JP2003227941A - Unimodal photonic bandgap fiber and glass preform therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a unimodal photonic bandgap fiber which is easily connected to an existing optical communication network and attains relaxation to a wavelength region in which propagation of light is difficult in a conventional glass core and the intensity of input light and to provide a glass preform therefor. <P>SOLUTION: In the unimodal photonic bandgap fiber, an optical core portion 1 has a region about several times the wavelength of light and numerous holes 2 extending in the lengthwise direction of the fiber are pierced in a cladding portion 4. The cladding portion 4 has a honeycomb shape using regular hexagons having a length d of one side as a basic grid 3 and constitutes a Bragg diffraction grating having a photonic bandgap structure. The basic grid 3 has a grid interval equal to 1/2 of the wavelength of light, one portion of the basic grid includes the hollow core portion 1, and for example, the holes 2 are pierced in the vertexes of the regular hexagons of the whole basic grid 3 except the core portion 1. The holes may be pierced in the central positions of the whole basic grid 3 except the core portion 1. Each single hole may be replaced with a group of holes as an aggregate of a plurality of holes. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a single-mode optical fiber used in an optical communication network, and more particularly to a single-mode photonic bandgap fiber having a diffraction grating having a photonic bandgap structure in a clad portion and a glass matrix thereof. Regarding materials

[0002]

2. Description of the Related Art FIG. 18 shows a cross-sectional structure of a conventional optical fiber having a diffraction grating having a photonic bandgap structure in the cladding. Here, 31 is a core located at the center of the optical fiber, 32 is a photonic bandgap clad having a diffraction grating with a photonic bandgap structure surrounding the core, and 33 is an outer protective jacket.

FIG. 19 shows a detailed structure of the photonic bandgap clad 32. In general, a three-dimensional photonic bandgap structure is a diffraction grating that Bragg-reflects light in all directions, and as shown in FIG. 19, the grating constant d of the diffraction grating is set to about the optical wavelength in the propagating medium. It is realized by doing.

As the structure of the crystal lattice forming the photonic bandgap, some structures other than the triangular lattice as shown in the example of implementation of FIG. 19 are conceivable.
FIG. 20 shows an example of the structure of the crystal lattice that constitutes the photonic band gap. FIG. 20A shows a square lattice structure having a high refractive index, which is embedded in a medium having a low refractive index. FIG. 20B shows a square lattice structure with a low refractive index embedded in a medium with a high refractive index. Figure 20
(C) shows a triangular lattice structure with a high refractive index embedded in a medium with a low refractive index. FIG. 20D shows
3 shows a triangular lattice structure with a low refractive index embedded in a medium with a high refractive index. FIG. 20 (E) shows a honeycomb structure (honeycomb shape, hexagonal pattern) having a high refractive index embedded in a medium having a low refractive index.

Further, as the shape of the lattice, FIG. 19 and FIG.
In the above, a lattice structure of a cylinder or a circular hole is assumed, but this is not limited to a cylinder or a circular hole, and a shape such as a triangular prism or a triangular hole, a square prism or a square hole, a hexagonal prism or a hexagonal hole can be used. It is possible to realize the photonic band gap even in the lattice structure having the photonic band gap.

Reference [1]: JD Joannopoulous e
t al., Photonic Crystals, Princeton University Pre
According to ss, pp. 122-126, 1995, in these lattice structures, there is a photonic band gap, which results in light confinement.

In fact, when a photonic bandgap structure is provided around the core to form a clad, light is strongly confined in the core. Therefore, when it is desired to guide light through a structure, as shown in FIG.
With a photonic bandgap structure, light can be confined and propagated within the structure. That is, this photonic bandgap structure 32
Are arranged around the core 31 of the optical fiber, thereby confining light from the center of the core 31 of the optical fiber so as not to propagate in the radial direction.

In this case, as shown in FIG. 18, when the cross section of this optical fiber is seen, it has a lattice-like structure,
The same structure is maintained in the length direction. In other words, the cross section of this optical fiber has the same structure everywhere (ignoring the fluctuation of the shape due to the manufacturing process of the optical fiber),
There is no structure that is orthogonal or oblique to the length direction of the optical fiber.

In particular, when the refractive index of the core portion 31 is made lower than that of the periphery 32, light is confined in the core 31 only by the Bragg diffraction due to the photonic bandgap structure. This is a structure in which the refractive index of the core part is higher than the refractive index of the surrounding part in the single-mode optical fiber currently in practical use, and light is confined in the core by total reflection due to the difference in the refractive index. , Different principles.

An example of realizing an optical fiber based on the above principle using Bragg diffraction is given in Reference [2]: RF Cregan et al., "Single-mode".
photonic band gap guidance of light in air, "Scien
ce, vol. 285, pp. 1537-1539, 1999, and reference [3]: JA West et al., "Demonstration.
of an IR-optimized air-core photonic band-gap fibe
r, "Tech. Digest of ECOC 2000, vol. 4, pp.41-42,
Reported in 2000.

In the optical fiber using such a photonic bandgap structure for the cladding, it is possible to suppress higher-order modes more effectively than the conventional optical fiber by total reflection, and the core diameter is reduced. There is an excellent advantage that the single mode condition can be maintained even if the value is expanded.

[0012]

However, when the conventional optical fiber having the photonic band gap as described above is actually used for high-speed optical communication,
The following problems occur.

In the fiber structure shown in FIG. 20 (D) of the reference [2] and FIG. 18 of the reference [3], a hole lattice arranged in an equilateral triangle is formed in glass, By removing the 7 holes in the core part, this part is shaped as an air core. The problem here is that when light is guided through the optical fiber of this structure, the fundamental mode is not a concentric mode having a peak at the center of the core. Table 1 below shows the eigenmodes of the optical field distribution that can exist in this structure in order of increasing eigenvalue using the finite element method.

[0014]

[Table 1]

In Table 1 above, the quantity defined by E is: E = (light intensity at the center of the core) / (light intensity that maximizes the light intensity in the entire fiber) (1) That is, the mode with E = 1 is a concentric mode having a peak at the center of the core.

As shown in Table 1, the light intensity at the center of the core in the fundamental mode does not become maximum in the fiber width. In the single-mode optical fiber currently used for practical use, the fundamental mode is a concentric mode having a peak at the center of the core, while Table 1 shows different mode distributions. Usually, when propagating an optical signal in an optical waveguide such as a single-mode optical fiber, a fundamental mode is used from the viewpoint of mode stability. This is because the fundamental mode is the most stable in terms of energy and the distribution of the light intensity in the waveguide is simple, so that connection or the like is easy. By using a waveguide structure capable of propagating only the fundamental mode, stable optical signal propagation is possible.

However, in the conventional optical fiber having a photonic bandgap, the concentric mode having a peak at the center of the core is a higher-order mode (12th harmonic in Table 1). Inevitably, a fiber that can propagate is a multimode fiber. When propagating a high-speed optical signal in a multimode fiber,
The optical signal waveform is deteriorated due to multimode dispersion, and the signal speed cannot be increased, and the fiber connection loss increases.

On the other hand, the structure of an optical fiber having a photonic bandgap in which the fundamental mode is a concentric mode whose peak is at the center of the core is described in Reference [4]: Ushijima et al. Mode evaluation "1
1988 IEICE General Conference No. C-3-121, p28
Proposed in 7.

FIG. 21 shows a sectional structure of the optical fiber proposed in the reference [4]. This optical fiber includes a hollow core in the shape of an air hole and a clad in which glass rods are arranged in a lattice.

However, the structure shown in FIG. 21 is a structure in which the glass rod floats in the air and does not have a mechanism for holding the glass rod at the lattice position. However, this structure cannot be realized in reality.

The present invention has been made in view of the above-mentioned problems of the prior art, and an object thereof is to make it easy to connect to an existing optical communication network, and to transmit light with a conventional glass core at a wavelength which is difficult to propagate. It is intended to provide a single mode photonic bandgap fiber and its glass preform that can provide relaxation to the region and input light intensity.

[0022]

The present invention is characterized by the lattice structure of the above-mentioned reference [4], which has a photonic bandgap in which the fundamental mode is a concentric mode having a peak at the center of the core. As a means for actually realizing the fiber structure, it is characterized in that a hole group for forming a black diffraction grating existing at each grating position is provided.

In other words, in order to achieve the above object, the single mode photonic bandgap fiber of the present invention has a core portion having a region of several times the wavelength of light and an optical element disposed around the core portion. A clad portion provided at least in a peripheral region adjacent to the core portion, and a diffraction grating having a photonic bandgap structure having a grating spacing equal to ½ of the wavelength of the Bragg diffraction grating is formed. A single mode optical fiber comprising a plurality of regularly arranged grating portions, each of the grating portions being formed in the cladding portion and formed by holes extending in the longitudinal direction of the optical fiber. Each of the lattice portions has a honeycomb shape whose basic lattice is a regular hexagon whose one side is d in a cross section of an optical fiber, and one of the basic lattices has the hollow core portion. And wherein the Rukoto.

Here, preferably, the holes are provided at each vertex of a regular hexagon of all the basic lattices except the core portion.

Preferably, the holes are provided at the centers of all the basic lattices except the core portion.

Further, it is preferable that the holes have a first type hole group consisting of a set of seven holes and a single hole, and in the cross section of the optical fiber, the core portion is excluded. 2 out of the center of the core of the regular hexagonal vertices of the basic lattice
The group of holes of the first type is arranged only at vertices separated by xd or less, and among the vertices of the regular hexagon of the basic lattice excluding the core portion, the vertices separated by more than 2 × d from the center of the core portion. The single hole is arranged in only.

Further, it is preferable that the holes have a hole group of the first kind consisting of a set of 7 holes, and the regular hexagonal vertices of all the basic lattices except the core portion have the first holes. 1
A group of seed holes is arranged.

[0028] Preferably, the core portion further comprises a second type hole group consisting of a set of six holes as the holes, and the core portion is included in the center of all the basic lattices except the core portion. The second type hole group is arranged only at the center of the basic lattice, which is separated from the center of the center by 2 × d or less.

Preferably, the hole further comprises a second type hole group consisting of a set of six holes as the holes, and the second type hole is provided at the center of all the basic lattices except the core portion. Of holes are arranged.

Preferably, the holes include a first type hole group consisting of a set of seven holes and a single hole, and in the cross section of the optical fiber, the core portion is excluded. The hole group of the first type is arranged only in a center of the center of the basic lattice that is 2 × d or less from the center of the core unit, and the center of the core unit in the center of the basic lattice excluding the core unit The single hole is located only in the center, which is more than 2 × d from.

Further, it is preferable that the holes have a group of holes of the first kind consisting of a set of seven holes, and the holes of the first kind are located at the centers of all the basic lattices except the core portion. A group of holes is arranged.

Further, preferably, the hole further comprises a second type hole group consisting of a set of six holes as the holes, and among the vertexes of regular hexagons of all the basic lattices except the core portion. The second type hole groups are arranged only at the vertices of the basic lattice that are separated from the center of the core portion by 2 × d or less.

Preferably, the hole group further comprises a second type hole group consisting of a set of 6 holes, and the aforesaid hexagonal vertices of all of the basic lattices except the core portion are aforesaid. A second type hole group is arranged.

Further, preferably, a gap between the core and holes adjacent to the core, and / or a gap between the core and the first type hole group and / or the second type hole group. Further holes are arranged in the.

To achieve the above object, the glass preform of the single mode photonic bandgap fiber of the present invention is a glass preform for forming a single mode optical fiber, and the glass preform is a core part. In the cross section of the glass preform, the hollow glass rod for core arranged in, and a plurality of hollow or solid glass rods arranged in parallel with the hollow glass rod for core around the core portion. The center of the hollow or solid glass rod is arranged at the apex or center of a regular hexagonal basic lattice having a side length of d, and one of the basic lattices has the core portion.

Here, preferably, the hollow glass rods are arranged at the vertices of regular hexagons of all the basic lattices except the core part, and the hollow glass rods are arranged at the centers of all the basic lattices except the core part. Place a real glass rod.

Further, preferably, the solid glass rods are arranged at the vertices of regular hexagons of all the basic lattices excluding the core portion, and the hollow glass is placed at the center of all the basic lattices excluding the core portion. Place a glass rod.

Further, preferably, it has a hollow glass rod group which is an assembly of 7 hollow glass rods, and a solid glass rod group which is an assembly of 7 solid glass rods, and the glass mother In the cross section of the material, the hollow glass rod group is arranged only at the vertices of the regular hexagon of the basic lattice excluding the core portion, which are distant by 2 × d or less from the center of the core portion, and the hollow glass rod group is excluded. Of the regular hexagonal vertices of the basic lattice, a single solid glass rod is arranged only at the vertices farther than 2 × d from the center of the core portion, and the core is included in the center of the basic lattice excluding the core portion. The solid glass rod group is arranged only at the center 2 × d or less away from the center of the core portion, and 2 × from the center of the core portion among the centers of the basic lattice excluding the core portion.
A single solid glass rod is placed only in the center further away than d.

Preferably, the hollow glass rod group is a group of seven hollow glass rods, and the solid glass rod group is a group of seven solid glass rods. In the cross section of the material, the hollow glass rod group is arranged at the vertices of regular hexagons of all the basic lattices except the core portion, and the solid glass rod group is at the center of all the basic lattices except the core portion. Will be placed.

Preferably, the solid glass rod groups are each replaced with a mixed glass rod group which is an assembly in which one solid glass rod is surrounded by six hollow glass rods.

Further, preferably, the hollow glass rod groups are each replaced with a mixed glass rod group which is an assembly in which one solid glass rod is surrounded by six hollow glass rods.

Further, preferably, it has a hollow glass rod group which is an assembly of seven hollow glass rods, and a solid glass rod group which is an assembly of seven solid glass rods, and the glass mother In the cross section of the material, the hollow glass rod group is arranged only in the center apart from the center of the core portion by 2 × d or less among the centers of the basic lattice excluding the core portion, A single solid glass rod is arranged only in the center, which is more than 2 × d away from the center of the core,
Of the regular hexagonal vertices of the basic lattice excluding the core portion, the solid glass rod group is arranged only at the vertices 2 × d or less from the center of the core portion, and the regular hexagonal shape of the basic lattice excluding the core portion. 2 × from the center of the core part of the vertex of the polygon
A single solid glass rod is placed only at the vertices farther than d.

Further, preferably, it has a hollow glass rod group which is an assembly of 7 hollow glass rods, and a solid glass rod group which is an assembly of 7 solid glass rods, and the glass mother The hollow glass rod group is arranged at the center of all the basic lattices excluding the core portion in the cross section of the material, and the regular hexagonal apex of all the basic lattices except the core portion in the cross section of the glass base material A group of solid glass rods is arranged.

Preferably, the solid glass rod groups are each replaced by a mixed glass rod group which is an assembly in which one solid glass rod is surrounded by six hollow glass rods.

Preferably, the hollow glass rod groups are each replaced by a mixed glass rod group which is an assembly in which one solid glass rod is surrounded by six hollow glass rods.

Further, preferably, a hollow glass rod is further arranged so as to be in contact with the hollow glass rod adjacent to the core portion and / or the solid glass rod and the hollow glass rod for core.

[0047]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(First Embodiment) FIG. 1 shows a sectional structure of a single-mode photonic bandgap fiber according to a first embodiment of the present invention. FIG. 2 shows the overall appearance of the optical fiber. Here, 1 is a core portion located at the center of the single mode optical fiber. The core part 1 is hollow and has a region of several times the wavelength of the propagating light. Reference numeral 4 is a clad portion arranged around the core portion 1. A large number of holes (hereinafter referred to as holes) 2 extending in the longitudinal direction of the optical fiber are opened in the clad portion 4, and the cross section of the optical fiber has a lotus root-like shape as shown in FIG. .

The positions of the holes 2 in the clad portion 4 are not disordered, and as shown in FIG. 1, the holes 2 have a honeycomb shape in which a regular hexagon having a side length d is a basic lattice 3. The regular arrangement of the holes 2 constitutes a Bragg diffraction grating having a photonic bandgap structure. Each basic grating 3 has a grating interval equal to ½ of the wavelength of propagating light, one of the basic gratings includes a hollow core portion 1, and as a representative example, as shown in FIG. Voids 2 are provided at each vertex of a regular hexagon of all the basic lattices 3 except the core portion 1.

Further, instead of providing the holes 2 at each vertex of the regular hexagon as described above, as shown in FIG. 3, the holes 5 are provided at the central positions of all the basic lattices 3 except the core portion 1. Also,
A similar effect can be expected.

Since the core portion 1 is hollow, its refractive index (1.0 because it is air) is the refractive index of the cladding portion 4 forming the wall of the holes 2 around it (1 in the case of silica). ．
45). Thereby, the light is confined in the core portion 1 only by the Bragg diffraction due to the photonic bandgap structure. At that time, a stable fundamental mode can be matched with a concentric mode having a peak at the center of the core, so that a mode distribution and mode stability similar to those of currently used single-mode optical fibers can be obtained. Light can be confined.

As described above, the basic light confining effect in the present invention is the same as that of the conventional technique described in the reference [4]. A major part of the subject matter of the invention is the construction of the lattice of the photonic bandgap cladding.

(Second Embodiment) FIG. 4 shows a sectional structure of a single-mode photonic bandgap fiber according to a second embodiment of the present invention. FIG. 5 shows the appearance of the main part of the optical fiber. In the present embodiment, the diameter of the hole (hole) of the clad portion 4 is large or small. That is, the large holes 2 are individually formed in the clad, and the seven small holes 21 are collected and formed in the clad. The set 22 of seven small holes 21 is referred to as a first type hole group in the present application. Big hole 2
Are drilled in the same arrangement as in the first embodiment shown in FIG. However, as shown in FIG.
As shown in FIG. 6, all of them are replaced by the first type hole group 22.

More specifically, the first type hole group 22 is
The regular hexagon whose one side has a length of d is the regular hexagon apex having the basic lattice 3, and is arranged only at the apex 2 × d or more away from the center of the core portion 1. In addition, FIG. 4 shows two points from the center of the core portion 1 among the vertices of the basic lattice excluding the core portion 1.
FIG. 6 shows an example in which the first-type hole groups 22 are arranged only at the vertices separated by xd, and FIG. 6 shows an example in which the first-type hole groups 22 are arranged at all the vertices of the basic lattice except the core portion 1. Is shown.

(Third Embodiment) FIGS. 7 and 8 show the sectional structure of a single mode photonic bandgap fiber according to a third embodiment of the present invention. In the present embodiment, in addition to the above-described first type hole group 22 which is a set of seven small holes 21, a set 23 of six small holes 21 is provided.
Also used. This set of six small holes 21 is referred to as a second type hole group in the present application. The large holes 2 are drilled in the same arrangement as in the first embodiment shown in FIG. However, as shown in FIG. 7, a part thereof or, as shown in FIG. 8,
All of them are the first type hole group 22 and the second type hole group 23.
It is replaced by the combination of.

More specifically, the second type hole group 23 is
Similar to the first-type hole group 22, the vertex of the regular hexagon having a regular hexagon whose one side has a length of d as the basic lattice 3 and which is 2 × d or more away from the center of the core portion 1. Only placed. In addition, FIG. 7 shows that the first-type hole group 22 and the second-type hole group 23 are present only at the vertices apart from the center of the core portion 1 by 2 × d of the vertices of the basic lattice excluding the core portion 1. FIG. 8 shows an example in which the first type hole groups 22 and the second type hole groups 23 are alternately arranged at the vertices of the basic lattice except the core portion 1. Shows.

(Fourth Embodiment) FIGS. 9 and 10 show the sectional structure of a single mode photonic bandgap fiber according to a fourth embodiment of the present invention. Figure 9
All the basic lattices 3 shown in FIG. 3 except the core portion 1
In a structure in which a large hole 5 is provided at the center position of the core part 1 of the center of the basic lattice excluding the core part 1,
An example is shown in which the first-type hole group 22 is replaced only in the center separated by xd. Instead of the first type hole group 22, the second group
You may arrange the hole group 23 of a seed.

FIG. 10 shows the center of the basic lattice 3 excluding the core portion 1 in the structure shown in FIG. 3 in which a large hole 5 is provided at the central position of all the basic lattices 3 except the core portion 1. Of the first type hole group 22 and the second type hole group 23 only at the center and the apex of the vertices that are 2 × d away from the center of the core portion 1.
It shows an example of arranging. In the example of FIG. 10, the first-type hole group 22 is arranged at the center of the basic lattice 3 and the second-type hole group 23 is arranged at the apex of the basic lattice 3, but this arrangement relationship is replaced. May be.

(Fifth Embodiment) FIGS. 11 and 12 show the sectional structure of a single-mode photonic bandgap fiber according to a fifth embodiment of the present invention. FIG.
Shows the appearance of the glass preform of the optical fiber. The present embodiment exemplifies a case where a single mode photonic bandgap fiber according to the present invention is formed from a glass base material. Here, 11 is a hollow glass rod for core (glass tube for core) arranged in the core portion. Reference numeral 24 denotes a plurality of hollow glass rods (glass tubes) arranged in parallel around the core hollow glass rod 11 of the core portion. Reference numeral 25 denotes a plurality of solid glass rods (glass rods) arranged in parallel around the core hollow glass rod 11 of the core portion.

The arrangement of these glass rods 24, 25 is not disordered, and as shown in FIGS. 11 to 13, the center of the hollow or solid glass rods 24, 25 in the cross section of the glass base material is the length of one side. Are arranged so as to form a honeycomb structure having a regular hexagonal basic lattice of d, and one of the basic lattices includes a hollow glass rod 11 for a core of a core portion.

In the configuration of FIG. 11, hollow glass rods 24 are arranged at the vertices of all the basic lattices except the core portion, and solid glass rods 25 are arranged at the centers of all the basic lattices except the core portion. There is.

In the structure of FIG. 12, contrary to the structure of FIG. 11, the solid glass rods 25 are arranged at the vertices of all the basic lattices except the core portion, and the solid glass rods 25 are arranged at the centers of all the basic lattices except the core portion. A hollow glass rod 24 is arranged.

(Sixth Embodiment) FIGS. 14 and 15 show a sectional structure of a single mode photonic bandgap fiber according to a sixth embodiment of the present invention, which uses a glass preform. Here, 26 is a hollow glass rod group consisting of seven small hollow glass rods, and 27 is a solid glass rod group consisting of seven small solid glass rods.

In FIG. 14, the core hollow glass rod 11 is the apex of a regular hexagon whose basic lattice 3 is a regular hexagon having a side length d from the center of the core hollow glass rod 11. The hollow glass rod group 26 is arranged only at the apex 2 × d away from the center of, and is the center of the regular hexagon,
An example is shown in which the solid glass rod group 27 is arranged only at the center 2 × d away from the center of the core hollow glass rod 11.

Other than that, at the vertices and the center of the basic lattice 3 which are more than 2 × d from the center of the core hollow glass rod 11,
Similar to the arrangement configuration of FIG. 11, hollow glass rods 24 are arranged at the vertices of all the basic lattices, and solid glass rods 25 are arranged at the centers of all the basic lattices. Instead of this, FIG.
Similar to the arrangement configuration of 2, the hollow glass rods 24 may be arranged at the centers of all the basic lattices, and the solid glass rods 25 may be arranged at the vertices of all the basic lattices.

On the other hand, in the configuration shown in FIG. 15, the hollow glass rod group 26 is arranged at the apexes of the basic lattice except the core portion, and the solid glass rod group 27 is arranged at the center of the basic lattice except the core portion. Are arranged.

Although not shown, a hollow glass rod group 26 is arranged at the center of the basic lattice except for the core portion, and a solid glass rod group 27 is provided at the apex of the basic lattice except for the core portion.
May be arranged. That is, in the arrangement configuration shown in FIG. 12, the hollow glass rod 24 can be replaced with the hollow glass rod group 26, and the solid glass rod 25 can be replaced with the solid glass rod group 27.

(Seventh Embodiment) FIGS. 16 and 17 show the cross-sectional structure of a single mode photonic bandgap fiber according to a seventh embodiment of the present invention using a glass preform. Here, 28 is a mixed glass rod group composed of one small solid glass rod at the center and six small hollow glass rods around the solid glass rod.

The structure shown in FIG. 16 is obtained by replacing the solid glass rod group 27 with the mixed glass rod group 28 in the arrangement shown in FIG.

In the configuration of FIG. 17, the solid glass rod group 27 is replaced by the mixed glass rod group 28 in the arrangement configuration of FIG.
It has been replaced with.

(Other Embodiments) The optical fiber having the structure of the above-described embodiment of the present invention can be manufactured by, for example, a method of filling a large number of thin glass tubes inside a glass tube having a large inner diameter. Further, for example, it can be manufactured by a method of making a hole at a predetermined position of the glass base material, but of course, it may be manufactured by a combination thereof or another method.

In the fifth to seventh embodiments of the present invention described above, the hollow glass rod (shown in the figure) is brought into contact with the hollow glass rod or the solid glass rod adjacent to the core portion and the core hollow glass rod. No) may be further arranged.

In the second to fourth embodiments, the gap between the core and the holes adjacent to the core, and / or the core and the first type hole group and / or the second type hole group. Further holes may be arranged in the gap.

[0074]

As described above, according to the present invention,
A stable fundamental mode can be matched with a concentric mode with a peak at the center of the core, so that confinement to light is achieved with a mode distribution and mode stability similar to those of currently used single-mode optical fibers. It can be performed.

Therefore, according to the present invention, in addition to facilitating the connection to the existing optical communication network, since the core is hollow, it is difficult to propagate light in the glass core. It can be expected to reduce the intensity of input light, and it can be expected to have an extremely large effect when it is used for optical communication and optical functional parts.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view showing a cross-sectional structure of a single-mode photonic bandgap fiber according to a first embodiment of the present invention in which holes are provided at each apex of all basic lattices except a core portion.

FIG. 2 is a schematic perspective view showing the overall appearance of the optical fiber of FIG.

FIG. 3 is a vertical cross-sectional view showing a cross-sectional structure of the single mode photonic bandgap fiber according to the first embodiment of the present invention in which a hole is provided at the central position of all the basic lattices except the core portion.

FIG. 4 is a single-mode photonic device according to a second embodiment of the present invention in which the holes close to the core portion of the holes shown in FIG. 1 are replaced with holes of the first type each consisting of seven small holes. It is a longitudinal section showing a section structure of a band gap fiber.

5 is a schematic perspective view showing an appearance of a main part of the optical fiber of FIG.

FIG. 6 is a vertical cross-sectional view showing a cross-sectional structure of a single-mode photonic bandgap fiber according to a second embodiment of the present invention, in which holes of the first kind are arranged at the vertices of all basic lattices except the core portion. Is.

FIG. 7 is a diagram showing the structure of the third embodiment of the present invention in which, in addition to the configuration of FIG. 4, a second type hole group consisting of six small holes is arranged at the center of each basic lattice adjacent to the basic lattice of the core portion. It is a longitudinal section showing a section structure of a single mode photonic band gap fiber of an embodiment.

FIG. 8 shows a cross-sectional structure of a single-mode photonic bandgap fiber according to a third embodiment of the present invention in which a part of the first type hole group of FIG. 6 is replaced with a second type hole group. FIG.

FIG. 9 is a single mode of the fourth embodiment of the present invention in which the holes in the center of the basic lattice close to the core part of the holes of FIG. 3 except for the core part are replaced with a hole group of the first type. It is a longitudinal section showing a section structure of a photonic band gap fiber.

10 is a vertical cross-sectional view showing a cross-sectional structure of a single-mode photonic bandgap fiber according to a fourth embodiment of the present invention in which a second type hole group is added to the configuration of FIG.

FIG. 11 shows a single-mode photonic bandgap fiber according to a fifth embodiment of the present invention in which hollow glass rods are arranged at the vertices of the basic lattice except for the core portion, and solid glass rods are arranged at the central positions of the basic lattices. It is a longitudinal cross-sectional view showing a cross-sectional structure.

FIG. 12 is a single-mode photonic bandgap fiber according to a fifth embodiment of the present invention in which hollow glass rods are arranged at the central positions of all the basic lattices except for the core portion, and solid glass rods are arranged at the vertices of the basic lattices. FIG. 3 is a vertical sectional view showing the sectional structure of FIG.

FIG. 13 is a perspective view showing an appearance of a glass preform of the optical fiber shown in FIGS. 11 and 12.

FIG. 14 is a sixth embodiment of the present invention in which a part of FIG. 11 is replaced with a hollow glass rod group including a plurality of small-diameter hollow glass rods and a solid glass group including a plurality of small-diameter solid glass rods. FIG. 3 is a vertical sectional view showing a sectional structure of the single-mode photonic bandgap fiber of FIG.

FIG. 15 shows all the hollow glass rods in FIG. 11 in a hollow glass rod group consisting of a plurality of small diameter hollow glass rods, and all the solid glass rods in a solid glass group consisting of a plurality of small diameter solid glass rods. It is a longitudinal cross-sectional view which shows the cross-section of the single mode photonic band gap fiber of the 6th Embodiment of this invention which replaced.

FIG. 16 is a single mode photonic according to the seventh embodiment of the present invention in which the solid glass rod group of FIG. 14 is replaced with a mixed glass rod group including a mixture of a small diameter hollow glass rod and a small diameter solid glass rod. It is a longitudinal section showing a section structure of a band gap fiber.

17 is a vertical cross-sectional view showing a cross-sectional structure of a single mode photonic bandgap fiber according to a seventh embodiment of the present invention in which the solid glass rod group of FIG. 15 is replaced with a mixed glass rod group.

FIG. 18 is a vertical cross-sectional view showing a cross-sectional structure of a conventional optical fiber having a diffraction grating having a photonic bandgap structure in a clad part.

FIG. 19 is an enlarged view showing a configuration of a photonic bandgap of a conventional optical fiber.

FIG. 20 is a schematic view showing a configuration example of a crystal lattice that constitutes a photonic band gap.

FIG. 21 is a conceptual diagram showing a structure of an optical fiber having a photonic band gap in which a fundamental mode is a concentric mode in which the center of the core is a peak.

[Explanation of symbols]

1 hollow core 2 holes (large holes) 3 basic lattice 4 flood part 5 holes (large holes) 11 Hollow glass rod for core (glass tube for core) 21 small holes 22 Group 1 vacancy group 23 Voids of the second kind 24 Hollow glass rod (glass tube) 25 solid glass rod (glass rod) 26 Hollow glass rods 27 Solid glass rods 28 Mixed glass rods 31 core 32 Photonic bandgap cladding 33 Protective jacket

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hirokazu Kubota             2-3-1, Otemachi, Chiyoda-ku, Tokyo             Inside Telegraph and Telephone Corporation (72) Inventor Kazunori Suzuki             2-3-1, Otemachi, Chiyoda-ku, Tokyo             Inside Telegraph and Telephone Corporation (72) Inventor Masatoshi Tanaka             4-3 Ikejiri, Itami City, Hyogo Prefecture Mitsubishi Electric Cable             Industrial Co., Ltd. Itami Works (72) Inventor Shigeki Koyanagi             4-3 Ikejiri, Itami City, Hyogo Prefecture Mitsubishi Electric Cable             Industrial Co., Ltd. Itami Works (72) Inventor Moriyuki Fujita             4-3 Ikejiri, Itami City, Hyogo Prefecture Mitsubishi Electric Cable             Industrial Co., Ltd. Itami Works F-term (reference) 2H050 AA01 AB03Z AC62 AC71                       AD16                 4G021 BA13

Claims (24)

[Claims] 1. A diffraction grating having a photonic bandgap structure, which has a core portion having a region of several times the wavelength of light and has a grating interval which is arranged around the core portion and is equal to ½ of the wavelength of light. And at least a clad portion provided in a peripheral region adjacent to the core portion, and the diffraction grating is composed of a plurality of grating portions arranged regularly to form a Bragg diffraction grating. Is a single-mode optical fiber formed by holes formed in the clad portion and extending in the longitudinal direction of the optical fiber, and each of the grating portions has a side length d in the optical fiber cross section.
Is a honeycomb shape having a regular hexagon as a basic lattice, and one of the basic lattices has the hollow core portion. 2. The single mode photonic bandgap fiber according to claim 1, wherein the holes are provided at each vertex of a regular hexagon of all the basic lattices except the core portion. 3. The hole is provided in the center of all the basic lattices except the core portion.
A single-mode photonic bandgap fiber according to. 4. A hole group of the first kind consisting of a set of 7 holes and a single hole as the holes, and in the cross section of the optical fiber, of the basic lattice excluding the core portion. 2 × d from the center of the core part among the vertices of a regular hexagon
The holes of the first type are arranged only at vertices that are distant from each other, and only at vertices more than 2 × d from the center of the core part among the regular hexagonal vertices of the basic lattice excluding the core part. 2. The single hole is arranged.
A single-mode photonic bandgap fiber according to. 5. A hole group of the first kind composed of a set of seven holes is provided as the holes, and the first kind of holes of the first kind are provided at the vertices of regular hexagons of all the basic lattices except the core portion. The single-mode photonic bandgap fiber according to claim 1, wherein holes are arranged. 6. A hole group of the second kind consisting of a set of 6 holes as said holes, further comprising: from the center of said core part among the centers of all said basic lattices except said core part. The single mode photonic bandgap fiber according to claim 4, wherein the second type hole group is arranged only in the center of the basic lattice that is separated by 2 × d or less. 7. The hole group further comprises a second type hole group composed of a set of six holes as the holes, and the second holes are formed at the centers of all the basic lattices except the core portion.
A single-mode photonic bandgap fiber according to claim 5, characterized in that a group of holes is arranged. 8. A hole group of the first kind consisting of a set of 7 holes and a single hole as the holes, and in the cross section of the optical fiber, the basic lattice excluding the core portion is formed. The first-type hole group is arranged only in a center apart from the center of the core portion by 2 × d or less, and 2 × from the center of the core portion in the center of the basic lattice excluding the core portion. The single mode photonic bandgap fiber according to claim 1, wherein the single hole is arranged only in a center that is farther than d. 9. The hole has a hole group of the first kind consisting of a set of 7 holes as the holes, and the first hole is provided at the center of all the basic lattices except the core portion.
The single-mode photonic bandgap fiber according to claim 1, wherein a group of holes are arranged. 10. The core part further comprises a second type hole group consisting of a set of 6 holes as the holes, and the core part of all the regular hexagonal vertices of the basic lattice except the core part. 9. The single-mode photonic bandgap fiber according to claim 8, wherein the holes of the second type are arranged only at the vertices of the basic lattice, which are separated from the center by 2 × d or less. 11. A hole group of the second kind consisting of a set of six holes as said holes, further comprising the second kind at the apex of a regular hexagon of all said basic lattices except said core part. 10. The single-mode photonic bandgap fiber according to claim 9, wherein the group of holes is arranged. 12. A gap between the core and a hole adjacent to the core, and / or a gap between the core and the first type hole group and / or the second type hole group. The single mode photonic bandgap fiber according to any one of claims 4 to 11, wherein holes are arranged. 13. A glass base material forming a single-mode optical fiber, wherein the glass base material is a hollow glass rod for core arranged in a core portion, and the hollow glass for core around the core portion. It is composed of a plurality of hollow or solid glass rods arranged in parallel with the rod, and in the cross section of the glass base material, the center of the hollow or solid glass rod is a regular hexagon whose side length is d. A glass preform for a single mode photonic bandgap fiber, which is disposed at the apex or center of a basic lattice, and one of the basic lattices has the core portion. 14. The hollow glass rod is arranged at each vertex of a regular hexagon of all the basic lattices except the core portion, and the solid glass rod is placed at the center of all the basic lattices except the core portion. The glass base material of the single mode photonic bandgap fiber according to claim 13, wherein 15. The solid glass rods are arranged at the vertices of regular hexagons of all the basic lattices except the core portion, and the hollow glass rods are placed at the centers of all the basic lattices except the core portion. The glass preform of a single mode photonic bandgap fiber according to claim 13, wherein the glass preform is arranged. 16. A cross section of the glass preform, comprising a hollow glass rod group which is an assembly of seven hollow glass rods, and a solid glass rod group which is an assembly of seven solid glass rods. In the above, the hollow glass rod group is arranged only at apexes of the regular hexagons of the basic lattice excluding the core portion, which are separated by 2 × d or less from the center of the core portion. A single solid glass rod is arranged only at vertices more than 2 × d from the center of the core portion among the vertices of a regular hexagon, and the center of the core portion among the centers of the basic lattice excluding the core portion. From the center of the basic lattice excluding the core portion, the solid glass rod group is arranged only at a center distant from the core portion by 2 × d or less. 14. The solid glass rod of claim 1 is arranged. A glass preform of the described single-mode photonic bandgap fiber. 17. A cross section of the glass base material, comprising a hollow glass rod group which is an assembly of 7 hollow glass rods, and a solid glass rod group which is an assembly of 7 solid glass rods. In, the hollow glass rod group is arranged at the apex of a regular hexagon of all the basic lattices except the core portion, and the solid glass rod group is arranged at the center of all the basic lattices except the core portion. The glass preform of the single mode photonic bandgap fiber according to claim 13, wherein 18. The group of solid glass rods is replaced with a group of mixed glass rods each of which is an assembly in which the circumference of one solid glass rod is surrounded by six hollow glass rods. Item 18. A glass preform for a single-mode photonic bandgap fiber according to Item 16 or 17. 19. The group of hollow glass rods is replaced with a group of mixed glass rods, each of which is an assembly in which one solid glass rod is surrounded by six hollow glass rods. The glass preform of the single mode photonic bandgap fiber according to 16 or 17. 20. A hollow glass rod group, which is an assembly of 7 hollow glass rods, and a solid glass rod group, which is an assembly of 7 solid glass rods, wherein the glass base material has a cross section. In the center of the basic lattice excluding the core portion, the hollow glass rod group is arranged only at a center 2 × d or less from the center of the core portion, and among the centers of the basic lattice excluding the core portion. A single solid glass rod is arranged only at a center that is more than 2 × d from the center of the core portion, and 2 × from the center of the core portion among the regular hexagonal vertices of the basic lattice excluding the core portion. The solid glass rod group is arranged only at the vertices separated by d or less, and only one of the regular hexagonal vertices of the basic lattice excluding the core is separated from the center of the core by more than 2 × d. 14. The solid glass rod of claim 1 is arranged. A glass preform of the described single-mode photonic bandgap fiber. 21. A hollow glass rod group, which is an assembly of 7 hollow glass rods, and a solid glass rod group, which is an assembly of 7 solid glass rods, wherein the glass base material has a cross section. In, the hollow glass rod group is arranged at the center of all the basic lattices except the core portion, and the solid glass at the apex of the regular hexagon of all the basic lattices except the core portion in the cross section of the glass base material. The glass preform of a single-mode photonic bandgap fiber according to claim 13, wherein a group of rods is arranged. 22. Each of the solid glass rod groups is replaced with a mixed glass rod group which is an assembly in which one solid glass rod is surrounded by six hollow glass rods. Item 22. A glass preform for a single-mode photonic bandgap fiber according to Item 20 or 21. 23. The hollow glass rod group is replaced with a mixed glass rod group, which is an assembly in which one solid glass rod is surrounded by six hollow glass rods. The glass preform of the single mode photonic bandgap fiber according to 20 or 21. 24. A hollow glass rod is further arranged so as to be in contact with the hollow glass rod adjacent to the core portion and / or the solid glass rod and the hollow glass rod for core. Item 24. A glass preform for a single-mode photonic bandgap fiber according to any one of Items 16 to 23.