JPH05257034A - Connection structure between optical fiber and optical waveguide - Google Patents

Abstract

PURPOSE:To contrive a device of simple constitution which is easily manufactured and widely used to practical use by nearly tapering and putting the core of the optical fiber or optical waveguide close, and connecting the optical fiber and optical waveguide by the distribution coupling between their cores. CONSTITUTION:The tapered optical fiber core 1b is put close to the optical waveguide core 2a and coupled. The optical waveguide is a completely embedded type and in this case, the upper clad is partially peeled by etching using, for example, hydrofluoric acid to put the coupling part cores closer. In this constitution, propagation constants are matched and they are fixed where necessary coupling length is obtained, thereby obtaining complete coupling. The coupling length of this complete coupling is adjusted even to provide a multiplexing and demultiplexing function which multiplexes only light having specific wavelength.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a connecting structure for an optical fiber and an optical waveguide, and more particularly to a connecting structure for an optical fiber and a thin film optical waveguide.

[0002]

2. Description of the Related Art Conventionally, there is an optical waveguide type device having a function of branching / coupling light in an optical transmission line, multiplexing / demultiplexing, modulating, and switching of a propagation direction in an optical communication system. , The optical waveguide and the optical fiber are usually coupled by butt jointing such as a butt joint shown in FIG. 5, but the end face shape mismatch, the mode field diameter difference in the single mode, the surface at the contact surface. There was a loss due to scattering and reflection due to the difference in roughness and refractive index, which hindered efficient light transmission. Particularly in the case of single mode, in the case of mechanical contact, the connection characteristics greatly depend on the alignment at the time of joining, and each end face must be treated by polishing. On the other hand, there is also a method in which the cores are brought into close contact with each other from the side and the light is propagated, but in this case, the side end faces of each core are in direct contact bonding, so polishing is performed However, there is a problem that it is difficult to perform complete coupling as it is, means for changing the propagation constant must be provided, and the structure becomes complicated.

[0003]

SUMMARY OF THE INVENTION The present invention aims to solve these problems and to put into practical use a device that has a simple structure, is easy to manufacture, and has wide applicability. We propose a connection structure of an optical fiber and an optical waveguide in which the cores are arranged in a substantially tapered shape and are connected to each other by distributed coupling between the two cores.

[0004]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 4 show an embodiment of the present invention, FIG. 1 is a schematic side cross-sectional view of a core close-coupling type connection structure in which a core of an optical fiber is tapered, and FIG. 2 is a schematic view of both cores of an optical fiber and an optical waveguide. Schematic of the side cross section of the core close coupling type connection structure
FIG. 3 is a schematic view of a structure in which a plurality of optical fibers are connected on an optical waveguide, and FIG. 4 is a schematic view showing a propagation state of light. In each drawing, the same members are designated by the same reference numerals, 1 is an optical fiber, and 1 is an optical fiber.
a is an optical fiber core, 1b is a tapered optical fiber core,
1c is an optical fiber cladding, 2 is an optical waveguide, 2a is an optical waveguide core, 2b is a tapered optical waveguide core, 2c is an optical waveguide cladding, 2d is an optical waveguide buffer layer, 2e is an optical waveguide substrate, and 3 is an adhesive. .. 5 is a support plate,
Reference numeral 5 is an optical fiber connecting portion.

In the embodiment shown in FIG. 1, the tapered optical fiber core 1b is brought close to the optical waveguide core 2a to be coupled.
The optical waveguide 2 is a completely buried type, and in this case, the upper clad is partially removed by etching using, for example, hydrofluoric acid so that the cores of the coupling portion are close to each other. The optical fiber having the tapered optical fiber core to be used can be easily produced by heating and drawing. For example, in the case of single-mode transmission, light propagating in the LP01 mode in the optical fiber core has a small core diameter in the optical fiber, and the light leaks from the core to increase the evanescent field. The mode field diameter increases. When a part of the mode field of the evanescent wave reaches the optical waveguide core side, mode coupling occurs with the optical waveguide core, and the light moves while propagating with the optical waveguide side under a periodic condition. In order to achieve complete coupling, it is necessary to make the propagation constants of the optical fiber core and the optical waveguide core substantially the same in advance. Otherwise, incomplete coupling will result. The optical fiber is fixed at a place where the coupling length of the required branching ratio is obtained. An adhesive is used for fixing, but its refractive index is almost the same as that of the optical fiber and the optical waveguide cladding.

FIG. 2 shows a case in which both cores of the optical fiber and the optical waveguide are tapered. With such a structure, the propagation constants are matched, and fixed at a place where a required coupling length is obtained, whereby complete coupling can be achieved. .. By adjusting the coupling length by perfect coupling in this way, it is possible to provide a multiplexing / demultiplexing function in which only light of a specific wavelength is coupled.

Further, as shown in the mounting embodiment of FIG. 3, it is also possible to adopt a connection structure in which optical fiber coupling portions are provided at a plurality of locations on a single optical waveguide. In this embodiment, one optical waveguide core has two connecting portions, but the present invention is not limited to this, and an arbitrary number of optical waveguide cores can have arbitrary connecting portions. ..

FIG. 4 shows the state of the light intensity in the propagation of light in the portions A, B, and C in the embodiment of the present invention shown in FIG. 1, in which light is guided from the taper optical fiber core 1b adjacent to it. The wave gradually propagates to the waveguide core 2a. This situation is almost the same in the case of the core close coupling type connection structure in which both cores of the optical fiber and the optical waveguide are tapered as shown in FIG. Although the core has a square cross section in this embodiment, it may have a circular shape or any other shape.

[0009]

As described above, according to the optical fiber and / or the optical fiber / optical waveguide connection structure in which the cores of the optical fiber and / or the optical waveguide are arranged close to each other in a substantially tapered shape, the structure is simple and the manufacture is easy. It is possible to put into practical use a device that is easy and has wide applicability. That is, since it is the coupling of the optical fiber and the optical waveguide by the distributed coupling by the evanescent wave, it is the alignment on the side surface in the length direction, the alignment at the coupling portion is easy, and the coupling is not the coupling between the cores, Evanescent coupling between the separation cores eliminates the need for polishing and propagation constant conversion elements.
It is possible to arbitrarily adjust the coupling ratio by the coupling length, can be configured as a multiplexer / demultiplexer by adjusting the coupling length in the completely coupled state, and it is possible to provide multiple optical fiber coupling parts in one optical waveguide. In addition, since the connection is made from the upper surface, there are effects such as easy miniaturization and integration.

[Brief description of drawings]

1 to 4 show an embodiment of the present invention, and FIG. 5 shows a conventional example.

FIG. 1 is a schematic side sectional view of a core close-coupling type connection structure in which a core of an optical fiber is tapered.

FIG. 2 is a schematic side sectional view of a core close-coupling type connection structure in which both cores of an optical fiber and an optical waveguide are tapered.

FIG. 3 is a schematic view of a structure in which a plurality of optical fibers are connected on an optical waveguide.

FIG. 4 is a schematic diagram showing a propagation state of light.

FIG. 5 is a schematic view of the structure of a conventional butt joint.

[Explanation of symbols]

 1 Optical fiber 2 Optical waveguide 3 Adhesive

Claims (1)

[Claims] 1. A connection structure for an optical fiber and an optical waveguide, characterized in that the optical fiber and / or the core of the optical waveguide are arranged in a substantially tapered shape and close to each other, and are connected by distributed coupling between the two cores.