JPH06300903A - Objective - Google Patents

Abstract

(57) [Summary] [Object] To provide an objective lens that can be easily incorporated into various devices with a simple configuration and that can reduce the size of such devices. In the objective lens 10, which comprises a single lens made of glass or plastic, a first surface 1
In either one of the first surface 12 and the second surface 12, the lens surface region 11b on the outer side of the effective diameter is set so that the light beam incident on this region is largely deviated from the light beam transmitted through the lens surface within the effective diameter. The objective lens 10 is characterized by being formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an objective lens suitable for use in, for example, an optical pickup for an optical disc.

[0002]

2. Description of the Related Art Conventionally, for example, an objective lens for an optical pickup is constructed as shown in FIG.
In the figure, the objective lens 1 is composed of one single-lens aspherical convex lens. And this objective lens 1 is
The optical pickup (not shown) is fixed to the lens mounting portion 2a of the lens holder 2 with an adhesive.

Here, the lens mounting portion 2a of the lens holder 2 is provided with an aperture portion 2b formed so as to cover the outer side portion of the effective diameter of the objective lens 1.

[0004]

However, in the objective lens 1 for an optical pickup having such a structure, when the objective lens 4 is attached to the lens attachment portion 2a of the lens holder 2, the lens attachment portion 2a of the lens holder 2 is attached. There is a problem that it is necessary to accurately center the aperture portion 2b, and the assembly cannot be easily performed.

Further, since the lens holder 2 has the aperture portion 2b in the lens mounting portion 2a, the lens holder 2 becomes thicker accordingly. Therefore, both the objective lens 1 and the lens holder 2 are restricted in shape,
There was a problem that the degree of freedom in setting was low.

Further, the objective lens 1 is attached to the lens holder 2
When strongly adhered to the lens mounting portion 2a, the objective lens 1 is distorted and the optical performance is deteriorated. Further, if the adhesive is loosely adhered, there is a problem that the adhesive strength becomes insufficient and the adhesive may come off during use.

In view of the above points, the present invention provides an objective lens having a simple structure, which can be easily incorporated into various devices and which can be downsized. Has an aim.

[0008]

According to the present invention, the above object is to provide an objective lens comprising a single lens made of glass or plastic, which is either the first surface or the second surface of the single lens. On the other hand, the lens surface area on the outer side of the effective diameter is configured so that the light flux incident on this area and the light flux transmitted through the lens surface within the effective diameter are largely displaced. To be achieved.

The objective lens according to the invention is preferably
The lens surface region of the outer side portion of the effective diameter is formed in a conical shape extending in the tangential direction in a cross section.

Further, in the objective lens according to the present invention, it is preferable that the lens surface region of the outer side portion of the effective diameter is formed as a spherical surface centering on the focal point.

Further, in the objective lens according to the present invention, preferably, a portion corresponding to a half circumference of an outer peripheral edge of the single lens is surrounded and fixedly held by a lens holder.

[0012]

According to the above construction, the light incident from the first surface of the objective lens is emitted from the second surface to the outside. At that time, the light flux that passes through the inner portion of the effective diameter is converged in a predetermined direction by the refraction effect of the objective lens itself. Further, the light flux passing through the outer side portion of the effective diameter is emitted in a direction largely deviated from the predetermined direction based on the shape of the lens surface thereof.

Therefore, the light flux that transmits the outer portion of the effective diameter does not converge like the light flux that transmits the inner portion of the effective diameter, and does not contribute to image formation on the surface of the optical disk, for example. Thus, in the objective lens, the outer portion of the effective diameter acts as the aperture portion.

The lens surface area on the outer side of the effective diameter is
In the cross-section, a conical shape extending in the tangential direction is formed, and the light flux passing through this lens surface area is emitted as a parallel light flux rearward from the focus position.

Further, when the lens surface area on the outer side of the effective diameter is formed as a spherical surface with the focus at the center, the light flux passing through this lens surface area has an optical axis in front of the focus position. It will be emitted as a light beam that converges toward the upper position.

Further, when the portion corresponding to the half circumference of the outer peripheral edge of the single lens is surrounded and fixedly held by the lens holder, the lens holder does not need to have an aperture portion, and the objective lens is laterally mounted. It is a simple structure that only surrounds from.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described in detail below with reference to FIGS. It should be noted that the examples described below are suitable specific examples of the present invention, and therefore, various technically preferable limitations are given, but the scope of the present invention particularly limits the present invention in the following description. Unless otherwise stated, the present invention is not limited to these modes.

FIG. 1 shows an embodiment of the objective lens according to the present invention. In the figure, the objective lens 10 is composed of one substantially convex lens.

In the objective lens 10, one of the first surface 11 and the second surface 12 thereof, in the illustrated case, the first surface 11 on the left side is inside the effective diameter D. In the surface region 11a, it is formed as a spherical surface or an aspherical surface having a curvature so as to obtain a predetermined optical performance. Further, the lens surface region 11b outside the effective diameter D of the objective lens 10 is configured to have a curvature largely different from the curvature of the lens surface region 11a.

Specifically, the lens surface regions 11a and 11b are formed as shown in FIG. 2 (A). In FIG. 2A, the lens surface area 11a
Is formed as an aspherical surface, and the lens surface region 11b
Is formed in a conical shape so that its cross section extends in the tangential direction at the boundary 11c with the lens surface region 11a.

Therefore, in the drawing, the light incident from the left side enters inside the objective lens 10 from the lens region 11a of the first surface 11 inside the effective diameter of the objective lens 10, and the second surface 12 (see FIG. 1) is emitted to the right. Thereby, the incident light flux is
It is refracted by the lens region 11a of 1a and the second surface 12 to be converged in a desired direction.

On the outside of the effective diameter of the objective lens 10, the incident light beam is incident on the lens region 11b of the first surface 11 and largely deviates from the above predetermined direction based on the shape of the conical lens surface. It is emitted in the direction of the arrow and does not form an image.

Therefore, only the light beam that passes through the inside of the effective diameter is imaged by the objective lens 10. At this time, the light flux that transmits outside the effective diameter does not converge and does not contribute to image formation on the surface of the optical disc, for example. That is, the lens area 11b acts as an aperture portion.

Although the lens surface region 11b of the first surface 11 of the objective lens 10 is formed as a conical surface extending in the tangential direction, it may have another shape.
For example, the lens surface area 11b of the objective lens 10 is shown in FIG.
As shown in (B), for example, it is formed as a spherical surface centered on the focal position of the objective lens 10.

As a result, the lens surface area 11b is
The lens is inclined inward more than the lens surface area 11a. Therefore, the incident light flux converges on the optical axis considerably before the focal position of the objective lens 10, and then diverges.

Thus, also in this case, in the same manner, only the light beam that passes through the inside of the effective diameter is imaged at the focal position by the objective lens 10. At this time, the light flux that transmits outside the effective diameter does not converge and does not contribute to image formation on the surface of the optical disc, for example. That is, the lens area 11b acts as an aperture portion.

The lens surface area 11b of the first surface of the objective lens 10 may be constructed as shown in FIG. 2 (C). In this case, the lens surface region 11b is formed to have a step at the boundary portion with the lens surface region 11a, and is formed into a conical shape so as to extend in the tangential direction at the boundary with the lens surface region 11a. There is.

According to such a configuration, only the light beam that passes through the inside of the effective diameter is imaged by the objective lens 10. At this time, the light flux that transmits outside the effective diameter does not converge and does not contribute to image formation on the surface of the optical disc, for example. That is, the lens area 11b acts as an aperture portion.

Further, since the light flux incident on the boundary between the lens surface areas 11a and 11b is bent in completely different directions due to the step, the lens surface area 11 near the boundary.
The light flux incident on b does not travel near the focal position of the objective lens 10. Therefore, the aberration of image formation at the focal position is improved.

FIG. 3 shows the objective lens 10 having such a configuration.
It shows the case where is attached to the lens holder 13.
The lens holder 13 includes a semicircular lens mounting portion 13a. In this case, since the objective lens 10 itself has the function of the aperture portion in the portion outside the effective diameter, the lens holder 13 needs to provide the lens attachment portion 13a with an aperture portion that surrounds the objective lens 10 from the optical axis side. There is no.

The lens mounting portion 13a formed in this way
On the other hand, by mounting the objective lens 10, the assembling of the objective lens 10 into the lens holder 13 is completed.

The objective lens 1 is attached to the lens mounting portion 13a.
The mounting of 0 may be performed by an adhesive agent or the like, and the lens holder 12 may be integrally molded with the objective lens 10 by, for example, two-color molding.

Further, by integrally forming an extension portion extending from one side of the objective lens 10 to the side,
By holding the tip of the extension, the distortion of the lens due to holding the objective lens 10 can be further reduced.

As described above, according to the above-described embodiment, since the portion outside the effective diameter of the objective lens has the function of the aperture portion, alignment and centering of the objective lens and the aperture are unnecessary. Therefore, the assembly cost can be reduced because the assembly can be easily performed.

Since the lens holder for holding such an objective lens does not need to have an aperture portion, it is thin and lightweight. As a result, when the objective lens is used in an optical pickup such as an optical disc recording / reproducing apparatus, the entire apparatus is compact and lightweight.

Further, the portion corresponding to the half circumference of the outer peripheral edge is
When the lens holder is surrounded and fixedly held, since the lens holder only surrounds the objective lens from the side, the distortion of the objective lens does not occur and therefore the optical performance of the objective lens is improved. It will not be damaged.

Further, since the shapes of the objective lens 10 and the lens holder 12 are not limited by the aperture portion, the degree of freedom in design is increased, and the objective lens 10 and the lens holder 12 can be easily designed.

[0038]

As described above, according to the present invention, an excellent objective lens which has a simple structure, can be easily incorporated into various devices, and can be downsized such devices. Can be provided.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing an embodiment of an objective lens according to the present invention.

FIG. 2 is a partially enlarged cross-sectional view showing a configuration example of a main part of the objective lens in FIG.

FIG. 3 is a schematic plan view showing a state in which the objective lens of FIG. 1 is attached to a lens holder.

FIG. 4 is an exploded perspective view showing an example of an objective lens used in a conventional optical pickup.

[Explanation of symbols]

 10 Objective Lens 11 First Surface 12 Second Surface 13 Lens Holder 13a Lens Mounting Part

Claims (4)

[Claims] 1. An objective lens comprising a single lens made of glass or plastic, wherein a lens surface region of an outer portion of an effective diameter is provided on either the first surface or the second surface of the single lens. The objective lens is characterized in that the light flux incident on this region and the light flux passing through the lens surface within the effective diameter are largely displaced. 2. The objective lens according to claim 1, wherein a lens surface region of an outer portion of the effective diameter is formed in a conical shape extending in a tangential direction in a cross section. 3. The objective lens according to claim 1, wherein the lens surface region of the outer side portion of the effective diameter is formed as a spherical surface centered on the focal point. 4. The objective according to claim 1, wherein a portion corresponding to a half circumference of an outer peripheral edge of the single-lens is surrounded and fixedly held by a lens holder. lens.