JPH04317438A - High-dispersion optical fiber - Google Patents

Abstract

PURPOSE:To provide a high-dispersion optical fiber with the wavelength dispersion value per unit length increased and the loss per unit length reduced. CONSTITUTION:This high-dispersion optical fiber 1 is formed with a core 2 of pure quartz and the clads 3 and 4 of fluorine-added quartz. The difference in specific refractive index between the clad 3 and the core 2 is controlled to <=-0.6%, and that between the clad 4 and the core 2 is adjusted to <=-0.2%. The ratio of the diameter (b) of the clad 3 to the diameter (a) of the core 2 is preferably controlled to 1.7-2.5. A dispersion simulator low in loss is obtained. Although the number of parts to be set in a circuit to be tested is increased, the loss in the entire length of the whole circuit is kept low, and the transmission characteristic of even an intricate optical circuit can be investigated and subjected to an experiment.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low-loss, high-dispersion optical fiber used for investigating the transmission characteristics of optical fibers particularly used in the 1.55 μm band.

0002

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

By the way, as an optical fiber to be used when conducting an experiment to investigate the anomalous dispersion region of a system using the above-mentioned 1.55 μm band dispersion-shifted optical fiber, we are trying to downsize the experimental equipment and to In order to suppress transmission loss as much as possible, there is a demand for an optical fiber that exhibits a high dispersion value (large dispersion value per unit length) even in short lengths and has low transmission loss.

[0004] Conventionally, optical fibers used in experiments to investigate the anomalous dispersion region of the above system have Ge in the core.
1.3μm band optical fiber (hereinafter referred to as 1.3S) doped with
It is abbreviated as M fiber. )It has been known.

[0005]

[Problems to be Solved by the Invention] However, the chromatic dispersion value of the conventional 1.3 SM fiber in the 1.55 μm band is limited to approximately 16 to 17 ps/km/nm. There is a need for an optical fiber that has higher wavelength dispersion than the wavelength dispersion value and has low loss.

The present invention was made in view of the above circumstances, and an object of the present invention is to provide a high dispersion optical fiber having a large wavelength dispersion value per unit length and a small loss per unit length.

[0007]

[Means for Solving the Problems] This problem is solved by providing a first cladding by laminating fluorine-doped quartz on the outside of the core made of pure quartz, and forming a first cladding on the outside of the first cladding. A second cladding is provided by laminating fluorine-doped quartz on the substrate, the first cladding has a relative refractive index difference of -0.6% or less with the core, and the second cladding has a relative refractive index difference with the core of -0.6% or less. -0.2% or less, and the first cladding outer diameter/core diameter value is 1.7 to 2.
This can be solved by creating a structure configured such that 5. For example, according to the optical fiber having the above configuration, 20 to 2
A large wavelength dispersion value of about 4 ps/km/nm can be obtained.

[0008]

[Operation] In the high dispersion optical fiber of the present invention, the above structure increases the optical fiber structural dispersion value,
As a result, the wavelength dispersion value determined by the sum of the structural dispersion value and the material dispersion value is increased to the positive side, and the transmission loss per unit length is reduced.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the high dispersion optical fiber of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing an embodiment of a high dispersion optical fiber of the present invention, and reference numeral 1 in the figure indicates the high dispersion optical fiber.

The high dispersion optical fiber 1 includes a core 2 made of pure quartz, a cladding 3 made of fluorine-doped quartz and formed on the outside of the core 2, and a cladding 3 made of fluorine-doped quartz and formed on the outside of the cladding 3. It is composed of a cladding 4 formed in

The cladding 3 (first cladding) is made of fluorine-doped quartz glass as described above,
Further, 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.

[0012] Also, the cladding 4 (second cladding)
Like the cladding 3 described above, it is made of fluorine-doped silica glass, and the amount of fluorine doped in the cladding 4 is adjusted so that the relative refractive index difference with the core 2 is less than -0.2%. There is. Also, the diameter of the core 2 is (a)
It is desirable that the value of b/a be 1.7 or more and 2.5 or less when the diameter of the cladding 3 is (b).

As described above, in the high dispersion optical fiber of the present invention, the relative refractive index difference between the core 2 and the cladding 3 is -0.
．． 6% or less, and the relative refractive index difference between the core 2 and the cladding 4 is smaller than -0.2%, and the outer diameter of the cladding 3/
The reason why the value of the second core diameter is limited to 1.7 to 2.5 is based on the relationship between the refractive index distribution and wavelength dispersion value of the optical fiber shown below (Experimental Example 1) and the first cladding diameter/core diameter. (Experimental Example 2)
According to the results.

(Experimental Example 1) FIG. 2 is a model profile of an optical fiber for explaining the above-mentioned experiment regarding the relationship between the refractive index distribution and the wavelength dispersion value of the optical fiber. In the figure, symbol a is the diameter of the first core, b is the outer diameter of the first cladding, and 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 with b/a of 1.2, d2 is set to -0.2, -0.3, -0.4, -0.
Measure the dispersion value for d1/d2 when it is 5%, and
When the change in the dispersion value with respect to d1/d2 was investigated using 2 as a parameter, the results shown in FIG. 3 were obtained. However, the cutoff wavelength λc at this time was set to 1.6 μm and the measurement wavelength λ was set to 1.55 μm in order to increase waveguide dispersion. Further, experiments similar to those described above were conducted for samples with b/a of 1.5 and 2.0, and the results are shown in FIGS. 4 and 5.

As a result of the above experiment, the optical fiber with d2=-0.2% has a large bending loss and cannot be put to practical use, and the other ones with d2=-0.3, -0.4, and -0.5% It was found that the bending loss was sufficiently small to be practical. Also, from FIGS. 3 to 5 above, d2 increases and/or d1
It was found that as the /d2 value increases, the dispersion value also increases. In addition, considering the limit of the amount of fluorine added by the VAD method etc., the relative refractive index difference that d1 can take is -0.7%.
Since it is difficult to make it smaller, the relative refractive index difference of d1 was fixed at -0.7% in this experimental example.

From the above experimental results, it is desirable that d2 be less than -0.2% and d1 be less than -0.6%. Also, under the condition of b/a=2.0, d2=-0.4%, d
It is more preferable to set 1=-0.7%, and as a result of manufacturing an optical fiber under this condition and measuring its chromatic dispersion,
Among the optical fibers used in Experimental Example 1, the highest wavelength dispersion value of 23.8 ps/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 cladding and the second cladding is set as (d1=-0.7%, d2=-0. 4%
), and prepare multiple optical fibers with different values of b/a, measure the wavelength dispersion of these multiple optical fibers, and calculate the value indicated by the diameter of the first cladding/core diameter. The relationship with wavelength dispersion value was investigated. However, the cutoff wavelength and measurement wavelength were the same as in Experimental Example 1 above. Furthermore, similar experiments were carried out with the relative refractive index differences of the first cladding and the second cladding being (d1=-0.6%, d2=-0.4%) and (d
The test was also carried out with the conditions fixed at 1=-0.5%, d2=-0.4%). The results of this Experimental Example 2 are shown in FIG. According to the results of Experimental Example 2 shown in FIG.
It is clear that high dispersion can be obtained if /a is in the range of about 1.7 to 2.5.

As described above, since the core of the high dispersion optical fiber 1 is made of pure silica, the transmission loss is small, and the material dispersion is also small (because no Ge or the like is added). . Furthermore, cladding 3 outer diameter/
Since the value of the core diameter 2 is set to be 1.7 to 2.5, the structural dispersion is larger than that of the conventional one. Therefore, the high dispersion optical fiber 1 can have greater wavelength dispersion than the conventional 1.3SM fiber.

(Experimental Example 3) A high dispersion optical fiber 1 of the embodiment having the structure shown in FIG. 1 and the refractive index distribution shown in FIG.
The 3SM fibers were compared in terms of items such as (1) chromatic dispersion value, (2) transmission loss, (2) the fiber length required to obtain a total chromatic dispersion of 3000 ps/nm and the transmission loss in the total length.

The high dispersion optical fiber 1 of the above embodiment has a relative refractive index difference d1 of -0.68% between the core 2 and the cladding 3 (first cladding), and a difference between the core 2 and the cladding 4 (second cladding). The relative refractive index difference d2 is -0.41, and the outer diameter of the cladding 3 is 22.4 μm and the diameter of the core 2 is 11.5 μm, so that the value of the outer diameter of the cladding 3/the diameter of the core 2 is 1.95. Created.

When the chromatic dispersion value and transmission loss of the above-mentioned high dispersion optical fiber 1 were measured, the chromatic dispersion value was 23 ps/km/nm and the transmission loss was 0.182 d at a λc wavelength of 1.59.
It was B/km. Further, the fiber length necessary to obtain a total chromatic dispersion of 3000 ps/nm using this high dispersion optical fiber 1 was 130.4 km, and the loss in the entire fiber length at this time was 23.7 dB.

A 1.3SM fiber as a comparative example was prepared, and the chromatic dispersion value and transmission loss of this 1.3SM fiber were measured.The cutoff wavelength was 1.21, and the measurement wavelength was 1.21.
At 55 μm, the wavelength dispersion value was 16.8 ps/km/nm, and the transmission loss was 0.21 dB/km. Also this 1.3S
The fiber length required to obtain a total chromatic dispersion of 3000 ps/nm using the M fiber was 178.6 km, and the loss in the entire fiber length at this time was 37.5 dB.

From the results of Experimental Example 2 above, it was found that the high dispersion optical fiber 1 of the example has an extremely high dispersion value per unit length and low transmission loss compared to the conventional 1.3SM fiber. confirmed.

[0025]

[Effects of the Invention] As described above, in the high dispersion optical fiber of the present invention, on the outside of the core made of pure quartz,
A first cladding is provided by laminating fluorine-doped quartz, the relative refractive index difference of the first cladding is -0.6% or less, and the relative refractive index difference of the second cladding is smaller than -0.2%, In addition, since the value of the first cladding outer diameter/core diameter is configured to be 1.7 to 2.5, the structural dispersion value of the optical fiber becomes large, which is determined by the sum of the structural dispersion value and the material dispersion value. It is possible to increase the chromatic dispersion value to the positive side. Therefore, a high wavelength dispersion of 20 to 24 ps/km/nm can be obtained, and when used as a dispersion simulator used when investigating transmission characteristics, the length of the fiber used can be shortened and the experimental equipment can be made smaller. Can be done.

Furthermore, since the transmission loss per unit length can be reduced, when used as a dispersion simulator, the fiber length can be shortened as described above, and this makes it possible to create a dispersion simulator with extremely low loss. be able to. Additionally, when investigating transmission characteristics, even if the number of components installed in the circuit under test is increased, the loss over the entire length of the circuit can be kept small, so even complex optical circuits can be investigated for transmission characteristics. becomes possible.

[Brief explanation of drawings]

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

FIG. 2 is a model profile of an optical fiber for explaining an experiment regarding the relationship between the refractive index distribution and the wavelength dispersion value of the optical fiber.

FIG. 3: For an optical fiber with a numerical value of 1.2, indicated by b/a in FIG. 2, d2 is set to −0.2, −0.3, −0.
4. It is a graph showing the results of measuring the wavelength dispersion value with respect to the d1/d2 value when -0.5%.

FIG. 4 For an optical fiber with a numerical value of 1.5, indicated by b/a in FIG. 2, d2 is -0.2, -0.3, -0.
4. It is a graph showing the results of measuring the wavelength dispersion value with respect to the d1/d2 value when -0.5%.

FIG. 5: For an optical fiber with a numerical value of 2.0, indicated by b/a in FIG. 2, d2 is set to −0.2, −0.3, −0.
4. It is a graph showing the results of measuring the wavelength dispersion value with respect to the d1/d2 value when -0.5%.

FIG. 6 is a graph showing the results of an experiment conducted in Experimental Example 2 to investigate the relationship between the value represented by the diameter of the first cladding/core diameter and the wavelength dispersion value.

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

[Explanation of symbols]

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

Claims (1)

[Claims] 1. In a single mode optical fiber consisting of a core and a cladding, a first cladding is provided by laminating fluorine-doped quartz on the outside of the core made of pure quartz, and the first cladding is
A second cladding is provided by laminating fluorine-doped quartz on the outside of the cladding, the first cladding has a relative refractive index difference of -0.6% or less with the core, and the second cladding has a relative refractive index difference with the core of the second cladding. 1. A high dispersion optical fiber characterized in that the ratio difference is smaller than -0.2% and the first cladding outer diameter/core diameter value is 1.7 to 2.5.