JPS60221710A - Branching method of multicore optical fiber - Google Patents

Abstract

PURPOSE:To branch the multicore optical fiber stably by specifying respective refractive index distributions of two kinds of cascaded distributed index rod lens as principal constituent elements of a demultiplexing part. CONSTITUTION:The multicore optical fiber 3 and a single-core optical fiber 5 are connected mutually by using two kinds of distributed index rod lens 4 and 4'. Refractive index distributions of those rod lenses 4 and 4' are specified as shown by equations I and II. In the equations, n0 is a maximum refractive index, A1 and A2 are different refractive index constants, and (r) is the radius of the rod lenses. Then, when lengths of the rod lenses 4 and 4' are denoted as l1 and l2 and a quarter as long as a snaking period, namely, when l1=pi/2(A1)<1/2> and l2=pi/2(A2)<1/2>, an image on an end surface of one rod lens 4 is magnified and formed on an end surface of the other rod lens 4' to (A1/A2)<1/2>.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a method for branching optical signals of each core of a multi-core optical fiber.

[Prior art and its problems] Figures 1 (tL) and (6) illustrate a multi-core optical fiber in a cross-sectional view.

In the figure, 1 is the core, 2 is the cladding layer,
An optical fiber consisting of a core 1 and a cladding layer 2 is usually made of quartz glass, and as shown in the (tL) figure,
There is one in which the cladding layers 2 of a plurality of optical fibers are fixed to each other in a planar shape, and there is one in which the cladding layers 2 of a plurality of optical fibers are fixed to each other in a bundled state as shown in the figure. .

Such multi-core optical fibers are important because they further enhance the advantages of optical fibers, such as light weight and small diameter, and can realize high-density optical fiber cables.

However, since multi-core optical fibers have multiple cores integrated into one, special methods are required to separate and extract the optical signals propagating through each core, or to branch and connect them to separate optical fibers. technology is required.

The branching method that has been proposed so far is to first change the cross-sectional dimensions of the multi-core optical fiber into a tapered shape, make one side the same size as the multi-core optical fiber to be connected, and make the other side similar in core arrangement. There is a method using a tapered branching multi-core optical fiber having the same cross-sectional shape as the cross-sectional shape of a plurality of single-core optical fibers arranged so as to have the same dimensions.

However, the use of a multi-core optical fiber having such a shape requires strict dimensional accuracy at both ends, making it extremely difficult to manufacture.

;'j By enlarging the end face of a multi-core optical fiber to an appropriate magnification with a lens and focusing it on the end face of a single-core optical fiber whose cores are arranged in a similar manner,
A branching method in which each core corresponds to another may also be considered.

However, in this case, the image magnification depends on the distance between the lens and the end face of each optical fiber, and in order to prevent leakage between the cores, the end face of the optical fiber must be placed precisely at the imaging position. Because it is essential to It cannot be called a branching method.

[Disclosure of the Invention] The present invention solves the above-mentioned drawbacks of the prior art and provides a method for branching a multi-core optical fiber that can be easily produced and handled.

FIG. 2 shows the configuration of a branch section according to the invention.

The main components of the branch section are two types of gradient index rod lenses 4 and 4' connected in series.

Here, each refractive index distribution is approximately ', but no
is the maximum refractive index, AI+A2 is the different refractive index distribution constant, r
indicates the radius of the rod lens, and if the length of each rod lens Ql and Q2 is formed to be 1/4 of the meandering period, that is, Q+=π/25+ + Q2:π/2, then the third As shown in the figure, the image on the end surface of one rod lens 4 is magnified by a factor of F and formed on the end surface of the other rod lens 4'.

The reason for the above is as follows. Usually, the refractive index distribution of the rod lens R has a nearly parabolic distribution, as shown in FIG. This is expressed as a mathematical formula. Now, considering the trajectory of the light source traveling inside this rod lens R, the fifth
As shown in the figure, in the case of a rod lens with meandering A '' A +, the length 91 is 1/4 of the meandering period, Q + = □ 0 In the case of a rod lens with A = A2, the length 91 is 1/4 of the meandering period The length Q2 is Q2=2.

2r revision Therefore, as shown in FIG. 3, the end face of the multi-core optical fiber 3 is brought into close contact with the end face of one rod lens 4, and the core of the multi-core optical fiber is placed on the end face of the other rod lens 4'. If the single-core optical fibers 5 are arranged and closely connected in a shape similar to that of the convex i times the convexity, the individual cores will have a one-to-one correspondence, so the propagation of each core will be The optical signals can be separated and extracted.

[Effect λ] In the implementation of the branching method according to the present invention, the component parts are 2
It is only a kind of graded refractive index rod lens and can be produced extremely easily.

When connecting an optical fiber, it is only necessary to bring the end face of the optical fiber into close contact with the end face of the rod lens, so there is no need to adjust the position in the axial direction. Furthermore, by injecting a refractive index matching liquid between the end faces, Fresnel reflection can be prevented.
Loss can be reduced.

Furthermore, since the imaging magnification is determined only by the relationship between the refractive index constants of the two rod lenses, it is extremely stable.

As described above, the present invention allows multi-core optical fibers to be easily and stably branched using a simple splitter.

[Brief explanation of drawings]

FIGS. 1(^) and 1(6) are cross-sectional views of examples of multi-core optical fibers. FIG. 2 shows the configuration of a branch section according to the invention. FIG. 3 is an explanatory diagram of the principle using two rod lenses. FIG. 4 shows the internal refractive index distribution in the cross section of the rod lens. FIG. 5 is an explanatory diagram showing a light source locus. DESCRIPTION OF SYMBOLS 1... Core, 2... Clad layer, 3... Multicore optical fiber, 4.4'... Gradient index rod lens, 5... Single core optical fiber. Agent, Patent Attorney Hidemi Aoki W1 Figure (a) (b') Inori Figure 3

Claims (2)

[Claims] (1) Different refractive index distribution constant A1. Due to A2, the refractive index-ship distribution is approximately n(r)=no(1+A+r')
and r is the lens radius), and the lengths of the rod lenses are π/2a1 and π/2a1, respectively, and the end face of a multi-core optical fiber is connected to one end. The method is characterized in that single-core optical fibers are arranged and closely connected at the other end in a shape that is similar to the core arrangement of the multi-core optical fiber and has a convexity i times the size. A method for branching multi-core optical fibers. (2) A method for branching a multi-core optical fiber according to claim 1, characterized in that a refractive index matching liquid is injected between the end faces.