JPH11183736A - Optical fiber, optical attenuator using same and optical filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decrease the influence of a cladding mode caused at the time of connection and to provide an optical fiber having an excellent characteristic by containing a dopant having a low refractive index in a cladding layer for decreasing the refractive index. SOLUTION: An optical fiber 4 is formed by a core 1 propagating light and a cladding composed of an inner cladding layer 2 and an outer cladding layer 3 in this order around the core. The core 1 contains attenuation dopant Co<2> , Ge. F is added to the inner cladding layer 2 for decreasing the refractive index. P and Co<2> are added to the outer cladding layer 3 for confining/ dissipating the cladding mode. Consequently, an optical fiber having no problem in the manufacturing process of the optical fiber and being hardly affected by the influence of a cladding mode is provided. When this optical fiber is used, an attenuation material of high density can be contained in a part confining the cladding mode and also the cladding mode is effectively confined.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber used for transmitting an optical signal through an optical fiber and performing communication and sensing, and an optical attenuator and an optical filter using the same. The present invention relates to an optical fiber that attenuates and adjusts an optical signal, an optical attenuator using the same, and an optical filter that blocks an optical signal.

[0002]

2. Description of the Related Art Heretofore, there have been proposed several methods for attenuating a certain amount of an optical signal in an optical attenuator using an optical fiber. As a method of such optical attenuation, a method of adding a transition metal into the core of an optical fiber is mass-producible,
Excellent in terms of reliability. Such a technique is introduced in, for example, JP-A-6-303156.

A fixed attenuator generally has optical fibers for optical transmission connected to both ends. For this reason, the light corresponding to the connection loss generated due to the axis deviation or the difference in the mode field at the connection point with the optical transmission fiber becomes a clad mode that propagates through the clad. If the attenuation of the fixed attenuator is large and the size is as short as several tens of mm, the cladding mode propagates to the output end of the fixed attenuator, and the core propagation mode and the cladding mode recombine at the output end. Is known.

[0004] When such recombination occurs, the phases of the core and the cladding mode are shifted from each other at the emission end because the refractive index of the core is different from that of the cladding mode. Therefore, a beat phenomenon occurs in the wavelength dependence of the attenuation, and the attenuation becomes unstable. Also, if the wavelength used is shifted even a little (several nm), the same fixed attenuator will have different attenuation. FIG. 5 shows the wavelength dependence of the attenuation of the fixed attenuator in such a state.

It is obvious that such a problem has a similar problem not only with a fixed attenuator but also with an optical filter that blocks a certain amount of an optical signal. In order to solve such a problem, a technique has been disclosed in which a part of the refractive index of the cladding is increased, the cladding mode is confined in that part, and the cladding mode is annihilated by containing a light-attenuating dopant in that part. ing. Such a technology is disclosed in
No. 109923. Japanese Patent Application Laid-Open No. 8-4 discloses a technique in which an attenuating dopant is contained in the entire cladding to eliminate the cladding mode. Also, a method of incorporating metals into an optical fiber is disclosed in Japanese Patent Publication No. 58-3980.

[0006]

However, these methods have problems in manufacturing optical fibers. When Ge is added to raise a part of the clad and a light-attenuating transition metal is added at a high concentration, there is a problem that crystallization occurs. This crystallization causes a change in the outer diameter of the fiber when the optical fiber is spun, thereby lowering the yield of the attenuating fiber. Although it is generally known that crystallization is eliminated by adding P and Al, it is difficult to easily obtain a refractive index difference that can sufficiently confine a cladding mode with P and Al. This makes it impossible to eliminate the cladding mode. Thus, it is apparent that it is difficult to effectively eliminate the cladding mode of the fixed attenuator and reduce the cost.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to reduce the influence of a clad mode generated at the time of connection, to provide a structure excellent in characteristics and to eliminate the clad mode easily in manufacturing. And an optical attenuator and an optical filter using the same.

[0008]

SUMMARY OF THE INVENTION To achieve this object, an optical fiber of the present invention and an optical attenuator and an optical filter using the same reduce recombination between a propagation mode of a core and a cladding mode occurring at the time of connection. It was done for. In the conventional attenuating fiber, it is difficult to prevent crystallization caused by the inclusion of the light attenuating dopant, and it is not enough to effectively eliminate the cladding mode. In order to solve this, first, P was doped with an attenuating dopant to prevent crystallization. The cause of crystallization is segregation of the damping dopant. This was done by doping P in the fabrication of the optical fiber to weaken the bond bonds in the glass matrix so that the attenuating dopant was dispersed in the glass. Second, F was added to the clad inner layer in order to increase the difference between the refractive index of the clad inner layer near the core and the refractive index of P and the clad containing the attenuating dopant.

Therefore, by adding F to the inner layer of the clad, the clad mode is effectively confined in the clad containing P and the attenuating dopant, and the cladding mode is extinguished by the attenuating dopant and the core generated at the time of connection is formed. It was confirmed that the recombination between the propagation mode and the cladding mode was reduced. The same effect can be obtained by adding Al, which has an effect of suppressing crystallization, instead of P in the cladding containing the attenuating dopant. This A
l also has the effect of increasing the refractive index. It is also possible to add a small amount of Ge, Ti, Zr, Na or the like to increase the refractive index. On the other hand, the same effect can be obtained by doping the clad inner layer with B, which has the effect of lowering the refractive index.

As described above, the optical fiber of the present invention is an optical fiber formed of a core and a clad composed of a clad inner layer and a clad outer layer which are sequentially formed around the core. Contains a low-refractive-index dopant for causing In this optical fiber, the composition of the cladding inner layer is mainly composed of quartz glass.

In this optical fiber, the low refractive index dopant is one or more components of F and B. In this optical fiber, the composition constituting all or a part of the cladding outer layer is mainly composed of quartz glass, and the cladding outer layer contains a high refractive index dopant for increasing the refractive index.

In this optical fiber, the high refractive index dopant is one or more of Ge, P, Al, and Ti. In this optical fiber, the outer cladding layer contains an attenuating dopant for attenuating an optical signal and / or has a scattering structure for scattering.

In this optical fiber, the attenuating dopant contains at least one type of transition metal or rare earth metal. In this optical fiber, the light signal scattering structure is made of ceramics or crystallized glass. In this optical fiber, the core in the optical fiber contains an attenuating dopant and / or has a structure for attenuating.

In this optical fiber, the attenuating dopant in the core includes at least one transition metal or rare earth metal.
Including type. An attenuator and an optical filter are configured by using this optical fiber.

[0015]

According to the optical fiber configured as described above, it is possible to obtain an optical fiber which has no problem in the conventional optical fiber manufacturing process and has a structure which is hardly affected by the cladding mode. If this optical fiber is used, a high-concentration attenuating material can be contained in the portion where the cladding mode is confined, and the cladding mode can be confined effectively, improving the yield of the optical fiber and improving productivity. This makes it possible to manufacture an optical fixed attenuator and an optical filter that are excellent in cost, thereby reducing costs.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of an optical fiber of the present invention and an optical attenuator and an optical filter using the same will be described below with reference to the drawings. [Embodiment 1] As shown in FIG.
And an optical fiber 4 formed of a clad composed of a clad inner layer 2 and a clad outer layer 3 which were sequentially formed around the core.

The core 1 has Co ²⁺ as an attenuating dopant.
The SC adapter-type optical fixed attenuator was manufactured using an attenuating fiber containing F and Co ²⁺ in the cladding outer layer 3, and the amount of attenuation was confirmed. . FIG. 1 shows the refractive index distribution. Core 1
Contains the attenuating dopants Co ²⁺ and Ge.
F is added to the cladding inner layer 2 to lower the refractive index. The cladding outer layer 3 contains P and Co ²⁺ for confining the cladding mode and for extinguishing the cladding mode. The core 1 is designed to propagate under a single mode condition, and the relative refractive index difference between the inner cladding layer 2 and the core 1 is 0.4%.
Has a core diameter of about 7 μm. The relative refractive index difference between the outer clad layer 3 and the inner clad layer 2 is designed to be 0.5%, and the diameter of the inner clad layer 2 is designed to be 50 μm. The fiber diameter is 125 μm, which is the same as a normal optical fiber. In the attenuating fiber 4, almost no change in the fiber outer diameter during spinning caused by crystallization was observed. This attenuating fiber 4 was mounted on an SC adapter type optical fixed attenuator shown in FIG. 2, and the amount of attenuation was measured. The optical fiber 4 is built in the Zr ferrule 5 in FIG. In FIG. 2, reference numeral 6 denotes a sweep, and 7 denotes a housing.

When the attenuation of the SC adapter type optical fixed attenuator incorporating the attenuating fiber was measured, the attenuation was about 21 to 2
It was 2 dB. In addition, the variation in attenuation due to the beat from a wavelength of 1.5 μm to 1.6 μm was 0.2 dB or less, and it was confirmed that there was almost no variation in the wavelength dependence of the attenuation due to the recombination of the core and cladding modes. . FIG. 3 shows the wavelength dependence of the attenuation.

[Example 2] An SC adapter type light was formed by an attenuating fiber in which the core 1 contained Co ²⁺ as an attenuating dopant, F was added to the inner cladding layer 2, and Ge was contained in the outer cladding layer 3. A fixed attenuator was fabricated and the amount of attenuation was confirmed. The refractive index distribution has a distribution similar to that of FIG. The core 1 is designed to propagate under a single mode condition, and has a relative refractive index difference of 0.3% between the cladding inner layer 2 and the core 1 and a core diameter of about 8 μm. The relative refractive index difference between the outer clad layer 3 and the inner clad layer 2 is designed to be 0.3%, and the diameter of the inner clad layer 2 is designed to be 60 μm. The fiber diameter is 125 μm, which is the same as that of a normal optical fiber. This attenuating fiber was mounted on an SC adapter type optical fixed attenuator shown in FIG. 2, and the amount of attenuation was measured. The optical fiber is Zr in FIG.
Built in ferrule 5.

When the attenuation of the SC adapter type optical fixed attenuator incorporating the attenuating fiber was measured, the attenuation was 28 to 32.
dB. The variation in attenuation due to the beat from a wavelength of 1.5 μm to 1.6 μm is about 2.0 dB, and the variation in the wavelength dependence of the attenuation due to the recombination of the core and cladding modes is slightly larger than that in the first embodiment. Was small. This is the Zr ferrule 5 holding the fiber.
This is because the cladding mode is scattered on the inner wall of the substrate.
FIG. 4 shows the wavelength dependence of the attenuation.

[0021]

As is apparent from the above description, according to the present invention, it is possible to obtain an optical fiber having no problem in the optical fiber manufacturing process and having a structure which is hardly affected by the cladding mode. it can. By using the optical fiber of the present invention, a high-concentration attenuating material can be contained in a portion where the clad mode is confined, and confinement of the clad mode can be performed effectively. By improving the yield of optical fibers, it is possible to manufacture an optical fixed attenuator and an optical filter that are excellent in mass productivity, and cost reduction can be achieved.

[Brief description of the drawings]

FIG. 1 is a diagram showing a cross section and a refractive index distribution of an optical fiber according to Embodiments 1 and 2 of the present invention.

FIG. 2 is a diagram showing an SC adapter type optical fixed attenuator according to Embodiments 1 and 2 of the present invention.

FIG. 3 is a diagram of measurement results showing the wavelength dependence of the amount of attenuation in Example 1 of the present invention.

FIG. 4 is a diagram of measurement results showing the wavelength dependence of the amount of attenuation in Example 2 of the present invention.

FIG. 5 is a diagram showing the wavelength dependence of the amount of attenuation in the related art.

[Explanation of symbols]

 1 ... core 2 ... clad inner layer 3 ... clad outer layer

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yumi Ariga 2-1-1, Sakae Oda, Kawasaki-ku, Kawasaki City, Kanagawa Prefecture Inside Showa Electric Wire & Cable Co., Ltd. (72) Kenichi Muta 2 Ei Oda, Kawasaki-ku, Kawasaki City, Kanagawa 1-1-1, Showa Electric Wire & Cable Co., Ltd. (72) Inventor Masashi Saijo 2-1-1, Oda Sakae, Kawasaki-ku, Kawasaki-shi, Kanagawa Prefecture In-Showa Electric Wire & Cable Co., Ltd. (72) Inventor Kazunari Sugi Showa Electric Wire & Cable Co., Ltd. 2-1-1, Sakae Oda, Kawasaki-ku (72) Yoshiaki Takeuchi Inventor, Nippon Telegraph and Telephone Corporation 3-9-1, Nishi-Shinjuku, Shinjuku-ku, Tokyo, Japan (72) Inventor Ryo Nagase, Tokyo Nippon Telegraph and Telephone Corporation, 3-19-2 Nishi Shinjuku, Shinjuku-ku Nippon Telegraph and Telephone Corporation (72) Inventor Makoto Sumita 3-19-2 Nishi-Shinjuku, Shinjuku-ku, Tokyo Japan Nippon Telegraph and Telephone Corporation Within the company (72) inventor Mitachi Nariyuki Tokyo Nishi-Shinjuku, Shinjuku-ku, Third Street No. 19 No. 2, Nippon Telegraph and Telephone Corporation in the

Claims (12)

[Claims] 1. An optical fiber formed from a core and a cladding comprising an inner cladding layer and an outer cladding layer which are sequentially formed around the core, wherein the cladding inner layer has a low refractive index for lowering the refractive index. An optical fiber comprising a dopant. 2. The optical fiber according to claim 1, wherein said cladding inner layer has a composition mainly composed of quartz glass. 3. The optical fiber according to claim 2, wherein said low refractive index dopant is one or more components of F and B. 4. A composition constituting a whole or a part of the cladding outer layer is mainly composed of quartz glass, and the cladding outer layer contains a high refractive index dopant for increasing a refractive index. 2. The optical fiber according to 1. 5. The high refractive index dopant is Ge, P, A.
5. The optical fiber according to claim 4, wherein the optical fiber is one or more components of l and Ti. 6. The cladding outer layer contains an attenuating dopant for attenuating an optical signal and / or has a scattering structure for scattering. The optical fiber according to claim 1. 7. The optical fiber according to claim 6, wherein said attenuating dopant contains at least one kind of transition metal or rare earth metal. 8. The optical fiber according to claim 6, wherein said light signal scattering structure is made of ceramics or crystallized glass. 9. The optical fiber according to claim 1, wherein the core contains an attenuating dopant and / or has a structure for attenuating the core. Optical fiber. 10. The optical fiber according to claim 9, wherein the attenuating dopant in the core contains at least one kind of transition metal or rare earth metal. 11. An optical attenuator using the optical fiber according to any one of claims 1 to 10. 12. An optical filter using the optical fiber according to any one of claims 1 to 10.