JP2004271689A - Method for manufacturing optical fiber grating and manufacture apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing an optical fiber grating and manufacturing apparatus with a reduced cost by lowering the deposition rate of foreign substances sticking to a phase mask and increasing the washing intervals and lifetime of the phase mask. <P>SOLUTION: In manufacturing of the optical fiber grating, gas is passed from a gas supply port 4 to a gas suction opening 5 at a prescribed flow rate between the phase mask 6 and an optical fiber glass area 9. The rate at which the residual coating resin existing on the surface of the optical fiber glass area 9 is scattered and deposited as gas and foreign substances by ultraviolet rays onto the surface of the phase mask 6 is thereby lowered. The progression rate of the contamination on the surface of the phase mask 6 is eased and the washing intervals and lifetime of the phase mask are increased. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【００６０】
表１からわかるように、窒素を流しながら製造する方が、位相マスク６の洗浄を要するまでに作製できた光ファイバグレーティングの本数が多くなっている。これは、位相マスク表面が汚染されるまでの時間が長くなっていることを示すものであり、明らかに発明の効果が認められる。
【００６１】
また、従来の技術と比較するために、光ファイバガラス部位９と位相マスク６の問に石英板を置いた場合についても同様の調査を行った。石英板の寸法は、４０ｍｍ×４０ｍｍであり、厚さは１００μｍである。前記石英板を位相マスク６と光ファイバガラス部位９の間に設置し、表１に結果を示した実験と同じ条件で光ファイバグレーティングの作製を行った。
【００６２】
この場合には、前記実験における、位相マスク６が交換必要となる条件と同じ条件で、石英板が交換必要となるまでの光ファイバグレーティング作製本数を求めた。その結果を表２に示す。表２の結果は、同一実験１０回の平均値である。
【００６３】
【表２】

【００６４】
表２から、窒素を流しながら製造する方が、位相マスク６の洗浄または石英板の交換までに作製できた光ファイバグレーティングの本数が多くなっており、明らかに発明の効果があることがわかる。
【００６５】
さらに、窒素を流した場合と流さない場合とで位相マスク表面の汚染進行の違いを見るために、同じ本数の光ファイバグレーティングを製造した後、位相マスク表面に付着した異物の個数を顕微鏡により調査した。異物検出は、顕微鏡に接続した市販の画像処理装置を用いて行い、異物の面積が１μｍ^２ 以上のものを異物としてカウントする設定とした。その結果は表３に示すものである。表３は同一実験を１０回行った平均値である。
【００６６】
【表３】

【００６７】
表３より、窒素を流しながら製造する方が、位相マスク表面の異物が少ない、すなわち汚れが少なくなつており、明らかに発明の効果があることがわかる。なお、窒素に替えて、乾燥空気、Ｈｅ、Ａｒなどのガスを用いてもよい。
【００６８】
また、窒素の流量と異物検出個数の関係を調査した。その結果を図３に示す。この図からわかるように、窒素流量が５０ｍｌ／ｍｉｎ未満では、異物個数が増加する。これは、窒素の流れが、位相マスク表面に向かって飛散してくる異物を十分に吹き流すことができないため、異物の付着防止効果が低下するためであると考えられる。
【００６９】
従って、窒素は、５０ｍｌ／ｍｉｎ以上の流量に設定することが必要である。なお、流量を１０００ｍｌ／ｍｉｎ以上に設定すると窒素の流れによる光ファイバ８の振動が大きくなり、結果として光ファイバガラス部位９上に投影された紫外光の光強度の周期構造が乱れ、屈折率分布の周期的構造を正確に製作することが不能となった。
【００７０】
【発明の効果】
以上説明したように、本発明の製造方法および製造装置を用いて、ファイバと位相マスクの問にガスを流すことで、被覆樹脂除去後にファイバ表面に残留存する微量の被覆樹脂が紫外光によりガス化あるいは飛散したものが位相マスク表面に付着することを、効果的に抑制できる。従って、本発明を用いることで、位相マスク表面に汚れが付着し洗浄が必要になるまでの時間を大幅に長くすることが可能である。前記の効果により、洗浄に要する費用の低減が可能であり、また洗浄頻度の低下により、位相マスクの寿命が延びることも期待できる。その結果として、より安価に光ファイバグレーティングを製造することが可能になる。
また、従来技術である位相マスクとファイバの問に石英板を置く方法に比べ、より安い費用で位相マスクの洗浄頻度を低減することができる。その結果としてより安価に光ファイバグレーティングを製造することが可能になる。
【図面の簡単な説明】
【図１】本発明の光ファイバグレーティング製造装置の一例を示す概略構成図である。
【図２】従来の光ファイバグレーティングの製造方法の一例を示す図である。
【図３】実施例において、窒素の流量と位相マスク表面に付着した異物の個数の関係を示したグラフである。
【符号の説明】
１…ガス供給装置、２…ガス供給部、３…真空ポンプ接続部、４…ガス吹出口、５…ガス吸引口、６…位相マスク、７…位相マスク固定部、８…光ファイバ、９…光ファイバガラス部位、１０…光ファイバ固定台、１１…紫外光光源、２１…光ファイバガラス部位、２３…位相マスク。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method and an apparatus for manufacturing an optical fiber grating, which reduces foreign substances adhering to the surface of a phase mask for exposure and reduces the manufacturing cost by increasing the interval of phase mask cleaning. is there.
[0002]
[Prior art]
An optical fiber grating is an optical component that extracts light of a specific wavelength by transmitting or reflecting light of a specific wavelength among light propagating in an optical fiber. Or a gain equalizer in an optical amplifier.
[0003]
Such an optical fiber grating has a periodic variation in the refractive index of the core in the longitudinal direction of the fiber, and the periodic variation structure of the refractive index acts as a diffraction grating for light propagating through the core. I do. By this function as a diffraction grating, a function of reflecting / transmitting light of a specific wavelength in a wavelength multiplexed optical signal propagating through a core, and a function of coupling signal light of a specific wavelength to clad propagation light and attenuating it. Occurs.
[0004]
The most common method of manufacturing an optical fiber grating is to change the refractive index of the core by a photorefractive (UV-induced increase in refractive index) effect. The photorefractive effect is a phenomenon in which, for example, when a quartz glass fiber doped with germanium as a dopant is irradiated with ultraviolet light having a wavelength of about 240 nm, the refractive index of the germanium-doped quartz glass increases.
[0005]
FIG. 2 shows an example of a conventional method for manufacturing an optical fiber grating. In the figure, reference numeral 21 denotes a glass part where the coating of the optical fiber is removed and the bare optical fiber is exposed. Reference numeral 21a is a core in the glass part 21, and reference numeral 21b is a clad. Reference numeral 22 denotes a coating resin that covers the glass part 21. The clad 21b is usually made of pure quartz glass, and the core 21a is made to have a higher refractive index than the clad by adding a dopant such as germanium to quartz glass, and confine signal light to this portion to propagate in the longitudinal direction. Has functions.
[0006]
The purpose of the coating resin 22 is to protect the surface of the glass portion 21 and serve as a buffer layer against external force. Reference numeral 23 denotes a phase mask formed of a thin plate of quartz glass. Periodic fine grooves are formed on one surface of the phase mask 23 and function as a diffraction grating.
[0007]
Hereinafter, a method for manufacturing an optical fiber grating will be described. First, a part of the coating resin 22 of the optical fiber is removed over the entire outer periphery to expose the cladding 21b and is placed parallel to the diffraction grating surface of the phase mask 23. A grating is formed on the glass part 21 from which the coating resin 22 has been removed. The glass part 21 is irradiated with ultraviolet light having a wavelength of about 240 nm through the phase mask 23.
[0008]
The ultraviolet light that has passed through the phase mask 23 is diffracted by a periodic grating on the surface of the phase mask 23 and becomes ± first-order diffracted light. These diffracted lights overlap and interfere with each other in the space after passing through the phase mask 23, so that the ultraviolet light forms a distribution having a periodic variation in light intensity in the longitudinal direction of the optical fiber.
[0009]
Ultraviolet light having this periodic light intensity distribution is applied to the glass portion 21 of the optical fiber located immediately below the phase mask 23, and reaches the core 21a, whereupon the photorefractive effect causes the core 21a to have a periodic refractive index. Fluctuations are formed.
[0010]
The periodic fluctuation of the refractive index in the longitudinal direction of the optical fiber obtained in this way gives the optical fiber a function as a filter for generating a loss in light of a specific wavelength band. In order to efficiently irradiate the core 21a with ultraviolet light, the coating resin 22 having an ultraviolet light absorbing action is removed before the irradiation, and the ultraviolet light is directly irradiated on the glass portion 21, but the following problem exists.
[0011]
That is, there are a mechanical method and a chemical method to remove the coating resin 22. In the former, for example, a thin blade is applied to the coating resin 22 and the thin blade or the resin coating 22 is moved to peel the resin and remove the resin. I do. In this case, when the thin blade comes into contact with the glass portion 21, fine scratches are generated on the glass surface and cause breakage. Therefore, a protective function is provided so that the thin blade does not contact the glass portion 21, or the glass is scratched. Uses a thin blade made of a material of low hardness that is difficult.
[0012]
However, by doing so, the resin coating 22 slightly remains on the surface of the glass portion 21. In the chemical method, an optical fiber is impregnated with an acid capable of dissolving the coating resin 22. However, it takes a long time to completely dissolve the coating resin 22, so that the working efficiency is poor. As in the case of the mechanical method, minute residual resin was often generated.
[0013]
By the way, the periodic fluctuation of the light intensity generated by diffracting the ultraviolet light by the phase mask 23 occurs only up to a distance of several hundred μm from the periodic grating on the surface of the phase mask 23. Therefore, the distance between the surface of the phase mask 23 and the optical fiber glass part 11 needs to be close to several hundred μm.
[0014]
Therefore, if the coating resin 22 remains on the surface of the optical fiber glass portion 21, the residual resin is gasified or scattered by ultraviolet light, and adheres to and contaminates the surface of the phase mask 23.
[0015]
This problem becomes even more remarkable particularly when a plurality of fibers are fixed in parallel to mass-produce optical fiber gratings and a plurality of optical fiber gratings are manufactured at one time.
[0016]
The phase mask 23 diffracts ultraviolet light by fine grooves on its surface. However, when gasified resin or scattered resin adheres to the surface of the phase mask 23, ultraviolet light is scattered at the attachment site. In addition, the light intensity of the ± 1st-order diffracted light required to form the periodic fluctuation of the light intensity in the space is reduced.
[0017]
Therefore, the contrast (the ratio between the maximum value and the minimum value of the light intensity) of the periodic light intensity distribution formed in the space is reduced. In order to obtain a predetermined reflection / transmission characteristic in an optical fiber grating, the refractive index fluctuation of a core formed by ultraviolet light having a periodic light intensity distribution must reach a predetermined range. When the contrast of the periodic light intensity distribution of the light decreases, a long-time ultraviolet light irradiation is required to cause a necessary change in the refractive index, which significantly reduces the workability.
[0018]
Incidentally, it is known that the contamination of the surface of the phase mask due to the residual resin can be removed by washing with an acid or an alkali. However, since this cleaning operation must be performed without damaging the fine grooves on the surface of the phase mask, the skill and skill of the operator are required, and a long working time is required. Therefore, it is important to reduce the number of times of cleaning the phase mask as much as possible from the viewpoint of reducing the manufacturing cost of the optical fiber grating.
[0019]
Moreover, the cleaning does not completely remove the contamination on the surface of the phase mask, but rather accumulates a small amount of dirt. Therefore, it can be said that the number of times the phase mask can be cleaned is limited. Therefore, it is very important to reduce the contamination of the phase mask surface as much as possible and to increase the time required for cleaning when considering the manufacturing cost of the optical fiber grating.
[0020]
[Patent Document 1]
JP 2002-48926 A
With respect to the contamination of the phase mask surface, a method of placing a quartz plate between the phase mask and the fiber (Japanese Patent Application Laid-Open No. 2002-48926) is known. The invention in the above publication is to prevent dirt adhering to the phase mask with a quartz plate so that the surface of the phase mask is not contaminated.
[0022]
[Problems to be solved by the invention]
However, in the above prior art, although effective for suppressing contamination of the phase mask surface, there is a problem that the surface of the quartz plate itself placed between the phase mask and the optical fiber is contaminated. Therefore, it is necessary to replace or clean the quartz plate.
[0023]
In addition, the reflected light generated between the phase mask and the quartz plate is superimposed on the diffracted light and disturbs the periodic light intensity distribution due to the interference of the diffracted light, thereby deteriorating the optical characteristics of the optical fiber grating. Further, since the intensity of ultraviolet light is attenuated by the quartz plate, it becomes necessary to use ultraviolet light having higher intensity.
[0024]
Further, as described above, since the distance between the phase mask and the fiber needs to be close to several 100 μm, the thickness of this quartz plate is required to be several hundred microns or less and to be uniform. Therefore, this quartz plate has to be very expensive. By manufacturing using such expensive components, the manufacturing cost of the optical fiber grating becomes high as a result.
[0025]
The present invention effectively suppresses contamination of the phase mask surface without deteriorating the optical characteristics of the optical fiber grating to be manufactured, thereby increasing the time until the phase mask needs to be cleaned, and as a result, It is an object of the present invention to provide a method for manufacturing an optical fiber grating at low cost and an apparatus for manufacturing the same.
[0026]
[Means for Solving the Problems]
In order to solve this problem, the invention according to claim 1 is a method of manufacturing an optical fiber grating by fixing one or more optical fibers in parallel and irradiating the optical fibers with ultraviolet light through a phase mask. 3. The method of manufacturing an optical fiber grating according to claim 1, wherein a gas is flowed between the phase mask and the optical fiber.
[0027]
The invention according to claim 2 is the method for manufacturing an optical fiber grating according to claim 1, wherein the gas flowing direction is the same as the longitudinal direction of the optical fiber.
[0028]
The invention according to claim 3 is the method for manufacturing an optical fiber grating according to claim 1, wherein the type of gas is an inert gas.
[0029]
The invention according to claim 4 is the method for manufacturing an optical fiber grating according to claim 1, wherein the flow rate of the gas is not less than 50 ml / min and not more than 1000 ml / min.
[0030]
The invention according to claim 5 is an optical fiber grating manufacturing apparatus for forming a grating on an optical fiber by irradiating the optical fiber with ultraviolet light through a phase mask for exposure, wherein a gas outlet and a gas suction port face each other. An optical fiber grating manufacturing apparatus is provided between the phase mask and the optical fiber.
[0031]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 is a diagram showing an embodiment of a fiber grating manufacturing method and a manufacturing apparatus according to the present invention. The optical fiber grating manufacturing apparatus in this example includes an ultraviolet light source denoted by reference numeral 11, a gas supply device denoted by reference numeral 1, a phase mask denoted by reference numeral 6, a phase mask fixed base denoted by reference numeral 7, an optical fiber denoted by reference numeral 8, and a reference numeral 8. It comprises an optical fiber glass part indicated by 9 and an optical fiber fixing base indicated by reference numeral 10.
[0032]
First, the gas supply device 1 will be described. A gas supply unit indicated by reference numeral 2 is connected to one end of the gas supply device 1, and the gas supply unit 2 is connected to a gas outlet indicated by reference numeral 4 via a pipe (not shown). The other end of the gas supply device 1 is connected to a vacuum pump connection portion indicated by reference numeral 3, and the vacuum pump connection portion 3 is connected to a gas suction port indicated by reference numeral 5 by piping not shown.
[0033]
A vacuum pump (not shown) is connected to the vacuum pump connection unit 3. The gas outlet 4 and the gas suction port 5 face each other, and the gas ejected from the gas outlet 4 is sucked from the gas suction port 5.
[0034]
The number and shape of the gas outlets 4 are optimal for the effect of blowing out gas and foreign matter scattered from the optical fiber glass part 9 in consideration of the number and shape of the optical fibers 8, the length of the optical fiber glass part 9, and the like. What is necessary is just to design. Similarly, the number, size, and shape of the gas suction ports 5 may be designed so that the gas ejected from the gas outlets 4 can be efficiently sucked.
[0035]
The gas blowing direction to the optical fiber glass part 9 is arbitrary, but the longitudinal direction of the fiber and the gas blowing direction may be the same so that the fixed fiber does not vibrate due to the flow of the gas blowing. desirable. In FIG. 1, a through portion is provided on the surface of the gas supply device 1 facing the optical fiber glass portion 9, and the phase mask 6 and the phase mask fixing stand 7 are installed in this through portion.
[0036]
The gas supply device 1 may not be provided with a penetrating portion, and may have a structure in which the gas supply device 1 and the phase mask fixing base 7 are integrated, but a mechanism for finely adjusting the height of the gas outlet 4 with respect to the phase mask 6. Is desirably provided.
[0037]
The gas supplied to the gas supply device 1 is used to blow off foreign matter scattered from the optical fiber glass portion 9 toward the surface of the phase mask 6, and is preferably an inert gas or dry air. In addition, those gases must be purified by removing foreign substances sufficiently through a filter or the like.
[0038]
The phase mask 6 is mounted on the phase mask fixing unit 7, and ultraviolet light is emitted from behind the phase mask fixing unit 7 toward the phase mask 6. On the surface of the phase mask fixing base 7 on which the phase mask 6 is mounted, a penetration portion for transmitting ultraviolet light to the phase mask 6 is provided.
[0039]
The optical fiber 8 is fixed to the phase mask 6 by an optical fiber fixing base 10 with a constant tension. The optical fiber 8 may be a single fiber or a plurality of fibers, and may be a multi-core fiber such as a tape fiber.
[0040]
The optical fiber fixing base 10 fixes the optical fiber at a constant tension by vacuum suction or a pressing member, but the interference fringes of the ultraviolet light formed by the phase mask 6 exist within several hundred μm from the surface of the phase mask 6. Therefore, it is necessary to have a mechanism capable of finely adjusting the distance between the phase mask 6 and the optical fiber glass part 9.
[0041]
Further, the optical fiber fixing base 10 may be integrated with the gas supply device 1 and the phase mask fixing section 7. The phase mask fixing part 7, the gas supply device 1, and the optical fiber fixing stand 10 are desirably installed on a base having an anti-vibration structure such as an anti-vibration stand in order to minimize vibration during irradiation with ultraviolet light. .
[0042]
Reference numeral 11 denotes an ultraviolet light source, for which an ultraviolet lamp, an excimer laser, or the like is used. Ultraviolet light emitted from the ultraviolet light source 11 is applied to the phase mask 6, and an optical system (not shown) for condensing or changing an optical path by a quartz lens, an ultraviolet light reflecting mirror, or the like is usually provided between the two. used.
[0043]
A method for manufacturing an optical fiber grating using such an optical fiber grating manufacturing apparatus will be described below. The ultraviolet light emitted from the ultraviolet light source 11 passes through the penetrating portion of the phase mask fixing unit 7 and is applied to the phase mask 6.
[0044]
The ultraviolet light transmitted through the phase mask 6 becomes ± 1st-order diffracted light due to the diffraction effect of the phase mask 6, and forms an interference fringe having a periodic light intensity fluctuation structure in the space after transmitting through the phase mask 6. The optical fiber glass part 9 is placed in the space where the interference fringes are generated, and a periodic fluctuation structure of the refractive index is formed in the core due to the periodic fluctuation of the ultraviolet light intensity.
[0045]
The interval between the phase mask 6 and the optical fiber glass part 9 is adjusted so that the refractive index variation effect is optimized because the region where the ultraviolet light interference fringes are generated is limited. In addition, the height of the gas outlet 4 and the gas suction port 5 from the surface of the phase mask 6 is adjusted so that the gas flow is optimal for blowing gas or foreign matter scattered from the optical fiber glass part 9.
[0046]
Since the gas outlet 4 and the gas suction port 5 face each other and are arranged between the phase mask 6 and the optical fiber glass part 9, the gas outlet 4 is provided between the phase mask 6 and the optical fiber glass part 9. Is formed on the surface of the optical fiber glass part 9, and the coating resin gasified or scattered by the ultraviolet light is blown off by the gas flow layer, The gas is sucked by the gas suction port 5 and discharged to the outside.
[0047]
Therefore, the frequency of foreign matter reaching the surface of the phase mask 6 is significantly reduced. Due to such an effect, the progress of the contamination on the surface of the phase mask 6 is significantly slower than in the case where there is no gas flow, so that the cleaning interval of the phase mask 6 is lengthened and the life of the phase mask 6 itself is improved. .
[0048]
As described above, the direction in which the gas flows can be arbitrarily set with respect to the longitudinal direction of the optical fiber glass part 9. However, if both are not parallel but have an angle, the gas flow is reduced. In the case of No. 9, micro vibration may be generated.
[0049]
Due to this minute vibration, the periodic light intensity distribution of the ultraviolet light projected on the optical fiber glass part 9 may be disturbed, and a desired periodic refractive index fluctuation may not occur. Therefore, it is desirable that the direction in which the gas flows and the longitudinal direction of the optical fiber glass part 9 are the same.
[0050]
The type of gas used is not particularly limited as long as minute foreign matters are removed, but in consideration of safety and the like, an inert gas such as nitrogen, Ar, or He, or dry air may be used. desirable.
[0051]
The gas flow rate is an important factor that determines the effect of the blowing when the gas or foreign matter generated by the residual resin is blown. If the flow rate is small, the effect of the blow-off is weak, and the adhesion of foreign matter to the phase mask 6 is not reduced. If the flow rate is too large, a minute vibration is given to the optical fiber glass portion 9 as described above, and the refractive index is reduced. The periodic fluctuation is disturbed.
[0052]
Therefore, the gas flow rate has a range in which foreign matter adhesion can be effectively prevented. From experimental studies in examples and the like described later, a flow rate range of 50 ml / min or more and 1000 ml / min or less is suitable. Has been confirmed. If the flow rate is 50 ml / min, the flow rate is too small to prevent foreign matter from adhering to the surface of the phase mask 6 sufficiently. , And the periodic refractive index fluctuation is disturbed.
[0053]
The details will be described below with reference to examples.
[Example]
With a plurality of optical fibers 8 arranged in parallel, an optical fiber grating was produced while flowing nitrogen as a gas between the optical fiber 8 and the phase mask 6. The wavelength of the ultraviolet light used is 248 nm.
[0054]
In the gas outlet 4, three holes each having a diameter of 1 mm are arranged on a straight line at intervals of 3 mm. The gas suction port 5 has a rectangular shape of 1 mm × 25 mm. The height of the straight line connecting the centers of the holes of the three gas outlets 4 is equal to the height of the straight line connecting the midpoints of the short sides of the gas suction ports 4, and they are in a positional relationship to face each other. The gas flow rate was set to 100 ml / min.
[0055]
The optical fiber 8 used has an outer diameter of 250 μm, and the outer diameter of the optical fiber glass part 9 from which the resin coating has been removed is 125 μm. The removal length of the resin coating was 40 mm. The dimensions of the phase mask 6 used were 20 mm × 30 mm, the pitch of the grooves formed on the surface of the phase mask was about 1 μm, and the depth of the grooves was about 250 nm.
[0056]
First, in order to compare the initial characteristics, optical fiber gratings were manufactured with and without flowing nitrogen, and their optical characteristics were examined. The obtained optical characteristics were almost the same, and the time required for the production was almost the same.
[0057]
Next, an optical fiber grating was manufactured in a state where nitrogen was not flown, and the number of manufactured optical fiber gratings requiring cleaning of the phase mask 6 was obtained. In this experiment, the phase mask 6 needs to be cleaned when the transmittance of the optical fiber grating at 1550 nm, which is the measurement wavelength, does not reach 50% of the target value due to ultraviolet irradiation within a predetermined time. We are investigating the number of units produced up to this condition.
[0058]
Next, the phase mask 6 was replaced with a new one of the same standard, an optical fiber grating was prepared under the same conditions while flowing nitrogen, and the number of products requiring cleaning was determined. The results are shown in Table 1. The values in Table 1 indicate the average number of the same experiment repeated 10 times.
[0059]
[Table 1]

[0060]
As can be seen from Table 1, the number of optical fiber gratings that can be manufactured before the phase mask 6 needs to be cleaned increases when manufacturing with flowing nitrogen. This indicates that the time until the surface of the phase mask is contaminated is long, and the effect of the present invention is clearly recognized.
[0061]
In addition, for comparison with the conventional technique, the same investigation was performed on a case where a quartz plate was placed between the optical fiber glass part 9 and the phase mask 6. The dimensions of the quartz plate are 40 mm × 40 mm, and the thickness is 100 μm. The quartz plate was placed between the phase mask 6 and the optical fiber glass part 9, and an optical fiber grating was produced under the same conditions as those in the experiment shown in Table 1.
[0062]
In this case, the number of optical fiber gratings to be manufactured until the quartz plate needed to be replaced was determined under the same conditions as those in the above experiment under which the phase mask 6 needed to be replaced. Table 2 shows the results. The results in Table 2 are the average values of 10 identical experiments.
[0063]
[Table 2]

[0064]
From Table 2, it can be seen that the number of optical fiber gratings that could be manufactured before the phase mask 6 was washed or the quartz plate was replaced was larger when manufacturing with flowing nitrogen, and the effect of the present invention was clearly apparent.
[0065]
Furthermore, in order to see the difference in the progress of contamination on the surface of the phase mask between when nitrogen was flowed and when nitrogen was not flowed, the same number of optical fiber gratings were manufactured, and then the number of foreign substances adhering to the phase mask surface was examined with a microscope did. Foreign matter detection was performed using a commercially available image processing device connected to a microscope, and a setting was made such that foreign matter having an area of 1 μm ² or more was counted as foreign matter. The results are shown in Table 3. Table 3 shows the average value of the same experiment performed 10 times.
[0066]
[Table 3]

[0067]
From Table 3, it can be seen that the production under flowing nitrogen reduces the amount of foreign substances on the surface of the phase mask, that is, reduces the amount of dirt. Note that a gas such as dry air, He, or Ar may be used instead of nitrogen.
[0068]
In addition, the relationship between the flow rate of nitrogen and the number of detected foreign substances was investigated. The result is shown in FIG. As can be seen from this figure, when the nitrogen flow rate is less than 50 ml / min, the number of foreign substances increases. This is considered to be because the flow of nitrogen cannot sufficiently blow foreign matter scattered toward the surface of the phase mask, and thus the effect of preventing foreign matter from adhering is reduced.
[0069]
Therefore, it is necessary to set the flow rate of nitrogen to 50 ml / min or more. When the flow rate is set to 1000 ml / min or more, the vibration of the optical fiber 8 due to the flow of nitrogen increases, and as a result, the periodic structure of the light intensity of the ultraviolet light projected on the optical fiber glass portion 9 is disturbed, and the refractive index distribution is changed. It has become impossible to accurately manufacture the periodic structure of.
[0070]
【The invention's effect】
As described above, by using the manufacturing method and the manufacturing apparatus of the present invention, by flowing a gas between the fiber and the phase mask, a small amount of the coating resin remaining on the fiber surface after the coating resin is removed is gasified by ultraviolet light. Alternatively, it is possible to effectively prevent the scattered matter from adhering to the phase mask surface. Therefore, by using the present invention, it is possible to greatly lengthen the time until the surface of the phase mask becomes dirty and cleaning is required. Due to the above effects, the cost required for cleaning can be reduced, and the life of the phase mask can be expected to be prolonged due to the reduction in cleaning frequency. As a result, it becomes possible to manufacture the optical fiber grating at lower cost.
Further, the frequency of cleaning the phase mask can be reduced at a lower cost as compared with the prior art method of placing a quartz plate between the phase mask and the fiber. As a result, it becomes possible to manufacture the optical fiber grating at lower cost.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing one example of an optical fiber grating manufacturing apparatus of the present invention.
FIG. 2 is a diagram illustrating an example of a conventional method for manufacturing an optical fiber grating.
FIG. 3 is a graph showing the relationship between the flow rate of nitrogen and the number of foreign particles attached to the surface of a phase mask in the example.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Gas supply apparatus, 2 ... Gas supply part, 3 ... Vacuum pump connection part, 4 ... Gas outlet, 5 ... Gas suction port, 6 ... Phase mask, 7 ... Phase mask fixing part, 8 ... Optical fiber, 9 ... Optical fiber glass part, 10 ... optical fiber fixing base, 11 ... ultraviolet light source, 21 ... optical fiber glass part, 23 ... phase mask.

Claims (5)

In a method of manufacturing an optical fiber grating by fixing one or more optical fibers in parallel and irradiating these optical fibers with ultraviolet light via a phase mask, a gas is flowed between the phase mask and the optical fibers. An optical fiber grating manufacturing method, comprising: 2. The method for manufacturing an optical fiber grating according to claim 1, wherein a direction in which the gas flows is the same as a longitudinal direction of the optical fiber. 2. The method according to claim 1, wherein the gas is an inert gas. 2. The method for manufacturing an optical fiber grating according to claim 1, wherein the flow rate of the gas is 50 ml / min or more and 1000 ml / min or less. In an optical fiber grating manufacturing apparatus for forming a grating on an optical fiber by irradiating an optical fiber with ultraviolet light through a phase mask for exposure, a gas outlet and a gas suction port face each other, and the phase mask and the gas An optical fiber grating manufacturing apparatus disposed between optical fibers.

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