JPS6118492Y2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to an optical information processing device that emits a parallel light beam having a desired beam width. Background technology and its problems For example, the divergence shape of the emitted light beam of a semiconductor laser LD has anisotropy, and the cross-sectional shape in the far field is
As shown in Figure 1, the spread angle θ in the X direction
〓 and its spread θ in the Y direction perpendicular to the X direction
It has an elliptical shape, unlike 〓, and the light intensity distribution becomes as shown in FIG. Note that the X direction, which is the minor axis direction of the elliptical shape, is the direction perpendicular to the optical axis of the emitted light beam within the junction surface 1 of the semiconductor laser LD, and the Y direction, which is the major axis direction, is the
direction and the direction perpendicular to the optical axis. On the other hand, in optical information processing devices for recording information recorded on disks, etc., it is necessary to obtain the amount of light, so for example, the numerical aperture of the collimating lens is
It is necessary to increase NA. However, the numerical aperture NA
As shown by the diagonal lines in FIG. 3, if the angle is large, a light beam with an elliptical cross section will be incident on the aperture surface 2 due to the anisotropy of the divergence shape of the emitted light beam of the semiconductor laser LD, as shown by diagonal lines in FIG. It becomes non-uniform within surface 2. This means that the light beam that has been parallelized by the collimating lens becomes an elliptical light beam in cross section (hereinafter referred to as a parallel elliptical light beam), and for example, when condensed by an objective lens, the light beam enters the objective lens surface with uniform light intensity. It will not be done. In other words, the light beam is less likely to be narrowed down by the objective lens. This is because the objective lens is designed to focus the light beam in the best condition only when the light beam is incident on the entire surface with uniform light intensity, and the required light intensity cannot be obtained at the periphery of the lens. This is because particularly high spatial frequency components become difficult to pass through, and the high frequency frequency characteristics of the recorded or reproduced signal deteriorate. Therefore, either the short axis direction (X direction) of the parallel elliptical light beam is expanded, or the long axis direction (Y direction)
It is necessary to compress or correct it. To solve this problem, the following two methods have been proposed in the past. (a) First, as shown in Figure 4, the collimator
A triangular shape that enters the light beam in a predetermined direction and inclination angle from one surface into the optical path of the light beam emitted from the semiconductor laser LD, which has been converted into a parallel elliptical light beam by the lens 3, and emits the light beam from the other surface. A prism 4 is provided to extend and correct the beam width in the short axis direction (X direction) of the parallel elliptical beam. In this case, one triangular prism 3
Since the optical axes of the light beam on the incident side and the light beam on the output side are not parallel, it is difficult to adjust the position of the triangular prism 4 and the like. (b) Next, as shown in FIG. 5, the light beam emitted from the triangular prism 4 in the previous section is made to enter the triangular prism 4 in a predetermined direction and at a predetermined angle from one surface, and exit from the other surface of the triangular prism. A prism 5 is provided to extend the luminous flux width in two stages in the short axis direction (X direction) of the parallel elliptical luminous flux. In this case, since two triangular prisms 4 and 5 are used, these prisms 4,
The optical axes of the light beam on the incident side and the light beam on the output side with respect to 5 can be made parallel. Therefore, the position adjustment of the triangular prisms 4, 5, etc. becomes easy when viewed from one side. However, two triangular prisms 4, 5
Since the prisms 4 and 5 are arranged independently in the optical path of the parallel light beam, it is necessary to adjust the positions of the prisms 4 and 5, which again has the drawback that it is difficult to adjust the positions of the triangular prisms 4 and 5. have Purpose of the Invention The present invention was devised to eliminate the above-mentioned drawbacks, and aims to provide an optical information processing device in which the position of a triangular prism etc. can be easily and simply adjusted. Summary of the invention The optical information processing device of the invention is made up of a semiconductor laser that emits a light beam, a collimating lens that converts the light beam into a parallel light beam, and a plurality of triangular prisms having different refractive indexes. and a compound prism disposed in the optical path, and by selecting the apex angle of the triangular prism, the refractive index, and the incident angle of the parallel light beam to the compound prism, The parallel light flux that is emitted is made parallel to the parallel light flux that enters the composite prism, and the beam width of the parallel light flux that exits from the composite prism is corrected. This eliminates the need for positional adjustment between the triangular prisms, reducing the degree of freedom required for adjustment and making positional adjustment easy and simple. Embodiment Next, an embodiment of the optical information processing apparatus of the present invention will be described with reference to the drawings. FIG. 6 is a cross-sectional view along the optical axis within the junction surface 1 of the semiconductor laser LD. The emitted light beam from the semiconductor laser LD in the far field, which has a minor diameter in the X direction and an elliptical cross section, is converted into a parallel elliptical light beam by the collimating lens 11 and enters the compound prism 12. . This compound prism 12 includes one triangular prism 12A which becomes the first triangular prism in the present invention with a predetermined refractive index n ₁ and apex angle γ, and a triangular prism 12A which becomes the first triangular prism in the present invention with a predetermined refractive index n 1 and a refractive index n ₂ larger than the refractive index n ₁ . The other triangular prism 12B serving as the second triangular prism is pasted together so that their axial directions are parallel to each other. Further, the compound prism 12 includes one triangular prism 12 on the incident side in the optical path of the parallel light beam.
The triangular prism A is located so that one surface 12a thereof is the incident surface, and the other triangular prism 12B is located on the exit side and one surface 12b is the exit surface. That is, the compound prisms 12 are arranged such that one triangular prism 12A and the other triangular prism 12B are positioned in the order of increasing luminous flux width, as will be understood from the description below. The parallel elliptical light beam from the collimating lens 11 is directed in the major axis direction (Y
direction) is the same direction as the axial direction of the triangular prism 12A, and is incident so that a predetermined inclination angle α is formed in the short axis direction (X direction). Further, the parallel light flux that has passed through the triangular prism 12A is further incident on the triangular prism 12B, and is emitted perpendicularly from the exit surface 12b of the composite prism 12. As a result, the parallel elliptical light beam from the collimating lens 11 is directed only in the minor axis direction (X direction) to each of the triangular prisms 12 constituting the compound prism 12.
The beam is refracted by A and 12B, the beam width is expanded, and the beam is emitted with a wide width. On the other hand, in the major axis direction (Y direction), the composite prism 1 is not expanded or compressed.
Two triangular prisms 12A and 12B forming 2
pass through. Therefore, the luminous flux on the exit side emitted from the composite prism 12 has a luminous flux width expanded in the short axis direction (X direction) and becomes wide, and becomes a parallel luminous flux with a circular cross section. Moreover, the optical axis of the circular parallel light beam is parallel to the optical axis of the parallel elliptical light beam incident on the compound prism 12. Next, the luminous flux width in the short axis direction (X direction) of the parallel elliptical luminous flux incident on the composite prism 12' is expanded and widened, and the cross section of the emitted parallel luminous flux becomes circular, and the composite prism 12' The conditions for the optical axis of the incident side light beam and the optical axis of the output side light beam to be parallel to each other will be explained with reference to FIG. Now, the refractive index of the air layer; n ₀ ′ The refractive index and apex angle of the triangular prism 12A ′; n ₁ ′, γ′ The refractive index of the triangular prism 12B ′ ; n ₂ ′ With respect to the surface 12a′ of the triangular prism 12A ′ Inclination angle of the incident light beam; α' Inclination angle of the optical axis of the output light beam from the triangular prism 12A' with respect to the optical axis of the incident light beam into the triangular prism 12A';β' Incident light beam into the triangular prism 12A', triangular prism 12A' The beam width of each of the light beams inside the triangular prism 12A' and the light beams emitted from the triangular prism 12A'; Inclination angle of the light beams with respect to the normal at each surface 12a', 12c' of the triangular prism 12A' (D1 _, D2 _{, D3} ) ; θ ₁ , θ ₂ , θ ₃ , θ If the incident width or output width of the luminous flux at each surface 12a ′, 12c′ of the _four- triangular prism 12A ′ is a, b, then the following equation holds true. θ ₁ = π/2−α′ (1) n ₀ ′・sinθ ₁ = n ₁ ′・sinθ ₂ (〓Snell's law) (2) γ′=θ ₂ +θ ₃ (〓π=(π/2− θ ₃ )+ (π/2−θ ₂ )+γ′) (3) n ₁ ′・sinθ ₃ =n ₂ ′・sinθ ₄ (〓Snell's law) (4) β′=θ ₄ +π/2−( γ′+α′) (〓β′+(γ′+α′)=π/2+θ ₄ ) (5) D ₁ =a・sinα′ (6) D ₂ =a・cosθ ₂ (7) =b・cosθ ₂ (8) D ₃ =b・cosθ ₄ (9) And from the above equations (1) to (4) Also, from equations (5) and (10) above, Furthermore, from the above formulas (6) to (9), D ₃ /D ₁ =cosθ ₂ /sin α′・cosθ ₄ /
cos θ ₃ (12) is derived. Therefore, from equation (11) above, n ₁ ′, n ₂ ′ and α′,
If γ' is selected appropriately, the inclination angle β' can be set to 0, that is, the optical axis of the incident side beam and the optical axis of the output side beam become parallel, and at the same time, from the above equation (12), the short axis direction of the beam The expansion rate (=D ₃ /D ₁ ) at which the luminous flux width of is expanded to make it wider is also determined. From the above formula, the case where β≒0 with n ₁ ′=1.51 and n ₂ ′=1.76 is determined as shown in the attached table. (However, the air layer n ₀ '=1.)

[Table] In the above embodiment, an example was shown in which a parallel light beam having a circular cross section is obtained by extending the short axis direction (X direction) of a parallel elliptical light beam. A configuration may be adopted in which a parallel elliptical light beam is input and compressed in the major axis direction (Y direction) to obtain a parallel light beam having a circular cross section. Further, instead of a parallel light beam having a circular cross section, a parallel light beam having an elliptical cross section with a desired ratio of the major axis to the minor axis may be obtained. In order to efficiently obtain the required expansion ratio (compression ratio) when the compound prism 12 is composed of three or more triangular prisms 12A, 12B... The triangular prisms 12A, 12B may be configured so that their respective refractive indices n ₁ , n ₂ , . Next, a modification will be explained. Note that the same reference numerals as in the above embodiment indicate the same contents, and overlapping explanations will be omitted. 2. Description of the Related Art In recorded information reproducing devices such as disks, a beam splitter is used to separate the outgoing path of a light beam from the return path of a light beam reflected and diffracted from a recording medium such as a disk. First, as a first modification, as shown in FIGS. 8A and 8B, the triangular prism 1 in the above embodiment is
Beam splitter prism 12 instead of 2B
B'' is used to transmit the light beam from the semiconductor laser LD that has passed through the triangular prism 12A to the polarizing film or semi-transparent film 13 of the beam splitter prism 12B'', and then the objective lens is placed on the reading surface of the disk 14. The light is reflected and diffracted by the reading surface and enters the objective lens 15.
Beam splitter prism 1 to reflect the reflected light beam through
2B'' polarizing film or semi-transparent film 13, and enters the photodetector 17 via the lens 16.Next, as a second modification, the light is shown in FIGS. 9A and 9B. Like Beam Splitter Prism 12B
As a result, the light flux from the semiconductor laser LD that has passed through the triangular prism 12A is incident on the polarizing film or semi-transparent film 13' of the beam splitter prism 12B in an S-polarized direction and reflected, and then the object is placed on the reading surface of the disk 14. The lens 15 narrows down the incident light, while the reflected light from the reading surface is passed through the objective lens 15 to the beam splitter prism 12.
The light is transmitted through the B polarizing film or semi-transparent film 13' and is incident on the photodetector 17 via the lens 16. The beam splitter prisms 12B″, 12B in this modification are substantially triangular prisms 1
It goes without saying that this prism is included in the technical idea of the present invention since it is a prism with a cross-sectional shape that exhibits optical characteristics similar to those of 2B. Furthermore, if the reflective films of the beam splitter prisms 12B'' and 12B are polarizing films, it goes without saying that a 1/4 wavelength plate or the like is required in the optical path. The number of points is reduced, making the adjustment much easier and simpler than in the embodiments described above.Application Examples The optical information processing device of the present invention can be used not only for information reproducing devices from optical disks, but also for information recording devices (disk master manufacturing). device, etc.), information transmission device, etc. Effects of the invention The present invention has the following advantages: Although the parallel beam width can be corrected, at least two Since it is composed of triangular prisms, the optical axes of the light flux on the incident side and the light flux on the output side can be made parallel.Also, since it is a composite prism made by pasting these triangular prisms together, the triangular prism There is no need to adjust the position between them. Therefore, the degree of freedom required for adjustment is reduced and adjustment can be made easily and easily. The triangular prisms are pasted together, and the triangular prisms are not independent from each other as in the conventional example. Since there is no air layer between the two, it can be made compact.By bonding the triangular prisms together, the number of interfaces is reduced and the transmittance of the light beam is high.

[Brief explanation of the drawing]

1 to 3 are diagrams for explaining the cross-sectional shape in the far field of the emitted light beam of the semiconductor laser, the light intensity distribution, and the shape of the light beam incident on the collimating lens, respectively. FIG. 6 is a cross-sectional view along the optical axis within the bonded surface of a semiconductor laser LD showing the configuration of an optical information processing device according to the present invention. FIG. 7 is a diagram for explaining the conditions of the composite prism, and Figures 8A and B are diagrams for explaining the configuration of a modified example of light within the junction plane of the semiconductor laser LD. A cross-sectional view along the axis and a perspective view of the main part, and FIGS. 9A and 9B are semiconductor lasers for explaining the configuration of other modified examples.
FIG. 2 is a cross-sectional view along the optical axis in a plane perpendicular to the bonding surface of the LD and a perspective view of the main parts. In addition, in the symbols used in the drawings, LD
...Semiconductor laser, 11...Collimating lens, 12...Compound prism, 12A, 12B...
It is a triangular prism.

Claims (1)

[Claims for Utility Model Registration] 1. A semiconductor laser that emits a luminous flux, a collimating lens that converts the luminous flux into a parallel luminous flux, and a plurality of triangular prisms having different refractive indexes are laminated together to form a laser beam in the optical path of the parallel luminous flux. By selecting the apex angle of the triangular prism, the refractive index, and the angle of incidence of the parallel light beam on the compound prism, the parallel light beam emitted from the compound prism is An optical information processing device configured to make a luminous flux parallel to the parallel luminous flux entering the composite prism and to correct a luminous flux width of the parallel luminous flux exiting from the composite prism. 2. The optical information processing device according to claim 1, wherein the refractive index of each of the plurality of triangular prisms increases sequentially along the optical path along which the parallel light beam travels.