KR20020027028A - A method for a manufacturing an arc induced long period gratings in optical fiber - Google Patents

Abstract

PURPOSE: A method for fabricating a long period grating of an optical fiber fabricated with an arc is provided, which fabricates the long period grating more stably without using an expensive ultraviolet light source, an amplitude mask and a photo sensitive fiber. CONSTITUTION: According to the method, an optical fiber(18) is fixed and a weight(17) is connected to a contrary side of the optical fiber so that a constant tensile force is applied to the optical fiber. And a long period grating is formed by generating a high voltage as moving an electrode plug installed on a side of the optical fiber by a constant interval. The above long period grating formation step is repeated on the formed grating several times. An optical signal is inputted to the optical fiber and a variation of a wavelength is measured by a wavelength measurement apparatus, and then the long period grating formation step is repeated according to the extent of a coupling from a core mode to a clad mode. The movement interval of the electrode plug is 300-800 micrometer.

Description

A METHOD FOR A MANUFACTURING AN ARC INDUCED LONG PERIOD GRATINGS IN OPTICAL FIBER}

The present invention relates to a method for manufacturing a long period grating of an optical fiber, and more particularly, to generate a high voltage repeatedly in the same place by applying an arc discharge in a cycle of several hundred μm so that the coupling between the core mode and the clad mode occurs in the direction of light The present invention relates to a method for manufacturing a long period grating of an optical fiber that overlaps to produce a long period grating.

In general, if the refractive index of the optical fiber core is changed at regular intervals to the optical fiber, the light traveling in the core mode at the specific wavelength is combined in the clad mode and proceeds to the cladding in the same direction as the traveling direction. As such, the refractive index of the optical fiber core is changed at regular intervals using an ultraviolet (190-250 nm) light source and an amplitude mask. At this time, the optical fiber used is a photosensitive optical fiber which can change the refractive index in the ultraviolet region.

The specific wavelength from core mode to clad mode is determined by the following equation.

,

Where β _co is the propagation constant in the core mode

β _clad : propagation constant in clad mode

Λ: grid spacing

Since the propagation constant is a function of the wavelength and the refractive index (β = 2πn / λ), the specific wavelength advances to the cladding by changing the refractive index and the lattice spacing to progress from the core mode to the clad mode. As a result, it can be seen that the wavelength proceeding to the clad is band-stopped. In the commonly used method, the band blocking wavelength is determined by changing the lattice spacing.

Disadvantages of the conventional method are the use of expensive ultraviolet lasers and various bands of amplitude masks in order to change the wavelength of the wavelength band, and expensive optically sensitive optical fibers must be used. In addition, the fabricated optical fiber grating device has a lot of wavelength shift due to temperature change.

The present invention has been made in view of the above problems, and an object thereof is to provide a method of manufacturing a long period grating of an optical fiber more stably without using an expensive ultraviolet light source, an amplitude mask, and a photosensitive optical fiber.

Another object of the present invention is to provide a method for manufacturing a long period grating of an optical fiber which is excellent in reproducibility and reliability, has low background loss, and is capable of mass production.

1 is a configuration diagram showing the configuration of an apparatus for manufacturing an optical fiber long period grating according to the present invention;

2 is an axial cross section of a glass fiber in which deformation occurs;

3 is a wavelength analysis diagram of an optical signal traveling through an optical fiber having a lattice formed at 600 μm intervals,

4 shows wavelength characteristics of an arc-induced superimposed long-period grating,

In the arc-induced superimposed long-period grating in FIG. 5, the characteristics of the wavelength are reduced.

♣ Explanation of symbols for the main parts of the drawing

11 high voltage generator 12 motor drive unit

13: control unit 14: electrode support

15: electrode 16: automatic transfer device

17: weight 18: optical fiber

19: light wavelength measuring device 20: light source

21: optical fiber fixing device

In order to achieve the above object, the optical fiber manufacturing method according to the present invention comprises the steps of fixing the optical fiber and the weight in the opposite direction so that a certain degree of tension acts on the optical fiber; Forming a long period grating by generating a high voltage while moving the electrode bar provided on the side surface of the optical fiber at a predetermined interval; Repeating the long period lattice forming step on a previously formed lattice and repeating the predetermined number of times; The optical signal is input to the optical fiber, and the wavelength change is measured by the optical wavelength measuring device, and the long period lattice forming step is repeated according to the degree of coupling from the core mode to the clad mode.

Hereinafter, with reference to the accompanying drawings showing a preferred embodiment of the present invention will be described in detail.

1 is a block diagram showing the configuration of an optical fiber manufacturing apparatus having a long period grating according to the present invention.

The optical fiber 18 is supported and fixed to the optical fiber fixing device 21, and the weight 17 is attached to the other side. The weight 17 is about several grams, and the weight of the optical fiber 18 is tensioned to maintain the tension. The control unit 13 sends a control signal to the high voltage generator 11 to generate a high voltage. This high voltage is applied to the electrodes 15 and 15 to generate an arc discharge between the two electrodes 15 and 15. The optical fiber 18 therebetween by the arc discharge receives heat and the core and the clad are instantaneously melted to deform the optical fiber 18 by the tension of the weight 17.

The motor driver 12 drives the motor according to the control signal and is used to generate a grating at a position different from that of the optical fiber. The transfer device 16 receives a signal from the motor driver 12 to move the optical fiber fixing device 21 to move the optical fiber 18. The weight 17 is attached to the optical fiber 18 to provide tension to the optical fiber 18. The optical wavelength measuring device 19 analyzes the wavelength of the light source output through the optical fiber 18. The light source 20 provides light to the optical fiber 18. The optical fiber fixing device 21 fixes the optical fiber 18 so as not to shake.

2 shows the axial cross section of the glass fiber in which the deformation occurred.

When arc discharge is applied to the optical fiber 18, the clad 23 and the core 24 of the arc discharged portion have a deformation smaller in diameter than the normal clad 21 and the core 22. The light 25 traveling through the core 32 enters the clad 23 without being totally reflected at the portion where the deformation occurs, and proceeds in the clad 33.

16 to 32 such gratings can be formed at intervals of 300 μm to 800 μm, the number and spacing of which depend on the wavelength and loss to be filtered. In this embodiment, the long lattice was formed by overlapping 32 lattice three times at intervals of 600 mu m. After forming one lattice, the motor drive unit 12 is controlled to move the feeder 16 to move the optical fiber holding device 21 to move the optical fiber 18 to 600 mu m. Subsequently, the high voltage generator 11 is controlled to generate a high voltage, and arc discharge is generated between the electrodes 15 and 15 by the high voltage. The long period lattice is formed by this arc discharge. Repeat this 32 times to form 32 grids.

3 shows a wavelength analysis diagram of an optical signal traveling through an optical fiber having a lattice formed at 600 μm intervals.

As can be seen from this analysis, the mainband stop loss is 25dB, which causes 3dB of background loss. Increasing the amount of arc generation will result in high band stop loss, but will increase background loss. In addition, increasing the amount of arc generation under the same conditions, the lack of reproducibility, the production reliability is low.

The present invention forms an overlapping long period grating to address this lack of reproducibility and reliability. It reduces the amount of arc generation by several percent and repeats 32 times at 600 µm cycles to form 32 gratings. After forming the grating once, the feeder is controlled to return the position of the optical fiber 18 to the initial position. In the same manner as before, the arcs are discharged where the long period lattice is formed to form an overlapping lattice. This process is repeated three times to form 32 overlapping grids three times.

4 shows wavelength characteristics of the superposed long-period grating induced by the arc.

Mainband stop loss is 28dB and background loss is below 1dB. In case of reproducibility and change of wavelength, superposition was excellent. As shown, in the grating formed by one arc discharge, a loss of about 3 dB appears at wavelengths of 1355 nm, 1390 nm, 1470 nm, and 1620 nm, and when overlapped twice, 1360 nm, 1395 nm, 1470 nm, and 1625 nm. A loss of about 5 to 10 dB appeared at the wavelength of, and when overlapped three times, a loss of about 6 dB at 1370 nm, 16 dB at 1400 nm, 28 dB at 1475 nm, and about 20 dB at a wavelength of 1630 nm appeared. In this way, the center wavelength is shifted to the long wavelength every time it overlaps. In addition, the loss is gradually increased in the generated band-stop area, and the depth grows more rapidly two or three times than the depth shown in the first time. If the repetition is continued, the wavelength shifts and the loss decreases.

In FIG. 5, when the lattice in the arc-derived long-period grating is reduced to 16, the characteristic of the wavelength measured while increasing the number of superpositions from one to five is shown.

A loss of 5 dB or more occurs in the range of ± 15 nm in the vicinity of the wavelengths of 1400 nm, 1470 nm, and 1645 nm, thereby increasing the width of the wavelength of the band blocking line width.

According to the present invention, by forming a plurality of long-period gratings overlapping a predetermined number of times at regular intervals, the reproducibility and reliability are high, and the background loss is less generated, which enables mass production.

Claims (6)

Fixing the optical fiber and connecting the weight in the opposite direction so that a certain degree of tension is applied to the optical fiber; Forming a long period grating by generating a high voltage while moving the electrode bar provided on the side surface of the optical fiber at a predetermined interval; Repeating the long period lattice forming step on a previously formed lattice and repeating the predetermined number of times; Inputting the optical signal to the optical fiber and measuring the change in the wavelength with an optical wavelength measuring device manufacturing a long period grating of the optical fiber, characterized in that the step of repeating the long period grating forming step according to the degree of coupling from the core mode to the clad mode Way. The method of claim 1, wherein the movement interval of the electrode is 300 to 800 µm. The method of claim 1, wherein the long period grating formed in the optical fiber is several tens of times. The method of manufacturing a long period grating of an optical fiber according to claim 1, wherein the number of times of overlapping the long period grating is two or more and ten times or less. The method of claim 1, wherein the number and spacing of the long period gratings are determined according to the wavelength and the loss of the filtering. 2. The method of claim 1, wherein the degree of deformation changes by varying the amount of arc depending on the lattice position, and the degree of deformation can be expressed as the diameter of the core. A method for manufacturing a long period grating of an optical fiber in which side lobes existing on a short wavelength side are removed by using a function.