JP2010102138A - Hole providing type single mode optical fiber and manufacturing method of the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hole providing type single mode optical fiber used for construction of a single mode optical communication line using a communication band of 1,260 nm or more of wavelength having 1,260 nm or less of 22 m-effective cutoff wavelength and a bending loss property at 1,625 nm of wavelength and 0.1 dB/roll or less at 5 mm of bending radius, and a simple designing method of the hole providing type single mode optical fiber. <P>SOLUTION: This hole providing type single mode optical fiber has a clad part having a uniform refractive index, a core part which has a higher refractive index than the clad part and is arranged in the center of the clad part, and at least six holes arranged at equal intervals concentrically with the core part inside the clad part. The occupancy rate of the holes in the clad part and the relative index difference of the core part in relation to the clad part are controlled. The desired bending loss property and the 22 m-effective cutoff wavelength property are thus obtained. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a hole-providing single-mode optical fiber used for construction of a single-mode optical communication line and a method for manufacturing the same.

  In general, in single mode optical communication using a communication wavelength band of 1260 nm or more, a clad part having a uniform refractive index and a core having a higher refractive index than the clad part and arranged in the center of the clad part A single mode optical fiber is used. The transmission characteristics such as the 22 m effective cutoff wavelength characteristic, bending loss characteristic, chromatic dispersion characteristic, and mode field diameter characteristic of the single mode optical fiber take into account the refractive index distribution in the diameter direction in the cross section of the single mode optical fiber. This makes it easy to analyze and design.

  In recent years, a single mode optical fiber having an allowable bending radius improved from 30 mm to about 10 mm or less has been developed by optimizing the refractive index distribution from the viewpoint of improving handling of the single mode optical fiber. . However, in general, a single mode optical fiber with an optimized refractive index profile has a problem in that the mode field diameter decreases as the bending loss characteristics are improved.

  For this reason, in Non-Patent Document 1, a clad part having a uniform refractive index, a core part having a higher refractive index than the clad part, arranged in the center of the clad part, and concentrically from the core part In a hole-providing single mode optical fiber having six holes arranged at equal intervals in the clad part, by appropriately controlling the distance of the holes from the core part, bending loss A technique for improving characteristics and suppressing reduction in mode field diameter is disclosed.

K. Nakajima, et al., "Hole-assisted fiber design for small bending and splice losses," Photon. Technol. Lett., Vol.15, No.12, pp.1737-1739, 2003

  However, in general, in a hole-providing single mode optical fiber in which bending loss characteristics are drastically improved by holes, the holes may have a light confinement effect even for higher-order modes. For this reason, when the higher-order mode of the hole-providing single mode optical fiber is efficiently excited, there is a possibility that the 22 m effective cutoff wavelength characteristic required for single mode optical communication may not be satisfied. There was a problem.

  In addition, in order to design in detail the transmission characteristics of an optical fiber having a structure that does not satisfy perfect symmetry in the direction around the axis in the cross section of the optical fiber, such as a hole-providing single-mode optical fiber, Considering the two-dimensional refractive index distribution of the fiber cross section, there is a problem that it is necessary to perform more complicated analysis using the finite element method.

  The present invention has been made in view of the above problems, and has the object of having an effective cutoff wavelength of 22 m or less and a bending loss characteristic of 0.1 dB / winding or less at a communication wavelength of 1625 nm and a bending radius of 5 mm. An object of the present invention is to provide a hole-providing single mode optical fiber for use in construction of a single mode optical communication line using a communication band having a wavelength of 1260 nm or more. Another object of the present invention is to provide a simple method for producing the hole-providing single mode optical fiber.

  A hole-providing single-mode optical fiber according to a first aspect of the present invention for solving the above problems includes a cladding portion having a uniform refractive index, a refractive index higher than that of the cladding portion, and the cladding portion. A core portion disposed in the center of the core portion, and at least six or more holes arranged at equal intervals on the concentric circle with the core portion in the cladding portion, and the occupation ratio of the holes in the cladding portion and By controlling the relative refractive index difference of the core part with respect to the cladding part, the bending loss characteristic and the 22m effective cutoff wavelength characteristic are designed to desired values.

  A hole-providing single mode optical fiber according to a second invention for solving the above-described problems is a hole-providing single mode optical fiber according to the first invention, wherein the single-mode optical fiber without holes is provided. The occupancy and the relative refractive index difference are derived using the bending loss and the dependence on the relative refractive index difference of the effective cutoff wavelength of 22 m derived by numerical analysis of the refractive index distribution of

  A method for manufacturing a hole-providing single-mode optical fiber according to a third aspect of the present invention for solving the above-described problem has a cladding part having a uniform refractive index, and a refractive index higher than that of the cladding part, A hole-providing single mode light having a core part disposed in the center of the cladding part and at least six or more holes arranged at equal intervals in the cladding part concentrically from the center of the core part. A method of manufacturing a fiber, comprising controlling the occupation ratio of the holes in the cladding part and the relative refractive index difference of the core part with respect to the cladding part, and bending loss characteristics of the hole-providing single-mode optical fiber, and The 22m effective cutoff wavelength characteristic is designed to a desired value.

  A hole-providing single-mode optical fiber manufacturing method according to a fourth aspect of the present invention for solving the above-described problems is the hole-providing single-mode optical fiber according to the third aspect of the present invention. The occupancy ratio and the relative refractive index difference are derived by using the bending loss derived by numerical analysis of the refractive index distribution of the mode optical fiber and the dependence on the relative refractive index difference of the 22 m effective cutoff wavelength. And

  According to the hole-providing single mode optical fiber according to the present invention, by appropriately controlling the hole occupation ratio and the relative refractive index difference, a wavelength of 1625 nm and a bending radius of 5 mm that contribute to improving the handleability of the optical fiber. Easily achieves both a bending loss characteristic of 0.1 dB / winding or less and a 22 m effective cutoff wavelength characteristic of 1260 nm or less for use in construction of a single mode optical communication line using a wavelength band longer than 1260 nm. It has the effect of making it possible

  In addition, according to the method for manufacturing a hole-providing single mode optical fiber according to the present invention, the bending loss and the dependency on the hole occupation ratio of the 22 m effective cutoff wavelength and the dependency on the relative refractive index difference are used. As a result, it is possible to easily design a hole-providing single mode optical fiber having a desired bending loss characteristic and a desired 22 m effective cutoff wavelength characteristic. More specifically, since the dependence of the bending loss and the relative refractive index difference of the 22 m effective cutoff wavelength on the relative refractive index can be derived by numerical analysis of the refractive index distribution in the single-mode optical fiber without holes, the two-dimensional refractive index There is an effect that complicated analysis and design in consideration of the distribution are not required.

  Hereinafter, a hole-providing single mode optical fiber and a method for manufacturing the same according to the present invention will be described in detail with reference to the drawings.

  A first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a cross-sectional view showing the structure of a hole-providing single mode optical fiber according to this embodiment.

  In this example, as a hole-providing single mode optical fiber having a bending loss characteristic of 0.1 dB / winding or less at a wavelength of 1625 nm and a bending radius r = 5 mm, and a 22 m effective cutoff wavelength characteristic of 1260 nm or less, A case where the core portion 12 of the grant type single mode optical fiber is formed with a step type refractive index profile having a radius a of about 4.5 μm will be described.

  As shown in FIG. 1, the hole-providing single mode optical fiber according to the present embodiment has a clad part 11 having a uniform refractive index, a refractive index higher than that of the clad part 11, and the center of the clad part 11. And a core portion 12 having a radius a, and at least six (10 in FIG. 1) holes 13 arranged at equal intervals on a concentric circle with the core portion 12 in the clad portion 11.

  The clad portion 11 and the core portion 12 can be formed using any glass material, similarly to a single mode optical fiber having no hole structure (hereinafter referred to as a single mode optical fiber without a hole). For example, when the cladding part 11 is made of pure quartz glass, the refractive index distribution of the core part 12 can be formed by adding a material such as germanium. In addition, although the hole 13 has shown the case of circular sectional view as an example, it may be arbitrary shapes, such as an ellipse and a rectangle, for example.

  Here, in this embodiment, the relative refractive index difference Δ (%) of the core portion 12 with respect to the cladding portion 11 is defined by the following equation (1).

In equation (1), n _core and n _clad represent the refractive indexes of the core portion 12 and the clad portion 11, respectively.

Further, the radii of circles inscribed and circumscribed to the holes 13 (circles indicated by broken lines in FIG. 1) are R ₁ and R ₂ respectively, and the cladding in the ring-shaped region surrounded by the inscribed circle and the circumscribed circle The ratio of the area occupied by the holes 13 to the portion 11 is defined as the hole occupation ratio S by the following equation (2).

  N represents the number of holes 13 and d represents the diameter of the holes 13.

FIG. 2 shows the relationship between the bending loss α _b (dB / winding) and the hole occupancy S in the hole-providing single-mode optical fiber according to this example.

The characteristics shown in FIG. 2 are bending loss characteristics at a wavelength of 1625 nm and a bending radius r = 5 mm. In FIG. 2, white circles represent characteristics of a hole-providing single mode optical fiber having holes. The black circles represent the characteristics of the single-mode optical fiber without holes. The number N of holes in the hole-providing single mode optical fiber is 6 or 10, the normalized inscribed circle radius R ₁ / a is 1.9 to 3.0, and the normalized hole diameter d / 2a Was set to 0.33 to 1.7. Regardless of the presence or absence of holes, the relative refractive index difference Δ of all the optical fibers shown in FIG. 2 is about 0.35%.

From FIG. 2, the bending loss α _b of the hole-providing single mode optical fiber decreases exponentially with respect to the hole occupation ratio S regardless of the number of holes N, and the relationship is expressed by the following empirical formula (3 ) Can be approximated.

Here, the coefficient A ₁ represents the bending loss α _b in the single-mode optical fiber without holes (S = 0). In the present embodiment, the coefficient A ₁ is about 43.3. The coefficient A ₂ represents the effect of improving the bending loss characteristics due to the hole occupancy S. In this example, the coefficient A ₂ in the hole-providing single mode optical fiber is approximately equal to FIG. Can be described uniquely as -19.8.

FIG. 3 shows the relationship between the bending loss α _b (dB / winding) and the relative refractive index difference Δ (%) in the hole-providing single mode optical fiber according to this example.

The characteristic shown in FIG. 3 is a bending loss characteristic at a wavelength of 1625 nm and a bending radius r = 5 mm. In FIG. 3, white circles and solid lines represent measurement results and approximate curves in the hole-providing single mode optical fiber, respectively. The broken line shows the calculation result for the single-mode optical fiber without holes. The core radius a of the hole-providing single mode optical fiber is about 4.5 μm, the number of holes N is 10, the hole occupation ratio S is about 33%, and the normalized inscribed circle radius R ₁ / a is about 2.1.

FIG. 3 shows that the bending loss α _b of the hole-providing single mode optical fiber decreases exponentially with respect to the relative refractive index difference Δ, and the relationship can be approximated by the following empirical formula (4).

Here, the coefficient A ₃ is a coefficient depending on the hole occupation ratio S, and in the present embodiment, the coefficient A ₃ is about 453.7. The coefficient A ₄ represents the dependency of the bending loss characteristic on the relative refractive index difference Δ. In the present embodiment, the coefficient A ₄ is about −24.9.

As can be seen from FIG. 3, the dependence of the bending loss characteristic on the relative refractive index difference Δ is almost the same regardless of the presence or absence of holes. Therefore, the coefficient A ₄ in the empirical formula (4) can be easily obtained by deriving the bending loss characteristics in the single-mode optical fiber without holes by simple numerical analysis in consideration of the refractive index distribution of the optical fiber. Can do.

  From the above results, the bending loss characteristics of the hole-providing single mode optical fiber according to this example can be approximated by the following empirical formula (5) as a function of the hole occupation ratio S and the relative refractive index difference Δ. .

Here, .DELTA..delta uses a reference relative refractive index difference delta _r, it is represented by the following formula (6), in this embodiment, delta When 0.35% of _r, the coefficient in the empirical formula (5) A ₁ and A ₄ can be determined as about 43.3 and -24.9, respectively.
δΔ = Δ−Δ _r (6)

FIG. 4 shows the relationship between the 22 m effective cutoff wavelength λ _c (nm) and the hole occupancy S in the hole-providing single mode optical fiber according to this example.

The effective cut-off wavelength λ _c shown in FIG. 4 is that when a fundamental mode and a higher-order mode are simultaneously excited in a 22-m long optical fiber having a bent portion having a bend radius of 140 mm, the higher-order mode loss is the fundamental mode. It represents a wavelength that increases 0.1 dB over the loss.

In FIG. 4, white circles and solid lines represent the measurement results and approximate straight lines in the hole-providing single mode optical fiber, respectively. A black circle represents a measurement result in a single-mode optical fiber without a hole. The core radius a of the hole-providing single mode optical fiber is about 4.5 μm, the number of holes N is 6 or 10, and the normalized inscribed circle radius R ₁ / a is 1.9 to 3.0. The standardized hole diameter d / 2a was 0.33 to 1.7. Regardless of the presence or absence of holes, the relative refractive index difference Δ of all the optical fibers shown in FIG. 4 is about 0.35%.

From FIG. 4, it can be seen that the 22 m effective cutoff wavelength λ _c of the hole-providing single mode optical fiber becomes longer as the hole occupation ratio S increases regardless of the number of holes 13. When the hole occupation ratio S is 30% or less, the 22 m effective cutoff wavelength λ _c of the hole-providing single mode optical fiber is equal to the 22 m effective cutoff wavelength λ _{c of the} single mode optical fiber without holes. It turns out that it becomes. Therefore, in this embodiment, the dependency of the 22 m effective cutoff wavelength λ _{c on} the hole occupancy S in the hole-providing single mode optical fiber can be approximated by empirical formula (7).

However, when the hole occupation ratio S is 30% or less, the 22 m effective cutoff wavelength λ _c becomes a constant value (B ₁ + 0.3B ₂ ). Here, the coefficient B ₁ is a coefficient depending on the 22 m effective cut-off wavelength characteristic of the single-mode optical fiber without holes, and in the present embodiment, this coefficient B ₁ is about 847.2. The coefficient B ₂ represents the dependency of the 22 m effective cutoff wavelength λ _{c on} the hole occupancy S. In this embodiment, the coefficient B ₂ does not depend on the number of holes N and is approximately 1224.3 from FIG. Can be described uniquely.

FIG. 5 shows the relationship between the effective cutoff wavelength λ _c (nm) of 22 m and the relative refractive index difference Δ (%) in the hole-providing single mode optical fiber according to this example.

In FIG. 5, white circles and solid lines represent the measurement results and approximate straight lines in the hole-providing single mode optical fiber, respectively. The core radius a of the hole-providing single mode optical fiber is about 4.5 μm, the number of holes N is 10, the hole occupation ratio S is about 33%, and the normalized inscribed circle radius R ₁ / a is about 2.1.

From FIG. 5, the 22m effective cutoff wavelength λ _c of the hole-providing single-mode optical fiber becomes longer in a linear function as the relative refractive index difference Δ increases, and the relationship can be approximated by the following empirical formula (8). I understand.

Here, the coefficient B ₃ is a coefficient depending on the hole occupancy S, and B ₃ is about 518.7 in this embodiment. The coefficient B ₄ represents the dependency of the 22 m effective cutoff wavelength λ _{c on} the relative refractive index difference Δ, and B ₄ is about 2100 in this embodiment.

In the single-mode optical fiber without holes, the calculation results of the 22 m effective cutoff wavelength λ _c when the relative refractive index difference Δ is 0.3, 0.35, and 0.4% are 1147 and 1254, respectively. , And 1355 nm, which is almost coincident with the dependency of the 22 m effective cutoff wavelength characteristic on the relative refractive index difference Δ in the hole-providing single mode optical fiber of the present embodiment shown in FIG. Therefore, the coefficient B ₄ in the empirical formula (8) can be easily obtained by deriving the effective cutoff wavelength λ _c of 22 m in the holeless single mode optical fiber by simple numerical analysis in consideration of the refractive index of the optical fiber. Can get to.

  From the above results, the 22m effective cutoff wavelength characteristic of the hole-providing single-mode optical fiber according to this example is expressed by the relational expression (6) as a function of the hole occupation ratio S and the relative refractive index difference Δ. It can be approximated by empirical formula (9) using δΔ.

In the present embodiment, when the reference relative refractive index difference delta _r to 0.35%, the coefficient B ₁ and B ₄ in the empirical formula (9) may be determined as approximately 847.2,2100 respectively.

  FIG. 6 shows design conditions for the hole occupancy S and the relative refractive index difference Δ (%) in the hole-providing single mode optical fiber according to the present embodiment.

In FIG. 6, the solid line represents the relationship between the hole occupancy S at which the bending loss α _b is 0.1 dB / turn at a wavelength of 1625 nm and the bending radius r = 5 mm, and the relative refractive index difference Δ. The bending loss α _b can be derived by substituting 0.1 (dB / winding). Here, based on the empirical formula (5), the bending loss α _b at a wavelength of 1625 nm and a bending radius r = 5 mm is 0.1 dB / in the right side of the solid line in the drawing, that is, in the region where the hole occupation ratio S increases. It becomes possible to make it below the volume.

The broken line in FIG. 6 represents a vacancy occupancy relation S and the relative refractive index difference Δ of 22m effective cutoff wavelength lambda _c is 1260 nm, in the empirical formula (9), as 22m effective cutoff wavelength lambda _c 1260 It can be derived by substituting (nm). Here, based on the empirical formula (9), the 22 m effective cutoff wavelength λ _c can be set to 1260 nm or less on the left side of the broken line in FIG. 6, that is, in the region where the hole occupancy S decreases. .

Accordingly, the hole occupancy S of the hole-providing single mode optical fiber of the present embodiment is set so as to be a value within a region surrounded by a solid line and a broken line in the drawing (a hatched region in the drawing). In addition, by setting the relative refractive index difference Δ, the bending loss α _b at a wavelength of 1625 nm and a bending radius of 5 mm can be 0.1 dB / turn or less, and the 22 m effective cutoff wavelength λ _c can be 1260 nm or less. When the relative refractive index difference Δ is lower than 0.3%, it becomes difficult to form an optical waveguide structure by the core portion 12 and the cladding portion 11. Therefore, the relative refractive index difference Δ in the hole-providing single mode optical fiber of this embodiment is preferably set to 0.3% or more.

FIG. 7 shows a normalized inscribed circle radius R ₁ / a with a hole occupancy S of 35%, a normalized hole diameter d / 2a, and a void in the hole-providing single mode optical fiber according to the present embodiment. The relationship of the number of holes N is shown.

6 and 7, in the hole-providing single mode optical fiber of this example having a step-type refractive index distribution with a core radius of 4.5 μm, for example, the hole occupation ratio S is 35% and the normalized inscribed When the circular radius R ₁ / a is 2.5 and the number of holes N is 10, the relative refractive index difference Δ is about 0.32 to 0.34%, and the normalized hole diameter d / 2a is about 0.00. 4, it can be seen that the bending loss α _b at a wavelength of 1625 nm, a bending radius of 5 mm can be 0.1 dB / winding or less, and the 22 m effective cutoff wavelength λ _c can be 1260 nm.

According to Non-Patent Document 1, by setting the standardized inscribed circle radius R ₁ / a to 2 or more, the mode field diameter is reduced due to the provision of holes in the hole-providing single mode optical fiber. Since it can be suppressed to about 10% or less, it is preferable to design the hole-providing single mode optical fiber of this embodiment in a region where the standardized inscribed circle radius is 2 or more.

  Table 1 shows one characteristic example of the hole-providing single mode optical fiber according to the present embodiment.

  From Table 1, by satisfying the design conditions shown in FIG. 6 and FIG. 7, it has a bending loss characteristic of a wavelength of 1625 nm, a bending radius of 5 mm and 0.1 dB / winding or less, and a 22 m effective cutoff wavelength characteristic of 1260 nm or less. It can be seen that the hole-providing single mode optical fiber of this example can be realized.

From the above results, according to the present embodiment, the clad part 11 having a uniform refractive index, the core part 12 having a higher refractive index than the clad part 11 and disposed in the center of the clad part 11, In a hole-providing single mode optical fiber including at least six holes 13 arranged in the clad part 11 concentrically from the core part 12, the bending loss characteristic and the 22m effective cutoff wavelength characteristic are obtained. By considering the dependence on the hole occupancy S and the dependence on the relative refractive index difference Δ of the core, a bending loss α _b of 0.1 dB / winding or less at a wavelength of 1625 nm, a bending radius of 5 mm, and 1260 nm It is possible to realize the hole-providing single mode optical fiber of this example having the following 22m effective cutoff wavelength characteristics.

  A second embodiment of the present invention will be described with reference to FIGS. In this embodiment, a method for manufacturing a hole-providing single mode optical fiber using the dependency of the bending loss characteristic and the 22 m effective cutoff wavelength characteristic on the hole occupation ratio S and the dependency on the relative refractive index difference Δ is used. Will be described. Note that the structure of the hole-providing single mode optical fiber in this embodiment is substantially the same as that shown in FIG. 1 and described above, and hereinafter, the same members as those shown in FIG. Thus, overlapping description is omitted, and different points will be mainly described.

  In this embodiment, as an example, the core portion 12 is formed with a refractive index distribution of the power of α, the core radius a of the core portion is 4.6 μm, and α of the power of α distribution is formed as 10. A one-mode optical fiber will be described.

As described above, the dependency of the bending loss α _{b on} the hole occupancy S and the relative refractive index difference Δ in the hole-providing single mode optical fiber of this embodiment is described by empirical formula (10).

Here, .DELTA..delta the use of the reference relative refractive index difference delta _r, described by the following equation (11).
δΔ = Δ−Δ _r (11)

FIG. 8 shows the relationship between the bending loss α _b and the relative refractive index difference Δ in the holeless single mode optical fiber. The characteristics shown in FIG. 8 can be derived by numerically analyzing the α power refractive index distribution by a normal multilayer division approximation method. From FIG. 8, the dependence of the bending loss α _{b on} the relative refractive index difference Δ can be approximated by the following equation (12).

Here, when the 0.35% reference relative refractive index difference delta _r in the equation (11), the coefficient A ₄ in the above empirical formula (10), said approximate expression from (12), A ₄ = -15 .4.

Next, the dependency of the 22 m effective cutoff wavelength λ _{c on} the hole occupation ratio S and the relative refractive index difference Δ in the hole-providing single mode optical fiber according to this example is described by empirical formula (13).

However, when the hole occupation ratio S is 30% or less, the 22 m effective cutoff wavelength λ _c becomes a constant value (B ₁ + 0.3B ₂ ).

FIG. 9 shows the relationship between the effective cutoff wavelength λ _c of 22 m and the relative refractive index difference Δ in the single-mode optical fiber without holes. The characteristic shown in FIG. 9 can be derived by numerically analyzing the α power refractive index distribution by a normal multilayer division approximation method. From FIG. 9, the dependency of the 22 m effective cutoff wavelength λ _{c on} the relative refractive index difference Δ can be approximated by the following equation (14).

From the approximate expression (14), the 22 m effective cutoff wavelength λ _c when the relative refractive index difference Δ is 0.35% is about 1156 nm. Here, when the reference relative refractive index difference delta _r and 0.35%, the coefficient B ₁ in the empirical formula (13), the 1156 (nm) as 22m effective cutoff wavelength lambda _c, as the pore occupation rate S 0 By substituting .3, it can be determined as B ₁ = 782.7. The coefficient B ₄ in the empirical formula (13) is determined as B ₄ = 1852 from the approximate formula (14).

Here, assuming that the design condition of the bending loss α _b is 1625 nm, the bending radius r = 5 mm is 0.1 dB / winding or less, and the design condition of the 22 m effective cutoff wavelength λ _c is 1260 nm or less, the void formation of this embodiment is performed. The design conditions for the hole occupation ratio S and the relative refractive index difference Δ in the type single-mode optical fiber are derived from the empirical formula (10) and the empirical formula (14).

  FIG. 10 shows the relationship between the hole occupation ratio S and the relative refractive index difference Δ derived from the empirical formula (10) and the empirical formula (14) in this embodiment.

In FIG. 10, the solid line represents the relationship between the hole occupancy S and the relative refractive index difference Δ where the bending loss α _b is 0.1 dB / turn at a wavelength of 1625 nm and a bending radius of 5 mm. It is possible to realize a bending loss α _b of 1 dB / winding or less. The broken line represents the relationship between the hole occupancy S and the relative refractive index difference Δ where the 22 m effective cutoff wavelength λ _c is 1260 nm, and realizes the 22 m effective cutoff wavelength λ _c of 1260 nm or less in the region on the left side of the broken line. Is possible. Therefore, the design conditions for the hole-providing single mode optical fiber in the present embodiment are set in a region surrounded by a solid line and a broken line in the figure. For example, when the hole occupancy S is 34%, the design region of the relative refractive index difference Δ is in the range of 0.3 to 0.375%.

FIG. 11 shows the relationship between the normalized inscribed circle radius R ₁ / a, the normalized hole diameter d / 2a, and the number N of holes, where the hole occupation ratio S is 34% in the present embodiment. As shown in FIG. 11, for example, when the standardized inscribed circle radius R ₁ / a is 2.5 and the number of holes N is 8, the standardized hole diameter d / 2a is about 0.5. Thus, the hole-providing single mode optical fiber of the present invention can be realized.

FIG. 12 shows a flow for deriving design conditions for the hole-providing single mode optical fiber according to the present embodiment. As shown in FIG. 12, when setting the design conditions of the hole-providing single mode optical fiber in this embodiment, first, the bending loss α _b (dB / winding of the hole-providing single mode optical fiber is set. ) And 22m effective cutoff wavelength λ _c (nm) is set (step P1).

Subsequently, by numerical analysis of the refractive index distribution of the single-mode optical fiber without holes, the coefficients A ₁ and A ₄ in the empirical formula (15) are changed to the bending loss α _{b at} the reference relative refractive index difference Δ _{r and} the bending, respectively. It is determined as the dependence of the loss α _{b on} the relative refractive index difference.

However, it is δΔ = Δ-Δ _r.

Subsequently, by a numerical analysis of the refractive index distribution of the single-mode optical fiber without holes, the coefficient B ₁ in the empirical formula (16) is determined using the 22 m effective cutoff wavelength λ _c at the reference relative refractive index difference Δ _r . Further, by numerical analysis of the refractive index distribution of the single-mode optical fiber without holes, the coefficient B ₄ in the empirical formula (16) is determined as the relative refractive index dependency of the 22 m effective cutoff wavelength characteristic (step P3).

Subsequently, using the empirical formulas (15) and (16), the desired bending loss α _b set in step P1 and the hole occupation ratio S and the relative refractive index difference Δ realizing the 22 m effective cutoff wavelength λ _c are calculated. Design conditions are derived (step P4).

Subsequently, the relationship between the number N of holes, the standardized inscribed circle radius R ₁ / a, and the standardized hole diameter d / 2a for realizing the hole occupancy S obtained in step P4 is derived (step P5). ).

  Through the above steps, it is possible to easily derive design conditions for a hole-providing single mode optical fiber that simultaneously satisfies a desired bending loss characteristic and a 22 m effective cutoff wavelength characteristic.

From the above results, according to the present embodiment, the bending loss α _b and the dependency of the 22 m effective cutoff wavelength λ _{c on} the hole occupation ratio S are taken into consideration, and further, bending in a single-mode optical fiber without holes is considered. By using the loss and the dependency of the 22m effective cutoff wavelength on the relative refractive index difference, it is possible to easily design a hole-providing single mode optical fiber having a desired bending loss and 22m effective cutoff wavelength, It is possible to easily manufacture the hole-providing single mode optical fiber.

  Thus, according to the present embodiment, the desired ratio can be easily obtained by controlling the hole occupancy S and the relative refractive index difference Δ without performing a complicated analysis using a conventional finite element method or the like. It becomes possible to manufacture a hole-providing single mode optical fiber that realizes bending characteristics and 22 m effective cutoff wavelength characteristics.

  The present invention is suitable for application to a hole-providing single mode optical fiber.

It is sectional drawing which shows the structure of one Embodiment of the hole provision type | mold single mode optical fiber which concerns on this invention. It is a graph which shows the relationship between the bending loss (alpha) _b and the hole occupation rate S in the hole provision type | mold single mode optical fiber which concerns on the 1st Example of this invention. It is a graph which shows the relationship between bending loss (alpha) _b and specific refractive index difference (DELTA) in one Embodiment of the hole provision type | mold single mode optical fiber which concerns on the 1st Example of this invention. It is a graph which shows the relationship between 22m effective cutoff wavelength (lambda) _c and hole occupation rate S in one Embodiment of the hole provision type | mold single mode optical fiber which concerns on the 1st Example of this invention. It is a graph which shows the relationship between 22m effective cutoff wavelength (lambda) _c and relative refractive index difference (DELTA) in one Embodiment of the hole provision type | mold single mode optical fiber which concerns on the 1st Example of this invention. It is a graph which shows the design conditions of the hole occupation rate S and relative refractive index difference (DELTA) in one Embodiment of the hole provision single mode optical fiber which concerns on the 1st Example of this invention. In one embodiment of the hole-providing single mode optical fiber according to the first embodiment of the present invention, the normalized inscribed circle radius R ₁ / a with the hole occupation ratio S being 35%, the normalized hole diameter It is a graph showing the relationship between d / 2a and the number of holes N. It is a graph which shows the relationship between bending loss (alpha) _b and relative refractive index difference (DELTA) in a single mode optical fiber without a hole. It is a graph which shows the relationship between 22m effective cutoff wavelength (lambda) _c and relative-refractive-index difference (DELTA) in a single mode optical fiber without a hole. It is a graph showing the relationship between the hole occupation rate S derived | led-out by empirical formula (10) and empirical formula (14) and relative refractive index difference (DELTA) in the 2nd Example of this invention. In the second embodiment of the present invention, a graph showing the relationship between the normalized inscribed circle radius R ₁ / a, the normalized hole diameter d / 2a, and the number of holes N, where the hole occupation ratio S is 34%. is there. It is a flowchart which shows the flow which derives | leads-out the design conditions of the hole provision type | mold single mode optical fiber which concerns on the 2nd Example of this invention.

Explanation of symbols

11 Clad part 12 Core part 13 Hole

Claims (4)

A clad part having a uniform refractive index, a core part having a higher refractive index than the clad part, arranged at the center of the clad part, and arranged at equal intervals on the concentric circle with the core part in the clad part And controlling the occupancy ratio of the holes in the clad part and the relative refractive index difference of the core part with respect to the clad part, thereby controlling the bending loss characteristics and the effective cutoff of 22 m. A hole-providing single-mode optical fiber characterized in that the wavelength characteristic is designed to a desired value. Using the dependency on the relative refractive index difference of the bending loss and the effective cutoff wavelength of 22 m derived from the numerical analysis of the refractive index distribution of the single-mode optical fiber without holes, the occupation ratio and the relative refractive index difference are The hole-providing single mode optical fiber according to claim 1, wherein the hole-providing single mode optical fiber is derived. A clad part having a uniform refractive index, a core part having a higher refractive index than the clad part, and a core part arranged at the center of the clad part, and an equal interval from the center of the core part to the clad part on a concentric circle A method for producing a hole-providing single mode optical fiber having at least six or more holes arranged in
The occupancy ratio of the holes in the cladding part and the relative refractive index difference of the core part with respect to the cladding part are controlled, and the bending loss characteristic and the 22 m effective cutoff wavelength characteristic of the hole-providing single mode optical fiber are set as desired. A method for manufacturing a hole-providing type single-mode optical fiber, characterized by being designed to have a value. Using the dependence of the bending loss and the 22m effective cutoff wavelength on the relative refractive index difference derived from the numerical analysis of the refractive index profile of the single-mode optical fiber without holes, the occupation ratio and the relative refractive index difference are calculated. The method for producing a hole-providing single mode optical fiber according to claim 3, wherein:

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