JPH07128544A - Connecting structure for optical fiber and optical waveguide - Google Patents

Abstract

PURPOSE:To provide the connecting structure for an optical waveguide which is easily adjustable and has high reliability to optical axis misalignment by an environmental fluctuation by aligning and connecting the optical waveguide and optical fibers and simultaneously and locally heat treating the junctures thereof, then fixing the junctures. CONSTITUTION:This connecting structure for the optical waveguide 1 and the optical fibers 2 is constituted to connect the core end face of the optical fiber 2 with the incident side end face and exit side end face of the optical waveguide 1 formed in a substrate. The juncture of the optical waveguide 1 and the optical fibers 2 are simultaneously and locally heat treated in the state of connecting the junctures and are then fixed in order to expand and nearly align the mode field diameter of the junctures of the optical waveguide 1 and the optical fibers 2. The mode field diameters are simultaneously expanded, by simultaneously heating the junctures of the optical waveguide 1 and the optical fibers 2 in such a manner and, therefore, the easy connection with high efficiency is executed by rough alignment even if the optical waveguide 1 and optical fibers 2 which are previously expanded in the cores of the junctures are not prepared.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a connection structure of optical waveguide type components used for branching / combining or demultiplexing / combining light in an optical communication network.

[0002]

2. Description of the Related Art Conventionally, in order to connect an optical waveguide and an optical fiber, a butt joint method of abutting the end faces of both has been used. That is, a method is used in which the optical axis of the core through which each light passes is aligned so that the core is fixed at the position where the loss is lowest. This method can be easily connected when there is only one connection point, but has the following problems when there are many connections and the propagating light is single mode waveguide. .

[0003]

In the prior art, due to an error between the core pitch of the optical waveguide used and the core pitch of the optical fiber side (fiber array side), a power loss occurs in the propagating light, which is caused by the port. Is different.
The mode field diameter of the light propagating in the core is about 10μ.
In the order of m, the sub-micron accuracy is required as the alignment accuracy, and the sub-micron accuracy is also required for the inter-core spacing, which makes it difficult to manufacture such parts. Also, because the optical path diameter of the connection part is small,
There is a problem that the characteristics of the connection portion fluctuate due to the optical axis shift due to environmental changes such as temperature and humidity and vibration, resulting in poor reliability. Therefore, the above problem is improved by increasing the mode field diameter of the connection part, that is, by connecting the optical fiber with the core expansion fiber and the optical waveguide having the mode field diameter of the connection part expanded corresponding to the waveguide side. There is also something to try, but in this case, it is necessary to prepare the core expansion fiber and the same waveguide in advance, and each is manufactured through special processing, so it is improved but the cost is high There was a problem that it took a long time.

[0004]

SUMMARY OF THE INVENTION In order to solve these problems, the present invention provides an optical waveguide which connects the end faces of an optical fiber formed in a substrate to the end faces of an optical fiber at the incident end face and the output end face. A connection structure of a waveguide and an optical fiber, in which the both are locally heat-treated at the same time in the state where the connection is connected in order to enlarge and substantially match the mode field diameter of the connection between the optical waveguide and the optical fiber, and then fixed. The connection structure realized by is provided.

[0005]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an enlarged view showing a side surface of a connection portion of an embodiment according to the present invention, and FIG. 2 is a top view thereof. In the figures, the same parts are designated by the same reference numerals. The light may be guided in either direction. For example, light guided from the waveguide side propagates in the waveguide core as light of a mode field having the intensity distribution shown in the lower part of FIG. Incident on and propagate while expanding the mode field. After that, the flat portion of the mode field expansion region is reached, and the mode field shape shown in the lower part of FIG. 1 is obtained. In this state, this time, the incident light propagates to the fiber side core expansion region. At this time, if the shape of the waveguide-side mode field does not match the shape of the fiber-side mode field, a loss occurs due to diffraction and reflection. After that, it propagates to the optical fiber core through the transition region of the expanded fiber core portion.

Usually, in order to form such a connecting portion, an optical fiber and an optical waveguide whose cores on the end faces are enlarged are prepared in advance, but here, an ordinary optical fiber and optical waveguide are used. A method of enlarging the core of the connection part will be described with reference to FIG.

FIG. 3 shows a method of manufacturing a core enlarged portion of a connecting portion according to the present invention, which comprises an optical fiber on a fiber support, an optical waveguide whose ends are aligned and connected, and a heating source on the connecting portion. As a heating source, a gas burner, an electric heater or the like capable of locally heating. The heating temperature is about 1400 ° C. In order to make the temperature distribution due to heating uniform, it is advisable to slightly reciprocate the heating source along the optical axis. By doing so, Ge added for increasing the refractive index in the optical fiber and the optical waveguide core is diffused to the clad side, and is expanded and distributed almost in a Gaussian distribution. Thereby, the guided light propagates in a spread state. Although there is a tapered transition region between the core and the non-heated region,
If the shape is steep, diffraction causes a radiation mode,
Propagation loss increases. Therefore, it is desirable that the tapered transition region is long. For example, when the magnification of the single mode field is n times, if the length of the transition region is n ² times or more, the propagation takes place with almost no loss.

By this method, the joint mode cores of the optical fiber and the end face of the optical waveguide are heated at the same time, so that the mode field diameters of both joints can be increased at the same time.
Further, in this case, it can be applied to a structure having a large number of array fibers such as a multi-branching device, and they can be simultaneously heated and the mode field can be expanded. By expanding the mode field of the connection part, the error range of loss variation is expanded. For example, the range of fluctuation of 0.1 dB becomes n ² times when the mode field diameter becomes n times. As a result, loss fluctuation due to the error amount at the time of port connection is mitigated. Therefore, if the mode field diameter of the connection part is tripled, the connection position error range of 0.1 dB fluctuation will be 9 times the initial value, and due to the increased error range, rough alignment and connection with parts with low accuracy are possible. is there. Subsequently, the connecting portion is fixed and mounted by adhering or welding the ends.

[0009]

As described above, according to the present invention, since the mode field is simultaneously expanded by simultaneously heating the connection portion of the optical waveguide and the optical fiber, the optical waveguide and the optical fiber in which the connection portion core is expanded in advance are used. Even if you do not prepare it, you can easily achieve highly efficient connection by rough alignment.
It can also be used for structures with multiple connections, in which case
The output fluctuation between the ports due to the pitch error between cores is mitigated by the expansion of the mode field diameter, the alignment accuracy at the time of adjustment is mitigated, the component accuracy can be reduced, and the fluctuation of the loss due to the optical axis fluctuation is reduced. Therefore, it is possible to realize the connection structure of the optical waveguide which is easy to adjust and highly reliable against the optical axis shift due to the environmental change, and the manufacturing time can be shortened as compared with the conventional case.

[Brief description of drawings]

FIG. 1 is a schematic view showing an embodiment of the present invention, FIG. 1A is a side sectional view, and FIG. 1B is a view showing intensity distribution of a mode field of each waveguide.

FIG. 2 is a schematic plan view of a connecting portion according to the embodiment of the present invention.

FIG. 3 is a schematic diagram showing a method for heating a connection portion according to the present invention.

[Explanation of symbols]

1 Optical Waveguide 1a Optical Waveguide Core 2
Optical fiber 2a optical fiber core 3 heating source
4 Adhesive 5 Optical fiber support

Claims (1)

[Claims] 1. A connection structure of an optical fiber and an optical waveguide for connecting an optical fiber core end surface to an incident side end surface and an output side end surface of an optical waveguide formed on or in a substrate, respectively. In order to increase the mode field diameter by enlarging the core of the optical waveguide and each end face of the optical fiber, the optical waveguide and the optical fiber are aligned and connected, and the connecting source is heated locally at the same time by the moving heating source, and then fixed. A connection structure between an optical fiber and an optical waveguide, which is characterized by the following.