WO2016047675A1 - 光ファイバおよびその製造方法 - Google Patents
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- WO2016047675A1 WO2016047675A1 PCT/JP2015/076899 JP2015076899W WO2016047675A1 WO 2016047675 A1 WO2016047675 A1 WO 2016047675A1 JP 2015076899 W JP2015076899 W JP 2015076899W WO 2016047675 A1 WO2016047675 A1 WO 2016047675A1
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/02—Optical fibres with cladding with or without a coating
- G02B6/02004—Optical fibres with cladding with or without a coating characterised by the core effective area or mode field radius
- G02B6/02009—Large effective area or mode field radius, e.g. to reduce nonlinear effects in single mode fibres
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/02—Optical fibres with cladding with or without a coating
- G02B6/028—Optical fibres with cladding with or without a coating with core or cladding having graded refractive index
- G02B6/0281—Graded index region forming part of the central core segment, e.g. alpha profile, triangular, trapezoidal core
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/02—Optical fibres with cladding with or without a coating
- G02B6/036—Optical fibres with cladding with or without a coating core or cladding comprising multiple layers
- G02B6/03605—Highest refractive index not on central axis
- G02B6/03611—Highest index adjacent to central axis region, e.g. annular core, coaxial ring, centreline depression affecting waveguiding
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/02—Optical fibres with cladding with or without a coating
- G02B6/036—Optical fibres with cladding with or without a coating core or cladding comprising multiple layers
- G02B6/03616—Optical fibres characterised both by the number of different refractive index layers around the central core segment, i.e. around the innermost high index core layer, and their relative refractive index difference
- G02B6/03622—Optical fibres characterised both by the number of different refractive index layers around the central core segment, i.e. around the innermost high index core layer, and their relative refractive index difference having 2 layers only
- G02B6/03627—Optical fibres characterised both by the number of different refractive index layers around the central core segment, i.e. around the innermost high index core layer, and their relative refractive index difference having 2 layers only arranged - +
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/02—Optical fibres with cladding with or without a coating
- G02B6/036—Optical fibres with cladding with or without a coating core or cladding comprising multiple layers
- G02B6/03616—Optical fibres characterised both by the number of different refractive index layers around the central core segment, i.e. around the innermost high index core layer, and their relative refractive index difference
- G02B6/03622—Optical fibres characterised both by the number of different refractive index layers around the central core segment, i.e. around the innermost high index core layer, and their relative refractive index difference having 2 layers only
- G02B6/03633—Optical fibres characterised both by the number of different refractive index layers around the central core segment, i.e. around the innermost high index core layer, and their relative refractive index difference having 2 layers only arranged - -
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/02—Optical fibres with cladding with or without a coating
- G02B6/036—Optical fibres with cladding with or without a coating core or cladding comprising multiple layers
- G02B6/03616—Optical fibres characterised both by the number of different refractive index layers around the central core segment, i.e. around the innermost high index core layer, and their relative refractive index difference
- G02B6/03638—Optical fibres characterised both by the number of different refractive index layers around the central core segment, i.e. around the innermost high index core layer, and their relative refractive index difference having 3 layers only
- G02B6/0365—Optical fibres characterised both by the number of different refractive index layers around the central core segment, i.e. around the innermost high index core layer, and their relative refractive index difference having 3 layers only arranged - - +
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- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B2201/00—Type of glass produced
- C03B2201/02—Pure silica glass, e.g. pure fused quartz
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B2201/00—Type of glass produced
- C03B2201/06—Doped silica-based glasses
- C03B2201/30—Doped silica-based glasses doped with metals, e.g. Ga, Sn, Sb, Pb or Bi
- C03B2201/31—Doped silica-based glasses doped with metals, e.g. Ga, Sn, Sb, Pb or Bi doped with germanium
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- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B2203/00—Fibre product details, e.g. structure, shape
- C03B2203/10—Internal structure or shape details
- C03B2203/22—Radial profile of refractive index, composition or softening point
- C03B2203/23—Double or multiple optical cladding profiles
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B2203/00—Fibre product details, e.g. structure, shape
- C03B2203/10—Internal structure or shape details
- C03B2203/22—Radial profile of refractive index, composition or softening point
- C03B2203/26—Parabolic or graded index [GRIN] core profile
Definitions
- the present invention relates to an optical fiber having a low bending loss and a manufacturing method thereof.
- This application is based on Japanese Patent Application No. 2014-195937 and Japanese Patent Application No. 2014-195938 filed on September 26, 2014, and 2014-249846 filed on Dec. 10, 2014. Is incorporated herein by reference.
- An optical fiber having a low bending loss is particularly required for FTTH (Fiber To The Home) for introducing an optical fiber into an office, home, or the like.
- FTTH Fiber To The Home
- a small bend may occur.
- a portion (excess length portion) of the extra length due to routing is wound and stored with a predetermined radius or more.
- the storage space can be reduced by bending the extra length portion small. Therefore, an optical fiber in which a so-called bending loss (macrobend loss) is reduced in which loss does not increase even when a small bend is inserted is important.
- ITU-T Recommendation G a standard for standard single mode optical fiber (S-SMF).
- S-SMF standard single mode optical fiber
- the mode field diameter is reduced (see, for example, Patent Documents 1 and 2 and Non-Patent Document 1), and a trench (low refractive index portion) is formed around the core.
- the refractive index distribution of the core is ⁇ power distribution (graded index type) (for example, refer to Patent Documents 4 and 6).
- the low bending loss optical fiber has a single-peak type refractive index distribution composed of a core and a clad while maintaining the same MFD as that of a general-purpose optical fiber.
- the bending loss is reduced by making the refractive index distribution of the core an ⁇ power distribution. Therefore, an optical fiber having a core refractive index distribution in which bending loss is smaller than the ⁇ power distribution is required. Further, even when a trench is provided around the core, an optical fiber having a core refractive index distribution in which bending loss is smaller than the ⁇ power distribution is required.
- the present invention has been made in view of the above circumstances, and provides an optical fiber having a core refractive index distribution in which a bending loss is smaller than an ⁇ power distribution and a method for manufacturing the same.
- the first aspect of the present invention includes a core and a clad surrounding the outer periphery of the core, and has a refractive index distribution in which a relative refractive index difference with respect to a distance r from the center of the core is represented by ⁇ (r),
- the unit of r is ⁇ m
- the unit of relative refractive index difference ⁇ (r) is%
- ⁇ ref (r) ⁇ 0.064r + 0.494
- MFD 1.31 has a wavelength of 1.
- the value of A represented by a mode field diameter at 31 ⁇ m is 0.3% ⁇ ⁇ m or less.
- the mode field diameter MFD 1.31 at a wavelength of 1.31 ⁇ m is preferably 8.93 ⁇ m or more and 9.4 ⁇ m or less.
- the fourth aspect of the present invention is to provide an optical fiber of any one aspect of the first to third embodiments, the maximum relative refractive index difference delta max in the entire core is preferably greater than 0.39%.
- a fifth aspect of the present invention is to provide an optical fiber of any one aspect of the first to fourth embodiments, it is preferred maximum relative refractive index difference delta max in the entire core is less than 0.50%.
- the cable cutoff wavelength ⁇ cc is preferably 1260 nm or less.
- the cable cutoff wavelength ⁇ cc is preferably 1170 nm or more.
- a ratio between a mode field diameter MFD 1.31 at a wavelength of 1.31 ⁇ m and a cable cutoff wavelength ⁇ cc , MFD The MAC value represented by 1.31 / ⁇ cc is preferably 7.38 or more and 7.7 or less.
- an optical fiber having a higher relative refractive index difference closer to the center of the core and easier to confine light at the center of the core is obtained, and loss when the optical fiber is bent is reduced. can do.
- FIG. 1 It is sectional drawing which shows typically the optical fiber which concerns on 1st Embodiment of this invention. It is a graph which shows the relationship between the value of A and the bending loss in the Example of 1st Embodiment.
- 3 is a graph showing a refractive index distribution of the optical fiber of Example 1.
- 6 is a graph showing the refractive index distribution of the optical fiber of Example 2.
- 10 is a graph showing the refractive index distribution of the optical fiber of Example 3.
- 10 is a graph showing the refractive index distribution of the optical fiber of Example 4.
- 10 is a graph showing the refractive index distribution of the optical fiber of Example 5.
- 10 is a graph showing the refractive index distribution of the optical fiber of Example 6.
- 10 is a graph showing the refractive index distribution of the optical fiber of Example 7.
- 10 is a graph showing the refractive index distribution of the optical fiber of Example 8.
- 10 is a graph showing the refractive index distribution of the optical fiber of Example 9. It is a figure which shows typically the refractive index distribution of the optical fiber which concerns on 1st Embodiment of this invention. It is a figure which shows typically the refractive index distribution used by simulation. It is a figure which shows typically the refractive index distribution used by simulation. It is a figure which shows typically the refractive index distribution used by simulation. It is a figure which shows typically the refractive index distribution used by simulation. It is a figure which shows the calculation result of a bending loss. It is a figure which shows the calculation result of a bending loss. It is a figure which shows the calculation result of a bending loss.
- the optical fiber 5 of the present embodiment includes a core 1 provided at the center of the optical fiber 5 and a clad 4 surrounding the outer periphery of the core 1.
- the clad 4 is generally concentric with the core 1, but the clad 4 and the core 1 may be eccentric within an allowable range.
- the refractive index distribution of the core is expressed by ⁇ (r) as a function of the relative refractive index difference ⁇ with respect to the distance r from the center of the core.
- the distance r is non-negative (r ⁇ 0).
- the relative refractive index difference ⁇ of the core means a relative refractive index difference based on the refractive index of the cladding. In the clad, the relative refractive index difference is zero.
- a range of A values defined by the following mathematical formula (definition formula of A) is specified as a condition for obtaining a low bending loss optical fiber. The derivation of the definition formula will be described later.
- ⁇ ref (r) ⁇ 0.064r + 0.494.
- MFD 1.31 is a mode field diameter at a wavelength of 1.31 ⁇ m.
- the MFD is not necessarily equal to the core diameter (diameter), but is generally the same as the core diameter. Then, since 0.5 MFD 1.31 is substantially equal to the core radius, the region where r ⁇ 0.44MFD 1.31 represents most of the core (excluding the peripheral portion). The region where r ⁇ 0.22MFD 1.31 represents the center of the core.
- the definition formula of A is defined as a definite integral (first definite integral) in a section of 0 ⁇ r ⁇ 0.22MFD 1.31, and a constant in a section of 0.22MFD 1.31 ⁇ r ⁇ 0.44MFD 1.31.
- Integration second definite integration.
- the first definite integral and the second definite integral have the same integration interval width (0.22MFD 1.31 ) and the same integrand ( ⁇ (r) ⁇ ref (r)). Is the opposite and the contribution to A is different.
- the refractive index distribution having a higher relative refractive index difference tends to have a smaller A value as it is closer to the center of the core.
- the value of A is preferably 0.3% ⁇ ⁇ m or less. As a result, an optical fiber that can easily confine light at the center of the core can be obtained, and loss when the optical fiber is bent can be reduced.
- the value of A is more preferably 0.2% ⁇ ⁇ m or less, and further preferably 0.1% ⁇ ⁇ m or less.
- ⁇ ref (r) in the definition formula of A represents a refractive index distribution (reference refractive index distribution) referred to in the definition formula of A.
- the value of A is, for example, 0% ⁇ ⁇ m or more, ⁇ 0.01% ⁇ ⁇ m or more, ⁇ 0.02% ⁇ ⁇ m or more, ⁇ 0.03% ⁇ ⁇ m or more, ⁇ 0.05% ⁇ ⁇ m or more, ⁇ It may be 0.1% ⁇ ⁇ m or more, ⁇ 0.2% ⁇ ⁇ m or more, ⁇ 0.3% ⁇ ⁇ m or more, and the like.
- the optical fiber manufacturing method of the present embodiment includes a step of calculating the value of A using the definition formula of A, and the value of A is within a predetermined range (for example, 0.3% ⁇ ⁇ m or less). A step of confirming this.
- the calculation step and the confirmation step of A are a series of steps performed when manufacturing an optical fiber, for example, a step of designing a refractive index distribution of an optical fiber, a step of manufacturing an optical fiber preform having the refractive index distribution, It can be performed at an arbitrary stage regardless of before and after the step of spinning an optical fiber from a fiber preform.
- the optical fiber according to the present embodiment is manufactured by producing an optical fiber preform by a known preform producing method such as a shaft attaching method (VAD method), an external attaching method (OVD method), or an internal attaching method (CVD method). It can be manufactured by spinning an optical fiber from a fiber preform.
- a method for producing the optical fiber preform at least the glass constituting the core is produced by the OVD method or the CVD method, and the remaining glass portion is produced by further depositing silica (SiO 2 ) glass, a quartz tube jacket, or the like. Can be mentioned.
- the entire core or all of the core and a part of the clad are produced by the VAD method, and the remaining part of the clad is produced by the OVD method.
- the part manufactured by the OVD method or the CVD method may be only glass (part or all) constituting the core, and may further include part of the glass constituting the cladding.
- the size of the optical fiber is not particularly limited, examples of the cladding diameter include 125 ⁇ m and 80 ⁇ m.
- one or more coatings such as a resin may be laminated on the outer periphery of the clad.
- the mode field diameter MFD 1.31 at a wavelength of 1.31 ⁇ m is preferably about 9.2 ⁇ m.
- MFD 1.31 is 9.2 ⁇ m ⁇ 0.2 ⁇ m, or 8.93 ⁇ m or more and 9.4 ⁇ m or less.
- the refractive index profile of the core is preferably unimodal with only one peak within the core diameter range.
- the single-peak type means that the point where the relative refractive index difference of the core takes the maximum value is only one point within the core diameter range.
- the range of the core diameter includes not only the side where the coordinate value on the radius is positive, but the side where the coordinate value on the radius is negative, with the core center being 0. If the refractive index distribution of the core is concentric, the relative refractive index difference takes the maximum value at the core center. Therefore, the maximum relative refractive index difference delta max in the entire core, the distance r from the center of the core is preferably equal to the maximum relative refractive index difference delta c in the range below 1 [mu] m.
- the core In order to confine light in the core in an optical fiber, it is sufficient that the core has a higher refractive index than in the clad. However, if the relative refractive index difference is too small, light confinement becomes weak. Therefore, it is preferred maximum relative refractive index difference delta max in the entire core is greater than 0.39%. On the other hand, if the relative refractive index difference is too large, the required amount of dopant increases and the cost increases. Therefore, it is preferred maximum relative refractive index difference delta max in the entire core is less than 0.50%.
- the cable cutoff wavelength ⁇ cc of the optical fiber (that is, the cutoff wavelength ⁇ c 22m of 22 m ) is preferably 1260 nm or less. ⁇ cc may be greater than or equal to 1170nm.
- the MAC value represented by the ratio (MFD 1.31 / ⁇ cc ) of the mode field diameter MFD 1.31 and the cable cutoff wavelength ⁇ cc at a wavelength of 1.31 ⁇ m is 7.38 or more and 7.7 or less. More preferably.
- the dopant used for the production of the silica-based optical fiber include germanium (Ge), phosphorus (P), fluorine (F), boron (B), and aluminum (Al). Two or more dopants may be used.
- the core material includes Ge-added silica
- the clad material includes pure silica.
- the refractive index distributions used are shown in FIGS. 13A to 13C. 13A to 13C, ( ⁇ cc [ ⁇ m] / MFD [ ⁇ m]) is (1.20 / 9.00), (1.23 / 9.15), (1.26 / 9.3) in order, respectively. ).
- the dispersion value is set to ITU-T G. 652.
- adjustment is performed depending on the refractive index distribution by providing the cladding portion with a slight low refractive index portion (depressed portion).
- the calculation results of the bending loss in these refractive index profiles are shown in FIGS. 14A to 14C. From these results, it can be seen that the bending loss decreases as the relative refractive index difference at the core central portion increases (or the core shape inclination ⁇ (r1) / ⁇ c decreases).
- the inventors have found that the relationship with the bending loss can be expressed from the deviation from the refractive index distribution (reference refractive index distribution) in which the bending loss is minimized in the simulation.
- FIG. 15 shows the normalized electric field strength distribution in the reference refractive index distribution.
- optical fiber having a core part and a clad part provided around the core part was manufactured.
- the optical fiber was manufactured by drawing (spinning) an optical fiber preform.
- the optical fiber preform was manufactured by forming a core member composed of the entire core and a part of the clad by the VAD method or the CVD method and then forming the remaining clad portion around the core member by the OVD method.
- the core base material was manufactured by the VAD method
- Example 9 the core base material was manufactured by the CVD method.
- the refractive index distribution of the obtained optical fiber is represented by a relative refractive index difference ⁇ with respect to the radius [ ⁇ m].
- the shapes of the refractive index profiles of the optical fibers of Examples 1 to 9 are shown in FIGS. 3 to 11, respectively.
- the radius [ ⁇ m] is 0 [ ⁇ m] at the core center and can take either positive or negative values.
- the distance r [ ⁇ m] from the center of the core in the definition formula of A is an absolute value of the radius [ ⁇ m] and takes 0 or a positive value.
- Table 1 shows the parameters of the optical fibers of Examples 1 to 9.
- ⁇ max is the maximum relative refractive index difference [%] in the entire core.
- the delta c within a distance r from the center of the core the following 1 [mu] m (i.e., -1 ⁇ m ⁇ radius ⁇ 1 [mu] m) is the maximum relative refractive index difference at [%].
- r 1 is the radius [ ⁇ m] of the core.
- Distance r is the core radius r 1 greater than the area from the center of the core is clad, the relative refractive index difference in the cladding is zero.
- ⁇ min is the minimum relative refractive index difference [%] in the entire core.
- ⁇ cc is the cable cutoff wavelength [ ⁇ m].
- MFD 1.31 is a mode field diameter [ ⁇ m] at a wavelength of 1.31 ⁇ m.
- MAC represents the value of the ratio expressed by MFD 1.31 / ⁇ cc.
- the bending loss is a bending loss [dB / 10 turn] at a bending radius of 15 mm and a wavelength of 1.55 ⁇ m.
- the optical fibers of Examples 1 to 9 are ITU-T G. 652.
- A [% ⁇ ⁇ m] was calculated according to the definition formula of A.
- the relationship between the value A and the bending loss (wavelength 1.55 ⁇ m, radius 15 mm, 10 turns) in Examples 1 to 9 is shown in the graph of FIG. As the value of A became smaller, the bending loss tended to take a smaller value.
- Examples 1 to 6 and Example 9 correspond to A ⁇ 0.3% ⁇ ⁇ m.
- the bending loss was 0.034 dB / 10 turn
- the mode field diameter MFD 1.31 was 9.2 ⁇ m
- the clad 4 may have the following configuration.
- FIG. 16 shows a schematic configuration of the optical fiber 10 according to the second embodiment of the present invention.
- the optical fiber 10 includes a core 1 disposed in the center, and a clad 4 provided concentrically with the core 1 on the outer peripheral side of the core 1.
- the cladding 4 has at least an inner cladding part 2 adjacent to the outer peripheral side of the core 1 and an outer cladding part 3 formed on the outer peripheral side of the inner cladding part 2.
- FIG. 17 schematically shows the refractive index distribution of the optical fiber 10.
- the refractive index of the core 1 is ⁇ 1, and the maximum refractive index is ⁇ 1max.
- the refractive index of the inner cladding portion 2 is ⁇ 2, and the minimum refractive index is ⁇ 2min.
- the maximum refractive index ⁇ 1max of the core 1 is the refractive index of the core 1 that is maximum in the radial range from the center of the core 1 to the outer periphery.
- the refractive index ⁇ 1 is equal to the maximum refractive index ⁇ 1max over the entire range.
- the minimum refractive index ⁇ 2min of the inner cladding portion 2 is the refractive index of the inner cladding portion 2 that is the smallest in the radial range from the inner periphery to the outer periphery of the inner cladding portion 2.
- the refractive index ⁇ 2 is equal to the minimum refractive index ⁇ 2min over the entire range.
- the following equation (11) is established. ⁇ 1max> ⁇ 2min and ⁇ 1max> ⁇ 3 (11)
- the maximum refractive index ⁇ 1max of the core 1 is set larger than the minimum refractive index ⁇ 2min of the inner cladding portion 2 and the refractive index ⁇ 3 of the outer cladding portion 3.
- the minimum refractive index ⁇ 2 min of the inner cladding portion 2 is set to be smaller than the refractive index ⁇ 3 of the outer cladding portion 3.
- Equation (12) means that the absolute value of the difference between the minimum refractive index ⁇ 2min of the inner cladding portion 2 and the refractive index ⁇ 3 of the outer cladding portion 3 exceeds 0.01% and is less than 0.03%. To do.
- the bending loss may not be sufficiently reduced.
- the absolute value of the difference between ⁇ 2min and ⁇ 3 is too large, the mode field diameter becomes small, resulting in a large connection loss when connected to another optical fiber (for example, a normal single mode optical fiber (S-SMF)).
- S-SMF normal single mode optical fiber
- the bending loss can be reduced by setting the absolute value of the difference between ⁇ 2min and ⁇ 3 to a range exceeding 0.01%.
- the absolute value of the difference between ⁇ 2min and ⁇ 3 to less than 0.03%, the mode field diameter (MFD) can be optimized and the connection loss when connected to another optical fiber can be kept low.
- the following equation (11A) is established regarding the magnitude relationship among ⁇ 1max, ⁇ 2min, and ⁇ 3.
- ⁇ 1max> ⁇ 3> ⁇ 2min (11A) As shown in Expression (11A), the maximum refractive index ⁇ 1max of the core 1 is set to be larger than the refractive index ⁇ 3 of the outer cladding portion 3.
- the refractive index ⁇ 3 of the outer cladding part 3 is set larger than the minimum refractive index ⁇ 2min of the inner cladding part 2.
- Equation (12A) means that the difference between the refractive index ⁇ 3 of the outer cladding portion 3 and the minimum refractive index ⁇ 2min of the inner cladding portion 2 is more than 0.01% and less than 0.03%.
- the outer peripheral radii of the core 1, the inner cladding part 2, and the outer cladding part 3 are r1, r2, and r3, respectively. Between the outer peripheral radii r1 to r3 of the core 1, the inner cladding portion 2, and the outer cladding portion 3, there is a relationship expressed by the following equation (13). r1 ⁇ r2 ⁇ r3 (13)
- the ratio r1 / r2 between the outer peripheral radius r1 of the core 1 and the outer peripheral radius r2 of the inner cladding portion 2 is in the range shown in the following equation (14). 0.2 ⁇ r1 / r2 ⁇ 0.5 (14)
- r1 / r2 If r1 / r2 is too small, the mode field diameter becomes small, and there is a possibility that the connection loss when connected to another optical fiber (for example, S-SMF) becomes large. On the other hand, if r1 / r2 is too large, bending loss may increase.
- the optical fiber 10 by setting r1 / r2 to be 0.2 or more, the mode field diameter can be optimized and the connection loss when connecting to another optical fiber can be kept low. By making r1 / r2 0.5 or less, bending loss can be reduced.
- the optical fiber 10 has a cable cutoff wavelength ⁇ cc of 1260 nm or less. That is, the following equation (15) is established. ⁇ cc ⁇ 1260 nm (15) As a result, ITU-T Recommendation G. 652 can be satisfied.
- the cutoff wavelength ⁇ cc is, for example, ITU-T Recommendation G. It can be measured by the measurement method described in 650.
- the optical fiber 10 is set such that the mode field diameter (MFD) at a wavelength of 1310 nm is 8.6 ⁇ m or more and 9.5 ⁇ m or less by adjusting the refractive index and the outer radius. That is, the following equation (16) is established. 8.6 ⁇ m ⁇ MFD ⁇ 9.5 ⁇ m (16) By setting the mode field diameter within this range, connection loss when connected to another optical fiber (for example, S-SMF) can be kept low.
- the optical fiber 10 has an ITU-T G.D. It satisfies the provisions of 652.
- the optical fiber 10 preferably has a loss increase of 0.25 dB or less at a wavelength of 1550 nm when it is wound 10 times on a cylindrical mandrel having a diameter of 15 mm. Further, the increase in loss at a wavelength of 1625 nm when wound around a cylindrical mandrel having a diameter of 15 mm 10 times is preferably 1.0 dB or less.
- the core 1 can be made of silica glass whose refractive index is increased by adding a dopant such as germanium (Ge).
- the inner cladding portion 2 can be made of silica glass whose refractive index is lowered by adding a dopant such as fluorine (F).
- the inner cladding portion 2 may be made of silica glass whose refractive index is increased by adding a dopant such as chlorine (Cl).
- the outer cladding part 3 can be comprised, for example with a pure silica glass.
- the outer cladding portion 3 may adjust the refractive index by adding a dopant (eg, Ge, F, etc.).
- Each layer constituting the optical fiber 10 can be formed by a known method such as an MCVD method, a PCVD method, a VAD method, an OVD method, or a combination thereof.
- the optical fiber preform can be manufactured as follows.
- a glass deposition layer serving as the inner cladding portion 2 is formed inside a silica glass tube serving as the outer cladding portion 3 (for example, a glass tube made of pure silica glass) using a raw material containing a dopant such as fluorine (F). .
- the refractive index of the inner cladding part 2 can be adjusted by the amount of dopant added.
- a glass deposition layer to be the core 1 is formed inside the glass deposition layer using a raw material containing a dopant such as germanium (Ge).
- the core 1 can also be formed using the core rod produced separately.
- the silica glass tube on which the glass deposition layer is formed is made into an optical fiber preform through processes such as transparency and solidification.
- the optical fiber 10 shown in FIG. 16 is obtained by drawing this optical fiber preform.
- the CVD method is preferable in that the refractive index distribution can be accurately adjusted by adding a dopant.
- the VAD method and the OVD method are also applicable.
- the VAD method and the OVD method have an advantage of high productivity.
- the difference in refractive index between the inner cladding portion 2 and the outer cladding portion 3 is in the above range (see formula (12)), and the ratio of the outer peripheral radius between the core 1 and the inner cladding portion 2 is in the above range (formula). (Refer to (14)), the connection loss when connecting to another optical fiber can be kept low, and the bending loss can be reduced.
- the present inventor has found that the bending loss can be reduced without reducing the mode field diameter.
- a refractive index distribution that can be reduced.
- the conventional manufacturing method for example, a normal S-SMF manufacturing method
- the refractive indexes of the part 2 and the outer cladding part 3 can be adjusted easily and accurately.
- the difference in refractive index between the inner cladding portion 2 and the outer cladding portion 3 is small, there are few restrictions based on the manufacturing method. For example, not only the CVD method suitable for adjusting the refractive index distribution but also a VAD method and an OVD method can be employed. Therefore, the optical fiber 10 can be easily manufactured, and the manufacturing cost can be kept low.
- the optical fiber 10 has a small difference in refractive index between the inner cladding portion 2 and the outer cladding portion 3, the amount of dopant such as fluorine (F) and chlorine (Cl) for forming the inner cladding portion 2 can be reduced.
- the source gas (for example, SiF 4 ) used for doping such as fluorine (F) is expensive, the source cost can be suppressed and the manufacturing cost can be reduced by reducing the dopant addition amount.
- the optical fiber 10 since the minimum refractive index ⁇ 2min of the inner cladding portion 2 is smaller than the refractive index ⁇ 3 of the outer cladding portion 3, the optical fiber 10 has good confinement of light in the core 1 and reduces bending loss. it can.
- FIG. 18 shows a schematic configuration of an optical fiber 20 according to the second embodiment of the present invention.
- the optical fiber 20 includes a core 1 disposed in the center, and a clad 14 provided concentrically with the core 1 on the outer peripheral side of the core 1.
- the clad 14 has at least an inner clad portion 12 adjacent to the outer peripheral side of the core 1 and an outer clad portion 13 formed on the outer peripheral side of the inner clad portion 12.
- FIG. 19 schematically shows the refractive index distribution of the optical fiber 20.
- the refractive index of the core 1 is ⁇ 1, and the maximum refractive index is ⁇ 1max.
- the refractive index of the inner cladding portion 12 is ⁇ 2, and the minimum refractive index is ⁇ 2min.
- the following equation (17) is established, as in the optical fiber 10 of the first embodiment. ⁇ 1max> ⁇ 2min and ⁇ 1max> ⁇ 3 (17)
- the optical fiber 20 differs from the optical fiber 10 of the first embodiment in that the minimum refractive index ⁇ 2min of the inner cladding portion 12 is larger than the refractive index ⁇ 3 of the outer cladding portion 13.
- the following equation (18) is established, as in the optical fiber 10 of the first embodiment. 0.01% ⁇
- the mode field diameter (MFD) can be optimized, the connection loss when connected to another optical fiber can be kept low, and the bending loss can be reduced. it can.
- the optical fiber 20 has a cable cutoff wavelength ⁇ cc of 1260 nm or less.
- the mode field diameter (MFD) at a wavelength of 1310 nm is 8.6 ⁇ m or more and 9.5 ⁇ m or less.
- the optical fiber 20 preferably has a loss increase of 0.25 dB or less at a wavelength of 1550 nm when it is wound 10 times on a cylindrical mandrel having a diameter of 15 mm. Further, the increase in loss at a wavelength of 1625 nm when wound around a cylindrical mandrel having a diameter of 15 mm 10 times is preferably 1.0 dB or less.
- the core 1 can be made of silica glass whose refractive index is increased by adding a dopant such as germanium (Ge).
- the inner cladding portion 12 can be made of, for example, pure silica glass.
- the inner cladding portion 12 may adjust the refractive index by adding a dopant such as chlorine (Cl).
- the outer cladding portion 13 can be made of, for example, pure silica glass.
- the outer clad part 3 may be made of silica glass whose refractive index is lowered by adding a dopant such as fluorine (F).
- the optical fiber 20 can be manufactured by the MCVD method, the PCVD method, the VAD method, the OVD method, or the like, similarly to the optical fiber 10 of the first embodiment.
- the optical fiber preform can be manufactured as follows. Using a raw material such as pure silica glass, a glass deposition layer to be the inner cladding portion 12 is formed inside a silica glass tube to be the outer cladding portion 13 (for example, a silica glass tube containing a dopant such as fluorine (F)). . Next, a glass deposition layer to be the core 1 is formed inside the glass deposition layer using a raw material containing a dopant such as germanium (Ge).
- the core 1 can also be formed using the core rod produced separately.
- the silica glass tube on which the glass deposition layer is formed is made into an optical fiber preform through processes such as transparency and solidification. By drawing the optical fiber preform, an optical fiber 20 shown in FIG. 18 is obtained.
- the difference in refractive index between the inner cladding portion 12 and the outer cladding portion 13 is set in the above range, and the ratio of the outer peripheral radius between the core 1 and the inner cladding portion 12 is set in the above range.
- Connection loss when connected can be kept low, and bending loss can be reduced. Since the optical fiber 20 can be used without greatly changing the conventional manufacturing method, it is easy to manufacture and the manufacturing cost can be kept low.
- the clads 4 and 14 are composed of two clad portions (an inner clad portion and an outer clad portion). It may have a layer.
- FIG. 20 shows a schematic configuration of an optical fiber 30 according to the fourth embodiment of the present invention.
- the optical fiber 30 includes a core 21 disposed in the center, and a clad 25 provided concentrically with the core 21 on the outer peripheral side of the core 21.
- the cladding 25 includes at least an inner cladding portion 22 adjacent to the outer peripheral side of the core 21, a trench portion 23 formed adjacent to the outer peripheral side of the inner cladding portion 22, and an outer portion formed on the outer peripheral side of the trench portion 23.
- a clad portion 24 is a schematic configuration of an optical fiber 30 according to the fourth embodiment of the present invention.
- the optical fiber 30 includes a core 21 disposed in the center, and a clad 25 provided concentrically with the core 21 on the outer peripheral side of the core 21.
- the cladding 25 includes at least an inner cladding portion 22 adjacent to the outer peripheral side of the core 21, a trench portion 23 formed adjacent to the outer peripheral side of the inner cladding portion 22, and an outer portion formed on the outer
- FIG. 21 schematically shows the refractive index distribution of the optical fiber 30.
- the refractive index of the core 21 is ⁇ 1, and the maximum refractive index is ⁇ 1max.
- the refractive index of the inner cladding portion 22 is ⁇ 2, and the minimum refractive index is ⁇ 2min.
- the refractive index of the trench portion 23 is ⁇ 3, and the minimum refractive index is ⁇ 3 min.
- the refractive index of the outer cladding part 24 is assumed to be ⁇ 4.
- the maximum refractive index ⁇ 1max of the core 21 is the refractive index of the core 21 that is maximized in the radial range from the center of the core 21 to the outer periphery.
- the refractive index ⁇ 1 is equal to the maximum refractive index ⁇ 1max over the entire range.
- the minimum refractive index ⁇ 2min of the inner cladding portion 22 is the refractive index of the inner cladding portion 22 that is the smallest in the radial range from the inner periphery to the outer periphery of the inner cladding portion 22.
- the refractive index ⁇ 2 is equal to the minimum refractive index ⁇ 2min over the entire range.
- the minimum refractive index ⁇ 3min of the trench portion 23 is the refractive index of the trench portion 23 that is the smallest in the radial range from the inner periphery to the outer periphery of the trench portion 23.
- the refractive index ⁇ 3 is equal to the minimum refractive index ⁇ 3min over the entire range.
- the following formula (21) is established. ⁇ 1max> ⁇ 2> ⁇ 3min (21)
- the maximum refractive index ⁇ 1max of the core 21 is set larger than the refractive index ⁇ 2 of the inner cladding portion 22.
- the refractive index ⁇ 2 of the inner cladding portion 22 is set to be larger than ⁇ 3 min of the trench portion 23.
- the following expression (22) is further established. ⁇ 1max> ⁇ 4> ⁇ 3min (22)
- the maximum refractive index ⁇ 1max of the core 21 is set to be larger than the refractive index ⁇ 4 of the outer cladding portion 24.
- the refractive index ⁇ 4 of the outer cladding portion 24 is set to be larger than ⁇ 3 min of the trench portion 23.
- Equation (23) means that the difference between the refractive index ⁇ 4 of the outer cladding portion 24 and the minimum refractive index ⁇ 3min of the trench portion 23 exceeds 0.01% and is less than 0.03%.
- the bending loss may not be sufficiently reduced.
- the difference between ⁇ 4 and ⁇ 3min is too small, the bending loss may not be sufficiently reduced.
- the difference between ⁇ 4 and ⁇ 3min is too large, the mode field diameter becomes small, and there is a possibility that the connection loss when connecting to another optical fiber (for example, a normal single mode optical fiber (S-SMF)) becomes large. is there.
- the bending loss can be reduced by setting the difference between ⁇ 4 and ⁇ 3min to a range exceeding 0.01%.
- the difference between ⁇ 4 and ⁇ 3min to be less than 0.03%, the mode field diameter (MFD) can be optimized and the connection loss when connecting to another optical fiber can be kept low.
- the outer peripheral radii of the core 21, the inner cladding part 22, the trench part 23, and the outer cladding part 24 are r1, r2, r3, and r4, respectively.
- the ratio r2 / r1 between the outer peripheral radius r2 of the inner cladding portion 22 and the outer peripheral radius r1 of the core 21 is in the range shown in the following equation (25). 1 ⁇ r2 / r1 ⁇ 5 (25)
- r2 / r1 If r2 / r1 is too small, bending loss may increase. On the other hand, if r2 / r1 is too large, the mode field diameter becomes small, and there is a possibility that the connection loss becomes large when connected to another optical fiber (for example, S-SMF). In the optical fiber 30, bending loss can be reduced by setting r2 / r1 to 1 or more. By setting r2 / r1 to 5 or less, the mode field diameter can be optimized and the connection loss when connected to another optical fiber can be kept low.
- S-SMF optical fiber
- the ratio r3 / r2 between the outer peripheral radius r3 of the trench part 23 and the outer peripheral radius r2 of the inner cladding part 22 is in the range represented by the following equation (26). 1 ⁇ r3 / r2 ⁇ 2 (26)
- r3 / r2 If r3 / r2 is too small, bending loss may increase. On the other hand, if r3 / r2 is too large, the mode field diameter becomes small, and the connection loss when connected to another optical fiber (for example, S-SMF) may increase. In the optical fiber 30, by making r3 / r2 greater than 1, bending loss can be reduced. By setting r3 / r2 to 2 or less, the mode field diameter can be optimized and the connection loss when connected to another optical fiber can be kept low.
- S-SMF optical fiber
- the optical fiber 30 has a cable cutoff wavelength ⁇ cc of 1260 nm or less. That is, the following equation (27) is established. ⁇ cc ⁇ 1260 nm (27) As a result, ITU-T Recommendation G. 652 can be satisfied.
- the cable cutoff wavelength ⁇ cc is, for example, ITU-T Recommendation G. It can be measured by the measurement method described in 650.
- the optical fiber 30 is set so that the mode field diameter (MFD) at a wavelength of 1310 nm is 8.6 ⁇ m or more and 9.5 ⁇ m or less by adjusting the refractive index and the outer radius. That is, the following equation (28) is established. 8.6 ⁇ m ⁇ MFD ⁇ 9.5 ⁇ m (28) By setting the mode field diameter within this range, connection loss when connected to another optical fiber (for example, S-SMF) can be kept low.
- the optical fiber 30 has an ITU-T G.D. It satisfies the provisions of 652.
- the optical fiber 30 preferably has a loss increase of 0.25 dB or less at a wavelength of 1550 nm when it is wound 10 times on a cylindrical mandrel having a diameter of 15 mm. Further, the increase in loss at a wavelength of 1625 nm when wound around a cylindrical mandrel having a diameter of 15 mm 10 times is preferably 1.0 dB or less.
- the core 21 can be made of silica glass whose refractive index is increased by adding a dopant such as germanium (Ge).
- the inner cladding portion 22 and the trench portion 23 can be made of silica glass whose refractive index is lowered by adding a dopant such as fluorine (F).
- the outer cladding portion 24 can be made of, for example, pure silica glass. The outer cladding portion 24 may adjust the refractive index by adding a dopant (eg, Ge, F, etc.).
- Each layer constituting the optical fiber 30 can be formed by a known method such as an MCVD method, a PCVD method, a VAD method, an OVD method, or a combination thereof.
- the optical fiber preform can be manufactured as follows.
- a glass deposition layer to be the trench portion 23 is formed inside a silica glass tube to be the outer cladding portion 24 (for example, a glass tube made of pure silica glass) using a raw material containing a dopant such as fluorine (F).
- a glass deposition layer to be the inner cladding portion 22 is formed inside the glass deposition layer using a raw material containing a dopant such as fluorine (F).
- the refractive indexes of the trench portion 23 and the inner cladding portion 22 can be adjusted by the amount of dopant added.
- a glass deposition layer to be the core 21 is formed inside the glass deposition layer using a raw material containing a dopant such as germanium (Ge).
- the core 21 can also be formed using a separately prepared core rod.
- the silica glass tube on which the glass deposition layer is formed is made into an optical fiber preform through processes such as transparency and solidification.
- the optical fiber 30 shown in FIG. 20 is obtained by drawing this optical fiber preform.
- the CVD method is preferable in that the refractive index distribution can be accurately adjusted by adding a dopant.
- the VAD method and the OVD method can also be applied to manufacture the optical fiber 30.
- the VAD method and the OVD method have an advantage of high productivity.
- the difference in refractive index between the trench portion 23 and the outer cladding portion 24 is set to the above range (see formula (23)), and the ratio of the outer peripheral radii of the core 21, the inner cladding portion 22, and the trench portion 23 is set.
- the present inventor has found that the bending loss can be reduced without reducing the mode field diameter.
- the optical fiber 30 is technically significant in that it adopts this refractive index distribution to achieve both suppression of connection loss and reduction of bending loss when connected to another optical fiber.
- the conventional manufacturing method for example, a normal S-SMF manufacturing method
- the refractive index of the outer cladding part 24 can be adjusted easily and accurately.
- the difference in refractive index between the trench portion 23 and the outer cladding portion 24 is small, there are few restrictions based on the manufacturing method. For example, not only the CVD method suitable for adjusting the refractive index distribution but also a VAD method and an OVD method can be employed. Therefore, the optical fiber 30 can be easily manufactured, and the manufacturing cost can be kept low.
- the optical fiber 30 has a small difference in refractive index between the trench portion 23 and the outer cladding portion 24, the amount of dopant such as fluorine (F) for forming the trench portion 23 can be reduced. Since the source gas (for example, SiF 4 ) used for doping such as fluorine (F) is expensive, the source cost can be suppressed and the manufacturing cost can be reduced by reducing the dopant addition amount.
- the source gas for example, SiF 4
- the outer radius radii r1 to r4 of the core 21, the inner clad part 22, the trench part 23, and the outer clad part 24 have the relationship shown in the equation (24).
- r1 ⁇ r2 ⁇ r3 ⁇ r4 (24)
- the clad 25 includes only the trench part 23 and the outer clad part 24 formed on the outer peripheral side of the trench part 23.
- the clad 25 includes three layers (an inner clad part, a trench part, and an outer clad part), but the clad may have other layers.
Abstract
Description
本願は、2014年9月26日に出願された日本国特許出願2014-195937号及び日本国特許出願2014-195938号、及び2014年12月10日に出願された2014-249846号に基づき優先権を主張し、その内容をここに援用する。
標準シングルモード光ファイバ(S-SMF)の規格であるITU-T Recommendation G.652に準拠しつつ、標準シングルモード光ファイバに比べて曲げ損失が低減された光ファイバの規格として、ITU-T Recommendation G.657がある。
結果として、いずれの方法でも製造コストが増大する。
本発明の第3態様は、上記第1または第2態様の光ファイバにおいて、コア全体における最大比屈折率差Δmaxと、コアの中心からの距離rが1μm以下の範囲内における最大比屈折率差Δcとが等しいことが好ましい。
本発明の第4態様は、上記第1~第3態様のうちいずれか1態様の光ファイバにおいて、コア全体における最大比屈折率差Δmaxが0.39%よりも大きいことが好ましい。
本発明の第5態様は、上記第1~第4態様のうちいずれか1態様の光ファイバにおいて、コア全体における最大比屈折率差Δmaxが0.50%よりも小さいことが好ましい。
本発明の第7態様は、上記第1~第6態様のうちいずれか1態様の光ファイバにおいて、ケーブルカットオフ波長λccが1170nm以上であることが好ましい。
本発明の第8態様は、上記第1~第7態様のうちいずれか1態様の光ファイバにおいて、波長1.31μmにおけるモードフィールド径MFD1.31とケーブルカットオフ波長λccとの比、MFD1.31/λccで表されるMAC値が7.38以上7.7以下であることが好ましい。
以下、本発明の好適な第1実施形態を説明する。
本実施形態の光ファイバ5は、図1に示すように、光ファイバ5の中心部に設けられるコア1と、コア1の外周を取り囲むクラッド4とを有する。クラッド4は、一般にコア1に対して同心状であるが、許容範囲内でクラッド4とコア1とが偏心することがあり得る。
光ファイバのサイズは特に限定されないが、例えばクラッド径として125μm、80μm等が挙げられる。紡糸後の光ファイバには、クラッドの外周に樹脂等の被覆が1層または2層以上積層されてもよい。
石英系光ファイバの製造に使用されるドーパントは、ゲルマニウム(Ge)、リン(P)、フッ素(F)、ホウ素(B)、アルミニウム(Al)等が挙げられる。2種以上のドーパントを使用してもよい。コアおよびクラッドの組成の一例として、コア材料はGe添加シリカ、クラッド材料は純シリカが挙げられる。
以上、本発明の第1実施形態を説明してきたが、これらは本発明の例示であり、追加、省略、置換、およびその他の変更は、本発明の範囲から逸脱することなく行うことができる。
(定義式の導出)
まず、コア形状及び曲げ損失の関係を確認するために、コア形状が異なるが、ケーブルカットオフ波長λcc、波長1.31μmのMFDが一定となる屈折率分布でシミュレーションを実施した。コア径r1、コア中心部の比屈折率差Δc、半径r1における比屈折率差Δ(r1)を変数として特性を調整した(図12)。
これらの屈折率分布における曲げ損失の計算結果を図14A~図14Cに示す。これらの結果からコア中心部の比屈折率差が大きくなるほど(またはコア形状の傾きΔ(r1)/Δcが小さくなるほど)、曲げ損失が小さくなることがわかる。
コア部およびその周囲に設けられたクラッド部を有する光ファイバを作製した。光ファイバは、光ファイバ母材を線引き(紡糸)することで、製造した。光ファイバ母材は、VAD法またはCVD法でコアの全部とクラッドの一部からなるコア部材を作製した後、コア部材の周囲にOVD法で残りのクラッド部を形成する方法で製造した。例1~8ではコア母材をVAD法で作製し、例9ではコア母材をCVD法で作製した。
上記実施形態では、光ファイバ5がコア1とクラッド4とを有する形態を説明したが、クラッド4について、以下の構成を有していてもよい。
光ファイバ10は、中心部に配されるコア1と、コア1の外周側にコア1と同心状に設けられたクラッド4とを有する。
コア1の屈折率をΔ1とし、最大屈折率をΔ1maxとする。
内クラッド部2の屈折率をΔ2とし、最小屈折率をΔ2minとする。
外クラッド部3の屈折率をΔ3とする。
内クラッド部2の最小屈折率Δ2minは、内クラッド部2の内周から外周までの径方向範囲において最小となる内クラッド部2の屈折率である。図17に示す屈折率分布では、内クラッド部2の屈折率Δ2は径方向位置にかかわらず一定であるため、屈折率Δ2は全範囲で最小屈折率Δ2minに等しい。
Δ1max>Δ2min、かつΔ1max>Δ3 ・・・(11)
式(11)に示すように、コア1の最大屈折率Δ1maxは、内クラッド部2の最小屈折率Δ2minおよび外クラッド部3の屈折率Δ3より大きく設定されている。
また、光ファイバ10では、内クラッド部2の最小屈折率Δ2minは、外クラッド部3の屈折率Δ3より小さく設定されている。
0.01%<|Δ2min-Δ3|<0.03% ・・・(12)
式(12)は、内クラッド部2の最小屈折率Δ2minと外クラッド部3の屈折率Δ3との差の絶対値が、0.01%を越え、かつ0.03%未満であることを意味する。
光ファイバ10では、Δ2minとΔ3との差の絶対値を0.01%を越える範囲とすることによって、曲げ損失を低減することができる。また、Δ2minとΔ3との差の絶対値を0.03%未満とすることによって、モードフィールド径(MFD)を適正化し、他の光ファイバと接続した際の接続損失を低く抑えることができる。
Δ1max>Δ3>Δ2min ・・・(11A)
式(11A)に示すように、コア1の最大屈折率Δ1maxは、外クラッド部3の屈折率Δ3より大きく設定されている。
外クラッド部3の屈折率Δ3は、内クラッド部2の最小屈折率Δ2minより大きく設定されている。
0.01%<(Δ3-Δ2min)<0.03% ・・・(12A)
式(12A)は、外クラッド部3の屈折率Δ3と内クラッド部2の最小屈折率Δ2minとの差が、0.01%を越え、かつ0.03%未満であることを意味する。
コア1と内クラッド部2と外クラッド部3との外周半径r1~r3の間には、次の式(13)に示す関係がある。
r1<r2<r3 ・・・(13)
0.2≦r1/r2≦0.5 ・・・(14)
光ファイバ10では、r1/r2を0.2以上とすることによって、モードフィールド径を適正化し、他の光ファイバと接続した際の接続損失を低く抑えることができる。r1/r2を0.5以下とすることによって、曲げ損失を低減することができる。
λcc≦1260nm ・・・(15)
これによって、ITU-T Recommendation G.652の規定を満足することができる。
カットオフ波長λccは、例えばITU-T Recommendation G.650に記載の測定法により測定することができる。
8.6μm≦MFD≦9.5μm ・・・(16)
モードフィールド径をこの範囲にすることによって、他の光ファイバ(例えばS-SMF)と接続した際の接続損失を低く抑えることができる。
光ファイバ10は、モードフィールド径をこの範囲とすることによって、ITU-T G.652の規定を満たす。
また、直径15mmの円筒形のマンドレルに10回巻回したときの波長1625nmにおける損失増加は1.0dB以下となることが好ましい。
内クラッド部2は、例えばフッ素(F)等のドーパントを添加することによって屈折率を低くしたシリカガラスで構成することができる。内クラッド部2は、例えば塩素(Cl)等のドーパントを添加することによって屈折率を高くしたシリカガラスで構成してもよい。
外クラッド部3は、例えば純粋シリカガラスで構成することができる。外クラッド部3は、ドーパント(例えばGe、Fなど)を添加することによって屈折率を調整してもよい。
例えば、MCVD法を採用する場合には、光ファイバ母材を次のようにして作製することができる。
ガラス堆積層が形成されたシリカガラス管は、透明化、中実化などの工程を経て光ファイバ母材とする。この光ファイバ母材を線引きすることによって、図16に示す光ファイバ10を得る。
CVD法は、ドーパントの添加によって屈折率分布を精度よく調整できる点で好ましい。
光ファイバ10の製造には、VAD法、OVD法も適用可能である。VAD法、OVD法には、生産性が高いという利点がある。
光ファイバ10は、この屈折率分布を採用することにより、他の光ファイバと接続した際の接続損失の抑制と曲げ損失の低減とを両立させている。
また、内クラッド部2と外クラッド部3の屈折率の差が小さいため、製造方法に基づく制約が少ない。例えば、屈折率分布の調整に適しているとされるCVD法だけでなく、VAD法、OVD法を採用することもできる。
従って、光ファイバ10の製造が容易であり、製造コストを低く抑えることができる。
フッ素(F)等のドープに用いられる原料ガス(例えばSiF4)は高価であるため、ドーパント添加量の削減によって、原料コストを抑制し、製造コストを低く抑えることができる。
本発明の実施形態において、光ファイバはさらに以下の構成を有していてもよい。
図18に、本発明の第2実施形態に係る光ファイバ20の概略構成を示す。
光ファイバ20は、中心部に配されるコア1と、コア1の外周側にコア1と同心状に設けられたクラッド14とを有する。
クラッド14は、少なくとも、コア1の外周側に隣接した内クラッド部12と、内クラッド部12の外周側に形成された外クラッド部13とを有する。
コア1の屈折率をΔ1とし、最大屈折率をΔ1maxとする。内クラッド部12の屈折率をΔ2とし、最小屈折率をΔ2minとする。外クラッド部13の屈折率をΔ3とする。
光ファイバ20では、第1実施形態の光ファイバ10と同様に、次の式(17)が成り立つ。
Δ1max>Δ2min、かつΔ1max>Δ3 ・・・(17)
0.01%<|Δ2min-Δ3|<0.03% ・・・(18)
Δ2minとΔ3との差の絶対値を上記範囲とすることによって、モードフィールド径(MFD)を適正化し、他の光ファイバと接続した際の接続損失を低く抑え、かつ曲げ損失を低減することができる。
r1<r2<r3 ・・・(19)
0.2≦r1/r2≦0.5 ・・・(20)
r1/r2を0.2以上とすることによって、モードフィールド径を適正化し、他の光ファイバと接続した際の接続損失を低く抑え、かつ曲げ損失を低減することができる。
また、波長1310nmにおけるモードフィールド径(MFD)は、8.6μm以上、かつ9.5μm以下とされる。
光ファイバ20は、直径15mmの円筒形のマンドレルに10回巻回したときの波長1550nmにおける損失増加は0.25dB以下となることが好ましい。また、直径15mmの円筒形のマンドレルに10回巻回したときの波長1625nmにおける損失増加は1.0dB以下となることが好ましい。
内クラッド部12は、例えば純粋シリカガラスで構成することができる。内クラッド部12は、例えば塩素(Cl)等のドーパントを添加することによって屈折率を調整してもよい。
外クラッド部13は、例えば純粋シリカガラスで構成することができる。外クラッド部3は、例えばフッ素(F)等のドーパントを添加することによって屈折率を低くしたシリカガラスで構成してもよい。
例えば、MCVD法を採用する場合には、光ファイバ母材を次のようにして作製することができる。
外クラッド部13となるシリカガラス管(例えばフッ素(F)等のドーパントを含むシリカガラス管)の内側に、純粋シリカガラスなどの原材料を用いて、内クラッド部12となるガラス堆積層を形成する。
次いで、ガラス堆積層の内側に、例えばゲルマニウム(Ge)等のドーパントを含む原材料を用いて、コア1となるガラス堆積層を形成する。なお、コア1は、別途作製したコアロッドを用いて形成することもできる。
ガラス堆積層が形成されたシリカガラス管は、透明化、中実化などの工程を経て光ファイバ母材とする。この光ファイバ母材を線引きすることによって、図18に示す光ファイバ20を得る。
光ファイバ20は、従来の製造方法を大きく変更せずに利用できるため、製造が容易であり、製造コストを低く抑えることができる。
例えば、図17、図19に示す光ファイバ10,20では、クラッド4,14は2つのクラッド部(内クラッド部および外クラッド部)からなるが、クラッドは、内クラッド部および外クラッド部以外の層を有していてもよい。
本発明の実施形態において、光ファイバはさらに以下の構成を有していてもよい。
図20に、本発明の第4実施形態に係る光ファイバ30の概略構成を示す。
光ファイバ30は、中心部に配されるコア21と、コア21の外周側にコア21と同心状に設けられたクラッド25とを有する。
クラッド25は、少なくとも、コア21の外周側に隣接した内クラッド部22と、内クラッド部22の外周側に隣接して形成されたトレンチ部23と、トレンチ部23の外周側に形成された外クラッド部24とを有する。
コア21の屈折率をΔ1とし、最大屈折率をΔ1maxとする。
内クラッド部22の屈折率をΔ2とし、最小屈折率をΔ2minとする。
トレンチ部23の屈折率をΔ3とし、最小屈折率をΔ3minとする。
外クラッド部24の屈折率をΔ4とする。
トレンチ部23の最小屈折率Δ3minは、トレンチ部23の内周から外周までの径方向範囲において最小となるトレンチ部23の屈折率である。図21に示す屈折率分布では、トレンチ部23の屈折率Δ3は径方向位置にかかわらず一定であるため、屈折率Δ3は全範囲で最小屈折率Δ3minに等しい。
Δ1max>Δ2>Δ3min ・・・(21)
式(21)に示すように、コア21の最大屈折率Δ1maxは、内クラッド部22の屈折率Δ2より大きく設定されている。
内クラッド部22の屈折率Δ2は、トレンチ部23のΔ3minより大きく設定されている。
Δ1max>Δ4>Δ3min ・・・(22)
式(22)に示すように、コア21の最大屈折率Δ1maxは、外クラッド部24の屈折率Δ4より大きく設定されている。
外クラッド部24の屈折率Δ4は、トレンチ部23のΔ3minより大きく設定されている。
0.01%<(Δ4-Δ3min)<0.03% ・・・(23)
式(23)は、外クラッド部24の屈折率Δ4とトレンチ部23の最小屈折率Δ3minとの差が、0.01%を越え、かつ0.03%未満であることを意味する。
光ファイバ30では、Δ4とΔ3minとの差を0.01%を越える範囲とすることによって、曲げ損失を低減することができる。また、Δ4とΔ3minとの差を0.03%未満とすることによって、モードフィールド径(MFD)を適正化し、他の光ファイバと接続した際の接続損失を低く抑えることができる。
コア21と内クラッド部22とトレンチ部23と外クラッド部24との外周半径r1~r4の間には、次の式(24)に示す関係がある。
r1≦r2<r3<r4 ・・・(24)
1≦r2/r1≦5 ・・・(25)
光ファイバ30では、r2/r1を1以上とすることによって、曲げ損失を低減することができる。r2/r1を5以下とすることによって、モードフィールド径を適正化し、他の光ファイバと接続した際の接続損失を低く抑えることができる。
1<r3/r2≦2 ・・・(26)
光ファイバ30では、r3/r2を1より大きくとすることによって、曲げ損失を低減することができる。r3/r2を2以下とすることによって、モードフィールド径を適正化し、他の光ファイバと接続した際の接続損失を低く抑えることができる。
すなわち、次の式(27)が成立する。
λcc≦1260nm ・・・(27)
これによって、ITU-T Recommendation G.652の規定を満足することができる。
ケーブルカットオフ波長λccは、例えばITU-T Recommendation G.650に記載の測定法により測定することができる。
8.6μm≦MFD≦9.5μm ・・・(28)
モードフィールド径をこの範囲にすることによって、他の光ファイバ(例えばS-SMF)と接続した際の接続損失を低く抑えることができる。
光ファイバ30は、モードフィールド径をこの範囲とすることによって、ITU-T G.652の規定を満たす。
また、直径15mmの円筒形のマンドレルに10回巻回したときの波長1625nmにおける損失増加は1.0dB以下となることが好ましい。
内クラッド部22およびトレンチ部23は、例えばフッ素(F)等のドーパントを添加することによって屈折率を低くしたシリカガラスで構成することができる。
外クラッド部24は、例えば純粋シリカガラスで構成することができる。外クラッド部24は、ドーパント(例えばGe、Fなど)を添加することによって屈折率を調整してもよい。
例えば、MCVD法を採用する場合には、光ファイバ母材を次のようにして作製することができる。
前記ガラス堆積層の内側に、例えばフッ素(F)等のドーパントを含む原材料を用いて、内クラッド部22となるガラス堆積層を形成する。
トレンチ部23および内クラッド部22の屈折率はドーパントの添加量によって調整することができる。
ガラス堆積層が形成されたシリカガラス管は、透明化、中実化などの工程を経て光ファイバ母材とする。この光ファイバ母材を線引きすることによって、図20に示す光ファイバ30を得る。
CVD法は、ドーパントの添加によって屈折率分布を精度よく調整できる点で好ましい。
光ファイバ30の製造には、VAD法、OVD法も適用可能である。VAD法、OVD法には、生産性が高いという利点がある。
光ファイバ30は、この屈折率分布を採用することにより、他の光ファイバと接続した際の接続損失の抑制と曲げ損失の低減とを両立させた点に技術的意義がある。
また、トレンチ部23と外クラッド部24の屈折率の差が小さいため、製造方法に基づく制約が少ない。例えば、屈折率分布の調整に適しているとされるCVD法だけでなく、VAD法、OVD法を採用することもできる。
従って、光ファイバ30の製造が容易であり、製造コストを低く抑えることができる。
フッ素(F)等のドープに用いられる原料ガス(例えばSiF4)は高価であるため、ドーパント添加量の削減によって、原料コストを抑制し、製造コストを低く抑えることができる。
r1≦r2<r3<r4 ・・・(24)
図20および図21に示す光ファイバ30では、r1とr2とr3とは互いに異なる値であるが、本発明は、r1=r2、かつr2≠r3の場合を含む。
この光ファイバでは、r1とr2とが等しいため、クラッド25は、トレンチ部23と、トレンチ部23の外周側に形成された外クラッド部24のみからなる。
例えば、図20に示す光ファイバ30では、クラッド25は3つの層(内クラッド部、トレンチ部および外クラッド部)からなるが、クラッドは、これら以外の層を有していてもよい。
Claims (9)
- 波長1.31μmにおけるモードフィールド径MFD1.31が8.93μm以上9.4μm以下である、請求項1に記載の光ファイバ。
- コア全体における最大比屈折率差Δmaxと、コアの中心からの距離rが1μm以下の範囲内における最大比屈折率差Δcとが等しい、請求項1または2に記載の光ファイバ。
- コア全体における最大比屈折率差Δmaxが0.39%よりも大きい、請求項1~3のいずれか1項に記載の光ファイバ。
- コア全体における最大比屈折率差Δmaxが0.50%よりも小さい、請求項1~4のいずれか1項に記載の光ファイバ。
- ケーブルカットオフ波長λccが1260nm以下である、請求項1~5のいずれか1項に記載の光ファイバ。
- ケーブルカットオフ波長λccが1170nm以上である、請求項1~6のいずれか1項に記載の光ファイバ。
- 波長1.31μmにおけるモードフィールド径MFD1.31とケーブルカットオフ波長λccとの比、MFD1.31/λccで表されるMAC値が7.38以上7.7以下である、請求項1~7のいずれか1項に記載の光ファイバ。
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US11714227B2 (en) * | 2019-06-17 | 2023-08-01 | Sterlite Technologies Limited | Universal optical fiber |
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