JP6068278B2 - Evaluation method of longitudinal distribution of fictive temperature of optical fiber - Google Patents

Description

  The present invention relates to a method for evaluating a virtual temperature of an optical fiber.

  In recent years, further increases in capacity and distance have been advanced in optical fiber communications. An optical fiber using quartz glass used for long-distance communication has a feature of low loss. In addition to this feature, with the advent of optical amplifiers such as erbium-doped fiber amplifiers (EDFAs), long-distance communication has been realized even longer. In a long-distance communication system such as submarine communication, a plurality of EDFAs are arranged in an optical transmission line to compensate for optical loss due to transmission. From the viewpoint of cost reduction of the transmission system, the relay interval when using the EDFA needs to be increased as much as possible. From the above, it can be said that the reduction of optical fiber loss will continue to be a very important issue as the capacity and distance are further increased.

The fictive temperature _Tf of glass refers to a lower limit temperature at which the glass structure is frozen in the cooling process from a high-temperature melt state, and structural relaxation does not occur at a lower temperature. Therefore, the fictive temperature _Tf varies depending on the heat treatment conditions (thermal history) during glass production. The fictive temperature T _f is a parameter that affects various properties of glass, such as density, refractive index, strength, etc., but it has been shown to be closely related to Rayleigh scattering loss, especially in optical fibers. ing.

Specifically, the Rayleigh scattering loss α _R is inversely proportional to the fourth power of the wavelength λ of light, and is given by Equation (1) using the Rayleigh scattering coefficient R.
α _R = R / λ ⁴ (1)
Rayleigh scattering coefficient R is given by Equation (2) as the sum of the density fluctuation component _{R d} and composition fluctuation component _{R c.}
R = R _d + R _c (2)
Further, a proportional relationship is established between the density fluctuation component _Rd and the virtual temperature _Tf . In particular, in a material composed of a single molecular component, the composition fluctuation component R _c = 0. In an optical fiber having a pure silica glass core, it is clear that the Rayleigh scattering coefficient R changes in proportion to the fictive temperature _Tf . Specifically, it has been demonstrated that the fictive temperature _Tf can be reduced by setting the drawing temperature _Td at the time of production low and drawing slowly at a low speed. As shown in FIG. 1, when the fictive temperature _Tf is reduced, the Rayleigh scattering coefficient R is reduced in proportion to the fictive temperature _Tf .

FIG. 2 is a conceptual diagram showing the relationship between the holding time and the Rayleigh scattering coefficient R using the holding temperature as a parameter. In order to reduce the fictive temperature _Tf , it is advantageous to hold (draw) at a low temperature, but the holding time requires a longer time as the holding temperature becomes lower (for example, see Non-Patent Documents 1 and 2). .) Holding temperature refers to the temperature at which the optical fiber is heat treated. The holding time is a time for heat-treating the optical fiber at the holding temperature.

As described above, the virtual temperature T _f of the optical fiber is a very important parameter that is closely related to Rayleigh scattering loss, which is the most dominant loss factor in the communication wavelength band. As a method for measuring and evaluating the fictive temperature _Tf of an optical fiber, a method using infrared spectroscopic analysis is known (for example, see Non-Patent Document 3).

However, in the above method, the measurement accuracy (measurement resolution) is relatively rough, about + -15 ° C., and further, the longitudinal distribution of the fictive temperature T _f that is important for a long optical fiber cannot be measured. In particular, a method for realizing the measurement of the longitudinal distribution of the fictive temperature _Tf has not been known so far.

K. Tsujikawa, K. et al. Tajima, and J.A. Zhou, “Intrinsic loss of optical fibers,” Opt. Fiber Technol. 11, pp. 319, 2005. K. Saito, E .; H. Sekiya, A .; J. et al. Ikushima, K .; Ohsono, and Y. Kurosawa, "Control of glass-forming process-during fiber-drawing to reduce the Rayleigh scattering loss," J. Am. Ceram. Soc. , Vol. 89, no. 1, pp. 65-69, 2006. Anand Agarwal, Kenneth M .; Davis, and Minoru Tomozawa, “A simple IR spectroscopic method for determining fictive temperature of silica glass,“ Journal of Non-Solly. 191-198, 1995. A. Wada, T .; Nozawa, T .; Tsun, and R.M. Yamauchi, “Suppression of stimulated Brillouin scattering by intentedly induced peripheral residual-strain in single-mode optical ICs. Commun. , Vol. E76-B, no. 4, pp. 345-351, 1993. Shinichi Kushibiki, Mototaka Arakawa, Yuji Ohashi, Yuko Maruyama, Takanori Kondo, Tetsuo Yoshida, “Study on virtual temperature evaluation of synthetic quartz glass by ultrasonic microspectroscopy technology”, IEICE technical report. US, Ultrasound 110 (213), pp. 23-28, 2010. Norio Tokunaga, Kenichi Inoue, Hideo Kikuchi, Yasuo Hino, “Examination of measurement systems using optical fiber sensors”, Civil Engineering Planning and Lectures (CD-ROM), 27, IX (248), 2003 June Kazuo Oishi, Satoshi Matsuura, Shoji Adachi, Yahei Koyamada, “High-precision double pulse BOTDR using signal processing technology”, IEICE technical report OFT, Optical fiber application technology, 109 (59), pp. 75-78, 2009-05-21

  As described above, the conventionally proposed methods have a problem that the measurement evaluation accuracy of the virtual temperature is relatively coarse and the longitudinal distribution cannot be measured.

  The present invention has been made in view of the above circumstances, and an object thereof is to realize a method for evaluating a longitudinal distribution of a virtual temperature of an optical fiber with high measurement accuracy (measurement resolution).

In order to achieve the above object, the present invention measures the longitudinal distribution νB (z) of the Brillouin frequency shift amount of the optical fiber, and determines the measured longitudinal distribution ν _B (z) of the Brillouin frequency shift amount of the optical fiber. Based on this, the longitudinal distribution T _f (z) of the fictive temperature of the optical fiber is calculated.

Specifically, the present invention provides a longitudinal length of the Brillouin frequency shift amount of a plurality of virtual temperature control optical fibers having a predetermined core diameter, the same structure and the same glass composition distribution, and different virtual temperatures _Tf. A Brillouin frequency shift amount measuring step for measuring the directional distribution ν _B (z);
Based on the virtual temperature T longitudinal distribution of the Brillouin frequency shift amount of the fictive temperature adjusting optical fiber each _f ν _{B (z),} between the virtual temperature adjustment Brillouin frequency shift amount of the optical fiber [nu _B and the virtual temperature T _f An empirical formula derivation step that determines T _f (z) = g (ν _B )
Based on the empirical formula: T _f (z) = g (ν _B ), an optical fiber to be measured having the predetermined core diameter and the same structure and the same glass composition distribution as the virtual temperature control optical fiber A virtual temperature measuring step for calculating a longitudinal distribution T _f (z) of the virtual temperature of
Which is the order evaluation method of longitudinal distribution of the fictive temperature of the run to an optical fiber, characterized in Rukoto.

In the virtual temperature measurement step of the present invention,
In an optical fiber having the same composition as the core of the optical fiber, an empirical formula established between the longitudinal wave velocity V _g and the fictive temperature T _f in a glass having the same composition as the core of the optical fiber: V _g = f (T _f ) and
Longitudinal distribution ν _B (z) of the Brillouin frequency shift amount of the optical fiber, the measurement wavelength λ in the Brillouin frequency shift amount measurement step, the refractive index n of the propagation optical mode of the optical fiber, and the longitudinal wave sound velocity of the optical fiber The theoretical formula that holds between the longitudinal distributions V _f (z) of: V _f (z) = ν _B (z) λ / (2n),
Based on the above, the longitudinal direction distribution T _f (z) of the virtual temperature of the optical fiber is calculated as V _g = V _f (z). is there.

Further, the present invention is the virtual temperature adjustment optical fiber, after holding the optical fiber at a holding temperature T _a, by quenching, the optical fiber der adjusting the holding temperature T _a to the virtual temperature T _f Rukoto This is a method for evaluating the longitudinal distribution of the fictive temperature of an optical fiber.
Further, in the present invention, the plurality of virtual temperature adjustment optical fibers have different production parameters,
An adjusted virtual temperature measuring step for measuring the virtual temperature _Tf of the virtual temperature adjusting optical fiber may be executed before the empirical formula deriving step .

The present invention also executes the optical fiber fabrication step of making the virtual temperature adjusting optical fiber by Rukoto changing the value of the fabrication parameters during drawing of the optical fiber temporally before the Brillouin frequency shift amount measuring step This is a method for evaluating the longitudinal distribution of the fictive temperature of an optical fiber.
Here, the manufacturing parameters numerology determining a value of the fabrication parameters obtained any fictive temperature T _f from the virtual temperature measuring virtual temperature measured in step longitudinal distribution T _{f (z)} Virtual It may be performed after the temperature measurement step.

Further, the present invention is the manufacturing parameter, drawing speed of the optical fiber during drawing of the optical fiber, drawing temperature of the optical fiber preform, the feed speed of the optical fiber preform, the optical fiber drawing tension and the optical fiber preform It is a method for evaluating the longitudinal distribution of the fictive temperature of an optical fiber, characterized in that it is one of neck-down lengths.

  ADVANTAGE OF THE INVENTION According to this invention, even if it is a long optical fiber, measurement accuracy (measurement resolution) is high and it becomes possible to implement | achieve the method of calculating the longitudinal direction distribution of virtual temperature.

It is a figure explaining the relationship between fictive temperature _Tf and Rayleigh scattering coefficient R. It is a conceptual diagram showing the relationship between holding time and Rayleigh scattering coefficient R using holding temperature as a parameter. It is a diagram illustrating the relationship between the longitudinal wave acoustic velocity V _g of pure silica glass and the virtual temperature T _f. It is a measured value of the longitudinal direction distribution of the Brillouin frequency shift amount ν _B and an evaluation value of the longitudinal direction distribution of the virtual temperature T _f . It is a figure which shows the relationship between the drawing temperature _Td of a quartz core optical fiber, and Brillouin frequency shift amount (nu) _B. It is a figure explaining the relationship between Brillouin frequency shift amount (nu) _B and virtual temperature _Tf . It is an example of longitudinal direction distribution of Brillouin frequency shift amount (nu) _{B of} an optical fiber.

  Embodiments of the present invention will be described with reference to the accompanying drawings. The embodiment described below is one embodiment of the present invention, and the present invention is not limited to the following embodiment. In the present specification and drawings, the same reference numerals denote the same components. Here, unless otherwise specified, the optical fiber refers to a single mode optical fiber.

(Embodiment 1)
In the present embodiment, a Brillouin frequency shift amount measuring step for measuring the longitudinal distribution ν _B (z) of the Brillouin frequency shift amount of the optical fiber, and the longitudinal direction of the Brillouin frequency shift amount of the optical fiber measured in the Brillouin frequency shift amount measuring step. A virtual temperature measurement step of calculating a longitudinal distribution T _f (z) of the virtual temperature of the optical fiber based on the direction distribution ν _B (z), and a method for evaluating the longitudinal distribution of the virtual temperature of the optical fiber in order explain.

Longitudinal wave velocity distribution V _f (z) in the optical fiber is given by equation (3) using the Brillouin frequency shift amount ν _B (z) measured at the longitudinal position z of the optical fiber ( For example, refer nonpatent literature 4.).
V _f (z) = ν _B (z) λ / (2n) (3)
Here, n is the refractive index of the optical mode propagating in the core, and λ is the measurement wavelength.

On the other hand, it has been reported that the longitudinal sound velocity V _g of longitudinal acoustic waves propagating in pure silica glass, which is also a material for optical fibers, increases linearly with respect to the virtual temperature T _f (for example, non-patent literature). 5). From the data of Non-Patent Document 5, when the relationship between the longitudinal sound velocity V _g and the fictive temperature T _{f of} pure quartz glass is plotted, Equation (4) is obtained.
V _g = 0.1371 × T _f +5798.6 (4)

FIG. 3 shows the relationship between the two expressed by equation (4). From FIG. 3, the longitudinal sound velocity V _g changes by about 40 m / s with respect to the change of the virtual temperature T _f of about 300 ° C. From this, it can be seen that the sensitivity of the longitudinal sound velocity V _g to the virtual temperature T _f is 7.3 ° C · s · m ⁻¹ . Further, Non-Patent Document 5 shows that the measurement accuracy (measurement resolution) of the virtual temperature T _f obtained from the value of the longitudinal wave sound velocity V _g is very good at about 0.4 ° C.

In the present invention, the Brillouin frequency shift amount ν _B is measured for the corresponding optical fiber, and the value of T _f is determined using the value of the Brillouin frequency shift amount ν _B as an index. BOTDR (Brillouin Optical Time Domain Reflectometry) or BOTDA (Brillouin Optical Time Domain Analysis), which are existing technologies, can be used to measure the Brillouin frequency shift amount ν _B. It is premised on the use of BOTDR that enables measurement evaluation from one side of the fiber.

In Equation (3), it can be assumed that V _f (z) = V _g with sufficient accuracy as a first order approximation for a silica-based optical fiber. Accordingly, when the measurement wavelength λ = 1.55 μm and the refractive index n = 1.444, the sensitivity of the Brillouin frequency shift amount ν _B to the virtual temperature T _f is about 4 ° C./(MHz). On the other hand, the measurement resolution in the longitudinal direction of the Brillouin frequency shift amount ν _B in a normal BOTDR measurement device also depends on the optical pulse width at the time of measurement. By setting the optical pulse width to 20 ns or more, + −2.5 MHz (corresponding to distortion resolution + −0.005%) can be realized (for example, see Non-Patent Document 6).

However, if the optical pulse width is too wide, the distance resolution in the longitudinal direction is degraded. Therefore, the optimum optical pulse width in the general-purpose BOTDR is around 20 ns, and the distance resolution in the longitudinal direction can be 2 m under the condition of 20 ns. Therefore, in the present invention, a fiber having a total length of 10 km or more (a loss of about 0.2 dB / km is assumed under the condition that the measurement resolution of the virtual temperature _Tf is + −10 ° C. and the distance resolution is 2 m by the BOTDR measuring instrument. ) On the other hand, it is possible to calculate the longitudinal distribution T _f (z) of the virtual temperature, which was impossible with the existing technology.

In addition, the measurement resolution of the fictive temperature _Tf of + −10 ° C. is a value better than + −15 ° C. (for example, see Non-Patent Document 3) of typical existing infrared spectroscopy. is there. Further, in order to improve this value, a double pulse BOTDR measurement technique as shown in Non-Patent Document 7 may be used for measuring the Brillouin frequency shift amount ν _B. With this technique, it is possible to realize + -0.25 MHz (corresponding to distortion resolution + -0.0005%) as the measurement resolution of the Brillouin frequency shift amount ν _B under the condition of a distance resolution of 20 cm. This corresponds to + −1 ° C. (= + − 0.25 MHz × 4 ° C./(MHz)) when converted to the measurement resolution of the virtual temperature T _f . Therefore, if the double pulse BOTDR measurement technique is used, the calculation of the longitudinal distribution T _f (z) of the virtual temperature with higher accuracy can be realized.

(Embodiment 2)
This embodiment is a method for determining the longitudinal distribution T _f (z) of the virtual temperature from the longitudinal wave sound velocity V _{g in} the glass having the same composition as the core of the corresponding optical fiber and the principle of the present invention.

Longitudinal distribution ν _B (z) of the Brillouin frequency shift amount of a hole-type pure quartz photonic crystal fiber (PCF: Photonic Crystal Fiber) having a wavelength of λ = 1.552 μm and a pulse width of 100 ns measured by a BOTDR measuring instrument. ) Is shown on the left vertical axis in FIG. The hole-type PCF has a periodic hole structure in the cross section, but the core portion is pure quartz glass.

The empirical formula (5) is established between the longitudinal wave velocity V _g and the virtual temperature T _{f in} the glass having the same composition as the core of the corresponding optical fiber.
V _g = f (T _f ) (5)
Here, assuming that V _g = V _f (z) approximately, and substituting Equation (5) of longitudinal wave velocity V _{g in} glass having the same composition as the core of the optical fiber into Equation (3), Equation (3) 6) is obtained.
T _f (z) = [ν _B (z) λ / (2n) −5798.6] /0.1371 (6)
By using the measured value of the longitudinal direction distribution ν _B (z) of the Brillouin frequency shift amount, the measurement wavelength λ = 1.552 μm, and the refractive index n = 1.444 of pure quartz glass in the equation (6), the hypothesis with respect to the position z A longitudinal distribution T _f (z) of temperature can be calculated. The calculated longitudinal distribution T _f (z) of the fictive temperature is shown on the right vertical axis of FIG.

The average value of the obtained longitudinal distribution T _f (z) of the fictive temperature is a value around 1300 ° C. Considering that the corresponding PCF was drawn at a drawing temperature T _d as low as about 1850 ° C. and the possibility that the core was gradually cooled by the pore structure, this value of 1300 ° C. is a reasonable value. is there. In the hole-type PCF, scattering loss due to unevenness on the hole surface is affected. For this reason, it is difficult to determine the Rayleigh scattering coefficient R from the spectrum of the loss wavelength characteristic, and it is also difficult to determine the loss factor. According to the present invention, by evaluating and determining the virtual temperature T _f of the hole-type optical fiber, it is possible to determine whether the main cause of the loss is Rayleigh scattering or scattering due to the unevenness of the hole surface. .

(Embodiment 3)
In this embodiment, in the optical fiber having the same structure and the same glass composition distribution as the corresponding optical fiber, the longitudinal distribution of the virtual temperature from the empirical formula established between the Brillouin frequency shift amount ν _B and the virtual temperature T _f This is a method of calculating T _f (z).

FIG. 5 shows the relationship between the drawing temperature T _d and the Brillouin frequency shift amount ν _{B of} a GeO ₂ doped quartz core SMF drawn from a base material of a single mode optical fiber (SMF). The SMF has a specification defined by an international standard (ITU-T G.652). Since it is known that the value of the Brillouin frequency shift amount ν _B varies depending on the core diameter a, the outer diameters of the four types of SMFs are set to 125 + −0.5 μm, and the influence of fluctuation of a can be ignored. The range is suppressed. It has already been known that by reducing the drawing temperature T _d , the effect of reducing the holding temperature shown in FIG. 1 is obtained, and the virtual temperature T _f is also reduced (see, for example, Non-Patent Document 1). Therefore, FIG. 4 is a result qualitatively showing the validity of the principle of the present invention in which the change in the virtual temperature T _f is observed as the change in the Brillouin frequency shift amount ν _B. The direction of change also coincides with the direction predicted from equation (6).

As described above, since the sensitivity of the Brillouin frequency shift amount ν _B with respect to the virtual temperature T _f is considered to be about 4 ° C / (MHz), the observed change in the Brillouin frequency shift amount ν _B of about 40 MHz is about 160 This is considered to correspond to a change in the fictive temperature T _f at ° C. In Non-Patent Document 1, by changing the drawing temperature _Td , the value of about 200 ° C. and the fictive temperature _Tf is changed, which is qualitatively consistent with the current observation result.

Quantitatively, the values of the drawing temperature T _d and the fictive temperature T _f generally do not match. That is, since the generally towards the drawing temperature T _d becomes larger than the fictive temperature T _f, in order to obtain the relationship established between the virtual temperature T _f and Brillouin frequency shift amount [nu _B quantitatively the For example, the virtual temperatures _Tf of the four SMFs in FIG. 5 may be determined by infrared spectroscopy that is an existing technique. In this way, the empirical formula (7) between the Brillouin frequency shift amount ν _B related to the SMF and the longitudinal distribution T _f (z) of the virtual temperature is determined in advance.
T _f (z) = g (ν _B ) (7)

(Embodiment 3-1)
When the Brillouin frequency shift amount ν _B is measured for SMFs having the same structure and the same glass composition distribution manufactured under various drawing conditions, the length of the virtual temperature of each SMF can be calculated from the equation (7). The direction distribution T _f (z) can be determined.

Embodiment 3-2
As a method for determining the equation (7), an SMF having the same structure and the same glass composition distribution is rapidly applied after a suitable holding time has elapsed at _a holding temperature T _a (T _a1 , T _a2 ,... T _am ). There is a method in which the value of the holding temperature T _a (T _a1 , T _a2 ,... T _am ) is adjusted so as to become the virtual temperature T _f by cooling to a predetermined value. Then, by measuring the Brillouin frequency shift amount ν _B of each of the m fibers corresponding to the holding temperatures T _a (T _a1 , T _a2 ,... T _am ), the Brillouin frequency shift amount ν _B and The empirical formula (7) between the longitudinal distributions T _f (z) of the fictive temperature can be determined. In this way, when the holding temperature T _a much set to a high temperature, offset value of the virtual temperature T _f is the value of the holding temperature T _a, it should be noted that the error becomes large. In order to increase the reliability of Equation (7), it is desirable that the number of m is large.

FIG. 6 shows a conceptual diagram of an example of the procedure of the two methods for determining the relational expression (7) between the Brillouin frequency shift amount ν _B and the longitudinal distribution T _f (z) of the fictive temperature described above. It was. Of course, once the equation (7) is determined, for the fibers having the same structure and the same glass composition distribution, by measuring the longitudinal distribution νB (z) of the Brillouin frequency shift amount, The longitudinal distribution T _f (z) of the fictive temperature can be obtained using Equation (7).

(Embodiment 4)
In this embodiment, the Brillouin frequency shift measurement is performed in the optical fiber manufacturing step of manufacturing an optical fiber having the same structure and glass composition distribution as the corresponding optical fiber by temporally changing the manufacturing parameter value at the time of drawing the optical fiber. In preparation for the step, the value of the production parameter for obtaining an arbitrary virtual temperature T _f is determined from the longitudinal distribution ν _B (z) of the measured Brillouin frequency shift amount or the longitudinal distribution T _f (z) of the virtual temperature A production parameter value determination step is provided after the virtual temperature measurement step.

That is, an optical fiber having the same structure and the same glass composition distribution as the corresponding optical fiber is manufactured while temporally changing values of various manufacturing parameters set in advance when drawing the optical fiber. Thereafter, the longitudinal distribution νB (z) of the Brillouin frequency shift amount measured in the above-described embodiment, or the longitudinal direction distribution of the virtual temperature of the optical fiber calculated using the longitudinal distribution νB (z) of the Brillouin frequency shift amount. From T _f (z), the value of the production parameter when the virtual temperature T _f is set to an arbitrary value is determined.

As described above, generally, in order to increase the fictive temperature _{Tf of} glass, it is only necessary to rapidly cool from a high temperature, and to lower the fictive temperature _Tf , annealing is performed in an appropriate low temperature range. That's fine. Therefore, when the optical fiber is drawn, the virtual temperature _Tf can be increased by drawing at a high drawing temperature and at a high speed. On the other hand, in order to lower the fictive temperature _Tf , the drawing may be performed at a low drawing temperature and at a low speed.

The production parameters include the optical fiber drawing speed, the optical fiber preform drawing temperature, the optical fiber preform feed speed, the optical fiber draw tension, and the optical fiber preform neck-down length when drawing the optical fiber. . Other than these, light can be adjusted by adjusting the molecular composition and flow rate of the atmospheric gas, spraying the cooling gas onto the optical fiber, and additionally installing a slow cooling furnace (installed at the bottom of the original heating furnace). The fictive temperature _Tf of the fiber can be changed. Furthermore, the value of the fictive temperature _Tf can also be changed by deformation of the shape of the neck-down portion when the base material is drawn.

Therefore, light having the same structure and the same glass composition distribution as the corresponding optical fiber while controlling the outer diameter of the optical fiber to be constant (for example, 125 μm) and changing the values of various production parameters over time. Fabrication by drawing a fiber and calculating a virtual temperature longitudinal distribution T _f (z) to give an arbitrary virtual temperature T _f , for example, a maximum value, maximum value, minimum value, or minimum value of the virtual temperature T _f The value of the parameter can be determined. Furthermore, as a simpler method, a production parameter when an arbitrary virtual temperature T _f is set to a maximum value, a maximum value, a minimum value, or a minimum value from the longitudinal distribution νB (z) of the measured Brillouin frequency shift amount. The value of can be determined.

  FIG. 7 shows an example of the longitudinal distribution νB (z) of the Brillouin frequency shift amount of the SMF produced while changing various parameters with time. The SMF was manufactured from an SMF base material by controlling the outer diameter to 125 + -2 μm by PID (Proportional Integral Derivative) control. Therefore, the influence of the fluctuation of the core diameter a on the longitudinal distribution νB (z) of the Brillouin frequency shift amount can be ignored.

In the area A of FIG. 7, the drawing temperature is a main production parameter, the temperature is reduced from 2150 ° C. to 1850 ° C., and the drawing speed, the base material feed speed, and the drawing tension are only finely adjusted to control the outer diameter. It was. As a result, in the region A, a clear decrease peak occurred in the longitudinal distribution νB (z) of the Brillouin frequency shift amount due to the decrease in the fictive temperature _Tf . On the other hand, in the region B, when the drawing speed, the drawing temperature, and the drawing tension were substantially fixed, it was necessary to reduce the feed rate of the optical fiber preform from the initial value to about 1/10 in order to maintain the outer diameter. . This indicates that the optical fiber preform is deformed and the neck-down diameter is increased. As a result, the optical fiber was gradually cooled, and even in the region B, a clear decrease peak occurred in the longitudinal distribution νB (z) of the Brillouin frequency shift amount due to the decrease in the fictive temperature _Tf .

According to the present invention, it is possible to evaluate the longitudinal distribution T _f (z) of the fictive temperature closely related to Rayleigh scattering, which is the main cause of optical fiber loss, with high accuracy, and to reduce the fictive temperature T _f and the Rayleigh scattering loss. Therefore, it is possible to easily determine the optimum optical fiber manufacturing conditions.

  The present invention is not limited to the description of the above embodiment as it is, and can be embodied by modifying the components without departing from the scope of the invention in the implementation stage. You may combine suitably the component covering different embodiment.

  The present invention is a technology useful in the information and communication industry, particularly in the manufacture of optical fibers.

Claims (6)

Measurement of longitudinal distribution ν _B (z) of Brillouin frequency shift amounts of a plurality of virtual temperature-adjusting optical fibers having a predetermined core diameter, the same structure and the same glass composition distribution, and different virtual temperatures T _f A Brillouin frequency shift measurement step to perform,
Based on the virtual temperature T longitudinal distribution of the Brillouin frequency shift amount of the fictive temperature adjusting optical fiber each _f ν _{B (z),} between the virtual temperature adjustment Brillouin frequency shift amount of the optical fiber [nu _B and the virtual temperature T _f An empirical formula derivation step that determines T _f (z) = g (ν _B )
Based on the empirical formula: T _f (z) = g (ν _B ), an optical fiber to be measured having the predetermined core diameter and the same structure and the same glass composition distribution as the virtual temperature control optical fiber A virtual temperature measuring step for calculating a longitudinal distribution T _f (z) of the virtual temperature of
Evaluation of the longitudinal distribution of the fictive temperature of the optical fiber to be sequentially executed to said Rukoto a. Claim wherein the virtual temperature adjustment optical fiber, after holding the optical fiber at a holding temperature T _a, by quenching, characterized in that the holding temperature T _a Ru optical fiber der adjusted to the virtual temperature T _f of The evaluation method of longitudinal direction distribution of fictive temperature of the optical fiber of 1 . The plurality of virtual temperature control optical fibers have different production parameters,
Virtual temperature T of the virtual temperature adjusting optical fiber _f The adjustment virtual temperature measurement step for measuring
The evaluation method of the longitudinal distribution of the fictive temperature of the optical fiber according to claim 1 or 2. And wherein the that perform optical fiber fabrication step of making the virtual temperature adjusting optical fiber by Rukoto changing the value of the fabrication parameters during drawing of the optical fiber temporally before the Brillouin frequency shift amount measuring step The evaluation method of the longitudinal direction distribution of the fictive temperature of the optical fiber according to claim 3 . Longitudinal distribution T _f value produced parameter numerology the fictive temperature measuring step determining the said manufacturing parameters from _(z) obtained any fictive temperature T _f of the virtual temperature measuring virtual temperature measured in step evaluation of the longitudinal distribution of the fictive temperature of the optical fiber according to claim 3 or 4, characterized in that to run after. The production parameter is any of the drawing speed of the optical fiber, the drawing temperature of the optical fiber preform, the feeding speed of the optical fiber preform, the drawing tension of the optical fiber, and the neckdown length of the optical fiber preform when drawing the optical fiber. The evaluation method of the longitudinal distribution of the fictive temperature of the optical fiber according to any one of claims 3 to 5, wherein:

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