

[0002]

2. Description of the Related Art A conventional optical head is disclosed in, for example,
There is one described in JP-A-9-201240.
In this conventional optical head, a light source composed of a laser diode, an optical system that guides a light beam emitted from the light source to an objective lens, an actuator that performs focusing control and tracking control by displacing the objective lens in the optical axis direction, A light receiving element including a photodiode for receiving the light beam reflected from the recording medium via an objective lens is provided.

Further, in another conventional optical head, a diffraction grating and a lens are arranged in the outward path from the light source to the recording medium, and a spot is projected to the recording medium side through these optical elements.

[0004]

However, in the conventional optical head, since each optical component forming the optical system is attached to the optical head main body, the number of assembling man-hours is increased, and furthermore, the distance between each optical component is increased. There is a problem that the optical accuracy is deteriorated due to the variation of the distance. For example,
When the diffraction grating and the lens are constructed and arranged as two optical elements having their respective functions, the accuracy of the distance and tilt between the diffraction grating and the lens deteriorates, the spot on the recording medium changes, and the recording / reproducing signal is changed. Is deteriorated, and focusing control and tracking control cannot be performed accurately.

Further, there is a disadvantage that the number of parts and the number of assembling steps are increased, and the cost is increased. An object of the present invention is to provide an optical head that solves such a drawback.

[0006]

The optical head of the present invention comprises a light source, a diffractive means arranged in the optical path between the light source and the recording medium, and an optical path between the diffractive means and the recording medium. In an optical head including an optical element having a lens function disposed therein and a photodetector that receives reflected light from the recording medium, the diffractive means and the optical element are integrally formed of the same material by an optical unit. Configured as.

According to this structure, since the distance between the diffracting means and the optical element is determined at the stage of molding the optical unit, it is possible to solve the problem of adjusting the distance between the diffracting means and the optical element. it can. Further, since the optical head body is integrally molded as a single component, the number of assembly steps can be greatly reduced.

It is desirable to form the optical unit by integrally molding the holding member for holding the diffracting means and the optical element in order to reduce the number of parts. Further, it is desirable that the material of the optical unit is a plastic material in order to make it inexpensive.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the drawings. 1 and 2 are sectional views diagrammatically showing a reference diagram for explaining the principle of the present invention. In the reference diagram of FIG. 1, a light beam emitted from a laser diode 1 constituting a light source is made to enter a polarizing prism 3 as a parallel beam by a collimator lens 2 and transmitted through the polarizing film, and the transmitted light is ¼ The light is reflected at a right angle by the reflection prism 5 through the wave plate 4, and is guided by the actuator 6 to the objective lens 7 which is displaceable in the optical axis direction and the tracking direction orthogonal to the optical axis 8
Project in a spot shape on top. In this reference example, information recorded on the optical disk 8 is reproduced. The reflected light from this optical disk travels along the same optical path as the outward path to the polarizing prism 3 and is incident on the polarizing film. , All the return light is reflected by the polarizing film. The return light from the optical disk reflected by this polarizing film is reflected by a critical angle prism 9 having a reflecting surface 9a set at a substantially critical angle with respect to its central ray, as shown in a perspective view in FIG. Light is received by the photodetector 10 having a divided light receiving region, and an information signal, a focusing error, and a tracking error are detected.

Although the internal structure of the actuator 6 is not shown in FIG. 1, this actuator 6 is disclosed in, for example, Japanese Unexamined Patent Publication No. 56-94311.
The objective lens 7 is supported by a spring so as to be displaceable in its optical axis and in a direction perpendicular to the optical axis. By flowing a current corresponding to the focusing error and the tracking error through the focusing coil and the tracking coil, the objective lens 7 is moved in the focusing direction and in the focusing direction. It is configured so that it can be displaced in the tracking direction.

In this reference example, the collimator lens 2 and its holding frame 11 are formed of a transparent plastic integral molding, and the diameter of the incident light beam is made clear around the entrance side of the collimator lens 2 and at the same time the holding frame 11 is formed. The metal washer 12 is insert-molded to prevent harmful light from entering the collimator lens 2 through. The holding frame 11 is mounted on the optical head body 13, and the laser diode 1 is mounted on the incident side end of the collimator lens 2.

Also, in this reference example, the optical head main body 13
Is formed by integral molding of plastic, and the reflecting prism 5 is integrally molded with the optical head body 13.
A metal washer 14 is insert-molded around the reflection prism 5 in order to similarly define the diameter of the incident light beam and to prevent harmful light from entering the reflection prism 5.
Here, as a plastic material for integrally forming the collimator lens 2 and its holding frame 11, when the light beam is, for example, an infrared ray having a wavelength of 780 to 800 nm used for a compact disc or a video disc,
Polycarbonate, acrylic, or the like can be used.
Further, as the plastic material for integrally molding the reflection prism 5 and the optical head main body 13, PPS other than the above materials may be used as long as the reflection prism 5 can reflect the light beam.
(Polyphenyl sulfide), PEEK (poly
Ether, ether, ketone), PES (polyether sulfone), PEI (polyether imide),
An epoxy resin or the like can be used.

According to this reference example, the collimator lens 2
And the holding frame 11 and the reflection prism 5 and the optical head main body 13 are formed by integral molding of plastic, respectively, so that the number of parts and the number of assembling steps are reduced, so that the cost can be reduced.

Further, since the plastic molded body can be molded extremely accurately if the dimensional accuracy of the mold is secured, the assembly accuracy can be easily obtained. Further, since the metal washers 12 and 14 are insert-molded around the entrance of the collimator lens 2 and the reflection prism 5, respectively, the incident light beam diameter can be made clear and the harmful light can be effectively prevented from entering.

Therefore, the optical adjustment can be easily performed, the focusing control and the tracking control servo can be accurately performed, and the information can be recorded and reproduced with high accuracy. Further, since the plastic material is about 1/2 to 1/3 lighter than metal, the weight of the optical head can be reduced. Therefore, the power source for driving the optical head in the direction orthogonal to the information tracks via the carriage, that is, in the radial direction of the disk-shaped recording medium, requires only a low output and can move at high speed. Time can be reduced.

Furthermore, since the plastic material has a lower thermal conductivity than metal, the heat generated in the coil of the actuator 6 is transmitted to the optical head body 13 and hard to reach the laser diode 1, and the life of the laser diode is extended. can do.

In this reference example, the metal washer 12 is insert-molded around the collimator lens 2 so as to prevent the harmful light from entering. However, as shown in FIG. As shown in FIG. 3B, the sand frame 15 is formed, or as the plastic forming the holding frame 11, black plastic or black paint is mixed, and the holding frame 11 is formed of a two-color molded body that is opaque. Alternatively, the same effect can be obtained by applying an opaque coat to the inner circumference and / or the outer circumference of the holding frame 11 except for the collimator lens 2. The same can be applied to the reflection prism 5 integrally formed with the optical head body 13. FIG. 4 is a diagrammatic sectional view showing another reference example for explaining the principle of the present invention. In this reference example, a laser diode 20 that emits a light beam is mounted on an optical system support 21 made of a plastic molded body, and a light beam is projected toward a diffraction grating 22. The diffraction grating 22 is composed of a transparent plastic molded body in which a grating portion 22a in which a large number of grooves are formed and a peripheral annular lens barrel portion 22b which is a holding member thereof are integrally molded. It is attached directly to the system support body 21.

The light beam transmitted through the diffraction grating 22 is split into three light beams, transmitted through the half mirror surface 23a of the beam splitter 23, and incident on the collimator lens 24. This collimator lens also has a lens portion 24a that also functions as a lens and a surrounding lens barrel portion 24 that is a holding member thereof.
The lens barrel 24b is directly mounted on the optical system support main body 21 by adjusting the lens barrel 24b in the optical axis direction. The three light beams emitted from the collimator lens 24 are converted into parallel light beams, respectively, are incident on an objective lens 26 which is displaced in an optical axis direction and a tracking direction orthogonal thereto by an actuator 25, and are irradiated as spots on a recording medium 27. .

In this reference example, it is assumed that the information recorded on the recording medium 27 is reproduced. The reflected light beam from the recording medium 27 is condensed by the objective lens 26, passes through the collimator lens 24 again, is reflected by the half mirror surface 23a of the beam splitter 23, and enters the concave lens 28. Concave lens 28
Similarly, the concave lens portion 28a and an annular lens barrel portion 28b, which is a holding member for the concave lens portion 28a, are integrally formed by a transparent plastic molding, and the lens barrel portion 28b is adhesively bonded after the position is adjusted in the optical axis direction. Then, it is mounted on the optical head body 29 made of a plastic molding. The light beam transmitted through the concave lens 28 enters a cylindrical lens 30 disposed coaxially with the concave lens 28. This cylindrical lens 30 also has a lens portion 30a which also has a lens function.
And an annular cylindrical portion 30a, which is a holding member thereof, are integrally formed into a molded body of transparent plastic. The light beam transmitted through the cylindrical lens 30 enters a photodiode 31 having a light receiving area corresponding to each beam, and is photoelectrically converted to extract an information signal, a focusing error signal, and a tracking error signal.

In this reference example, in order to prevent undesired invasion of harmful light, a part of each of the molded bodies in which the diffraction grating 22, the collimator lens 24, the convex lens 28, the cylindrical lens 30 and the holding member thereof are integrally molded is used. To prevent light transmission. That is, the diffraction grating 22
In the case of the concave lens 28, a metal washer 22c is inserted in the inner periphery of the lens barrel portion 22b, and in the collimator lens 24, metal washers 24c, 24d are inserted in the inner periphery of both sides of the lens portion 24a of the lens barrel portion 24b. A metal washer 28c is inserted so as to define a concave lens portion 28a at the incident side end portion of the lens barrel portion 28b, and in the cylindrical lens 30, similarly, a lens portion 30a is defined at the incident side end portion of the lens barrel portion 30b. Insert the metal washer 30c as shown in FIG.

Further, in this reference example, the effect of preventing harmful light can be obtained similarly to the reference example shown in FIG. In addition, instead of inserting a metal washer, as shown in FIG.
The holding member may be two-color molded as an opaque plastic, or an opaque coat may be applied to the inner and / or outer periphery of the holding member. In this case, instead of the metal washer, as shown in FIG. 3A, by forming the sand joint 15, the invasion of harmful light can be suppressed more easily and at lower cost than the above-described metal washer or two-color molding.

5A and 5B are other reference examples for explaining the principle of the present invention. 5A and 5B are schematic sectional views showing the configuration of an optical component in which the concave lens and the cylindrical lens shown in FIG. 4 are integrally formed. In the example shown in FIG. 5A, the concave lens portion 40a and the cylindrical lens portion 40b and the surrounding annular lens barrel portion 40c are mutually connected and integrated, and light transmission prevention is provided at the end of the incident side lens barrel portion 40c. As a treatment, a metal washer 40d is inserted.

The example shown in FIG. 5B is an example in which the space between the concave lens portion and the cylindrical lens portion is filled with transparent plastic, and a concave spherical surface 41a for forming the concave lens on the incident side is provided. A metal washer 41b for preventing light transmission is inserted so as to define the spherical surface 41a, and a cylindrical surface 41c forming a cylindrical lens is formed on the emission side.

As described above, in this embodiment, the two optical elements of the concave lens and the cylindrical lens and their holding members are integrally molded with plastic so that one integrated molded body has two optical functions. I chose

Since such a plastic molded body has a high molding accuracy, high accuracy can be secured even if two optical elements of a concave lens and a cylindrical lens are integrally molded as in this embodiment, and the optical axis can be secured. Adjustment of direction can be unnecessary.

Further, since the light transmission preventing treatment is applied, it is possible to effectively prevent the entry of harmful light. Therefore, focusing control and tracking control can be performed with high accuracy, and information recording and reproduction can be performed accurately.

Incidentally, it is a matter of course that the light transmission preventing treatment is not limited to the insert of the metal washer as described above, and sand joint, two-color molding or opaque coat can be applied. FIG. 6 is a schematic cross-sectional view showing the configuration of the embodiment of the present invention.

In the present embodiment, the optical components forming each optical system, the optical system supporting body and the optical head body are formed by integral molding of transparent plastic, and an optical system similar to the optical system shown in FIG. have. Therefore, the same members as those used in FIG.

In this embodiment, the following optical surface is formed on each part of the integrally molded body (optical unit) 50 of transparent plastic. That is, a mounting surface on which the laser diode 20 is mounted is formed on the integrally molded body 50, the surface facing the emitting surface of the laser diode 20 is made concave, and a large number of strip-shaped groove portions 50a are provided on the bottom surface thereof. A diffraction grating (diffraction means) is formed.

Further, the integrally molded body 50 is provided with a mounting portion for the beam splitter 23, and the beam splitter 23
A convex spherical surface 50b is provided on the surface through which the light beam is emitted to the objective lens 26 through the mounting portion of, and a collimator lens (collimator lens) is formed.

Further, a concave spherical surface 50c is provided on the surface on which the light beam reflected by the recording medium and reflected by the half mirror surface 23a of the beam splitter 23 is formed, forming a concave lens surface as the second optical surface. A cylindrical surface 50d is formed on the exit surface to form a cylindrical lens.

Optical surfaces (50a, 50) of the integrally molded body 50
An opaque coating layer 51 is provided as a light transmission preventing treatment around the integrally molded body 50 except for the surfaces (b, 50c, 50d, etc.) and the mounting surface of the beam splitter 23.

In addition to the provision of the opaque coating layer, the light transmission preventing treatment is carried out by inserting metal, forming two colors, or forming a sand joint around the optical surface so as to form an optical path portion. It can also be applied by roughening the surface. By performing the light transmission processing, intrusion of harmful light can be prevented, focusing control and tracking control can be performed with high accuracy, and information can be recorded and reproduced accurately.

As described above, according to the present embodiment, each optical element constituting the optical system, its supporting member, and supporting are provided only by providing various spherical or strip-shaped grooves on each surface of the plastic molded body 50. An optical head body that supports the member can be configured. Therefore, each optical element can be obtained very easily.

Further, a plurality of optical elements such as a diffraction grating having a deflecting or lens action, a collimator lens, a concave lens, and a cylindrical lens are formed on each surface of the molded body, and a holding member thereof is an integrally molded body made of a plastic material. Configured. In addition, the beam splitter was directly attached to the integrally molded body to be integrated with other optical elements. Therefore, the positional accuracy between the optical elements is remarkably improved, and the assembly is significantly simplified.

Further, in this embodiment, since the laser diode and the photodiode are directly attached to the integrally molded body, the diffraction grating, the collimator lens, the concave lens,
The positional accuracy of the laser diode and the photodiode with respect to each optical element of the cylindrical lens is significantly improved.
In addition, the optical element, the collimator lens, and other parts for holding both the laser diode are not necessary, and the configuration is greatly simplified. Further, in this embodiment, a diffraction grating integrally formed and a lens having a condensing function are arranged in the outward path of the light beam from the laser diode to the recording medium. Therefore, the accuracy of the distance and the inclination between the diffraction grating and the lens having the condensing function is good, the accuracy of the three spots generated via the diffraction grating and the lens and projected on the recording medium side is good, and the recording / reproducing signal is Focusing control and tracking control can be accurately performed without deterioration, and as a result, information recording and reproduction can be accurately performed.

It should be noted that the present invention is not limited to the above-described embodiments, and many variations and modifications are possible. For example, there are various types of light sources, optical systems and light receiving elements mounted on the optical head body, and there are various types of actuators. Also, the present invention can be effectively applied to a case where the objective lens and its holding member are formed of a plastic integral molded body. Further, in the above-described embodiment, the optical head main body and the optical system supporting main body are also formed by integral molding of plastic. Prevention treatment can be performed, and the optical head main body and the optical system support main body can also be formed of a metal formed body.

[0038]

As described above, the optical head of the present invention includes the light source, the diffractive means arranged in the optical path between the light source and the recording medium, and the optical path between the diffractive means and the recording medium. In an optical head including an optical element having a lens function to be arranged and a photodetector that receives reflected light from the recording medium, the diffracting means and the optical element are integrally formed of the same material to form an optical unit. Therefore, compared with the conventional optical head, the light spot projected on the recording medium is good, and the focusing control and tracking control can be performed accurately without deterioration of the recording signal and the reproduction signal, and as a result, Recording or reproduction can be performed accurately.

Further, since the number of parts and the number of assembling steps are reduced and the optical position adjustment between the diffracting means and the optical element is unnecessary, an inexpensive optical head can be provided.
Further, since the optical unit is integrally formed of a plastic material, the optical surface having the diffracting means and the lens function can be easily formed, and the mass productivity is excellent and the cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a reference diagram for explaining the principle of the present invention.

FIG. 2 shows a partial perspective view of FIG.

FIG. 3A and FIG. 3B are cross-sectional views as reference views for explaining the principle of the present invention.

FIG. 4 is a cross-sectional view showing a reference diagram for explaining the principle of the present invention.

5A and 5B are reference diagrams for explaining the principle of the present invention.

FIG. 6 is a sectional view for explaining an embodiment of the present invention.

[Explanation of symbols]

 1 Laser Diode 2 Collimator Lens 3 Polarizing Prism 4 1/4 Wave Plate 5 Reflecting Prism 6 Actuator 7 Objective Lens 8 Optical Disc 10 Photodetector 11 Holding Frame 13 Optical Head Main Body 20 Laser Diode 23 Beam Splitter 26 Objective Lens 31 Concave Lens 50 Integrated Molding Body 50a Groove 50b Convex spherical surface 50c Concave spherical surface 50d Cylindrical surface 51 Opaque coating layer

Claims (3)

[Claims] 1. A light source, a diffractive unit arranged in an optical path between the light source and a recording medium, an optical element having a lens action arranged in an optical path between the diffractive unit and the recording medium, An optical head comprising a photodetector that receives reflected light from a recording medium, wherein the diffracting means and the optical element are integrally molded of the same material to form an optical unit. 2. The optical head according to claim 1, wherein the optical unit is also formed by integrally molding a holding member for holding the optical unit with the same material. 3. The optical head according to claim 1, wherein the optical unit is integrally formed of a plastic material.