JP2613756B2 - Light head - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a compact disc,
The present invention relates to an optical head for recording and reproducing information on an optical recording medium such as an optical disk such as a video disk, an optical disk such as a magneto-optical disk, and a magneto-optical disk.

[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. As a method of detecting a tracking error signal, a so-called "three-beam method" is often used.
In the three-beam method, a diffraction grating is used to diffract the beam.

Japanese Patent Application Laid-Open No. 56-47933 discloses an optical head using an off-axis hologram lens as a diffraction grating in order to simplify an optical element. This off-axis hologram lens forms a gelatin-based photosensitive film on a glass substrate, forms an interference image on it, develops it, and forms a protective cover glass on it with an ultraviolet curable resin. And have gained.

[0004]

However, since the conventional diffraction grating has a flat shape, it is directly applied to the surface of a work table or a storage box when processing the diffraction grating or when assembling it into an optical head. Diffraction is likely to occur due to contact of the diffraction grating with scratches and dust. When the diffraction grating is formed of fine irregularities, the dust cannot enter into the fine particles and cannot be wiped cleanly, and the edges are easily damaged by the fine irregularities. If the diffraction grating is scratched or dusty,
There is a drawback that light diffracted by the diffraction grating is scattered and normal signal detection cannot be performed.

[0005] The diffraction grating is formed by forming a diffraction grating on one side of a flat glass substrate, incorporating the diffraction grating into a holding frame, and incorporating the diffraction grating into an optical head or the like.

Therefore, a holding frame is required, the number of parts and the number of assembling steps are increased, and the cost is increased. In addition, a mounting error between the optical element and the holding member and a mounting between the holding member and the optical head main body are required. There is a disadvantage that errors accumulate and the assembling accuracy of the optical system deteriorates.

[0007] It is an object of the present invention to provide an optical head which solves such a drawback.

[0008]

[Means for Solving the Problems] The optical head of the present invention comprises:
In an optical head configured to record and / or reproduce information by projecting a light beam emitted from a light source onto a recording medium as a spot, a first optical element having a diffraction grating formed in an optical path of the light beam. Along with disposing the element, the peripheral portion of the diffraction grating is configured to be more convex than the diffraction grating (the term “configured to be convex” refers to a portion protruding from the surface of the diffraction grating). Wherein two optical elements are arranged, and the first optical element and the second optical element are integrally formed (refer to a form formed by a continuous member).

The optical head according to the present invention is characterized in that the first and second optical elements are formed of a plastic material. Still further, the optical head according to the present invention is characterized in that the first optical element and the second optical element are formed integrally with the holding member.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a sectional view schematically showing a reference drawing of the present invention. The reference diagram of FIG. 1 shows that a light beam emitted from a laser diode 1 constituting a light source is made incident on a polarizing prism 3 as a parallel beam by a collimator lens 2 to be transmitted through the polarizing film, and the transmitted light is reduced to 1/4. The light is reflected at right angles by a reflection prism 5 via a wave plate 4, guided to an objective lens 7 that can be displaced in an optical axis direction and a tracking direction orthogonal to the optical axis direction by an actuator 6, and projected on an optical disk 8 in a spot shape. 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 the polarizing film is reflected by a critical angle prism 9 having a reflection surface 9a set at a substantially critical angle with respect to the center ray, as shown also in a perspective view in FIG. The light is received by the photodetector 10 having the four divided light receiving areas, and an information signal, a focusing error and a tracking error are detected.

Although FIG. 1 does not show the internal structure of the actuator 6, this actuator 6 is disclosed, for example, in Japanese Patent Application Laid-Open 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 integrally formed body, and the diameter of the incident light beam is made clear around the incident side of the collimator lens 2 while the holding frame 11 is made clear. The metal washer 12 is insert-molded to prevent harmful light from entering the collimator lens 2 through the through hole. 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.

In this embodiment, the optical head 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 embodiment, 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. In addition, the plastic molded body can be molded very accurately as long as the dimensional accuracy of the mold is secured, so that the assembly precision can be easily obtained. Further, the metal washers 12 and 14 are insert-molded around the entrance of the collimator lens 2 and the reflection prism 5, respectively, so that the diameter of the incident light beam can be clarified.
Intrusion of harmful light can be effectively prevented. Therefore, the optical adjustment can be easily performed, and the servo of the focusing control and the tracking control can be accurately performed, so that 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 a direction perpendicular 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 a high speed. Shortening can be achieved. 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 main body 13 and hardly reaches the laser diode 1, and the life of the laser diode can be extended. it can. In this reference example, the metal washer 12 is insert-molded around the collimator lens 2 to prevent intrusion of harmful light. However, as shown in FIG. Or a two-color molded article that makes the holding frame 11 opaque by using black plastic or black paint mixed as the plastic forming the holding frame 11 as shown in FIG. 3B, or The same effect can be obtained even if an opaque coat is applied to the inner periphery and / or outer periphery 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 schematic sectional view for explaining an embodiment developed up to 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. Diffraction grating 22
Is formed of a transparent plastic molded body in which a lattice portion 22a having a large number of grooves and a peripheral annular lens barrel portion 22b as a holding member are integrally molded. In addition, the periphery of the lattice portion 22a is raised to form a lens barrel 22b. In the diffraction grating 22, the lens barrel 22b is directly mounted on the optical system support body 21. At this time, the grating portion 22a is formed on a surface facing the laser diode 20. Lattice part 22a and surrounding annular lens barrel part 2 as a holding member
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 as a plastic material for integrally molding 2b.

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, information recorded on the recording medium 27 is reproduced. The reflected light beam from the recording medium 27 is
The light 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. Similarly, the concave lens portion 28
8a and an annular lens barrel 28b as a holding member thereof are integrally formed of a transparent plastic molded body,
After adjusting the position in the optical axis direction, the lens barrel 28b is attached to the optical head body 29 made of a plastic molded body with an adhesive. The light beam transmitted through the concave lens 28 enters a cylindrical lens 30 disposed coaxially with the concave lens 28. Similarly, the cylindrical lens 30 is formed of a transparent plastic molded body in which a lens portion 30a having a lens function and an annular cylindrical portion 30a as a holding member are integrally formed. 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 embodiment, the optical element and the holding member thereof are integrally formed of plastic, that is, each of the diffraction grating 22, the collimator lens 24, the concave lens 28, and the cylindrical lens 30 has an undesirable harmful effect on the optical element. In order to prevent light from entering, a part of the part is subjected to light transmission prevention processing. That is, in the diffraction grating 22, a metal washer 22c is inserted into the inner periphery of the lens barrel 22b, and in the collimator lens 24, the lens barrel 24 is inserted.
b, a metal washer 2 is provided on the inner circumference on both sides of the lens portion 24a.
4c and 24d are inserted, and in the concave lens 28, a metal washer 28c is inserted into the incident side end of the lens barrel 28b so as to define the concave lens 28a. Similarly, in the cylindrical lens 30, the light enters the lens barrel 30b. A metal washer 30c is inserted at the side end so as to define the lens portion 30a.

As in this embodiment, the diffraction grating and the holding member were integrally formed of a plastic material, and the lens barrel around the grating was made higher than the grating. As a result, the grid is protected by the lens barrel, and when placed on a workbench or storage box, the grid does not come into direct contact with the workbench or storage box, effectively preventing the grid from being dusted or scratched. it can. Furthermore, since the diffraction grating is formed of a plastic material, it can be extremely accurate as long as the accuracy of the mold is secured, so that mass production is excellent and a holding member that also protects the diffraction grating can be easily formed at the same time. Further, since the holding member is formed around the flat grid portion, the holding member is reinforced, and the deformation of the grid portion during molding is suppressed, and the flatness of the grid portion is good. In addition, since the holding member is also integrally molded, the number of parts is reduced and the number of assembly steps can be reduced.
Assembly errors can be reduced and the cost can be reduced.

In this embodiment, the effect of preventing harmful light can be obtained as in the embodiment 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.

FIGS. 5A and 5B show another embodiment for explaining the embodiment 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.

FIG. 5B shows 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 is formed on the incident side. In addition, a metal washer 41b for preventing light transmission is inserted so as to define the spherical surface 41a, and a cylindrical surface 41c constituting a cylindrical lens is formed on the emission side.

Since such a plastic molded article has high molding precision, high precision can be ensured even when two optical elements are integrally molded, and adjustment in the optical axis direction is not required. 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 two-color molding or an opaque coat can be applied. In addition, metal washer,
By forming a grain joint in place of the two-color molding or the opaque coat, it is possible to more easily and inexpensively suppress the invasion of harmful light than a metal washer or a two-color molding or an opaque coat.

FIG. 6 is a schematic sectional view showing the structure of the embodiment of the present invention. In this embodiment, each optical element, an optical system support main body for supporting the optical system, and an optical head main body are formed by integral molding of plastic, and have an optical system similar to the optical system shown in FIG. . Therefore, the same members as those used in FIG.

In this embodiment, an optical element is formed by providing the following surface on each part of the transparent plastic integral molded body 50. First, the laser diode 20 is attached to the integrally formed body 50.
The surface facing the emission surface of the laser diode 20 was formed concave, and a number of narrow grooves 50a were provided at the bottom to form a diffraction grating. Further, the integrated molded body 50 is provided with a mounting portion for the beam splitter 23, and a convex spherical surface 50b is provided on a surface on which the objective lens 26 emits a light beam via the mounting portion for the beam splitter 23, thereby forming a collimator lens. . Also,
A concave lens is formed by providing a concave spherical surface 50c on the surface of the beam splitter 23 on which the light beam reflected by the half mirror surface 23a enters, and a cylindrical lens is formed by forming a cylindrical surface 50d on the exit surface.

Also in this embodiment, the diffraction grating and the holding member were integrally formed of a plastic material, and the periphery of the diffraction grating was made higher than the diffraction grating. Therefore, the same effect as that of the embodiment shown in FIG. 4 is obtained. Further, in this embodiment, in addition to the diffraction grating, various spherical or strip-shaped grooves, such as a collimator lens, a concave lens, and a cylindrical lens, are provided on each surface of the plastic molded body 50 to form an optical system. Since the element, the supporting member and the optical head body supporting the supporting member are configured, the number of parts and the number of assembling steps are extremely reduced, and the assembling error between the optical elements is also reduced.

In FIG. 6, the optical surface (50
a, 50b, 50c, 50d, etc.) and an opaque coat layer 51 as a light transmission preventing treatment around the molded body 50 except for the mounting surface of the beam splitter 23, or two-color molding in place of the opaque coat layer 51. In this embodiment, the opaque coat layer 51 is replaced with the opaque coat layer 51 in the optical head shown in FIG. To make the surface rougher than the surface of the optical surface through which light passes. If the periphery of the molded body 50 other than the optical surface of the optical element is configured as described above, the intrusion of harmful light can be suppressed more easily and at a lower cost than the above-described opaque coat, metal insert, or two-color molding. be able to.

The present invention is not limited to the above-described embodiment, but can be variously modified or changed.
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. In the present invention, however, the optical element and its holding member are integrally molded of plastic, and a part thereof is formed. The optical head main body and the optical system support main body may be formed of a metal formed body.

[0029]

According to the optical head of the present invention, a light beam emitted from a light source is projected as a spot on a recording medium to record and / or reproduce information. A first optical element having a diffraction grating formed therein is arranged, a periphery of the diffraction grating is configured to be more convex than the diffraction grating, and a second optical element is arranged in the optical path; Since the optical element and the second optical element are formed by integral molding,
The optical head of the present invention has an advantage that the diffraction grating is less likely to be dusted or scratched.

Further, since the first optical element and the second optical element are integrally formed, there are advantages that the number of parts is reduced, the number of assembling steps can be reduced, assembling errors are reduced, and the cost is reduced.

[Brief description of the drawings]

FIG. 1 shows a cross-sectional view in a reference view of the present invention.

FIG. 2 shows a partial perspective view of FIG.

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

FIG. 4 is a cross-sectional view for explaining an embodiment of the present invention developed up to the present invention.

FIG. 5A and FIG. 5B are reference diagrams of the present invention.

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

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Laser diode 2 Collimator lens 3 Polarizing prism 4 1/4 wavelength plate 5 Reflection prism 6 Actuator 7 Objective lens 8 Optical disk 10 Photodetector 11 Holding frame 13 Optical head main body 20 Laser diode 21 Optical system support 22 Diffraction grating 23 Beam splitter 26 Objective lens 27 Recording medium 28 Concave lens 30 Cylindrical lens 30 Molded body

Claims (3)

(57) [Claims] In an optical head for recording and / or reproducing information by projecting a light beam emitted from a light source onto a recording medium as a spot, a diffraction grating is formed in an optical path of the light beam. A first optical element, a peripheral portion of the diffraction grating is configured to be more convex than the diffraction grating, and a second optical element is further arranged in the optical path, and the first optical element and the second optical element are arranged. An optical head, wherein the optical element and the optical element are integrally formed. 2. The optical head according to claim 1, wherein said first and second optical elements are formed of a plastic material. 3. The optical head according to claim 2, wherein the first optical element and the second optical element are formed integrally with a holding member.