JPH11218649A - Optical coupling device with beam shaping function and laser diode module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical coupling device which has both a light converging function and a beam shaping function and eliminates the need to adjust the assembly position of a lens and is superior in long-period stability by providing a concave cylindrical surface on one end surface of a converging rod lens and a convex cylindrical surface which operates coaxially with the above concave cylindrical surface on the other end surface. SOLUTION: The incidence end surface 2 of the converging rod lens is formed into the concave cylindrical curved surface which operates at right angles to the major axis of the elliptic cross section of an incident beam 4 and the output end surface 3 is formed into the convex cylindrical curved surface which operates axially. The radii of curvature of the concave and convex surfaces are so set that the beam waist positions of the major and minor axes of the beam cross section meet each other and the sectional shape at the beam waist position is circular. Consequently, an incident elliptic parallel beam 4 has the same beam waist position as to the major and minor axes and is optically coupled with a single-mode optical fiber 6 with high efficiency.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser diode module for optical communication on which a laser diode having a cross-sectional shape of emitted divergent light is elliptical or elliptical, and an optical system thereof. The present invention relates to an optical system having a beam shaping function of shaping a beam section into a substantially circular shape.

[0002]

2. Description of the Related Art In order to efficiently couple output light from a laser diode to an optical fiber, divergent light emitted from the laser diode is focused by an optical system such as a lens, and the sectional shape of the focused light at the beam waist is adjusted. It is important to have the same size and circular shape as the mode field diameter of the optical fiber.

When a lens having a center axis symmetrical, such as a spherical lens or a converging rod lens, is used, the output light of a laser diode having an elliptical or elliptical cross section of emitted divergent light is approximately equal to the mode field diameter of the optical fiber. Even when the beams are focused to the same size, the cross-sectional shape of the focused light at the beam waist remains a circle or an ellipse, and the difference between the shapes increases the coupling loss. In order to reduce the coupling loss, an optical system having a function of shaping the beam cross section into a circle is required.

[0004] As a conventional focusing lens with a beam shaping function, two cylindrical lenses are arranged to face each other and are coupled so that their axes are orthogonal to each other. There is an example in which high coupling efficiency is obtained by matching the shape of the fiber core (Japanese Patent Laid-Open No. 57-176014).

[0005]

In the above conventional example, two
In order to arrange the opposed cylindrical lenses so that their axes are orthogonal to each other, it is necessary to adjust the assembling position.
In addition, since the two cylindrical lenses are bonded and fixed with a transparent adhesive, time required for fixing is required,
The adhesive fixing portion adversely affects the long-term stability of the optical system.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned conventional problems. When a laser diode having an elliptical or elliptical cross-sectional shape of emitted divergent light is used, both a light condensing function and a beam shaping function are provided. It is an object of the present invention to provide an optical coupling device having excellent long-term stability without having to adjust the lens assembly position.

[0007]

SUMMARY OF THE INVENTION An optical coupling device according to the present invention couples an incident beam to a single mode optical fiber with high efficiency. For a focusing rod lens having a focal length such that the spot size at the beam waist position of the major axis of the elliptical cross section of the incident beam coincides with the mode field diameter of the single mode optical fiber, the incident end face of the lens is changed to the elliptical shape of the incident beam. With a concave cylindrical shape acting on an axis perpendicular to the long axis of the cross section,
The output end surface is a convex cylindrical curved surface acting on an axis in the same direction as the incident end surface. The radius of curvature of each of the concave surface and the convex surface is set such that the beam waist positions of the major axis and the minor axis of the beam cross section match, and the beam cross section at the beam waist position is circular.

That is, according to the above means, the incident end surface of the lens is a concave cylindrical surface acting on the axis perpendicular to the major axis of the elliptical cross section of the incident beam, so that the incident angle is diffused only in the direction perpendicular to the major axis. Acts as if it were increased on the side, so that the major and minor axes of the beam cross section at the output end face have the same dimensions. Further, by making the output end face a convex cylindrical face acting on the same axis as the concave cylindrical face, it acts so as to correct the convergence angle of the axis orthogonal to the long axis after passing through the output end face so as to match with the long axis direction. . Correcting the convergence angle is equivalent to correcting the beam waist position and the beam cross-sectional dimension at the beam waist.
As described above, one lens has both the focusing function and the beam shaping function. In addition, since the lens is integrally shaped and the fixed part is eliminated, adjustment of the assembly position is unnecessary,
Excludes effects on long-term stability.

[0009]

FIG. 1 is a top view of an embodiment of the present invention.
(A) and a side view is shown in FIG. 1 (b). The lens body 1 is a refractive index distribution type focusing rod lens, and has a central axis refractive index of 1.595, a refractive index distribution constant of 0.333, and a lens length of 3.573 mm at a wavelength of 980 nm. The light incident end face 2 has a concave cylindrical shape, and the output end face 3 has a convex cylindrical shape. Curved surface direction is incident end face 2
And the output end face 3 are arranged to act on the same axis,
The radii of curvature are 0.695 mm and 1.253 mm, respectively. The dotted line indicates the locus of the beam 4. The incidence end face 2 has a wavelength of 980 nm, a cross section of a vertically long ellipse and a major axis diameter of 0.490.
mm and a parallel beam having a minor axis diameter of 0.152 mm.

At this time, the minor axis of the elliptical cross section is made to coincide with the direction in which the curvature of the incident end face 2 acts. The long axis of the incident parallel beam is converged by the lens body 1 having a refractive index distribution and condensed on the beam waist 5. The short axis of the incident parallel beam is once converted into a diverging beam by the concave cylindrical surface of the incident end surface 2, and is converted into converged light when passing through the lens body 1 having a refractive index distribution, and reaches the output end surface 3.

Although the beam cross-sections of the major axis and the minor axis at the output end face 3 are almost the same, the focusing angles are different. When the output end face 3 is a plane, the beam converging angles are different, so that the beam waist position and the cross-sectional diameter dimension of the long axis and the short axis are different, and this difference causes an increase in coupling loss with the single mode optical fiber 6. .

In the case of this embodiment, the converging angle of the short axis is corrected by the convex cylindrical shape of the output end face 3 so as to match the converging angle of the long axis. As a result, the incident elliptical parallel beam has the same beam waist position in both the long axis and the short axis, has a cross-sectional diameter almost the same as the mode field diameter of the single mode optical fiber 6, and has a high efficiency with the single mode optical fiber 6. Optical coupling.

[0013]

According to the present invention, there are two functions, that is, a function of converging an elliptical parallel beam to one lens to a cross-sectional diameter dimension substantially equal to the mode field diameter of a single mode optical fiber, and a function of shaping the beam into a substantially circular shape. And the effect of improving the coupling efficiency to the single mode optical fiber is obtained. In the embodiment of the present invention, a coupling efficiency approximately 20% higher than that obtained by using a gradient index focusing rod lens having a flat end face was obtained. Further, there is no need to bond and fix a plurality of lenses, and it is not necessary to adjust the assembling position. Further, since there is no adhesive portion, there is an effect of improving long-term stability.

[Brief description of the drawings]

FIG. 1 is a top view of an optical coupling device according to an embodiment of the present invention (a).
And a side view (b).

[Explanation of symbols]

1 ... lens body, 2 ... entrance end face,
3 ... Outgoing end face, 4 ... Beam, 5 ...
Beam waist, 6 ... Single mode optical fiber.

Claims (3)

[Claims] A converging rod lens has a concave cylindrical surface on one end surface and a convex cylindrical surface acting on the same axis as the concave cylindrical surface on the other end surface, so that one lens has an optical system. And a function of shaping the cross-sectional shape of the converged light into a specific shape. 2. A laser diode in which the cross-sectional shape of the emitted divergent light is elliptical or elliptical, a collimator lens for converting the divergent light emitted from the laser diode into parallel or pseudo-parallel light, and focusing the parallel or pseudo-parallel light. A laser diode module having an optical system including a focusing lens to be focused and an optical fiber in which the focused light is optically coupled, wherein the laser diode and the optical system are housed in the same case and fixed.
A laser diode module using the optical coupling device according to claim 1 for the condenser lens. 3. An optical system comprising a laser diode having a cross-sectional shape of an emitted divergent light having an elliptical or elliptical shape, a focusing lens for focusing the emitted divergent light of the laser diode, and an optical fiber for optically coupling the focused light. A laser diode module comprising a laser diode module and the optical system housed and fixed in the same case, wherein the optical coupling device according to claim 1 is used for the condenser lens.