JPS62215206A - Low-dispersion single mode fiber with wide wavelength range - Google Patents

Abstract

PURPOSE:To reduce the bending loss of a multistructure distributed index single mode fiber which varies stepwise in refractive index of each layer and to enable use over a wide wavelength range by specifying differences in reflective index between the innermost layer and outermost layer, the 2nd layer and outermost layer, and the 3rd layer and outermost layer, and the ratio of the diameters of the innermost layer and the 2nd and the 3rd layers respectively. CONSTITUTION:The innermost layer 1 with a diameter d1, the 2nd layer with a diameter d2, the 3rd layer 3 with a diameter d3, and the outermost layer 4 with a diameter d4 which have refractive indexes n1-n4 respectively are constituted concentrically in order into multiple structure to form the multistructure distributed index single mode fiber which varies in refractive index stepwise. In this case, the difference DELTA1 between the refractive index n1 of the innermost layer 1 and the refractive index n4 of the outermost layer 4 is 0.45-0.55%, the difference DELTA2 between the refractive index n2 of the 2nd layer 2 and the refractive index n4 of the innermost layer 4 is -0.2--0.3%, and the difference DELTA3 between the refractive index n3 of the 3rd layer 3 and the refractive index n4 of the outermost layer 4 is 0.45-0.55%. Further, the diameter d1 of the innermost layer 1 is 6-7mum, the ratio of the diameter d1 of the innermost layer 1 and the diameter d2 of the 2nd layer 2 is 2.2-2.4, and the ratio of the diameter d1 of the innermost layer 1 and the diameter d3 of the 3rd layer 3 is 2.6-2.8.

Description

[Detailed Description of the Invention] [Shield Required] The innermost layer constituting the core, the second layer, the third layer, and the outermost layer constituting the cladding are sequentially arranged in concentric circles from the inside, and each layer A multi-structured refractive index single mode fiber is constructed by changing the refractive index of the fiber in stages.
The difference between the refractive index of the innermost layer and the refractive index of the outermost layer and the difference between the refractive index of the third layer and the refractive index of the outermost layer are set to positive predetermined values (0, 45
% to 0.55%), the difference between the refractive index of the second layer and the refractive index of the outermost layer is a predetermined negative value (-0.2% to -0.3%), and the diameter of the innermost layer is set to a predetermined value. (6 to 7 μm), and the ratio of the diameter of the innermost layer to the diameter of the second N and the ratio of the diameter of the innermost layer to the diameter of the third layer are set to predetermined values (2, 2 to 2.4, 2.6, respectively). ~2゜6
), it can be used in a wide wavelength range and the loss due to bending can be reduced.

(Industrial Field of Application) The present invention relates to a wide wavelength range low dispersion single mode fiber, and particularly to a wide wavelength range low dispersion single mode fiber that can be used in a sufficiently wide wavelength range and has low loss due to bending.

Optical communications require a wide usable wavelength range. Broad wavelength low dispersion single mode fiber is
Development is underway to meet this purpose, but there is a demand for a device that can be used in a wider wavelength range and has less loss due to bending.

[Conventional technology]

Conventionally, as a wide wavelength range low dispersion single mode fiber,
A W-type single mode fiber has been proposed. The cross-sectional structure of this is shown in FIG. 5, and the refractive index of the core 11 is n5. The refractive index of the cladding 12 is n2
When (nl>n2), core 11 and cladding 12
An intermediate layer 13 having a refractive index n3 (n3<n2) is provided between the two. The characteristic of the delay time τ in this case is as shown in FIG. 6(a) based on the difference in the group refractive index with respect to the wavelength of each part. i.e. core 1]
The characteristics of the fiber have the shape of a cubic curve, as shown by D, due to the characteristic A of the portion , the characteristic B of the cladding 12 portion, and the characteristic C of the intermediate layer 13 portion. Note that E shows the characteristics of a normal single mode fiber for comparison. As a result, the chromatic dispersion m exhibits the characteristic that it becomes 0 at two wavelengths as shown by F in the figure (in the same figure),
Compared to the case of a normal single mode fiber shown by G, the dispersion is low over a wide wavelength range.

[Problem that the invention seeks to solve]

However, the conventional W-type single mode fiber has the problem that not only is its usable area not necessarily wide enough, but also that the radiation loss when the fiber is bent is so large that it becomes a practical problem.

In the case of a W-type single mode fiber, this is shown in Figure 6 (a
), there is a cutoff in the fundamental mode, which prevents transmission beyond a certain wavelength, and this is thought to be because bending aggravates this tendency.

[Means for solving problems]

Figure 1 shows the basic structure of the present invention.

an innermost layer 1 of diameter d, and a second layer 2 of diameter d2, each having a refractive index nI+ n2+ ``3+''4;
The third layer 3 of 3 and the outermost layer 4 of diameter d4 are sequentially concentrically multiplexed to form a multi-structured refractive index single mode fiber in which the refractive index changes stepwise. Difference Δ between the refractive index nl and the refractive index n4 of the outermost layer 4
, is 0.45% to 0.55%, and the refractive index n of the second layer 2 is
2 and the refractive index n4 of the outermost layer 4 is -0.2% to -
0.3%, and the refractive index n3 of the third layer 3 and the refractive index n of the outermost layer 4.

The difference Δ3 between the two layers is 0.45% to 0.55%, the diameter d of the innermost layer 1 is 6 to 7 μm, and the ratio of the diameter d of the innermost layer 1 to the diameter d2 of the second layer 2 is 2. 2～
2.4, and the ratio of the diameter d of the innermost layer and the diameter d3 of the third layer 3 is 2.6 ~
2.8.

[For production]

FIG. 2 shows the delay characteristics (al and wavelength dispersion) in the wide wavelength range low dispersion single mode fiber whose basic configuration is shown in FIG. 1. That is, as shown in (al), the characteristics of the fiber are determined by the characteristics a of the innermost layer 1 constituting the core, the characteristics of the second layer, the characteristics C of the third layer, and the characteristics d of the outermost layer constituting the cladding. The characteristic of the delay time τ has the shape of a quartic curve as shown by e. As a result, the chromatic dispersion m has a characteristic that slopes upward to the right as shown by the peak. Comparing this with the case of the W-type single mode fiber shown in FIG. 6, the range of low dispersion is wide and there is no cutoff region, so the loss due to bending is also reduced.

〔Example〕

FIG. 3 shows one embodiment of the present invention.
The same parts as in the figure are indicated by the same numbers.

The design conditions in this example are as follows.

■2cm radius, 180° bending loss <0.5dB ■Theoretical cutoff wavelength <1.38μm ■Groove refractive index difference>-0
, 3% ■Maximum refractive index difference <0.5% ■Mode field diameter> 6 μm (wavelength 1.3 μm ~ 1.5%)
As shown in FIG. 3, the diameters of each part in this example are: d,=6 μm d2=14 μm d3=16 μm d,−clad diameter. The three dishes on the 1st floor are as follows: Δ+-0.52% Δ2= 0.30% Δ3= 0.51%. The main specifications in this case were as shown in Table 1.

Table 1 An example of the chromatic dispersion of the wide wavelength range low dispersion single mode fiber according to this embodiment is as shown by the solid line in FIG. It can be seen that the performance is sufficiently good compared to the case of the W type single mode fiber shown in . Note that the illustrated W-type single mode fiber has a bending loss of 10 dB or more, which poses a practical problem.

It has been experimentally confirmed that in the wide wavelength range low dispersion single mode fiber of the present invention, good characteristics can be obtained when the refractive index and diameter of each layer are within the above ranges. When is set to approximately 0.2 times the radius of the innermost layer,
It was found that the best results were obtained.

〔Effect of the invention〕

As explained above, the wide wavelength range low dispersion single mode fiber of the present invention has: (1) low bending loss;

■Can be used in a wide wavelength range (1.2 μm to 1.7 μm).

This is much better than the conventional technology.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the principle configuration of the present invention, FIG. 2 is a diagram showing the characteristics of the wide wavelength range low dispersion single mode fiber of the present invention, and FIG. 3 is a diagram showing an embodiment of the present invention. Figure 4 shows an example of chromatic dispersion of the wide wavelength range low dispersion single mode fiber according to the present invention, Figure 5 shows the configuration of a W type single mode fiber, and Figure 6 shows the characteristics of the W type single mode fiber. It is a figure which shows an example. 1 - Innermost layer 2 - 2nd layer 3 - 3rd N 4 - Outermost layer wa 0 Unprisoned middle tax ε Kaku

Claims (2)

[Claims] (1) Innermost layer (1), second layer (2), and third layer (3)
In a multi-structured refractive index single mode fiber in which the refractive index of the innermost layer (1) and the outermost layer (4) are sequentially concentrically arranged from the inside and the refractive index of each layer changes stepwise, the refractive index of the innermost layer (1) and the The difference between the refractive index of the outer layer (4) is 0.45% to 0.55%, and the difference between the refractive index of the second layer (2) and the refractive index of the outermost layer (4) is -0.2%. -0.3%, the difference between the refractive index of the third layer (3) and the refractive index of the outermost layer (4) is 0.45% to 0.55%, and the diameter of the innermost layer (1) is is 6 to 7 μm, and the ratio of the diameter of the innermost layer (1) to the diameter of the second layer (2) is 2.2 to 7 μm.
2.4, and the ratio of the diameter of the innermost layer (1) to the diameter of the third layer (3) is 2.6 to
A wide wavelength range low dispersion single mode fiber characterized by a coefficient of 2.8. (2) The wide wavelength range low dispersion single mode fiber according to claim 1, wherein the thickness of the third layer is approximately 0.2 times the radius of the innermost layer.