JPH0396915A - Beam shaping optical system - Google Patents

Abstract

PURPOSE:To make incident light and projection light parallel and to obtain the compact beam shaping optical system by making either one of an incidence or projection surface a diffraction grating. CONSTITUTION:The diverged beam from a laser 1 is collimated through a collimator lens 2 into nearly parallel light and the beam with elliptic section is converted by a shaping prism 6 into a circularly sectioned beam. A prism 6 has an incidence surface 7, a reflecting surface 8, and a projection surface 9, which is a diffraction grating surface and increases the diameter of the beam parallel to the paper surface. When the diffraction grating surface is formed in a saw-tooth shape, high diffraction efficiency is obtained and the generation of diffracted light other than desired light can be suppressed sufficiently low. Further, the magnification corresponding to an incidence angle theta1, a refraction angle theta2, and a diffraction angle theta3 is M1=costheta2/costheta1 on the incidence surface and M2=1/costheta3 on the projection surface and the total beam enlargement rate M is represented as M=M1XM2. This constitution holds the optical axes of the incident light and projection light parallel, the enlargement rate of the beam can be set optionally to some extent by varying the angle of the projection surface and the pitch of the diffraction grating, and only one component is required, so that the device becomes compact.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to a device for shaping the cross-sectional shape of a light beam.
In particular, the present invention relates to a beam shaping prism that shapes the cross-sectional shape of a parallel light beam.

[Prior Art] Optical recording and reproducing devices that use optical means to record and reproduce information on a rotating disk-shaped information recording medium and optical information processing devices such as laser beam printers use small and lightweight light sources as light sources. Since then, semiconductor lasers have been used. The light emitted from this semiconductor laser is diverging light, and the divergence angle is different in the direction perpendicular to and parallel to the P-n junction surface of the semiconductor laser, and generally the divergence angle is larger in the direction perpendicular to the junction surface. , is small in the parallel direction, so the cross section of the optical axis becomes elliptical.

Therefore, in order to use semiconductor laser light efficiently and to focus it on a spot with an optical axis symmetrical intensity distribution,
Anamorphic optics will be required. Anamorphic optical systems are also used for laser beams with a circular cross section to adjust the vertical and horizontal resolution to desired values by changing the aspect ratio of the laser beam width entering the imaging lens. may be done.

What is shown in FIG. 3 is a conventional optical information processing apparatus including a beam shaping optical system described in Japanese Patent Laid-Open No. 61-216145. (1) is a semiconductor laser that emits light with different divergence angles in vertical and horizontal directions, (2) is a collimator lens that converts the divergent beam from the semiconductor laser into a substantially parallel beam, and (3) is the anisotropic beam cross section from the collimator lens. (4) is an objective lens for condensing the parallel light flux from the beam shaping prism, and (5) is an information recording medium.

Next, the operation will be explained. First, a semiconductor laser (
1. ) differs depending on the structure of the semiconductor laser device, and the aspect ratio of the emitting region is not 1, but the horizontal and vertical centers of the emitted light distribution in the far-field pattern from the semiconductor laser device. The divergence angle at the position where the intensity is half is θ, . For example, in the semiconductor laser (1) shown in FIG. 3, θ = 100, θ = 2 5°, and θi / θ7t''25.

The light emitted from the semiconductor laser (1) is converted into approximately parallel light by the circular collimator lens (2), but if the numerical aperture NA of the collimator lens (2) is relatively small, for example, NA = about 0.1. When using a collimator lens (2), the parallel light beam emitted from the collimator lens (2) becomes a nearly isotropic beam, but the incident angle of the light passing through the outermost circumference of the lens is relative to the center of the optical axis. Since the angle of divergence is 57°, out of the light emitted from the semiconductor laser, light having a divergence angle of 011.4° or more is not used. Therefore, in order to efficiently utilize the light emitted from the semiconductor laser, it is necessary to greatly deviate the numerical aperture NA of the collimator lens (2).

For example, if the numerical aperture of the collimator lens (2) is NA=03
In this case, NA=0. Compared to the collimator lens No. 1, it can be used approximately three times more effectively. However, when comparing the divergence angle θa of the emitted light from the semiconductor laser (1) and the angle (θ) formed by the point of incidence on the outermost periphery of the collimator lens (2), we find that θ7 〈θ〈θ, . Therefore, the cross section of the light emitted from the collimator lens (2) has an elliptical shape.

Therefore, as shown in FIG. 3, this light beam having an elliptical cross section is shaped using a beam shaping prism (3). In other words, the beam shaping prism (3) expands the short axis direction of the ellipse and converts it into a substantially circular beam. Therefore, the objective lens (4
), the light spot focused and irradiated onto the information recording medium (5) becomes approximately circular.

This type of optical device has a configuration in which reflected light from the information recording medium (5) is detected to obtain focusing and tracking control signals and information reproduction signals.
The information recording medium (5) and reflected light detection means are not shown in the apparatus shown in FIG.

[Problems to be Solved by the Invention] Since the conventional beam shaping optical system is configured as described above, the optical axis is bent as shown in Fig. 3, and the shape of the device is limited, making it difficult to design. Freedom is lost. Furthermore, if a placement error occurs in the beam shaping prism (3), the optical axis of the emitted light is likely to shift or tilt.
Strict placement accuracy is required.

Further, there is a beam shaping optical system other than the one shown in FIG. 3 that uses a cylindrical lens, but since this system usually uses two cylindrical lenses, the number of parts inevitably increases. Furthermore, placement accuracy is also very strict, and wavefront aberration deteriorates with the slightest misalignment of components.

This invention was made to solve the above-mentioned problems, and its purpose is to obtain a beam shaping optical system that is resistant to misalignment without bending the optical axis of the light emitted from the collimator lens. [Means for Solving the Problems] A beam shaping optical system according to the present invention has an entrance surface, a reflection surface, and an exit surface, and at least one of the entrance surface and the exit surface is a diffraction grating surface, and the optical system The structure is such that when an incident light beam is made incident at a certain angle with respect to the incident plane, the outgoing light becomes parallel to the incident light.

[Effect]

In the beam shaping optical system according to the present invention, at least one of the entrance surface and the exit surface is made into a diffraction grating, so that the incident light and the output light can be made parallel, and a compact beam shaping optical system can be obtained.

[Embodiment] An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a configuration diagram of a beam shaping optical system according to the present invention. Semiconductor laser (1) and collimator lens (
2) is similar to the conventional device. (6) is a beam shaping prism according to the present invention, which has an entrance surface (7), a reflection surface (8) and an exit surface (9). In the embodiment shown in FIG. 1, the output surface (9) is a diffraction grating surface.Next, the operation will be explained. The diverging laser beam emitted from the semiconductor laser (1) is passed through a collimator lens (
In step 2), the light is converted into substantially parallel light, from which a light beam with an elliptical cross section is emitted. This light beam is converted into a light beam with a circular cross section by a beam shaping prism (6) according to the invention. The beam shaping prism (6) in the present invention has an entrance surface (
7) It consists of a reflecting surface (8) and an exit surface (9), and the exit surface (9) is a diffraction grating surface, which enlarges the beam diameter in the direction parallel to the plane of the paper in FIG.

FIG. 2 shows how light is diffracted by the diffraction grating surface of the exit surface (9). The diffraction angle of the emitted light is 03, the pitch of the diffraction grating is A, and the refractive index of the glass material is n' (the refractive index of air n=1
), the wavelength of light is 9, then θs = sin-' (-) n' of ---
・The relationship A holds true. Further, by forming the diffraction grating surface into a sawtooth shape as shown in FIG. 2, high diffraction efficiency can be obtained, and the generation of diffracted light other than desired light can be suppressed to a sufficiently low level.

Next, we will discuss the beam expansion ratio. As shown in FIG. 1, the light beam is refracted (diffracted) at the entrance surface (7) and the exit surface (9), and the beam is expanded. If the magnification of the beam expansion performed at the entrance surface is M1, and the rate of beam expansion performed at the exit surface is M2, the overall beam expansion factor M is given by M=MI XM2 -11. Note that the magnifications M, , M2 are given as follows.

However, θ1 is the angle of incidence on the incident surface (7), and θ2 is the angle of incidence on the incident surface (7).
The refraction angle at 7) and θ3 are the diffraction angle at the exit surface (9).

In addition, in the embodiment shown in FIG.
Although the diffraction grating surface is used as the diffraction grating surface, the incident surface (7) may also be used as the diffraction grating surface, and the same effect as in the above embodiment can be obtained.

Furthermore, the transmission efficiency of the beam shaping prism (6) can be improved by applying an anti-reflection coating to the exit surface (9) or the entrance surface (7) and the exit surface (9), which are diffraction grating surfaces. The same effects as in the above embodiment are achieved.

Further, in the above embodiment, the configuration is such that the light beam is expanded, but the light beam may be made incident from the exit surface (9) side in FIG. 1 and the beam may be reduced. be effective.

Further, in the above embodiment, the output surface (9) and the output light are perpendicular to each other, but the output surface (9) and the output light do not have to be perpendicular to each other, and the beam expansion ratio is also the same in this case. The same effects as in the above embodiment are achieved.

Further, in the above embodiment, a semiconductor laser (1) is used as a light source.
Although the case is shown in which the method is used, the present invention is not limited to this.

〔Effect of the invention〕

As described above, according to the present invention, in a beam shaping prism having an entrance surface, a reflection surface, and an exit surface, at least one of the entrance surface and the exit surface is made a diffraction grating surface, so that the incident light and the output light of the beam shaping prism are The optical axes of the beam can be kept parallel, and the beam expansion rate can be set arbitrarily to some extent by changing the angle of the exit surface and the pitch of the diffraction grating, increasing the degree of freedom in design. moreover,
Since there is only one part, the entire device is compact.

[Brief explanation of drawings]

Fig. 1 is a side view of a beam shaping optical system according to an embodiment of the present invention, Fig. 2(a) is a partially enlarged view explaining the operation of an embodiment of the invention, and Fig. 2(b) is a further enlarged view. FIG. 3 is a side view of an optical device using a conventional beam shaping optical system. In the figure, (1) is a semiconductor laser, (2) is a collimator lens, (6) is a beam shaping prism (7) is an incident surface, (8) is a reflective surface, and (9) is an original dimension surface.

Claims (1)

[Claims] (1) An optical system for converting the cross-sectional shape of a light beam, which has an entrance surface on which the light beam enters, a reflection surface, and an exit surface from which the light beam exits. In a beam shaping optical system configured so that when light is incident at a certain predetermined angle, the input optical axis and the output optical axis are parallel, at least one of the output surface and the input surface is a diffraction grating surface. A beam shaping optical system characterized by: