JP2007041166A - Photonic band gap fiber and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photonic band gap fiber (PBGF) having a broad waveguide band and a low transmission loss. <P>SOLUTION: A lot of first pore lines 22, in which a lot of hexagonal pores 21 are aligned with a first pitch Λ on a line on the cross section of a fiber via a partition, and a lot of second pore lines 23, in which a lot of hexagonal pores are aligned with a second pitch Γ which is twice the first pitch via a hexagonal quartz part 20 and the aforesaid pores and the pores in the first pore lines are arranged to form triangle lattices, are alternately laminated. The PBGF is characterized in that the PBGF has a core in which a clad has an expanded triangular lattice pore periodic structure in which the length ω<SB>r</SB>between two opposing sides of the quartz part is substantially equal to the first pitch Λ and pore cores or a lot of hexagonal pores are aligned in triangles. <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 can suppress the surface mode peculiar to a normal photonic bandgap fiber and can widen the transmission band of the fiber. It can be used for optical transmission in the optical region and far infrared region, fiber laser light transmission, and the like.

  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.
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. 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.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a PBGF having a wide waveguide bandwidth and low transmission loss.

In order to achieve the above object, the present invention provides a PBGF in which a plurality of holes are provided in a quartz portion along the longitudinal direction of the fiber, and a plurality of hexagonal quartz portions having a constant pitch Γ in the cross section of the fiber. Arranged in a triangular lattice pattern, and a gap is formed between the quartz parts, and a periodic structure in which the length ω _r between two opposing sides of the quartz part is equal to the half length Λ of the pitch Γ is used as the cladding. The PBGF is characterized by having a hollow core or a core in which a large number of hexagonal holes are arranged in a triangular lattice shape.

The present invention also provides a PBGF in which a large number of holes are provided in a quartz portion along the longitudinal direction of the fiber, and a large number of hexagonal holes are arranged in a row through a partition wall at a first pitch Λ in the cross section of the fiber. A plurality of hexagonal holes are arranged through a hexagonal quartz portion at a first hole array arranged in a row and at a second pitch Γ that is twice the first pitch. And a plurality of second hole arrays in which the holes of the first hole array are arranged so as to form a triangular lattice, and a length ω between two opposing sides of the quartz portion is overlapped. _a core having an extended triangular lattice-shaped hole periodic structure in which _r and the first pitch Λ are substantially equal in the cladding, and a hole core or a plurality of hexagonal holes arranged in a triangular lattice shape A PBGF characterized by comprising:

In the PBGF, the thickness ω _b of the quartz partition wall surrounding the hole is preferably in the range of 0.005Λ ≦ ω _b ≦ 0.2Λ.

  In the PBGF of the present invention, the core diameter D is preferably in a relation of 0.7Λ ≦ D ≦ 3.3Λ with respect to the pitch Λ.

  In the PBGF of the present invention, the diameter D of the core may have a relationship of 4.7Λ ≦ D ≦ 7.3Λ with respect to the pitch Λ.

  In the PBGF of the present invention, the diameter D of the core may have a relationship of 8.7Λ ≦ D ≦ 11.3Λ with respect to the pitch Λ.

  In the PBGF of the present invention, it is preferable that three or more layers of the extended triangular lattice-shaped hole periodic structure provided in the cladding are provided outside the core.

  The PBGF of the present invention preferably has a core mode in which 60% or more of the propagation power is concentrated in the hole core region, and has an optical characteristic that substantially does not have a surface mode.

  The PBGF of the present invention preferably has an optical characteristic in which only a single core mode (however, all modes that degenerate have a mode number of 1) exist.

  The PBGF of the present invention preferably has an optical characteristic in which the core mode exists within a range where the wavelength λ satisfies 0.6 ≦ Γ / λ ≦ 1.5.

  The PBGF of the present invention may have an optical characteristic in which the core mode exists within a range where the wavelength λ satisfies 1.4 ≦ Γ / λ ≦ 2.3.

  The PBGF of the present invention may have an optical characteristic in which a core mode exists within a range where the wavelength λ satisfies 2.2 ≦ Γ / λ ≦ 3.2.

  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 combined so that the capillary arrangement of the cross section becomes an expanded triangular lattice, and the central quartz rod or the central quartz rod and the surrounding capillary and quartz rod are eliminated to form a hole core region, or quartz Capillary bundles with quartz rods are made by replacing the rods with capillaries to form capillary core regions, and then the capillary bundles with quartz rods are heated and integrated while maintaining the pressure in the capillary inner space higher than the pressure in the space around the capillaries. To produce a fiber spinning base material, and then spin the fiber spinning base material to obtain the PBGF according to the present invention. To provide a process for the preparation of that 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 manufacturing method described above, in the bundle of capillaries inserted into the holes of the quartz tube, only the internal space of the capillaries is maintained at atmospheric pressure or higher, and the space portion other than the internal space of the capillaries is decompressed to perform the integration. Preferably it is done.

  In the method for producing PBGF of the present invention, it is preferable to form a hole core region by eliminating one quartz rod at the center of the cross section of the capillary bundle containing the quartz rods.

  In the method for producing PBGF according to the present invention, the hollow core region is formed by eliminating one quartz rod at the center of the cross section of the capillary bundle containing the quartz rods and one to five layers of capillaries and quartz rods surrounding the quartz rod. It may be formed.

  In the method for producing PBGF of the present invention, a capillary core region may be formed by replacing one quartz rod at the center of the cross section of the capillary bundle containing the quartz rods with a capillary.

  In the method for producing PBGF of the present invention, the capillary core region may be formed by replacing one quartz rod at the center of the cross section of the capillary bundle with quartz rods and the surrounding quartz rod with a capillary.

  In the method for producing PBGF of the present invention, the capillary bundle with quartz rods is provided such that an extended triangular lattice-shaped hole periodic structure surrounding the core region has three or more layers of quartz rods radially outward. It is preferred that

Since the PBGF of the present invention has an extended triangular lattice-like hole periodic structure in the cladding, the core edge can constitute a hole core or a capillary core without traversing the bulk mode, and only the core mode does not generate a surface mode. Can be obtained, the waveguide bandwidth can be widened, and the transmission loss can be reduced.
The PBGF production method of the present invention has an expanded triangular lattice-like hole periodic structure in the same manner as the method using the conventional capillary except that a part of the capillary is replaced with a quartz rod and combined. Since PBGF can be manufactured, PBGF having optical properties superior to those of conventional PBGF can be manufactured easily and inexpensively by the same method as that of conventional PBGF.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 4 is a diagram showing an example of an extended triangular lattice (ETL) extended hole periodic structure used for the cladding portion of the PBGF of the present invention. In this figure, reference numeral 20 denotes a quartz portion, and 21 denotes a quartz portion. Hexagonal holes, 22 is a first hole array, and 23 is a second hole array.

  This extended triangular lattice-shaped hole periodic structure includes a first hole array 22 in which a large number of hexagonal holes 21 are arranged in a row with partition walls 25 at a first pitch Λ in the fiber cross section; A large number of hexagonal holes 21 are arranged through a hexagonal quartz portion 20 at a second pitch Γ (Γ = 2Λ) which is twice the first pitch Λ, and the holes 21 and the first pitch Λ are arranged. A periodic structure (hereinafter referred to as hexagonal-hole-extended-triangular-lattice or six-hole-hole-triangular-lattice) It is written as a square-hole-extended triangular lattice structure.)

FIG. 5 is a diagram showing a unit cell structure of the hexagonal hole expanded triangular lattice. In this unit cell, the distance (first pitch) between the centers of adjacent air holes 21 is Λ, and the length ω _r between two opposing sides of the quartz portion 20 is equal to the first pitch Λ ( ω _r = Λ). Further, a ₁ and a ₂ , which are basic vectors representing the periodicity of the lattice, are inclined at 30 degrees and −30 degrees with respect to the x axis, respectively, and the second pitch Γ is 2Λ.

  When this hexagonal hole expanded triangular lattice structure is used for the cladding of PBGF, if a core region is appropriately designed, a hole layer can be provided between the core and the cladding. As a result, the surface mode can be avoided and a wide transmission band can be realized (see Non-Patent Document 3).

  Further, in the present invention, a hexagonal hole expanded triangular lattice structure in which the hexagonal holes 21 and the hexagonal quartz portion 20 are combined is employed, so that the circular holes 10 as shown in FIG. 6 are used. Optical characteristics different from those of the extended triangular lattice-like hole periodic structure (hereinafter referred to as a circular hole extended triangular lattice structure) can be obtained.

  FIG. 6 is a diagram illustrating a circular hole expanded triangular lattice structure, and FIG. 7 is a graph showing a band structure of this circular hole expanded triangular lattice structure. The periodic structure shown in FIG. 6 has a structure in which the hole diameter d is equal to the first pitch Λ and the quartz portion 10 is the smallest in the circular hole expanded triangular lattice structure. In FIG. 6, the black portion is the quartz portion 10, and the white circle is the hole 11. 7 was calculated using the plane wave expansion method described in Non-Patent Document 4. In FIG. 7, β represents the wave number in the propagation direction (direction perpendicular to the periodic structure), Γ = 2Λ represents the lattice constant of the extended triangular lattice, 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 clad of the fiber and a hole is used for the core, a region where 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 0.77 to 1.10, and the second waveguide region exists in the range of 1.54 to 1.80. Here, λ represents a wavelength.

On the other hand, FIG. 9 shows a band structure of the hexagonal hole expanded triangular lattice structure according to the present invention shown in FIG. In the hexagonal hole expanded triangular lattice structure shown in FIG. 8, a large number of hexagonal quartz portions 20 are arranged in a triangular lattice shape at a constant pitch Γ in the cross section of the fiber, and voids 21 are formed between the quartz portions 20. The length ω _r between two opposing sides of the quartz portion is equal to the half length Λ of the pitch Γ. In other words, the hexagonal hole expanded triangular lattice structure shown in FIG. 8 is a hexagonal shape when the thickness ω _b = 0 of the partition wall 25 in the hexagonal hole expanded triangular lattice structure shown in FIGS. 4 and 5. The hole expansion triangular lattice structure is illustrated. However, in practice, in order to hold the quartz portion 20, there may be intermittent partition walls, coupling portions, etc., not shown.

  In this case, as shown in FIG. 9, the first waveguide region in the range of Γ / λ of 0.82 to 1.30, the second waveguide region in the range of 1.58 to 2.13, and 2.38 to 3 It can be seen that there is a third waveguiding region at .00 and there is a wide band gap as compared to the circular hole extended triangular lattice structure shown in FIG.

FIG. 10 is a diagram illustrating a hexagonal hole expanded triangular lattice structure in which the ratio of the thickness ω _b of the partition wall 25 to the first pitch Λ is 0.06 (ω _b /Λ=0.06). FIG. 11 is a graph showing the band structure. In this case, the first waveguide region exists in the range of Γ / λ of 0.79 to 1.13, the second waveguide region exists in the range of 1.60 to 1.83, and d / Λ = 1 in FIG. It can be seen that there is a band gap equivalent to the circular hole expanded triangular lattice structure shown.

The PBGF of the present invention has the above-described hexagonal hole expanded triangular lattice structure in the cladding, and has a core 24 in which a hollow core or a large number of hexagonal holes are arranged in a triangular lattice at the center. Yes. In the PBGF of the present invention, the material of the quartz portion 20 other than the holes can be the same throughout the fiber. For example, pure quartz (SiO ₂ ) or the like is preferably used, but fluorine, germanium oxide, etc. Quartz glass to which a dopant for adjusting the refractive index is added can also be used.

  In a preferred embodiment of the present invention, the diameter D of the core 24 has a relationship of 0.7Λ ≦ D ≦ 3.3Λ with respect to the pitch Λ, a relationship of 4.7Λ ≦ D ≦ 7.3Λ, or 8.7Λ ≦ It is desirable to have a relationship of D ≦ 11.3Λ. By setting the diameter D of the core 24 within the above range, PBGF having no surface mode can be provided.

Further, as shown in FIG. 10, when there is a quartz partition wall 25 surrounding the hole, the thickness ω _b of the partition wall 25 is 0.005Λ ≦ ω _b ≦ 0.2Λ with respect to the first pitch Λ. A range is preferable. If the thickness of the partition wall 25 is less than the above range, it is difficult to maintain the pore structure. If the thickness of the partition wall 25 exceeds the above range, the band gap becomes narrower.

  In addition, the hexagonal hole expanded triangular lattice structure provided in the cladding is preferably provided in three or more layers outside the core 24. If the number of hexagonal hole-extended triangular lattices provided in the clad is two or less, light confinement may be insufficient and loss may increase.

  The PBGF of the present invention is a core mode in which 60% or more, preferably 70% or more, more preferably 80% or more of the propagation power is concentrated in the core region, and has an optical characteristic that the surface mode does not substantially exist. It is preferable. If the ratio of the core mode is less than 60%, light is transmitted into the quartz, which is not preferable.

  The PBGF of the present invention preferably has an optical characteristic in which the core mode exists within a range where the wavelength λ satisfies 0.6 ≦ Γ / λ ≦ 1.5. If Γ / λ is less than 0.6, no band gap exists and light cannot be transmitted. If Γ / λ exceeds 1.5, no band gap exists and light cannot be transmitted.

When PBGF operates in a high-order band gap, the Γ / λ is preferably in the range of 1.4 ≦ Γ / λ ≦ 2.3. 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 2.3, it is out of the high-order band gap and does not operate.
Furthermore, it may have an optical characteristic in which the core mode exists within a range where the wavelength λ satisfies 2.2 ≦ Γ / λ ≦ 3.2.

Next, an example of the manufacturing method of PBGF of this invention is demonstrated. In this example, the PBGF shown in FIG. 12 is provided with a core 24 (capillary core) having the hexagonal hole expanded triangular lattice structure shown in FIG. 10 in the clad and the central quartz portion 20 replaced with the hole 21. The case of manufacturing will be described.
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. A capillary bundle containing quartz rods is produced by combining the columns so that the columns are alternately overlapped so that the capillary arrangement in the cross section is an expanded triangular lattice, and the central quartz rod is replaced with a capillary. 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 shown in FIG. 18 is manufactured, a capillary core region having a large diameter D is formed by substituting the quartz rod at the center of the hexagonal hole expanded triangular lattice structure and the six quartz rods surrounding it with a capillary. is doing. Further, when forming a hole core, the quartz rod at the center of the hexagonal hole expanded triangular lattice structure is eliminated, or the center quartz rod and the capillaries and quartz rods of 1 to 5 layers surrounding it are surrounded. The void core region is formed by eliminating

  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 pressure in the internal space of the capillary can be kept higher than the pressure in the space around the capillary, and the gap between the capillaries or between the capillaries and the quartz rod can be filled. By increasing the pressure in the capillary internal space during this integration, the cross-sectional shape of the capillary holes can be made closer to a hexagon.

  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 PBGF shown in FIG. 12 is obtained by spinning the preform for fiber spinning produced as described above. This spinning process is preferably performed in a state where the pressure in the capillary internal space is kept higher than the pressure in the space around the capillary and the pressure between the capillary cavities is balanced. By this pressure adjustment, the pores of the capillary become hexagonal in cross section, and the cross section of the quartz rod also becomes hexagonal.

Since the PBGF according to the present example has the above-described hexagonal hole expanded triangular lattice structure in the clad, when the core is formed at the center thereof, the core edge can constitute the hole core or the capillary core without crossing the bulk mode, Optical characteristics in which only the core mode exists without surface mode being generated can be obtained, the waveguide bandwidth can be widened, and transmission loss can be reduced.
In addition, the PBGF manufacturing method according to the present example can easily form an extended triangular lattice-like hole periodic structure in the same manner as the conventional method using a capillary except that a part of the capillary is replaced with a quartz rod. Therefore, PBGF having optical properties superior to those of conventional PBGF can be easily and inexpensively manufactured by the same method as that of conventional PBGF.

[Example 1]
As shown in FIG. 12, the cladding has a hexagonal hole expanded triangular lattice structure in which the ratio of the thickness ω _b of the partition wall 25 to the first pitch Λ is 0.06 (ω _b /Λ=0.06). Then, PBGF having a core 24 (capillary core) in which the central quartz portion 20 was replaced with a hole 21 was manufactured, and the dispersion of the core mode was examined. FIG. 13 is a graph showing dispersion within the first band gap of the PBGF. In FIG. 13, β represents the wave number in the propagation direction (direction perpendicular to the periodic structure), Γ = 2Λ represents the lattice constant of the extended triangular lattice, 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. As shown in FIG. 13, only the core mode exists and no surface mode exists within the band gap of Γ / λ (= ωΓ / 2πc) = 0.82 to 1.16.

  FIG. 14 is a diagram showing a typical power distribution in the core mode at that time. FIG. 15 shows the dielectric constant of the fiber on the same scale as FIG. As shown in the figure, it can be seen that the power of the core mode is slightly distributed in the quartz portion 20 in the immediate vicinity of the core, and almost all is distributed in the core 24.

  FIG. 16 is a graph showing the dispersion within the second band gap in the PBGF of this example. As shown in the figure, the core mode exists at Γ / λ = 1.64 to 1.85, but the surface mode does not exist. Also in this case, the core mode is a single mode (including a degenerate mode).

  FIG. 17 shows a typical power distribution in the core mode at that time. As shown in the figure, almost all of the core mode power is distributed in the core 24.

[Example 2]
As shown in FIG. 18, the cladding has a hexagonal hole-extended triangular lattice structure in which the ratio of the thickness ω _b of the partition wall 25 to the first pitch Λ is 0.06 (ω _b /Λ=0.06). Then, a PBGF having a core 24 (capillary core) in which a central quartz rod and six quartz portions 20 on one layer outside the central quartz rod 20 were replaced with holes 21 was manufactured, and the dispersion of the core mode was examined. FIG. 19 is a graph showing dispersion within the first band gap of the PBGF. As shown in the figure, core mode 1 exists when Γ / λ = 0.84 to 1.11, core mode 2 exists when Γ / λ = 0.89 to 1.16, and no surface mode exists. However, each core mode includes a degenerate mode.

  FIG. 20 is a diagram showing a typical power distribution in the core mode at that time. FIG. 21 shows the dielectric constant of the fiber on the same scale as FIG. As shown in the figure, almost all of the core mode power is distributed in the core 24.

  FIG. 22 is a diagram showing the power distribution of the core mode 2 of the same fiber.

  FIG. 23 is a graph showing dispersion within the second band gap in the PBGF of this example. As shown, core mode 1 exists when Γ / λ = 1.66 to 1.82, and core mode 2 exists when Γ / λ = 1.65 to 1.87, but no surface mode exists. However, each core mode includes a degenerate mode. The core mode dispersion is also present in the region below the light line because quartz remains in the core 24 as a partition wall.

  FIG. 24 is a diagram showing a typical power distribution in the core mode 1 at that time. FIG. 25 is a diagram showing a typical power distribution in the core mode 2 at that time.

[Example 3]
A band structure of a hexagonal hole expanded triangular lattice structure in which the ratio of the thickness ω _b of the partition wall 25 to the first pitch Λ is 0.12 (ω _b /Λ=0.12) as shown in FIG. It shows in FIG. In this case, the waveguide region exists in the range of Γ / λ = 0.81 to 1.00.

  Thus, it can be seen that when the partition wall 25 becomes thicker, the band gap becomes narrower. Further, when PBGF is formed by forming a capillary core as in Examples 1 and 2, it has been confirmed that only the core mode exists without generating a surface mode, as in Examples 1 and 2. .

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 illustrates the hole periodic structure of the extended triangular lattice used for PBGF of this invention. It is an expanded sectional view which shows the unit cell of the extended triangular lattice of FIG. It is sectional drawing which shows the circular hole expansion triangular lattice structure mentioned as a reference example. It is a graph which shows the band structure in the circular hole expansion triangular lattice structure of FIG. It is sectional drawing which shows the hexagonal hole expansion triangular lattice structure of (omega) _b = 0 as a 1st example of the hexagonal hole expansion triangular lattice structure used for PBGF of this invention. It is a graph which shows the band structure of the hexagonal hole expansion triangular lattice of FIG. It is sectional drawing which shows the hexagonal hole expansion triangular lattice structure of (omega) _{b / (} LAY ₎ = 0.06 as the 2nd example of the hexagonal hole expansion triangular lattice structure used for PBGF of this invention. It is a graph which shows the band structure of the hexagonal hole expansion triangular lattice of FIG. 2 is a cross-sectional view of PBGF using a hexagonal hole expanded triangular lattice structure of ω _b /Λ=0.06 manufactured in Example 1. FIG. 4 is a graph showing dispersion within the first band gap of the PBGF of Example 1. It is a figure which shows the power distribution of the core mode in the 1st band gap of PBGF of Example 1. FIG. It is a figure which shows the dielectric constant distribution of PBGF of Example 1. FIG. 6 is a graph showing dispersion within the second band gap of the PBGF of Example 1. It is a figure which shows power distribution of the core mode in the 2nd band gap of PBGF of Example 1. FIG. 6 is a cross-sectional view of PBGF using a hexagonal hole expanded triangular lattice structure of ω _b /Λ=0.06 manufactured in Example 2. FIG. 6 is a graph showing dispersion within the first band gap of the PBGF of Example 2. It is a figure which shows the power distribution of the core mode 1 in the 1st band gap of PBGF of Example 2. FIG. It is a figure which shows the dielectric constant distribution of PBGF of Example 2. It is a figure which shows the power distribution of the core mode 2 in the 1st band gap of PBGF of Example 2. FIG. 6 is a graph showing dispersion within a second band gap of the PBGF of Example 2. It is a figure which shows the power distribution of the core mode 1 in the 2nd band gap of PBGF of an Example. It is a figure which shows the power distribution of the core mode 2 in the 2nd band gap of PBGF of an Example. 6 is a cross-sectional view showing a hexagonal hole expanded triangular lattice structure of ω _b /Λ=0.12 manufactured in Example 3. FIG. 7 is a graph showing a band structure of a hexagonal hole expanded triangular lattice structure of Example 3.

Explanation of symbols

20 ... quartz part, 21 ... hole, 22 ... first hole array, 23 ... second hole array, 24 ... core, 25 ... partition.

Claims (21)

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 large number of hexagonal quartz portions are arranged in a triangular lattice pattern at a constant pitch Γ in the cross section of the fiber, the space between the quartz portions is a hole, and the length ω _r between two opposite sides of the quartz portion; A photonic having a periodic structure in the clad equal to half the length Λ of the pitch Γ, and a core in which a hole core or a plurality of hexagonal holes are arranged in a triangular lattice shape Bandgap fiber. A photonic bandgap fiber in which a large number of holes are provided in the quartz portion along the longitudinal direction of the fiber,
In the fiber cross section, a first hole array in which a number of hexagonal holes are arranged in a line through a partition wall at a first pitch Λ, and a second pitch Γ that is twice the first pitch. A plurality of hexagonal holes are arranged through a hexagonal quartz portion, and the second holes are arranged so that the holes and the holes of the first hole array form a triangular lattice. A plurality of hole arrays are alternately stacked, and the cladding has an extended triangular lattice-like hole periodic structure in which the length ω _r between two opposite sides of the quartz portion and the first pitch Λ are substantially equal. And a photonic bandgap fiber having a hollow core or a core in which a large number of hexagonal holes are arranged in a triangular lattice pattern. 3. The photonic bandgap fiber according to claim 2, wherein a thickness ω _b of a quartz partition wall surrounding the hole is in a range of 0.005Λ ≦ ω _b ≦ 0.2Λ.   4. The photonic bandgap fiber according to claim 1, wherein the diameter D of the core has a relationship of 0.7Λ ≦ D ≦ 3.3Λ with respect to the pitch Λ.   The photonic bandgap fiber according to any one of claims 1 to 3, wherein the diameter D of the core has a relationship of 4.7Λ≤D≤7.3Λ with respect to the pitch Λ.   The photonic bandgap fiber according to any one of claims 1 to 3, wherein the diameter D of the core has a relationship of 8.7Λ≤D≤11.3Λ with respect to the pitch Λ.   The photonic bandgap fiber according to claim 1, wherein three or more layers of extended triangular lattice-shaped hole periodic structures provided in the cladding are provided outside the core.   The core mode in which 60% or more of the propagation power is concentrated in the region of the hole core, and has an optical characteristic that the surface mode does not substantially exist. The described photonic bandgap fiber.   9. The photonic band according to claim 1, which has an optical characteristic in which only a single core mode (however, all degenerate modes have a mode number of 1) exists. Gap fiber.   The photonic according to any one of claims 1 to 9, wherein the photonic has an optical characteristic in which a core mode exists in a range where the wavelength λ satisfies 0.6 ≦ Γ / λ ≦ 1.5. Bandgap fiber.   The photonic according to any one of claims 1 to 9, wherein the photonic has an optical characteristic in which a core mode exists within a range where a wavelength λ satisfies 1.4 ≦ Γ / λ ≦ 2.3. Bandgap fiber.   The photonic according to any one of claims 1 to 9, wherein the photonic has an optical characteristic in which a core mode exists in a range where the wavelength λ satisfies 2.2 ≦ Γ / λ ≦ 3.2. Bandgap fiber.   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. Combined so that the cross-sectional capillary arrangement is an expanded triangular lattice, and the central quartz rod or central quartz rod and the surrounding capillary and quartz rod are eliminated to form a hollow core region, or the quartz rod is replaced with a capillary Then, a capillary bundle containing a quartz rod as a capillary core region is manufactured, and then the capillary bundle containing a quartz rod is heated and integrated while maintaining the pressure in the capillary inner space higher than the pressure around the capillary. A photonic band gap according to any one of claims 1 to 12, wherein a base material is prepared and then the base material for fiber spinning is spun. Method of manufacturing a photonic bandgap fiber, characterized in that to obtain a fiber.   14. The method of manufacturing a photonic bandgap fiber according to claim 13, 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 method for producing a photonic bandgap fiber according to claim 13 or 14, wherein the fiber bundle is produced by integrating the capillary bundle containing a quartz rod while being inserted into a hole of a quartz tube.   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 15.   The photonic bandgap fiber according to any one of claims 13 to 16, wherein the hollow core region is formed by eliminating one quartz rod at the center of the cross section of the capillary bundle containing the quartz rod. Method.   The void core region is formed by eliminating one quartz rod at the center of the cross section of the capillary bundle containing the quartz rods and one or more and five or less capillaries and quartz rods surrounding the quartz rod. The manufacturing method of the photonic band gap fiber in any one of 13-16.   The photonic band gap fiber according to any one of claims 13 to 16, wherein a capillary core region is formed by replacing one quartz rod at the center of a cross section of the capillary bundle containing the quartz rod with a capillary. Manufacturing method.   The capillary core region is formed by replacing one quartz rod at the center of the cross section of the capillary bundle containing the quartz rods and a quartz rod surrounding the quartz rod with a capillary to form a capillary core region. The manufacturing method of the photonic band gap fiber of description.   14. The capillary bundle with quartz rods is provided such that an extended triangular lattice-like hole periodic structure surrounding a core region has three or more layers of quartz rods outward in the radial direction. The manufacturing method of the photonic band gap fiber in any one of -20.

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