JP2005208453A - Method for adjusting attenuation of optically attenuating optical fiber and optically attenuating optical fiber using the method, and optical fixed attenuator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for adjusting attenuation subsequently even for an optically attenuating optical fiber once manufactured, to provide an optically attenuating optical fiber in which attenuation is adjusted using this method, and also to provide an optical fixed attenuator using this fiber. <P>SOLUTION: The coating in the longitudinal direction of the optically attenuating optical fiber 1 is partly removed, with both sides of the coating removed part 2 fixed by a fixing tool 3 and heated by a burner 4. Thus, attenuation is adjusted by diffusing a dopant for optical attenuation such as Co. The fluctuation of the attenuation is constantly monitored by an optical power meter 6 and recorded by a recorder 7. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for adjusting the attenuation of an optical attenuating optical fiber, and a method for finely adjusting the attenuation of the manufactured optical attenuating optical fiber, and to the optical attenuating optical fiber by this method and the optical attenuation The present invention relates to an optical fixed attenuator using a tunable optical fiber.

  In recent years, the development of optical fiber communication networks has been remarkable, and various optical devices have been used. An optical fixed attenuator which is a kind of this optical device is a device for adjusting the optical power level in an optical fiber communication network to an appropriate range.

  The optical attenuating optical fiber used for the fixed optical attenuator is usually one or all of the cores made of quartz glass doped with Ge (germanium), P (phosphorus) or the like, which are dopants for controlling the refractive index, to increase the refractive index. A transition metal element or a rare earth element that attenuates an optical signal is contained as a dopant in the part (see, for example, Patent Document 1 and Patent Document 2). In some cases, a dopant for light attenuation is also added to the cladding.

  The optical attenuating optical fiber is used after being made into a predetermined length and heat-sealed with a transmission optical fiber, or with a connector attached to a terminal and connected to the transmission optical fiber. The optical fixed attenuator is used by inserting a light-attenuating optical fiber into a ferrule and placing it in a connector together with the ferrule, or further storing it in a housing (for example, see Patent Document 3).

When manufactured as a normal optical attenuating optical fiber, the attenuation cannot be changed later, so optical attenuators used in the optical communication network are prepared with various optical attenuating optical fibers depending on the application. It is necessary to keep it. Therefore, it is called an optical fixed attenuator because the amount of attenuation cannot be changed.
Japanese Patent Laid-Open No. 9-184919 Japanese Patent Laid-Open No. 5-264816 Japanese Utility Model Publication No. 63-96506

  By the way, the conventional techniques as described above have the following problems to be solved.

  That is, as described in the prior art, the addition amount of the optical attenuating dopant varies depending on the attenuation amount of the target optical attenuating optical fiber, so that various types of optical fixed attenuators can be used. There is a problem that it is necessary to prepare a large number of attenuation optical fibers, and therefore it is difficult to reduce the cost.

  When the optical attenuating optical fiber is connected by a connector, the attenuation may vary by about ± 0.3 dB due to the eccentricity of the optical attenuating optical fiber itself and the connector. Furthermore, the optical fixed attenuator to which a transition metal is added has a large allowable value of attenuation of about ± 0.5 dB. However, depending on the user, there is a demand for setting within ± 0.1 dB. In such a case, the fixed optical attenuator must be manufactured with extremely high accuracy, and it was inevitable that the cost would increase due to the yield.

  The optical attenuating optical fiber needs to be connected to various transmission optical fibers, but some transmission optical fibers have a mode field diameter different from that of the optical attenuating optical fiber. In such a case, when the transmission optical fiber and the optical attenuating optical fiber are connected, the connection loss increases due to the mismatch of the mode field diameter at the connection portion, and the attenuation amount becomes larger than the attenuation amount designed in advance. There was a problem that. In order to solve such a problem, it is only necessary to fabricate an optical attenuating optical fiber adapted to optical fibers having various mode field diameters. Even if an optical attenuating optical fiber capable of dealing with the mode field diameter is prepared, there is a problem that a considerable increase in cost cannot be avoided.

  The present invention has been made by paying attention to the above points. A method of adjusting the attenuation amount of an optical attenuating optical fiber manufactured once, and an optical attenuating light adjusted by using this method. A fiber and a fixed optical attenuator using the optical attenuating optical fiber are provided.

  The present invention adopts the following configuration in order to solve the above points.

<Configuration 1>
A method for adjusting an attenuation amount of an optical attenuating optical fiber in which both a refractive index controlling dopant and an optical attenuating dopant are added to a core, wherein a part of the optical attenuating optical fiber in the longitudinal direction is heated from the outside to emit light. An attenuation adjustment method for an optical attenuating optical fiber, wherein the attenuation is adjusted by diffusing an attenuation dopant.

  With such a configuration, the attenuation can be adjusted so that the target attenuation can be obtained even after the optical attenuating optical fiber is manufactured.

<Configuration 2>
The attenuation adjustment method for an optical attenuating optical fiber according to Configuration 1, wherein the heating is performed after removing the coating of the heating part of the optical attenuating optical fiber.

  When heating is performed after removing the coating, the diffusion efficiency of the light-attenuating dopant by heating is improved, and the effect can be improved in a short time.

<Configuration 3>
3. A method for adjusting an attenuation amount of an optical attenuating optical fiber according to Configuration 2, wherein the coated portion of the optical attenuating optical fiber is removed and the heated portion is protected again.

  Since the portion from which the coating has been removed is weak in strength, if the portion is protected again, it can be handled in the same way as a normal optical fiber.

<Configuration 4>
The attenuation adjustment method for an optical attenuating optical fiber according to Configuration 1, wherein the attenuation is adjusted while constantly monitoring changes in the attenuation due to heating from the outside of the optical attenuating optical fiber.

  In this configuration, the attenuation amount is adjusted while being constantly monitored, so that the target attenuation amount can be accurately adjusted.

<Configuration 5>
The light-attenuating dopant is one or more dopants selected from Co, V, Fe, Ni, Cu, Cr, Mn, Pt, Er, Pr, Sm, Tm, and Yb. An attenuation adjustment method for an optical attenuating optical fiber according to Configuration 1.

  In this configuration, it is possible to select a light attenuating dopant that is most suitable for the target light attenuating optical fiber.

<Configuration 6>
6. The attenuation adjustment method for an optical attenuating optical fiber according to Configuration 5, wherein the optical attenuating dopant is Co.

  Co is an element that is most easily handled and preferable in terms of manufacturing an optical attenuating optical fiber and from the characteristics of the optical attenuating optical fiber.

<Configuration 7>
An optical attenuating optical fiber, wherein the attenuation is adjusted by the method described in Configuration 1.

  With such a configuration, even if an optical attenuating optical fiber having a certain amount of attenuation prepared in advance is used, the amount of attenuation can be adjusted by the method of Configuration 1 thereafter. An optical attenuating optical fiber can be provided.

<Configuration 8>
An optical fixed attenuator, wherein an optical attenuating optical fiber whose attenuation is adjusted by the method described in Configuration 1 is housed in a housing.

  With such a configuration, it is possible to provide an optical fixed attenuator having an accurate attenuation amount according to the purpose by housing the optical attenuating optical fiber whose attenuation amount is adjusted according to Configuration 7 in the housing.

  Hereinafter, embodiments of the present invention will be described using specific examples.

  FIG. 1 is a diagram for explaining an embodiment of an attenuation adjustment method for an optical attenuating optical fiber according to the present invention. In FIG. 1, the optical attenuating optical fiber 1 has both a refractive index controlling dopant Ge and an optical attenuating dopant Co added to the core. The clad has a three-layer structure, Co is added to the intermediate clad, and the inner clad and the outer clad are pure quartz. In the case of such a clad structure, a clad mode unnecessary for transmission characteristics is removed, and the characteristics of the optical attenuating optical fiber are further improved.

The optical attenuating optical fiber 1 has a part of the coating in the longitudinal direction removed, and a part where the coating on both sides of the coating removal part 2 is not removed is fixed by a fixing jig 3. The coating removal portion 2 is heated by the burner 4. For example, 1300 nm or 1550 nm light from the wavelength signal light source 5 is input to the optical attenuating optical fiber 1, and the output light from the optical attenuating optical fiber 1 is constantly monitored by the optical power meter 6. It is to be recorded.

  A specific method for adjusting the amount of light attenuation is, for example, by inputting 1550 nm light, which is a wavelength signal light used, to the light attenuating optical fiber 1 in which Co is added to the core as a light attenuating dopant, and the amount of attenuation at that time is the optical power meter. 6. Measure with 6 and record with recorder 7. For example, when the value at that time is 5.2 dB, the value of the optical power meter 6 is constantly monitored and recorded by the recorder 7 while the coating removal portion 2 of the optical attenuating optical fiber 1 is heated by the burner 4. At this time, the Co in the core is diffused by heating, and the attenuation amount of the optical attenuating optical fiber 1 gradually decreases. FIG. 2 shows a situation where changes in attenuation are measured with an optical power meter. The values in FIG. 2 represent the amount of increase in the light transmitted through the optical attenuating optical fiber 1, and the increase in the amount of transmitted light indicates that the amount of attenuation is gradually decreasing. Yes.

  The change in the amount of transmitted light in FIG. 2 first increases linearly immediately after the start of heating, and stabilizes at a constant attenuation in about 5 minutes after heating. Stabilization to a certain amount of attenuation indicates that a light attenuating dopant such as Co has reached the maximum region where it can diffuse in the cross section of the light attenuating optical fiber. Therefore, the attenuation can be adjusted by controlling the heating time and temperature from such a situation.

As described above, the situation is constantly monitored by the optical power meter 6, and the heating is stopped when the attenuation amount becomes 5.0 dB, for example. In this way, it becomes possible to finely adjust the attenuation amount of the initially produced optical attenuating optical fiber after production, and it is troublesome to prepare a large number of optical attenuating optical fibers having various attenuation amounts in advance. Can be avoided.

Note that for the heating, for example, a burner such as a gas may be used as in this embodiment, or an electric heater or a discharge method may be used. The most suitable method may be used depending on the situation and is not particularly limited. The heating temperature may be selected so that the coating removal portion of the optical attenuating optical fiber is not deformed, and the optimum temperature may be determined while monitoring the attenuation amount with an optical power meter. Furthermore, with regard to the heating area, for example, a light-attenuating optical fiber with a large attenuation such as that used for connectors is narrowed, and a heating area is widened with a light-attenuating optical fiber having a small attenuation such as that used for pigtails. And so on, depending on the situation.

Further, when the attenuation adjustment method as in the present invention is used, the refractive index control dopant such as Ge is diffused by heating, so that the core is enlarged. That is, the mode field diameter can be adjusted simultaneously. Therefore, if the diffusion time of the optical attenuating dopant is adjusted according to the mode field diameter of the optical fiber for transmission connected to the optical attenuating optical fiber or the optical fixed attenuator, the mode field diameter can be adjusted together with the amount of attenuation. Unnecessary attenuation due to the connection with the optical fiber can be prevented.

  When the dopant is diffused by heating, Ge, which is a refractive index controlling dopant, and other commonly used P have a diffusion coefficient sufficiently smaller than that of a light attenuating dopant such as Co. The function as a fiber is not impaired.

  FIG. 3A shows a situation in which the diffusion of Co, which is a light-attenuating dopant, due to heat changes with time, and FIG. 3B shows a situation of a similar change in the refractive index control dopant Ge. FIG. As can be seen from FIG. 3, it is clear that the diffusion of Co is faster than that of Ge, and the core diameter is enlarged from the state of diffusion of Ge, and the mode field diameter can be adjusted. It is clear.

  The light attenuation dopant is most preferably Co in view of production and characteristics, but other transition metal elements such as V, Fe, Ni, Cu, Cr, Mn, Pt, Er, Pr, Sm, Tm, Yb, and rare earths. One or more elements may be added. That is, the optical attenuating optical fiber is not particularly limited as long as it is a dopant that can be configured.

  Here, the heated portion of the optical attenuating optical fiber is weak in strength because the coating is removed. Therefore, it is desirable to perform protection again after adjusting the attenuation. That is, it is only necessary to recoat the coating removal portion with an ultraviolet curable resin or a polyimide resin, or to protect it using a shrink sleeve. Further, it is also possible to protect by removing the covering removal portion into the ferrule. In short, the most suitable protection may be performed according to the application of the optical attenuating optical fiber, for example, the application for a connector or pigtail.

  The optical attenuation optical fiber after the attenuation is adjusted by applying the attenuation adjustment method of the present invention to the optical attenuation optical fiber and the optical attenuation optical fiber are inserted into a ferrule, attached with a connector, The fixed optical attenuator housed in the body is also within the scope of the present invention, and the most suitable form can be adopted according to the application and purpose.

It is a figure explaining one embodiment of the present invention. It is a figure showing the change of the transmitted light amount. It is a figure showing the condition of the diffusion of Co and Ge.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical attenuating optical fiber 2 Cover removal part 3 Fixing jig 4 Burner 5 Light source 6 Optical power meter 7 Recorder

Claims (8)

A method for adjusting an attenuation amount of an optical attenuating optical fiber in which both a refractive index control dopant and an optical attenuating dopant are added to a core, wherein a part of the optical attenuating optical fiber in the longitudinal direction is heated from the outside to produce light. An attenuation adjustment method for an optical attenuating optical fiber, wherein the attenuation is adjusted by diffusing an attenuation dopant.   2. The attenuation adjustment method for an optical attenuating optical fiber according to claim 1, wherein the heating is performed after removing the coating of the heating portion of the optical attenuating optical fiber.   3. The method of adjusting an attenuation amount of an optical attenuating optical fiber according to claim 2, wherein the coated portion of the optical attenuating optical fiber is removed and the heated portion is protected again. The method of adjusting an attenuation amount of an optical attenuating optical fiber according to claim 1, wherein the adjustment of the attenuation amount is performed while constantly monitoring a change in the attenuation amount due to heating from the outside of the optical attenuating optical fiber. The light-attenuating dopant is one or more dopants selected from Co, V, Fe, Ni, Cu, Cr, Mn, Pt, Er, Pr, Sm, Tm, and Yb. The attenuation adjustment method of the optical attenuating optical fiber according to claim 1. 6. The method of adjusting an attenuation amount of an optical attenuating optical fiber according to claim 5, wherein the optical attenuating dopant is Co. An optical attenuating optical fiber, wherein the attenuation is adjusted by the method according to claim 1. An optical attenuator comprising: an optical attenuating optical fiber whose attenuation is adjusted by the method according to claim 1;

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