JPS5868249A - Optical information reader - Google Patents

Abstract

PURPOSE:To focus three light sports on a disk by arranging a light source, a collimator lens, a diffraction grating, and an objective in order. CONSTITUTION:Light emitted from a laser diode 1 is collimated by a collimator lens 4 and then diffracted in three directions by a diffraction grating 3. Those pieces of luminous flux are converged onto an optical disk 6 through an objective 5. Consequently, the number of relay lenses are decreased by two.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical information reading device, and more particularly to a device for condensing a light beam from a point light source into three minute spots on the information surface of an optical disk.

FIG. 1 is a schematic diagram showing an example of a conventional optical information reading device of this type, which is disclosed in Japanese Patent Laid-Open No. 56-61045. To explain this conventional example, 1 is a laser diode that generates a point light source.

2 and 2B are relay lenses, 3 is a diffraction grating, 4 is a collimator lens, 5 is an object lens, 6 is an optical disk, and 6a is its information surface.

In the figure, light generated from a point light source 11 such as a laser diode 1 is transmitted through a relay lens 2 with a diffraction grating 3 disposed between them.
A, 2B, and become three beams 7A, 7B, and 7C. These beams are turned into a parallel light beam by a collimator lens 4, and are converged onto an information surface 6 of an optical disk via an objective lens 5.

As described above, conventionally, in order to condense the light beam generated by the point light source 1a into three minute spots on the information surface 6a of the optical disk 6, the diffraction grating 5, the collimator lens 4.
In addition to the object lens 5, relay lenses 2A, 2
B is required, thus generally increasing the length of the optical system.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-described drawbacks of the prior art and to provide an optical information reading device that can reduce the length of the optical system.

In order to achieve the first objective, the present invention directly creates five beams by arranging a diffraction grating between a collimator lens and an object lens without using an optical disc lens. Three spots are formed on the information surface.

FIG. 2 is a schematic configuration diagram showing an embodiment of an optical information reading device according to the present invention, in which 1 is a point light source such as a laser diode, 3 is a diffraction grating, 4 is a collimator lens, 5 is an object lens, and 6 is a point light source such as a laser diode. This is the information side of the optical disc.

In the figure, light generated from a point light source 11 such as a laser diode 1 is turned into a parallel beam by a collimator lens 4, and this parallel beam is divided into six directions by a diffraction grating 3. These light beams pass through the object lens 5 and are converged onto the information surface 6 of the optical disc.

When the parallel light beam is divided into three directions by the diffraction grating 3,
The imaginary 11A and IB of the point light source 1 are formed on both sides of the point light source 1, and these are the two real images 7A for the point light source 1 formed by the combination of the relay lens and the diffraction grating shown in the conventional example.
, 7B, and functions to form three beams similarly to the conventional example.

Figure 3 shows the 2nd v! This is a diagram showing the state of the light flux at the aperture surface of the object lens 5 in the configuration J, where 9 is the aperture of the object lens 5, 8A, 8B, and 8C are the 11th-order light fluxes whose directions are separated by the diffraction grating 3, respectively. o
This is a light flux in three directions: a second-order light flux and a +1st-order light flux.

In the conventional example, the image on the three surfaces of the diffraction grating is transmitted through the relay lens 2B.
and the object lens 5 by the collimator lens 4
By configuring the optical system so that the image is formed on the zero entrance pupil, -1st order light flux 8A, 0th order light flux 8B, -1st order light flux 8C
However, in the configuration according to the present invention,
As shown in the figure, the six light beams 8A, 8B, and 8C are shifted, so
Depending on the position of the object lens 5, a problem can be expected that an imbalance in the amount of light will occur between the primary light beam 8A and the +1-dimensional light beam 8C that reach the information surface 6. However, this problem is caused by the aperture 9 of the object lens is eliminated by making it included in the common portion of the −1-dimensional light flux 8A and the +1-dimensional light flux 8C. Moreover, by reducing the distance between the diffraction grating 3 and the object lens 5 by 1rt and employing the diffraction grating 3 with a large grating interval, the degree of deviation of this light beam can be suppressed to a sufficiently small degree, so that it does not pose a problem in practice.

As explained above, the present invention eliminates the need for two relay lenses, thereby improving economic efficiency and downsizing the optical system.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an example of a conventional optical information reading device, FIG. 2 is a schematic diagram showing an example of an optical information reading device according to the present invention, and FIG. 6 is an aperture of the object lens in FIG. FIG. 2 is a schematic diagram showing a state of light flux on a surface. 1... Point light source, 3... Diffraction grating, 4...
・Collimator lens, 5...Object lens, 6...Information surface, 8A...-1st order light flux, 8B
...0th order luminous flux, 8C...+1st order luminous flux, ? ...
Object lens aperture 0

Claims (1)

[Claims] 1. A light beam 2 generated from a light source considered as a point light source is condensed as at least five minute spots on the information surface of an optical disc by optical means such as a lens and a diffraction grating. In an optical information reading device, a collimator lens converts the light beam from the light source into parallel light, a diffraction grating divides the parallel light beam into at least three directions, and a diffraction grating converts the light beam separated into three directions into information on an optical disk. An optical information reading device characterized in that object lenses condensing light onto a surface are sequentially arranged.