JP2537335B2 - Optical 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,
Some are described in Japanese Patent Publication No. 9-201240.
In this conventional optical head, a light source composed of a laser die yard, an optical system for guiding a light beam emitted from the light source to an objective lens, and a focusing control or a tracking control by displacing the objective lens in the optical axis direction thereof. An actuator for performing the operation, a light receiving element including a photodiode for receiving the light beam reflected from the recording medium through an objective lens, and the like are provided.

[0003]

However, in the conventional optical head, for example, the collimating lens forming the optical system for guiding the light beam emitted from the light source to the objective lens is mounted on the holding member, and the holding member is held. Since it is fixed to the optical head via a member, the number of parts and the number of assembling steps increase, and the cost increases, and the mounting error between the optical element and its holding member and the holding member and the optical head main body The installation error between
There is a problem that the accuracy of assembling the optical system deteriorates.

In the optical head, in the optical path between the light source and the photodetector, not only the collimator lens described above, but also a cylindrical lens for detecting the focal position of the objective lens is used. It is necessary to arrange a point aberration generating element. The above-mentioned problems also occur in the arrangement of the astigmatism generating element. In order to solve such a problem, a technique in which a lens and a lens barrel are integrally formed of a plastic material is described in Japanese Utility Model Laid-Open No. 60-184012.

[0005]

However, the above-mentioned configuration of the prior art is only one optical element integrally molded with the outer peripheral frame by a plastic material.
Such a configuration is still insufficient in terms of reduction in the number of parts, and adjustment of the optical axis with other optical elements is required, and the assembly work of the device is troublesome. As a result, the price of the optical head is low. It has the drawback of not becoming.

An object of the present invention is to provide an optical head which solves the above drawbacks.

[0007]

In the optical head of the present invention, a recording medium on which information is recorded in a track shape is irradiated with a light beam as a spot and the information is read in the same optical path. A lens and an optical element for generating astigmatism apart from the lens are arranged, and the lens, the optical element and their supporting members are integrally formed of a plastic material, and The surface of the molded body excluding each optical surface of the optical element is constituted by a surface rougher than the lens and each optical surface of the optical element.

[0008]

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 diagrammatically showing a reference diagram for explaining the principle of the present invention. The reference diagram in Figure 1 is
A light beam emitted from a laser diode 1 which constitutes a light source is collimated by a collimator lens 2 and is incident on a polarizing prism 3 as a parallel beam to pass through the polarizing film, and the transmitted light is transmitted through a quarter wavelength plate 4 to a reflecting prism. The light is reflected at a right angle by 5 and guided by an actuator 6 to an objective lens 7 which is displaceable in the optical axis direction and the tracking direction orthogonal thereto, and projected onto an optical disk 8 in a spot shape. In this reference example, the information recorded on the optical disk 8 is reproduced. The reflected light from the optical disk follows the same optical path as the outward path up to the polarization prism 3 and is incident on the polarizing film. However, in the returning path, the polarization direction of the reflected light with respect to the polarization direction of the outward path is due to the action of the quarter wavelength plate 4. Since they are orthogonal to each other, all the returning light is reflected by the polarizing film. As shown in the perspective view of FIG. 2, the return light from the optical disk reflected by the polarizing film is reflected by the critical angle prism 9 having the anti-slope 9a set at a substantially critical angle with respect to the central ray. Four
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, the actuator 6 is disclosed in, for example, 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 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.

Further, in this reference example, the optical head main body 13
Is integrally formed of plastic, and the reflection prism 5 is integrally formed on the optical head body 13.
A metal washer 14 is insert-molded around the reflection prism 5 in order to clarify the incident light beam diameter and prevent harmful light from entering the reflection prism 5.
Here, as the plastic material for integrally molding the collimator lens 2 and the holding frame 11 thereof, polycarbonate is used when the light beam is infrared rays having a wavelength of 780 to 800 nm used for compact discs and video discs, for example. Acrylic or the like can be used. Further, as the plastic material for integrally molding the reflecting prism 5 and the optical head main body 13, it is sufficient that the reflecting prism 5 reflects the light beam.
It is possible to use S (polyphenyl sulfide), PEEK (poly ether ether ketone), PES (polyether sulfine), PEI (poly ether imide), epoxy resin and the like.

According to this reference example, the collimator lens 2
Since the holding frame 11, the holding frame 11, and the reflection prism 5 and the optical head main body 13 are integrally formed of plastic, the number of parts and the number of assembling steps are reduced, and 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. Furthermore, since the metal washers 12 and 14 are insert-molded around the entrance of the collimator lens 2 and the reflecting prism 5, respectively, the incident light beam diameter can be made clear by this, and
It can effectively prevent the entry of harmful light. Therefore, the optical adjustment can be easily performed, and 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 the 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 less likely to reach the laser diode 1 by being transmitted to the optical head body 13, 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 harmful light from entering. However, as shown in FIG. 3B, the holding frame 11 is made of black plastic or plastic. This holding frame 1 using the one mixed with black paint
The same effect can be obtained by forming a two-color molded body in which 1 is opaque, or 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. This is the case with the optical head body 13
The same can be applied to the reflection prism 5 integrally molded with.

As shown in FIG. 3A, the collimator lens 2
By forming the sand joints 15 in the peripheral portion of the above, it is possible to suppress the entry of harmful light more easily and cheaply than the above-mentioned metal washer or two-color molding. 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 22a has a large number of grooves formed therein, and the surrounding annular lens barrel portion 2 which is a holding member for the grating portion 22a.
The lens barrel portion 22b is directly attached to the optical system support body 21 by being formed of a transparent plastic molded body integrally molded with 2b. The light beam that has passed through the diffraction grating 22 is split into three light beams, passes through the half mirror surface 23 a of the beam splitter 23, and enters the collimator lens 24.
This collimator lens is also formed by a transparent plastic molded body in which a lens portion 24a that similarly performs a lens function and a surrounding lens barrel portion 24b that is a holding member thereof are integrally formed, and the lens barrel portion 24b is adjusted in the optical axis direction. Is directly attached to the optical system support body 21. The three light beams emitted from the collimator lens 24 are made into parallel light beams, enter the objective lens 26 which is displaced by the actuator 25 in the optical axis direction and the tracking direction orthogonal thereto, and are irradiated onto the recording medium 27 as a shepot. . In this reference example, 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 is reflected by the concave lens 28.
Incident on. Similarly, the concave lens 28 has a concave lens portion 28a.
And a ring-shaped lens barrel portion 28b, which is a holding member thereof, are integrally molded to form a molded body of transparent plastic. It is attached to the head body 29. The light beam transmitted through the concave lens 28 is reflected by the concave lens 2
8 enters the cylindrical lens 30 arranged coaxially. The cylindrical lens 30 is also 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 thereof are integrally molded. The light beam that has passed through the cylindrical lens 30 enters a photodiode 31 having a light receiving region 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, an undesired harmful effect on the optical element is obtained for each of the molded body, that is, the diffraction grating 22, the collimator lens 24, the concave lens 28, and the cylindrical lens 30, in which the optical element and its holding member are integrally molded of plastic. In order to prevent the entry of light, a part of it is subjected to a light transmission preventing treatment. That is, in the diffraction grating 22, the metal washer 22c is inserted into the inner circumference of the lens barrel portion 22b, and in the collimator lens 24, the lens barrel portion 24 is inserted.
The metal washers 2 are provided on the inner circumferences on both sides of the lens portion 24a of FIG.
4c and 24d are inserted, and in the concave lens 28, a metal washer 28c is inserted so as to define the concave lens portion 28a at the incident side end of the lens barrel portion 28b. A metal washer 30c is inserted so as to define the lens portion 30a at the side end portion.

With this structure, the same effect as that of the reference example shown in FIG. 1 can be obtained. Instead of inserting the metal washer, as shown in FIG. 3B, 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 circumference of the holding member. Good. In this case, instead of a metal washer,
As shown in FIG. 3A, by forming the sand joints 15, it is possible to suppress the penetration of harmful light more easily and at a 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 cross-sectional views showing the configuration of an optical component in which the concave lens and the cylindrical lens shown in FIG. 4 are integrally molded. In the example shown in FIG. 5A, the annular lens barrel portion 40c around the concave lens portion 40a and the cylindrical lens portion 40b is coupled and integrated with each other, and light transmission prevention is performed at the end portion of the lens barrel portion 40c on the incident side. 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 a concave lens on the incident side is shown. 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 body 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 the sand joint instead of the two-color molding or the opaque coat, it is possible to suppress the penetration of harmful light more easily and cheaply than the metal washer and the two-color molding or the opaque coat.

FIG. 6 is a diagrammatic sectional view showing the structure of an 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. That is, a diffraction grating is formed by providing a large number of narrow grooves 50a on the surface facing the emission surface of the laser diode 20, and passes through the objective lens 26 through the beam splitter 23.
A collimator lens is formed by providing a convex spherical surface 50b on the surface from which a light beam is emitted. Further, a concave lens is formed by providing a concave spherical surface 50c on the surface of the beam splitter 23 where the light beam reflected by the half mirror surface 23a is incident, and a cylindrical lens is formed by forming a cylindrical surface 50d on the exit surface. .

As described above, by merely providing various spherical or strip-shaped grooves on each surface of the plastic molded body 50, each optical element constituting the optical system, its supporting member, and the optical head for supporting the supporting member are provided. The body can be configured. In FIG. 6, the optical surfaces (50a, 50b, 50c,
50d or the like) and the periphery of the molded body 50 excluding the mounting surface of the beam splitter 23, an opaque coating layer 51 is provided as a light transmission preventing treatment, or two-color molding is applied in place of the opaque coating layer 51 to remove harmful light. However, in the embodiment of the present invention, in the optical head shown in FIG. 6, the opaque coat layer 51 is replaced with the opaque coat layer 51 as, for example, a sand joint to allow light to pass therethrough. Make the surface rougher than the optical surface.

Thus, the molded body 5 other than the optical surface of the optical element
If the circumference of 0 is configured as described above, it is possible to suppress the penetration of harmful light more easily and cheaply than the above-mentioned opaque coat, metal insert, or two-color molding. The present invention is not limited to the above embodiment,
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 actuators of various types. The present invention can also be effectively applied to the case where the objective lens and its holding member are formed of a plastic integrally molded body. Furthermore, in the above-mentioned embodiment,
The optical head main body and the optical system support main body are also formed by integral molding of plastic, but in the present invention, the optical element and its holding member are integrally molded by plastic, and it is also possible to perform a light transmissive prevention treatment on a part thereof, The optical head main body and the optical system support main body may be formed of a metal forming body.

[0023]

According to the optical head of the present invention, a recording medium on which information is recorded in a track shape is irradiated with a light beam as a spot, and in the optical head for reading the information, the lens and the lens are separated from each other in the same optical path. And an optical element for generating astigmatism are arranged, and the lens, the optical element, and their supporting members are integrally formed by a plastic material, and each optical surface of the lens and the optical element is formed. Since the surface of the molded body excluding the above is constituted by a surface that is rougher than the optical surfaces of the lens and the optical element, the optical head of the present invention is compared with the optical head of the prior art. As a result, the number of parts can be reduced, the number of assembly steps can be reduced, and the assembly error can be reduced.
Assembly of the device is remarkably simple and light transmission can be suppressed, and as a result, the optical head of the present invention has an advantage of being inexpensive and having high performance.

[Brief description of 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.

3A and 3B are sectional views showing reference diagrams 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 sectional views for explaining the principle of the present invention.

FIG. 6 is a sectional view for explaining one 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 21 Optical System Support 22 Diffraction Grating 23 Beam Splitter 26 Objective Lens 27 Recording Medium 28 Concave Lens 30 Cylindrical Lens 50 Molded Body

Claims (1)

(57) [Claims] 1. An optical head for irradiating a recording medium on which information is recorded in a track shape with a light beam as a spot and reading the information, the lens and the lens are separated from each other in the same optical path to generate astigmatism. The optical element to be arranged is arranged, and the lens, the optical element, and these supporting members are integrally formed by a plastic material,
An optical head characterized in that the surface of the molded body excluding the optical surfaces of the lens and the optical element is made rougher than the optical surfaces of the lens and the optical element.