JP2749643B2 - Light coupler - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical coupler which is one of optical components.

(Prior Art) A distributed coupling type optical device in which two optical waveguides are arranged close to each other and utilizing the distributed coupling between the two is used as an optical coupler.

For example, as shown in FIG.
An optical fiber 2 comprising a fiber core 2b and an optical fiber 2 'comprising a fiber cladding 2'a and a fiber core 2'b are fused and integrated by the fiber claddings 2a and 2'a to form a tapered portion 3. Fused tapered optical coupler 1
It has been known.

The optical coupler 1 is actually used as an optical branching / combining device for branching / combining light of a certain wavelength or an optical demultiplexing / combining device for demultiplexing / combining light of different wavelengths. ing.

An example of its use is shown in FIG. FIG. 3 shows a schematic diagram of a so-called optical multi-drop system. This system sequentially distributes optical information from one optical transmitter 4 to optical receivers 5, 5, 5,... Installed at a plurality of remote locations. In this system, the above-described optical couplers 1, 1, 1,... Are arranged in series in the optical fiber line 6 from the optical transmitter 4 as optical taps, and the optical information from the optical transmitter 4 It is distributed to the receiver 5.

By the way, in this optical multi-drop system, in order for the optical receiver 5 to be able to secure a predetermined S / N ratio, the received light power needs to be a predetermined value.

Therefore, in each optical tap (optical coupler) 1,
The branching ratio cannot be reduced below a certain value. Therefore, the optical information is the optical tap (optical coupler) 1
, The division loss must be increased toward the downstream side.

For example, when the input level of the incident light to a certain optical tap (optical coupler) 1 is 0 dBm and the light receiving level of the optical receiver 5 is -10 dBm, the branching ratio in the optical tap (optical coupler) is 9:
Must be less than or equal to 1, then at least 10
% Light loss.

For this reason, in the conventional optical multi-drop system, there is a problem that a large number of optical receivers cannot be installed continuously.

To cope with such a problem, it has been proposed to use a fiber having an optical amplification function, for example, a fiber doped with erbium (Er), as the optical fiber.

(Problems to be Solved by the Invention) If this optical fiber is used, the above-mentioned optical loss will be compensated by optical amplification by using a pump source, so that a large number of optical receivers are continuously installed. It becomes possible to do.

However, in the case of an optical amplifier, if the pumping source is removed, it usually functions as an optical absorber. Therefore, if the pumping source goes down for some reason, the entire system constituting the downstream side becomes inoperable. Problem arises.

An object of the present invention is to provide an optical coupler capable of preventing the whole system from being down even when the excitation source for optical amplification is removed in the above-described system.

(Means for Solving the Problems) In order to achieve the above object, in the present invention,
In an optical coupler in which a plurality of optical fibers or optical waveguides are arranged close to each other to generate distributed coupling, at least one of the optical fibers or optical waveguides is made of a medium transparent to light of a used wavelength, and An optical coupler is provided, wherein at least one optical fiber or optical waveguide is made of a medium for amplifying the light of the used wavelength, and excitation light is incident from the outside.

(Operation) In the optical coupler of the present invention, since the amplifying function of the amplification medium can be used, the branching ratio of the optical coupler can be increased and a large number of optical receivers can be installed. If the excitation source for the amplification medium goes down for some reason and the optical amplifier changes to an optical absorber, the distributed coupling with the transparent medium is lost, and the optical information is output from the transparent medium side and transmitted. The problem of interruption to the downstream system is eliminated.

(Example) Hereinafter, an example of the present invention is described based on an accompanying drawing. FIG. 1 shows a schematic view of a fusion tapered optical coupler of the present invention.

In the figure, an optical coupler 11 has a fiber clad 12a.
And an optical fiber 12 comprising a fiber core 13b and an optical fiber 13 comprising a fiber clad 13a and a fiber core 13b.
And a part of each clad is welded and fused
14 is formed.

Here, the optical fiber 12 is made of a medium that is transparent to light of the used wavelength, and is, for example, a normal quartz fiber. The optical fiber 13 is made of a medium that amplifies light having a used wavelength, and is, for example, an erbium-doped fiber.

In the case of the optical coupler having this structure, when the optical coupler operates without any trouble as an optical amplifier, the optical information incident on the optical fiber 12 is transmitted to the optical fiber 12 as shown by the solid line p in the figure.
As solid p ₁ from also output from the optical fiber 13 are distributed coupling with the optical fiber as a solid p _2. At that time, since the amplifying action of the optical fiber 13 can be used, a large branching ratio can be realized.

For example, if the input level of the incident light is 0 dBm, the light receiving level of the optical receiver is −10 dBm, and the amplification of the optical fiber 13 is 10 dB, the branching ratio of this optical coupler must be 99: 1 or less, The light loss at that time can be reduced to only 1%. Therefore, a large number of optical receivers can be installed in the system.

On the other hand, if the pump source of this optical amplifier goes down due to some accident and the optical amplifier changes to an optical absorber, the distributed coupling between the optical fiber 12 and the optical fiber 13 is lost, and the optical fiber 12 is connected to the optical fiber 12 as a dotted arrow q. The incident optical information is output as it is from the through port of the optical fiber 12 as q ', so that the interruption of the downstream system does not occur.

FIG. 2 is a schematic view showing another embodiment of the present invention. In the illustrated optical coupler, a branch waveguide 16 is arranged close to a main waveguide 15 made of quartz. This branch waveguide
In 16, a portion 16 a adjacent to the main waveguide 15 is made of quartz, and the other portion 16 b is doped with erbium to form a fiber having an amplifying action. Then, the gap S ₁ between the main waveguide 15 and the branch waveguide portions 16a is on the order of the wavelength used (e.g. 5 [mu] m), it is therebetween are formed distributed coupling.

Excitation light waveguide 17 is disposed in proximity to the branch waveguide 16b, the gap S ₂ between both distributions bond has become the order of use wavelength is formed.

In the case of the optical coupler having this structure, when the pumping light enters from the port A 'of the pumping light waveguide 17, the power of the pumping light is distributed to the branching waveguide 16 due to the distributed coupling with the portion 16b, thereby operating as an optical amplifier. I do.

Therefore, most of the optical information incident from the port A of the main waveguide 15 exits from the through port B, and a very small portion is distributed to the branch waveguide 16 by the distributed coupling between the main waveguide 15 and the portion 16a. The signal is amplified by the portion 16b and is output from the port B '.

Even when the pumping light from the port A 'is not incident, the light distributed from the main waveguide 15 to the branching waveguide 16 is absorbed, but the light output from the through port B is affected. Instead, the light is emitted downstream as it is, so that the normal operation of the optical receiver disposed downstream is ensured.

(Effects of the Invention) As is clear from the above description, the optical coupler of the present invention has at least one configuration in an optical coupler in which a plurality of optical fibers or optical waveguides are arranged close to each other to generate distributed coupling. One of the optical fibers or the optical waveguides is made of a medium transparent to light of the used wavelength, and at least one of the other optical fibers or optical waveguides is made of a medium for amplifying the light of the used wavelength, and is externally pumped. Since light is incident, for example, when configuring an optical transmission system of an optical multi-drop system using this optical coupler, the optical coupler can have a large branching ratio, and many optical receivers can be remotely controlled. It can be installed up to the ground. Also, in the system, even if the pumping source goes down due to some kind of accident, the through port operates normally, so that the optical receiver installed downstream is not adversely affected. .

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a fusion tapered optical coupler of the present invention, FIG. 2 is a schematic diagram of another embodiment, FIG. 3 is a schematic diagram of an optical multi-drop system, and FIG. It is the schematic of an optical coupler. 11… Optical coupler, 12a, 13a… Fiber clad, 12
b, 13b: fiber core, 14: tapered portion, 15: main waveguide, 16: branched waveguide, 16a: portion, 16b: portion exhibiting amplifying action, 17: waveguide for excitation light .

Claims (1)

(57) [Claims] An optical coupler in which a plurality of optical fibers or optical waveguides are arranged close to each other to generate distributed coupling, wherein at least one optical fiber or optical waveguide is formed from a medium transparent to light of a used wavelength. And at least one other optical fiber or optical waveguide is made of a medium that amplifies the light of the use wavelength, and most of the light of the use wavelength that is incident on the optical coupler when excitation light is incident from the outside is transparent. An optical coupler, wherein the light passes through the at least one optical fiber or optical waveguide made of a medium, and a part of the light passes through the at least one optical fiber or optical waveguide made of an amplifying medium.