JPS63146238A - Optical head - Google Patents

Abstract

PURPOSE:To prevent an appearance of stray light without enlarging optical elements in shape by providing an aperture of a specific shape with an elliptical opening between a collimator lens and a beam shaping means. CONSTITUTION:The aperture 7 is provided having an approximately elliptical opening with its minor axis (p) and major axis (q) in the same direction with those minor and major axes of a parallel beam cross section under the condition of q/p b/a and p<c and is positioned between the collimator lens 2 from which a parallel beam having an approximately elliptical cross section with a minor axis (a) and major axis (b) is outgoing and the beam shaping means having an incident effective opening diameter on minor axis side (c) which magnifies the minor axis of said parallel beam by b/a approximately. Thus, even if a radiation angle on the side of parallel to the coupling direction of a semiconduc tor laser chip is larger than the standard, an incident beam into the optical elements is limited by the aperture so that genetic stray light can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical disc device such as an optical disc device.

Conventional Technology The modern era is called the information age, and the technology development of high-density, large-capacity memory, which forms the core of this age, is actively being carried out.

In addition to the above-mentioned high density and large capacity, the capabilities required of memory include high reliability and high speed access, and optical disk memory is attracting the most attention as a device that satisfies all of these requirements. An optical disk memory is a device that optically records information on a recording medium, and recently, a lot of research has been conducted on magneto-optical disks that can also erase recorded information.

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

In the past, numerous research publications have been made regarding technology related to optical heads, which are described in detail in literature related to optical disk memories.

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

FIG. 3 explains the 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, and 4 is a semiconductor laser.
6 is an objective lens, 6 is a disk that is an information recording medium, and 6 is a detection means, and the side parallel to the semiconductor laser chip bonding direction is illustrated.

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

Divergent light from the semiconductor laser 1 is converted into parallel light by the collimating lens 2. Generally, the light emitted by a semiconductor laser is diverging light, and the radiation angle is small on the side parallel to the semiconductor laser chip bonding direction and large on the side perpendicular to the semiconductor laser chip bonding direction. Therefore, the parallel light beam output from the collimating lens 2 has a substantially elliptical cross-sectional shape with its short axis in a plane parallel to the plane of the paper of FIG. 3 and its long axis in a plane perpendicular to the plane of the paper in FIG. The optical element 3 has two functions: beam shaping and beam separation.
By refracting the parallel light from the collimating lens 2, the diameter on the minor axis side is expanded and converted into a parallel light beam having a substantially circular cross-sectional shape. The output light from the optical element 3 is transmitted to the objective lens 4.
The light is then focused onto the disk 6, and information is recorded, reproduced, etc. The reflected light from the disk 6 follows the opposite path, is reflected and separated by the optical element 3, and the detection means 6 detects an information signal, a focus error signal, a tracking error signal, etc. on the disk 6. As described above, the conventional example shown in FIG. 3 can perform beam shaping with a relatively simple configuration, and is therefore currently widely used in optical heads for recording and reproduction.

Problems to be Solved by the Invention However, with the above configuration, when light hits points A and B, which are the edge portions of the optical element 3, scattering of light occurs there, and this scatters onto the inner wall surface of the optical head housing. This causes even more diffuse reflection and stray light. When this stray light enters the detection means 6, there is a problem in that the detection of focus and tracking error signals may be erroneous, and the quality of the reproduced information signal may deteriorate. Generally, the effective entrance aperture of the optical element 3 is determined by a standard radiation angle on the side parallel to the direction in which the semiconductor laser chips are bonded, and in this case, stray light is not generated. However, since there are considerable individual differences in the radiation angle of the semiconductor laser 1, if the radiation angle is larger than the standard, stray light as described above is likely to occur. In order to prevent this, there is a method of enlarging the shape of the optical element 3 and increasing the effective entrance aperture, but this has the drawback of increasing the size of the optical head.

The present invention has been made in view of the above-mentioned conventional problems, and it is an object of the present invention to prevent the generation of stray light without increasing the size of the optical element even when the radiation angle on the side parallel to the joining direction of semiconductor laser chips is larger than the standard. The purpose of this invention is to provide an optical head that can perform the following functions.

Means for Solving the Problems In order to achieve the above object, the optical head of the present invention includes a collimating lens, and a cross-sectional shape from the collimating lens in which the short axis is a short axis and the long axis is an approximately elliptical short axis of a parallel light beam. Approximately b/a side
, the short axis side effective entrance aperture which is expanded twice is located between the beam shaping means C, and the short axis p and the long axis are arranged so as to have the same direction as the short axis and long axis of the cross-sectional shape of the parallel beam. It has a substantially elliptical opening of q, and has an aperture of q/p/a p<c.

Effect of the Invention With the above-described configuration, the present invention prevents the generation of stray light because the light flux incident on the optical element is limited by the aperture even when the radiation angle on the side parallel to the semiconductor laser chip bonding direction is wider than standard. becomes possible.

Example Hereinafter, one embodiment of the present invention will be described based on the drawings.

FIG. 1 shows a schematic diagram of an optical head in an 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 detection means, and 7 is an aperture.

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

The basic operation is the same as that of the conventional example explained using FIG. When the semiconductor laser 1 has a standard radiation angle, the collimating lens 2 provides a parallel light beam having a substantially elliptical cross-sectional shape with the short axis a and the long axis s.

The optical element 3 refracts the diameter of the light beam on the short axis side, thereby enlarging it approximately b/a times and converting it into a parallel light beam having a substantially circular cross-sectional shape.

Here, when the radiation angle of the semiconductor laser 1 in the chip joining direction is larger than the standard, the cross-sectional shape of the parallel beam obtained by the collimating lens 2 increases on the short axis side and becomes larger than the effective entrance aperture C of the optical element 3. As described in the conventional example, stray light is generated at the edge portion of the optical element 3. The annotation 7 is intended to prevent this, and has a substantially elliptical opening with a short axis p and a long axis q, as shown in FIG. If axis A is arranged parallel to the plane of the paper in Figure 1, and the relationship between a, b, c and p, q is q/pb/a p<c, then the semiconductor Even if the radiation angle of the laser 1 in the chip bonding direction is larger than the standard, the output light flux of the collimating lens 2 is regulated by the aperture, so a light flux smaller than C enters the optical element 3, so no stray light occurs. . Further, by setting q/p''F b /a, it is possible to obtain a substantially circular parallel light beam with the optical element 3.

Note that in this example, the shape of the aperture is
Although the hole type is used as shown in the figure, any type may be used as long as it limits unnecessary light flux.

As described above, according to this embodiment, the collimating lens,
The short axis side of the parallel light beam from the collimating lens, which has a cross-sectional shape of approximately ellipse with a short axis a and a long axis D, is magnified by approximately b/a times.
An annular aperture having a substantially elliptical aperture with a short axis p and a long axis q arranged in the same direction is provided between optical elements having an effective incident aperture on the short axis side C, and q / p aperture b. / a ea , even if the radiation angle of the semiconductor laser on the side parallel to the chip bonding direction is larger than standard, it is possible to prevent the generation of stray light without using a large diameter optical element.

Effects of the Invention The present invention provides an optical head including a collimating lens and a cross-sectional shape from the collimating lens having a short axis d.

A beam shaping means having an effective entrance aperture on the short axis side that magnifies the short axis side of the approximately ellipsoidal parallel light beam by a factor of about /a is connected between the long axis p and the long axis q. By providing an aperture with an elliptical opening and making q/p/a p<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 large diameter beam shaping means can be used. It is possible to prevent the occurrence of stray light, detect high-precision focusing and tracking error signals, and
This makes it possible to realize an excellent optical head that can detect information signals with a good N ratio.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of an optical head according to an embodiment of the present invention, Fig. 2 is a schematic diagram of its main parts, and Fig. 3 is a schematic diagram of a conventional optical head. Laser, 2...Collimating lens, 3...Optical element, 4...Objective lens, 6...Disk, 6...Detection means , 7...Aperture.

Claims (1)

[Scope of Claims] A semiconductor laser, a collimating lens that converts the diverging light of the semiconductor laser into a parallel beam, and a cross-sectional shape formed by the collimating lens having a substantially elliptical shape with a short axis a and a long axis b. a beam shaping means having an effective entrance aperture on the short axis side of c for enlarging the short axis side of a certain parallel light beam by about b/a times and converting the cross-sectional shape into a substantially circular shape; and information recording of the output light of the beam shaping means. an objective lens for condensing light onto a medium, and a detection means for detecting a focus error signal, a tracking error signal, an information signal, etc. using reflected light from the information recording medium;
a substantially elliptical aperture with a short axis p and a long axis q, located between the collimating lens and the beam shaping means, and arranged so as to have the same direction as the short axis and long axis of the cross-sectional shape of the parallel beam. An optical head comprising an aperture having the following relationship: q/p≒b/a p<c.