JPH02210406A - Optical coupling circuit - Google Patents

Abstract

PURPOSE:To allow efficient coupling of a semiconductor light emitting element and an optical fiber with high efficiency by providing a semiconductor light emitting element and a circular cylindrical hemispherical lens, the end face of which is formed to a hemispherical shape and the end face on the opposite side is fusion-spliced to the incident end of the optical fiber. CONSTITUTION:The circular cylindrical hemispherical lens 4, the 1st end face of which is formed to the hemispherical shape and the 2nd end face 3 is formed to a plane shape is fusion-spliced to the incident end face of the single mode optical fiber 5 on the optical axis of the light beam (a) outputted from the semiconductor laser 1. The light beam outputted from the semiconductor laser 1 in this constitution is condensed by the hemispherical part 7 and is coupled to the single mode optical fiber 5 fusion-spliced to the circular cylindrical hemi spherical lens 4. The optical coupling circuit which has high efficiency, is rela tively gentle in the tolerance of axis adjustment, is simple in constitution and has high reliability is obtd. in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an optical coupling circuit for optical communication for coupling an output light beam of a light emitting element to an optical fiber.

(Prior Art) An optical coupling circuit that couples output light from a semiconductor light emitting device, which is an optical signal source, to an optical fiber, which is an optical transmission line, in an optical communication system is one of the important devices in configuring the optical communication system. It is.

Conventionally, as an optical coupling circuit, for example, Appliecl Optics (1980),
One example is one using a tipped fiber described in an article by Mr. Kuwabara in Vol. 19, p. 2578. In this optical coupling circuit, a single mode fiber having a hemispherical input end is placed close to an output end of a semiconductor laser, and output light from the semiconductor laser is coupled to the single mode fiber.

(Problem to be Solved by the Invention) This optical coupling circuit has a simple configuration, but since the core of the optical fiber is formed up to the input end of the single mode fiber, the light beam reaches the input end. The problem is that the spot size at the time of incidence is very small, and the tolerance for axis adjustment of the single mode fiber is very strict. For example, when mounting a star-mode fiber, it is necessary to adjust the position of the semiconductor laser in a direction perpendicular to the optical axis with a positional accuracy within Ipm. Therefore, in practice, this optical coupling circuit poses a major problem in assembly and adjustment.

On the other hand, as an optical coupling circuit with relatively loose tolerance for optical fiber axis adjustment, there is a conventional one that uses two focusing rod lenses to couple the output light from a semiconductor laser into a single mode fiber. Since the method uses two focusing rod lenses, it has the disadvantage that the configuration of the optical coupling circuit becomes complicated.

The present invention solves the above-mentioned problems and provides an optical coupling that can couple a semiconductor light emitting device and an optical fiber with high efficiency, has a relatively loose tolerance for axis adjustment of the optical fiber, and has a simple configuration. The purpose is to provide circuits.

(Means for Solving the Problems) An optical coupling circuit of the present invention has a semiconductor light emitting element and an end face near the semiconductor light emitting element formed in a hemispherical shape, and an outer diameter of a glass portion of an optical fiber. It is characterized in that it includes a cylindrical hemispherical lens having approximately the same outer diameter and whose end face opposite to the hemispherical end face is fusion-spliced to the input end of the optical fiber.

(Function) The optical coupling circuit of the present invention has an input end face formed in a hemispherical shape instead of a conventional optical fiber having an input end formed in a hemispherical shape, and the outer diameter is the outer diameter of the glass portion of the optical fiber. It has a configuration using a cylindrical hemispherical lens that is approximately equal to , and an optical fiber that is fusion-spliced to the cylindrical hemispherical lens. In this configuration, since a cylindrical hemispherical lens is provided at the input end of the optical fiber, the distance between the core end of the optical fiber and the hemispherical portion is shorter than that of the conventional one. This makes it possible to increase the distance between the semiconductor laser and the hemispherical part.
The spot size when the light beam output from the semiconductor laser enters the hemispherical portion can be made larger than before. The tolerance of an optical fiber increases as the spot size of the light beam on its hemispherical portion increases. Therefore, the tolerance of the optical fiber fusion-spliced to the cylindrical hemispherical lens of the present invention is greater than that of the conventional one. Become.

In addition, by making the refractive index of the hemispherical portion of the present invention larger than the refractive index of the optical fiber, the acceptance angle of the hemispherical portion can be made larger than before, so the light beam can be transmitted with higher efficiency. It can be coupled to a fiber.

(Example) The present invention will be described below with reference to the drawings. 1st
The figure is a sectional view showing one embodiment of the present invention. A first end face 2 is formed in a hemispherical shape on the optical axis of a light beam with a wavelength of 1.55 pm output from the semiconductor laser 1, and a second end face 3 is formed in a hemispherical shape.
The radius of curvature is approximately 65p.
A cylindrical hemispherical lens 4 with a length of about 650 pm has a spot size of 511 m, a cutoff wavelength of 1.1 pm, and an outer diameter of 12
It is fusion spliced to the input end face of a 5 pm single mode optical fiber 5. Further, the semiconductor laser 1 is fixed on a heat sink 6 in order to emit heat. In addition, the material of the hemispherical portion 7 of the cylindrical hemispherical lens 4 has a refractive index of approximately 1.9, which is thicker than the refractive index of approximately 1.5 of the single mode optical fiber 5, in order to increase the acceptance angle. A glass material with

Note that the cylindrical portion 8 is a positional glass having a refractive index that is approximately the same as that of the single mode optical fiber 5. It is relatively easy to manufacture this cylindrical hemispherical lens 4. For example, the end face of the single mode optical fiber 5 is attached to the end face of a cylindrical member having an outer diameter approximately equal to the outer diameter of the single mode optical fiber 5. be melted by electric discharge and connected. Next, the cylindrical member is cut to a desired length. Next, by immersing the cut surface in a melt of high refractive index glass, a hemispherical portion 7 made of high refractive index glass is formed due to the surface tension of the high refractive index glass. The method for forming this high refractive index hemispherical portion 7 is described, for example, in Electronics Letters (
Electronics Letters), 1983, Vol. 19, p. 205, by KHOE, "Efficient Coupling of a High Refractive Index Spherical Optical Fiber and a Laser Die-Tote"
La5er Diodes to TaperedM
onomode fibers with High-
It is described in detail in a paper entitled Indes End). Here, the radius of curvature of 65 pm of the hemispherical portion 7 was determined as follows. First, let the distance between the output end of the semiconductor laser and the tip of the hemispherical portion 7 be a (see Figure 1), and the radius of curvature and image magnification of the hemispherical portion 7 be R and m, respectively, then the relationship between them is as follows. It can be expressed by the formula.

R(m+1)=am(nl-1) , , , , , , ,
, , , , , , , , , where nl is the refractive index of the hemispherical portion 7 . In this embodiment, the image magnification m is set to 5 based on the ratio of the spot size of the semiconductor laser 1 and the spot size of the single mode optical fiber 5, and the refractive index n1 is set to 1.9.
And so. Substituting these values into equation (2), R=0.75a , , , , , , , , , , , 01.
−−−−1−−−−1−−− ■. The distance a between the output end of the semiconductor laser and the tip of the hemispherical portion 7 becomes as large as the water valve, and the radius of curvature R becomes larger.
It becomes easy to manufacture.

However, on the other hand, when a becomes longer, the amount of the light beam taken in by the hemispherical portion 7 decreases due to the spread of the light beam, resulting in a coupling loss. FIG. 2 shows the relationship between the distance 9 and the beam spread ratio with respect to the spot size of the semiconductor laser 1. If the beam divergence ratio is about 50 or more, the amount of light beam taken in by the hemispherical part 7 will not decrease much, and if the radius of curvature R is about 50 pm or more, it can be manufactured relatively easily (see Fig. 2). (shaded area). Taking this into consideration, in this example, the radius of curvature R is set to approximately 6511
It was set as m. On the other hand, the length of the cylindrical hemispherical lens 4 was determined as follows. First, assuming that the length of the cylindrical hemispherical lens 4 is 1, the relationship with the radius of curvature R can be expressed by the following equation.

Here, n2 is the refractive index of the cylindrical portion 8, which is about 1.5, which is about the same as the refractive index of the single mode optical fiber 5. ■Substituting the value into the formula: 1,=1OR, , , , , , , , , , , , , , ,
, , , , , , , , , , ■. Since the radius of curvature R is about 65 pm, the length 1 of the cylindrical hemispherical lens 4 is about 650 μm.

The light beam output from the semiconductor laser 1 with the above-described configuration is focused by the hemispherical portion 7 and coupled to the single mode optical fiber 5 which is fusion-spliced to the cylindrical hemispherical lens 4. The tolerance in the direction perpendicular to the optical axis of the single moat optical fiber 5 in this embodiment is shown in FIG. 3 together with the case of a conventional tipped optical fiber. The amount of increase in coupling loss due to positional deviation of the single mode optical fiber 5 is very gentle compared to the case of a conventional optical fiber with a tip end, and the amount of increase in loss is 1 clB.
By the way, when comparing the conventional example and this embodiment, it can be seen that the allowable axis deviation amount is increased by about 7 times. Also,
In this embodiment, a highly efficient optical coupling circuit with a coupling loss of about 3 dB can be obtained.

In this example, the semiconductor laser 1 with an oscillation wavelength of 1.55 pm was used, but the invention is not limited to this.
．． A 3 pm band semiconductor laser may also be used.

In addition, in this embodiment, the second end face 3 is formed parallel to the plane perpendicular to the optical axis, and is fusion spliced to the input end of the single mode optical fiber 5, but the second end face 3 is formed parallel to the plane perpendicular to the optical axis, and is fusion spliced to the input end of the single mode optical fiber 5. In order to prevent light from entering, the second end face and the input end of the single mode optical fiber may be formed obliquely with respect to the optical axis, and fusion spliced. Furthermore, the first end surface 2 may be coated with an anti-reflection coating.

Further, in this embodiment, positional glass was used as the material for the cylindrical portion 8, but in consideration of the manufacturability of the hemispherical portion 7, if the radius of curvature is made larger than in this embodiment,
As the material of the cylindrical portion 8, a material having a refractive index distribution (for example, a focusing multimode optical fiber) may be used.

(Effects of the Invention) As described above, it is possible to obtain a highly reliable optical coupling circuit in which the semiconductor light emitting device and the optical fiber are coupled with high efficiency, the tolerance of the axis adjustment of the optical fiber is relatively loose, and the configuration is simple. It will be done.

[Brief explanation of the drawing]

FIG. 1 is a side view showing the configuration of an embodiment of the present invention.
Fig. 2 is an explanatory diagram for explaining the amount of beam spread, and Fig. 3 is a diagram showing the evaluation results of the amount of increase in coupling loss with respect to the amount of positional deviation of the optical fiber in the embodiment of the present invention and the conventional example. be. 1 is a semiconductor laser, 2 is a first end facet, 3 is a second
, 4 is a cylindrical hemispherical lens, 5 is a single mode optical fiber, 6 is a heat sink, 7 is a hemispherical portion, and 8 is a cylindrical portion. Diagram

Claims (2)

[Claims] (1) A semiconductor light emitting element, an end face on a side close to the semiconductor light emitting element is formed in a hemispherical shape, and has an outer diameter of a glass portion of an optical fiber; An optical coupling circuit comprising: a cylindrical hemispherical lens whose opposite end surface is fusion-spliced to an input end of an optical fiber. (2) The optical coupling circuit according to claim (1), wherein the refractive index of the hemispherical portion of the cylindrical hemispherical lens is higher than the refractive index of the glass portion of the optical fiber. optical coupling circuit.