KR0160326B1 - How to prevent increased chromatic dispersion and random bending losses in single-mode fiber - Google Patents

Abstract

The present invention relates to a single mode optical fiber, in particular, to reduce the refractive index of the fiber core in a double or more multi-stage from the core center to shift the zero dispersion wavelength to 1550 nm, and to reduce the double or more multi-stage refractive index in the clad of the optical fiber By forming the layer, there is an outstanding effect that can prevent the increase of random bending loss.

Description

How to prevent increased chromatic dispersion and random bending losses in single-mode fiber

1 is a refractive index distribution diagram of an optical fiber having a double core and a double clad according to the present invention.

2 is a refractive index distribution diagram of an optical fiber having triple core and triple clad according to the present invention.

3 is a change in refractive index distribution according to the change in q value in the present invention.

TECHNICAL FIELD The present invention relates to a dalilmode fiber, and in particular, the refractive index of the optical fiber core is reduced from the core center in two or more multi-stages to shift the zero-dispersion wavelength to 1550 mm, and to reduce the double or more multistage refractive index in the clad of the optical fiber By forming a layer, the present invention relates to a method for preventing the increase in color dispersion and random loss of a single mode optical fiber which can prevent the increase in random bending loss.

In general, single-mode optical fibers used for wideband long-distance transmission require minimum optical loss and zero color dispersion in the optical fiber's operating wavelength.

In order to meet this requirement, the condition that the light loss is minimized was possible by using 1550nm as the operating wavelength, which minimizes the theoretical loss of single-mode optical fiber (eg silica optical fiber). Done. Since color dispersion is expressed as the sum of mass dispersion and waveguide dispersion, light loss can be minimized by appropriately adjusting the double waveguide dispersion.

Waveguide dispersion is determined by the refractive index distribution, the radius of the core, and the difference in relative refractive index between the core and the cladding. Thus, by varying these waveguide parameters, the chromatic dispersion can be made zero at the desired wavelength (i.e., 1550 nm). At this time, since the radius of the core or the relative refractive index difference between the core and the clad among the waveguide variables is determined according to the refractive index distribution, it is very important to first determine the refractive index distribution in order to manufacture a desired single mode optical fiber.

Conventionally, in order to solve the problem of minimizing light loss and increasing color dispersion as described above, various refractive index distributions have been proposed to obtain a characteristic that the color dispersion becomes zero at 1550 mm, but random bending loss is higher than that of the conventional optical fiber. The increasing trend led to an urgent need for supplements.

On the other hand, the equation for the experimentally determined bending (bending) is as follows.

bending ∝ (core radius / fiber radius) ² * (1 / opening) ⁴

In order to reduce the bending loss, it is necessary to reduce the size of the core and increase the outer diameter of the entire optical fiber, which is fixed due to the optical transmission characteristic. Therefore, it is preferable to reduce the bending loss by increasing the numerical aperture, which is the next term.

These methods include increasing the refractive index of the core and decreasing the refractive index of the cladding layer around the core. When the refractive index of the core is increased, it is large for the conditions such as loss of light, dispersion, and cutoff. There will be a change.

In particular, in terms of losses, the result is poor, if the refractive index of the clad to increase the numerical aperture, this can be seen to reduce the bending loss.

The present invention has been made as part of the above-mentioned countermeasures, which prevents the increase in random bending loss of the optical fiber by shifting the zero dispersion wavelength of the optical fiber to 1550 nm and forming a lower layer of double or more multi-stage refraction in the clad. There is a purpose.

In addition, the portion in which the refractive index of the clad (hereinafter referred to as trench) is maintained while being stepped is formed in the shape of the core obtained by the calculation of the wavelength equation, which is extended to the bottom of the trench and is the result of the calculation. Is designed to extend to the bottom of the trench.

As a means for achieving the above object,

Single mode with double core (1,2) and double clad (3,4)

The refractive index distribution in an optical fiber is

Refractive index n (r)

here,

ego,

The refractive index distribution in a single mode optical fiber having triple cores (1 ', 2', 3 ') and triple clads (4', 5 ', 6'),

Tangerine ratio n (r) is

here,

Is achieved by distributing as follows.

The present invention thus made will be described below with reference to the accompanying drawings.

1 is a refractive index distribution related to the refractive index versus the radial distance of a single mode optical fiber having a double core (1, 2) and a double clad (3, 4) of the present invention, the refractive index distribution in the core,

here

ego

The refractive index distribution in the clad

here

to be.

2 is a refractive index distribution diagram related to the refractive index versus the radial distance of a single mode optical fiber having the triple cores (1, 2, 3) and triple clads (4, 5, 6) of the present invention.

here

ego

The refractive index distribution in the clad is

here

to be.

Determination of b / d, which is the size of the clad in the case of the dual structure shown in FIG. 1, and c / f, which is the size of the cradle in the case of the triple structure shown in FIG. Is an important factor in process cost and light loss. If it is too large, a large number of deposition layers are required in the manufacturing process, which leads to an increase in process cost. When the size of the clad is too small, the optical fiber is bent. Since the light loss increases due to the leaky mode generated, an appropriate value should be selected.

On the other hand, the q value used above can be written from 1 to infinity, the proposed core structure is stepped, but this shows the case where q value is infinity, and if q value is 0, it becomes a triangular structure. The overall trivalent structure is achieved.

Therefore, the expression of this expression is the expression that the core's refraction is applied to everything from the convex structure above the triangle to the step shape.

The shape of the cutoff rate for this value is shown in FIG.

As described above, the present invention allows the zero dispersion wavelength to be minimized to 1550 mm to minimize the loss of the optical fiber by retaining the refractive index distribution in the optical fiber core and to form a double or more multi-level refractive index lowering layer in the clad. Therefore, there is an extraordinary effect that can prevent the increase in random bending loss of the optical fiber.

Claims (2)

In a single mode optical fiber, the color dispersion of the optical fiber becomes zero (0) at a wavelength (1550 nm) by having a double or more multistage refractive index distribution in the core of the optical fiber and a double or more multistage refractive index lowering layer in the clad. A method for preventing the increase in color dispersion and random bending loss of a single mode optical fiber, characterized by preventing the increase in random bending loss. The method of claim 1 wherein the birefringence distributions of cores (1,2) and clads (3,4) here, ego, The refractive index distribution of the cores 1 ', 2', 3 'and the clads 4', 5 ', 6' is a refractive index. here, A method for preventing the increase in chromatic dispersion and random bending loss of a single mode optical fiber characterized in that.