JPS63152190A - Mode field conversion type semiconductor laser - Google Patents

Abstract

PURPOSE:To achieve improvement of the coupling efficiency with an optical fiber without using a complex optical system by making the refractive index waveguide take a predetermined shape. CONSTITUTION:A waveguide, formed by an active layer 1 and having a rectangular entrance end face, of a semiconductor laser 5 provided with a mode field conversion part 7 has a circular exit end face 3 on the conversion part 7 side. And, in the conversion part 7, a refractive index waveguide 4 is formed in which the rectangular part and the circular part are smoothly coupled, whereby the coupling efficiency with an optical fiber is enhanced without using a complex optical system.

Description

Detailed Description of the Invention Overview A semiconductor laser has a circumferential surface that connects a rectangular incident surface and a circular exit surface opposite to a rectangular active layer end surface with a continuous curved surface, and a mode field at the active layer end surface. The present invention provides a mode field conversion type semiconductor laser which has a converting section having a waveguide that converts a circular mode field into a circular mode field, and which has a high coupling efficiency to an optical fiber.

FIELD OF THE INVENTION The present invention relates to the structure of a semiconductor laser having rectangular active layer end faces.

In the field of optical communications that has been put to practical use, semiconductor lasers are generally directly modulated with time-series electrical signals, and this modulated light is guided to an optical fiber as a transmission path. Therefore, in terms of transmission loss, the higher the intensity of <Oi; On the other hand, in consideration of the life of the semiconductor laser, it is desirable to operate the semiconductor laser at a predetermined upper limit optical output power value or less, and therefore, it is necessary to efficiently input the output light of the semiconductor laser into the optical fiber.

BACKGROUND ART FIG. 3 schematically shows the general structure of a conventional buried semiconductor laser. In the figure, 11 is the active layer, 1
2 represents an n-type semiconductor material, 13 represents an n-type semiconductor material, and 14 represents an electrode.

The end face shape of the active layer 11 serving as a light emitting portion is usually an elongated rectangle, and its near-field image A is approximately elliptical with a major axis in the width direction of the active layer 11, as shown in FIG. On the other hand, regarding the spread of the emitted light, the spread in the thickness direction of the active layer 11 is larger than the spread in the width direction. A lens system causes the emitted light to enter the core of an optical fiber having a circular cross section.

Problems to be Solved by the Invention However, using the above-mentioned special optical system requires complicated assembly and adjustment work, and due to the astigmatism of the lens system, it is not always possible to achieve sufficient coupling efficiency ( There is a problem in that the ratio of the power of light entering the optical fiber to the total power of light emitted from the semiconductor laser may not be obtained.

The present invention was created in view of these problems, and its purpose is to provide a mode field conversion type semiconductor radar that improves coupling efficiency to an optical fiber without using a complicated optical system. be.

Means for Solving the Problems The problem with the prior art described above is that in a semiconductor laser having a rectangular active layer end face, a rectangular entrance face and a circular exit face facing the active layer end face are formed of continuous curved surfaces. This problem is solved by integrally providing a converting section having a refractive index waveguide that is connected at the peripheral surface and converts the mode field at the end face of the active layer into a circular mode field.

In the seven-field conversion type semiconductor laser of the present invention, the light emitted from the rectangular end face of the active layer is incident from the rectangular entrance surface of the refractive index waveguide and then passes through the circular exit surface. When propagating to , it is transformed into a circular mode field. Therefore, the optical fiber concentric with the exit surface of the refractive index waveguide =
By arranging the end face 17 to face the output surface, the semiconductor laser and the optical fiber can be efficiently coupled without using a lens system.

Embodiments Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

FIG. 1 shows a front view (a) and a side view (b) of a mode field conversion type semiconductor laser according to a preferred embodiment of the present invention.
, and a rear view (C). 1 is an active layer of a semiconductor laser 5, and this active layer 1 has a rectangular end face.

4 is a refractive index waveguide extending from the active layer 1 . As schematically shown in FIG. 2, the entrance surface 2 of the refractive index waveguide 4 on the active layer 1 side is rectangular like the active layer 1, and the side opposite to the active layer 11 of the refractive index waveguide 4 The output surface 3 of is circular. The refractive index waveguide 4 has a peripheral surface 6 consisting of a continuous smooth curved surface connecting the entrance surface 2 and the exit surface 3, and the refractive index inside thereof has a predetermined distribution in the longitudinal direction and the cross-sectional radial direction. is doing. The refractive index distribution is such that the intensity distribution in any radial direction of the exit surface 3 of the light that has propagated through the refractive index waveguide 4 and reached the exit surface 3 becomes a Gaussian distribution, that is, connected in a single transverse mode. Pump optical fiber 1f
It is desirable to set it so that Note that the refractive index outside the circumferential surface 6 of the refractive index waveguide 4 is lower than that of the refractive index waveguide 4, and the mode field conversion section 7 including the refractive index waveguide 4 is located inside the refractive index waveguide 4. Contain light.

When forming the active layer 1 on a semiconductor substrate, the refractive index waveguide 4 is formed by either avoiding crystal growth on the semiconductor substrate together with the active layer 1, or by making the position where the refractive index waveguide 4 is to be formed hollow in advance. After that, it may be formed to have a predetermined refractive index distribution by normal mass transfer means, heat treatment, etc.

The light amplified within the active layer 1 has different intensity distributions in the horizontal (left-right direction in Figure 1(a)) transverse mode and the vertical (up-down direction in the same figure) transverse mode; Although unsuitable for coupling to the core of the fiber,
When the light propagates through the refractive index waveguide 4 and is emitted from the output surface 3, it becomes a circular mode field, that is, the intensity distribution in any diametrical direction of the output surface 3 becomes the same Gaussian distribution.

Therefore, by placing an optical fiber (not shown) having a core diameter equal to or larger than that of the output surface 3 in close contact with the output surface 3, the semiconductor laser 5 and the optical fiber can be coupled with high coupling efficiency. It is.

Effects of the Invention As detailed above, according to the present invention, there is provided a mode field conversion type semiconductor laser which has a relatively simple configuration and improves coupling efficiency to an optical fiber without using a complicated external optical system. This has the effect of making it possible to provide the following.

[Brief explanation of the drawing]

FIG. 1 is a front view (a) and a side view (b) of a mode field conversion type semiconductor laser showing a preferred embodiment of the present invention.
, and a rear view (C), FIG. 2 is a schematic perspective view of the refractive index waveguide of the mode field conversion section, and FIG. 3 is a diagram not schematically showing the structure of a conventional general semiconductor laser. , FIG. 4 is an explanatory diagram showing a near-field image of the same semiconductor laser. 1.11... Active layer, 4... Refractive index waveguide, 5...
- Semiconductor laser, 7... mode field conversion section. (a) (b) (C) Front view of the sword (q), opening (b), and armpit of the present invention. ω-ku (c) Fig. 1 2: Nirishikigen 3: Resistance to lead 4:

Claims (1)

[Claims] In a semiconductor laser having a rectangular active layer (1) end face, a rectangular face (2) formed on one end face and facing the active layer (1) end face, and a circular face formed on the other end face. A conversion section (4) in which a waveguide (4) having a surface (3) and a peripheral surface connecting the square surface (2) and the circular surface (3) with a continuous curved surface is formed.
7) is integrally provided, and converts the mode field at the end face of the active layer (1) into a circular mode field.