WO2006090519A1

WO2006090519A1 - Induction brillouin scatter suppresing optical fiber

Info

Publication number: WO2006090519A1
Application number: PCT/JP2005/022363
Authority: WO
Inventors: Yuichi Morishita; Hiroshi Oyamada; Dai Inoue
Original assignee: Showa Electric Wire & Cable Co., Ltd.; Shin-Etsu Chemical Co., Ltd.
Priority date: 2005-02-24
Filing date: 2005-12-06
Publication date: 2006-08-31
Also published as: TW200630309A; JP4664703B2; JP2006232599A

Abstract

An SBS suppressing optical fiber which adds additives such as Ge, P, F singly or in combination to a core consisting of quartz glass, forms a stepwise core refractive index distribution, and increases SBS threshold power by setting the difference in concentration of an additive between adjacent steps of this stepwise refractive index distribution to at least a specified concentration difference, or by setting the difference in refractive index between adjacent steps to at least a specified refractive index difference. Since the constitution of the SBS suppressing optical fiber can increase SBS threshold power, SBS can be suppressed and zero-dispersion wavelength and mode field diameter are set to function as parameters equivalent to those of a normal SMF, whereby no disadvantage such as an increase in connection loss will not occur even if applied to a transmission line.

Description

Specification

Stimulated Brillouin scattering suppression optical fiber

Technical field

TECHNICAL FIELD [0001] The present invention relates to an optical fiber that is required to input high power to an optical fiber transmission line, for example, an optical CATV system for FTTH.

Background art

[0002] In recent years, introduction of FTTH (Fiber To The Home) system has been required. An optical CATV system or the like is used for the FTTH system. In this optical CATV system, it is necessary to input a high-power optical signal into the core of a single mode optical fiber. This is because the optical CATV system power used in the FTTH system is to reduce the noise first, so that the optical input power at the receiver needs to be as high as possible, for example, to have a light receiving sensitivity of about −10 dBm. In order to compensate for the loss of the splitter, the power of the optical signal output from the optical transmitter is, for example, 16 for a 32-branch splitter. It is also a force with reasons such as having to increase it to about 5 to 17 dB.

[0003] Further, in order to shorten the length of the optical fiber used as a transmission line to the user or to distribute light as close as possible to the user, the transmission line fiber from the optical transmitter to the splitter is used. It is desired to increase the length. In addition, this optical fiber TVTV system has a transmission fiber that is expected to have a maximum length of 10 to 20 km in the FTTH system design and is distributed by a 32-branch splitter with a length of about 20 km. Therefore, since the transmission loss of the optical fiber is about 0.25 dBZkm at the wavelength of 1550 nm, the transmission loss between the optical transmitter and the receiver is 22 dB. In other words, the optical output at the optical transmitter needs about 12 dB. Also, if the length of the transmission line fiber is increased to 20 km or more, or the number of optical distributions is increased to more than 32 branches, the optical output will need to be increased.

[0004] In this way, it is expected that in the future it will be necessary to increase the optical output beyond the present level. When a high-power optical signal is input into an optical fiber, stimulated Brillouin scattering ( It is known that a phenomenon called SBS (Stimulated Brillouin Scattering) occurs.

[0005] SBS is a phenomenon in which the frequency (frequency) of light is slightly shifted by ultrasonic waves, and the power of light is scattered more backward than it is scattered in the forward emission direction. . In addition, when the optical power in the core of the optical fiber increases, stimulated emission of Brillouin scattering starts and the backscattered light power increases rapidly. As a result, this backscattered light adversely affects the optical transmitter, increasing the noise of the light source or saturating the optical signal ratio propagating forward, resulting in an optical signal-to-noise ratio (SZN ratio). It gets worse. In this way, the SBS phenomenon determines the upper limit of the optical power that can be incident on the transmission line fiber.

[0006] By the way, in general, Ge, P, F, and the like are used as additives in order to obtain a low-loss silica glass-based optical fiber. Of these, Ge and P are often added to the core because adding them gives a refractive index higher than that of quartz glass. In addition, when F is added, the refractive index is lower than that of Sekiei glass and is often added to the clad because the refractive index is obtained. However, co-addition of Ge, P, and F may add F into the core or add Ge or F into the cladding.

[0007] Here, it is known that there is a correlation between the additive in quartz glass and the center frequency shift amount of SBS. First, at a relatively low concentration of GeO concentration of 10 ^% or less

2

GeO concentration and SBS center frequency shift amount are linearly correlated.

The SBS center frequency shift amount of 2 2 has been reported to be 89 MHzZwt% (= 154 MHzZmol%) (for example, see Non-Patent Document 1). At this time, the full width at half maximum of SBS (the spectral width at half the peak value of the SBS spectrum intensity) is about 30 to 100 MHz.

[0008] The relationship between the GeO concentration, the PO concentration, and the SBS center frequency shift amount is 125 respectively.

2 2 5

There are also reports of MHzZmol% and 162MHzZmol% (for example, see Non-Patent Document 1). The full width at half maximum of SBS at this time is said to be 150MHz to 270MHz. In the reports above, Ge and P are added to the core, and the optical fiber with pure silica glass power is used as the cladding, and the optical fiber with pure silica glass and F in the cladding is used.

[0009] Furthermore, the SBS center frequency shift amount of the optical fiber with Ge and F co-attached to the core was investigated. There are also reports. According to this report, the amount of F added is shifted by about 350 MHz with a relative refractive index difference of 0.2%. This is 600 MHz Zmol% when converted to a frequency shift amount per mol% (for example, see Non-Patent Document 2).

[0010] In response to the above situation, several optical fibers or SBS suppression methods that suppress SBS have been proposed. First, there has been proposed an optical fiber in which the core diameter of the optical fiber is equal to the refractive index of the core or the strain remaining in the core is changed in the longitudinal direction of the optical fiber (see, for example, Patent Document 1). As a method for changing the core diameter, the conditions for forming the optical fiber preform are changed as appropriate, and as a method for changing the refractive index of the core, the type and amount of the additive to the glass are changed. As a method of changing the residual strain in the core, the drawing tension is changed in the longitudinal direction, and the residual strain is periodically changed in the longitudinal direction of the optical fiber. This is because the SBS center frequency changes as the residual strain in the core changes, so the SBS spectrum broadens and the stimulated emission threshold rises.

[0011] In addition, a method for changing the concentration of the additive in the core and the clad in the longitudinal direction of the optical fiber has been proposed. In other words, in an optical fiber in which Ge and F are added to the core and F is added to the cladding, the concentration of F in the core and cladding is changed in the longitudinal direction (see, for example, Non-Patent Document 3).

[0012] Furthermore, a method of suppressing SBS by changing the core diameter in the longitudinal direction of the optical fiber has also been proposed (see, for example, Patent Document 1 and Non-Patent Document 4). In Non-Patent Document 4, the Brillouin frequency is shifted by changing the core diameter, and the threshold is raised by broadening the spectrum width of SBS.

[0013] In addition, a method has also been proposed in which glass with P or F added in the radial direction of the core of the optical fiber is alternately arranged in layers (for example, see Patent Document 2). In this method, the SBS threshold power is increased by broadening the SBS spectrum width by generating non-uniform thermal expansion and viscosity distributions in the core.

[0014] Non-Patent Document 1: R.W.Tkach et al., Electron.Lett., Vol.22, No.l9, p.l011,1986

Non-Patent Document 2: N. SWbata et al., Opt 丄 ett., Vol.l2, No.4, p.269, 1987

Non-Patent Document 3: Proceedings of the 1994 IEICE Autumn Conference C 137 Non-Patent Document 4: Proceedings of the 1995 IEICE Communication Society Conference B-661 Patent Document 1: JP-A-4-367539

Patent Document 2: Special Table 2001-510903

Disclosure of the invention

Problems to be solved by the invention

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

[0016] That is, in the method of changing the core diameter in the longitudinal direction of the optical fiber disclosed in Patent Document 1 and Non-Patent Document 4, the structure of the optical fiber changes in the longitudinal direction, which is effective in suppressing SBS. However, since other parameters also change, there is a problem that it is not preferable in terms of characteristics, for example, when connecting to a normal transmission single mode optical fiber (hereinafter referred to as SMF).

[0017] Further, in the method of changing the refractive index of the core in Patent Document 1, the type and amount of the additive are changed in the longitudinal direction of the optical fiber. However, the manufacturing process becomes complicated and the length is stabilized. It is difficult to manufacture a long optical fiber. Furthermore, the method of changing the residual strain of the core in the longitudinal direction of the optical fiber is by using an optical fiber in which the core is pure silica glass and the cladding is silica glass with F added thereto. The fiber has the advantage that the influence of the drawing tension tends to concentrate on the core because the viscosity of the clad with F is lower than that of the core made of pure silica glass. However, it is difficult to adjust the drawing tension compared to pure quartz glass because optical fibers that are widely used for commercial use have Ge added to the core. Therefore, this method has a problem that its application is limited.

[0018] In addition, in the method disclosed in Non-Patent Document 3, the concentration of F added to the core and the cladding is changed so that the concentration of Ge in the core is uniform so that the entire refractive index distribution does not change. However, since the manufacturing process is complicated, it is difficult to obtain an optical fiber having a stable characteristic in the longitudinal direction, which is a problem for mass production.

[0019] Further, the method disclosed in Patent Document 2 has a problem that the manufacturing process is complicated and the cost is increased because it is necessary to form layers having different glass compositions alternately in the radial direction of the core. . [0020] The present invention solves the above-described problems. An SBS-suppressing optical fiber that suppresses SBS and has stable characteristics in the longitudinal direction of the optical fiber and that can be used with a normal manufacturing method is provided. It is to provide.

Means for solving the problem

[0021] In order to solve the above points, the present invention has the following constitutional power.

That is, the SBS-suppressing optical fiber of the present invention is, as a first aspect, an optical fiber composed of a core having a silica glass force and a clad having a silica glass force having a refractive index lower than that of the outer peripheral core. In addition, Ge or P is added to the core alone, or Ge and P are added at the same time, and the core has a step-like refractive index distribution, and GeO in adjacent steps of the step-like refractive index distribution. Concentration difference or PO concentration difference or GeO

2 2 5

And the total concentration difference of P 2 O is 0.3 mol% or more.

2 2 5

[0023] Further, as a second aspect, in the first aspect, a GeO concentration difference or a P O concentration difference or a GeO and PO difference between adjacent staircases in the stepwise refractive index distribution.

2 2 5 2 2 5 The total concentration difference is 0.6 mol% or more.

[0024] Further, as a third aspect, in the first or second aspect, wherein the refractive index difference at the staircase adjacent of the refractive index distribution of the stepwise is 3 X 10_ ⁴ or more.

[0025] Further, as a fourth aspect, in the third aspect, wherein the refractive index difference at the step-fit Ri next to the refractive index distribution of the stepwise is 8 X 10_ ⁴ or more.

[0026] Further, as a fifth aspect, in any one of the first to fourth aspects, the clad is pure quartz glass.

[0027] Further, as a sixth aspect, in any one of the first to fourth aspects, the clad is characterized in that F is added to quartz glass.

[0028] Further, as a seventh aspect, there is provided an optical fiber composed of a core having a quartz glass force and a clad having a lower refractive index than that of the outer peripheral core and also having a quartz glass force. Is added, and the core has a stepped refractive index distribution, and the F concentration difference in adjacent steps of the stepped refractive index distribution is 0.08 mol% or more.

[0029] Further, as an eighth aspect, in the seventh aspect, the stepwise refractive index profile is adjacent to the stepwise refractive index distribution. It is characterized in that the difference in the concentration of F in the stairs is 0.16 mol% or more.

[0030] Further, as a ninth aspect, in the seventh or eighth aspect, wherein the refractive index difference at the staircase adjacent of the refractive index distribution of the stepwise is 3 X 10_ ⁴ or more.

[0031] Further, as a tenth aspect, in the ninth aspect, wherein the refractive index difference at the staircase adjacent of the refractive index distribution of the stepwise is 8 X 10_ ⁴ or more.

[0032] Further, as an eleventh aspect, there is provided an optical fiber composed of a core having a quartz glass force and a clad having a quartz glass force having a refractive index lower than that of the outer peripheral core, wherein the core is made of Ge or P. Independently, or Ge and P are added at the same time, F is further added, and the core has a stepped refractive index profile, and the difference in refractive index between adjacent steps of the stepped refractive index profile. characterized in that There are 3 X 10_ ⁴ or more.

[0033] Further, as a twelfth aspect, in the eleventh aspect, wherein the refractive index difference at the staircase adjacent of the refractive index distribution of the stepwise is 8 X 10_ ⁴ or more.

[0034] Further, as a thirteenth aspect, in the eleventh or twelfth aspect, the clad is pure quartz glass.

[0035] Further, as a fourteenth aspect, in the eleventh or twelfth aspect, the clad is characterized in that F is added to an amorphous glass.

[0036] Further, as a fifteenth aspect, there is provided an optical fiber comprising a core having a quartz glass force and a clad having a refractive index lower than that of the outer peripheral core and also having a quartz glass force, and the core includes pure silica glass and The addition of F also adds to the quartz glass force, the addition of F to the cladding, the core has a step-like refractive index profile, and the refractive index at the adjacent steps of the step-like refractive index profile. wherein the difference is 3 X 10_ ⁴ or more.

[0037] Further, as a sixteenth aspect, in the fifteenth aspect, wherein the refractive index difference at the staircase adjacent of the refractive index distribution of the stepwise is 8 X 10_ ⁴ or more.

[0038] Further, as a seventeenth aspect, in any one of the first to sixteenth aspects, a difference between the maximum refractive index of the core and the refractive index of the clad is 0.008 or less. It is a feature.

[0039] Further, as an eighteenth aspect, in any one of the first to seventeenth aspects, the spectral width of stimulated Brillouin scattering of the optical fiber is 200 MHz or more. To do.

[0040] Furthermore, as a nineteenth aspect, in the eighteenth aspect, the spectral width of stimulated Prien scattering of the optical fiber is 300 MHz or more.

[0041] Further, as a twentieth aspect, in any one of the first to nineteenth aspects, a zero dispersion wavelength of the optical fiber is in a range of 1300 nm to 1324 nm.

[0042] Furthermore, as a twenty-first aspect, in any of the first to twentieth aspects, the mode field diameter of the optical fiber at a wavelength of 1310 nm is in the range of 8.6 to 9.5 m. It is characterized by being.

The invention's effect

[0043] According to the SBS-suppressed optical fiber of the present invention, the amount of additive such as Ge, P, or F added to the core cladding is adjusted and the refractive index distribution of the core is stepped. It can broaden the spectrum width, suppress SBS, has stable characteristics in the longitudinal direction, can be manufactured by the conventional method, and can be stably connected to ordinary SMF.

Brief Description of Drawings

FIG. 1 is a diagram for explaining a refractive index distribution of Example 1 of the present invention.

FIG. 2 is a diagram illustrating a measurement system for measuring SBS threshold power.

FIG. 3 is a diagram showing a measurement result of SBS threshold power.

FIG. 4 is a diagram for explaining a refractive index distribution of Example 2 of the present invention.

FIG. 5 is a diagram for explaining a refractive index distribution of Example 3 of the present invention.

FIG. 6 is a view for explaining a refractive index distribution of Example 4 of the present invention.

FIG. 7 is a view for explaining a refractive index distribution of Example 5 of the present invention.

FIG. 8 is a view for explaining a refractive index distribution of Example 6 of the present invention.

FIG. 9 is a view for explaining a refractive index distribution of Example 7 of the present invention.

FIG. 10 is a view for explaining a refractive index distribution of Example 8 of the present invention.

FIG. 11 is a diagram illustrating a refractive index distribution of a comparative example for the present invention.

Explanation of symbols

[0045] 1 · · · Distributed feedback laser 2 · · · Optical amplifier

3 · · · Light bra

4 "'SBS suppression fiber

5 ... Output light power meter

6 · · · Incident light power meter

7 ... Reflected power meter

BEST MODE FOR CARRYING OUT THE INVENTION

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

[0047] First, in order to increase the threshold of stimulated emission, it is necessary to widen the spectral width of SBS. The SBS threshold depends on the loss, length, mode field diameter, etc. of the optical fiber. In general, the threshold value can be simply expressed as follows.

[0048] Pth = k (Aeff / Leff)

Where Pth'—SBS threshold

Aeff '' 'effective area

Leff ... interaction distance

k coefficient

Aeff and Leff can be expressed by the following equations.

[0049] Aeff W2

Lef I = {1— exp (― a L) / a}

Where W '·' mode fino red diameter

L: Optical fiber length

«Loss factor

As described above, Aeff and Leff are related to the mode field diameter, optical fiber loss and length. Therefore, when comparing the SBS threshold value of each optical fiber, it can be seen that comparing the coefficient k does not depend on the mode field diameter, loss, length, etc. of the optical fiber. Note that the normal SMF has a k coefficient of about 7.6 x 10 ¹⁴ mWZm, so if the k coefficient is larger than this value, the SBS threshold power is large.

[0050] In order to increase the k coefficient, it is necessary to widen the spectrum width of the SBS. The Specifically, it was found that the spectrum width of SBS for effectively suppressing SBS needs to be 200 MHz or more, preferably 300 MHz or more. In the case of normal SMF, the spectrum width of SBS is 130 to 150 MHz. However, when the spectrum width of SBS is less than 200 MHz, the SBS suppression effect of ordinary SMF is not so different, and the suppression effect of SBS is sufficient. Because I can not say. In the present invention, the spectrum width of SBS refers to the spectrum width that is 1/10 of the peak value of the intensity of the SBS spectrum.

[0051] From the conventional technology, the SBS center frequency shift amount is approximately 150MHzZmo for GeO.

2

It is known that 1%, PO is 160MHzZmol%, and F is 600MHzZmol%.

twenty five

It is. When the refractive index distribution is stepped as in the present invention in order to widen the SBS spectrum width, the shift amount of the SBS center frequency in each step portion should not overlap the SBS center frequency in other step portions. There is a need.

[0052] In order to prevent the shift amount of the SBS center frequency in each staircase part from overlapping the SBS center frequency in the other staircase parts, the addition amount of Ge, P, or F in the adjacent staircases is changed to the above shift amount. It is recommended to adjust optimally based on the above. As a result of examination by the applicants, when the additive is Ge or P, the difference in GeO concentration or PO concentration difference between adjacent steps in the stepwise refractive index distribution is 0.3 mol% or more, preferably 0. 6mol%

2 2 5

It turns out that the above is good. In addition, when Ge and P are co-added, GeO and P O

It has been found that the total concentration difference of 2 2 5 is 0.3 mol% or more, preferably 0.6 mol% or more.

[0053] Concentration difference of GeO, P O concentration, or total concentration difference of GeO and P O is 0.3m

2 2 5 2 2 5

The reason why it is ol% or more is that if it is less than 0.3 mol%, it has only the same SBS suppression effect as ordinary SMF. The reason why it is preferably set to 0.6 mol% or more is because an SBS suppressing effect can be further exhibited. Also, GeO concentration difference, P O concentration difference, or GeO and P O concentration.

The upper limit of the total concentration difference of 2 2 5 2 2 is that this SBS-suppressed optical fiber is connected to normal SMF.

Five

However, the refractive index distribution should be set appropriately so that it does not affect the transmission characteristics, such as no increase in connection loss!

[0054] In the above-described embodiment, when Ge or P or Ge and P is added to the core to form a stepped refractive index distribution, the stepped refractive index distribution is bent in adjacent steps. The folding index difference 3 X 10_ ⁴ or more, preferably may be 8 X 10_ ⁴ or more. Thus, even if the present invention is configured with the difference in refractive index between the adjacent steps in the stepwise refractive index distribution that is not based on the concentration of the additive, the same effect as that obtained when the concentration difference of the additive is configured can be obtained. The reason why the refractive index difference at stepped adjacent stepped refraction index distribution 3 X 10_ ⁴ or more, 3 X 10_ ⁴ Not Mitsurude is because there is only normal SMF and comparable SBS suppression effect . The preferred was 8 X 10 _ ⁴ above is because it is possible to obtain a more SBS suppression effect. In addition, the upper limit of the refractive index difference between adjacent stairs is that the refractive index is adjusted so that it does not affect the transmission characteristics, such as the connection loss does not increase even if this SBS suppression optical fiber is connected to a normal SMF. Decide what you want in the design of the distribution!

[0055] The refractive index is increased because the core diameter is reduced while the force is applied, but the refractive index difference between adjacent stairs depends on the number of stairs due to the effect of diffusion of the additive during glass synthesis or spinning. The upper limit is limited. For example, when the number of steps is one, the number of steps is small, so the upper limit of the difference in refractive index between adjacent stairs can be up to the maximum difference in refractive index between the core and the cladding, and the degree of freedom is large. On the other hand, when the number of steps is two or more, the length between steps becomes shorter, so it is preferable to design the refractive index distribution so that the upper limit of the difference in refractive index between adjacent steps is about 0.0015. Regardless of the number of steps, the shape of the stairs is not necessarily rectangular due to the effects of diffusion described above, but is often slightly rounded.

[0056] Here, in the above embodiment, the clad may be pure quartz glass, or F may be added to pure silica glass. In other words, you can select the required characteristics of the optical fiber as appropriate!

[0057] As another embodiment of the SBS-suppressing optical fiber of the present invention, F is added to the core and the clad, and the core has a step-like refractive index distribution. It is also possible to adopt a configuration in which the difference in the concentration of F in the adjacent stairs is 0.08 mol% or more, preferably 0.16 mol% or more.

[0058] The reason why the difference in F concentration was set to 0.08 mol% or more is that if it is less than 0.08 mol%, the SBS suppression effect is the same as that of normal SMF. The reason why the content is preferably 0.16 mol% or more is that an SBS suppressing effect can be further exerted. In addition, the upper limit of the F concentration difference is that transmission loss does not increase even if this SBS suppression optical fiber is connected to normal SMF. The refractive index distribution may be determined appropriately so as to be within a range without affecting the characteristics.

[0059] In the above embodiment, when F is added to the core and the clad to form a stepped refractive index distribution, the difference in refractive index between adjacent steps of this stepped refractive index distribution is obtained. the 3 X 10- ⁴ or more, preferably may be 8 X 10- ⁴ or more. As in the case of Ge and P, even if the additive is F, even if the present invention is configured with the difference in refractive index between adjacent steps in the stepwise refractive index distribution that does not depend on the concentration of the additive, The effect is the same as when configured with a density difference. Then, also had a the refraction index difference in the staircase adjacent stepped refractive index distribution 3 X 10_ ⁴ or more is because there is only normal SMF and comparable SBS suppression effect is less than 3 X 10_ ⁴ . Preferably to that the 8 X 10_ ⁴ above is because it is possible to obtain a more SBS suppression effect. In addition, the upper limit of the refractive index difference between adjacent stairs is that the SBS-suppressed optical fiber is connected to normal SMF, so that the connection loss does not increase and the transmission characteristics are not affected. Depending on the design, it may be determined appropriately.

[0060] As yet another embodiment, the SBS-suppressed optical fiber of the present invention has Ge and F, P and F, or Ge, P and F co-doped into the core, and the refractive index distribution of the core is stepped. refractive index difference at adjacent stairs of the stepwise refractive index distribution 3 X 10_ ⁴ or more, preferably be configured to be 8 X 1 0_ ⁴ or more. Again had a refractive index difference at stairs adjacent stepped refractive index distribution 3 X 10_ ⁴ or more is because there is only normal SMF and comparable SBS suppression effect is less than 3 X 10_ ^4. Preferably to that the 8 X 10_ ⁴ above is because it is possible to obtain a good Ri SBS suppression effect. In addition, the upper limit of the refractive index difference between adjacent stairs is such that the connection loss does not increase even if this SBS-suppressed optical fiber is connected to ordinary SMF! It can be determined appropriately for the design of the refractive index distribution.

[0061] Again, the upper limit of the difference in refractive index between adjacent tiers depends on the number of steps, due to the effects of diffusion during glass synthesis or spinning of an additive that increases or decreases the refractive index because the core diameter is reduced. For example, if the number of steps is 1, the number of steps is small, so the upper limit of the refractive index difference between adjacent stairs can be as high as the maximum refractive index difference between the core and the cladding. Although the degree of freedom is large, the length between steps is shortened when the number of steps is 2 or more. The refractive index distribution is designed so that the upper limit of the refractive index difference between adjacent steps is about 0.0015. It is preferable to do the same as described above. In addition, the shape of the staircase is not necessarily rectangular due to the influence of diffusion described above, regardless of the number of steps, and is often slightly rounded as described above. In this embodiment also, F may be added to pure quartz glass, which may be pure quartz glass. In other words, select the appropriate optical fiber characteristics.

[0062] As yet another embodiment, the SBS-suppressed optical fiber of the present invention has a core made of pure silica glass, F is added to the cladding, and F is partially added to the core pure silica glass. There was to have a refractive index profile of step-like refractive index difference at stairs adjacent the stepped refractive index distribution 3 X 10_ ⁴ or more, preferably is configured as a 8 X 10_ ⁴ more than it can. To that the refractive index difference at stepped adjacent stepped refractive index distribution 3 X 10_ ⁴ above is for still 3 X 10_ only normal SMF and comparable SBS suppression effect is less than ^4. The preferred was 8 X 10_ ⁴ or more is because as possible out to achieve a more SBS suppression effect. In addition, the upper limit of the refractive index difference between adjacent stairs is that the refractive index is adjusted so that it does not affect the transmission characteristics, such as the connection loss does not increase even if this SBS suppression fiber is connected to normal SMF. Decide on the distribution design as appropriate!

[0063] And again, the upper limit of the difference in refractive index between adjacent steps depends on the number of steps, due to the effects of diffusion during glass synthesis or spinning of additives that increase or decrease the refractive index because the core diameter decreases. For example, if the number of steps is 1, the number of steps is small, so the upper limit of the difference in refractive index between adjacent stairs can be up to the maximum difference in refractive index between the core and the cladding. As above, it is preferable to design the refractive index distribution so that the upper limit of the refractive index difference between adjacent stairs is about 0.0015. . In addition, the shape of the staircase is not necessarily rectangular due to the influence of diffusion described above, regardless of the number of steps, and is often slightly rounded as described above.

In the embodiment described above, it is desirable that the difference between the maximum refractive index of the core and the refractive index of the cladding of the SBS-suppressed optical fiber of the present invention is 0.008 or less. Also book It is desirable that the zero-dispersion wavelength of the inventive SBS-suppressing optical fiber is in the range of 1300 nm to 1324 nm. Furthermore, it is desirable that the mode field diameter of the SBS-suppressed optical fiber of the present invention at a wavelength of 1310 nm is in the range of 8.6 to 9.5 / zm.

[0065] This is so that even when the SBS-suppressing optical fiber of the present invention is connected to a normal SMF, no connection loss occurs and the transmission characteristics of the optical fiber are not adversely affected. Because. In other words, the configuration in which the refractive index distribution of the core is stepped is a force conventionally known as dispersion-shifted fiber (DSF). This DSF shifts the zero dispersion wavelength from around 1300 nm to around 1550 nm. Therefore, the difference between the maximum refractive index of the core and the refractive index of the cladding is set to 0.01 or more. As a result of such a configuration, the mode field diameter of the DSF is 7 to 8 μm at a wavelength of 1310 nm, which is smaller than that of normal SMF. Therefore, when DSF and ordinary SMF are connected, the difference in refractive index increases the mismatching power of the mode field diameter and the connection loss does not affect the entire transmission line.

[0066] The SBS-suppressed optical fiber of the present invention has a zero-dispersion wavelength equivalent to that of SMF used in conventional transmission lines, that is, a zero-dispersion wavelength near 1300 nm, and the maximum refractive index of the core and the refractive index of the cladding. Even if the rate difference is connected to ordinary SMF, the connection loss does not occur. It is less than 0.008, and the mode field diameter at 1310 nm wavelength is the same value as ordinary SMF, so it is applied to the transmission line. Even so, there is no problem in characteristics.

[0067] The SBS-suppressing optical fiber of the present invention may be used in combination with a conventionally known technique such as changing the core diameter in the longitudinal direction or changing the residual stress. As long as it is effective in suppressing SBS, it is not particularly limited as long as it is permitted in the manufacturing method.

Example 1

[0068] As shown in Fig. 1 (a), Ge was added to a quartz glass core, and an SMF having a refractive index distribution of this core in a single stepped shape was produced. Clad C is pure quartz glass. In the step-like refractive index distribution, if the high refractive index portion is Nh and the low refractive index portion is N1, the GeO concentration in the Nh portion is 5.2 mol%, and the GeO concentration in the N1 portion is 3 mol. %.

twenty two

That is, the GeO concentration difference between adjacent stairs in the step-like refractive index profile is 2.2 mol%. It has become. At this time, the difference between the maximum refractive index of the core (Nh part) and the refractive index of the cladding Δηΐ is 0.007, and the difference between the refractive index of the core N1 part and the refractive index of the cladding Δη2 is 0.004. The refractive index difference Δη3 between adjacent stairs in the stepwise refractive index distribution was 0.003. The core diameter of the core part with high refractive index (Nh part) is 3 m, and the core diameter of the core part with low refractive index (N1 part) is 8 μm.

[0069] An SBS suppression optical fiber having such a configuration was prepared for 20 km, and the reflected light power with respect to the incident light power at a wavelength of 1 550 nm was measured with a measurement system as shown in FIG. The measurement system in Fig. 2 amplifies the light from a distributed feedback laser (DFB—LD) 1 having a wavelength of 1550 nm by an optical amplifier (EDFA; Erbium Doped Fiber Amplifier) 2 and introduces it to the optical power plastic 3. This light is branched by an optical power bra 3 to an outgoing light power meter 5 for measuring the power of light transmitted from the SBS suppression optical fiber 4 to be measured, and the other is incident light for monitoring the incident light power. Branch to power meter 6. Then, the light reflected from the SBS suppression optical fiber 4 is again measured by the reflected light power meter 7 through the optical power bra 3. By measuring the reflected light with this reflected light power meter 7, the degree to which SBS is suppressed and power is improved!

FIG. 3 shows the result of measuring the SBS-suppressed optical fiber of Example 1 with the measurement system of FIG. The horizontal axis represents the incident light power, and the vertical axis represents the output light power and the reflected light power. From Fig. 3, it can be seen that the reflected light power increases rapidly when the incident light power reaches lOdBm. The k coefficient at this time was ^1.5 X 10 ¹⁵ mWZm. This lOdBm incident optical power is the threshold (Pth) at which SBS occurs. In ordinary SMF, the SBS threshold power is about 7 dBm, so the optical fiber of Example 1 shows an improvement of about 3 dBm, and the SBS suppression effect can be realized even for high incident light power. In addition, the k factor of ordinary SMF was 7.6 X 10 ¹⁴ mWZm. The transmission loss at 1550 nm of the optical fiber in Example 1 was 0.2 dBZkm, and the mode field diameter was 10.5 μm. The spectral width of SBS was 330 MHz. The measurement of the spectral width of the SBS is performed using a BOTDR (Brillouin Optical Time Domain Reflectometer), and the same applies to the measurement of each of the following examples.

[0071] As described above, the shape of the refractive index profile is actually affected by the diffusion of the additive and the like. As shown in Fig. 1 (b), which is not a perfect rectangle, the corners often have a slightly rounded shape. However, in this embodiment and each embodiment described below, the refractive index distribution is expressed as a rectangular shape for the sake of explanation.

Example 2

[0072] As shown in FIG. 4, Ge was added to a core made of quartz glass, and an SMF having a refractive index distribution of the core in a single stepped shape was produced. Clad C is pure quartz glass. In the stepwise refractive index distribution, if the high refractive index portion is Nh and the low refractive index portion is N1, the GeO concentration in the Nh portion is 6 mol% and the GeO concentration in the N1 portion is 3 mol%. is there. Ie floor

twenty two

GeO concentration difference Ac between adjacent stairs of stepped refractive index profile is 3 mol%.

2

The At this time, the difference between the maximum refractive index of the core (Nh part) and the refractive index of the cladding Δη クラッド is 0.008, and the difference between the refractive index of the N1 part of the core and the refractive index of the cladding Δη2 is 0.004. The refractive index difference Δη3 between adjacent stairs in the stepwise refractive index distribution was 0.004. Also, the refractive index is high, the core part (Nh part) has a core diameter of 8 μm, the refractive index is low !, and the core part (N1 part) has a core diameter of 5 μm.

[0073] An SBS suppression optical fiber having such a configuration was prepared for 20 km, and the reflected light power with respect to the incident light power at a wavelength of 1 550 nm was measured with a measurement system as shown in FIG. As a result, the SBS threshold power of the optical fiber of Example 2 is 9.5 dBm, which is 2.5 dBm higher than the normal SMF threshold power, and SBS can be suppressed. . The k coefficient at this time was ^1.5 X 10 ¹⁵ mWZm. The transmission loss at a wavelength of 1550 nm was 0.2 dBZkm, and the mode field diameter was 10 m. The spectrum width of SBS was 300MHz.

Example 3

[0074] As shown in Fig. 5, Ge was added to a core made of quartz glass, and an SMF having a refractive index distribution of the core in two steps was produced. Clad C is pure quartz glass. In the two-step stepwise refractive index distribution, if the high refractive index portion is Nh, the middle refractive index portion is Nm, and the low refractive index portion is N1, the GeO concentration in the Nh portion is 6 mol%, Nm Part of Ge

2

The concentration of O is 5.3 mol%, and the concentration of GeO in the N1 part is 4 mol%. That is, stepped

twenty two

The GeO concentration difference between adjacent steps in the refractive index profile is Nh and Nm, respectively. Difference from the minute A cl force SO. 7mol%, the difference Ac2 between the Nm part and the N1 part is 1.3mol%. At this time, the difference between the maximum refractive index of the core (Nh part) and the refractive index of the cladding Δη クラッド is 0.008, and the difference between the refractive index of the Nm part of the core and the refractive index of the cladding Δη2 is 0.007. The difference between the refractive index of the N1 part of the core and the refractive index of the clad Δη3 is 0.0053, and the refractive index difference between adjacent stairs in the stepwise refractive index distribution is the difference between the Nh part and the Nm part, respectively. Δ η4 was 0.001, and the difference Δ η5 between the Nm portion and the N1 portion was 0.0015. In addition, the core diameter of the core part with high refractive index (Nh part) is 8 μm, the core part of the core part with refractive index (Nm part) is 5 μm, and the refractive index is low! The core diameter of the core part (N1 part) is 3 μm.

[0075] An SBS suppression optical fiber having such a configuration was prepared for 20 km, and the reflected light power with respect to the incident light power at a wavelength of 1 550 nm was measured with a measurement system as shown in FIG. As a result, the SBS threshold power of the optical fiber of Example 3 is 10.5 dBm, which is 3.5 dBm higher than the normal SMF threshold power, and SBS can be suppressed. . The k coefficient at this time was 1.6 × 10 ¹⁵ mWZm. The transmission loss at a wavelength of 1550 nm was 0.23 dBZkm and the mode field diameter was 10. The spectral width of SBS was 350 MHz.

Example 4

[0076] As shown in FIG. 6, P was added to a core made of quartz glass to produce an SMF having a refractive index profile of the core in a single stepped shape. Clad C is pure quartz glass. In the stepwise refractive index distribution, if the high refractive index portion is Nh and the low refractive index portion is N1, the PO concentration in the Nh portion is 6 mol% and the PO concentration in the N1 portion is 4.5 mol. %. Ie floor

2 5 2 5

The concentration difference Ac of PO in adjacent stairs of the stepped refractive index profile is 1.5 mol%.

twenty five

Yes. The difference between the maximum refractive index of the core (Nh part) and the refractive index of the cladding Δηΐ is 0.008, and the difference between the refractive index of the N1 part of the core and the refractive index of the cladding Δη2 is 0.006. The refractive index difference Δη3 between adjacent stairs in the stepwise refractive index distribution was 0.002. In addition, the refractive index is high, the core part (Nh part) has a core diameter of 4 μm, the refractive index is low, and the core part (N1 part) has a core diameter of 8 μm.

[0077] An SBS-suppressed optical fiber having such a configuration was prepared for 20 km, and the measurement system shown in Fig. 2 The reflected light power relative to the incident light power at a wavelength of 550 nm was measured. As a result, the SBS threshold power of the optical fiber of Example 4 was 9 dBm, and the threshold power increased by 2 dBm compared to the normal SMF threshold value, and SBS could be suppressed. The k coefficient at this time was 1.4 × 10 ¹⁵ mWZm. The transmission loss at a wavelength of 1550 nm was 0.3 dBZkm, and the mode field diameter was 10. The spectral width of SBS was 250 MHz.

Example 5

[0078] As shown in FIG. 7, F was added to the outer periphery of a core made of pure silica glass, and an SMF having a refractive index distribution of the core in a single stepped shape was produced. F was also added to the clad C quartz glass. In the step-like refractive index distribution, if the high refractive index portion is Nh and the low refractive index portion is N1, the F concentration in the Nh portion is Omol% (pure quartz glass) and the F concentration in the N1 portion. The degree is 0.3 mol%. The clad F concentration is 1.6 mol%. Therefore, the F concentration difference Ac between adjacent staircases in the refractive index profile of the staircase-shaped core is 0.3 mol%. At this time, the difference Δηΐ between the maximum refractive index of the core (Nh portion) and the refractive index of the cladding is 0.008, and the difference Δη2 between the refractive index of the N1 portion of the core and the refractive index of the cladding is 0.007. The refractive index difference Δη3 between adjacent stairs in the stepwise refractive index distribution was 0.0015. The core diameter of the core part with high refractive index (Nh part) is 4 m, and the core diameter of the core part with low refractive index (N1 part) is 8 μm.

[0079] An SBS suppression optical fiber having such a configuration was prepared for 20 km, and the reflected light power with respect to the incident light power at a wavelength of 1 550 nm was measured with a measurement system as shown in FIG. As a result, the SBS threshold power of the optical fiber of Example 5 is 10.5 dBm, which is 3.5 dBm higher than the normal SMF threshold power, and SBS can be suppressed. . The k coefficient at this time was ^1.5 X 10 ¹⁵ mWZm. The transmission loss at a wavelength of 1550 nm was 0.27 dB / km, and the mode field diameter was 10. The spectral width of SBS was 340 MHz.

Example 6

[0080] As shown in Fig. 8, Ge was added to a core made of quartz glass, and an SMF having a refractive index distribution of the core in two steps was fabricated. Clad C is pure quartz glass. Two steps If the refractive index distribution is Nh for the high refractive index portion, Nm for the middle refractive index portion and N1 for the low refractive index portion, the GeO concentration in the Nh portion is 5.7 mol%, the Nm portion. of

2

The GeO concentration is 5.3 mol%, and the GeO concentration in the N1 part is 4.5 mol%. Ie floor

twenty two

The GeO concentration difference between adjacent steps in the step-shaped refractive index profile is Nh and

2

The difference A cl is 1.2 mol% from the N1 part, and the difference A c2 is 0.8 mol% between the Nm part and the N1 part. At this time, the difference Δηΐ between the maximum refractive index of the core (Nh portion) and the refractive index of the clad is 0.0075, and the difference between the refractive index of the core Nm portion and the refractive index of the clad Δη2 is 0.0. 07, the difference between the refractive index of the N1 part of the core and the refractive index of the cladding Δη3 is 0.006, and the refractive index difference between adjacent stairs of the stepwise refractive index distribution is the difference between the Nh part and the N1 part, respectively. The difference Δη4 force S0. 0015, the difference Δη5 between the Nm part and the N1 part was 0.001. In addition, the core diameter of the core part with the high refractive index (Nh part) is 8 μm, the core part of the intermediate part of the refractive index (Nm part) is 4 μm, and the refractive index is low. ! The core diameter of the core part (N1 part) is Ό μm.

[0081] An SBS suppression optical fiber having such a configuration was prepared for 20 km, and the reflected light power with respect to the incident light power at a wavelength of 1 550 nm was measured with a measurement system as shown in FIG. As a result, the SBS threshold power of the optical fiber of Example 6 is 10.5 dBm, which is 3.5 dBm higher than the normal SMF threshold power, and SBS can be suppressed. . The k coefficient at this time was 1.8 × 10 ¹⁵ mWZm. The transmission loss at a wavelength of 1550 nm was 0.19 dBZkm, and the mode field diameter was 10. The spectral width of SBS was 350 MHz.

Example 7

[0082] As shown in FIG. 9, Ge and P were added together to a quartz glass-powered core, and an SMF having a two-step staircase distribution was produced. Clad C is pure quartz glass. In a two-step stepwise refractive index distribution, if the high refractive index portion is Nh, the middle refractive index portion is N m, and the low refractive index portion is N1, the GeO concentration in the Nh portion is 4 mol%. PO

2 2 5 Concentration is 0.5 mol%, GeO concentration in Nm part is 3 mol%, PO concentration is 0.8

2 2 5

The concentration of GeO in the N1 part is 2.8 mol%, and the concentration of PO is 0.6 mol.

2 2 5

%. In other words, the total of GeO and PO in adjacent stairs with a step-like refractive index profile. The difference in concentration is that the difference A cl between the Nh and Nl parts is 1. lmol%, and the difference Ac2 between the Nm and N1 parts is 0.4 mol%. The difference between the maximum refractive index of the core (Nh part) and the refractive index of the cladding Δη 屈折 is 0.006, and the difference between the refractive index of the core Nm part and the refractive index of the cladding Δη2 is 0.005. The difference between the refractive index of the core N1 portion and the refractive index of the cladding Δη3 is 0.0045, and the refractive index difference between adjacent steps of the stepwise refractive index distribution is Nh and N1 respectively. The difference Δη4 between the parts was 0.0015, and the difference Δη5 between the Nm part and the N1 part was 0.0005. Also, the core diameter of the core part with high refractive index (Nh part) is 8.5 μm, the core part of the intermediate part of refractive index (Nm part) is 4 / ζ πι, and the refractive index The core diameter of the lower core part (N1 part) is 6 μm.

[0083] An SBS suppression optical fiber having such a configuration was prepared for 20 km, and the reflected light power with respect to the incident light power at a wavelength of 1 550 nm was measured with a measurement system as shown in FIG. As a result, the SBS threshold power of the optical fiber of Example 7 is 9.7 dBm, which is 2.7 dBm higher than the normal SMF threshold power, and SBS can be suppressed. . The k coefficient at this time was 1.3 X 10 ¹⁵ mWZm. The transmission loss at a wavelength of 1550 nm was 0.21 dBZkm, and the mode field diameter was 10. The spectral width of SBS was 230 MHz.

Example 8

[0084] As shown in Fig. 10, Ge, P, and F were added together to a core that also has quartz glass power, and an SMF having a refractive index distribution of this core in one stepped shape was produced. Clad C is pure silica glass. In the stepwise refractive index distribution, Nh is the high refractive index part and N1 is the low refractive index part. The GeO concentration in the Nh part is 4.5 mol%, the PO concentration is 1.5 mol%, F of

2 2 5

The concentration is 0.2 mol%, the GeO concentration in the N1 part is 4.5 mol%, and the PO concentration is 0

2 2 5

8mol%, F concentration is 0.4mol%. In other words, the total concentration difference Ac of GeO, PO, and F in adjacent stairs in the step-like refractive index profile is 0.5 mol%. In addition, this

2 2 5

The difference between the maximum refractive index of the core (Nh part) and the refractive index of the cladding Δηΐ is 0.007, and the difference between the refractive index of the N1 part of the core and the refractive index of the cladding Δη2 is 0.004, The difference in refractive index Δη3 between adjacent stairs in the stepwise refractive index distribution was 0.003. In addition, the core diameter of the core part with high refractive index (Nh part) is 8 μm, the refractive index is low !, the core part (N1 part) The core diameter is 4 μm.

[0085] An SBS suppression optical fiber having such a configuration was prepared for 20 km, and the reflected light power with respect to the incident light power at a wavelength of 1 550 nm was measured with a measurement system as shown in FIG. As a result, the SBS threshold power of the optical fiber of Example 8 was lOdBm, and the threshold power increased by 3 dBm compared to the normal SMF threshold power, and SBS could be suppressed. The k coefficient at this time was 1.4 × 10 ¹⁵ mWZm. The transmission loss at a wavelength of 1550 nm was 0.25 dBZkm, and the mode field diameter was 10. The spectrum width of SBS was 300MHz.

Here, in the SBS-suppressed optical fibers of the above-described embodiments, all zero dispersion wavelengths were in the range of 1300 nm to 1324 nm. In addition, the mode field diameter at a wavelength of 13 lOnm was all between 8.6 and 9.5 m.

[0087] The method for producing the base material for producing the SBS-suppressed optical fiber of the present invention is not particularly limited, such as a commonly used MCVD method, plasma CVD method, VAD method, OVD method, etc. The most suitable method may be used depending on the method.

(Comparative example)

[0088] For comparison, as shown in FIG. 11, an SMF having a stepped refractive index distribution was prepared by adding Ge to a quartz glass core. Clad C is pure quartz glass. In the step-like refractive index distribution, if the high refractive index portion is Nh and the low refractive index portion is N1, the GeO concentration in the Nh portion is 5.3 mol% and the GeO concentration in the N1 portion is 5. lmol

twenty two

%. That is, the GeO concentration difference Ac between adjacent stairs in the step-like refractive index profile is 0.

2

It is 2mol%. At this time, the difference Δηΐ between the maximum refractive index of the core (Nh part) and the refractive index of the clad is 0.007, and the difference between the refractive index of the N1 part of the core and the refractive index of the clad Δη2 is 0. The refractive index difference Δη3 between adjacent stairs in the stepwise refractive index distribution was 0.0002. In addition, the core diameter of the core part (Nh part) with a high refractive index is 8 m, the refractive index is low !, and the core diameter of the core part (N1 part) is 3 μm.

[0089] An SBS suppression optical fiber having such a configuration was prepared for 20 km, and the reflected light power with respect to the incident light power at a wavelength of 1 550 nm was measured with a measurement system as shown in FIG. As a result, the optical fiber of this comparative example has a transmission loss of 0.2 dB / km at a wavelength of 1550 nm and a mode. The field diameter was 10 / xm, which was equivalent to normal SMF, but the SBS threshold power was 7.5 dBm, and the threshold power increased by 0.5 dBm compared to the normal SMF threshold power. , SBS could not sufficiently suppress the power. The k coefficient at this time was 9.4 X 10 ¹⁴ mW / m, and the spectral width of SBS was 180 MHz.

Claims

The scope of the claims

[1] An optical fiber composed of a quartz glass-powered core and a cladding having a lower refractive index than that of the core around the silica glass-powered silica glass. The core is composed of Ge or P alone, or Ge And P are added at the same time, and the core has a step-like refractive index profile, and the difference in GeO concentration in the adjacent steps of the step-like refractive index profile or PO

2 2 5 The difference in concentration or the total concentration difference between GeO and PO is 0.3 mol% or more.

2 2 5

Stimulated Brillouin scattering suppression optical fiber.

[2] GeO concentration difference between adjacent steps of the step-like refractive index profile or P O

2 2 5 The difference in concentration or the total concentration difference between GeO and PO is 0.6 mol% or more.

2 2 5

The stimulated Brillouin scattering suppressing optical fiber according to claim 1.

[3] according to claim 1 or claim 2 stimulated Brillouin scattering suppression optical fiber, wherein the refractive index difference at stepped adjacent of the refractive index distribution of the stepwise is 3 X 10_ ⁴ or more.

[4] stimulated Brillouin scattering suppression optical fiber according to claim 3, wherein the refractive index difference at stepped adjacent of the refractive index distribution of the stepwise, characterized in that it is 8 X 10_ ⁴ or more.

[5] The stimulated Brillouin scattering-suppressing optical fiber according to any one of claims 1 to 4, wherein the clad is pure silica glass.

[6] The stimulated Brillouin scattering suppression optical fiber according to any one of claims 1 to 4, wherein F is added to quartz glass in the cladding.

[7] An optical fiber composed of a quartz glass-powered core and a cladding having a lower refractive index than that of a core around the silica-glass power, and a silica glass-powered clad, wherein F is added to the core and the cladding, and the core A stimulated Brillouin scattering-suppressing optical fiber, characterized in that has a step-like refractive index distribution, and the F concentration difference between adjacent steps in the step-like refractive index distribution is 0.08 mol% or more.

8. The stimulated Brillouin scattering-suppressing optical fiber according to claim 7, wherein the difference in F concentration in adjacent steps of the step-like refractive index profile is 0.16 mol% or more.

[9] according to claim 7 or claim 8 stimulated Brillouin scattering suppression optical fiber, wherein the refractive index difference at stepped adjacent of the refractive index distribution of the stepwise is 3 X 10_ ⁴ or more.

[10] refractive index difference at stepped adjacent of the refractive index distribution of the stepwise is 8 X 10- ⁴ or more 10. The stimulated Brillouin scattering suppression optical fiber according to claim 9,

[11] An optical fiber composed of a silica glass-powered core and a silica glass-powered clad having a refractive index lower than that of the outer peripheral core. The core is composed of Ge or P alone, or Ge. P is added simultaneously, cut further has a refractive index profile of the core is stairs like with F is added, the refractive index difference at stepped adjacent of the refractive index distribution of the stepwise 3 X 10_ ⁴ or more A stimulated Brillouin scattering-suppressing optical fiber, characterized in that

[12] stimulated Brillouin scattering suppression optical fiber of claim 11 wherein the refractive index difference at stepped adjacent of the refractive index distribution of the stepwise, characterized in that it is 8 X 10- ⁴ or more.

13. The stimulated Brillouin scattering suppression optical fiber according to claim 11 or 12, wherein the clad is pure silica glass.

[14] The stimulated Brillouin scattering-suppressing optical fiber according to [11] or [12], wherein the clad is obtained by adding F to quartz glass.

[15] An optical fiber composed of a quartz glass force core and a clad glass force clad having a refractive index lower than that of the outer peripheral core, wherein the core is pure silica glass and quartz glass to which F is added. becomes a force, wherein the core with cladding to F are added has a refractive index distribution of the stairs-like, the refractive index difference at stepped adjacent of the refractive index distribution of the stepwise is 3 X 10_ ⁴ or more A stimulated Brillouin scattering-suppressing optical fiber.

[16] stimulated Brillouin scattering suppression optical fiber of claim 15 wherein the refractive index difference at stepped adjacent of the refractive index distribution of the stepwise, characterized in that it is 8 X 10- ⁴ or more.

[17] The induction Brillouin according to any one of claims 1 to 16, wherein a difference between a maximum refractive index of the core and a refractive index of the clad is 0.008 or less. Scatter suppression optical fiber.

18. The stimulated Brillouin scattering-suppressed optical fiber according to any one of claims 1 to 17, wherein the spectral width of the stimulated Brillouin scattering of the optical fiber is 200 MHz or more.

[19] The stimulated Brillouin scattering-suppressed optical fiber according to [18], wherein the spectrum width of the stimulated Brillouin scattering of the optical fiber is 300 MHz or more.

[20] The zero-dispersion wavelength of the optical fiber is 1300ηπ! ~ 1324nm range The stimulated Brillouin scattering-suppressing optical fiber according to any one of claims 1 to 19.

21. The guided Brillouin according to claim 1, wherein a mode field diameter of the optical fiber at a wavelength of 1310 nm is in a range of 8.6 to 9.5 ^ m. Scatter-suppressing optical fiber.