JP5165648B2 - How to set up single-mode optical fiber with holes - Google Patents

Description

The present invention relates to a method of setting the holes with a single mode optical fiber that will be subjected to the construction of the optical transmission line for long distance and large volume optical communication.

  Conventionally, an optical fiber amplifier using a rare earth doped fiber or the like is widely used as an optical signal amplifying means in a long distance and large capacity optical communication system. In addition, with the spread of wavelength division multiplexing transmission systems and Raman distribution amplification transmission systems, the intensity of light propagating in optical fibers has increased dramatically.

On the other hand, an optical nonlinear phenomenon that occurs in an optical fiber is one of the factors that degrade transmission characteristics in a long-distance / large-capacity optical communication system. The optical nonlinear phenomenon becomes prominent in proportion to the product of the nonlinear constant n ₂ / Aeff obtained by dividing the nonlinear refractive index n ₂ of the optical fiber by the effective area Aeff and the light intensity propagating in the optical fiber. The effective area Aeff is related to the mode field diameter (MFD) of 2 W of the optical fiber. Especially when the light intensity distribution in the optical fiber can be approximated by a Gaussian distribution, the relationship between the ^two is handled as Aeff≈πW ^2. Can do.

  Therefore, the optical nonlinear phenomenon in the optical fiber can be reduced by increasing the effective cross-sectional area Aeff of the optical fiber, in other words, the mode field diameter. For this reason, various optical fibers for long-distance and large-capacity transmission whose mode field diameter is expanded by optimizing the refractive index distribution of the optical fiber core have been studied (for example, Patent Document 1).

  In recent years, as with conventional optical fibers, it has a core structure formed by adding materials, and with holes that realize suitable transmission characteristics by arranging a plurality of hole regions around the core. Various studies have been made on optical fibers.

  For example, in Non-Patent Document 1, in a holey optical fiber in which six hole regions are arranged at equal intervals around a core equivalent to a conventional optical fiber, the diameter of the hole region is set to a core radius of 0. A technique is disclosed in which the bending loss characteristic is improved by an order of magnitude or more from the characteristic before imparting holes by setting it to four times or more. Further, by setting the radius of the circle inscribed in the hole region to be about 1.8 times or more of the core radius, the amount of change accompanying the addition of the hole of the mode field diameter at the wavelength of 1550 nm is 0 to −10%. Techniques within the scope of the above are also disclosed.

  Further, in Non-Patent Document 2, in a holey optical fiber having a clad part and a core part similar to those of a conventional optical fiber, and six or more hole parts arranged concentrically with respect to the core part, A technique is also disclosed in which the cut-off wavelength and bending loss of the holey optical fiber are made to have desired characteristics by controlling the area ratio of the hole in the cladding.

JP-A-11-218632

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 (particularly, Fig. 2 And Fig. 3) Nakajima et al., “Considerations on Low Bending Loss Hole Assisted Optical Fiber,” IEICE Tech., OFT2008-47, pp.5-8, 2008 (especially Figures 2 and 3) Kawakami et al., "Optical fiber and fiber type device", Baifukan, 1996 (especially Section 4.4.2, pp.82-83) D. Marcuse, “Loss analysis of single-mode fiber splice”, Bell Sys. Tech. J., vol.56, p.703, 1977 (especially, Equation 8)

  However, in general, shortening the cutoff wavelength in an optical fiber and increasing the mode field diameter are in a trade-off relationship with each other. For this reason, when the mode field diameter is increased by optimizing the refractive index distribution, it is equal to or greater than that of a single mode optical fiber (SMF) having a zero dispersion wavelength in the 1.3 μm band currently used for general purposes. A problem that it is difficult to maintain a cutoff wavelength characteristic of 1260 nm or less when realizing both a mode field diameter characteristic and a cutoff wavelength characteristic, more specifically, when realizing a mode field diameter characteristic of 9 μm or more at a wavelength of 1310 nm. was there.

  Further, when the mode field diameter is increased by the holey optical fiber disclosed in Non-Patent Document 1 or Non-Patent Document 2, the same cutoff wavelength characteristic as that of a conventional single-mode optical fiber is maintained, and The control technology of the holey optical fiber that realizes a mode field diameter characteristic equivalent to or better than that of the single mode optical fiber has not been sufficiently clarified.

  More specifically, the mode field diameter control technique disclosed in Non-Patent Document 1 is a control technique derived for a specific core structure, and a control technique applicable to an arbitrary core structure is It was not revealed.

The present invention has been made in view of such problems, and its purpose is to provide a cutoff wavelength characteristic equal to or higher than that of a conventional single mode optical fiber and a mode field diameter characteristic, more specifically, a cutoff of 1260 nm or less. A method for setting a single-mode optical fiber with a hole suitable for construction of an optical transmission line for long-distance and large-capacity optical communication having both wavelength characteristics and mode field diameter characteristics of 9 μm or more at a wavelength of 1310 nm It is to provide.

Setting of the holes with a single mode optical fiber according to the first invention for solving the above SL problem, a core portion of the core radius a, and uniform lower than the refractive index n ₁ of the core portion The _two circles are formed in a clad part having a refractive index n ₂ and in a region surrounded by a circle of R _{IN and} a circle of R _OUT within the region of the clad part and having a radius from the center of the core part. A method of setting a single-mode optical fiber with a hole having a plurality of hole portions arranged so as to circumscribe, and for a mode field diameter of a single-mode optical fiber without a hole together defining said holes with a single mode optical fiber mode field relative changes the mode field diameter-to-change R _MFD diameter of the core radius a of the holes with a single mode optical fiber, the refractive index n ₁ and normalized using the refractive index n ₂ Deriving a wavenumber V value, based on a relationship between the mode field diameter-to-change R _MFD and the normalized radius of an inscribed circle R _IN / a in the derived normalized frequency V value, of 0 or less -0.1 or more A minimum value of a normalized inscribed circle radius R _IN / a for obtaining a mode field diameter relative change R _MFD is set. Here, the normalized inscribed circle radius R _IN / a is a value obtained by normalizing the radius R _{IN of the} inscribed circle by the core radius a, and the mode field diameter relative change R _MFD is in a state where no holes are given. It is a relative change of the mode field diameter of the single mode optical fiber having a hole with respect to the mode field diameter of the single mode optical fiber.

Further, in the method for setting a single-mode optical fiber with holes according to the second invention, the minimum value of the normalized inscribed circle radius R _IN / a and the normalized frequency V value at a wavelength of 1310 nm are expressed by the following formula ( characterized in that satisfying the relation 1).

In the method for setting a single-mode optical fiber with holes according to a third aspect of the invention, the core radius a is 5.4 μm or less, and the hole occupation ratio S and the core radius a In addition to satisfying the relationship of (2), the relative refractive index difference Δ defined using the refractive index n ₁ and the refractive index n ₂ and the core radius a satisfy the relationship of the following expression (3). And Here, the hole occupation ratio S indicates an area ratio occupied by the hole portion in an annular region surrounded by the circle with the radius R _{IN and} the circle with R _OUT .

In equations (2) and (3), a is a numerical value when the core radius is expressed in μm units, and Δ is a numerical value when the relative refractive index difference is expressed in%.

According to a fourth aspect of the present invention, there is provided a method for setting a single-mode optical fiber with holes, wherein the core radius a is 4.9 μm or less, and the hole occupation ratio S and the core radius a are lower. fulfills the relationship of formula (4), wherein the refractive index n ₁ and the refractive index n ₂ of the specific refractive index difference is defined using Δ and the core radius a satisfy the relation of the following formula (5) And

In equations (4) and (5), a is a numerical value when the core radius is expressed in μm units, and Δ is a numerical value when the relative refractive index difference is expressed in%.

According to the method for setting a single-mode optical fiber with holes according to the present invention, a core portion, a cladding portion having a uniform refractive index lower than the refractive index of the core portion, and within the region of the cladding portion And a plurality of hole portions disposed so as to circumscribe the two circles in a region surrounded by a circle of R _{IN and} a circle of R _OUT having a radius from the center of the core portion. In a single-mode optical fiber with a hole, a minimum value of a normalized inscribed circle radius R _IN / a obtained by normalizing the distance R _IN with the core radius a is determined from the core radius a and the relative refractive index difference Δ. The mode field diameter can be obtained for a single-mode optical fiber with a hole having a desired cut-off wavelength by controlling using the relation with the relative change in mode field diameter R _MFD in the normalized frequency V value derived. Set the relative change within the desired range Theft has become possible.

In other words, in the present invention, the minimum value of the normalized inscribed circle radius R _IN / a, which is related to the reduction of the mode field diameter of the single-mode optical fiber with holes accompanying the provision of the hole, is normalized frequency V value. And the realization of a single-mode optical fiber with a hole having a mode field diameter characteristic equal to or better than that of a conventional single-mode optical fiber. Can be controlled simultaneously.

Further, according to the method for setting a single-mode optical fiber with a hole of the present invention, as described above, the minimum value of the normalized inscribed circle radius R _IN / a is changed to the mode field diameter relative change at the normalized frequency V value . Since the control is performed using the relationship with R _MFD , the change rate of the mode field diameter is kept within the desired range while maintaining the cutoff wavelength even when an arbitrary refractive index distribution is applied to the core. There is also an effect that it can be set.

An example of the structure of the engagement Ru in Example 1 vacancies with single mode optical fiber of the present invention is a cross-sectional view illustrating. Is a relative change and graphs representing the normalized inscribed circle radius of the relationship between the mode field diameter at the engagement Ru pores with a single mode optical fiber in Example 1 of the present invention. It is a graph showing the relationship between relative change and normalized hole diameter of the mode field diameter at engagement Ru in Example 1 vacancies with single mode optical fiber of the present invention. It is a graph showing the relationship between the minimum normalized radius of an inscribed circle and the normalized frequency in the first embodiment to engage Ru pores with a single mode optical fiber of the present invention. It is a graph showing a relationship between cutoff wavelength and pore occupancy in Example 2 in engagement Ru pores with a single mode optical fiber of the present invention. Example 2 of the present invention is a graph showing the relationship between relative refractive index difference and pore occupation rate of engagement Ru pores with a single mode optical fiber as a function of the cutoff wavelength. It is a graph showing the pore occupation rate and the relationship between the core radius as a function of the cut-off wavelength to the second embodiment of the engaging Ru pores with a single mode optical fiber of the present invention. Example 2 of the present invention is a graph showing the engagement Ru relative refractive index difference at the holes with a single-mode optical fiber and the core radius of the relationship as a function of the mode field diameter before the pore granted.

Hereinafter, details of how to set with reference to the drawings Ru engaged to the invention pores with a single mode optical fiber.

1 through a first embodiment of the engagement Ru pores with a single mode optical fiber of the present invention will be described with reference to FIG.

It shows the schematic structure of the engagement Ru pores with a single mode optical fiber in this embodiment in FIG. As shown in FIG. 1, the holes with a single mode optical fiber 1 Ru engaged in this embodiment, the core portion 11 of refractive index n _1, small and uniform refractive index n than the refractive index n ₁ of the core portion 11 ₂ , and a plurality of (six in FIG. 1) hole portions 13 formed in the region of the cladding portion 12.

More specifically, a circle having a radius R _IN (hereinafter referred to as a hole inscribed circle) C _IN and a circle having a radius R _OUT from the center of the core portion 11 to the cladding portion 12 provided around the core portion 11 having a radius a. (hereinafter, the air that hole circumcircle) to circumscribe the C _OUT, cavity 13 having a diameter d are provided in a generally equal intervals in the circumferential direction.

Although FIG. 1 shows an example in which six hole portions 13 are provided, the number of hole portions 13 is not limited to six and can be arbitrarily set. However, in order to reduce the birefringence characteristics of the single-mode optical fiber 1 with holes , it is preferable to arrange an even number of hole portions 13 symmetrically with respect to the center of the core portion 11.

Here, the ratio of the total area of all the hole portions 13 to the area of the annular region surrounded by the hole inscribed circle C _IN and the hole circumscribed circle C _OUT is the hole occupation ratio S. Is defined in the following formula (1).

Hereinafter, in this embodiment, the core portion 11 has a step-type refractive index distribution with a radius a [μm] and a relative refractive index difference Δ, and the N hole portions 13 are equally spaced in the circumferential direction in the optical fiber cross section. for holes with a single mode optical fiber cutoff wavelength lambda _C following 1260nm with its structure arranged in, realizing a conventional single-mode optical fiber equivalent (9 .mu.m) or more and becomes the mode field diameter at a wavelength of 1310 nm 2W _WH An example will be described. The relative refractive index difference Δ is defined by the following equation (7) using the refractive index n ₁ of the core portion 11 and the refractive index n ₂ of the cladding portion.

Further, for a single mode optical fiber 1 with shown to holes 1, the mode field diameter of the single-mode optical fiber in a state where the holes 13 is not applied (hereinafter, referred to pores imparting free mode field diameter) of 2W _{W / OH} , the mode field diameter of the single-mode optical fiber 1 having the hole 13 shown in FIG. 1 (hereinafter, the mode field diameter with holes added) is 2 W _WH, and the mode field diameter without holes is 2 _{W W /} pores imparting relative change of the chromatic mode field diameter 2W _WH for _OH (hereinafter, referred to as the mode field diameter-pair changes) defined by following equation R _MFD (8).

It shows the relationship between the mode field diameter-to-change R _MFD and the normalized radius of an inscribed circle R _IN / a of the engagement Ru pores with a single mode optical fiber in this embodiment in FIG. FIG. 2 shows the characteristics when the wavelength λ is 1310 nm, the number of holes N is 10, and the normalized hole diameter d / 2a is 0.25. The solid line, dotted line, and alternate long and short dash line in the figure correspond to the case where the hole-added non-mode field diameter 2 _{WW / OH} is 11 μm, 9 μm, and 7 μm, respectively, and is defined by the following equation (9). The values for the normalized frequency V values of 2 and 3 are shown.

As shown in FIG. 2, the absolute value of the mode field diameter relative change R _MFD increases as the normalized inscribed circle radius R _IN / a decreases. When the normalized frequency V value is constant, it can be seen that the absolute value of the mode field diameter relative change R _MFD increases as the hole-added non-mode field diameter 2 _{WW / OH} increases.

However, when the normalized inscribed circle radius R _IN / a is constant, the dependence of the mode field diameter relative change R _{MFD on} the pore-added non-mode field diameter 2 _{WW / OH} depends on the normalized frequency V value. For example, when the standardized inscribed circle radius R _IN / a is 1.5, the mode field diameter relative change R when the pore-added non-mode field diameter 2W _{W / OH} is 7 μm and 11 μm. _While the deviation of _MFD is about 2%, the deviation of the mode field diameter relative change R _MFD is larger when the normalized frequency V value is 2 and 3, and the mode field diameter relative change R _MFD is the normalized frequency. It can be seen that there is a clearer dependence on the V value.

Shows the relationship between the mode field diameter-to-change R _MFD engagement Ru pores with a single mode optical fiber in this embodiment and the normalized hole diameter d / 2a in FIG. FIG. 3 shows the characteristics when the wavelength λ is 1310 nm, the normalized inscribed circle radius R _IN / a is 2.25, the pore-free non-mode field diameter 2 _{WW / OH} is 11 μm, and the normalized frequency V value is 2. . The solid line, the dotted line, and the one-point difference line in the figure correspond to the case where the number of holes N is 10, 6, and 4, respectively.

As shown in FIG. 3, the absolute value of the mode field diameter relative change R _MFD slightly increases as the normalized hole diameter d / 2a increases, but the normalized inscribed circle radius R _IN shown in FIG. It can be seen that it is sufficiently smaller than the dependence on / a or the normalized frequency V value. Further, from FIG. 3, the dependence of the mode field diameter relative change R _{MFD on} the number of holes N is also compared with the dependence on the normalized inscribed circle radius R _IN / a or the normalized frequency V value shown in FIG. It turns out that it is small enough.

These results are engaged Ru leave vacancies with single-mode optical fiber in this embodiment, the mode field diameter-to-change R _MFD, the normalized frequency V value, and controls the normalized radius of an inscribed circle R _IN / a By doing this, it can be seen that a desired hole-added mode field diameter of 2 _WH can be obtained.

More specifically, first, a desired mode field diameter relative change R _MFD is set, while a normalized frequency V value is derived from the core structure of the single mode optical fiber with holes. Then, based on the relationship between the mode field diameter relative change R _MFD and the normalized inscribed circle radius R _IN / a shown in FIG. 2, the minimum normalized value that is the minimum value of the normalized inscribed circle radius R _IN / a Inscribed circle radius (R _IN / a) Determines _MIN . Thereby, it becomes possible to control the mode field size characteristics of the engagement Ru pores with a single mode optical fiber in this embodiment.

Figure 4 is a graph showing the relationship between the minimum normalized radius of an inscribed circle (R _IN / a) _MIN and the normalized frequency V value of the engagement Ru pores with a single mode optical fiber in this embodiment. The values shown in FIG. 4 indicate that the wavelength λ is 1310 nm, the normalized hole diameter d / 2a is 1, the hole-added non-mode field diameter 2W _{W / OH} is 11 μm, and the mode field diameter relative change R _MFD is −0.1. The case characteristics. FIG. 4 shows the average value of the minimum normalized inscribed circle radius (R _IN / a) _MIN when the number of holes N is 4, 6, 8, or 10.

In the example shown in FIG. 4, when the normalized frequency V value of the core structure satisfying the pore-added non-mode field diameter 2W _{W / OH} = 11 μm is 2, the normalized inscribed circle radius R _IN / a is about 2 By controlling to be 2 or more, the mode field diameter 2W _WH with holes added is set to 9.9 μm or more, which is −10% with respect to the mode field diameter 2W _{W / OH} (11 μm) with holes added. You can see that

Thus, according to the present embodiment, the hole-provided mode field diameter 2W _WH when the wavelength λ is 1310 nm is equal to or greater than the mode field diameter 2W _{W / OH of} the conventional single mode optical fiber, that is, 9 μm. it is possible to realize the pores with a single mode optical fiber Do that and more.

Note that the relationship between the minimum normalized inscribed circle radius (R _IN / a) _MIN and the normalized frequency V value shown in FIG. 4 is approximated by a polynomial shown in empirical formula (10) in consideration of a practical range. can do.

  Here, in the example mentioned above, the case where the core part 11 has step type refractive index distribution was demonstrated. On the other hand, when the core portion 11 has an arbitrary refractive index distribution n (r) in the radial direction, the characteristics of the single mode optical fiber having this core structure are obtained by assuming an equivalent step-type refractive index distribution. Can be estimated. Non-Patent Document 3 describes the effective normalized frequency V value of a single-mode optical fiber having an arbitrary refractive index distribution n (r) as an alternative normalized frequency T value by the relational expression (11). It states that it can be done.

By using the equation (11), even if the core portion 11 has an arbitrary refractive index distribution, the refractive index distribution n (r) in the radial direction of the core portion 11 is obtained, and the empirical equation (5) By applying an alternative normalization frequency T value instead of the normalization frequency V value of the above, the mode field diameter 2W _WH with hole addition in the case where the wavelength λ is 1310 nm is less than the hole addition of the conventional single mode optical fiber. mode field diameter 2W W _{/ OH} equivalent or more, that it is possible to realize the holes with a single mode optical fiber that Do or more 9 .mu.m.

Thus, according to the engagement Ru pores with a single mode optical fiber in this embodiment described above, normalized derived normalized radius of an inscribed circle R _IN / a core radius a and the relative refractive index difference Δ Since it is possible to perform control using dependency on the frequency V value, it is possible to set the mode field diameter relative change R _MFD accompanying the provision of the hole 13 within a desired range. The same applies to the case where an arbitrary refractive index distribution is applied to the core portion.

That is, in general, the cutoff wavelength of the optical fiber and the mode field diameter have a trade-off relationship, and the core radius a, the relative refractive index difference Δ, the radius R _{IN of} the hole inscribed circle, and the hole occupation rate S Even if only the dependency of a specific parameter is extracted from the four types of parameters, it is difficult to realize an optical fiber that achieves both a desired cutoff wavelength and mode field diameter characteristics. On the other hand, in this embodiment, the normalized inscribed circle radius R _IN / a and the normalized frequency V value, the hole occupation ratio S and the core radius a, and the correlation region between the core radius a and the relative refractive index difference Δ are expressed as follows. As a result of the finding, it has a cutoff wavelength characteristic of 1260 nm or less and a mode field diameter characteristic of 9 μm or more at a wavelength of 1310 nm, and is suitable for construction of an optical transmission line for long distance and large capacity optical communication. It has become possible to provide a single mode optical fiber.

5 to the second embodiment of the engagement Ru pores with a single mode optical fiber of the present invention will be described with reference to FIG.

In the present embodiment, the core portion 11 shown in FIG. 1 and described above in the first embodiment has a step-type refractive index distribution with a radius a [μm] and a relative refractive index difference Δ, and N holes 13 are optical fibers. in the holes with a single mode optical fiber 1 arranged at equal intervals in the circumferential direction in the cross section, cut-off wavelength characteristic is equal to or less than 1260 nm, the mode field diameter 2W _WH at a wavelength 1310nm and a conventional single-mode optical fiber least equivalent, that describes an example of realizing der Ru pores with a single mode optical fiber or 9 .mu.m. Hereinafter, description overlapping with the above description will be omitted, and different points will be mainly described.

According to Non-Patent Document 2, the cutoff wavelength lambda _C of the engagement Ru pores with a single mode optical fiber in this example, the dependence on the pore occupation rate S, the pore occupation rate of the relative refractive index difference delta S It becomes controllable by obtaining the dependence on.

It shows the relationship between the cutoff wavelength lambda _C and pore occupancy S of the engagement Ru pores with a single mode optical fiber in this embodiment is shown in FIG. FIG. 5 shows six types of single-hole optical fibers with holes having a core radius a of 4.3 to 4.5 μm and a relative refractive index difference Δ of 0.33 to 0.35%. The measurement result by a mode optical fiber is shown. The number of holes N was 6 or 10. Further, the solid line in the figure indicates an approximate curve with respect to the measurement result, and the broken line indicates a cutoff wavelength of a single mode optical fiber having no holes under the same conditions.

As shown in FIG. 5, the cutoff wavelength λ _C shifts to the short wavelength side as the hole occupation ratio S decreases. This cut-off wavelength λ _C is considered to have a tendency to converge to the cut-off wavelength characteristics of a single mode optical fiber to which no holes are provided.

Here, dependence on pore occupation rate S of the cutoff wavelength lambda _C shown in FIG. 5, can be described by the following empirical equation (12), in the example shown in FIG. 5, the coefficient C ₁ is 1121.1, factor C ₂ was 0.56. In the empirical formula (12), δΔ is defined by the following formula (13) as a change amount of the relative refractive index difference Δ with respect to the reference point Δr. Further, the coefficient C ₃ in the empirical formula (12) can be derived as the dependence of the cutoff wavelength on the specific refractive index difference Δ at a specific core radius a of the single-mode optical fiber not provided with holes.

It shows the relationship between the relative refractive index difference of the engaging Ru pores with a single mode optical fiber in this example Δ and the pore occupation rate S in FIG. FIG. 6 shows the characteristics when the core radius a is 4.5 μm. In the figure, the solid line, the broken line, and the one-point difference line show the results when the cutoff wavelength λ _C is 1260 nm, 1200 nm, and 1100 nm, respectively. In addition, the two dotted lines in the figure indicate the conditions of the relative refractive index difference Δ when the mode field diameter 2W _{W / OH} is 10 μm and 11 μm under the same conditions of a single mode optical fiber having no holes. Yes. This relative refractive index difference Δ is calculated by the empirical formula (14) of the core radius a disclosed in Non-Patent Document 4, the hole-added non-mode field diameter 2 _{WW / OH,} and the normalized frequency V value of the core 11. Can be derived uniquely.

From FIG. 6, when the core radius a of the single-mode optical fiber is 4.5 μm, by setting the relative refractive index difference Δ to about 0.22%, the hole-added non-mode field diameter 2W _{W / OH} is 11 μm. You can see that you can. Then, it is understood that the cutoff wavelength λ _C can be controlled to 1260 nm or less by setting the hole occupation ratio S to 0.55 or less under the condition of the relative refractive index difference Δ = 0.22%.

In this way, by examining the relationship between the relative refractive index difference Δ and the hole occupancy S with respect to an arbitrary core radius a, an arbitrary mode field diameter characteristic and a desired cutoff in a state having no holes are obtained. The relationship between the maximum value of the hole occupation ratio S that satisfies the wavelength λ _C and the arbitrary core radius a can be derived.

Shows the relationship between the pore occupation rate S and the core radius a in this example in the engagement Ru pores with a single mode optical fiber in FIG. FIG. 7 shows the characteristics when the wavelength λ is 1310 nm and the hole-added non-mode field diameter 2W _{W / OH} is 11 μm. The solid line, the broken line, and the one-point difference line in the figure are the results when the cutoff wavelength λ _C is 1260 nm, 1200 nm, and 1100 nm, respectively.

As shown in FIG. 7, in this embodiment, the core radius a and the hole occupancy S are set to values satisfying the region on the left side of the solid line, that is, the core radius a and the hole occupancy S are equal to the following inequality. In the case of satisfying (15), the cutoff wavelength λ _C of the hole-added mode field diameter 2W _WH can be controlled to 1260 nm or less equivalent to the cutoff wavelength of the conventional single mode optical fiber.

Furthermore, when the core radius a and the hole occupancy S are set to values satisfying the region on the left side of the one-point difference line, that is, when the core radius a and the hole occupancy S satisfy the following inequality (16), The cutoff wavelength λ _C of the hole-added mode field diameter 2 W _WH can be controlled to 1100 nm or less.

If the cutoff wavelength λ _C can be controlled to 1100 nm or less, the single mode wavelength region used for long-distance and large-capacity optical communication can be expanded, which is even more preferable.

Relative refractive index difference of the engaging Ru pores with a single mode optical fiber in this embodiment in FIG. 8 shows the relationship between Δ and the core radius a. FIG. 8 shows characteristics when the wavelength λ is 1310 nm. The solid line and the broken line in the figure are the results when the pore-added non-mode field diameter is 10 μm and 11 μm, respectively.

From FIG. 8, when the core radius a is 5.4 μm or less, the core radius a and the relative refractive index difference Δ satisfy the following inequalities (17) and (18), so It can be seen that 2 _{WW / OH} can be 10 μm or more and 11 μm or more.

Thus, according to the present embodiment, the normalized inscribed circle radius R _IN / a is controlled so as to satisfy the relationship of the above-mentioned empirical formula (4) from the relationship between the core radius a and the relative refractive index difference Δ. As a result, a mode field diameter of 2 W _WH with holes of 9 μm (= 10 μm-10%) or more, or 9.9 μm (= 11 μm-10%) or more suitable for long-distance and large-capacity optical communication is realized. It becomes possible to do.

  From the above results, for example, the core radius a is set to 5.4 μm or less, and the core radius a, the hole occupation ratio S, and the relative refractive index difference Δ are set to values satisfying the above inequality equations (15) and (17). Therefore, it is possible to simultaneously realize a cutoff wavelength characteristic of 1260 nm or less and a mode field diameter characteristic of 9.9 μm or more, which are suitable for long distance and large capacity optical communication.

  In addition, according to Non-Patent Document 2, it is disclosed that the bending loss characteristic can be improved by two orders of magnitude or more compared to the characteristic before the provision of the holes by setting the hole occupation ratio S to 0.3 or more. Has been. Therefore, also in the present embodiment, by setting the hole occupation ratio S to 0.3 or more, it is possible to expect a preferable effect on the bending loss characteristic disclosed in Non-Patent Document 2.

Further, the present invention is not limited to the first and second embodiments described above, and it goes without saying that various modifications can be made without departing from the spirit of the present invention. For example, in the foregoing Embodiments 1 and 2, although the shape of the holes 13 shows an example in which a cross section circular mode field characteristics in engagement Ru pores with a single mode optical fiber in the present invention core unit Since the cut-off wavelength characteristic is a characteristic depending on the hole occupancy S, the cross section of the hole portion 13 in the present invention is dependent on the normalized frequency V value of the hole and the radius R _IN of the hole inscribed circle. The shape can be set arbitrarily.

The present invention is applicable to the holes with a single mode optical fiber, in particular, suitably applied to the holes with a single mode optical fiber that will be subjected to the construction of the optical transmission line for long distance and large volume optical communication It is a thing.

1 vacancy with single-mode optical fiber 11 core 12 cladding 13 holes section C _IN vacancies inscribed circle C _OUT vacancies circumcircle

Claims (4)

A core portion having a core radius a, a cladding portion having a uniform refractive index n ₂ lower than the refractive index n _{1 of the} core portion, and a radius from the center of the core portion in the region of the cladding portion A method for setting a single-mode optical fiber with a hole having a plurality of hole portions arranged to circumscribe the two circles in a region surrounded by a circle of R _{IN and} a circle of R _OUT Because
A relative change in the mode field diameter of the single-mode optical fiber with holes with respect to the mode field diameter of the single-mode optical fiber without a hole is defined as a relative change in mode field diameter R _MFD .
Deriving a normalized frequency V value using the core radius a, the refractive index n ₁ and the refractive index n ₂ of the single-mode optical fiber with holes ,
Based on the relationship between the mode field diameter-to-change R _MFD and the normalized radius of an inscribed circle R _IN / a in the derived normalized frequency V values, 0 or less -0.1 or more mode field diameter-to-change R _MFD The minimum value of the standardized inscribed circle radius R _IN / a to obtain the above is set. Pores with a single mode optical according to claim 1, wherein the minimum value of the normalized radius of an inscribed circle R _IN / a and said normalized frequency V value is equal to or that meet the relation of the following formula (1) How to set up the fiber.

The hole occupancy S, which is the area ratio indicated by the holes in the annular region formed by the circle having the core radius a of 5.4 μm or less and the radius being R _{IN and} the circle being R _OUT , The core radius a satisfies the relationship of the following formula (2), and the relative refractive index difference Δ defined by using the refractive index n ₁ and the refractive index n ₂ and the core radius a are expressed by the following formula (3). The method for setting a single-mode optical fiber with holes according to claim 1 or 2, wherein the relationship is satisfied.

In equations (2) and (3), a is a numerical value when the core radius is expressed in μm units, and Δ is a numerical value when the relative refractive index difference is expressed in%. The hole occupancy S, which is the area ratio indicated by the holes in an annular region formed by a circle having a core radius a of 4.9 μm or less and a radius of R _{IN and} a circle of R _OUT , The core radius a satisfies the relationship of the following formula (4), and the relative refractive index difference Δ defined by using the refractive index n ₁ and the refractive index n ₂ and the core radius a are expressed by the following formula (5). The method for setting a single-mode optical fiber with holes according to claim 1 or 2, wherein the relationship is satisfied.

In equations (4) and (5), a is a numerical value when the core radius is expressed in μm units, and Δ is a numerical value when the relative refractive index difference is expressed in%.

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