JPH0374802B2 - - Google Patents

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 a very important issue to couple a light source such as a laser diode or light emitting diode with an optical fiber without loss. The first typical method of coupling conventional light sources and optical fibers is
The one shown in Fig. 2 is known. FIG. 1 shows a beam of emitted light from a laser diode 1 converged onto the end face of an optical fiber 2 by a focusing rod lens 3, and FIG.
This makes it converge on the end face of the optical fiber 2.

In a normal heterojunction laser diode having a stripe structure, the radiation angle of the emitted light beam has anisotropy as shown in FIG. That is, the radiation angle θp of the laser diode 1 in the direction perpendicular to the substrate (y direction) is
It is larger than the radiation angle θs in the direction parallel to the substrate (x direction), and the cross-sectional shape of the emitted light beam is elliptical. The coupling method shown in Figure 2 takes into consideration only the convergence of light that spreads widely in the y direction, and the coupling efficiency is approximately 30
It will only be about %. 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 y directions, but the anisotropy of the radiation angle is not considered. The binding efficiency is approximately 60%.

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 radiation beam so that the elliptical radiation beam enters 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 shown in 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 points, and
It is an object of the present invention to provide a grating lens for optical fiber coupling, which 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.

[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 base material as a coupler that couples the emitted light 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 wavelength-order grating pitches that become smaller from the center to the periphery, the diffraction angle of each part can be gradually adjusted. The difference is that it 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 element, the first lens surface facing the semiconductor light emitting element and The lens has a concentric elliptical unevenly spaced diffraction grating pattern formed on the second lens surface facing the optical fiber. In this case, the first lens surface has a concentric elliptical unevenly spaced diffraction grating pattern that converts the emitted light from the light emitting element into a parallel light beam within the lens material, and the second lens surface has a concentric elliptical irregularly spaced diffraction grating pattern that converts the light emitted from the light emitting element into a parallel light beam within the lens material. A concentric elliptical unevenly spaced diffraction grating pattern is used as a spot to converge on the input end face of the optical fiber. Further, the focal length of the second lens surface is set to be larger than the focal length of the first lens surface. Here, "concentric ellipses" 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. .

〔Effect 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 a transparent plastic substrate using a mold machined with an ultra-high precision lathe, or by creating a replica thereof. In addition, since the focal length of the first lens surface is set to be small and the focal length of the second lens surface is set to be large, the output beam of the light emitting element with a large divergence angle can be efficiently converged onto the optical fiber with a small numerical aperture. be able to.

[Embodiments of the invention]

Prior to specific examples, a lens in which a diffraction grating pattern is formed on only one side will be described. a
For example, b is a plan view of the surface facing the laser diode side, and b is a cross-sectional view. The lens base material 5 is made of plastic such as transparent acrylic, and has an unevenly spaced diffraction grating pattern 6 formed on one surface as shown. The x and y axes in the figure correspond to the x and y axes in FIG. 3, respectively. That is, the unevenly spaced diffraction grating pattern 6
corresponds to the anisotropy of the radiation angle of the emitted light beam from the laser diode explained in FIG. 3, and has a concentric elliptical shape in which the grating pitch is smaller in the y-axis direction than in the x-axis direction. 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.
Further, the surface of the unevenly spaced diffraction grating pattern 6 is a blazed surface having a sawtooth cross section.

If this grating lens is used as a coupler between a laser diode and an optical fiber, it is possible to focus the emitted light beam with an elliptical cross section from the laser diode into a circular spot on the end face of the optical fiber, achieving high coupling efficiency. I can do it. Moreover, this grating lens can be manufactured easily and inexpensively by creating an original plate by mechanical processing using plastic and then manufacturing a replica of the original plate.

FIG. 5 shows a grating lens according to an embodiment of the present invention, which is a further improvement of the above lens, in which a and b are plan views of the surfaces facing the laser diode and optical fiber, respectively, and c is a cross-sectional view. This grating lens uses a lens base material 7 also made of transparent plastic, and has concentric elliptical diffraction grating patterns 8 and 9 formed at irregular intervals on each surface.

This grating lens differs from the previous embodiment in that the diffraction grating pattern 8 on the laser diode side converts the emitted light beam from the laser diode into a parallel light beam, and guides the light beam inside the lens substrate 7 as a parallel light beam. The light is 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 designed to take into account the anisotropy of the spread of the emitted light beam from the laser diode, and at the same time to take into account the radiation angle of the emitted light beam from the laser diode and the optical fiber. The grid pitch is set taking into account the numerical aperture. Specifically, 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.

According to this embodiment, the laser diode is
At the focal position of the lens surface, it is possible to efficiently couple the widely spread emitted light 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 having anisotropy in the spread of its emitted light beam 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 is a diagram showing a grating lens with unevenly spaced diffraction gratings formed on one side,
FIG. 5 is a diagram showing a grating lens in which diffraction gratings are formed on both surfaces of the grating according to an embodiment of the present invention. 5, 7... Lens base material, 6, 8, 9... Unequally spaced diffraction grating pattern.

Claims (1)

[Claims] 1 A lens for coupling the emitted light beam from the semiconductor light emitting element to an optical fiber, the lens is made of a transparent plastic base material, and the emitted light from the light emitting element is coupled to the first lens surface facing the semiconductor light emitting element using the lens material. A concentric elliptical non-uniformly spaced diffraction grating pattern is formed within the optical fiber to convert the parallel light beam into a parallel light beam, and a concentric elliptical diffraction grating pattern is formed on a second lens surface facing the optical fiber to converge the parallel light beam into a circular spot on the input end face of the optical fiber. A gray for optical fiber coupling, characterized in that an elliptical unevenly spaced diffraction grating pattern is formed, and the focal length of the second lens surface is set larger than the focal length of the first lens surface. Teing lens.