JPH02129611A - Structure for connection part of optical fiber - Google Patents

Abstract

PURPOSE:To improve the degree of allowance of position accuracy and to realize a low-loss connection by fusing and connecting a multimode optical fiber to the connection side end part of a single-mode optical fiber. CONSTITUTION:The GI type multimode optical fiber 2 and single-mode optical fiber 3 are fused and connected and then the fusion part is elongated. Then a connected and elongated part 4 is fixed to a glass substrate 5 and charged in a plastic package body 6 to manufacture the connection part 1 to the optical fibers. Therefore, when the single-mode optical fiber 3 and a light source are connected to a member to be connected such as an optical device, the multimode fiber 2 which is fused and connected to the connection side end part of the single-mode optical fiber 3 and the member to be connected are only positioned. Consequently, the degree of allowance of position accuracy is increased and the low-loss connection is made.

Description

[Detailed Description of the Invention] <Industrial Application> The present invention improves positional accuracy in connecting a single mode optical fiber, which is a transmission medium for optical signals, and connected members such as light sources and optical devices. The present invention relates to an optical fiber connection structure that significantly improves tolerance and realizes low-loss connections.

<Prior art> Waveguide type optical device, optical I! In optical devices such as integrated circuits, if a waveguide mode exists in the waveguide,
Conversion to radiation mode due to interference between these modes or slight disturbance causes noise and increased loss in specifications, degrading performance. For this reason, most of these devices are configured in a single mode, and a single mode optical fiber is also used as a transmission path. In addition, single mode optical fibers have much smaller mode dispersion than multimode optical fibers, so there is less loss during long distance transmission, making them ideal transmission lines for large-capacity trunk optical communication systems.

<Problems to be Solved by the Invention> However, single mode optical fibers have a small core diameter of 5 to 10 μm, so it is difficult to connect them to light sources and optical devices, and to connect optical fibers to each other, compared to multimode optical fibers. It has the drawbacks of being difficult and prone to connection loss.

In particular, in conventional connections between semiconductor lasers (LDs) or waveguide optical devices and single-mode optical fibers, submicron alignment accuracy is required to reduce connection loss and connect the alignment devices. There is a problem that the optical fiber is large-scale, and the positional accuracy when fixing the optical fiber is insufficient (problem with reproducibility).

Furthermore, the fixing jig for avoiding the effects of temperature and impact after fixing is thicker than the optical device itself.

For example, when connecting a conventional single mode optical fiber and an LD light source, it is not possible to achieve a low-loss connection due to the difference in spot diameter, so by making the end face spherical, the spot diameter can be matched and the coupling loss can be reduced. I'm trying. However, the increase in connection loss due to misalignment between the optical fiber and the light source is 1 d.
In order to suppress the positional deviation within B, it is necessary to suppress the positional deviation to within 0.15 μm, and alignment equipment requires a submicron precision. There are some difficult technical issues, such as having to limit the Similarly, when connecting a single mode optical fiber and a waveguide type optical device, the tolerance for alignment between the single mode optical fiber and the waveguide is 1 μm or less, making it difficult to maintain it for a long period of time and reducing reliability. The problem is that there is a lack of

The present invention has been made in view of the above circumstances, and its purpose is to significantly improve tolerance and reduce positional accuracy in connecting a single mode optical fiber to connected members such as light sources and optical devices. An object of the present invention is to provide an optical fiber connection structure that realizes a lossy connection.

Means for Solving the Problems> An optical fiber connection structure according to the present invention that achieves the above object is a connection structure between a single mode optical fiber and a connected member such as a light source or an optical device. It is characterized in that a multimode optical fiber is fusion-spliced to the connecting end of a one-mode optical fiber.

When the optical fiber connection structure according to the present invention is adopted,
When connecting a single mode optical fiber to a member to be connected such as a light source or an optical device, alignment of the multimode fiber fusion spliced to the connecting end of the single mode optical fiber and the member to be connected. Since it is only necessary to shift the positional accuracy, the tolerance for positional accuracy is wide (and at the same time, a low-loss connection is realized.

That is, since a multimode optical fiber that is fusion spliced to a single mode fiber has a large NA (numerical aperture), the allowable range of the splicing position is wider than that of a single mode optical fiber. In this case, for example, the positional shift limit for reducing the connection loss with the LD light source to 1 dB or less is about 10 μm.

In addition, in order to reduce the loss at the part where a single mode optical fiber and a multimode optical fiber are fusion spliced, for example, a grated optical fiber is used as the multimode optical fiber, and the core with the single mode optical fiber is Reduce the difference in diameter (
do it. Additionally, in this case, the loss can be reduced by stretching the fusion splice between the single mode optical fiber and the multimode optical fiber or at least one location near the fusion splice on both sides in the longitudinal direction. . this is,
For example, when a section of multimode optical fiber is stretched, the multimode signal is converted to a low mode signal, and when a section of single mode optical fiber is stretched, the signal propagating in the cladding is converted to the core. This is thought to be due to the action of being collected inside. Note that such stretching may be performed after fusion splicing the optical fibers, or fusion splicing may be performed after stretching.

Embodiment Examples The present invention will be described in more detail below with reference to the drawings.
The embodiments disclosed below are merely illustrative of the present invention;
They are not intended to similarly limit the scope of the invention.

(Example 1) The optical fiber connection portion 1 shown in FIG. 1 was produced in the following procedure. Δ=0.3%, core diameter 50μm, cladding outer diameter 1
25μm GI type multimode optical fiber 2 and Δ=0.3%
After fusion splicing a single mode optical fiber 3 with a core diameter of 8 μm and a cladding outer diameter of 125 μm, the fused portion was stretched until the outer diameter became about 25 μm. Next, the connection/extension part 4 is fixed to the glass substrate 5, and the plastic mounting body 6 is
It was enclosed in. Here, the multimode optical fiber was cut so that the end surface became a mirror surface at a position approximately 3 (1) away from the center of the stretched portion.

Note that the length of the single mode optical fiber 3 was approximately 2 m.

A splice loss measurement test between an LD light source 7 with a wavelength of 1.3 μm and a single mode optical fiber 3 using the optical fiber type splicing element 1 was conducted using the method shown in FIG. The end of the single mode optical fiber 3 is connected to the photodetector 8, the connection part 1 is fixed to the fine movement table 9, and the other end of the multimode optical fiber 2 is butted against the LD light source 7 to measure the change in connection loss due to relative position. It was measured. Here, 10 is a ball lens.

The measurement results are shown in FIG.

As shown in Figure 3, the connection loss at the optimum position is 2.
It was 0dB. Further, the loss increase due to an axis deviation of ±15 μm in the direction perpendicular to the optical axis from that position was within 1 dB. This result shows that in the case of a connection using only a conventional single mode optical fiber, the increase in connection loss due to misalignment is reduced by 1 dB.
This is extremely stable compared to the case where it was necessary to suppress the positional deviation to within 0.15 μm.

Furthermore, ten parts in which an LD light source and a single mode optical fiber were connected were manufactured using this element, and in all cases, the connection loss was stable at 2.3 dB or less.

(Example 2) An optical fiber connection portion was produced using the following procedure. Example 1
After fusion-splicing the multimode optical fiber and the single-mode optical fiber used in the above, the single-mode optical fiber was stretched from the fused portion to an outer diameter of about 10 μm. Thereafter, the fused portion and the stretched portion were fixed to a glass substrate in the same manner as in Example 1, and then sealed in a plastic package. This was made into an optical fiber type connecting element. Here, the multimode optical fiber was cut so that the end surface became a mirror surface at a location approximately 3 cm from the center of the stretched portion. The length of the single mode optical fiber was approximately 2 m.

Using this optical fiber connection part, the wavelength 1
．． A connection test was conducted between a 3 μm LD light source and an optical fiber. That is, the end of a single mode optical fiber is connected to a photodetector, the connecting part of the optical fiber is fixed to a fine movement stage, and the other end of the multimode optical fiber is butted against an LD light source to measure the change in coupling loss depending on the relative position. did. The results are shown in FIG.

As shown in Figure 4, the connection loss at the optimum position is 2.
It was 1 dB. In addition, the increase in loss due to a positional deviation of ±13 μm in the direction perpendicular to the optical axis from that position was within 1 dB, which was very stable.

(Example 3) An optical fiber connection portion 1a was produced by the following procedure. After fusion splicing the single mode optical fiber used in Example 1 and a GI type multimode optical fiber with Δ=0.3% and a core diameter of 30 μm and a clad outer diameter of 125 μm, the spliced portion was heated for fusion splicing. Reinforced with shrink tubing. Next, the multimode optical fiber was cut 2 minutes from the fusion part so that the end surface became a mirror surface. Note that the single mode optical fiber length was 2 m.

As shown in FIG. 5, using a 1.3 μm LD light source 7a,
The above connection part 1aii! It was fixed on a fine movement table 9a, and the connection loss of the optical signal with the silica glass linear waveguide 11 was measured. In addition, in the figure, 8a is a photodetector. This measurement result is
As shown in the figure.

As shown in Figure 6, the connection loss at the optimum position is 2.
It was 5 dB. Furthermore, the effect of axis deviation in the direction perpendicular to the optical axis from that position was very stable, with loss increasing within 1 dB even with a variation of ±10 μm.

<Effects of the Invention> As described above, if the optical fiber connection structure according to the present invention is adopted, it is possible to connect a single mode optical fiber to a semiconductor laser, a single mode optical waveguide device, or other single mode optical fiber, etc. When connecting the connected members of When the connection part structure of the present invention is used to connect a single mode optical element and a multi-core single mode optical fiber or to connect multi-core single mode optical fibers, an arrayed single mode optical component can be formed. implementation becomes extremely easy.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram showing the splicing structure of an optical fiber according to Example II of the present invention, Fig. 2 is an explanatory diagram showing a splice loss variation system using the same, and Fig. 3 is a graph showing the measurement results. , FIG. 4 is a graph showing the measurement results of splice loss changes in Example 2, FIG. 5 is an explanatory diagram showing the splice loss system in Example 3, and FIG. 6 is a graph showing the measurement results. In the drawings, 1.1a is a connection part, 2 is a multimode optical fiber) 3 is a single mode optical fiber, 4 is a connection/extension part, 5 is a glass substrate, 6 is a plastic mounting body, 7.7a is a 1.3 μm LD A light source, 8.8a is a photodetector, 9.9a is a fine movement table, 10 is a spherical lens, and 11 is a silica glass linear waveguide.

Claims (1)

[Claims] A structure for connecting a single mode optical fiber to a member to be connected such as a light source or an optical device, characterized in that a multimode optical fiber is fusion spliced to the connecting end of the single mode optical fiber. Optical fiber connection structure.