JPH0727660B2 - Optical head - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head such as an optical disk device.

Conventional Technology It is said that the present age is the information age, and the technological development of high-density and large-capacity memory, which is the core of it, is being actively conducted.
In addition to the above-mentioned high density and large capacity, the ability required for the memory includes high reliability, high speed access, etc., and the optical disk memory is the focus of attention as a means to add all of them. The optical disk memory is for optically recording information on a recording medium, and recently, many studies have been conducted on a magneto-optical disk capable of erasing recorded information.

The present invention relates to an optical head in an optical disc memory as described above.

Conventionally, many research presentations and the like have been carried out as a technique relating to an optical head, which is described in detail in a literature relating to an optical disk memory.

Hereinafter, the conventional optical head as described above will be described with reference to the drawings.

FIG. 3 illustrates a schematic structure of a conventional optical head and its operating principle. In FIG. 3, 1 is a semiconductor laser, 2 is a collimating lens, 3 is an optical element, 4
Is an objective lens, 5 is a disk which is an information recording medium, and 6 is a detecting means, which is shown on the side parallel to the semiconductor laser chip bonding direction.

The operation of the conventional example configured as described above will be described below.

The divergent light from the semiconductor laser 1 is converted into parallel light by the collimator lens 2. Generally, the light emitted from a semiconductor laser is divergent light, and the emission angle is small on the parallel side in the semiconductor laser chip bonding direction and large on the vertical side. Therefore, the collimated light beam output from the collimator lens 2 has a substantially elliptical cross-section with a short axis in the plane parallel to the paper surface of FIG. 3 and a long axis in the plane perpendicular to the paper surface. The optical element 3 has two functions of beam shaping and beam separation,
By refracting the parallel light from the collimator lens 2, the diameter on the minor axis side is enlarged and converted into a parallel light flux having a substantially circular cross section. The output light from the optical element 3 is the objective lens 4
Thus, the light is focused on the disk 5 to record and reproduce information. The reflected light from the disk 5 follows an opposite path, is reflected and separated by the optical element 3, and the detection means 6 detects the information signal, the focus error signal, the tracking error signal, etc. on the disk 5. As described above, since the conventional example shown in FIG. 3 can perform beam shaping with a relatively simple structure, it is now widely used in recording / reproducing optical heads.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention However, in the above-mentioned configuration, when light hits the points A and B, which are the edge portions of the optical element 3, the light is scattered there, which is the inner wall surface of the optical head housing. Stray light is generated due to diffuse reflection. When the stray light is incident on the detecting means 6, there is a problem that the focus and tracking error signals are erroneously detected or the quality of the reproduction information signal is deteriorated. Generally, the effective incident aperture of the optical element 3 is determined by a standard radiation angle or the like on the side parallel to the semiconductor laser chip bonding direction, in which case stray light is not generated. However, since the emission angle of the semiconductor laser 1 has a considerable individual difference, when the emission angle is larger than the standard, the above-mentioned stray light is likely to occur. In order to prevent this, there is a means of enlarging the shape of the optical element 3 and enlarging the effective entrance aperture, but this has a drawback that the size of the optical head is increased.

The present invention has been made in view of the above conventional problems, and prevents the generation of stray light without enlarging the shape of the optical element even when the radiation angle on the parallel side of the semiconductor laser chip bonding direction is larger than the standard. It is an object of the present invention to provide an optical head that can be manufactured.

Means for Solving the Problems In order to achieve the above object, the optical head of the present invention comprises a collimator lens and a short axis of an elliptical parallel light flux whose cross-sectional shape from the collimator lens is a short axis a and a long axis b. The short-axis side which expands the side by about b / a times is located between the beam shaping means with an effective entrance aperture of c, and is arranged so as to have the same direction as the short axis and the long axis of the parallel light beam cross-sectional shape. It has a substantially elliptical opening with the axis p and the major axis q, and has an aperture with q / p≈b / ap <c.

With the above-described configuration, the present invention can prevent the generation of stray light because the light flux entering the optical element is limited by the aperture even when the radiation angle on the parallel side to the semiconductor laser chip bonding direction is larger than the standard. Become.

Example Hereinafter, an example of the present invention will be described with reference to the drawings.
FIG. 1 shows a schematic view of an optical head in one embodiment of the present invention. In FIG. 1, 1 is a semiconductor laser, 2 is a collimating lens, 3 is an optical element, 4 is an objective lens, 5 is a disk, 6 is a detecting means, and 7 is an aperture.

The operation of the embodiment of the optical head configured as described above will be described below.

The basic operation is the same as in the case of the conventional example described with reference to FIG. When the semiconductor laser 1 has a standard emission angle, the collimator lens 2 produces a substantially elliptical parallel light flux whose cross-sectional shape is the minor axis a and the major axis b.

The optical element 3 expands by about b / a times by refracting the above-mentioned light flux diameter on the short axis side, and converts it into a parallel light flux having a substantially circular cross section.

Here, when the radiation angle in the chip joining direction of the semiconductor laser 1 is larger than the standard, the parallel light flux cross-sectional shape obtained by the collimating lens 2 increases on the minor axis side and becomes larger than the incident effective aperture c of the optical element 3. As described above, the stray light is generated at the edge portion of the optical element 3 as described in the conventional example. The aperture 7 is for preventing this, and its shape has a substantially elliptical opening with a short axis p and a long axis q as shown in FIG. If the axis A is arranged so as to be parallel to the paper surface of FIG. 1 and the relationship between a, b, c and p, q is q / p≈b / a p <c, then the semiconductor is as described above. Even if the emission angle of the laser 1 in the chip joining direction is larger than the standard, the output light flux of the collimator lens 2 is regulated by the aperture 7, so a light flux smaller than c is incident on the optical element 3, so that no stray light is generated. . Further, by setting q / p≈b / a, it is possible to obtain a substantially circular parallel light flux by the optical element 3.

In the present embodiment, the shape of the aperture 7 is set to the second shape.
As shown in the figure, the perforated type is used, but any type may be used as long as it limits unnecessary light flux.

As described above, according to this embodiment, the collimating lens,
Between the optical elements with a short-axis side incident effective aperture of c that magnifies the short-axis side of the substantially elliptical parallel light flux whose cross-sectional shape is the short axis a and the long axis b from the collimator lens by about b / a times. , An aperture having a substantially elliptical opening with a short axis p and a long axis q arranged in the same direction is provided, and q / p≈b / a p <c is set, so that the semiconductor laser chip bonding direction is parallel. Even if the side emission angle is larger than the standard, it is possible to prevent generation of stray light without using a large-diameter optical element.

EFFECTS OF THE INVENTION The present invention, as an optical head, enlarges the collimating lens and the minor axis side of a substantially elliptical parallel light flux having a cross-sectional shape of the minor axis a and the major axis b from the collimating lens to about b / a times. The short axis p, the long axis q, and the beam shaping means having an incident effective aperture of the short axis side c
Even if the radiation angle on the side parallel to the chip bonding direction of the semiconductor laser is larger than the standard, a beam with a large diameter can be obtained by providing an aperture with a substantially elliptical aperture of q / p≈b / ap <c Stray light is prevented from occurring without using shaping means, and highly accurate focus and tracking error signal detection and SN
It is possible to realize an excellent optical head that can obtain the effect of being able to detect information signals with a good ratio.

[Brief description of drawings]

FIG. 1 is a schematic view of an optical head according to an embodiment of the present invention, FIG. 2 is a schematic view of a main part thereof, and FIG. 3 is a schematic view of a conventional optical head. 1 ... Semiconductor laser, 2 ... Collimating lens, 3 ...
Optical element, 4 ... Objective lens, 5 ... Disc, 6 ...
Detection means, 7 ... Aperture.

Claims (1)

[Claims] 1. A semiconductor laser, a collimator lens for converting divergent light of the semiconductor laser into a parallel light flux, and a cross-sectional shape formed by the collimator lens are substantially elliptical with a short axis a and a long axis b. A beam shaping means having an incident effective aperture of c on the short axis side for enlarging a parallel light beam on the minor axis side by about b / a times to convert the cross-sectional shape into a substantially circular shape, and output light from the beam shaping means on an information recording medium. An objective lens for focusing light on the above, a detection means for detecting a focus error signal, a tracking error signal, an information signal, etc. by the reflected light from the information recording medium, and a position between the collimator lens and the beam shaping means. Then, it is constituted by an aperture having substantially elliptical openings of the short axis p and the long axis q, which are arranged so as to have the same directions as the short axis and the long axis of the parallel light beam cross-sectional shape, and q / p≈b / a characterized by p <c Optical head to do.