JP2006243423A - Photonick crystal fiber, optical transmission line and optical communication system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photonic crystal fiber which has a large effective cross section and achieves wavelength dispersion opposite to that of a single mode optical fiber in a wide band. <P>SOLUTION: The photonic crystal fiber has a center core part 1, an inner layer clad part 2 which surrounds the center core part 1, and an outer layer clad part 3 which surrounds the inner clad part 2 with a space L in-between, and a plurality of holes 5, 6 are formed in the inner layer clad part 2 and the outer layer clad part 3, respectively while no hole is formed in the space L, and an outer peripheral radius a<SB>1</SB>of the inner layer clad part 2, an inner peripheral radius a<SB>2</SB>of the outer layer clad part 3, an hole interval Λ<SB>1</SB>of the holes 5 in the inner layer clad part 2 and the hole diameter d<SB>1</SB>satisfy the relation of a<SB>2</SB>-a<SB>1</SB>>Λ<SB>1</SB>-d<SB>1</SB>to raise an optical confinement effect of the outer layer clad part 3, so that an optical signal is propagated within the area surrounded by the outer layer clad part 3. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a photonic crystal fiber, an optical transmission line, and an optical communication system, and more particularly to a photonic crystal fiber having a dispersion compensation function.

  A photonic crystal fiber (PCF) is an optical fiber having a structure having a plurality of holes extending in a longitudinal direction. FIG. 4 shows a photonic crystal fiber having the most general structure. As shown in FIG. 4, inside the photonic crystal fiber 30 made of quartz glass, an annular hole 31 is formed in the axial center portion of the photonic crystal fiber 30 along the axial center of the photonic crystal fiber 30. A plurality of clads 33 surrounding the core 32 are formed, and the air holes 31 have a diameter d in the order of wavelengths and an equal interval Λ. In such a photonic crystal fiber 30, the air holes 31 lower the refractive index of the clad 33, so that an optical waveguide structure is formed between the core 32 and the clad 33. Here, since the refractive index difference between the hole 31 and the glass is large, the relative refractive index difference and the core diameter can be flexibly controlled by controlling the position and size of the hole 31 and the design freedom. The degree is very high.

  So far, attention has been paid to the controllability of chromatic dispersion over a wide band of a photonic crystal fiber, and studies have been made for application to dispersion flat fibers and dispersion compensation fibers. For example, in the above-described photonic crystal fiber, dispersion compensation of a 1310 nm band single mode optical fiber is realized over a wide band by optimizing the hole spacing and the hole size (see Non-Patent Document 1). reference). In addition, a dispersion-compensating photonic crystal fiber and a dispersion-compensating fiber that can obtain a large negative dispersion and a negative dispersion slope in a wavelength 1550 nm band by using a special hole arrangement are disclosed (Patent Document 1 and (See Patent Document 2).

JP-T-2004-527775 JP 2004-101565 A L.P.Shen et al., “Design and Optimization of Photonic Crystal Fibers for Broad-Band Dispersion Compensation”, IEEE Photonics Technology Letters, vol.15, No.4, April 2003 ITU-T, Recommendation G. 652 (revised March 2003) (Table 1 / G.652, p.12)

However, although the photonic crystal fiber described in Non-Patent Document 1 can provide dispersion compensation in a wide band, its effective area is as small as about 1 μm ^2, so that connection loss and nonlinear effect increase. There was a problem that. Moreover, although the dispersion compensating photonic crystal fiber described in Patent Document 1 and the dispersion compensating fiber described in Patent Document 2 can obtain large negative dispersion at a certain wavelength, the wavelength that can be compensated is as narrow as several tens of nm. There was a problem that the range was limited.

  Therefore, the present invention has been proposed in view of the above-mentioned problems, and has a large effective area and a photonic crystal fiber, an optical transmission line, and a broadband that realizes wavelength dispersion opposite to that of a single mode optical fiber in a wide band. An object is to provide an optical communication system.

A photonic crystal fiber according to a first invention that solves the above-described problem has a core portion, an inner-layer cladding portion that surrounds the core portion, and an outer-layer cladding portion that surrounds the inner-layer cladding portion with a space therebetween. A plurality of holes are respectively formed in the inner layer cladding part and the outer layer cladding part, but no hole is formed in the interval, and the outer peripheral radius a ₁ of the inner layer cladding part and the inner layer cladding part The circumferential radius a ₂ , the hole interval Λ _{1 of the} holes in the inner cladding portion, and the hole diameter d ₁ are in a relation of a ₂ −a ₁ > Λ ₁ −d _1. .

A photonic crystal fiber according to a second invention that solves the above-described problem is the photonic crystal fiber according to the first invention, wherein Λ ₁ is a hole spacing of the holes in the outer cladding portion. And d ₁ is equal to or smaller than a hole diameter of the hole in the outer cladding portion.

  A photonic crystal fiber according to a third invention for solving the above-described problem is the photonic crystal fiber according to the first invention or the second invention, wherein the holes of the outer clad portion are used as the inner layer. It is larger than the hole of the clad part.

  A photonic crystal fiber according to a fourth invention that solves the above-described problem is the photonic crystal fiber according to any one of the first to third inventions, wherein the zero dispersion wavelength is from 1300 nm to 1324 nm. It is in the range of.

  A photonic crystal fiber according to a fifth invention for solving the above-described problems is the photonic crystal fiber according to any one of the first to fourth inventions, wherein the inner layer cladding portion and the outer layer cladding are provided. The holes in the portion are periodically arranged in a ring shape or a regular polygonal lattice shape.

  A photonic crystal fiber according to a sixth invention for solving the above-described problem, wherein the photonic crystal fiber is described in any one of the first to fifth inventions, wherein the inner-layer cladding portion and the The holes in the outer cladding portion are filled with a medium having a refractive index lower than that of the core portion.

  An optical transmission line according to a seventh invention for solving the above-described problems, wherein the single-mode optical fiber having zero dispersion in a 1310 nm band is connected to the single-mode optical fiber, and the first to sixth inventions. And a residual cumulative dispersion at the output end thereof is 1000 ps / nm or less within a wavelength range of 1260 nm to 1650 nm.

  An optical communication system according to an eighth invention for solving the above-described problem, characterized in that an optical signal is transmitted to the optical transmission line described in the seventh invention.

  According to the photonic crystal fiber according to the first invention, the optical confinement effect of the outer layer cladding portion is enhanced, and the optical signal propagates in the region surrounded by the outer layer cladding portion. Compared to the effective area, the effective area increases. In addition, it is possible to realize wavelength dispersion opposite to that of a single mode optical fiber in a wide band.

  According to the photonic crystal fiber according to the second invention, the same effect as the photonic crystal fiber described in the first invention can be obtained, and the light confinement effect of the outer cladding portion can be further enhanced.

  According to the photonic crystal fiber according to the third invention, the same effect as the photonic crystal fiber described in the first and second inventions can be obtained, and the light confinement effect of the outer clad portion can be further enhanced. Can be increased.

  According to the photonic crystal fiber according to the fourth invention, in addition to the same effects as the photonic crystal fiber described in the first to third inventions, a 1310 nm band zero-dispersion single mode optical fiber If connected, dispersion compensation over a wide band is possible.

  According to the photonic crystal fiber according to the fifth aspect of the invention, the same operational effects as the photonic crystal fiber described in the first to fourth aspects of the invention can be obtained.

  According to the photonic crystal fiber according to the sixth aspect of the invention, the same effects as the photonic crystal fiber described in any of the first to fifth aspects of the invention can be achieved.

  According to the optical transmission line of the seventh invention, when a signal with a transmission rate of 10 Gbit / s is transmitted, the occurrence of distortion of the signal can be suppressed.

  According to the optical communication system of the eighth invention, chromatic dispersion can be compensated over a wide band.

  Hereinafter, the best mode for carrying out a photonic crystal fiber, an optical transmission line, and an optical communication system using the same according to the present invention will be specifically described based on examples.

  FIG. 1 shows a photonic crystal fiber according to a first embodiment of the present invention, FIG. 1 (a) shows a schematic cross section thereof, and FIG. 1 (b) shows a refractive index distribution thereof. FIG. 2 is a schematic diagram of an optical communication system using the photonic crystal fiber according to the first embodiment of the present invention.

As shown in FIG. 1, the photonic crystal fiber according to the first embodiment of the present invention includes a center core portion 1 of the axial center portion of the photonic crystal fiber 10 and an outer peripheral radius a surrounding the center core portion 1. _{1 has} an inner-layer cladding portion 2 and an outer-layer cladding portion 3 having an inner peripheral radius a ₂ surrounding the inner-layer cladding portion 2.

The inner layer cladding portion 2 is formed with a plurality of holes 5 having a circular cross section and a hole diameter d ₁ , and is periodically arranged so that the interval between adjacent holes 5 is Λ ₁ . Specifically, these holes 5 are periodically arranged in a hexagonal lattice shape having hexagonal vertices. Similarly, a plurality of holes 6 having a circular cross section and a hole diameter d ₂ are formed in the outer layer cladding portion 3 and are periodically arranged so that the interval between adjacent holes 6 is Λ _2. Is done. Specifically, these holes 6 are periodically arranged in a hexagonal lattice shape having hexagonal vertices. However, no holes are formed in the interval L.

  Here, two layers of holes 5 are formed in the inner cladding portion 2, that is, the number of holes 5 periodically arranged from the axial center of the photonic crystal fiber 10 toward the outer periphery 10 a thereof. The number of the holes 6 periodically arranged from the layer of the holes 6 in the outer cladding portion 3, that is, from the axial center of the photonic crystal fiber 10 toward the outer periphery 10 a is formed.

Here, the outer peripheral radius a ₁ of the inner cladding 2, and the inner radius a ₂ of the outer cladding portion 3, holes distance lambda ₁ of the holes 5 in the inner cladding 2 and its pore diameter d ₁ is The following expression (1) is satisfied.
a ₂ −a ₁ > Λ ₁ −d ₁ (1)
Therefore, the optical confinement effect of the outer cladding portion 3 is enhanced, and an optical signal is propagated in a region surrounded by the outer cladding portion 3. Accordingly, the interval L, that is, the region located between the outer cladding portion 3 and the inner cladding portion 2 and between the distance a ₂ and the distance a ₁ is defined as the second core portion 4.

The hole interval Λ ₁ of the holes 5 in the inner cladding portion 2 is set to be equal to or smaller than the hole interval Λ ₂ of the holes 6 in the outer cladding portion 3, and the hole diameter d ₁ of the holes 5 in the inner cladding portion 2 is The hole diameter d _{2 of the} holes 6 in the outer layer cladding portion 3 is set to be equal to or smaller than d ₂ . By adopting such a shape, the light confinement effect of the outer clad portion 3 is further enhanced.

When the number of holes 5 in the inner layer cladding portion 2 is N ₁ , the outer peripheral radius a ₁ of the inner layer cladding portion 2 satisfies the following expression (2).
_{a 1 = N 1 Λ 1 +} d 1/2 (2)
In the photonic crystal fiber 10, N ₁ = 2.

When the number of defective layers of the holes 6 in the outer cladding portion 3 is M ₂ , the inner peripheral radius a ₂ of the outer cladding portion 3 satisfies the following expression (3).
_{a 2 = (M 2 +1)} Λ 2 -d 2/2 (3)
The number of defective layers M ₂ indicates the number of layers in which the holes 6 are eliminated. In the photonic crystal fiber 10, M ₂ = 1 because there is no hole 6 in the first layer.

In the photonic crystal fiber 10, as shown in FIG. 1B, the center core portion 1 and the second core portion 4 have the same refractive index n _co . The effective refractive index n _cl2 of the outer cladding portion 3 is lower than the refractive indexes n _co of the center core portion 1 and the second core portion 4. The effective refractive index n _cl3 the inner cladding 2 is lower than the effective refractive index n _cl2 the outer cladding portion 3. Therefore, in the photonic crystal fiber 10, the optical signal propagates in the region surrounded by the outer layer cladding portion 3, so that the effective cross-sectional area is enlarged as compared with the conventional photonic crystal fiber.

  The holes 6 in the outer cladding portion 3 are formed larger than the holes 5 in the inner cladding portion 2. Therefore, according to the photonic crystal fiber 10, the light confinement effect of the outer cladding portion 3 is further enhanced.

  Here, as shown in FIG. 2, the optical communication system 20 includes a transmitter 21 that converts an electrical signal from a signal source (not shown) and transmits the optical signal, and a reception that receives the optical signal and converts it into an electrical signal. A single mode optical fiber (SMF) having zero dispersion in the 1310 nm band, as an optical transmission line 24 connected to the transmitter 22, the transmitter 21 and the receiver 22 and transmitting an optical signal; It has a photonic crystal fiber 10 connected to a single mode optical fiber 23, and an optical signal is transmitted and received (transmitted) between a transmitter 21 and a receiver 22.

The photonic crystal fiber 10 has a wavelength dispersion characteristic of a different sign from the 1310 nm band zero-dispersion single mode optical fiber 23 over a wide band, and enables dispersion compensation in the wide band. Therefore, the zero dispersion wavelength of the photonic crystal fiber 10 is equal to the zero dispersion wavelength of the 1310 nm band zero dispersion single mode optical fiber 23. Here, the zero dispersion wavelength of the 1310 nm band zero dispersion single mode optical fiber 23 is recommended to be in the range of 1300 nm to 1324 nm (see Non-Patent Document 2). Therefore, the size of the holes 5 in the inner layer cladding portion 2, its hole interval Λ ₁ , and its hole diameter d ₁ , the size of the holes 6 in the outer layer cladding portion 3, its hole interval Λ ₂ , and By appropriately changing design conditions such as the hole diameter d ₂ , the zero dispersion wavelength of the photonic crystal fiber 10 is set in the range of 1300 nm to 1324 nm.

  When the photonic crystal fiber 10 and the 1310 nm band zero-dispersion single mode optical fiber 23 are connected to transmit an optical signal, the residual accumulated dispersion is 1000 ps / nm or less within a wavelength band of 1260 nm to 1650 nm which is a communication band. Thus, when an optical signal having a transmission rate of 10 Gbit / s is transmitted through the optical transmission line 25, the occurrence of signal distortion can be suppressed.

FIG. 3 is a diagram showing the chromatic dispersion characteristics in the photonic crystal fiber according to the first embodiment of the present invention, and the chromatic dispersion characteristics in the optical transmission line connecting it to the single mode optical fiber. The solid line indicates the chromatic dispersion characteristic of the photonic crystal fiber 10 alone, and the broken line in FIG. 3 indicates the effective chromatic dispersion characteristic when the photonic crystal fiber 10 and the single mode optical fiber 23 are connected. In the figure, Λ ₁ is 1.56 μm, d ₁ / Λ ₁ is 0.5, Λ ₂ is 2.9 μm, and d ₂ / Λ ₂ is 0.64. From the formula (2), a ₁ is set to 3.51 μm, and from the formula (3), a ₂ is set to 4.87 μm.

  As can be seen from FIG. 3, in the single photonic crystal fiber 10, when the wavelength is gradually increased from 1300 nm to 1600 nm, the chromatic dispersion gradually decreases from about 0 ps / nm · km to about −85 ps / nm · km. In the optical transmission line 24 in which the photonic crystal fiber 10 and the single mode optical fiber 23 are connected, the effective chromatic dispersion is ± 5 ps not only in the C band (1530 nm to 1560 nm) but also in a wide wavelength range from 1300 nm to 1600 nm. / Nm · km.

  Therefore, according to the photonic crystal fiber 10 according to the first embodiment of the present invention, the optical confinement effect of the outer cladding portion 3 is enhanced, and the optical signal is propagated in the region surrounded by the outer cladding portion 3. Therefore, the effective effective cross-sectional area is expanded as compared with the conventional photonic crystal fiber. In addition, it is possible to realize wavelength dispersion opposite to that of a single mode optical fiber in a wide band.

  The photonic crystal fiber 10 according to the first embodiment of the present invention described above is an example, and the present invention is not limited to this photonic crystal fiber. That is, in the above description, the holes 5 in the inner cladding portion 2 have been described using the photonic crystal fiber 10 having two layers. However, the number of the holes 5 is not limited, and the number of the holes 5 is one layer. Or it is good also as three or more layers. Moreover, although the hole 6 in the outer-layer clad part 3 demonstrated using the photonic crystal fiber 10 with five layers, the number of layers of this hole 6 is not limited, The number of layers of the hole 6 is 1-4 layers or It is good also as six or more layers.

  In the above description, the holes 5 and 6 in the inner layer cladding portion 2 and the outer layer cladding portion 3 have been described using the photonic crystal fiber 10 in which the holes 5 and 6 are arranged in a regular hexagonal lattice shape. They may be arranged in a regular polygonal grid.

  The holes 5 and 6 in the inner cladding portion 2 and the outer cladding portion 3 are filled with a medium having a refractive index lower than the refractive index of the material constituting the center core portion 1 and the second core portion 4, for example, gas or liquid. May be. That is, it is only necessary that the effective refractive indexes of the inner layer cladding portion 2 and the outer layer cladding portion 3 are lower than those of the center core portion 1 and the second core portion 4.

  In the above description, the optical transmission path 24 between the transmitter and the receiver is described using the zero-dispersion single mode optical fiber 23 in the 1310 nm band and the photonic crystal fiber 10 connected to the single mode optical fiber 23. The photonic according to the first embodiment may be used between a transmitter and a repeater that relays an optical signal, between a receiver and the repeater, and between the repeaters. The same operational effects as the optical communication system 20 using the crystal fiber 10 and the single mode optical fiber 23 can be obtained.

  The present invention can be used for a photonic crystal fiber, an optical transmission line, and an optical communication system, particularly a photonic crystal fiber having a dispersion compensation function.

It is a figure which shows the photonic crystal fiber which concerns on the 1st Example of this invention. 1 is a schematic diagram of an optical communication system using a photonic crystal fiber according to a first embodiment of the present invention. It is a figure which shows the chromatic dispersion characteristic in the photonic crystal fiber which concerns on 1st Example of this invention, and the effective chromatic dispersion characteristic in the optical transmission line which connected it and the single mode optical fiber. It is sectional drawing of the conventional photonic crystal fiber.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Center core part 2 Inner layer clad part 3 Outer layer clad part 4 2nd core part 5, 6 Hole 10 Photonic crystal fiber

Claims (8)

A core part, an inner cladding part surrounding the core part, and an outer cladding part surrounding the inner cladding part with a space therebetween, and a plurality of holes are provided in the inner cladding part and the outer cladding part, respectively. While forming, do not form a hole in the interval,
The outer peripheral radius a ₁ of the inner layer cladding part, the inner peripheral radius a ₂ of the outer layer cladding part, the hole interval Λ _{1 of the} holes in the inner layer cladding part and the hole diameter d ₁ thereof,
a ₂ −a ₁ > Λ ₁ −d ₁
A photonic crystal fiber characterized by the following relationship. The photonic crystal fiber according to claim 1,
The photonic crystal fiber, wherein Λ ₁ is less than or equal to a hole interval of the holes in the outer layer cladding part, and d ₁ is less than or equal to a hole diameter of the holes in the outer layer cladding part. A photonic crystal fiber according to claim 1 or claim 2, wherein
A photonic crystal fiber characterized in that the holes in the outer cladding portion are made larger than the holes in the inner cladding portion. A photonic crystal fiber according to any one of claims 1 to 3,
A photonic crystal fiber having a zero-dispersion wavelength in a wavelength range of 1300 nm to 1324 nm. The photonic crystal fiber according to any one of claims 1 to 4,
The photonic crystal fiber, wherein the holes in the inner layer cladding part and the outer layer cladding part are periodically arranged in an annular or regular polygonal lattice shape. A photonic crystal fiber according to any one of claims 1 to 5,
The photonic crystal fiber, wherein the holes in the inner layer cladding part and the outer layer cladding part are filled with a medium having a refractive index lower than that of the core part. A zero-dispersion single-mode optical fiber in the 1310 nm band, and the photonic crystal fiber according to any one of claims 1 to 6, connected to the single-mode optical fiber,
An optical transmission line characterized in that residual accumulated dispersion at the output end is 1000 ps / nm or less within a wavelength range of 1260 nm to 1650 nm. An optical communication system that transmits an optical signal to the optical transmission line according to claim 7.

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