JPS60181701A - Grating lens for coupling optical fiber - Google Patents

Abstract

PURPOSE:To couple efficiently the light beam radiated from a semiconductor light emitting element having anisotropy to an optical fiber by forming an irregularly spaced diffraction grating pattern made into a concentrical elliptical shape on at least one surface of a lens consisting of a transparent plastic base material. CONSTITUTION:A lens base material 5 consists of plastic such as transparent acrylic and an irregularly spaced diffraction grating pattern 6 is formed on one surface. The pattern 6 has such a concentrical elliptical shape in which the grating pitch decreases in the y-axis direction than in the x-axis direction in accordance with the anisotropy of the radiation angle of the light beam radiated from a laser diode. The outer surface is flat. If such grating lens is used as a coupler between the laser diode and an optical fiber, the light beam of the elliptical section radiated from the laser diode is condensate as a circular spot to the end face of the optical fiber and high coupling efficiency is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a grating lens for coupling an emitted light beam from a semiconductor light emitting device such as a laser diode to an optical fiber.

[Technical background of the invention and its problems]

In optical communications, it is extremely important to couple a light source, such as a laser diode or light emitting diode, with an optical fiber without loss. As a typical conventional coupling method between a light source and an optical fiber, the method shown in FIGS. 1 and 2 is known.

In Fig. 1, the emitted light beam from the laser diode 1 is converged onto the end face of the optical fiber 2 by a converging rod lens 3, and in Fig. fpJ2, the emitted light beam from the laser diode 1 is converged by a rod lens 4 placed horizontally. It is made to converge on the end face of the optical fiber 2.

In a normal striped structure heterojunction laser diode, there is anisotropy in the radiation angle of the emitted light beam, as shown in the figure, ff<3. That is, the radiation angle UP of the laser diode 1 in the direction perpendicular to the substrate (X direction) is equal to the radiation angle UP in the direction parallel to the substrate (X direction).
direction) is larger than the radiation angle 08, and the cross-sectional shape of the emitted light beam becomes a 1 degree 1 circle. The connection method in Figure 2 is
This takes into consideration only the convergence of light that spreads widely in the X direction.
The coupling efficiency is only about 30-.

The focusing rod lens 3 in Figure 1 is cut from a large-diameter optical fiber with a square-law distribution of refractive index, and focuses in both the X and X directions, but this also takes into account the anisotropy of the radiation angle. The coupling efficiency is about 60 factors.

In order to sufficiently increase the coupling efficiency between the laser diode and the optical fiber, it is necessary to vary the radiation angle of the laser diode's synchrotron radiation beam so that the elliptical radiation beam is incident on the input end face of the optical fiber as a circular light spot. It is desirable to construct a coupler that takes orientation into consideration. However, for example, providing the converging rod lens 3 of FIG. 1 with such a function requires a complicated refractive index distribution, which is extremely difficult in terms of manufacturing technology.

[Purpose of the invention]

The present invention has been made in view of the above-mentioned points, and is a grating lens for optical fiber coupling that makes it possible to efficiently couple the emitted light beam of a semiconductor light emitting element having anisotropy in the radiation angle to an optical fiber. The purpose is to provide

[Summary of the invention]

The present invention uses a grating lens in which an unevenly spaced diffraction grating pattern is formed on the surface of a transparent plastic base material as a coupler for coupling a radiation beam from a semiconductor light emitting device to an optical fiber. A grating lens is a type of diffraction grating, and by forming an unevenly spaced diffraction grating pattern with a wavelength-order grating pitch that decreases from the center to the periphery, the diffraction angles of each part are slightly different. , which has a lens effect so that a certain amount of diffracted light from each part converges on one point.

In the present invention, in consideration of the radiation angle anisotropy of the emitted light beam from the semiconductor light emitting device, in order to make the elliptical beam enter the end face of the optical fiber as a circular spot, a concentric elliptical unequal shape is formed on at least one face. A grating lens with a thermal diffraction grating pattern formed thereon, here "concentric elliptical"
This refers to a state in which a plurality of similar ellipses are overlapped with the center point of the line segment connecting their respective bifocal points as a common center. Furthermore, "elliptical" is not limited to an ellipse in the strict sense, but refers to a state in which the lattice pitch within the lens surface has anisotropy, depending on the anisotropy of the emitted light beam from the light emitting element. [Effects of the Invention] According to the present invention, an optical fiber coupling lens with high coupling efficiency can be realized by considering the radiation angle anisotropy of the emitted light beam from the semiconductor light emitting device. Furthermore, the grating lens according to the present invention can be easily obtained by forming a diffraction grating pattern on the surface of the transparent plastic base 1 using a mold produced by ultra-high precision turning, or by creating a replica thereof.

[Embodiments of the invention]

The present invention will be explained in detail below. , FIG. 4 shows a grating lens according to an embodiment, in which (a) is a plan view of the surface facing the laser diode side, (bl is a cross-sectional view 1, and the lens crystal phase 5 is made of plastic such as transparent acrylic). As shown in Fig. 1, an unevenly spaced diffraction grating pattern 6 is formed on one surface.The x and y axes are x and y in Fig. 3.
Each corresponds to the y-axis. In other words, the irregularly spaced grating pattern 6 is arranged so that the grating pitch is smaller in the y-axis direction than in the It has a concentric elliptical shape. The other surface is a flat surface. Therefore, the focal length of this lens in the polarization plane in the y-axis direction is smaller than that in the x-axis direction. Also, unevenly spaced diffraction grating pattern 6
The surface is a blazed surface with a serrated cross section.

If this grating lens is used as a coupler between a laser diode and an optical fiber, it is possible to condense the emitted light beam with a circular cross section from the laser diode into a circular spot on the end face of the optical fiber, resulting in high coupling efficiency. can be obtained. Moreover, this grating lens can be easily and inexpensively made by making an original plate by machining using plastic and then making a replica thereof. Fig. 5 shows a grating lens according to another embodiment of this invention. (al, (bl is a plan view of the surface facing the laser diode and optical fiber, respectively, and (cl is a cross-sectional view.) This grating lens also includes 1) a lens base material 7 made of transparent plastic Using this method, concentric elliptical diffraction grating patterns 8 and 9 are formed at irregular intervals on each surface.

This grating lens differs from the previous embodiment in that it converts the emitted light beam from the laser diode into a parallel light beam using the diffraction grating pattern 8 on the laser diode side.
A parallel light beam is guided through the lens substrate 7 and focused on the end face of the optical fiber by the diffraction grating pattern 9 on the other surface. Therefore, in this embodiment, the diffraction grating patterns 8 and 9 on each surface are arranged in consideration of the anisotropy of the spread of the radiation beam from the laser diode, and at the same time, the radiation angle of the radiation beam from the laser diode and the optical fiber. The grating pitch is set in consideration of the numerical aperture. Specifically, according to this embodiment, the focal length of the diffraction grating pattern 9 on the optical fiber side is made sufficiently larger than the focal length of the diffraction grating pattern 8 on the laser diode side. In addition to this effect, it is possible to efficiently couple the widely spread radiation beam from the laser diode to an optical fiber having a sufficiently small numerical aperture compared to the spread.

Note that the present invention is effective not only when the light source is a laser diode, but also when a light emitting diode whose emitted light beam has anisotropy in its spread is used.

[Brief explanation of drawings]

Figures 1 and 2 are diagrams showing an example of a conventional laser diode and optical fiber coupler, Figure 3 is a diagram for explaining the radiation angle anisotropy of the emitted light beam of the laser diode, and Figure 4 1 is a diagram showing a grating lens according to one embodiment of the present invention, and FIG. 'L55 is a diagram showing a grating lens according to another embodiment. 5.7... Lens base material, 6,8.9... Unequally spaced diffraction grating pattern. Figure 1 Figure 2 Figure 3 Figure 4 (a) (b) Figure 5 (a) (b) (C)

Claims (4)

[Claims] (1) A lens that couples the emitted light beam from a semiconductor light emitting device to an optical fiber, and is made of cut transparent plastic and has a concentric elliptical unevenly spaced diffraction grating pattern formed on at least one surface. A grating lens for optical fiber coupling, which is characterized by: (2) The light beam emitted from the semiconductor light emitting element is incident on the surface facing the semiconductor light emitting element of the optical fiber.
The grating lens for optical fiber coupling according to claim S1, wherein a concentric elliptical unevenly spaced diffraction grating is formed on the surface to converge as a circular spot. (3) A concentric elliptical unevenly spaced diffraction grating that converts the emitted light beam from the semiconductor light emitting element into a parallel light beam within the lens material is formed on the surface facing the semiconductor light emitting element, and the optical fiber is connected to the optical fiber. 2. The grating lens for optical fiber coupling according to claim 1, wherein a concentric elliptical unevenly spaced diffraction grating pattern is formed on opposing surfaces to converge the parallel light beam as a circular spot. (4) The grating lens for optical fiber coupling according to claim 1, wherein the unevenly spaced diffraction grating pattern is formed as grating grooves having a sawtooth cross section on the surface of the transparent plastic base.