JPH0394207A - Branching state variable type optical coupler - Google Patents

Abstract

PURPOSE:To vary a branching state by uniting plural waveguides in an axially coupled state integrally with an extensible member. CONSTITUTION:Clads 16 and 17 whose flanks are cut are joined to constitute the coupling part 12 of two optical fibers so that cores 18 and 19 are made close to each other in the section. Here, the waveguides in the axially coupled state are united integrally with the extensible member. Then, the waveguides are extended or contracted to vary the coupling length of the waveguides, so the branching state is variable.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to an optical coupler used in the field of optical communication and measurement;
In particular, it relates to an optical coupler that couples optical fibers and makes the branching state variable.

(Prior art) Conventionally, as an optical coupler using optical fibers, a piconical optical fiber coupler is used in which two optical fibers are fused and stretched, and branching is performed by changing the refractive index of the medium surrounding the fused part. There are known methods that change the ratio, and methods that change the branching state by changing the distance between the cores of two optical fibers.

The optical switch using an optical fiber coupler described in U.S. Pat. No. 4,786,130 is of the former type, and as shown in the schematic diagram of FIG. As the medium 64 surrounding the coupling portion 63, a medium whose refractive index changes depending on temperature, such as silicone oil or liquid crystal, is used. By controlling the temperature of the medium using the heater 65 and changing the refractive index of the medium, the branching ratio of the optical coupler can be changed. In this method, the refractive index of the medium surrounding the fused portion is controlled by temperature, so the response speed is delayed and is not practical.

FIG. 7 shows a system in which the branching state is changed by changing the distance between the cores of two optical fibers. The figure (A) is a schematic diagram, and the figure (B) is a sectional view taken along line B-B. In the figure, 71.72 is an optical fiber, 73.74 is a cladding, and 75.76 is a core. As is clear from Figure (B), the side surfaces of the claddings of both optical fibers are polished and the cores are brought into close contact with each other. Therefore, a state of optical coupling occurs between the cores, and optical energy from one optical fiber is branched to the other optical fiber. Since the energy to be split depends on the distance between the cores, the distance between the cores can be changed by moving one optical fiber relative to the other at the contact point, as shown in Figure (C). This makes the branch state variable.

This method has a difficulty in realizing a mechanism for controlling the movement of the optical fiber, and it is difficult to ensure good accuracy.

(Problems to be Solved by the Invention) The present invention has been made in view of the above-mentioned circumstances, and has been made for the purpose of providing an optical coupler that can vary the branching state based on a completely different principle from the above-mentioned system. It is something.

(Means for Solving the Problems) The present invention is a variable branching state optical coupler, characterized in that a plurality of waveguides coupled in the axial direction and a stretchable member are integrated. be.

Multi-fibers having two or more cores in one cladding can be used as the plurality of waveguides.

As the expandable member, a cylindrical member that expands and contracts in the radial direction can be used, and the waveguide can be wound in the circumferential direction of the cylindrical member.

A multi-fiber can be used as the waveguide in this case.

An electrostrictive material or a magnetostrictive material can be used as the expandable and contractible member.

The optical coupler can be constructed by using a stretchable member as a member for fixing the optical fiber coupler in which a plurality of optical fibers are fused and stretched.

(Function) When the two waveguides 51 and 52 are arranged in parallel as shown in Fig. 5, the coupling constant C(h) of the two waveguides is 2πn1 aV2 {K, (W)} 2. expressed.

Here, λ: wavelength a: core diameter n1: core refractive index W: normalized frequency V"=kn12a2-2Δ k=2π/λ Ko, K,: Bessel function of the second kind Δ= (no2-n2)/( 2no''): This is the relative refractive index difference between no and n.

Let the bond length be L, and C0 be Then, the branching ratio is Branching ratio=P1/P. = sin2(CoL).

That is, it can be seen that the branch state is largely dependent on the bond length L.

Therefore, the present invention expands and contracts the waveguides by integrating a plurality of waveguides that are coupled in the axial direction with an expandable member, and changes the coupling length in the waveguides, thereby making the branching state variable. This is something that can be done.

(Embodiment) FIG. 1(A) is a perspective view for explaining an embodiment of the variable branching ratio optical coupler of the present invention, and FIG. 1(B) is an enlarged cross-section of the optical fiber at the coupling part. It is a diagram. In the figure, 1
0.11 is two optical fibers, 12 is a coupling part, 13 is a cylindrical piezoelectric element, 14 is an outer electrode, and 15 is an inner electrode. The end of the optical fiber is shown enlarged.

As shown in Figure (B), the coupling portion 12 of the two optical fibers is constructed by joining the cladding 16.17 with the side surfaces shaved off, and forming a cross section in which the core 18.19 is brought close to each other. There is.

The details will be explained with reference to FIG. As shown in Figure (A), the fragmented structure of each optical fiber at the coupling portion has a cladding diameter of 125 μm, a core diameter of 8 μm, and a distance between the shaved surface and the core center of 8 μm. This optical fiber with a broken structure is 1
．． After polishing one side of the base material of the 3 μm band communication optical fiber, it was drawn, and 300 mm was heat-fused (B
) Multi-fiber as shown in the figure was used. After polishing, heat fusion may be performed, and then wire drawing may be performed.

This optical fiber was wound around a piezoelectric element having an outer diameter of 20 mm and an inner diameter of 15 mm and made of a material mainly composed of lead zirconate titanate, with at least two ends thereof being glued. The outer diameter of this piezoelectric element can be changed by 1 μm by applying a voltage IV, and FIG. 3 shows the results of measuring the branching characteristics while varying the applied voltage. The curve in Figure 3 shows that when PO power is introduced into one optical fiber, the output of that optical fiber is Pl, and the output branched to the other optical fiber is P2, the branching ratio is PI /Pi +P2. The values are plotted.

FIG. 4 is for explaining another embodiment. (
Figure A) is a perspective view, and Figure (B) is a perspective view of the piezoelectric element.

In the figure, 41 is a molded case, 42 is a piezoelectric element, 43 is a slot, and 44 is an optical fiber coupler. The molded case 41 can be a case of a normal optical fiber coupler, and an optical fiber coupler made by heating and stretching a plurality of optical fibers is inserted into the slot 43 and fixed therein. A piezoelectric element 42 is attached to this molded case.

As shown in Figure (B), the piezoelectric element 42 has a flat plate shape, has an upper surface electrode 45 and a lower surface electrode, and expands and contracts in the longitudinal direction.

In the above embodiment, an example was explained in which a piezoelectric element was used as the expandable member, but the present invention is not limited to this, and the present invention uses a member that causes geometric dimensional changes such as a magnetostrictive element or a pie metal. It is clear that it can be done.

(Effects of the Invention) As is clear from the above description, the present invention is an optical coupler that can change the branching state based on a completely different principle from the conventional one, and uses the characteristics of the expandable member to generate light with various characteristics. It has the effect of providing Kabra.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram for explaining one embodiment of the optical coupler of the present invention, FIG. 2 is an explanatory diagram of the optical fiber of FIG. 1, and FIG. 3 is a characteristic diagram of the embodiment of FIG. 1. 4 are schematic configuration diagrams for explaining other embodiments, FIG. 5 is an explanatory diagram of the operation of the present invention, and FIGS. 6 and 7 are schematic diagrams of conventional optical couplers. be. 10.11... Optical fiber, 12... Coupling part, 1
3... Cylindrical piezoelectric element, 14... Outer electrode, 15...
...Inner electrode. Figure 2

Claims (1)

[Claims] A branching state variable optical coupler characterized by integrating a plurality of waveguides coupled in the axial direction and a stretchable member.