JP2786006B2 - Optical amplification parts - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to an optical transmission system using an optical fiber,
The present invention relates to an optical amplification component for amplifying and switching propagation light.

<Conventional technology> Conventionally, erbium ion (Er
A technique for amplifying propagating light by stimulated emission using population inversion of electrons in ³⁺ ) or neodymium ions (Nd ³⁺ ) is known.

In such a technique, in the region containing the light amplification element ions as described above, it is necessary that the excitation light and the propagation light for generating the population inversion act together, but in order to realize such a state, It is necessary to use a multiplexing part of the pumping light and the propagating light and a special optical fiber containing the above-described light amplification element ions, and the overall configuration is complicated.

Therefore, in order to improve such a point, an optical amplifying component having the function of the multiplexing component and the special fiber described above is being studied (IEEE Photonics Technology Lett).
ers, Vol. 2, No. 1, 1990, pp. 41-42). Such an optical amplification component is obtained by melting and drawing two optical fibers each including the optical amplification element ions as described above in a clad portion with their side surfaces aligned with each other. This will be described in more detail with reference to FIG.

As shown in FIG. 1, the optical amplifying component 1 is formed by joining two optical fibers 2 with their side surfaces joined together to form a joint 3 and extending a central portion of the optical fiber 2 in the axial direction of the fiber to reduce the diameter. This is part 4. Here, each optical fiber 2 is the fifth
As shown in the figure, around the core portion 2a, a waveguide cladding portion 2b and an amplification cladding portion 2c having a lower refractive index than the core portion 2a.
It has. The waveguide cladding part 2b is a part where the propagating light seeps out of the core part 2a, and the amplification cladding part 2c is
It contains a light amplification element which becomes an ion having the above-described amplification action. That is, the optical fiber 2
The cladding portion of the normal cladding portion other than the portion where the propagating light seeps out of the core portion contains the optical amplification element, and the propagating light does not normally seep into the amplification cladding portion 2c. As shown in FIG. 6, the joint portion 3 is formed by joining the side surfaces of the optical fiber 2 by surface tension at the time of melting, and has a small diameter located at the center of the joint portion 3 in the fiber axis direction. The portion 4 is formed by extending the joint portion as shown in FIG. 7, and includes a core portion 2a and a waveguide cladding portion.
The diameter 2b is reduced and the amplifying cladding 2c of the two optical fibers 2 is integrated.

In the optical amplifier component 1 having such a structure, the port A
As the light enters from the junction 3 and approaches the small diameter portion 4, the light propagates from the core portion 2 a and the waveguide cladding portion 2 b into the amplification cladding 2 c and propagates through the entire amplification cladding portion 2 c within the small diameter portion 4. Will be. Therefore, this propagating light is
The excitation light may be incident on either or both of the ports C and D. In this case, as described above, the pumping light also propagates through the core portion 2a and the waveguide cladding portion 2b of the optical fiber up to the joining portion 4, but leaks out to the amplification cladding portion 2c as the joining portion 4 approaches. Inside the portion 4, the light propagates in the amplification cladding portion 2c, whereby the pumping light is absorbed by the light amplification element ions contained in the amplification cladding portion 2c, and a population inversion occurs. Therefore, the propagation light passes through the region where the excitation light is absorbed as described above, and the propagation light is amplified by the small-diameter portion 4.

<Problem to be Solved by the Invention> However, the above-described optical amplification component 1 has the following problem.

In general, the excitation light has a shorter wavelength than the propagating light, and therefore has a narrower field distribution than the propagating light. For this reason, the area (the number of ions) where the propagating light acts is wider (more) than the area (the number of ions) where the excitation light forms the population inversion in the small diameter portion 4. Therefore, it is difficult to effectively achieve the amplification phenomenon, and it is difficult to compensate for the loss of the propagation light due to the absorption of the light amplification element ions.

As described above, the conventional optical amplification component has a problem that the field distribution of the excitation light is narrow and it is difficult to form an effective population inversion.

In view of such circumstances, an object of the present invention is to provide an optical amplifier component having a simple structure, a wide field distribution of pump light, and high amplification efficiency.

<Means for Solving the Problems> An optical amplification component according to the present invention that achieves the above object has two or more optical fibers connected to each other on a side surface thereof and has at least one optical fiber in a fiber axial direction of the joint. The portion is a small-diameter portion having an outer diameter smaller than the outer diameter of the optical fiber, and the cladding portion of the optical fiber is an optical amplification component containing at least a light amplification element in at least a part thereof. An optical fiber having a core diameter larger than that of the optical fiber is connected to at least one of the optical fibers connected to the joining portion. Further, the optical fiber is bent around the small diameter portion. It is characterized in that a rate variable substance is provided.

<Operation> In the optical amplification component having the above-described configuration, when excitation light is incident from an optical fiber having a large core diameter, the excitation light seeps into the entire cladding portion at the small diameter portion, and almost all ions of the optical amplification element are removed. Form a population inversion effectively.

Therefore, when the propagating light incident from one optical fiber on one side of the connecting portion seeps into the entire cladding portion at the small-diameter portion, it is effectively amplified by the population inversion described above, and any one of the other side of the connecting portion is used. Out of the optical fiber.

Whether the propagating light is emitted to any one of the optical fibers is determined by the refractive index difference between the small-diameter portion and the outside thereof. However, in an optical amplification component provided with a refractive index variable substance outside the small-diameter portion, ,
By controlling the refractive index of the variable refractive index substance, the optical fiber from which the propagating light is emitted can be set arbitrarily.

<Examples> Hereinafter, the present invention will be described based on examples.

FIG. 1A shows an optical amplification component according to one embodiment.
As shown in the figure, the optical amplification component 11 has two optical fibers.
The side surfaces of the twelve sides are joined together to form a joint portion 13 and a central portion in the fiber axis direction of the joint portion 13 is extended to form a small-diameter portion. Where the optical fiber 12
Has an amplifying cladding similarly to the optical fiber 2 shown in FIGS. 4 to 7, and the function of performing amplification in the small-diameter portion 4 is the same as that in the related art. In this embodiment, an optical fiber 15 is connected to the optical fiber 12 of the port D among the ports A to D.
This optical fiber 15 has a core portion as shown in FIG.
The core 15a has a diameter larger than the core diameter of the core 12a of the optical fiber 12.

In such an optical amplifying component 11, when, for example, propagating light is input from port A and excitation light is input from port D, both light seeps into the amplification cladding at the small diameter portion 14, and the excitation light enters the amplification cladding. Is formed, and the propagation light is amplified by this population inversion and emitted from the port B or the port D or both ports. This point is the same as that of the conventional optical amplification component (see FIGS. 4 to 7).

However, in the present embodiment, since the excitation light is incident from the optical fiber 15 having a large core diameter, the field distribution of the excitation light is wide, and the excitation light seeps into the entire amplification cladding portion in the small-diameter portion 14, Almost all population inversion distributions of the light amplification element ions can be formed effectively.

Here, whether the propagating light incident from the port A is amplified and then output to the port B or the port C depends on the amplification cladding part of the small diameter part 14 (the core part and the waveguide cladding part are sufficiently small, so No contribution) and the refractive index difference between it and the outside surrounding it. In other words, the small diameter part
Waveguide 14 is achieved by the refractive index difference between the amplification cladding portion of the small diameter portion 14 and the outside surrounding it, and it is considered that the mode of propagation is separated into the lowest order even mode and odd mode, Which of the ports B and C is emitted after passing through the small-diameter portion 14 is determined by the interference of the light distributed to the even-numbered mode and the odd-numbered mode by the small-diameter portion 14 when the small-diameter portion 14 is emitted.

FIG. 2 shows an example of an optical amplifying component capable of arbitrarily setting an output port of the propagation light incident from the port B. As shown in the figure, the optical amplification component 11A is provided around the small diameter portion 14 of the optical amplification component 11 described above.
16 is arranged. According to this, the refractive index variable substance
By controlling the refractive index of the port 16, for example, it is possible to arbitrarily set which of the ports B and C the propagating light incident from the port A will exit. Since the other parts are the same as those of the above-described embodiment, the same reference numerals are given to the members having the same operation, and the overlapping description will be omitted.

In addition, as the light amplification element, as shown in the previous section,
Rare earth elements such as Er, Nd, Pr, and Yb and transition metal elements such as Ti can be exemplified.

Further, in the optical amplifying component of the present invention, amplification has no particular polarization dependence, so that polarized light or ordinary light may be used as the excitation light, and polarizations whose polarization planes are orthogonal to each other may be used. Alternatively, two polarized waves whose polarization planes are not orthogonal may be used.

Next, an example of use of the optical amplifying component of the present invention will be described with reference to FIG.

In FIG. 3, reference numeral 11A denotes an optical amplifying component of the second embodiment described above. More specifically, as an optical fiber 12, approximately 1500 ppm of erbium as an optical amplifying element is added to an amplifying cladding portion. Using a dispersion-shifted single-mode optical fiber, a small-diameter portion 14 having a length of about 5 mm is formed in the middle portion by melt-drawing, and the port D has a core diameter of 50 μm at a point about 10 cm away from the small-diameter portion 14. An optical fiber 15 which is a multimode optical fiber is welded and connected.

An electric / optical converter (E / O converter) 18 incorporating a DFB laser and a pulse pattern generator 19 are sequentially connected to a port A of the optical amplification component 11A via a dispersion-shifted single mode optical fiber 17. doing. Ports B and C
Are connected to optical / electrical converters (O / E converters) 20A and 20B each having a built-in avalanche photodiode via a dispersion-shifted single mode optical fiber 17, respectively.
The converters 20A and 20B are both connected to the bit error rate measuring device 21. On the other hand, 1.48 μm
The pumping light source 22, which is a high-power semiconductor laser, is connected.

In such a configuration, the change in the bit error rate measured by the bit error rate measuring device 21 when the pumping light is incident from the pumping light source 22 and when the pumping light is not incident was measured to obtain the amplification degree of the propagation light.

As a result, with a pumping light of about 70 mW, a gain of 0.6 dB was obtained. The pump light required to obtain the same degree of amplification using the conventional optical amplification parts shown in FIGS. 4 to 7 is about 300 m.
Since it is W, it was found that the amplification effect of about 4 times was achieved in this example.

Next, a similar experiment was performed using a step-type multimode optical fiber having a core diameter of 50 μm as the optical fiber 15, and as a result, an amplification of 0.5 dB was obtained with an excitation light of about 70 mW.

Further, the amplification degree of the ports B and C was measured while changing the refractive index of the variable refractive index substance 16 using a temperature-controlled silicone resin matching agent as the variable refractive index substance. No difference was found in the degree.

<Effects of the Invention> As described above, the optical amplifying component according to the present invention can receive pumping light from a large core-type optical fiber.
The amplification efficiency is higher than that of the conventional one, and a required amplification degree can be obtained with a small excitation light. Therefore, by using the optical amplifying component of the present invention, the life of the pumping light source can be ensured for a long time, and the effect of improving the reliability of the optical communication system can be obtained. Can be achieved.

[Brief description of the drawings]

1 (a) and 1 (b) are explanatory diagrams showing an optical amplifying component according to one embodiment of the present invention, FIG. 2 is an explanatory diagram showing an optical amplifying component according to another embodiment, and FIG. Configuration diagram showing one use example,
FIG. 4 is an explanatory view showing an optical amplification component according to the prior art, and FIG.
FIG. 7 to FIG. 7 are sectional views taken along lines VV, VI-VI and VII-VII. In the drawings, 11 and 11A are optical amplification parts, 12 is an optical fiber, 12a is a core, 13 is a joint, 14 is a small diameter part, 15 is an optical fiber, 15a is a core, 15b is a clad, and 16 is refraction. Variable rate material, 17 is dispersion-shifted single mode optical fiber, 18 is E / O converter, 19 is pulse pattern generator, 20A and 20B are O / E converters, 21 is BER measuring instrument, 22 is pump light Light source.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G02F 1/35 501 G02B 6/00 376 H01S 3/07 3/10

Claims (2)

(57) [Claims] 1. A small-diameter portion having two or more optical fibers connected to each other on a side surface thereof and having at least a part of the joint portion in the fiber axial direction having an outer diameter smaller than the outer diameter of the optical fiber. And the cladding portion of the optical fiber is an optical amplification component containing at least one kind of optical amplification element in at least a part thereof, and at least one of the optical fibers connected to the bonding portion has the light An optical amplifier component, wherein an optical fiber having a larger core diameter than the fiber is connected. 2. An optical amplifying component according to claim 1, wherein a variable refractive index material is disposed around the small diameter portion of the optical amplifying component.