JPS62178909A - Multicore optical fiber for constant polarized wave - Google Patents

Abstract

PURPOSE:To decrease the number of intermediate layers, and to make a diameter of a clad thin by providing >=two cores in the clad, and also, providing the intermediate layer for making each waveguide generate a double refraction, in the vicinity of a core, and holding the intermediate layer in common by >=two cores. CONSTITUTION:Stress providing layers 3 which are provided by placing a core 1 between them and also provide a stress for generating a double refraction to the core 1 are provided in the vicinity of the respective cores 1 in a clad 2. Among these stress providing layers 3, that of the center is held in common by its right and left cores 1, and comparing with a conventional one in which two pieces each of stress providing layers 3 are provided against one core 1, the diameter is made thin by a portion which has omitted one stress providing layer 3. In this way, a multicore optical fiber for constant polarized wave whose diameter has been made thin by omitting partially an intermediate layer can be obtained.

Description

Detailed Description of the Invention <Industrial Application Field> The present invention relates to a multi-core quantitative wave optical fiber in which each core has constant polarization characteristics due to birefringence among multi-core optical fibers having two or more cores in the cladding. .

<Conventional technology and problems> In recent years, development of coherent optical transmission systems has been active as a countermeasure against the increasing tendency of communication information11 and for application to sensors. Demand is increasing. As a means for obtaining a constant polarization optical fiber, a method is known in which a stress applying layer that applies stress to the core is provided in the cladding to cause birefringence in the waveguide to provide constant polarization characteristics. It is also known that a cavity is provided in the cladding instead of the stress applying layer, thereby providing constant polarization characteristics ("Proposal and Analysis of Side Tunnel Optical Fiber" IEICE Technical Report Vol. 182 No.
, 1000QE82-38 (1982)).

On the other hand, with the expansion of communication networks in recent years, the number of communication terminals has increased.
Since the number of optical fibers connecting them is increasing, it is necessary to accommodate a large number of optical fibers in one cable to increase the density of optical fibers in the cable. As a means for increasing the density of optical fibers in such a cable, it is effective to increase the density of the optical fiber itself by using a multi-core optical fiber having a plurality of cores in one cladding. For example, a single-core optical fiber that has one core with a diameter of 8 μm in its cladding has a cladding diameter of about 125 μm, but a multi-core optical fiber that has two cores with the same diameter in its cladding has a cladding diameter of about 125 μm. The diameter only needs to be about 150 μm, which is much more advantageous in terms of space than using two single-core optical fibers.

However, the above-mentioned means of increasing the density of optical fibers by making them multi-core cannot be as effective even when applied to polarization-controlled optical fibers having intermediate layers such as stress-applying layers and cavities as described above. There wasn't. That is,
Since the diameter of the intermediate layer is larger than the diameter of the core, even if the core and its accompanying intermediate layer were housed in several pairs of claddings, the diameter could not be reduced to that extent.

The present invention was made in view of the above-mentioned conventional circumstances, and an object of the present invention is to provide a small-diameter multi-core polarization constant optical fiber.

<Means for Solving the Problems> The multi-core polarization constant optical fiber of the present invention has two or more cores in the cladding, and an intermediate layer that causes birefringence in each waveguide in the vicinity of the core. It is characterized in that the intermediate layer is shared by two or more cores, and by sharing the intermediate layer, the number of required intermediate layers is reduced, thereby achieving a reduction in the clad diameter to 1.

<Example> Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a sectional view showing a multi-core polarization constant optical fiber according to an embodiment of the present invention. 1 in the figure is the core,
2 is a cladding, and 3 is a stress applying layer (intermediate layer) which is disposed near the core 1 with the core 1 in between and applies stress to the core 1 to cause birefringence. The center one of these stress applying layers 3 is shared by the cores 1 on the left and right sides, and compared to the conventional structure in which two stress applying layers 3 are provided for each core 1, only one stress applying layer is provided. 3 is omitted to reduce the diameter. The major axis of the cladding 2 is 170 μm, the minor axis is 80 μm, the diameter of the core 1 is 8 μm, and the relative refractive index difference Δn between the core 1 and the cladding 2 is 0.
．． 29%, the diameter of the stress applying layer 3 is 35 μm, the distance between the core 1 and the stress applying layer 3 is 7 μm, and the refractive index of the stress applying layer 3 is equal to the refractive index of the cladding 2. In addition, the composition is that core 1 is silica glass doped with germanium, cladding 2 is
is pure silica glass, and the stress applying layer 3 is silica glass doped with boron and germanium.

According to the above configuration, the loss at cutoff wavelengths of 1.18 μm and 1.19 μm and λ=1.3 μm is 0.86 ci.
a/Km and 0.92 dB/Km, extinction ratio is 30 dB and 28 de at I Km, crosstalk between both cores 1 is 1
A dicore constant polarization optical fiber having Km of 42 do was obtained.

FIG. 2 is a sectional view showing a multi-core polarization constant optical fiber according to another embodiment of the present invention. In this embodiment, three cores 1 are provided in a cladding 2, and two stress applying layers 3 each having an oval cross section are provided in the vicinity of these cores 1. Therefore, according to this embodiment, there are two stress applying layers 3 that sandwich the core 1 from both sides and apply stress, and one core 1 has two stress applying layers 3.
The optical fiber as a whole has a smaller diameter than the conventional optical fiber in which stress applying layers are provided one after another. The diameter of the cladding 2 is 175 μm, and the diameter of the core 1 is 8 μm.

Relative refractive index difference Δn between core 1 and cladding 2 = 0.30%,
The long axis of the stress applying layer 3 is 118 μm, the short axis is 40 μm, the distance between the cores 1 is 28 μm, the distance between the core 1 and the stress applying layer 3 is 8 μm, and the refractive index of the core 1° cladding 2 and stress applying layer 3 is And the composition is the same as in the above example.

According to the above configuration, the cutoff wavelength is 1.18 μm, 1
．． 18 μm and 1.21 μm.

The loss at λ-1.3 μm is 0.85c+e/KIn.

Three-core constant polarization light beam with 0.90c+B/n and 0.88dB/Km? Iba was obtained.

FIG. 3 is a sectional view showing a multi-core polarization constant optical fiber according to another embodiment of the present invention. This embodiment is similar to the above embodiment in that the stress applying layer 3 is shared by two cores 1, but the polarization directions of these two cores 1 are set to be the same, and identification is made on the outer surface of the cladding 2. A flat surface 2a for use is provided.

According to the above configuration, when connecting two optical fibers,
The polarization directions of the cores 1 can be matched by simply aligning the planes 2a. Note that this effect can also be obtained by making the shape of the clad 2 elliptical in cross section as shown in FIG. 1, and can also be achieved by not applying a distinguishing color to the outer surface of the clad 2. .

Each of the above embodiments has shown an optical fiber having a stress imparting layer as an intermediate layer, but an optical fiber in which the intermediate layer is hollow to give constant polarization characteristics to the core 1 in the same manner as above may also be used as an intermediate layer ( The diameter can be reduced by omitting part of the hollow part.

<Effects of the Invention> According to the present invention, it is possible to create a multi-core polarization constant optical fiber whose diameter is reduced by omitting a part of the intermediate layer.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a multi-core polarization constant optical fiber according to an embodiment of the present invention, FIG. 2 is a cross-sectional view of a multi-core polarization constant optical fiber according to another embodiment of the present invention, and FIG. 3 is a cross-sectional view of a multi-core polarization constant optical fiber according to another embodiment of the present invention. FIG. 3 is a cross-sectional view of a multi-core polarization constant optical fiber according to another example. In the drawings, 1 is a core, 2 is a cladding, and 3 is a stress applying layer (intermediate layer). Patent applicant Sumitomo Electric Industries Co., Ltd. Agent Patent attorney Mitsuishi Dobe (and 1 other person) Figure 1 Figure 2

Claims (4)

[Claims] (1) Two or more cores are provided in the cladding, and an intermediate layer that causes birefringence in each waveguide is provided in the vicinity of the core,
A multi-core polarization constant optical fiber characterized in that the intermediate layer is shared by two or more cores. (2) The multi-core polarization constant optical fiber according to claim 1, wherein the intermediate layer is a stress applying layer that applies stress to the core. (3) The multi-core polarization constant optical fiber according to claim 1, wherein the intermediate layer is hollow. (4) The method according to any one of claims 1 to 3, wherein the polarization directions of all the cores are aligned and an identification surface corresponding to the polarization direction of the cores is provided on the outer surface of the cladding. Multi-core polarization constant optical fiber.