JP2880618B2 - Broadband fiber optic coupler - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber coupler capable of equally splitting transmission light over a wide wavelength band.

[0002]

2. Description of the Related Art In an optical communication circuit, a plurality of wavelengths may be used for transmission light, and there is a case where such transmission light must be equally divided in the communication circuit. Equally branched optical fiber couplers are referred to as 3 dB optical fiber couplers. When the wavelength band of the transmission light is wide, an optical fiber coupler that can cope with a particularly wide band among the 3 dB optical fiber couplers is used.

There are several types of broadband optical fiber couplers. Fibers are obtained by twisting and fusing fibers together, fibers obtained by bundling a plurality of fibers of different materials in parallel, and fibers having different diameters by etching. Conventionally, such a broadband optical fiber coupler has not been easy to manufacture. For example, twisting while melting an optical fiber requires skill, and the yield is low in productivity.

[0004] In some cases, a plurality of optical fibers are arranged in parallel, heated together, and stretched in a linear direction while the portions are thermally fused. Such an optical fiber coupler is easy to manufacture without a twisting operation, and is particularly preferable when the branched transmission light is limited to a specific wavelength. If the wavelength of the transmitted light deviates from the specific wavelength, the branching ratio changes greatly. Therefore, it cannot be used as a broadband optical fiber coupler.

[0005]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and provides an equal-branch broadband optical fiber coupler which does not require a complicated manufacturing process such as twisting. The purpose is to:

[0006]

A broadband optical fiber coupler according to the present invention, which has been made to achieve the above object, will be described with reference to FIG. 1 corresponding to an embodiment. In the broadband optical fiber coupler of the present invention, a plurality of optical fibers 2 and 3 arranged in parallel are fused and drawn, and an optical coupling section 4 is formed on the way from the incident side to the emission side of the optical fibers 2 and 3. An optical fiber coupler formed, wherein the optical coupling portion 4 of the optical fiber and its vicinity are curved on the planes arranged in parallel, and the light on the incident side of each of the optical fibers 2 and 3 due to the curvature. The angle θ between the axis 3a and the optical axis 3b on the output side is 2 to 10
Degrees.

[0007]

Since the optical coupling portion 4 of the optical fiber and its vicinity are curved by 2 to 10 degrees on the planes of the optical fibers 2 and 3 arranged in parallel, the wavelength band of light that can be equally branched is widened.

[0008]

Embodiments of the present invention will be described below. FIG. 1 shows an embodiment of the broadband optical fiber coupler of the present invention fixed on a quartz glass table 1, in which A is a plan view and B is a side view. This optical fiber coupler splits a 1.31 μm transmission light equally, and two optical fibers 2 and 3 having the same diameter and the same diameter are arranged in parallel on a horizontal plane and fused and drawn to form an optical coupling section 4. ing. As shown in FIG. 1A, the optical fibers 2 and 3 are spread and fixed on a quartz glass table 1 with an adhesive 5. Therefore, two input ports and two output ports of the optical fibers 2 and 3 extend from the optical coupling unit 4 in all directions. As shown in FIG. 1B, the two optical fibers 2 and 3 of the optical coupling section 4 are curved in a bow shape so as to protrude upward along a surface arranged in parallel. The quartz glass table 1 to which the optical fiber coupler is fixed is formed of a hexahedron having upper and lower surfaces of different rectangular shapes and a peripheral side surface of a trapezoidal shape with an inclination of about 4 degrees. Therefore, the angle θ between the optical axis 3a on the input port side and the optical axis 3b on the output port side of each of the optical fibers 2 and 3 is about 4 degrees.

For an optical fiber coupler, the variation of the optical branching ratio due to the difference in wavelength was measured while changing the degree of curvature. FIG. 2 shows the relationship between the wavelength and the branching ratio. The degree of curvature is determined by the optical axis 3 on the incident side of each of the optical fibers 2 and 3 on the vertical plane.
a and the optical axis 3b on the output side are projected, the optical axis 3a on the incident side projected on the vertical plane thereof becomes the optical axis 3b on the output side.
The angle of intersection θ at which the angle is bent is 3 degrees, 3.5 degrees, and 4 degrees. A broken line a when θ is 3 degrees, and 2 when 3.5 degrees
The dashed-dotted line b and the case of 4 degrees are indicated by the dashed-dotted line c. Note that the light branching ratio when the optical coupling unit 4 is in a linear state is also shown by a solid line d. As θ is increased to 3 degrees, 3.5 degrees, and 4 degrees,
It has been found that the branching ratio close to 50% can be stably maintained over a wide wavelength range. From this result, it was found that a high-precision broadband optical fiber coupler can be obtained by a simple operation of slightly bending the fusion-stretched portion.

[0010]

As described in detail above, the broadband optical fiber coupler according to the present invention can be used for welding and fusing optical fibers, searching for and selecting different materials, or etching. It can be efficiently manufactured without complicated operation, and can divide light of a wide range of wavelengths into equal parts with high accuracy.

[Brief description of the drawings]

FIG. 1 is a plan view (A) and a side view (B) showing an embodiment of a broadband optical fiber coupler to which the present invention is applied.

FIG. 2 is a diagram showing a change in a branching ratio of a broadband optical fiber coupler to which the present invention is applied.

[Explanation of symbols]

1 is a quartz glass table, 2 and 3 are optical fibers, 3a is an optical axis on the incident side, 3b is an optical axis on the output side, 4 is an optical coupling portion, and 5 is an adhesive.

Claims (1)

(57) [Claims] 1. An optical fiber coupler, wherein a plurality of optical fibers arranged in parallel are fusion-stretched, and an optical coupling part is formed on the way from an incident side to an outgoing side of the optical fiber. The optical coupling portion of the optical fiber and its vicinity are curved on the planes arranged in parallel, and the angle between the optical axis on the incident side and the optical axis on the output side of each optical fiber due to the curvature is 2 to 10 degrees. A wide-band optical fiber coupler, characterized in that: