JP6276571B2 - Optical fiber - Google Patents

Description

  The present invention relates to an optical fiber and an optical fiber manufacturing method.

  In order to reduce the effective refractive index of the cladding, a hollow portion may be provided in the cladding around the core. In the optical fiber of Non-Patent Document 1, the core is surrounded by three or four hollow portions. Further, in the optical fiber of Non-Patent Document 2, a plurality of hollow portions arranged on the same circumference are provided around the core in a double manner.

T. Kohoutek, Z. Duan, H. Kawashima, X. Yan, T. Suzuki, M. Matsumoto, T. Misumi, and Y. Ohishi, Proc. Of SPIE Vol. 8257 82570D-1 (2012). C. Chaudhari, M. Liao, T. Suzuki, and Y. Ohishi, Journal of Lightwave Technology, Vol. 30, No. 13, 2069 (2012).

  In an optical fiber, when the refractive index difference between the core and the clad is small, part of the light propagating through the core oozes into the clad. At this time, the degree of light oozing varies depending on the wavelength of the light. For this reason, in an optical fiber having a small refractive index difference between the core and the clad, chromatic dispersion occurs. Therefore, the present inventors have studied an optical fiber that can reliably increase the effective refractive index difference between the core and the clad.

According to the present invention,
A core formed of chalcogenide glass;
A clad formed of a material having a lower refractive index than the core, and surrounding the core along a circumferential direction of the core;
With
The clad includes a plurality of hollow portions in a cross section perpendicular to the extending direction of the core,
The composition of the core is AsSe _m (1.5 ≦ m ≦ 2),
The composition of the _clad, the optical fiber is _{As 2 S n (3 ≦ n} ≦ 7) is provided.

According to the present invention,
A core formed of chalcogenide glass;
A clad formed of a material having a lower refractive index than the core, and surrounding the core along a circumferential direction of the core;
With
The clad includes a plurality of hollow portions in a cross section perpendicular to the extending direction of the core,
The composition of the core is Ge ₃₂ As ₇ Se ₃₀ Te ₃₀ ;
An optical fiber is provided in which the composition of the clad is Ge _α Ga _β Sb _γ S _η (15 ≦ α ≦ 20, 3 ≦ β ≦ 5, 10 ≦ γ ≦ 13, 65 ≦ η ≦ 70) .

  According to the present invention, chromatic dispersion can be effectively suppressed.

It is a perspective view which shows the optical fiber in 1st Embodiment. It is sectional drawing in plane S1 of FIG. It is a figure which shows the modification of FIG. It is sectional drawing in plane S2 of FIG. It is sectional drawing for demonstrating the manufacturing method of the optical fiber shown in FIG. It is sectional drawing for demonstrating the manufacturing method of the optical fiber shown in FIG. It is sectional drawing for demonstrating the manufacturing method of the optical fiber shown in FIG. It is sectional drawing which shows the optical fiber in 2nd Embodiment. 3 is a graph showing wavelength dispersion characteristics in Example 1.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In all the drawings, the same reference numerals are given to the same components, and the description will be omitted as appropriate.

(First embodiment)
FIG. 1 is a perspective view showing an optical fiber 100 according to the first embodiment. FIG. 2 is a cross-sectional view taken along plane S1 in FIG. The plane S1 is a plane perpendicular to the extending direction of the optical fiber 100. The optical fiber 100 includes a core 102 and a clad 104. The core 102 is made of chalcogenide glass. The clad 104 is made of a material having a lower refractive index than the core 102. The clad 104 surrounds the core 102 along the circumferential direction of the core 102. The clad 104 includes a plurality of first hollow portions 106 and a plurality of second hollow portions 108. The plurality of first hollow portions 106 are provided apart from each other on the same circumference centered on the center of the core 102 in a cross section perpendicular to the extending direction of the core 102. The second hollow portions 108 are separated from each other on the same circumference centering on the center of the core 102 outside the plurality of first hollow portions 106 with respect to the core 102 in a cross section perpendicular to the extending direction of the core 102. Is provided. Further, the second hollow portions 108 adjacent to each other along the circumferential direction of the core 102 in the cross section perpendicular to the extending direction of the core 102 have an outer edge 110. The outer edge 110 is an outer edge parallel to a straight line that spreads radially from the center of the core 102 and sews between the adjacent second hollow portions 108. In the plurality of second hollow portions 108, the outer edges 110 face each other along the circumferential direction of the core 102. Details will be described below.

The core 102 is made of chalcogenide glass. Specifically, the core 102 is, for example, an arsenic sulfide compound-based, arsenic selenide compound-based, germanium sulfide compound-based, or selenide telluride-based glass. More specifically, the core 102 may be a glass (eg, Ge ₁₅ Ga ₃ Sb ₁₃ S ₆₉ ) made of germanium, gallium, antimony, and sulfur.

The clad 104 is made of, for example, glass. The material of the clad 104 is not particularly limited as long as it has a refractive index lower than that of the core 102. Note that the difference between the refractive index of the material of the core 102 and the refractive index of the material of the clad 104 is preferably 0.1 or more. Specifically, the clad 104 is made of glass composed of tellurium oxide, bismuth oxide, lithium oxide, and zinc oxide (for example, 78 mol% TeO ₂ -5 mol% Bi ₂ O ₃ -12 mol% Li ₂ O-5 mol). % ZnO).

  A resin layer (not shown) may be provided between the core 102 and the clad 104. In this case, as the resin layer, for example, tetrafluoroethylene / hexafluoropropylene copolymer or polymethyl methacrylate (PMMA) can be used. By providing the resin layer between the core 102 and the clad 104, the molecules constituting the core 102 and the molecules constituting the clad 104 are prevented from being mixed.

  In the example shown in FIG. 1, the clad 104 has a cylindrical shape. The core 102 is provided on the clad 104 so that the central axis of the core 102 coincides with the central axis of the clad 104. However, the arrangement of the cores 102 is not limited to the example shown in FIG. For example, the central axis of the core 102 may be shifted from the central axis of the clad 104. FIG. 1 schematically shows the optical fiber 100. For this reason, the 1st hollow part 106 and the 2nd hollow part 108 are not shown by FIG. Further, although the optical fiber 100 is formed in a straight line in FIG. 1, the optical fiber 100 can be used even in a bent state.

  The first hollow portion 106 and the second hollow portion 108 are provided inside the clad 104. For this reason, the clad 104 is hollow in the first hollow portion 106 and the second hollow portion 108. As a result, the clad 104 contains gas (for example, inert gas or air) in the first hollow portion 106 and the second hollow portion 108. Therefore, the refractive index in the first hollow portion 106 and the second hollow portion 108 is about 1.

  In the cross section perpendicular to the extending direction of the core 102, the plurality of first hollow portions 106 and the plurality of second hollow portions 108 are arranged rotationally symmetrically with respect to the center of the core 102. In the example shown in FIG. 2, the first hollow portion 106 and the second hollow portion 108 are arranged in 6-fold rotational symmetry with respect to the center of the core 102. The number of the first hollow portions 106 and the number of the second hollow portions 108 are the same as 6 in the example shown in FIG. 2, but these numbers may be different from each other.

  In a cross section perpendicular to the extending direction of the core 102, the plurality of second hollow portions 108 are provided outside a circle surrounding the entirety of the plurality of first hollow portions 106 around the center of the core 102. That is, the first hollow portion 106 and the second hollow portion 108 do not overlap in the circumferential direction of the core 102.

  In the example illustrated in FIG. 2, the average cross-sectional area of the plurality of second hollow portions 108 is larger than the average cross-sectional area of the plurality of first hollow portions 106 in a cross section perpendicular to the extending direction of the core 102. However, the relationship between the average cross-sectional area of the plurality of first hollow portions 106 and the average cross-sectional area of the plurality of second hollow portions 108 is not limited to the example shown in FIG. For example, in the cross section perpendicular to the extending direction of the core 102, the average cross-sectional area of the plurality of second hollow portions 108 may be smaller than the average cross-sectional area of the plurality of first hollow portions 106.

  In the example shown in FIG. 2, in a cross section perpendicular to the extending direction of the core 102, straight lines extending radially from the center of the core 102 and passing through the centers of the plurality of first hollow portions 106 are a plurality of second hollows. A plurality of second hollow portions 108 are arranged so as to sew between the portions 108. Further, in the example shown in FIG. 2, the portion of the clad 104 sandwiched between the outer edges 110 is provided so as to be included inside the first hollow portion 106 when viewed from the center of the core 102 in the radial direction of the core 102. It has been.

  In addition, the 1st hollow part 106 and the 2nd hollow part 108 may be arrange | positioned as shown in FIG. In the example shown in FIG. 3, in a cross section perpendicular to the extending direction of the core 102, straight lines extending radially from the center of the core 102 and passing through the centers of the plurality of first hollow portions 106 are a plurality of second hollows. A plurality of second hollow portions 108 are arranged so as to pass through the portion 108. Specifically, in the example illustrated in FIG. 3, straight lines that radiate from the center of the core 102 and pass through the centers of the plurality of first hollow portions 106 pass through the centers of the plurality of second hollow portions 108. ing.

  Further, as shown in FIGS. 4A and 4B, the first hollow portion 106 and the second hollow portion 108 are formed in the extending direction of the core 102 (FIGS. 4A and 4B). In the example shown in FIG. 4, the clad 104 is continuously formed from one end to the other end in the z-axis direction). FIGS. 4A and 4B are cross-sectional views on the plane S2 and the plane S3 in FIG. 1, respectively.

  Next, a method for manufacturing the optical fiber 100 shown in FIG. 1 will be described with reference to FIGS. 5 to 7 are cross-sectional views for explaining a method of manufacturing the optical fiber 100, and correspond to FIG.

  First, a glass tube (first glass tube) 120 (FIG. 5), a core rod 130 (FIG. 6), a plurality of glass tubes (third glass tube) 140 (FIG. 6), and a jacket tube 150 (FIG. 7) Prepare.

  The glass tube 120 includes a tube portion 122 and a plurality of pieces 124. In the example shown in FIG. 5, the tube portion 122 extends in the z-axis direction (first direction). On the other hand, the plurality of pieces 124 extend in the z-axis direction and project radially from the tube part 122 in a cross section perpendicular to the z-axis direction. Note that the glass tube 120 forms the clad 104 in a later step. For this reason, the glass tube 120 is formed of the same material as that of the clad 104.

  The core rod 130 includes a glass tube (second glass tube) 132 and a core 102. The core 102 is located inside the glass tube 132. Note that the glass tube 132 forms the clad 104 in a later step. For this reason, the glass tube 132 is formed of the same material as that of the clad 104.

  The glass tube 140 and the jacket tube 150 form the clad 104 in a later step, like the glass tube 120 and the glass tube 132. For this reason, the glass tube 140 and the jacket tube 150 are also formed of the same material as the clad 104.

After these preparations are completed, as shown in FIG. 6, the core rod 130 and the plurality of glass tubes 140 are inserted into the tube portion 122 of the glass tube 120. In the example shown in FIG. 6, the glass tube 140 is disposed so as to surround the core rod 130. As a result, the core rod 130 is located at the center of the pipe portion 122. In the example shown in FIG. 6, the inner diameter R of the tube 122, the core rod 130, for inserting the glass tube 140, the inside of the tube portion 122, satisfies the _R ≧ _r C + 2r _g (However, r _C is the diameter of the core rod 130, and r _g is the diameter of the glass tube 140).

  Next, as shown in FIG. 7, the glass tube 120 is inserted into the jacket tube 150. As a result, a gap 152 is formed as shown in FIG. The gap 152 is a gap surrounded by the pipe part 122, the piece part 124, and the jacket pipe 150.

  Next, the jacket tube 150 into which the glass tube 120 is inserted is drawn by making the inside of the plurality of glass tubes 140 and the gap 152 positive. In this way, the optical fiber 100 shown in FIG. 2 is manufactured.

  Next, the operation and effect of this embodiment will be described. In the present embodiment, the outer edges 110 face each other along the circumferential direction of the core 102. For this reason, the several 2nd hollow part 108 can be efficiently arrange | positioned by the narrow space | interval on the same periphery. In this case, the low refractive index region formed by the second hollow portion 108 is reliably distributed around the first hollow portion 106. As a result, the effective refractive index difference between the core 102 and the clad 104 can be reliably increased. Thus, in this embodiment, chromatic dispersion can be effectively suppressed.

  In particular, in the example illustrated in FIG. 2, a plurality of second portions are formed such that straight lines spreading radially from the center of the core 102 and passing through the centers of the plurality of first hollow portions 106 sew between the plurality of second hollow portions 108. A hollow portion 108 is disposed. In this case, even if light oozing out from the core 102 oozes out between the first hollow portions 106, the light feels a decrease in refractive index due to the second hollow portion 108. That is, the effective refractive index difference between the core 102 and the clad 104 can be increased more reliably. This effect is provided so that the portion of the clad 104 sandwiched between the outer edges 110 is included inside the first hollow portion 106 when viewed from the center of the core 102 in the radial direction of the core 102. If you are better.

(Second Embodiment)
FIG. 8 is a cross-sectional view showing the optical fiber 100 according to the second embodiment, and corresponds to FIG. 2 of the first embodiment. The optical fiber 100 includes a core 102 and a clad 104. The core 102 is made of chalcogenide glass. The clad 104 is made of a material having a lower refractive index than the core 102. At the same time, the clad 104 surrounds the core 102 along the circumferential direction of the core 102. The clad 104 includes a plurality of first hollow portions 106 in a cross section perpendicular to the extending direction of the core 102.

In the present embodiment, the core 102 is glass made of arsenic and selenium. At the same time, the cladding 104 is a glass made of arsenic and sulfur. Specifically, the composition of the composition and the cladding 104 of the core 102, respectively, is _{AsSe m (1.5 ≦ m ≦ 2} ) and _{As 2 S n (3 ≦ n} ≦ 7). Preferably, the composition of the core 102 and the composition of the cladding 104 are AsSe ₂ and As ₂ S ₅ , respectively.

  In the present embodiment, the core 102 is a glass made of arsenic and selenium, and the clad 104 is a glass made of arsenic and sulfur. For this reason, the effective refractive index difference between the core 102 and the clad 104 can be made large in combination with the refractive index decrease due to the first hollow portion 106. Thus, in this embodiment, chromatic dispersion can be effectively suppressed.

  In addition, arrangement | positioning of the 1st hollow part 106 is not limited to the example shown in FIG. The first hollow portion 106 may be arranged, for example, like the first hollow portion 106 and the second hollow portion 108 in the example shown in FIG.

(Third embodiment)
The third embodiment is the same as the second embodiment except for the material of the core 102 and the clad 104. In the present embodiment, the core 102 is a glass made of germanium, arsenic, selenium, and tellurium. At the same time, the cladding 104 is a glass made of germanium, gallium, antimony and sulfur. Specifically, the composition of the core 102 and the composition of the cladding 104 are Ge ₃₂ As ₇ Se ₃₀ Te ₃₀ and Ge _α Ga _β Sb _γ S _η (15 ≦ α ≦ 20, 3 ≦ β ≦ 5, 10 ≦, respectively. γ ≦ 13, 65 ≦ η ≦ 70). Preferably, the composition of the cladding 104 is Ge ₁₇ Ga ₄ Sb ₁₀ S ₆₉ .

  Also in this embodiment, as in the second embodiment, the effective refractive index difference between the core 102 and the clad 104 can be increased. For this reason, in this embodiment, chromatic dispersion can be effectively suppressed.

Example 1
Similar to the first embodiment, an optical fiber having the same structure as the example shown in FIG. 2 was manufactured. The composition of the composition and the cladding 104 of the core 102, _{respectively,} and a Ge ₁₅ Ga _{3 Sb} 13 _{S 69} and 78 mol% _TeO 2 -5 _mol% Bi ₂ O 3 -12 mol% _Li 2 O-5 mol% ZnO. The structures of the core 102, the first hollow portion 106, and the second hollow portion 108 were as follows.
Diameter of core 102: 1.0 μm
Diameter of first hollow portion 106: 0.36 μm
Pitch of the first hollow portion 106: 0.68 μm
Diameter of second hollow portion 108: 2.0 μm
Pitch of second hollow part 108: 2.2 μm
Further, Teflon (registered trademark) FEP was provided between the core 102 and the clad 104. The refractive index difference between the core 102 and the clad 104 was 0.2.

  The chromatic dispersion characteristics of the optical fiber in this example are as shown in FIG. As shown in FIG. 9, in this example, chromatic dispersion could be zeroed and flattened at 1.6 μm and 3.45 μm. Further, when 1.6 μm and 3.45 μm excitation light was incident on the optical fiber in this example, parametric amplification and oscillation and wavelength conversion could be confirmed in the wavelength range of 1 μm to 5 μm.

  The transmission loss of the optical fiber in this example was 1 dB / m or less. In the case where the Teflon (registered trademark) FEP was not provided in the optical fiber in this example, the transmission loss was 200 dB / m. From this, it can be said that the transmission loss of the optical fiber is suppressed by Teflon (registered trademark) FEP.

  Further, in the optical fiber in this example, polymethyl methacrylate (PMMA) resin was provided between the core 102 and the clad 104 in place of Teflon (registered trademark) FEP. Even in this case, the transmission loss can be reduced as compared with the case where no resin is provided between the core 102 and the clad 104.

  Furthermore, in the optical fiber according to the present example, the pitch of the first hollow portions 106 is set to be larger than 0.67 μm and smaller than 0.68 μm. In this case, the chromatic dispersion could be suppressed from −100 ps / km / nm to 0 ps / km / nm in the wavelength range of 1 μm to 8 μm. Furthermore, when this optical fiber was excited with a 1.55 μm pulse laser, supercontinuum light with good coherence due to self-phase modulation could be generated from 1 μm to 8 μm.

(Example 2)
Similar to the second embodiment, an optical fiber having the same structure as the example shown in FIG. 8 was manufactured. The composition of the core 102 and the composition of the cladding 104 were AsSe ₂ and As ₂ S ₅ , respectively. The structures of the core 102, the first hollow portion 106, and the second hollow portion 108 were as follows.
Diameter of core 102: 1.2 μm
Diameter of first hollow portion 106: 2 μm
Pitch of the first hollow part 106: 3 μm
The refractive index difference between the core 102 and the clad 104 was 0.5.

  An optical pulse having a pulse width of 100 femtoseconds, a repetition frequency of 40 MHz, and an average output of 200 mW was incident on this optical fiber. At this time, supercontinuum light of 1.3 μm to 7 μm could be observed.

  Further, the diameter of the core 102 was changed from 0.8 μm to 1 μm, the diameter of the first hollow portion 106 was changed from 1.5 μm to 3 μm, and the pitch of the first hollow portion 106 was changed from 2.5 μm to 5 μm. In this case, the wavelength became zero dispersion in the wavelength region from 1.4 μm to 1.6 μm. At the same time, chromatic dispersion flattened in this wavelength region could be obtained. Further, when this optical fiber was excited with a continuous light laser of 1.55 μm, parametric amplification and wavelength conversion could be confirmed in the wavelength range of 1 μm to 2.5 μm.

(Example 3)
Similar to the third embodiment, an optical fiber having the same structure as the example shown in FIG. 8 was manufactured. The composition of the composition and the cladding 104 of the core 102, _{respectively,} and a Ge ₃₂ As ₇ Se _{30 Te} 30 and _{Ge 17 Ga 4 Sb 10 S 69} . The refractive index difference between the core 102 and the clad 104 was 0.4.

  The diameter of the core 102 was changed from 0.8 μm to 1.2 μm, the diameter of the first hollow portion 106 was changed from 1.2 μm to 3 μm, and the pitch of the first hollow portion 106 was changed from 2 μm to 5 μm. In this case, the wavelength became zero dispersion in the wavelength region from 1.4 μm to 1.6 μm. At the same time, chromatic dispersion flattened in this wavelength region could be obtained. Furthermore, when this optical fiber was excited with a continuous light laser of 1.55 μm, parametric amplification and oscillation and wavelength conversion could be confirmed in the wavelength range of 1 μm to 2.5 μm. In addition, although the number of the 1st hollow parts 106 in a present Example is 6, even if the number of the 1st hollow parts 106 is 3 or 4, the effect similar to a present Example can be acquired.

  Further, Teflon (registered trademark) resin (thickness: 10 μm) was provided between the core 102 and the clad 104. In this example, the transmission loss of the optical fiber not provided with Teflon (registered trademark) resin was 3 dB / m. In this example, the transmission loss of the optical fiber provided with Teflon (registered trademark) resin was 1 dB. / M. At the same time, the amplification efficiency was improved more than twice.

As mentioned above, although embodiment of this invention was described with reference to drawings, these are the illustrations of this invention, Various structures other than the above are also employable.
Hereinafter, examples of the reference form will be added.
1. A core formed of chalcogenide glass;
A clad formed of a material having a lower refractive index than the core, and surrounding the core along a circumferential direction of the core;
With
The cladding is
In a cross section perpendicular to the extending direction of the core, a plurality of first hollow portions provided on the same circumference centered on the center of the core and spaced apart from each other;
In a cross section perpendicular to the extending direction of the core, a plurality of gaps provided on the same circumference centered on the center of the core and spaced apart from each other outside the plurality of first hollow portions with respect to the core A second hollow portion;
Including
In a cross section perpendicular to the extending direction of the core, the second hollow portions adjacent to each other along the circumferential direction of the core spread radially from the center of the core and are between the adjacent second hollow portions. An optical fiber having an outer edge parallel to a straight line that sews the outer edges, and the outer edges face each other along the circumferential direction of the core.
2. 1. An optical fiber according to claim 1,
In a cross section perpendicular to the extending direction of the core, the plurality of first hollow portions and the plurality of second hollow portions are arranged in a rotationally symmetrical manner with respect to the center of the core.
3. 1. Or 2. An optical fiber according to claim 1,
In a cross section perpendicular to the extending direction of the core, the plurality of second hollow portions are provided outside a circle surrounding the whole of the plurality of first hollow portions with the center of the core as a center. fiber.
4). 1. To an optical fiber according to any one of 3 to 3,
In the cross section perpendicular to the extending direction of the core, the average cross-sectional area of the plurality of second hollow portions is larger than the average cross-sectional area of the plurality of first hollow portions.
5. 1. To 4, the optical fiber according to any one of
In a cross section perpendicular to the extending direction of the core, straight lines that radiate from the center of the core and pass through the centers of the plurality of first hollow portions sew between the plurality of second hollow portions. An optical fiber in which the plurality of second hollow portions are arranged.
6). 5. An optical fiber according to claim 1,
An optical fiber provided so that a portion of the clad sandwiched between the outer edges is included inside the first hollow portion when viewed in the radial direction of the core from the center of the core.
7). A first glass tube comprising: a tube portion extending in a first direction; and a plurality of pieces extending radially from the tube portion in a cross section extending in the first direction and perpendicular to the first direction; ,
A core rod including a second glass tube and a core located inside the second glass tube;
A plurality of third glass tubes;
A jacket tube,
The process of preparing
Inserting the core rod and the plurality of third glass tubes into the tube portion of the first glass tube;
Inserting the first glass tube into the jacket tube after inserting the core rod and the plurality of third glass tubes into the tube portion of the first glass tube;
A step of drawing the jacket tube in which the first glass tube is inserted by setting the inside of the plurality of third glass tubes and the gap surrounded by the tube portion, the piece portion, and the jacket tube to a positive pressure. When,
The manufacturing method of the optical fiber containing this.
8). A core formed of chalcogenide glass;
A clad formed of a material having a lower refractive index than the core, and surrounding the core along a circumferential direction of the core;
With
The clad includes a plurality of hollow portions in a cross section perpendicular to the extending direction of the core,
The core is a glass made of arsenic and selenium or a glass made of germanium, arsenic, selenium and tellurium,
When the core is a glass made of arsenic and selenium, the clad is a glass made of arsenic and sulfur,
When the core is a glass made of germanium, arsenic, selenium, and tellurium, the clad is an optical fiber made of glass made of germanium, gallium, antimony, and sulfur.

DESCRIPTION OF SYMBOLS 100 Optical fiber 102 Core 104 Clad 106 1st hollow part 108 2nd hollow part 110 Outer edge 120 Glass tube 122 Pipe part 124 Piece part 130 Core rod 132 Glass tube 140 Glass tube 150 Jacket tube 152 Gap

Claims (8)

A core formed of chalcogenide glass;
A clad formed of a material having a lower refractive index than the core, and surrounding the core along a circumferential direction of the core;
With
The clad includes a plurality of hollow portions in a cross section perpendicular to the extending direction of the core,
The composition of the core is AsSe _m (1.5 ≦ m ≦ 2),
The composition of the _clad, As _{2 S} n optical fibers is (3 ≦ n ≦ 7). A core formed of chalcogenide glass;
A clad formed of a material having a lower refractive index than the core, and surrounding the core along a circumferential direction of the core;
With
The clad includes a plurality of hollow portions in a cross section perpendicular to the extending direction of the core,
The composition of the core is Ge ₃₂ As ₇ Se ₃₀ Te ₃₀ ;
An optical fiber in which the composition of the cladding is Ge _α Ga _β Sb _γ S _η (15 ≦ α ≦ 20, 3 ≦ β ≦ 5, 10 ≦ γ ≦ 13, 65 ≦ η ≦ 70) . The optical fiber according to claim 1 or 2,
The plurality of hollow portions are:
In a cross section perpendicular to the extending direction of the core, a plurality of first hollow portions provided on the same circumference centered on the center of the core and spaced apart from each other;
In a cross section perpendicular to the extending direction of the core, a plurality of gaps provided on the same circumference centered on the center of the core and spaced apart from each other outside the plurality of first hollow portions with respect to the core A second hollow portion;
Including
In a cross section perpendicular to the extending direction of the core, the second hollow portions adjacent to each other along the circumferential direction of the core spread radially from the center of the core and are between the adjacent second hollow portions. An optical fiber having an outer edge parallel to a straight line that sews the outer edges, and the outer edges face each other along the circumferential direction of the core. The optical fiber according to claim 3 ,
In a cross section perpendicular to the extending direction of the core, the plurality of first hollow portions and the plurality of second hollow portions are arranged in a rotationally symmetrical manner with respect to the center of the core. The optical fiber according to claim 3 or 4 ,
In a cross section perpendicular to the extending direction of the core, the plurality of second hollow portions are provided outside a circle surrounding the whole of the plurality of first hollow portions with the center of the core as a center. fiber. An optical fiber according to any one of claims 3 to 5 ,
In the cross section perpendicular to the extending direction of the core, the average cross-sectional area of the plurality of second hollow portions is larger than the average cross-sectional area of the plurality of first hollow portions. The optical fiber according to any one of claims 3 to 6 , comprising:
In a cross section perpendicular to the extending direction of the core, straight lines that radiate from the center of the core and pass through the centers of the plurality of first hollow portions sew between the plurality of second hollow portions. An optical fiber in which the plurality of second hollow portions are arranged. The optical fiber according to claim 7 ,
An optical fiber provided so that a portion of the clad sandwiched between the outer edges is included inside the first hollow portion when viewed in the radial direction of the core from the center of the core.

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