JP2000012928A - Structure for holding optical fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve side excitation efficiency by forming a reel in a manner that the curvature of a drum part wound by an optical fiber differs from each other on the outgoing side of excitation light and the entry side thereof. SOLUTION: A reel 8 comprises a drum 8a on which is winding is made by an optical fiber 1 and a flange part 8b on both ends of the drum 8 and is formed in a manner such that the curvature of the drum 8a differs from each other on the outgoing side (left side) of excitation light and the entry side (right side) thereof. That is, the drum 8a is round on the entrance side of excitation light on the left side from the center of the axial direction, while it is elliptic on the outgoing side thereof on the right side therefrom, and the curvature on the outgoing side is made larger locally. Thus, since the propagation mode of excitation light changes and the numerical aperture becomes large, the frequency of the excitation light crossing with a first core 2 become high and a skew light is reduced. That is, the possibility of the excitation light being absorbed in the first core 2 is increased, the side excitation efficiency is increased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a structure for holding an optical fiber used as a medium for optical amplification or laser oscillation utilizing a stimulated emission phenomenon.

[0002]

2. Description of the Related Art In general, there is a so-called double-core type of optical fiber used as a medium for optical amplification or laser oscillation utilizing the stimulated emission phenomenon.

[0003] This double-core type optical fiber 1 is shown in FIG.
As shown in the figure, a second core 4 and a clad 6 are sequentially formed on the outer periphery of the first core 2.

[0004] The first core 2 is a single-mode or multi-mode of a quartz system, and is made of a rare earth element (for example, Nd).
And Er) are doped.

[0005] The second core 4 is a quartz-based multi-mode, and the first core 4 is used for efficiently introducing excitation light from an excitation light source such as a laser diode having a large emission area into an optical fiber. Has a cross-sectional area sufficiently larger than the cross-sectional area of.

The clad 6 is made of a polymer resin such as urethane acrylate or polymethyl methacrylate for protection and light confinement.

The specific dimensions of the optical fiber 1 are, for example, that the outer diameter of the first core 2 is about 10 μm,
The outer diameter of the core 4 is about 125 to 400 μm, and the outer diameter of the clad 6 is about 200 to 450 μm. As shown in FIG. 6, for example, the refractive index n ₂ of the first core ₂ is about 1.463 to 1.467, and the refractive index of the second core 4 is as shown in FIG.
n ₄ is about 1.45 to 1.46, the refractive index n ₆ of the cladding 6 is a about 1.40, as directed outward, the refractive index is set stepwise so gradually decreases.

When the optical fiber 1 having this configuration is used, for example, as an optical amplification medium, the first core 2 includes, for example, Nd
Is doped in the first core 2.
While the signal light in the 06 μm band is incident, the excitation light in the 0.80 μm band is incident not only in the first core 2 but also in the second core 4. Then, the first core 2 is pumped by the pumping light propagating in the first core 2 and the second core 4, and the signal light is amplified.

As described above, in the optical fiber 1 having this configuration, since a high-power pumping light can be introduced into the second core 4 occupying a relatively large area around the first core 2, a so-called lateral pumping effect is obtained. Thus, there is an advantage that high-output optical amplification can be performed more efficiently as compared with the case where pumping light is introduced only into the first core 2.

By the way, the double-core type optical fiber 1 shown in FIG. 5 is not suitable for obtaining desired optical amplification and laser oscillation.
Although a relatively long one is used, in order to incorporate such a long optical fiber into a device, it is necessary to collectively store the optical fibers in the device.

Therefore, in the prior art, the optical fiber 1 is wound on a reel. The usual reel used in this case has a cylindrical body formed with flanges on the left and right sides, and the body has the same outer diameter along the axial direction.

[0012]

However, when the optical fiber 1 having the configuration shown in FIG. 5 is used as a medium for optical amplification or laser oscillation while being wound on a normal reel, the excitation efficiency of the optical fiber 1 is sufficiently increased. Could not be increased.

That is, the pumping light propagating through the second core 4 is absorbed by the first core 2 when crossing the first core 2 and contributes to the pumping, but the optical fiber 1 has the same curvature. In such a case, only the light of a component that does not pass through the first core 2 (hereinafter, referred to as a skew light) remains in the excitation light that has entered the second core 4. Become. In other words, since the pump light initially incident on the optical fiber 1 has many propagation modes, it is absorbed with high efficiency, but after the easily absorbable mode disappears, only the skew light is constantly present. I will be. And
This skew light only turns in the second core 4 along the circumferential direction as shown by the broken line in FIG. 5 and does not cross the first core 2 thereafter. No contribution is made, and the side excitation efficiency cannot be increased.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problem. When a double-core type optical fiber is held, the frequency at which the light of the skew component in the second core crosses the first core is determined. It is another object of the present invention to increase the side excitation efficiency by making the height higher.

[0015]

According to the present invention, in order to solve the above-mentioned problems, a second core is formed on an outer periphery of a first core,
The first core is doped with a rare earth element.
The optical fiber holding structure in which the core has a smaller refractive index than the first core has the following configuration.

That is, in the invention according to claim 1,
The above optical fiber is wound and held on a reel,
This reel is formed such that the curvature of the body around which the optical fiber is wound is different between the position on the excitation light emission side and the position on the excitation light incidence side.

According to the second aspect of the present invention, in the holding structure according to the first aspect, the trunk portion of the reel is provided with a portion having a larger curvature at a position on the excitation light emission side than on the excitation light incidence side.

According to the third aspect of the present invention, in the holding structure of the first aspect, the body of the reel is formed such that the curvature gradually increases from the excitation light incident side to the excitation light emission side. ing.

According to the fourth aspect of the present invention, the optical fibers are arranged so that their orbital positions are shifted from each other in a plane, and are integrally held by a fixing sheet material such as an adhesive or a film. The optical fiber is circulated so that the curvature gradually increases from the excitation light incident side to the excitation light emission side.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 FIG. 1 is a front view showing an optical fiber holding structure according to Embodiment 1 of the present invention, FIG. 2 (a) is a cross-sectional view taken along line aa of FIG.
FIG. 2B is a sectional view taken along the line bb in FIG.

In the first embodiment, the double-core type optical fiber 1 shown in FIGS. 5 and 6 is wound and held on a reel 8. In this case, the shape of the reel 8 is different from the conventional one. I have.

That is, the reel 8 of the first embodiment is
A body 8a around which the optical fiber 1 is wound, and the body 8a
It is composed of flange portions 8b at both ends, and is formed such that the curvature of the body portion 8a is different from each other at a position on the excitation light emission side (left side in FIG. 1) and a position on the excitation light incidence side (right side in FIG. 1). . That is, the body 8a is a perfect circle as shown in FIG. 2 (a) on the excitation light incident side on the left side of the center in the axial direction, but has an oval shape as shown in FIG. 2 (b) on the right side. And the curvature on the emission side is formed to be slightly larger locally.

In this configuration, the pumping light firstly incident on the second core 4 of the optical fiber 1 is absorbed with high efficiency because there are many propagation modes, and among the pumping light components, The light of the component having a large numerical aperture is preferentially absorbed because it frequently intersects the first core 2.

However, when the radius of the body of the reel is the same along the axial direction as in the prior art, the aperture gradually increases as the excitation light propagates through the optical fiber 1 toward the emission side. Although light having a small number of components remains as skew light, the first embodiment is formed such that the curvature on the exit side of the excitation light is slightly larger than that on the incident side. Therefore, the propagation mode of the pump light changes and the numerical aperture also increases, so that the frequency of the pump light crossing the first core 2 increases, and the skew light decreases. That is, the probability that the pump light is absorbed in the first core 2 increases, so that the side pumping efficiency improves.

Embodiment 2 FIG. 3 is a front view of an optical fiber holding structure according to Embodiment 2 of the present invention.

In the second embodiment, the double-core type optical fiber 1 shown in FIGS. 5 and 6 is wound and held on a reel 9, but the shape of the reel 9 in this case is different from that in the first embodiment. are doing.

That is, the reel 9 of the embodiment 2
A trunk 9a around which the optical fiber 1 is wound, and the trunk 9a
The body 9a is formed in a tapered shape such that its radius gradually decreases along the axial direction from the excitation light incident side (left side) to the excitation light emission side (right side). I have. In other words, the body 9a of the reel 9 has a perfect circular cross section, but the curvature becomes larger from the excitation light incident side to the excitation light emission side.

Also in the second embodiment, the optical fiber 1
Since the curvature of the exit side of the excitation light becomes larger gradually than the entrance side of the excitation light, the propagation mode of the excitation light gradually changes and the numerical aperture also increases, so that when the excitation light propagates through the optical fiber 1, Since the probability that the skew light decreases and is absorbed in the first core 2 increases, the side excitation efficiency improves.

Although the reel 9 of the second embodiment is formed in a tapered shape, it is easier to process than the case where the reel 8 is formed stepwise as in the first embodiment.

Embodiment 3 FIG. 3 is a plan view of an optical fiber holding structure according to Embodiment 3 of the present invention.

The features of the third embodiment are shown in FIGS.
The double-core type optical fiber 1 shown in FIG. 1 is arranged with its orbital positions shifted from each other in a plane, and is integrally held by a fixing sheet material 10 such as an adhesive or a film.

Further, the optical fiber 1 is wound so that the excitation light incident side is located on the outer peripheral side and the excitation light emitting side is located on the inner peripheral side. In other words, the excitation light is circulated from the incident side to the exit side such that the bending diameter gradually decreases (in other words, the curvature gradually increases).

Therefore, in the case of the third embodiment as well, the curvature of the optical fiber 1 on the outgoing side of the pumping light is larger than that on the incident side, so that the propagation mode of the pumping light changes gradually and the numerical aperture also increases. The pump light is higher than optical fiber 1
When propagating inside, the skew light is reduced and the probability of being absorbed in the first core 2 is increased, so that the side excitation efficiency is improved.

In the case of the third embodiment, since the reels 8 and 9 of the first and second embodiments are not used and are flat, they are not bulky and flexible. Since the whole can be bent and deformed, mounting is easy.

[0035]

According to the present invention, when a double-core type optical fiber is held, the frequency of skew light in the second core is scattered and intersects with the first core.
The lateral excitation efficiency can be further improved as compared with the related art.

[Brief description of the drawings]

FIG. 1 is a front view showing an optical fiber holding structure according to a first embodiment of the present invention.

FIG. 2 is a sectional view of a reel used in the optical fiber holding structure of FIG. 1;

FIG. 3 is a front view showing an optical fiber holding structure according to a second embodiment of the present invention.

FIG. 4 is a plan view of an optical fiber holding structure according to a third embodiment of the present invention.

FIG. 5 is a cross-sectional view of a double-core optical fiber.

FIG. 6 is a characteristic diagram showing a refractive index distribution of the double-core optical fiber of FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Optical fiber, 2 ... 1st core, 4 ... 2nd core, 6 ... Cladding, 8, 9 ... Reel, 8a, 9a ... Body, 8b, 9b ...
Flange, 10 ... sheet material.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Katsuaki Kondo, 4-3-1 Ikejiri, Itami-shi, Hyogo Mitsubishi Cable Industries, Ltd. Itami Works (72) Yasuhide Sudo 4-3-1, Ikejiri, Itami-shi, Hyogo Mitsubishi Cable Industries Inside Itami Works (72) Inventor Yoshihito Hirano 2-3-2 Marunouchi, Chiyoda-ku, Tokyo Mitsubishi Electric Corporation (72) Inventor Yasuhiro Shoji 2-3-2 Marunouchi, Chiyoda-ku, Tokyo Mitsubishi Electric F term in reference (reference) 2H038 AA21 CA37 CA52 2H050 AC69 5F072 AK06 KK24

Claims (4)

[Claims] A first core formed on an outer periphery of the first core;
The first core is doped with a rare earth element.
The core is such that an optical fiber set to have a smaller refractive index than the first core is wound and held on a reel, and the reel has a body portion around which the optical fiber is wound and a curvature of the excitation light emission. A holding structure for an optical fiber, wherein the optical fiber holding structure is formed so as to be different from a position on a side of the optical fiber and a position on an incident side of the excitation light. 2. The optical fiber holding structure according to claim 1, wherein a portion of the body of the reel having a larger curvature at a position on the excitation light emission side than on the excitation light incidence side is provided. Optical fiber holding structure. 3. The optical fiber holding structure according to claim 1, wherein the body of the reel is formed such that the curvature gradually increases from the excitation light incident side to the excitation light emission side. Optical fiber holding structure. 4. A second core is formed around an outer periphery of the first core,
The first core is doped with a rare earth element.
An optical fiber, which is set so that the refractive index is smaller than that of the first core, is arranged in a state where the orbital positions are shifted from each other in a plane, and is integrally formed by a fixing sheet material such as an adhesive or a film. The optical fiber holding structure, wherein the optical fiber is circulated such that the curvature gradually increases from the excitation light incident side to the excitation light emission side.