JPH0722219B2 - Semiconductor laser light source - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser light source which is suitable for use as a light source for an optical disk device or a laser printer device and has astigmatism corrected.

[0002]

2. Description of the Related Art Recently, semiconductor lasers have undergone significant improvements such as stabilization of transverse modes, long life, and visualization, and are applied not only to optical communication fields but also to optical disk devices and laser printers that require precision optical systems. Application to devices is also being actively considered. A semiconductor laser has the outstanding features of being compact, highly efficient, high-speed, and capable of direct modulation, but due to the structure of its resonator, the beam waist position is generally a light beam that is perpendicular to and parallel to the joint surface. Misaligned in the axial direction. That is, since there is an astigmatic difference, there is a problem in that the wavefront, that is, the equiphase surface, is distorted as compared with an aplanatic wavefront created by an ideal point light source. When the semiconductor laser has an astigmatic difference, the beam waist position in the direction perpendicular to the joining surface is in the direction parallel to the end face side of the resonator behind the end face.

FIG. 1 is a diagram showing an example of the image formation relationship of a light source having such an astigmatic difference. In the figure, 1 is standard 3
A light source that emits a light beam along the axis Oz of the face piece Oxyz,
X is the beam waist position in the axis Ox direction parallel to the joint surface,
Y represents the beam waist position in the direction of the vertical axis Oy, and the distance XY is the astigmatic difference. A broken line 1 indicates a light ray in the axis Ox direction, and a solid line m indicates a light ray in the axis Oy direction. X ′ and Y ′ are X and Y image positions by the image forming optical system 2.

A light ray from a light source having an astigmatic difference as shown in FIG. 1 converges between a light ray 1 included in a horizontal plane xOz and a light ray m included in a plane yOz perpendicular to the horizontal plane xOz so as to be displaced. Results in ΔS. This image position deviation ΔS is called astigmatism.

[0005] When such a aberration exists, when the semiconductor laser is used as a light source of a precision optical system such as an optical disk device or a laser printer device, the optical system other than the light source such as a lens and a mirror is aberration-free. However, a so-called diffraction-limited system cannot be obtained. Therefore, in order to sufficiently ensure the resolution of the optical system and improve the light utilization efficiency of the light source, it is necessary to correct the aberration of the semiconductor laser itself. Conventionally, there has been one that uses a cylindrical lens to correct astigmatism of a semiconductor laser. However, the cylindrical lens is
The adjustment was extremely difficult because it was not rotationally symmetrical.

That is, since the converging power of the cylindrical lens varies depending on the direction, it is necessary to adjust not only the angular position with respect to the optical axis, but also the position in the optical axis direction and the position of power directivity with respect to astigmatism. It had the drawback of being difficult. In addition, when there are variations in the amount of aberration of semiconductor lasers, there are drawbacks such as the need to design and manufacture cylindrical lenses according to the characteristics of individual semiconductor lasers. It was impossible.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to correct astigmatism of a semiconductor laser with an optical element that is simple in design and manufacturing and inexpensive, and is integrated with the semiconductor laser. It is an object of the present invention to provide a small and inexpensive semiconductor laser light source that can be handled as a light source with corrected astigmatism.

[0008]

In order to achieve the above object, the present invention uses a plane parallel plate which is simple and inexpensive to design and manufacture, and the plane plane plate is placed in a light beam emitted from a semiconductor laser. Tilt and fix with laser diode,
A semiconductor laser and a plane-parallel plate are integrated to form a light source with astigmatism corrected.

[0009]

In general, it is well known that when a plane-parallel plate is inserted into an image-forming optical system, astigmatism occurs depending on the thickness of the plane-parallel plate, the refractive index, and the incident angle of a light ray (for example, Hiroshi Kubota "Optics" Iwanami Shoten, 1964, 12th
8 to 131). The present invention reversely utilizes this phenomenon, and corrects the astigmatism of the light source itself by arranging the plane-parallel plate in a light beam having astigmatism emitted from the semiconductor laser with inclination. .

It is well known that astigmatism occurs when a convergent light flux passes through an inclined plane-parallel plate. This is because a light flux from a point light source having no astigmatism is generated. It shows how much astigmatism occurs when passing through a plane-parallel plate, and deals with the case of a point light source with no astigmatism. On the other hand, the present invention has a problem of the astigmatism of the semiconductor laser itself, that is, the astigmatism of the light source itself, and has found that the plane-parallel plate is extremely useful for correcting the astigmatism of the light source itself. A semiconductor laser having astigmatism by arranging the plane-parallel plate in a light beam having astigmatism transmitted from the optical axis and tilting it, and integrating the semiconductor laser and the plane-parallel plate. The present invention is characterized in that it can be used as a point light source that is not adversely affected by astigmatism when used as a light source such as.

Further, the astigmatism can be accurately corrected by integrally arranging the semiconductor laser and the plane-parallel plate close to each other. That is, as described above, the light beam from the semiconductor laser has a position shift that converges between the light beam included in the bonding surface and the light beam included in the plane perpendicular thereto. In order to correct this positional deviation (astigmatism) accurately, it is necessary to accurately match the inclination of the plane-parallel plate within either plane. In addition, even if the angle of inclination does not conform to the design formula, it cannot be corrected. For such accurate alignment, it is desirable that the semiconductor laser and the plane-parallel plate are arranged as close to each other and strong as possible. Therefore, it is necessary to have an integrated structure as in the present invention.

[0012]

Embodiments will be described in detail below with reference to embodiments of the present invention. FIG. 2 is a diagram showing an embodiment of the present invention. In the figure, reference numeral 1 denotes a semiconductor laser. As shown in FIG. 1, a semiconductor laser 1 emits a light beam having astigmatism whose convergence points are different between a direction parallel to the cemented surface and a direction perpendicular thereto. Is released. Reference numeral 3 denotes a plane-parallel plate having a thickness d and a refractive index n, which is tilted in the light beam emitted from the semiconductor laser 1. The astigmatic difference Δ produced by the plane-parallel plate is described by Hiroshi Kubota in “Optics” (Iwanami Shoten, 196).
4 years) According to page 131, Δ = (d / ncosi ′) {1- (cos ² i / cos ² i ′)}. However, i is an incident angle (tilt angle), i'is a refraction angle, and i '= sin- ¹ (sini / n). Astigmatism occurring in the semiconductor laser 1 can be corrected by selecting the thickness d, the refractive index n, and the incident angle (tilt angle) i of the plane-parallel plate based on this equation.

As an example, FIG. 3 shows the relationship between i and Δ when n = 1.5 with d as a parameter. For example, if a plane parallel plate having a thickness of 0.5 mm and a refractive index of 1.5 is used, it is possible to correct astigmatism of 22 μm at an incident angle (tilt angle) of 20 °. Further, in the present embodiment, the semiconductor laser 1 and the plane-parallel plate 3 are arranged on the same mount 5, and the angle adjusting plate 6 is moved as shown by the arrow.
If the angle of the plane-parallel plate 3 is adjusted and then fixed, the semiconductor laser 1 and the plane-parallel plate 3 can be integrated to obtain a light source with astigmatism corrected.
It is possible to take advantage of the characteristics of a coherent light source that is ultra-small and low-cost.

[0014]

As described above, according to the present invention, astigmatism of a semiconductor laser can be corrected by a parallel plane plate which is simple in design and manufacturing and inexpensive, and moreover, the semiconductor laser and the plane parallel plate can be corrected. Are integrated into a light source with corrected astigmatism, so that by using it as a light source for an optical disk device, a laser printer device, etc., a diffraction-limited light spot can be obtained and the light utilization efficiency of the light source is improved. You can do things. As described above, according to the present invention, it is possible to obtain a small and inexpensive semiconductor laser light source that can be used as a point light source in which the astigmatism is suppressed to a sufficiently low level, even though a semiconductor laser having astigmatism is used. .

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an image formation relationship of a light source having astigmatism.

FIG. 2 is a conceptual diagram showing a configuration of an embodiment of the present invention.

FIG. 3 is a graph illustrating the operation of the present invention.

[Explanation of symbols]

1 ... Semiconductor laser, 2 ... Imaging optical system, 3 ... Parallel plane plate,
X ... Beam waist position in a direction parallel to the joint surface, Y ... Beam waist position in a direction perpendicular to the joint surface.

Claims (2)

[Claims] 1. A semiconductor laser having an astigmatic difference Δ, and a light beam emitted from the semiconductor laser, the light beam having an incident angle i.
, A translucent parallel plane plate having a refractive index n and a thickness d, which is inserted so as to be incident at, is combined with Δ ≈ (d / ncosi ′) {1- (cos ² i / cos
² i ′)} i ′ = sin to ¹ (sin i / n), and the parallel plane plate is tilted in a plane parallel or perpendicular to the bonding surface of the semiconductor laser. A semiconductor laser light source characterized in that 2. The parallel flat plate has a thickness of 1.0 mm to 0.
The semiconductor laser light source according to claim 1, wherein the semiconductor laser light source is in the range of 25 mm.