JPH03168726A - Optical branching and coupling device - Google Patents

Abstract

PURPOSE:To obtain the optical branching and coupling device which can constitute an optical amplifier with small loss by using a specific optical fiber as one of optical fibers. CONSTITUTION:The optical fibers 3 are connected by fusion splicing at one position and at least one of the optical fibers is composed of the optical fiber 2 which is doped with a rare earth element. Then specific exciting light is made incident from the optical fibers of the optical branching and coupling device 1, then a light signal propagated through an optical fiber 4 is amplified by the optical branching and coupling device 1 and the rare earth element doped fiber 2 which follows it. This amplifier 5 has no branch loss generated by the optical branching and coupling device and reduces the number of the positions of splicing to only two. Consequently, the constitution of the system is simplified on the whole and the coupling loss is reducible.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an optical branching coupler using a rare earth doped optical fiber.

[Prior Art] In recent years, it has been known that optical fibers doped with rare earth elements such as erbium (Er) have the function of amplifying signal light by providing a predetermined pumping light. An optical amplifier as shown in FIG. 3 has been proposed using the amplification function of a dove optical fiber.

This amplifier has a 2×2 branching coupler 10 and an Er-doped optical fiber 20 connected to a normal fiber 40e transmission path. The branch coupler 10 is made by fusing two optical fibers made of the same material such as quartz, and in order to excite the Er-doped optical fiber 20 from one of the optical fibers 30. excitation light is incident.

[Problems to be Solved by the Invention] Incidentally, in such a conventional optical amplifier, the optical fiber 40 is connected to the branching coupler 10 and the Er-doped optical fiber 2.
0, the number of splices (joint points) increases, and losses occur in the splices and the branch coupler 10, resulting in a problem in that the amplification function as a whole deteriorates.

[Purpose of the Invention] The present invention was made to solve these conventional problems, and aims to provide an optical branching coupler having an optical amplification function.
Another object of the present invention is to provide an optical branching coupler that can configure an optical amplifier with little loss.

[Means for Solving the Problems] The optical branching coupler of the present invention achieves the above object by fusing a plurality of optical fibers at one place, and in an optical branching coupler, at least one of the optical fibers is One of the fibers is made of optical fiber doped with rare earth elements.

[Operation] Signal light is input from one of the plurality of optical fibers, and predetermined excitation light is input from the other one.

This excitation light creates a population inversion between rare earth transition levels in the rare earth element-doped optical fiber, and the signal light causes stimulated emission and amplifies the signal light.

Therefore, this amplification offsets the loss due to branching,
Furthermore, the signal light is amplified while being transmitted through the rare earth doped optical fiber following the signal branch.

[Embodiment] FIG. 1 is a diagram showing an optical branching coupler 1 of the present invention, in which two optical fibers 2 and 3 are thermally fused at one location. One of these optical fibers 2 is an optical fiber doped with a rare earth element such as ervirum (Er), neodymium (Nd), or ytterbium (yb).

Such a rare earth doped optical fiber is, for example, a common V
Pure quartz soot produced by the AD method is ErC';I
It is obtained by dipping it in a solution, drying it, sintering it using the VAD method as the core part, providing a cladding part such as a fluorine-doped cladding, and drawing it. can also be produced in the same way.

By using pumping light in a predetermined wavelength range, the rare earth-doped optical fiber amplifies an optical signal in the 1.5 μm band with an amplification degree corresponding to the power of the pumping light.

As the other optical fiber 3, a normal optical fiber such as a quartz fiber or a polygonal fiber, or a rare earth doped optical fiber can be used. When using a rare earth doped optical fiber, one having a lower rare earth concentration than the optical fiber 2 is used.

These two optical fibers 2 and 3 can be made into the optical branching coupler 1 by thermally fusing them using a conventional method.

The optical branching coupler 1 can amplify the optical signal by inputting an optical signal from one of the input sides of the optical fibers 2 and 3 and by inputting a predetermined pumping light from the other side.

Therefore, the branching losses of the optical signals branched to the output sides of the optical fibers 2 and 3 are canceled out, so that output signal light with high output power can be obtained.

In the case of an Er-doped optical fiber, the optical signal is 1.5
Optical signals in the μm band are most effectively amplified.

Also, the excitation light is usually around 0.57 μm, 0.98 μm.
A wavelength range around 1.47 μm or around 1.47 μm is used.

FIG. 2 shows an embodiment of an optical amplifier 5 using such an optical splitter/coupler 1. The rare earth doped fiber 2 constituting the optical splitter/coupler 1 is continuously connected to the length necessary for amplification. An optical amplifier 5 is configured.

The length of the rare earth doped fiber 2 is set to an optimum value determined by the balance between the transmission loss caused by the fiber 2 and the amplification function. It is usually about several meters to several tens of meters.

By inputting a predetermined excitation light from the optical fiber 3 of the optical branch/coupler 1, the optical signal transmitted through the optical fiber 4 is amplified by the optical branch/coupler 1 and the rare earth doped fiber 2 following it. In this amplifier 5, there is no branching loss due to the optical branching coupler, and there can be only two splices, so the entire system can be configured simply and the coupling loss can be reduced.

In this embodiment, an optical branching coupler using two optical fibers has been described, but it goes without saying that the present invention can also be applied to an optical branching coupler using three or more optical fibers.

[Effects of the Invention] As is clear from the above embodiments, according to the optical branching coupler of the present invention, a rare earth doped fiber is used as the optical fiber constituting the optical branching coupler, so that losses due to branching can be offset. Therefore, it is possible to provide an optical branching coupler with extremely low loss.

Furthermore, when the optical branching coupler of the present invention is applied as an optical amplifier, splices can be reduced, the amplification function can be improved, and the system can be simplified.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an optical branching coupler according to the present invention, FIG. 2 is a diagram showing an example of an optical amplifier using the optical branching coupler of the present invention, and FIG. 3 is a diagram showing a conventional optical amplifier. be. 1... Optical branching coupler 2... Rare earth dove optical fiber 3...
optical fiber

Claims (1)

[Claims] 1. An optical branching coupler comprising a plurality of optical fibers fused at one location, wherein at least one of the optical fibers is an optical fiber doped with a rare earth element.