JP2884919B2 - Rare earth element doped multi-core fiber coupler - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rare-earth element-doped multi-core fiber type coupler made by bundling a plurality of rare-earth element-doped multi-core fibers and fusing and stretching the same, and particularly suitable for an optical power amplification type coupler. It is.

[0002]

2. Description of the Related Art Couplers having a function of splitting optical signals into equal distributions and merging a large number of optical signals are widely used for optical fiber communication, optical signal processing, optical measurement, optical sensors, and the like. ing.

Conventionally, as the above coupler, an optical fiber type, an optical waveguide type and the like have been studied. FIG. 5 shows a conventional example of an optical fiber type coupler. (A) is a plan view, and (B) and (C) are a left side view and a right side view. 2 consisting of core 4 and clad 5
The optical fibers 31 and 32 are arranged in parallel and bundled, and the central portion of the optical fiber is fused and drawn while being heated, so that the optical fiber goes from both ends to the center of the fused and drawn portion 3. Therefore, the outer diameter is tapered. With the structure of the fusion / extending portion 3, the input optical signal 16 incident on one optical fiber 31 is divided into two equal parts, that is, output optical signals 171 and 172. It should be noted that an equal distributor can be configured as described above or an optical demultiplexer having wavelength selectivity can be configured depending on the shape of the fusion / stretching section 3.

[0004]

However, the conventional coupler described above involves a branch loss (3 dB) by branching into two equal parts, and also absorbs and scatters generated by propagating in the optical fibers 31 and 32. With excess loss (1 dB). Further, as the number of distributions increases, for example, into four equal parts and eight equal parts, there is a disadvantage that a large branch loss and an excessive loss accompany.

Therefore, it has been proposed to construct a coupler using a rare earth element-doped optical fiber having an optical amplification function. However, although the branch loss and excess loss can be suppressed to some extent by the amplification function, the proposed optical fiber type is a single-core fiber type in which one clad has one core, However, if a rare earth element is added at a high concentration in order to increase the concentration, there is a problem that the amplification efficiency is lowered by concentration quenching. In addition, since there is only one core, high power amplification cannot be performed, and since fibers having the same structural parameters are used, wideband characteristics cannot be easily realized.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned disadvantages of the prior art by using an optical power amplification type optical fiber having a plurality of cores in one clad, to compensate for branch loss and excess loss of a coupler, It is an object of the present invention to provide a rare-earth element-doped multi-core fiber type coupler which can easily or equally distribute an optical signal having a larger output than an input optical signal to an output side.

[0007]

The rare earth element-doped multi-core fiber according to the first invention has a high refractive index n _w (n _w > n _c ) in which a rare earth element is doped in a cladding having a low refractive index n _C.
A plurality of rare-earth element-doped multi-core fibers having a plurality of embedded cores are bundled, fused and drawn while heating, and the central portion of the fused and drawn portion is reduced in diameter to couple the propagation modes.

[0008] A rare earth element-doped multi-core fiber according to a second aspect of the present invention is the coupler described above, wherein the structural parameters of each rare earth element-doped multi-core fiber are substantially equal.

A rare earth element-doped multi-core fiber according to a third aspect of the present invention is the above-mentioned coupler, wherein at least one of the rare earth element-doped multi-core fibers has a different structural parameter.

[0010] In a fourth aspect of the present invention, in the above-mentioned coupler, at least one rare-earth-element-doped multi-core fiber having a different structural parameter has a different amount of rare-earth element added.

Here, the structural parameters include the outer diameter and the outer diameter ratio of the clad and the core, the refractive index and the refractive index difference between the core and the clad, the core interval, and the like.

[0012]

According to the first and second aspects of the present invention, a high efficiency power amplifier is realized by multiplying a core to which a rare earth element is added, so that the branch loss and excess loss of the coupler are compensated, and the gain is further improved. Can be realized. In particular, when a plurality of cores to which a rare earth element is uniformly added are buried in the cladding, a so-called optical power amplification type coupler is realized in which even if the input optical signal is increased, the output optical signal is increased correspondingly. be able to. This is because light is closely coupled between a plurality of cores to which the rare earth element is added, and the optical signals are equally distributed and amplified, respectively. This is the reason why high power amplification is performed as compared to a coupler configured using a fiber. In addition, since the amount of the rare earth element added is more than plural times (the number of cores) more than the conventional one, a high amplification degree can be realized.

According to the third aspect, since at least one of the optical fibers has a different structural parameter, the wavelength dependency is reduced, and a wide-band optical power amplification type coupler can be realized. . For example, when Er is used as the rare earth element, the wavelength band of the input optical signal is 1.53 to 1.56 μm, whereas the wavelength of the pump light is 1.47 to 1.48 μm. Therefore, in order to make the pump light more efficiently contribute to the amplification and to realize a high degree of amplification by suppressing the attenuation of the input optical signal, the wavelength 1.
The coupler satisfies the necessary and sufficient conditions that a broadband coupler having a structure in which pump light and an input optical signal are less attenuated over a wide band of 47 to 1.56 μm is required.

According to the fourth aspect of the present invention, at least one of the optical fibers has a different addition amount of the rare earth element, so that the amplification degree is different, and consequently, the unequal distribution with different branching ratios. Can be realized. In particular, when applied to multi-core fibers having different structural parameters, for example, different core diameters, the optimum addition amount can be set according to the core diameter, so that the amplification degree can be varied without causing a decrease in amplification efficiency due to concentration quenching. it can.

[0015]

FIG. 1 shows a first embodiment of a rare earth element-doped multi-core fiber type coupler according to the present invention. (A) is a plan view, and (B) and (C) are a left side view and a right side view. Two rare-earth element-doped multi-core fibers 61 and 62 are bundled side by side, and the central part thereof is fused and drawn to reduce the diameter, and has a fused / drawn part 7 having a symmetrical tapered structure. This is a two-input two-output coupler. In the fusion / extension section 7, the propagation mode is coupled, where the light is coupled and distributed. Plurality rare earth element doped multi-core fiber 61 and 62 in the cladding 9 having a refractive index of n _c (9 pieces in this embodiment)
Core 8 (n _w >) with a refractive index n _w doped with a rare earth element
n _c) are those of buried structures.

The rare earth elements include Er, Nd, Pn,
A material containing at least one of Sm, Ce, Yb, Ho and the like can be used. The amount of addition is from several hundred ppm to several thousand ppm in one core 8. Therefore, the total concentration of the rare earth elements contained in the fiber 61 (or 62) is added to a high concentration that is 9 times the above value (that is, several thousand to tens of thousands ppm).
For example, as the rare earth element, in the case of using Er is, B to SiO ₂ or SiO _2, the cladding 9, F,
At least one refractive index controlling dopant such as P or Ge;
Use seed-containing material. The core 8 has a SiO ₂ G
e, P, Ti, Al, Zn, Nb, Ta and the like containing at least one dopant for controlling the refractive index are used, and Er is further added.

Incidentally, in FIG. 1, the diameter of each core 8 is equal to 0.1. It is selected from the range of several μm to several μm. It is preferable that the outer diameter of the multi-core which is an aggregate of these cores 8 is equal to the core diameter of a normal optical fiber (10 μm for a general optical fiber, 125 μm for a clad diameter). If the outer diameter of the multi-core is different from the normal core diameter,
The shape of the optical fiber is changed or the refractive index distribution is changed so as to achieve mode matching at the entrance and exit ends of the rare-earth element-doped multi-core fibers 61 and 62. Also, as the number of cores 8 increases, the amount of rare earth element added to each core 8 can be reduced.
As a result, a decrease in amplification efficiency due to concentration quenching can be suppressed.

FIG. 2 shows a second embodiment of the rare earth element-doped multi-core fiber type coupler of the present invention. This is one in which the structural parameters of the rare earth element-doped multi-core fibers 10 and 11 are different in order to realize the broadband characteristics of the coupler. Specifically, the cladding diameter and the core diameter of the optical fiber are different. That is, the outer diameter of the clad 14 forming one multi-core fiber 10 is made larger than the outer diameter of the clad 15 forming the other multi-core fiber 11, and
2 has an outer diameter larger than the outer diameter of the core 13. This makes it possible to realize a broadband optical power amplification type coupler. In particular, if more rare earth elements are added to the core having a larger outer diameter, the amplification degree of both multi-core fibers can be made different without difficulty. A coupler can be realized.

FIG. 3 shows a two-input, two-output rare-earth-element-doped multi-core fiber type coupler 181 to 187 of the above-described embodiment connected in multiple stages (three stages in the illustrated example). As shown in FIGS. 171 to 178, an output optical signal divided into eight is obtained. With this configuration, the pumping light signal 21 contributing to amplification is superimposed on the input light signal 16 and propagated. That is, a configuration is used in which the pumping light signal 21 also propagates so as to be divided into eight similarly to the input light signal 16. As a result, a large power multi-distribution system can be realized.

FIG. 4 shows a third embodiment of the rare earth element-doped multi-core fiber type coupler of the present invention. This is a coupler obtained by bundling and stretching four rare-earth element-doped multi-core fibers 191 to 194 having the same structural parameters, and optical signals input from any of the four input ports are equally distributed to the four output ports. It is. The rare earth element-doped multi-core fiber 191 used in this case
Reference numerals 194 to 194 indicate that five rare earth element-added cores 21 are embedded in the cladding 22. This can also realize a large power multi-distribution system.

The present invention is not limited to the above embodiment. First, couplers include those with N inputs and N outputs (N ≧ 2). This may be a multi-stage connection type as shown in FIG. 3 or a batch fusion / stretch type as shown in FIG. The material of the core and the clad may be made of multi-component glass, fluoride glass, phosphate glass, borosilicate glass, or the like, in addition to quartz glass. The optical fiber can be applied to both single mode transmission and multimode transmission. Further, the central part of the fused / extended portion of the coupler shown in FIGS. 1, 2 and 4 is cut, and a normal optical fiber is connected and connected to the cut surface to obtain one-input N.
It goes without saying that an output coupler can be realized.

[0022]

The present invention has the following effects.

(1) According to the rare earth element-doped multi-core fiber type coupler according to the first or second aspect, it is possible to realize an active type coupler which compensates the branch loss and excess loss of the coupler and further has a gain. Can be.
By embedding a plurality of cores to which a rare earth element is uniformly added in the clad, a so-called optical power amplification type coupler capable of amplifying an input optical signal a plurality of times larger than that of a conventional one can be realized.

(2) According to the rare earth element-doped multi-core fiber type coupler according to the third aspect, it is possible to realize a broadband optical power amplification type coupler.

(3) According to the rare earth element-doped multi-core fiber type coupler of the fourth aspect, it is possible to realize optical power amplification type couplers having different branching ratios.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a two-input, two-output rare earth element-doped multi-core fiber type coupler according to a first embodiment of the present invention.

FIG. 2 shows an embodiment of a two-input, two-output rare earth element-doped multi-core fiber type coupler having different structural parameters according to a second embodiment of the present invention.

FIG. 3 is a configuration diagram of a rare earth element-doped multi-core fiber type coupler which realizes one input and eight outputs in a multi-stage connection type according to an application example of the present invention.

FIG. 4 is a configuration diagram of a rare earth element-doped multi-core fiber type coupler having four inputs and four outputs according to a third embodiment of the present invention.

FIG. 5 is a configuration diagram of a two-input two-output optical fiber coupler according to a conventional example.

[Explanation of Symbols] 7 Fused / stretched section 8 Rare earth element-doped core 9 Clad 10 Rare earth element-doped multi-core fiber 11 Rare earth element-doped multi-core fiber 12 Rare earth element-doped core 13 Rare earth element-doped multi-core 14 Clad 15 Clad 16 Input optical signal 20 Fusion Attachment / extension section 21 Rare earth element-doped core 22 Cladding 41 Excitation light signal 61 Rare earth element-doped multi-core fiber 62 Rare earth element-doped multi-core fiber 171-178 Output light signal 181-187 Rare earth element-doped multi-core fiber type coupler 191-194 Rare earth-doped multi-core fiber fiber

Claims (4)

(57) [Claims] 1. A rare earth element-doped multi-core fiber in which a plurality of cores having a refractive index n _w higher than that of a rare earth element-doped cladding are embedded in a cladding having a refractive index n _c , and a plurality of bundles are fused while heating. -A rare-earth element-doped multi-core fiber coupler characterized in that the propagation mode is coupled by reducing the diameter of the stretched, fused and stretched central portion. 2. The rare earth element-doped multi-core fiber type coupler according to claim 1, wherein the structural parameters of each rare earth element-doped multi-core fiber are substantially equal. 3. The rare-earth element-doped multi-core fiber type coupler according to claim 1, wherein at least one of the rare-earth element multi-core fibers has a different structural parameter. 4. The rare earth element-doped multi-core fiber type coupler according to claim 1, wherein at least one of the rare earth element multi-core fibers has a different amount of added rare earth element.