JP2007127930A - Photonic bandgap fiber and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photonic bandgap fiber (PBGF) which can be easily manufactured, has excellent polarization holding property, has wide waveguide band width and has low transmission loss. <P>SOLUTION: A rectangular superlattice packed hole periodic structure formed by alternately stacking: a first hole array in which a large number of circular holes are arranged in a line with a first pitch Λ on a fiber cross-section face; and a second hole array in which a large number of circular holes are arranged via quartz parts with a second pitch Γ being twice of the first pitch and are located such that the holes and the holes of the first hole array form triangle lattices, in large numbers is disposed in a clad, and a hole core or a core consisting of one core on the fiber center and one or more layers of hole layers is disposed on the fiber center part, wherein fundamental vectors a<SB>1</SB>, a<SB>2</SB>representing periodicity of a lattice are respectively directed to x-axis and y-axis and respective lengths are 2Λ and √3Λ. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a photonic band gap fiber in which a large number of holes are provided in a quartz portion along the longitudinal direction of the fiber. The photonic bandgap fiber of the present invention is a polarization maintaining photonic bandgap fiber that exhibits absolute single polarization or maintains polarization. This fiber exhibits low nonlinearity, and is widely used in optical devices and optical parts such as polarizers, polarization separation elements, couplers, filters, and polarization controllers. A single polarization fiber is a fiber capable of propagating only a single polarization, and can eliminate polarization mode coupling and polarization mode dispersion, and is an ideal form of polarization maintaining fiber.

  A photonic bandgap fiber (hereinafter referred to as PBGF) uses a periodic structure of holes as a cladding, and confines light in the core using the photonic bandgap. Therefore, even if the core is air, it can be guided (see Non-Patent Document 1).

  However, even if the periodic structure of the holes provided in the cladding forms a band gap, the core mode in which the light is concentrated at the core center is coupled to the surface mode in which the light is concentrated on the quartz near the core edge, resulting in a large transmission loss. Therefore, there is a problem that optical waveguide cannot be obtained in the entire wavelength band of the band gap (see Non-Patent Document 2).

  The presence of the surface mode depends on the size of the core diameter. FIG. 1 is a diagram showing the dependency. In the conventional PBGF shown in FIG. 1, a large number of circular holes 11 are formed in a triangular lattice shape in the quartz portion 10 in the fiber cross section, and the hole in the center is a hole core 12. Hereinafter, such a hole structure in which a large number of circular holes 10 form a triangular lattice periodic structure at a constant pitch in the fiber cross section will be referred to as a “normal triangular lattice periodic structure”.

The “bulk mode” in FIG. 1 is a Γ point having a highest frequency in the lower pass band (band) of the band gap when the periodic structure of the holes constitutes a band gap (wavelength vector is in the propagation direction). This refers to the mode having only components.
In the PBGF having the structure shown in FIG. 1, it is known that a surface mode exists when the edge of the core 12 crosses the bulk mode, and no surface mode exists when the edge does not cross (see Non-Patent Document 3). .)

  2 and 3 are diagrams illustrating the positional relationship between the hole core 12 and the bulk mode in a conventional PBGF having a regular triangular lattice periodic structure. In the conventional PBGF shown in FIG. 2, a large number of circular holes 11 are provided in a triangular lattice shape in the quartz portion 10 which is a clad in the cross section of the fiber, and one central hole and six holes surrounding it are formed. A hole core 12 is provided which is formed by making a region including the hole into a hole. Further, in the conventional PBGF shown in FIG. 3, a large number of circular holes 11 are provided in a triangular lattice shape in the quartz portion 10 in the fiber cross section, and one hole in the center and 18 layers in two layers surrounding it are provided. It has a hole core 12 formed by making a region including holes a hole.

Furthermore, a PBGF having a hole core (air core) and having a polarization maintaining function has also been proposed (see, for example, Non-Patent Document 4).
This polarization maintaining type PBGF generally achieves polarization maintaining characteristics by making the core shape asymmetric.
RF Cregan, BJ Mangan, JC Knight, TA Birks, P. St. J. Russell, PJ Roberts, and DC Allan, “Single-mode photonic band gap guidance of light in air,” Science, vol. 285, no. 3 , pp. 1537-1539, 1999. JA West, CM Smith, NF Borrelli, DC Allan, and KW Koch, “Surface modes in air-core photonic band-gap fibers,” Opt. Express, vol. 12, no. 8, pp. 1485-1496, 2004. HK Kim, J. Shin, S. Fan, MJF Digonnet, and GS Kino, “Designing air-core photonic-bandgap fibers free of surface modes,” IEEE J. Quant. Electron., Vol. 40, no. 5, pp 551-556, 2004. X. Chen, M. -J. Li, N. Venkataraman, MT Gallagher, WA Wood, AM Crowley, JP Carberry, LA Zenteno, and KW Koch, “Highly birefringent hollow-core photonic gandgap fiber,” OFC2005, OTuI1, 2005 SG Johnson and JD Joannopoulos, “Block-iterative frequency-domain methods for Maxwell's equations in planewave basis,” Opt. Express, vol. 8, no. 3, pp. 173-190, 2001.

  However, when a regular triangular lattice periodic structure as shown in FIGS. 2 and 3 is used for the cladding, the edge of the hole core 12 crosses the region where the bulk mode 13 exists, so avoid the surface mode. Is difficult. As a result, the core mode light is coupled to the surface mode, resulting in a large transmission loss, an optical waveguide in the entire band gap wavelength band cannot be obtained, the waveguide bandwidth becomes narrow, and the transmission loss increases. There's a problem.

  Further, the conventional polarization maintaining type PBGF disclosed in Non-Patent Document 4 has a problem that it is difficult to use practically because the core cross-sectional shape is deformed.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a PBGF that is easy to manufacture and excellent in polarization maintaining characteristics.

In order to achieve the above object, the present invention provides a PBGF in which a large number of vacancies are provided in a quartz portion along a longitudinal direction of a fiber, and a plurality of circular vacancies are formed at a first pitch Λ in a fiber cross section. A plurality of circular holes are arranged through a quartz portion at a first hole array arranged in a line and at a second pitch Γ that is twice the first pitch, and the holes and the first holes are arranged. A rectangular superlattice-shaped hole periodic structure in which holes in one hole array and a plurality of second hole arrays arranged so as to form a triangular lattice are alternately stacked (however, the period of the lattice) The basic vectors a ₁ and a ₂ representing the characteristics are respectively oriented in the x-axis and y-axis directions, the lengths of which are 2Λ and √3Λ, respectively, in the cladding, and the hollow core in the center of the fiber PBGF characterized by the above is provided.

  In the PBGF, the diameter D of the hollow core is preferably in a range satisfying 0.5Λ ≦ D ≦ 2.5Λ.

  In the PBGF, the diameter d of the holes provided in the cladding is preferably in the range of 0.85Λ ≦ d ≦ Λ.

Further, the present invention is a PBGF in which a large number of holes are provided in a quartz portion along the longitudinal direction of the fiber, and a plurality of circular holes are arranged in a row at a first pitch Λ in the cross section of the fiber. A plurality of circular holes are arranged through a quartz portion at one hole array and a second pitch Γ that is twice the first pitch, and the holes and the first hole array A rectangular superlattice-shaped hole periodic structure in which a plurality of second hole arrays arranged so that the holes form a triangular lattice are alternately stacked (however, a basic vector a representing the periodicity of the lattice) ₁ and a ₂ are oriented in the x-axis and y-axis directions, respectively, and their lengths are 2Λ and √3Λ), respectively, and one hole or more surrounding the hole in the center of the fiber There is provided a PBGF characterized by having a core composed of a plurality of pore layers.

  In the PBGF, it is preferable that the core includes a total of seven holes including one hole at the center of the fiber and six layers surrounding the hole.

  In the PBGF, the diameter d of the holes provided in the cladding and the core is preferably in the range of 0.85Λ ≦ d ≦ Λ.

The PBGF of the present invention preferably has a birefringence exceeding 5 × 10 ⁻⁴ in a specific wavelength region.

  In the PBGF of the present invention, it is preferable that only a single polarized wave can propagate in a specific wavelength region.

  In the PBGF of the present invention, it is preferable that three or more layers of a periodic structure composed of cladding holes and a quartz portion are provided outside the core.

  The PBGF of the present invention preferably has an optical characteristic that preserves polarization within a range where the wavelength λ satisfies 0.7 ≦ Γ / λ ≦ 1.2.

  The PBGF of the present invention may have an optical characteristic in which polarization is preserved within a range where the wavelength λ satisfies 1.4 ≦ Γ / λ ≦ 2.0.

  In the PBGF of the present invention, the quartz portion is preferably composed of pure quartz or quartz to which one or more dopants selected from the group consisting of phosphorus, fluorine, and germanium are added.

  In the PBGF of the present invention, the pores may be filled with a material having a dielectric constant lower than that of quartz.

The present invention also includes a first capillary array in which a plurality of capillaries and quartz rods are arranged in a line, and a second hole array in which the capillaries and quartz rods are alternately arranged. Are alternately stacked, and the capillary arrangement in the cross section is a rectangular superlattice-shaped hole periodic structure (however, the basic vectors a ₁ and a ₂ representing the periodicity of the lattice are respectively directed in the x-axis and y-axis directions, The length is 2Λ, √3Λ), and a capillary bundle containing quartz rods is prepared by removing one central quartz rod and the surrounding capillary to form a hollow core region, There is provided a method for producing PBGF, characterized in that a capillary bundle containing quartz rods is heated and integrated to produce a fiber spinning preform, and then the fiber spinning preform is spun to obtain PBGF.

The present invention also includes a first capillary array in which a plurality of capillaries and quartz rods are arranged in a line, and a second hole array in which the capillaries and quartz rods are alternately arranged. Are alternately stacked, and the capillary arrangement in the cross section is a rectangular superlattice-shaped hole periodic structure (however, the basic vectors a ₁ and a ₂ representing the periodicity of the lattice are respectively directed in the x-axis and y-axis directions, The length is 2Λ, √3Λ.) A capillary bundle containing quartz rods is produced by replacing the single quartz rod in the center with a capillary to form a capillary core region. A method for producing PBGF is provided, wherein a bundle of bundles of capillaries is heated and integrated to produce a fiber spinning base material, and then the fiber spinning base material is spun to obtain PBGF.

  In the method for producing PBGF of the present invention, it is preferable that the capillary has an annular cross section, and the quartz rod has a circular cross section having the same outer diameter as the capillary.

  In the method for producing PBGF of the present invention, it is preferable to produce a fiber spinning base material by integrating the capillary bundle containing quartz rods while being inserted into a hole of a quartz tube.

  In the method for producing PBGF of the present invention, in the capillary bundle inserted into the hole of the quartz tube, only the capillary internal space is maintained at atmospheric pressure or higher, and the space other than the capillary internal space is in a reduced pressure state. It is preferable to perform the integration.

The PBGF of the present invention has a rectangular superlattice-shaped hole periodic structure in the cladding, and has a structure in which a hollow core or a core in which a large number of holes are arranged in a triangular lattice shape at the center of the fiber. Excellent polarization maintaining performance is obtained by anisotropy.
Further, the PBGF of the present invention can obtain optical characteristics in which only the core mode exists without generating the surface mode, can widen the waveguide bandwidth, and can reduce the transmission loss.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 4 is a diagram showing a first embodiment of the PBGF of the present invention. In FIG. 4, 20A is PBGF, 21 is a hole, 22 is a quartz part, 23A is a hole core (air core), 24 is a cladding, 25 is a first hole array, and 26 is a second hole array. is there.

  In the PBGF 20A of the present embodiment, a large number of holes 21 are provided in the quartz portion 22 along the longitudinal direction of the fiber, and a plurality of circular holes 21 are arranged in a row at a first pitch Λ in the fiber cross section. A large number of circular holes 21 are arranged through a quartz portion 22 at one hole row 25 and a second pitch Γ that is twice the first pitch, and the holes 21 and the first pitch The cladding 24 has a rectangular superlattice-shaped hole periodic structure in which a plurality of second hole arrays 26 arranged so that the holes 21 of the hole array 25 form a triangular lattice are alternately stacked. And it has the structure which has the hole core 23A in the fiber center part.

FIG. 5 is a view showing a unit cell having a rectangular superlattice-shaped hole periodic structure provided in the clad 24. In this rectangular superlattice-like hole periodic structure used in the present invention, basic vectors a ₁ and a ₂ representing the periodicity of the lattice are directed in the x-axis direction and the y-axis direction, respectively, and their lengths are 2Λ and √3Λ. (= 3 ^1/2 · Λ).

By using this rectangular superlattice-shaped hole periodic structure for the clad 24, the surface mode can be avoided and a wide transmission band can be realized.
Further, as shown in the figure, this superlattice has a different structure in the x and y directions, and has different band gaps for the polarization in each direction. Accordingly, when this rectangular superlattice-shaped hole periodic structure is used for the clad 24, the polarization in the x and y directions feels different band gaps even in the case of a normal hole core (air core). The ability to hold (polarization holding characteristic) or single polarization characteristic is exhibited.

  The hole core 23A (air core) of the PBGF 20A according to the present embodiment has a hole including a single quartz portion 22 at the center of the fiber and six holes 21 surrounding it in the rectangular superlattice described above. It is formed by doing. This hole core 23A combines a quartz rod and a capillary to form a capillary bundle containing a quartz rod having a rectangular superlattice-like hole periodic structure, and has one quartz rod in the center and six pieces surrounding it. It can be formed by removing the capillary.

  The size of the hole core 23A is not limited to this example, and can be increased or decreased. In the PBGF 20A of the present embodiment, the diameter D of the hole core 23A is preferably in a range satisfying 0.5Λ ≦ D ≦ 2.5Λ.

  FIG. 6 is a diagram showing a second embodiment of the PBGF of the present invention. The PBGF 20B of the present embodiment has a rectangular superlattice-shaped hole periodic structure clad 24 like the PBGF 20A according to the first embodiment. However, instead of the hole core 23A, one hole at the center of the fiber is used. The structure is characterized by having a core 23B (capillary core) made up of a total of seven holes 21 including six holes and one layer surrounding the hole.

  In the PBGF 20B of the second embodiment, the core 23B combines a quartz rod and a capillary to form a capillary bundle containing quartz rods having a rectangular superlattice-shaped hole periodic structure. It can be formed by removing six capillaries surrounding the.

  In each of the embodiments described above, the diameter d of the holes 21 of the cladding 24 or the holes 24 of the cladding 24 and the core 23B is preferably in the range of 0.85Λ ≦ d ≦ Λ. If the hole diameter d is in the above range, a rectangular superlattice-shaped hole periodic structure having substantially uniform holes 21 over the entire fiber can be constructed, and good optical characteristics can be obtained.

The PBGFs 20A and 20B of the present invention preferably have a birefringence B exceeding 5 × 10 ⁻⁴ in a specific wavelength region (use wavelength region). By having birefringence exceeding 5 × 10 ⁻⁴ , this PBGF can be used as a polarization-maintaining fiber. Using this PBGF, for example, a fiber polarizer, a polarization separation element, a coupler, a filter, a polarization, Various optical components such as a controller can be manufactured.

  Further, the PBGFs 20A and 20B of the present invention can constitute a single polarization fiber that can propagate only a single polarization in a specific wavelength region. A single polarization fiber is a fiber capable of propagating only a single polarization, and can eliminate polarization mode coupling and polarization mode dispersion, and is an ideal form of polarization maintaining fiber.

  In the PBGFs 20A and 20B of the present invention, it is preferable that three or more layers of the periodic structure including the holes 21 and the quartz portions 22 of the cladding 24 are provided outside the hole core 23A or the capillary core 23B. If the number of layers is 2 or less, light confinement becomes insufficient, loss may increase, and sufficient polarization maintaining characteristics cannot be obtained.

  The PBGFs 20A and 20B of the present invention preferably have an optical characteristic that preserves the polarization within a range where the wavelength λ satisfies 0.7 ≦ Γ / λ ≦ 1.2. If Γ / λ is less than 0.7, no band gap exists and light cannot be transmitted. If Γ / λ exceeds 1.2, no band gap exists and light cannot be transmitted.

  Further, when the PBGFs 20A and 20B operate in a high-order band gap, they may have optical characteristics that preserve the polarization within a range where the wavelength λ satisfies 1.4 ≦ Γ / λ ≦ 2.0. . If Γ / λ is less than 1.4, it is outside the high-order band gap and does not operate, and if Γ / λ exceeds 2.0, it is out of the high-order band gap and does not operate.

In the PBGFs 20A and 20B of the present invention, the quartz portion 22 has one or more dopants selected from the group consisting of pure quartz (SiO ₂ ) or phosphorus (P), fluorine (F), and germanium (Ge). It is preferable that it is composed of added quartz.

In the PBGFs 20A and 20B of the present invention, the air holes 21 may be filled with a material having a dielectric constant lower than that of quartz (SiO ₂ ). Examples of the material having a lower dielectric constant than quartz (SiO ₂ ) include transparent plastic and oil.

The PBGFs 20A and 20B of the present invention have a rectangular superlattice-like hole periodic structure in the cladding 24, and a core 23B in which a hole core 20A or a large number of holes are arranged in a triangular lattice shape at the center of the fiber. Due to the configuration, excellent polarization maintaining performance can be obtained by the anisotropy of the clad 24.
Further, the PBGFs 20A and 20B of the present invention can obtain optical characteristics in which only the core mode exists without generating the surface mode, can widen the waveguide bandwidth, and can reduce the transmission loss.

  Next, an example of the manufacturing method of PBGF of this invention is demonstrated. In this example, as shown in FIG. 6, the cladding 24 has a rectangular superlattice-like hole periodic structure, and a total of seven holes including one hole in the center of the fiber and six layers surrounding it. The case where PBGF20B provided with the core 23B (capillary core) which consists of the hole 21 is manufactured is demonstrated.

In this manufacturing method, first, a first capillary array in which a large number of capillaries are arranged in a row, and a second cavity in which the capillaries and quartz rods are alternately arranged are made of quartz capillaries and quartz rods. The columns are alternately overlapped and the cross-sectional capillary arrangement is a rectangular superlattice-shaped hole periodic structure (however, the basic vectors a ₁ and a ₂ representing the periodicity of the lattice are the short axis direction (x-axis direction) and Quartz that is combined in the long axis direction (y-axis direction and the length is 2Λ, √3Λ), and the central one quartz rod is replaced with a capillary to form a capillary core region A capillary bundle with rods is prepared. It is preferable that the capillary used in the manufacturing method has an annular cross section, and the quartz rod has a circular cross section having the same outer diameter as the capillary.

  In the method for producing PBGF of the present invention, the method for forming the core region is not limited to the above example, and can be appropriately changed according to the core structure of the PBGF to be produced. For example, when the PBGF 20A shown in FIG. 4 is manufactured, the hole core region is formed by removing one quartz rod at the center of the fiber and six capillaries surrounding it.

  Next, the fiber bundle is produced by heating and integrating the quartz rod-containing capillary bundle. This heat integration step can be carried out using the same apparatus and method as the heat integration in the conventional method for producing PBGF using a capillary bundle.

  Further, it is desirable that the capillary bundle containing a quartz rod is integrated into a fiber spinning preform while being inserted into a hole of a quartz tube. In this way, when integrating a bundle of capillary rods containing quartz rods while being inserted into a hole of a quartz tube, it becomes possible to individually adjust the pressure and gas composition in the space around the capillary and the internal space of the capillary. The gap between the capillaries or between the capillaries and the quartz rod can be filled while appropriately adjusting the pressure inside the capillaries. By appropriately adjusting the pressure in the capillary internal space during the integration, the cross-sectional shape of the capillary holes can be maintained in a substantially circular shape.

  When a capillary bundle containing quartz rods is inserted into a hole of a quartz tube for integration, only the capillary inner space of the inserted capillary bundle containing quartz rods is maintained at atmospheric pressure or higher, and the capillary inner space is maintained. It is preferable to perform the integration by setting a space portion other than that in a reduced pressure state.

Next, the base material for fiber spinning produced as described above is spun to obtain PBGF 20B shown in FIG.
In this manufacturing method, the capillary core can be configured by replacing one quartz rod at the center of the fiber with a capillary, so that a fiber that forms an air core with one large hole like a conventional air core fiber is used. In comparison, since the holes of the entire fiber have the same shape, it is much easier to manufacture.

[Example 1]
The band structure of the rectangular superlattice shown in FIG. 7 is shown in FIG. However, in the periodic structure, the hole diameter d is equal to the hole pitch Λ, and the refractive index n of quartz is 1.45. In FIG. 7, the black portion represents the quartz portion 22 and the white portion represents the hole 21. The band structure was calculated using the plane wave expansion method (see Non-Patent Document 5). In FIG. 8, β represents the wave number in the propagation direction (direction perpendicular to the periodic structure), Γ = 2Λ, ω represents the angular frequency, and c represents the speed of light. A light line represents a dispersion curve when light propagates in a vacuum medium, and a region surrounded by a band represents a region where light cannot propagate in any direction within the periodic structure cross section, that is, a band gap. When this periodic structure is used for the cladding of the fiber and a hole is used for the core, the band in which light can be guided to the core of the fiber is adjacent to the light line and is a band gap existing above the light line. In this case, the first waveguide region exists in the range of Γ / λ (= ωΓ / 2πc) of 0.83 to 1.10, and the second waveguide region exists in the range of 1.63 to 1.78. Here, λ represents a wavelength.

  Propagation mode dispersion was calculated for a PBGF 20A composed of a clad 24 having a rectangular superlattice structure of d / Λ = 1 as shown in FIG. 9 and a hole core 23A provided at the center thereof. FIG. 10 shows the dispersion within the first band gap. As shown in the figure, the core mode exists in the band gap of Γ / λ = 0.88 to 1.08. This mode is a single polarization and does not include a degenerate mode. There are no other modes and polarizations. That is, only an absolute single polarization can propagate.

  FIG. 11 shows a typical power distribution in the core mode at that time. FIG. 12 is a diagram showing the dielectric constant distribution of the fiber on the same scale. As shown in the figure, the power of the core mode is distributed in the vertical direction. This is because the lateral lattice constant is short and the lateral confinement effect is strong.

  FIG. 13 is a diagram illustrating dispersion in the second band gap in the PBGF 20A of the present embodiment. As shown in the figure, only the core mode exists within the band gap of Γ / λ = 1.62 to 1.78. However, also in this case, the core mode is a single polarization and does not include the degenerate mode.

  FIG. 14 is a diagram illustrating the power distribution of the core mode within the second band gap in the PBGF 20A of the present embodiment.

[Example 2]
A core 23B (capillary) comprising a clad 24 having a rectangular superlattice structure with d / Λ = 1 as shown in FIG. 15, a central hole and six holes (total of seven holes) surrounding it. The dispersion of the core mode was calculated for PBGF20B consisting of (core). FIG. 16 shows the dispersion within the first band gap. As shown in the figure, a propagation mode exists in the band gap of Γ / λ = 0.83 to 1.09. This mode is a single polarization and does not include a degenerate mode. There are no other propagation modes and polarizations. That is, only an absolute single polarization can propagate.

  FIG. 17 is a diagram showing a typical power distribution in the mode at that time. FIG. 18 is a diagram showing the dielectric constant distribution of the fiber on the same scale. As illustrated, the power of the propagation mode is distributed in the vertical direction. This is because the lateral lattice constant is short and the lateral confinement effect is strong.

FIG. 19 is a diagram illustrating dispersion within the second band gap in the PBGF 20B of the present embodiment. As shown, mode 1 exists in the band gap of Γ / λ = 1.62 to 1.73, and mode 2 exists in the band gap of Γ / λ = 1.60 to 1.75. However, also in this case, each mode is a single polarization and does not include a degenerate mode. In this case, the birefringence B = | β ₁ −β ₂ | / β ₀ is 5.0 × 10 ^{−3 to} 7.1 × 10 ⁻³ . Here, β ₁ and β ₂ represent the propagation constants of mode 1 and mode 2, respectively, and β ₀ = ω / c (ω represents angular frequency and c represents high speed, respectively).

  FIG. 20 is a diagram illustrating the power distribution of mode 1 in the second band gap in the PBGF 20B of the present embodiment. FIG. 21 is a diagram showing the power distribution of mode 2 in the second band gap. As shown in the figure, the power of mode 1 is elongated and distributed in the vertical direction, while mode 2 is more widely distributed in the horizontal direction.

It is sectional drawing which shows the relationship between the core diameter and surface mode in PBGF which has a periodic structure of a normal triangular lattice. It is sectional drawing which shows the relationship between the void | hole core and bulk mode in PBGF which has the periodic structure of a normal triangular lattice, and a void | hole core. It is sectional drawing which shows the relationship between the void | hole core and bulk mode in another PBGF which has the periodic structure of a normal triangular lattice, and a void | hole core. It is sectional drawing which shows 1st Embodiment of PBGF of this invention. It is sectional drawing which shows the unit cell of the clad rectangular superlattice used for PBGF of this invention. It is sectional drawing which shows 2nd Embodiment of PBGF of this invention. 2 is a cross-sectional view of a rectangular superlattice of d / Λ = 1 manufactured in Example 1. FIG. 3 is a diagram illustrating a band structure of a rectangular superlattice of d / Λ = 1 in Example 1. FIG. FIG. 3 is a cross-sectional view of a PBGF having a rectangular superlattice of d / Λ = 1 and a hole core in the central part manufactured in Example 1. FIG. 4 is a diagram showing dispersion within the first band gap of the PBGF of Example 1. FIG. 6 is a diagram showing a power distribution of a core mode within a first band gap in the PBGF of Example 1. It is a figure which shows the dielectric constant distribution of PBGF of Example 1. FIG. FIG. 3 is a diagram illustrating dispersion within a second band gap of the PBGF of Example 1. FIG. 6 is a diagram illustrating a power distribution of a core mode within a second band gap in the PBGF of Example 1. FIG. 5 is a cross-sectional view of a PBGF having a rectangular superlattice of d / Λ = 1 manufactured in Example 2 and a capillary core at the center. FIG. 6 is a diagram showing dispersion within the first band gap of the PBGF of Example 2. It is a figure which shows power distribution of the propagation mode in the 1st band gap in PBGF of Example 2. FIG. It is a figure which shows the dielectric constant distribution of PBGF of Example 2. FIG. 6 is a diagram showing dispersion within the second band gap of the PBGF of Example 2. It is a figure which shows the power distribution of the mode 1 in the 2nd band gap of PBGF of Example 2. FIG. It is a figure which shows the power distribution of the mode 2 in the 2nd band gap of PBGF of Example 2. FIG.

Explanation of symbols

20A, 20B ... PBGF, 21 ... hole, 22 ... quartz portion, 23A ... hole core, 23B ... core, 24 ... cladding, 25 ... first hole array, 26 ... second hole array.

Claims (18)

A photonic bandgap fiber in which a large number of holes are provided in the quartz portion along the longitudinal direction of the fiber,
A first hole array in which a large number of circular holes are arranged in a line at a first pitch Λ in the cross section of the fiber, and a number of circular holes at a second pitch Γ that is twice the first pitch. The holes are arranged through the quartz portion, and a plurality of second hole arrays in which the holes and the holes of the first hole array are arranged so as to form a triangular lattice are alternately stacked. A rectangular superlattice-like hole periodic structure (however, the basic vectors a ₁ and a ₂ representing the periodicity of the lattice are respectively directed in the x-axis and y-axis directions, and the lengths thereof are 2Λ and √3Λ, respectively. ) In the cladding and a hole core at the center of the fiber.   2. The photonic bandgap fiber according to claim 1, wherein the hole core has a diameter D in a range satisfying 0.5Λ ≦ D ≦ 2.5Λ.   3. The photonic bandgap fiber according to claim 1, wherein a diameter d of a hole provided in the clad is within a range of 0.85Λ ≦ d ≦ Λ. A photonic bandgap fiber in which a large number of holes are provided in the quartz portion along the longitudinal direction of the fiber,
A first hole array in which a large number of circular holes are arranged in a line at a first pitch Λ in the cross section of the fiber, and a number of circular holes at a second pitch Γ that is twice the first pitch. The holes are arranged through the quartz portion, and a plurality of second hole arrays in which the holes and the holes of the first hole array are arranged so as to form a triangular lattice are alternately stacked. A rectangular superlattice-like hole periodic structure (however, the basic vectors a ₁ and a ₂ representing the periodicity of the lattice are respectively directed in the x-axis and y-axis directions, and the lengths thereof are 2Λ and √3Λ, respectively. ) In the cladding, and a core composed of one hole in the center of the fiber and one or more hole layers surrounding the hole.   5. The photonic bandgap fiber according to claim 4, wherein the core is composed of a total of seven holes including one hole in the center of the fiber and six layers surrounding the hole.   6. The photonic bandgap fiber according to claim 4 or 5, wherein a diameter d of a hole provided in the clad and the core is in a range of 0.85Λ ≦ d ≦ Λ. The photonic bandgap fiber according to any one of claims 1 to 6, wherein the photonic bandgap fiber has birefringence exceeding 5 x ^10-4 in a specific wavelength region.   8. The photonic bandgap fiber according to claim 1, wherein only a single polarized wave can propagate in a specific wavelength region.   The photonic bandgap fiber according to any one of claims 1 to 8, wherein three or more layers of a periodic structure composed of holes in the cladding and a quartz portion are provided outside the core.   The photonic bandgap fiber according to any one of claims 1 to 9, wherein the photonic bandgap fiber has an optical characteristic that preserves polarization within a range where the wavelength λ satisfies 0.7 ≦ Γ / λ ≦ 1.2. .   The photonic bandgap fiber according to any one of claims 1 to 9, wherein the photonic bandgap fiber has an optical characteristic in which polarization is preserved within a range where the wavelength λ satisfies 1.4 ≦ Γ / λ ≦ 2.0. .   The quartz portion is made of pure quartz or quartz to which one or more dopants selected from the group consisting of phosphorus, fluorine, and germanium are added. A photonic bandgap fiber as described in 1.   The photonic bandgap fiber according to any one of claims 1 to 12, wherein the air holes are filled with a material having a dielectric constant lower than that of quartz. A first capillary array in which a large number of capillaries are arranged in a row and a second pore array in which the capillaries and quartz rods are alternately arranged are alternately overlapped with each other. Capillary periodic structure in which the cross-sectional capillary arrangement is a rectangular superlattice (however, the basic vectors a ₁ and a ₂ representing the periodicity of the lattice are oriented in the x-axis and y-axis directions, respectively, the lengths of which are 2Λ, √3Λ)), and a capillary bundle containing quartz rods is prepared by removing one central quartz rod and the surrounding capillary to form a hollow core region, and then the capillary containing the quartz rod A bundle of fibers is heated and integrated to produce a fiber spinning base material, and then the fiber spinning base material is spun to obtain a photonic band gap fiber. Fiber manufacturing method. A first capillary array in which a large number of capillaries are arranged in a row, and a second pore array in which the capillaries and quartz rods are alternately arranged overlap each other. Capillary periodic structure in which the cross-sectional capillary arrangement is a rectangular superlattice (however, the basic vectors a ₁ and a ₂ representing the periodicity of the lattice are oriented in the x-axis and y-axis directions, respectively, the lengths of which are 2Λ, √3Λ)), and a single quartz rod in the center is replaced with a capillary to produce a capillary bundle containing quartz rods as a capillary core region, and then the capillary bundle containing quartz rods is heated. A photonic band gap fiber comprising: a fiber spinning base material being integrated to produce a photonic band gap fiber by spinning the fiber spinning base material; The manufacturing method of ba.   The method for producing a photonic bandgap fiber according to claim 14 or 15, wherein the capillary has an annular cross section, and the quartz rod has a circular cross section having the same outer diameter as the capillary.   The photonic bandgap fiber according to any one of claims 14 to 16, wherein the fiber bundle is manufactured by integrating the capillary bundle containing the quartz rod while being inserted into a hole of a quartz tube. Production method. Of the bundle of capillaries inserted into the hole of the quartz tube, only the internal space of the capillary is held at atmospheric pressure or higher, and the space portion other than the internal space of the capillary is decompressed to perform the integration. The method for producing a photonic bandgap fiber according to claim 17.

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