JP4233736B2 - Manufacturing method of optical fiber grating - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing an optical fiber grating, and in particular, it is easy to remove a coating layer of an optical fiber and has high manufacturing efficiency.
[0002]
[Prior art]
An optical fiber grating is a periodic structural change in the longitudinal direction of the optical fiber, such as refractive index and core diameter, that selectively reflects light of a specific wavelength or couples it with a cladding mode to selectively lose it. Is an optical component. Optical fiber gratings are used in a wide range of optical communication fields such as wavelength selective filters, gain equalizers of optical amplifiers, and chromatic dispersion compensators.
[0003]
A general optical fiber grating uses a periodic change in refractive index, and can be manufactured by utilizing a phenomenon in which the refractive index of germanium-added quartz glass is increased by irradiation with ultraviolet light, for example.
As shown in FIG. 7, the optical fiber is usually an ultraviolet curable resin or the like from the viewpoint of ensuring mechanical strength on the bare optical fiber 3 composed of the core 1 and the clad 2 provided around the core 1. It is commercialized as an optical fiber 5 provided with a coating layer 4 made of plastic. Alternatively, an optical fiber core made of plastic such as nylon is also provided on the optical fiber 5.
[0004]
Accordingly, since the ultraviolet light is absorbed by the coating layer 4 and does not reach the bare optical fiber 3 as it is, a part of the coating layer 4 in the longitudinal direction of the optical fiber 5 is not covered with the bare optical fiber 3 as shown in FIG. Is removed over the entire circumferential direction, and the removed portion is irradiated with ultraviolet light from one direction of the side surface of the optical fiber 5.
As a method for removing the coating layer 4, a mechanical method in which the coating layer 4 is physically peeled off using a cutting jig, a chemical method in which the coating layer 4 is chemically removed by impregnation with a sulfuric acid solution or the like. For example.
[0005]
At this time, for example, if the core 1 is made of germanium-added quartz glass, the refractive index of the portion irradiated with ultraviolet light increases. Therefore, a periodic change in the refractive index of the core 1 is formed by irradiating ultraviolet light with a predetermined period in the longitudinal direction of the optical fiber 5 (bare optical fiber 3). Thereafter, if necessary, the portion where the bare optical fiber 3 is exposed is reinforced by providing a coating layer again, and an optical fiber grating is obtained.
As a method of periodically irradiating ultraviolet light, the interference method shown in FIG. 9, the phase mask method shown in FIG. 10, the intensity modulation mask method shown in FIG. 11, and the step-by-step method shown in FIG. Step) method is used. In general, the phase mask method is widely used.
[0006]
Recently, an optical fiber grating in which the refractive indexes of both the core 1 and the clad 2 are changed, and an optical fiber grating in which only the clad 2 is changed are proposed.
[0007]
On the other hand, as a method for mass-producing optical fiber gratings, a plurality of bare optical fibers are collectively irradiated with ultraviolet light using an optical fiber ribbon as shown in FIGS. 13 (a) to 13 (d). The method is effective.
First, as shown in FIGS. 13 (a) and 13 (b), a plurality of optical fiber strands 5, 5,... Are juxtaposed and collectively covered with a collective coating layer 6 made of plastic such as nylon. An optical fiber ribbon 7 is prepared.
Next, as shown in FIG. 13 (c), a part of the coating layer 6 in the longitudinal direction of the optical fiber ribbon 7 and the coating layers of the optical fiber strands 5, 5,. The bare optical fibers 3, 3 ... are exposed.
Then, the plurality of bare optical fibers 3, 3... Are collectively irradiated with ultraviolet light, and the grating portions 8, 8. Thereafter, if necessary, the optical fiber strands 5, 5... Are cut to obtain a plurality of optical fiber gratings.
[0008]
[Problems to be solved by the invention]
However, in the removal of the coating layer, the mechanical method has a problem that the strength of the optical fiber (bare optical fiber) decreases due to the blade of the cutting jig coming into contact with the bare optical fiber. Further, the chemical method has a problem that workability is low and manufacturing efficiency is low.
In particular, when an optical fiber ribbon is used, it is very difficult to remove a coating layer between adjacent bare optical fibers by a mechanical method. At this time, there is a problem that the bare optical fiber is easily damaged. Furthermore, since the amount of the coating layer to be removed is large, the chemical method has a problem that it takes a long time to remove all the coating layers.
In addition, since it is known that the strength of the bare optical fiber deteriorates after irradiation with ultraviolet light if a part of the coating layer remains, the coating layer in the part irradiated with ultraviolet light is entirely over the entire circumference of the bare optical fiber. Must be removed.
[0009]
Further, in the phase mask method shown in FIG. 10, the phase mask and the bare optical fiber 3 are arranged close to a distance of, for example, about several μm to several 100 μm, and irradiation with ultraviolet light is performed. Therefore, if a part of the coating layer remains under the phase mask, depending on the material of the coating layer, volatile gas may be generated from the remaining coating layer due to the irradiation of ultraviolet light, thereby causing the phase mask to become dirty. Adheres. Since a plurality of fine grooves are formed on the surface of the phase mask facing the bare optical fiber 3, it takes time for cleaning if dirt is attached. Therefore, continuous exposure cannot be performed, which hinders mass production.
[0010]
On the other hand, a method has also been proposed in which an optical fiber grating is manufactured by irradiating ultraviolet light from above a coating layer using an optical fiber strand formed of a plastic having a relatively high ultraviolet light transmittance. However, since the ultraviolet light transmittance of this coating layer is about 10 to 20%, the refractive index cannot be increased efficiently unless the germanium concentration added to the core is high and the photosensitivity is improved. . Such an optical fiber has a mode field that is greatly different from that of a normal optical fiber or dispersion-shifted optical fiber, so that the connection loss with these normal optical fibers may increase.
Japanese Patent Application Laid-Open No. 10-82919 proposes a method of using a very thin film as a coating layer of an optical fiber. However, it is technically difficult to coat such a thin film, and it is more widely used. Since the fiber structure is different from the conventional fiber structure, there is a problem that the manufacturing cost increases.
[0011]
The present invention has been made in view of the above circumstances, and an object thereof is to provide a method for manufacturing an optical fiber grating that can shorten the time required for removing a coating layer and improve the working efficiency.
It is another object of the present invention to provide a method of manufacturing an optical fiber grating that is unlikely to cause problems such as a decrease in strength of the optical fiber in the manufacturing process.
Furthermore, it aims at providing the manufacturing method of the optical fiber grating which can work efficiently in phase mask methods etc. Specifically, an object of the present invention is to provide a method of manufacturing an optical fiber grating that is not easily affected by volatile gas generated from the residual coating layer by irradiation with ultraviolet light.
And when it uses an optical fiber tape core wire, it aims at solving these subjects.
[0012]
[Means for Solving the Problems]
In order to solve the above-described problems, the method of manufacturing an optical fiber grating according to the present invention irradiates ultraviolet light from one side of an optical fiber including a bare optical fiber and a coating layer provided thereon. An optical fiber grating manufacturing method for manufacturing an optical fiber grating, wherein a coating layer having a substantially uniform thickness remains on the ultraviolet light irradiation surface side of the coating layer according to a length of a portion where a refractive index is changed. In this way, the laser light is irradiated with ultraviolet light using a continuous wave laser after being processed so that the ultraviolet light reaches the bare optical fiber underneath .
Preferably ultraviolet light transmittance of the working portion of the a can be covered layer is 20% or more.
When these manufacturing methods are applied to an optical fiber ribbon, a method for manufacturing an optical fiber grating suitable for mass production can be provided.
Irradiation with ultraviolet light can be performed through a phase mask.
At this time, it is preferable to arrange a plate that transmits ultraviolet light between the phase mask and the optical fiber and irradiate the ultraviolet light.
This plate is preferably a quartz plate.
Further, it is preferable that an antireflection film is provided on one side or both sides of the plate.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Fig.1 (a) is explanatory drawing of the manufacturing method of the optical fiber grating of this invention.
First, in the longitudinal direction of the optical fiber 5, the ultraviolet light irradiation surface of the coating layer 4 that forms the grating portion is scraped and processed so that the ultraviolet light is transmitted.
At this time, it is preferable to use a cutting jig having a single blade such as a plane so that the bare optical fiber 3 does not hit the blade.
The coating layer 4 on the ultraviolet light irradiation surface does not need to be completely removed, and may be processed so that the ultraviolet light transmittance is 20% or more. Although it does not specifically limit, when the coating layer 4 consists of a silicone resin, it processes so that it may become thickness of 15 micrometers or less, for example. The length of the processed portion of the coating layer 4 is set according to the length (grating length) of the portion where the refractive index is changed.
[0014]
In the present invention, since it is not necessary to completely remove the coating layer 4, it is difficult for the blade of the cutting jig to hit the bare optical fiber 3, and a decrease in strength of the bare optical fiber 3 during processing can be prevented. Moreover, depending on the case, the coating layer 4 in a predetermined range can be removed by an operation of putting a blade once into the coating layer 4 and shaving, and the working efficiency is remarkably improved. Needless to say, the coating layer 4 may be completely removed, or only part of it may be completely removed, and the bare optical fiber 3 may be partially exposed. In order to make the irradiation intensity uniform, it is preferable that the thickness of the coating layer in the processed portion is substantially uniform.
[0015]
Then, using a continuous wave (CW) laser, ultraviolet light is irradiated in the longitudinal direction of the bare optical fiber 3 at a predetermined cycle by an interference method, a phase mask method, a slit method, a pinpoint method, or the like. Conventionally, a pulse laser has been used as a light source. However, according to the study by the present inventors, when a continuous wave laser is used, there is a problem that the strength of the bare optical fiber 3 is lowered even if a part of the coating layer 4 remains. I found that there was no Examples of the continuous wave laser include a second harmonic of an argon laser and a fourth harmonic of a yag laser.
[0016]
That is, in the pulse laser, the peak value of the laser power (the maximum value of the instantaneous power) becomes very large, and the instantaneous laser power reaches several hundred million times that of the continuous wave laser. Therefore, the remaining coating layer 4 is deteriorated by irradiation with a very strong laser, and the bare optical fiber 3 is affected by a chemical change or heat at that time, and the strength of the bare optical fiber 3 is lowered. On the other hand, in a continuous wave laser, since the laser power is constant in time and the instantaneous maximum value is low, even if the coating layer 4 remains, it can cause a sudden change in the coating layer 4. In addition, the bare optical fiber 3 is not affected. Therefore, even if the coating layer 4 remains as described above, the grating can be formed by irradiating ultraviolet light without reducing the strength of the bare optical fiber 3.
This method can also be applied to other methods for irradiating an optical fiber or the like with ultraviolet light.
[0017]
When the phase mask 10 is used as shown in FIG. 1B, volatile gas is generated by irradiation with ultraviolet light depending on the material of the coating layer 4 as described above, and the optical fiber strand of the phase mask 10 is generated. In some cases, dirt adheres to the plurality of fine grooves 11, 11.
Therefore, it is preferable to arrange a plate 12 that transmits ultraviolet light between the optical fiber 5 and the phase mask 10 to prevent the volatile gas from adhering to the phase mask 10.
[0018]
By arranging the plate 12 in this way, the ultraviolet light is irradiated onto the optical fiber 5 through the phase mask 10 and the plate 12. Even if volatile gas is generated from the remaining coating layer 4, it is blocked by the plate 12 before reaching the phase mask 10, and the adhesion of dirt to the phase mask 10 can be completely prevented. As a result, the phase mask 10 can be used continuously, and the working efficiency is improved. Further, the lifetime of the expensive phase mask 10 is prolonged.
Further, since the plate 12 is much cheaper than the phase mask 10, it can be easily replaced. Further, since the surface of the plate 12 is usually smooth, it can be easily washed and used repeatedly.
[0019]
As the plate 12, it is preferable to use a quartz plate because the absorption at the laser wavelength used for the grating exposure is small and scattering can be suppressed by mirror-polishing the surface smoothly. The thickness of the plate 12 is not particularly limited as long as the intensity of the ultraviolet light is not greatly reduced, but is about 50 to 500 μm, for example. Further, in order to prevent the ultraviolet light from being reflected by the plate 12 and reducing its intensity before reaching the optical fiber 5, at the same time, to prevent multiple reflections on both sides of the plate and the phase mask surface, Alternatively, it is preferable to form an antireflection film on both sides. The antireflection film can be formed, for example, by applying a conductive multilayer film or the like on one or both surfaces of the plate 12. The thickness of the antireflection film is about 1 μm.
As described above, the method of arranging a light transmitting plate between the phase mask and the object to be irradiated with light can be applied to all methods using other phase mask methods.
[0020]
In the above-described example, the optical fiber strand has been described as an example. However, the present invention is not limited to this, and an optical fiber core wire in which a coating layer is further provided on the optical fiber strand, or an optical fiber strand. The present invention can also be applied to a plurality of optical fiber ribbons coated in parallel in parallel.
In the case of the optical fiber core wire, for example, the coating layer of the optical fiber core wire is cut at the same time as the coating layer of the optical fiber core wire, and the processing is performed in the same manner as described above.
In the case of an optical fiber ribbon, for example, by simultaneously processing a batch coating layer on one side of the tape and a coating layer on the underlying optical fiber, a plurality of bare optical fibers can be simultaneously exposed on the ultraviolet irradiation surface. Processing can be performed.
In particular, in the optical fiber ribbon, the coating layer between adjacent bare optical fibers does not need to be removed, so that the working efficiency of the coating layer removal operation is remarkably improved, which is optimal for mass production.
[0021]
【Example】
Hereinafter, the present invention showing examples will be described more specifically.
Example 1
First, a core made of germanium-added quartz glass and a clad made of pure quartz glass are provided with a coating layer made of a silicone resin-based ultraviolet curable resin. The outer diameter of the bare optical fiber is 125 μm, and the outer diameter of the coating layer is A 250 μm optical fiber was prepared. Then, the coating layer on the ultraviolet irradiation surface was removed by inserting the blade once using a single-blade can so that the coating layer having a thickness of about 15 μm remained over a range of about 15 mm in length and about 250 μm in width. .
Then, an optical fiber grating was formed by irradiating ultraviolet light with a predetermined period using a continuous wave laser having a wavelength of 244 nm or a pulse laser having a wavelength of 248 nm through a phase mask. The ultraviolet light transmittance of the coating layer on the ultraviolet irradiation surface at this time was 50%.
Note that a double wave of an argon laser was used as the continuous wave laser. An excimer laser was used as the pulse laser.
Then, the breaking strength of the optical fiber grating was measured by a breaking test, and the result is shown in a graph called a Weibull plot in FIG. The horizontal axis of the graph is the breaking strength, and the vertical axis is the logarithm of the cumulative breaking probability.
As can be seen from this graph, when the pulse laser was used, the breaking strength was greatly deteriorated compared to before the exposure (irradiation), whereas when the continuous wave laser was used, the same result as before the irradiation was obtained. Therefore, it was confirmed that by using the continuous wave laser, the strength of the optical fiber does not decrease even if the coating layer remains.
[0022]
(Example 2)
It was measured how the optical characteristics were affected when irradiated with ultraviolet light with the coating layer remaining.
FIG. 3 is a graph showing a spectrum of reflected light of an optical fiber grating manufactured by irradiating the same optical fiber as in Example 1 with ultraviolet light in a state where a coating layer does not remain using a continuous wave laser. .
FIG. 4 shows a 100 μm thick quartz plate coated with a continuous wave laser with a 1 μm thick antireflection film made of a dielectric multilayer film placed between the phase mask and the optical fiber. It is the graph which showed the spectrum of the reflected light of the optical fiber grating manufactured by irradiating with ultraviolet light in the state where a layer does not remain.
FIG. 5 is a graph showing a spectrum of reflected light of an optical fiber grating manufactured using a phase mask and a quartz plate in the same manner except that the ultraviolet light is irradiated with the coating layer remaining. At this time, the coating layer was removed in a range of about 15 mm in length and about 250 μm in width so that a coating layer having a thickness of about 15 μm remained. FIG. 6 is a graph showing the breaking strength of the optical fiber grating and the optical fiber before the coating layer is removed. The breaking strength did not change, and it was confirmed that the use of a continuous wave laser did not cause a decrease in strength even if the coating layer remained.
.
[0023]
The spectra of FIGS. 3 to 5 are almost the same, and it is clear that an optical fiber grating having desired optical characteristics can be obtained even if a coating layer remains or a quartz plate is disposed when irradiated with ultraviolet light. became.
[0024]
【The invention's effect】
As described above, in the optical fiber grating of the present invention, since a continuous wave laser is used as a light source, an optical fiber grating is manufactured by irradiating ultraviolet light without reducing the strength of the optical fiber even when the coating layer remains. can do. For this reason, the removal amount of a coating layer is small and working efficiency improves. Further, since the cutting jig blade can be prevented from hitting the bare optical fiber, it is possible to prevent the strength of the bare optical fiber from being lowered in the process of removing the coating layer.
In particular, an optical fiber ribbon is suitable for mass production because a plurality of optical fiber gratings can be manufactured at a time by processing one side of the tape.
[Brief description of the drawings]
FIG. 1A is an explanatory diagram of a manufacturing method of an optical fiber grating of the present invention, and FIG. 1B is an explanatory diagram of a manufacturing method of an optical fiber grating of the present invention using a phase mask method.
2 is a graph comparing the breaking strength when using a continuous wave laser and a pulse laser in Example 1. FIG.
FIG. 3 is a graph showing a spectrum of reflected light of an optical fiber grating manufactured by irradiating ultraviolet light using a phase mask in a state where a coating layer does not remain using a continuous wave laser in Example 2.
4 is a graph showing a spectrum of reflected light of an optical fiber grating manufactured by irradiating ultraviolet light using a phase mask and a quartz plate in a state where a coating layer does not remain using a continuous wave laser in Example 2. FIG. It is.
5 is a graph showing a spectrum of reflected light of an optical fiber grating manufactured by irradiating ultraviolet light using a phase mask and a quartz plate in a state where a coating layer remains in Example 2. FIG.
6 is a graph showing the breaking strength of the optical fiber grating shown in FIG. 5. FIG.
FIG. 7 is an explanatory diagram of a conventional method for manufacturing an optical fiber grating.
FIG. 8 is an explanatory diagram of a conventional method for manufacturing an optical fiber grating.
FIG. 9 is an explanatory diagram showing an interferometry as an example of a method for periodically irradiating an optical fiber with ultraviolet light.
FIG. 10 is an explanatory diagram showing a phase mask method as an example of a method of periodically irradiating an optical fiber with ultraviolet light.
FIG. 11 is an explanatory view showing an intensity modulation mask method as an example of a method of periodically irradiating an optical fiber with ultraviolet light.
FIG. 12 is an explanatory diagram showing a step-by-step method as an example of a method for periodically irradiating an optical fiber with ultraviolet light.
FIGS. 13A and 13B are explanatory diagrams of a method of manufacturing an optical fiber grating using an optical fiber ribbon, in which FIG. 13A is a plan view of the optical fiber ribbon, and FIG. 13B is an optical fiber tape; FIG. 13B is a plan view showing a state in which the coating layer of the optical fiber ribbon is removed, and FIG. 13D is a plan view showing a state in which a grating portion is formed.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Core, 2 ... Cladding, 3 ... Bare optical fiber, 4 ... Covering layer,
5. Optical fiber (optical fiber),
10 ... phase mask, 12 ... plate.

Claims (7)

An optical fiber grating manufacturing method for manufacturing an optical fiber grating by irradiating ultraviolet light from one side surface of an optical fiber including a bare optical fiber and a coating layer provided thereon, The ultraviolet light irradiation surface side is shaved so that the coating layer with a substantially uniform thickness remains in accordance with the length of the portion where the refractive index is changed, so that the ultraviolet light reaches the bare optical fiber below it. A method of manufacturing an optical fiber grating, wherein the optical fiber grating is irradiated with ultraviolet light using a continuous wave laser after being processed. 2. The method for manufacturing an optical fiber grating according to claim 1, wherein the processed portion of the coating layer has an ultraviolet light transmittance of 20% or more. 3. The method of manufacturing an optical fiber grating according to claim 1, wherein the optical fiber is an optical fiber ribbon. The method for manufacturing an optical fiber grating according to any one of claims 1 to 3 , wherein ultraviolet light is irradiated through a phase mask. 5. The method of manufacturing an optical fiber grating according to claim 4 , wherein a plate that transmits ultraviolet light is disposed between the phase mask and the optical fiber to irradiate the ultraviolet light. 6. The method of manufacturing an optical fiber grating according to claim 5 , wherein the plate is a quartz plate. The method for manufacturing an optical fiber grating according to claim 5 or 6 , wherein an antireflection film is provided on one side or both sides of the plate.

Images