JPH03268242A - Formation of beam spot of optical pickup - Google Patents

Abstract

PURPOSE:To reduce the converging spot diameter of a light beam and to simultaneously decrease the loss of a light quantity by expanding the diameter of the light beam simultaneously with alternation of the inner peripheral side and outer peripheral side of the light beam on the side where the diameter of the light beam is narrow. CONSTITUTION:The light beam 10 emitted from a semiconductor laser 1 is collimated to collimated light beams by a collimator lens 2. Of the collimated light beams, the light beam 12 on the narrower side is inverted in the inner and outer peripheral parts by a hexagonal cylindrical prism 7. The disk 5 is irradiated with a beam spot P thereupon after the beam passes an objective lens 4. The beam width on the narrow side is controlled if the size in the optical axis direction of this prism 7 is properly selected. Namely, the spot diameter of the light beam is reduced in the state in which there is substantially no loss of the light quantity.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a beam spot creation method for an optical pickup used for recording and reproducing optical discs.

(Prior Art) An example of the outward path portion of an optical system of an optical pickup conventionally used for recording and reproducing optical discs is shown in FIG. 2 (al).

In the figure, a light beam 10 emitted from a semiconductor laser 1
becomes a parallel light beam by the collimating lens 2.

In general, in the semiconductor laser 1, the radiation angle of the light beam is different between the direction parallel to the joint and the direction perpendicular to the joint, so the beam bond that irradiates the plane perpendicular to the traveling direction of this light beam is shown in Figure 2 ( It becomes an ellipse as shown in bl.In the figure, the light beam on the side corresponding to the major axis of the ellipse is 11, and the light beam on the side corresponding to the minor axis is 12.The width of the light beam on the minor axis side is In order to make the beam width the same as the longer diameter side,
A beam shaping prism 3 is used to shape the light beam into a substantially circular cross section as shown in FIG.

Normally, spots for recording and playback are obtained by the above method, but
In this example, measures are taken to further reduce the beam spot. That is, a light shielding band 6 is inserted into the light beam, and as shown in FIG.
As shown in d), the principle that the beam diameter can be reduced by blocking the inner part of the beam is used. (For example, A.

Written by PAPOVLTS, “SYSTEMS
AND TRANSFORMS WITHAPPL
ICATIONS IN 0PTICS'', p337
, 1968. McGRAW-HTLL BOOK C
(OMPANY) By this method, the beam spot can be made about 20% smaller.

[Problem to be solved by the invention]

However, in this conventional example, the optical axis does not become a straight line because beam shaping is required, and the light-shielding band blocks the central part where the beam intensity is strong, resulting in a loss of light quantity.

[Means to solve the problem]

The present invention eliminates this drawback by exchanging the narrow inner and outer circumferential portions of the parallel laser beam using a prism, simultaneously expanding the beam diameter, and then converging the beam using an objective lens.

[Effect]

The inner and outer parts of the light beam on the narrower side of the light beam are replaced by a hexagonal prism, and at the same time the light beam diameter is expanded, so that the light beam appears to converge in the same way as when using the light shielding plate described above. The spot diameter can be made smaller. Furthermore, since no light shielding plate is used, loss in the amount of light can be reduced.

〔Example〕

FIG. 1(a) shows a schematic configuration diagram of an embodiment of the present invention.

In the figure, a light beam 10 emitted from a semiconductor laser 1
is made into parallel light by the collimating lens 2, and the narrower light beam 12 of the parallel light is inverted by the hexagonal prism 7 to invert the inner and outer peripheral portions of the light beam. And objective lens 4
After passing through the disk 5, a beam sub-I-P is irradiated onto the disk 5. By appropriately selecting the dimensions of this hexagonal prism 7 in the optical axis direction, the beam width on the narrow side can be controlled.

That is, if the optical path length passing through the hexagonal prism 7 is lengthened, the beam width will be widened, and if it is shortened, the beam width will be narrowed. Therefore, the elliptical beam spot shown in Figure 1 (bl) is
The beam spot shape can be changed to that shown in FIG. 1, and the beam spot shape can be changed to the same as that when blocked by the light shielding band 6, with almost no loss of light quantity, and the spot diameter of the light beam can be reduced.

〔Effect of the invention〕

As described above, according to the present invention, a minute spot for an optical pickup can be easily obtained with a slight loss of light quantity.

[Brief explanation of drawings]

Figure 1 (al is a schematic configuration diagram showing one embodiment of the present invention, Figure 1 (b) and (C) are cross-sectional views showing the beam spot shape in the optical path, and Figure 2 (a) is a conventional example. Schematic configuration diagram, FIGS. 2(b), (C), and (d) are cross-sectional views showing the beam spot shape in the optical path. 1... Semiconductor laser 2.4... Collimating lens 7... Hexagonal prism prism

Claims (1)

[Claims] In an optical pickup, a light beam emitted from a semiconductor laser is made into a parallel beam by a collimating lens, and converged into a beam spot by an objective lens.In an optical pickup, a parallel beam with a narrow beam intensity distribution in a cross section perpendicular to the direction of travel of the parallel beam is converted into a parallel beam by a prism. 1. A method for creating a beam spot for an optical pickup, characterized in that the inner circumferential part and the outer circumferential part are exchanged using the same method, the beam diameter is expanded, and the beam spot is then converged by an objective lens.