JPS59187309A - Light converging device - Google Patents

Abstract

PURPOSE:To reduce the cost of a light converging device by forming a spherical reflecting mirror, beam splitter, and parallel plane glass without using any spherical lens, and reducing polished surfaces. CONSTITUTION:Projected light from a spot light source 12 placed in the center of curvature of the spherical mirror 13 is incident to a mirror 13 which crosses the contact plane of the mirror 13 at right angles, so the light returns through the original optical path accurately and reflected light is converged without any aberration, but converged light enters the original light source again. For this purpose, the beam splitter 14 with a reflecting spherical surface 15 is placed and the spot light source 12 is set in the center of curvature of the reflecting spherical surface 15, obtaining a nonaberration light spot 6 on the end surface of the beam splitter 14. When, however, the light spot is formed in the air, the converged light has aberrations because of the difference in refractive index between the beam splitter 14 and air, so a parallel plane plate 11 having a larger refractive index than the beam splitter 14 is arranged to compensate the aberrations, and then the aberrations of the convergence system are reduced by selecting the thickness of the parallel plane plate 11 properly.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a condensing device that condenses light to the order of microns.

As a conventional device of this type, the one shown in FIG. 1 is well known. In the figure, a light source 1 having a point-like emission center such as a semiconductor laser is provided, an emitted light 2 is emitted from the light source 1, and objective lens groups 3 for condensing the emitted light 2 are provided roughly. It is composed of constituent lenses 4a, 4b, 4c and a lens barrel 5. The light is focused by the lens group 3 to form a light spot 6.

Next, the functions of the apparatus shown in FIG. 1 will be explained.

Such devices are often used in optical information recording and reproducing devices such as video discs and audio discs. On the other hand, in such applied equipment, the light spot is
It is necessary to condense the light to about μll1). Therefore, the objective lens group 3 needs to reduce aberrations to the extent that it can focus a light spot close to the diffraction limit, and for this purpose it is composed of a plurality of lenses.

The light emitted from the light source 1 is incident on the objective lens group 3, and the constituent lenses 4a and 4b of this objective lens group.

The light is focused on a light spot 6 by 4C. In addition, at that time,
Each component objective lens is designed so that when the aberrations generated in the constituent lenses 4a, 4b, and 4C are viewed in the entire objective lens group, the aberrations cancel each other out and become smaller.

Conventional devices require multiple spherical lenses to reduce the aberrations of the objective lens as described above, which results in a large number of polished surfaces, which has the disadvantage of making the objective lens very expensive. there were.

The present invention is intended to improve the above-mentioned drawbacks of the conventional device, and instead of using a spherical lens, a condensing system is formed by a spherical reflecting mirror, a beam splitter, and a parallel plate glass.
The purpose is to reduce the cost of the condensing device by reducing the number of polished surfaces.

An embodiment of the present invention will be described below as a second example. In FIG. It is placed on the end face and is 0.

A spherical mirror 9 is provided, placed so that its center of curvature coincides with the light emitted from the light source 1, and is shaped to be a curved mirror of a plano-convex lens having the same refractive index as the beam splitter. A reflective surface 10 is formed on the spherical mirror 9,
It functions to reflect the emitted light 2 toward the light source 1 side. A parallel plate 11 having a larger refractive index than the beam splitter 7 is placed on the side surface of the beam splitter.

The light emitted from the light source 1 is reflected by the mirror surface 10, and the reflected light becomes convergent light directed toward the light source 1.

In this case, as shown in FIG. 3, the light emitted from the point light source 12 placed at the center of curvature of the spherical mirror 13 is
Since it is incident on the mirror 13 perpendicularly to the tangent plane of
Return exactly to the original optical path again. Therefore, the reflected light can be focused without any aberration. However, in the configuration shown in FIG. 3, the convergent light re-enters the original light source and cannot be used. Therefore, as shown in Figure 4, the reflecting spherical surface 1
If a beam splitter 14 having a diameter of 5 is placed and the center of curvature of this reflecting spherical surface 15 is set as a point light source 12, an aberration-free light spot 6 can be obtained on the end face of the beam splitter 14. However, although this may be acceptable depending on the application, there are many applications in which a light spot is extracted into the atmosphere.

Therefore, the preparation for extracting the light spot into the atmosphere constitutes a beam splitter as shown in FIG.

However, in this case, aberrations occur in the convergent light due to the difference in refractive index between the beam splitter 14 and the atmosphere. Therefore, in order to correct this aberration, a beam splitter 14 is used as shown in FIG.
A parallel plate 11 having a larger refractive index than the above is arranged. The principle of this aberration correction will be explained below. When convergent light enters a medium with a smaller refractive index than the current medium, negative longitudinal aberration occurs as shown in FIG. 7(a). On the other hand, if convergent light is incident on a medium with a larger refractive index than the current medium, positive longitudinal aberration will occur. Furthermore, as the thickness of the incident medium increases, aberrations also increase. Therefore, by appropriately selecting the thickness of the parallel plate 11 shown in FIG. 6, the aberrations of the focusing system can be reduced.

FIG. 7(b) shows a design example of the present invention, and it can be seen that aberrations are greatly improved compared to the case without the parallel plate 11 in FIG. 7(a). In addition, when calculating, cl, =
1+nw+.

d2=8.3mm, rl, -1,5, Ilz□=1. s
.

N, Δ, = n sin θ−〇, a value of 45 was assumed.

In the embodiment shown in FIG. 2, the beam splinter 7 and the spherical mirror 9 are separated, but they may be integrated as shown in FIG.

Further, as shown in FIG. 8, a polarizing beam splitter 17 is used as a beam splitter, and the beam splitter 1
A configuration may also be adopted in which a quarter wavelength phase plate 18 is sandwiched between the spherical mirror 7 and the spherical mirror 9.

Furthermore, as shown in FIG. 9, the end surface of the beam splitter 19 on the light source side may be made into a spherical surface, and the centers of curvature of the spherical surface 20 and the reflecting surface 10 may be made to coincide with each other, and the light source 1 may be placed at the center of the curvature. In this case, the light source can be separated from the end face of the beam splitter.

FIG. 10 shows an example of application of the light condensing device of the present invention to an optical information recording/reproducing device. In the figure, a video disk 29 is provided to rotate in a known manner outside the parallel W plate 11 on the side surface of the beam splitter, and a positional relationship is selected such that its information recording surface 31 coincides with the light spot 6. . This disc 29 may be a digital audio disc or other optical information record carrier. A collimating lens 40 is provided on the opposite side from which the light reflected by the information recording surface 31 passes through the beam splitter 7, so that the reflected light is made parallel. A prism 41 is provided next to the collimating lens 40, and the reflected light passing through it is reflected in areas I, II, I[[.

Enter the photodetector 42 with ■. Area 1 of photodetector 42.
Il, II[,■ means reading information from the information carrier,
The positions are chosen to obtain signals for actuators such as autofocusing, autotracking, etc.

As a result, the recorded information on the information recording surface 31 of the disc 29 is detected by the photodetector 42.

As described above, in the present invention, since the condensing optical system is configured by a combination of a spherical mirror, a beam splitter, and a parallel plate, a condensing device with fewer spherical surfaces that require polishing and less aberration can be obtained at low cost. effective.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a conventional light condensing device. Figure 2 shows
FIG. 1 is a diagram showing a light condensing device according to an embodiment of the present invention. Third
6 through 6 are diagrams for explaining the function and operating principle of the present invention. FIG. 7 is a diagram showing the improvement effect of the invention. FIGS. 8 and 9 are diagrams showing other embodiments of the present invention. FIG. 10 is a diagram showing an example of application of the present invention. In the figure, 1 is a light source, 7 is a beam splinter, 9 is a spherical mirror, and 11 is a parallel plate. Note that the same reference numerals in the figures indicate the same or corresponding parts. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 (a) (b) Figure 8 Figure 9 Figure 10 I Diagram procedure corrector (spontaneous) Mr. Commissioner of the Japan Patent Office 1. Indication of the case: Japanese Patent Application No. 58-62473 2. Name of the invention: Light condensing device 3. To the representative of the person making the amendment: Hitoshi Katayama Part 5: Subject of the amendment Claims column of the specification and Figure 10 6 of the drawings, Contents of amendment (1) The claims are corrected as shown in the attached sheet. (2) Figure 10 of the drawings will be corrected as shown in the attached sheet. Above 2, Claim (1) A light source, a spherical mirror placed such that the center of curvature thereof is located at the light source position, and 11. An output side optical interconnection arrangement of the light source placed between the spherical mirror and the light source. A beam splitter that separates reflected light into convergent light that is reflected by a spherical mirror and enters a 1L light source, and a parallel plate that corrects aberrations that cause the convergent light that has been separated by the beam splitter to be incident. A light condensing device featuring: (2) The condensing device according to claim 1, wherein the beam splitter and the spherical mirror are integrated. (3) A polarizing beam splitter is used as the beam splitter, and a quarter wavelength phase plate is interposed between the polarizing beam splitter and the spherical mirror. Device. (4) The light condensing device according to claim 1, wherein the light source side end face of the beam splitter is a spherical surface having a center of curvature at the light source position. 5) The condensing device according to claim 1, further comprising a plurality of parallel flat plates in addition to the parallel flat plate into which the convergent light separated by the beam splitter is incident. 1C-) 1ヲ9 ′I+ ＼30

Claims (5)

[Claims] (1) A light source, a spherical mirror placed so that its center of curvature is at the light source position, and a spherical mirror placed between the spherical mirror and the light source to reflect and converge the light emitted from the light source and the spherical mirror. A condensing device comprising: a beam splitter that separates reflected light that has become light; and a parallel plate that corrects aberrations that allow the convergent light separated by the beam splitter to enter. (2) The condensing device according to claim 1, wherein the beam splitter and the spherical mirror are integrated. (3) A polarizing beam splitter is used as the beam splitter, and a quarter wavelength phase plate is interposed between the polarizing beam splitter and the spherical mirror. Device. (4) The light condensing device according to claim 1, wherein the light source side end face of the beam splitter is a spherical surface having a center of curvature at the light source position. (5) The condensing device according to claim 1, further comprising a plurality of parallel flat plates in addition to the parallel flat plate into which the convergent light separated by the beam splitter is incident.