JP2006023399A - Optical transmission line - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical transmission line which includes a holey fiber, and which can make loss small. <P>SOLUTION: In the optical transmission line, a first optical fiber 11 is a holey fiber which has holes extending in the axial direction, and at whose one end a second optical fiber 12 is fused together and at whose other end a third optical fiber 13 is fused together. The mode field diameter MFD1 of the first optical fiber 11 and the mode field diameter MFD2 of the second optical fiber 12 satisfy relational expressions: MFD2>MFD1, MFD2≥2.8 and MFD2≤2.2MFD1-0.04. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical transmission line including a plurality of connected optical fibers.

An optical fiber having holes extending in the axial direction (hereinafter referred to as “holey fiber”) can have an effective refractive index profile in the radial direction based on the distribution of the holes in a cross section perpendicular to the axial direction. Compared with a solid ordinary optical fiber, the holey fiber can increase the relative refractive index difference of the core region with respect to the cladding region, and thus the light confinement in the core region is strong, and the optical power in the core region The density can be increased. That is, the holey fiber has higher nonlinearity than a normal optical fiber, and thus various applications such as those described in Non-Patent Document 1 are expected.
P. Petropoulos, et al., "A highly nonlinear holey fiber and its application in a regenerative optical switch", OFC2001, TuC3

  By the way, there are few cases where the optical transmission path is configured only from the holey fiber, and the optical transmission path is often configured by connecting the holey fiber and the normal optical fiber. However, in the optical transmission path configured as the latter, the loss of light at the connection portion is large.

  The present invention has been made to solve the above problems, and an object of the present invention is to provide an optical transmission line that includes a holey fiber and can reduce loss.

  An optical transmission line according to the present invention includes a first optical fiber having a hole extending in the axial direction, and a second optical fiber fusion-connected to one end of the first optical fiber, and has a wavelength range of 450 nm to 1550 nm. The mode field diameter MFD1 (μm) of the first optical fiber and the mode field diameter MFD2 (μm) of the second optical fiber satisfy the following expression (1) at any one of the wavelengths λ.

  The optical transmission line according to the present invention further includes a third optical fiber fusion-spliced to the other end of the first optical fiber, and at a wavelength λ, the mode field diameter MFD1 (μm) of the first optical fiber, It is preferable that the mode field diameter MFD3 (μm) of the third optical fiber satisfies the following expression (2).

  In addition, the optical transmission line according to the present invention further includes a fourth optical fiber fusion-spliced to the second optical fiber, and at the wavelength λ, the mode field diameter MFD2 (μm) of the second optical fiber and the fourth light The mode field diameter MFD4 (μm) of the fiber preferably satisfies the following expression (3). Further, in a certain range in the longitudinal direction including the fusion splicing point between the second optical fiber and the fourth optical fiber, the additive of the second optical fiber is thermally diffused to expand the mode field diameter of the second optical fiber. It is preferable.

  The optical transmission line according to the present invention further includes a fifth optical fiber fusion-spliced to the third optical fiber, and a mode field diameter MFD3 (μm) of the third optical fiber and a fifth light at the wavelength λ. The mode field diameter MFD5 (μm) of the fiber preferably satisfies the following expression (4). Further, in a certain range in the longitudinal direction including the fusion splicing point between the third optical fiber and the fifth optical fiber, the additive of the third optical fiber is thermally diffused, and the mode field diameter of the third optical fiber is expanded. It is preferable.

  The optical transmission line according to the present invention includes a holey fiber and can reduce loss.

  The best mode for carrying out the present invention will be described below in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted.

  FIG. 1 is a configuration diagram of an optical transmission line 1 according to the first embodiment. The optical transmission line 1 shown in this figure includes a first optical fiber 11, a second optical fiber 12, and a third optical fiber 13. The first optical fiber 11 is a holey fiber having a hole extending in the axial direction. The second optical fiber 12 is fusion-connected to one end, and the third optical fiber 13 is fusion-connected to the other end. .

  FIG. 2 is a cross-sectional view of the first optical fiber 11. This figure shows the distribution of holes in a cross section perpendicular to the axial direction of the first optical fiber 11. The first optical fiber 11, which is a holey fiber, is a long fiber-like material made of quartz glass as the main medium 11 a, and has a circular cross-sectional outer shape. As shown in this figure, the first optical fiber 11 has a plurality of holes 11b regularly arranged in the main medium 11a in the cross section thereof, and the radial direction effective based on the distribution of the holes 11b. A typical refractive index profile. The first optical fiber 11 can increase the relative refractive index difference of the core region with respect to the cladding region. Therefore, the light confinement in the core region is strong, and the optical power density in the core region can be increased. Has non-linearity.

  In any wavelength λ within the wavelength range of 450 nm to 1550 nm, the mode field diameter of the first optical fiber 11 is MFD1 (μm), the mode field diameter of the second optical fiber 12 is MFD2 (μm), and the third The mode field diameter of the optical fiber 13 is MFD3 (μm).

  At this time, the mode field diameter MFD1 of the first optical fiber 11 and the mode field diameter MFD2 of the second optical fiber 12 satisfy the following expression (5). Further, the mode field diameter MFD1 of the first optical fiber 11 and the mode field diameter MFD3 of the third optical fiber 13 satisfy the following expression (6).

  The above expressions (5a) and (6a) indicate that the mode field diameter MFD1 of the first optical fiber 11 is smaller than the mode field diameters of the second optical fiber 12 and the third optical fiber 13, respectively. The above formulas (5b) and (6b) represent the production limits of the second optical fiber 12 and the third optical fiber 13, respectively. In addition, the above formulas (5c) and (6c) represent a range in which the calculated value of the loss due to the mismatch of the mode field diameter at the connection portion is 5 dB or less.

  FIG. 3 is a diagram illustrating a range in which Expression (5) is satisfied in a two-dimensional plane in which the mode field diameter MFD1 of the first optical fiber 11 and the mode field diameter MFD2 of the second optical fiber 12 are stretched. In the figure, the range in which the above expression (5) is satisfied is indicated by hatching. Here, when the second optical fiber 12 and the third optical fiber 13 are of the same type, the mode field diameters are equal, and the length of each of the second optical fiber 12 and the third optical fiber 13 is 1 m. The excess loss at a wavelength of 1550 nm is also shown. The excess loss is the connection loss at the fusion splice point between the first optical fiber 11 and the second optical fiber 12, the connection loss at the splice splice point between the first optical fiber 11 and the third optical fiber 13, and the second optical fiber. It means the sum of the transmission loss of 12 and the transmission loss of the third optical fiber 13.

  The first optical fiber 11 is connected to another normal optical fiber (for example, an optical fiber defined in G.652 of the international standard ITU-T) via the second optical fiber 12 or the third optical fiber 13. Considering the case, it is necessary to satisfy the above equations (5a) and (6a) in order to reduce the connection loss. When a solid ordinary optical fiber is used as the second optical fiber 12 or the third optical fiber 13, the above formulas (5b) and (6b) are satisfied due to restrictions on physical properties that can be realized. Further, as can be seen from FIG. 3, the excess loss becomes 5 dB or less by satisfying the above equations (5c) and (6c). When the excess loss was calculated in the same manner as described above for each of the wavelength of 500 nm and the wavelength of 850 nm, the same range of mode field diameters MFD1 and MFD2 is preferable for any wavelength.

  FIG. 4 is a configuration diagram of the optical transmission line 2 according to the second embodiment. The optical transmission line 2 shown in this figure includes a first optical fiber 11, a second optical fiber 12, a third optical fiber 13, a fourth optical fiber 14, and a fifth optical fiber 15. Among these, the 1st optical fiber 11, the 2nd optical fiber 12, and the 3rd optical fiber 13 are the same as what was already demonstrated using FIGS. 1-3. The fourth optical fiber 14 is fused and connected to the second optical fiber 12. Further, the fifth optical fiber 15 is fusion-bonded to the third optical fiber 13.

  In any wavelength λ within the wavelength range of 450 nm to 1550 nm, the mode field diameter of the first optical fiber 11 is MFD1 (μm), the mode field diameter of the second optical fiber 12 is MFD2 (μm), and the third optical fiber is used. 11 is MFD3 (μm), the mode field diameter of the fourth optical fiber 12 is MFD4 (μm), and the mode field diameter of the fifth optical fiber 13 is MFD5 (μm).

  At this time, the mode field diameter MFD1 of the first optical fiber 11 and the mode field diameter MFD2 of the second optical fiber 12 satisfy the above formula (5). The mode field diameter MFD1 of the first optical fiber 11 and the mode field diameter MFD3 of the third optical fiber 13 satisfy the above expression (6). The mode field diameter MFD2 of the second optical fiber 12 and the mode field diameter MFD4 of the fourth optical fiber 14 satisfy the following expression (7). Further, the mode field diameter MFD3 of the third optical fiber 13 and the mode field diameter MFD5 of the fifth optical fiber 15 satisfy the following expression (8).

  When the first optical fiber 11, the second optical fiber 12, and the fourth optical fiber 14 are connected in order, and when the first optical fiber 11, the third optical fiber 13, and the fifth optical fiber 15 are connected in order. Considering that the above equations (5a) and (6a) are satisfied, it is necessary that the above equations (7a) and (8a) are satisfied. Further, when the above expressions (7b) and (8b) are satisfied, the fourth optical fiber 14 and the fifth optical fiber 15 are ordinary optical fibers (for example, specified in G.652 of the international standard ITU-T). Optical fiber).

  In a certain range in the longitudinal direction including the fusion splicing point between the second optical fiber 12 and the fourth optical fiber 14, the additive of the second optical fiber 12 is thermally diffused, and the mode field diameter of the second optical fiber 12 is expanded. It is preferred that Further, in a certain range in the longitudinal direction including the fusion splicing point between the third optical fiber 13 and the fifth optical fiber 15, the additive of the third optical fiber 13 is thermally diffused and the mode field diameter of the third optical fiber 13 is increased. Is preferably enlarged.

  FIG. 5 is a diagram showing a change in mode field diameter in a certain range in the longitudinal direction including the fusion splice point between the second optical fiber 12 and the fourth optical fiber 14. This figure shows a cross section including the optical axis and shows the distribution of the mode field diameter in the longitudinal direction. As shown in this figure, in a certain range in the longitudinal direction of the second optical fiber 12 including the fusion splicing point A, the mode field diameter gradually increases as the fusion splicing point A is closer. In the vicinity of the fusion splicing point A, the mode field diameters of the second optical fiber 12 and the fourth optical fiber 14 are preferably approximately the same. By doing so, the connection loss at the fusion splice point between the second optical fiber 12 and the fourth optical fiber 14 can be reduced, and the fusion between the third optical fiber 13 and the fifth optical fiber 15 can be reduced. Connection loss at the incoming connection point can be reduced.

In addition, this invention is not limited to the said embodiment, A various deformation | transformation is possible. For example, the first optical fiber 11 that is a holey fiber has a core region and a cladding region that are composed of main media having the same composition as in the configuration shown in FIG. 2 and that does not have a hole at the center position in the cross section. Not limited to this, the configuration shown in FIGS. 6A and 6B may be used. The holey optical fiber 11A whose cross section is shown in FIG. 6A is a long fiber-like fiber made of silica glass as the main medium 11a, and in the cross section, a plurality of holes 11b are formed in the main medium 11a. Are regularly arranged, and a hole 11c is arranged at the center position. The holey optical fiber 11B whose cross section is shown in FIG. 6B is a long fiber-like fiber made of silica glass as the main medium 11a, and in the cross section, a plurality of holes 11b are formed in the main medium 11a. Are regularly arranged, and a region to which a refractive index increasing agent (for example, GeO ₂ ) is added is arranged at the center position. These holey optical fibers 11A and 11B can also be suitably used as the first optical fiber 11 included in the optical transmission lines 1 and 2.

It is a block diagram of the optical transmission line 1 which concerns on 1st Embodiment. 2 is a cross-sectional view of a first optical fiber 11. FIG. It is a figure which shows the range with which (5) Formula is satisfy | filled in the two-dimensional plane which the mode field diameter MFD1 of the 1st optical fiber 11 and the mode field diameter MFD2 of the 2nd optical fiber 12 stretch | stretch. It is a block diagram of the optical transmission line 2 which concerns on 2nd Embodiment. It is a figure which shows the mode of the mode field diameter change in the fixed range of a longitudinal direction including the fusion splicing point of the 2nd optical fiber 12 and the 4th optical fiber 14. FIG. 6 is a cross-sectional view of another configuration example of the first optical fiber 11. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 2 ... Optical transmission line, 11 ... 1st optical fiber (holey fiber), 12 ... 2nd optical fiber, 13 ... 3rd optical fiber, 14 ... 4th optical fiber, 15 ... 5th optical fiber.

Claims (6)

A first optical fiber having a hole extending in the axial direction, and a second optical fiber fused and connected to one end of the first optical fiber,
At any wavelength λ within the wavelength range of 450 nm to 1550 nm, the mode field diameter MFD1 (μm) of the first optical fiber and the mode field diameter MFD2 (μm) of the second optical fiber are:

Satisfying the relational expression
An optical transmission line characterized by that. A third optical fiber fused and connected to the other end of the first optical fiber;
At the wavelength λ, the mode field diameter MFD1 (μm) of the first optical fiber and the mode field diameter MFD3 (μm) of the third optical fiber are:

Satisfying the relational expression
The optical transmission line according to claim 1. A fourth optical fiber fused and connected to the second optical fiber;
At the wavelength λ, the mode field diameter MFD2 (μm) of the second optical fiber and the mode field diameter MFD4 (μm) of the fourth optical fiber are:

Satisfying the relational expression
The optical transmission line according to claim 1.   In a certain range in the longitudinal direction including the fusion splicing point between the second optical fiber and the fourth optical fiber, the additive of the second optical fiber is thermally diffused to increase the mode field diameter of the second optical fiber. The optical transmission line according to claim 3, wherein A fifth optical fiber fused to the third optical fiber;
At the wavelength λ, the mode field diameter MFD3 (μm) of the third optical fiber and the mode field diameter MFD5 (μm) of the fifth optical fiber are:

Satisfying the relational expression
The optical transmission line according to claim 2, wherein: In a certain range in the longitudinal direction including the fusion splicing point between the third optical fiber and the fifth optical fiber, the additive of the third optical fiber is thermally diffused to increase the mode field diameter of the third optical fiber. 6. The optical transmission line according to claim 5, wherein:

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