JP2584145B2 - High dispersion optical fiber - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low-loss and high-dispersion optical fiber used for investigating transmission characteristics of an optical fiber used in the 1.55 .mu.m band.

[0002]

2. Description of the Related Art Chromatic dispersion is one of the important investigation items when investigating the transmission characteristics of a system using a 1.55 μm band dispersion-shifted optical fiber.

[0003] By the way, as an optical fiber used when conducting an investigation experiment on the anomalous dispersion region of a system using the 1.55 μm band dispersion-shifted optical fiber, the experiment apparatus was downsized and the size of the experimental apparatus was reduced. In order to suppress transmission loss as much as possible, there is a demand for an optical fiber that exhibits a high dispersion value even when it is short (having a large dispersion value per unit length) and a small transmission loss.

Conventionally, as an optical fiber used in an experiment for examining anomalous dispersion region of the above system, a Ge is used as a core.
1.3 μm band optical fiber (hereinafter referred to as 1.3SM)
Abbreviated as fiber. )It has been known.

[0005]

However, the chromatic dispersion value of the conventional 1.3SM fiber in the 1.55 μm band is limited to about 16 to 17 ps / km / nm. There is a need for an optical fiber having higher chromatic dispersion than the chromatic dispersion value and low loss.

The present invention has been made in view of the above circumstances, and has as its object to provide a high dispersion optical fiber having a large chromatic dispersion value per unit length and a small loss per unit length.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical fiber comprising a core and a clad, wherein a first clad is provided by laminating fluorine-doped quartz on the outside of the core made of pure quartz, and And a second clad is provided by laminating a fluorine-added quartz on the first clad, the relative refractive index difference between the first clad and the core is set to −0.6% or less, and the relative refractive index difference between the second clad and the core is reduced. −0.2%, and the value of the first clad outer diameter / core diameter is 1.7 to 2.5.
And a high chromatic dispersion value in the 1.55 μm band.
It is solved by adopting a new structure. For example, according to the optical fiber having the above configuration, a fiber having a large chromatic dispersion value of about 20 to 24 ps / km / nm can be obtained.

[0008]

According to the high dispersion optical fiber of the present invention, the above structure increases the dispersion value of the optical fiber structure.
As a result, the chromatic dispersion value determined by the sum of the structural dispersion value and the material dispersion value is increased to the plus side, and the transmission loss per unit length is reduced.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the high dispersion optical fiber of the present invention will be described below with reference to the drawings. FIG. 1 is a view showing an embodiment of a high dispersion optical fiber according to the present invention. In the figure, reference numeral 1 denotes a high dispersion optical fiber.

The high-dispersion optical fiber 1 comprises a core 2 made of pure quartz, a clad 3 made of fluorine-doped quartz and formed outside the core 2, and a clad 3 made of fluorine-doped quartz and And the cladding 4 formed on the substrate.

The clad 3 (first clad) is made of quartz glass doped with fluorine as described above,
The amount of fluorine added in the cladding 3 is adjusted so that the relative refractive index difference between the cladding 3 and the core 2 is -0.6 or less.

The clad 4 (second clad) also has
Like the clad 3 described above, it is made of quartz glass doped with fluorine, and the amount of fluorine added in the clad 4 is adjusted so that the relative refractive index difference from the core 2 becomes smaller than -0.2%. I have. Further, the diameter of the core 2 is set to (a)
It is desirable that the value of b / a when the diameter of the cladding 3 is (b) is 1.7 or more and 2.5 or less.

As described above, in the high dispersion optical fiber of the present invention, the relative refractive index difference between the core 2 and the clad 3 is-
0.6% or less, the relative refractive index difference between the core 2 and the clad 4 is made smaller than -0.2%, and the value of clad 3 outer diameter / core 2 diameter is limited to 1.7 to 2.5. The reason for this was as follows (Experimental Example 1) regarding the relationship between the refractive index distribution and the chromatic dispersion value of the optical fiber and to investigate the relationship between the value indicated by the first cladding diameter / core diameter and the chromatic dispersion value (Experiment 1). Example 2)
It depends on the result.

(Experimental Example 1) FIG. 2 is a model profile of an optical fiber for explaining an experiment on the relationship between the refractive index distribution and the chromatic dispersion value of the optical fiber described above. In the figure, symbol a represents the core diameter, b represents the outer diameter of the first cladding, d1 represents the relative refractive index difference of the first cladding, and d2 represents the relative refractive index difference of the second cladding.

First, for an optical fiber having b / a of 1.2, d2 is set to -0.2, -0.3, -0.4, -0.5%.
The dispersion value with respect to d1 / d2 at the time of was determined, and the change in the dispersion value with respect to d1 / d2 using d2 as a parameter was examined. The result shown in FIG. 3 was obtained. However, the cutoff wavelength λc at this time is 1.6 μm in order to increase the waveguide dispersion.
m and the measurement wavelength λ were 1.55 μm. Further, the same experiment as described above was carried out for b / a of 1.5 and 2.0, and the results are shown in FIG. 4 and FIG.

As a result of the above experiment, the optical fiber with d2 = -0.2% cannot be used practically because the bending loss of the optical fiber is large, and the optical fiber with other optical characteristics of -0.3, -0.4, -0.5% It was found that the bending loss was practical because it was sufficiently small. 3 to 5 that d2 increases and / or d1 / d2.
It was found that the variance value increased as the value increased. In consideration of the limit of the amount of fluorine added by the VAD method or the like, it is difficult to reduce the relative refractive index difference that d1 can take to less than -0.7%.
The relative refractive index difference of 1 was fixed at -0.7%.

From the above experimental results, it is desirable that d2 be less than -0.2% and d1 be less than -0.6%.
Further, under the condition of b / a = 2.0, d2 = -0.4% and d1 =
It is more preferable to set -0.7%. As a result of producing an optical fiber under this condition and measuring the chromatic dispersion thereof, the highest chromatic dispersion value of 23.8 ps / s among the optical fibers used in Experimental Example 1 was obtained. km / nm was obtained.

(Experimental Example 2) Next, in order to determine the optimum range of b / a, the relative refractive index difference between the first clad and the second clad was set to (d1 = -0.7% and d2 = -0. 4%), a plurality of optical fibers having different values of b / a are manufactured, and the chromatic dispersion of the plurality of optical fibers is measured, and is represented by the diameter of the first clad / core diameter. The relationship between the value and the chromatic dispersion value was examined. However, the cut-off wavelength and the measurement wavelength were the same as in the above-mentioned Experimental Example 1. Further, a similar experiment was performed by comparing the relative refractive index difference between the first clad and the second clad with (d
1 = -0.6%, d2 = -0.4%) and (d1 = -0.5%)
%, D2 = -0.4%). FIG. 6 shows the results of Experimental Example 2. FIG.
According to the results of Experimental Example 2 shown in Table 2, it is clear that a high dispersibility can be obtained when b / a is in the range of about 1.7 to 2.5.

As described above, the high-dispersion optical fiber 1 has a small transmission loss because the core is made of pure silica, and also has a small material dispersion (because Ge is not added). . Further, the cladding 3 outer diameter /
Since the value of the core diameter 2 is configured to be 1.7 to 2.5, the structural dispersion is larger than that of the conventional one. Therefore, the chromatic dispersion of the high dispersion optical fiber 1 can be made larger than that of the conventional 1.3 SM fiber.

(Experimental Example 3) A high-dispersion optical fiber 1 having the structure shown in FIG. 1 and having a refractive index distribution shown in FIG. 7 was manufactured.
The SM fiber was compared with respect to items such as a chromatic dispersion value, a transmission loss, a fiber length necessary for obtaining a total chromatic dispersion of 3000 ps / nm, and a transmission loss over the entire length at that time.

In the high dispersion optical fiber 1 of the above embodiment, the relative refractive index difference d1 between the core 2 and the clad 3 (first clad) is -0.68%, and the core 2 and the clad 4 (second clad) are different from each other. The relative refractive index difference d2 is set to −0.41 and the outer diameter of the clad 3 is set to 22.4 μm, the diameter of the core 2 is set to 11.5 μm, and the value of the outer diameter of the clad 3 / the diameter of the core 2 is set to 1.95. Produced.

When the chromatic dispersion value and the transmission loss of the high dispersion optical fiber 1 were measured, the chromatic dispersion value was 23 ps / km / nm, the transmission loss was 0.182 d at a λc wavelength of 1.59.
B / km. The fiber length required to obtain a total chromatic dispersion of 3000 ps / nm using the high-dispersion optical fiber 1 was 130.4 km, and the loss over the entire length of the fiber was 23.7 dB.

A 1.3SM fiber of a comparative example was prepared, and the chromatic dispersion value and transmission loss of the 1.3SM fiber were measured. The cutoff wavelength was 1.21, and the measured wavelength was 1.5.
At 5 μm, the chromatic dispersion value was 16.8 ps / km / nm, and the transmission loss was 0.21 dB / km. The fiber length required to obtain a total chromatic dispersion of 3000 ps / nm using this 1.3SM fiber was 178.6 km, and the loss over the entire length of the fiber was 37.5 dB.

From the results of Experimental Example 2, it can be seen that the high dispersion optical fiber 1 of the embodiment has a very high dispersion value per unit length and a low transmission loss as compared with the conventional 1.3 SM fiber. confirmed.

[0025]

As described above, in the high dispersion optical fiber according to the present invention, outside the core made of pure quartz,
Providing a first clad by laminating fluorine-doped quartz, making the relative refractive index difference of the first clad less than or equal to -0.6%, and making the relative refractive index difference of the second clad smaller than -0.2%; In addition, since the first clad outer diameter / core diameter value is configured to be 1.7 to 2.5, the structural dispersion value of the optical fiber is increased, thereby determining the sum of the structural dispersion value and the material dispersion value. The chromatic dispersion value in the 1.55 μm band can be increased to the plus side. Therefore, 20-24 ps / km / n
m is obtained and used in the 1.55 μm band.
When used as a dispersion simulator used when examining the transmission characteristics of an optical fiber, the length of the fiber used can be shortened, and the experimental apparatus can be miniaturized.

Further, since the transmission loss per unit length can be reduced, when used as a dispersion simulator, a dispersion simulator with extremely small loss is used in combination with the short fiber length as described above. be able to. In addition, when conducting transmission characteristic investigations, even if the number of components installed in the circuit under test is increased, the loss of the entire circuit length can be kept small. Becomes possible.

[Brief description of the drawings]

FIG. 1 is a diagram showing one embodiment of a high dispersion optical fiber of the present invention.

FIG. 2 is a model profile of an optical fiber for describing an experiment on a relationship between a refractive index distribution and a chromatic dispersion value of the optical fiber.

FIG. 3 shows an optical fiber having a numerical value of 1.2 indicated by b / a in FIG. 2 where d2 is -0.2, -0.3, -0.4, -0.4.
It is a graph which shows the result of having measured the wavelength dispersion value with respect to d1 / d2 value at 5%.

FIG. 4 is a diagram showing an example of an optical fiber having a numerical value b / a of 1.5 in FIG. 2 in which d2 is -0.2, -0.3, -0.4, -0.4.
It is a graph which shows the result of having measured the wavelength dispersion value with respect to d1 / d2 value at 5%.

FIG. 5 shows an optical fiber having a numerical value b / a of 2.0 in FIG. 2 in which d2 is -0.2, -0.3, -0.4, -0.4.
It is a graph which shows the result of having measured the wavelength dispersion value with respect to d1 / d2 value at 5%.

FIG. 6 is a graph showing the results of an experiment conducted in Experimental Example 2 for examining the relationship between the value indicated by the diameter of the first clad / core diameter and the chromatic dispersion value.

FIG. 7 is a model profile showing a refractive index distribution of a high dispersion optical fiber of an example manufactured in Experimental Example 2.

[Explanation of symbols]

1 high dispersion optical fiber, 2 core, 3 clad (first
Clad), 4 ... clad (second clad), a ... core diameter, b ... outer diameter of first clad, d1 ... difference in relative refractive index between core 2 and clad 3, d2 ... ratio between core 2 and clad 4 Refractive index difference

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Ryozo Yamauchi 1440 Mutsuzaki, Sakura-shi, Chiba Pref. Fujikura Electric Cable Co., Ltd. Sakura Plant (56) References Special Table 62-501733 (JP, A)

Claims (1)

(57) [Claims] In a single mode optical fiber comprising a core and a clad, a first clad is provided by laminating a fluorine-doped quartz outside the core made of pure quartz, and a fluorine-doped quartz is formed outside the first clad. A second clad is provided by laminating, the relative refractive index difference between the first clad and the core is -0.6% or less, and the relative refractive index difference between the second clad and the core is -0.2%. Constructed so that the value of 1st clad outer diameter / core diameter is 1.7 to 2.5
A high dispersion optical fiber having a high chromatic dispersion value in the 1.55 μm band .