JPH06214154A - Objective lens - Google Patents

Abstract

PURPOSE:To obtain an objective lens capable of manufacturing a small-sized pickup, etc., capable of being easily assembled with a simple constitution by constituting the objective lens constituted of one convex, lens so that light is reflected inside the first surface and the second surface of a lens. CONSTITUTION:The objective lens 10 constituted of one nearly, convex lens is provided with lens surfaces whose curvature are different on the central parts 11a and 12a of the first surface 11 and the second surface 12. Total reflection coating is performed on the outside part 11b of the first surface 11 and the inside of the central part 12a of the second surface 12, and reflection preventing coating is performed on the central part 11a of the first surface 11 and the ring-like outside part 12b of the second surface 12. Thus, the light is bent by bent surfaces 11a, and 12b and reflecting surfaces 12a and 12b. Consequently, the light is bent by four bent surfaces, so that entire bending force of the objective lens 10 is comparatively strong. Therefore, an optical path length can be comparatively short even in a condition where a specified operating distance is secured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an objective lens having a shortened optical path length, and more particularly to an objective lens used in an optical pickup for an optical disc.

[0002]

2. Description of the Related Art Conventionally, an optical pickup for an optical disk is constructed as shown in FIG. That is, in the figure, an optical pickup 1 includes a laser light source 2 such as a semiconductor laser element, and a reflecting surface 3 such as a prism or a mirror for reflecting laser light emitted from the laser light source 2 in the lateral direction in the figure downward. , And an objective lens 4 arranged below the reflecting surface 3.

The optical pickup 1 constructed in this way
In the above, the light emitted from the laser light source 2 travels in the lateral direction, is reflected downward by the reflecting surface 3, and then passes through the objective lens 4, where it is refracted by the action of the objective lens 4. As a result, an image is formed on the surface of the optical disc 5.

[0004]

However, in the optical pickup 1 having such a structure, the objective lens 4 is generally a single lens / aspherical lens as shown in FIG. Therefore, the laser light from the laser light source 2 is imaged on the surface of the optical disc by refracting the light only by the two aspherical surfaces. For this reason, since the refractive power of the two aspherical surfaces is limited, in order to secure a constant working distance, the optical path lengths from the laser light source 2 to the surface of the optical disk 5 via the objective lens 4 are compared. It will be long. Therefore, as shown in FIG. 5, by disposing the reflecting surface 3 in the middle and bending the optical axis,
The overall height is kept low. This allows
The overall height of the optical pickup 1 is lowered, and the size of the optical pickup 1 can be reduced.

By the way, in this structure, the reflecting surface 3 is provided as a means for bending the optical axis in order to reduce the size. For this reflecting surface 3, for example, a mirror, a prism or the like is used. Therefore, as the number of parts increases, the reflecting surface 3 needs to be accurately positioned with respect to the optical axis in the optical path from the laser light source 2 to the objective lens 4. For this reason, there is a problem that the assembly is troublesome and takes a long time, resulting in high cost.

In view of the above points, the present invention has an object to provide an objective lens having a simple structure and capable of manufacturing a small pickup or the like which can be easily assembled.

[0007]

According to the present invention, the above object is to provide an objective lens composed of a single convex lens that reflects light on the inner surface of the first surface and the inner surface of the second surface of the lens. This is achieved by an objective lens configured to

[0008] Preferably, the inner surface of the first surface is formed as a total reflection surface in a ring shape excluding the vicinity of the center.

Preferably, the inner surface of the second surface is formed as a total reflection surface or a semi-transmission surface near the center.

[0010]

According to the above structure, the light incident from the first surface is
After reflecting on the inner surface of the second surface, incident on the inner surface of the first surface,
After being reflected on the inner surface of this first surface, through the second surface,
Since the light is emitted to the outside, it is refracted by a total of four surfaces including the first surface and the second surface and the inner surface thereof. Therefore,
Even if a certain working distance is secured, the optical path length can be relatively short.

Further, when the inner surface of the first surface is formed as a total reflection surface in a ring shape excluding the vicinity of the center, the reflection efficiency when light is reflected on the inner surface of the first surface. Will be increased.

Further, when the inner surface of the second surface is formed as a total reflection surface or a semi-transmissive surface in the vicinity of the center, the reflection efficiency when light is reflected by the inner surface of the second surface is In addition to being increased, in the case of a semi-transmissive surface, the transmittance of the second surface is also improved.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will now be described in detail with reference to FIGS. The examples described below are preferred 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 a first embodiment of the objective lens according to the present invention. In the figure, the objective lens 10 is
It is composed of one roughly convex lens. The first surface 11 and the second surface 12 of the objective lens 10 are provided with lens surfaces having different curvatures in the central portions 11a and 12a, respectively.

Here, the central portions 11a and 12a of the first and second surfaces respectively have radii of curvature R1 and R2, and the ring-shaped outer portions 11b of the first and second surfaces. , 12b have radii of curvature R3, R4, respectively.

Further, the outer portion 11b of the first surface and the central portion 12a of the second surface are provided with a total reflection coating on the inner surface. The central portion 11a of the first surface and the ring-shaped outer portion 12b of the second surface are coated with antireflection coating.

The objective lens 10 according to the present embodiment is configured as described above, and in the drawing, the light incident from the left side is emitted from the central portion 11a of the first surface 11 of the objective lens 10 to the objective. The light enters the lens 10, is totally reflected by the inner surface of the central portion 12a of the second surface 12, and then is totally reflected by the inner surface of the ring-shaped outer portion 11b of the first surface 11, and finally, of the second surface 12. The light is transmitted through the ring-shaped outer portion 12b and emitted to the right.

As a result, the light is converted into two curved surfaces 11a,
12b, and two reflecting surfaces 12a and 11b,
Be bent. Therefore, since it is bent by a total of four bending surfaces, the bending force of the entire objective lens 10 is
Becomes relatively strong. Thus, the optical path length can be relatively short even when a certain working distance is secured.

When the objective lens 10 having such a structure is incorporated in an optical pickup, as shown in FIG.
Between the laser light source 13 and the objective lens 10, a mirror,
It is not necessary to dispose a reflecting surface such as a prism, and the laser light source 13 can be arranged directly above the objective lens 10. Therefore, the distance from the laser light source 13 to the surface of the optical disc 14 via the objective lens 10 is short, and the entire size can be reduced.

In the above objective lens 10, the central portion 11a and the outer portion 11b of the first surface 11 and the central portion 12a and the outer portion 12b of the second surface 12 are all aspherical. You can As a result, the degree of freedom in designing the lens is increased, and a good aberration curve can be obtained.

Further, the central portion 11a of the first surface 11 and the central portion 12a of the second surface are formed of the same aspherical surface, and the outer portion 11b of the first surface 11 and the central portion 12b of the second surface 12 are formed. If they are formed with the same aspherical surface, the lens surface can be easily processed.

Further, the ring-shaped outer portion 1 of the first surface 11
The inner surface of 1b and the central portion 12a of the second surface 12 may be formed as a semi-transmissive surface instead of the total reflection coating.

FIG. 3 shows a second embodiment of the objective lens according to the present invention. That is, in FIG. 3, the objective lens 20 includes a central portion 21 a and an outer portion 2 of the first surface 21.
1b and 1b have a common radius of curvature, that is, R1 = R3 in the first embodiment.

FIG. 4 shows a third embodiment of the objective lens according to the present invention. That is, in FIG. 4, the objective lens 30 includes the central portion 32a of the second surface 32 and the outer portion 3a.
2b and 2b have a common radius of curvature, that is, R2 = R4 in the first embodiment. Incidentally, in this embodiment, since the emitted light is relatively largely chipped by the central portion 32a of the second surface 32 and the loss is increased, the inner surface of the central portion 32a of the second surface is not covered by the total reflection coating. Instead, a semi-permeable coating (50 percent permeable membrane) is applied.

According to these embodiments, the light incident from the first surface of the lens is reflected by the inner surface of the second surface and the inner surface of the first surface, and then passes through the second surface to the outside. Because it emits
With a total of four surfaces, the first surface, the second surface, and the inner surface,
Since it is refracted, the total refracting power becomes relatively strong. Therefore, even if a certain working distance is secured, the optical path length becomes relatively short. Thus, for example, when incorporated in an optical pickup, even if the reflecting surface is not provided between the light source such as a laser light source and the objective lens and the light source is arranged directly above the objective lens, the overall height is relatively high. Get lower. Thus, the entire optical pickup can be made compact. At that time, since the reflecting surface is not necessary, the number of parts can be reduced, and the parts cost and the assembly cost can be reduced.

[0026]

As described above, according to the present invention,
It is possible to provide an objective lens having a simple structure and capable of manufacturing a small pickup or the like that can be easily assembled.

[Brief description of drawings]

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

FIG. 2 is a schematic view showing a configuration example of an optical disc pickup incorporating an objective lens according to the present invention.

FIG. 3 is a sectional view showing a second embodiment of the objective lens according to the present invention.

FIG. 4 is a sectional view showing a third embodiment of the objective lens according to the present invention.

FIG. 5 is a schematic diagram showing a configuration of a conventional optical pickup.

6 is a side view showing an example of an objective lens used in the optical pickup of FIG.

[Explanation of symbols]

 10 Objective Lens 11 First Surface 11a Central Part 11b Outer Part 12 Second Surface 12a Central Part 12b Outer Part 13 Laser Light Source 14 Optical Disc 20 Objective Lens 21 First Surface 22 Second Surface 30 Objective Lens 31 First Surface 32 Second Surface

Claims (4)

[Claims] 1. An objective lens comprising a single convex lens, characterized in that light is reflected on the inner surface of the first surface and the inner surface of the second surface of the lens. 2. The objective lens according to claim 1, wherein the inner surface of the first surface is formed as a total reflection surface in a ring shape excluding the vicinity of the center. 3. The inner surface of the second surface is formed as a total reflection surface near the center.
Alternatively, the objective lens described in 2. 4. The inner surface of the second surface is formed as a semi-transmissive surface in the vicinity of the center.
Alternatively, the objective lens described in 2.