JP2002082236A - Slant type short period grating - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a short period grating provided with a smooth spectrum characteristic without easily generating fine ripple. SOLUTION: In the slant type short period grating forming a grating part 3 whose refractive index is changed at a prescribed slant angle in a prescribed period along the longitudinal direction on both or either one of a core 1 and a clad 2 formed on the periphery of the core 1, a 1st coat layer consisting of plastic having a refractive index more than -5% refractive index of the clad 2 is formed on the clad 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a slant type short-period grating used as an optical filter in the field of optical communication and the like.

[0002]

2. Description of the Related Art In long-distance optical communication, an optical signal attenuated by transmitting an optical fiber is amplified by an optical amplifier during transmission. Erbium doped fiber amplifier (Erbium doped fiber amplifier)
fier (hereinafter abbreviated as EDFA) is generally used. FIG. 16 shows an example of an optical communication system, in which a transmitter and a receiver are provided at both ends of a transmission line (optical fiber), and an amplifier is inserted in the middle. However, as shown in FIG. 17, since the EDFA has a wavelength dependence of gain, the intensity of the amplified optical signal varies depending on the wavelength as it is. This is inconvenient, especially in wavelength multiplex transmission. Therefore, in an optical communication system, as shown in FIG.
An optical amplifier is used in which the gain is flattened by combining A with a gain equalizer (hereinafter abbreviated as GEQ). FIG. 19 shows a configuration example of a wavelength division multiplexing transmission system using the optical amplifier shown in FIG. 18, for example. MU shown in the figure
X is an optical multiplexer, and D-MUX is an optical demultiplexer. here,
GEQ shown in FIG. 18 is a transmission type optical filter, and examples thereof include those using a dielectric multilayer film, an etalon plate, an optical fiber grating, and the like. The optical fiber grating includes a long-period grating (LPG) and a short-period grating (SPG). As the GEQ, a long-period grating (LPG-GEQ) is most commonly used.

FIG. 20 is a side sectional view showing an example of a general LPG. A clad 2 having a lower refractive index than the core 1 is provided on the outer periphery of a cylindrical core 1.
The optical fiber is provided concentrically with the optical fiber.
A grating portion 3 in which a plurality of high-refractive-index portions 1a, 1a,... Is intermittently arranged at a predetermined period along a length direction of the optical fiber is formed in a part of the length direction of the core 1. Have been. Both end surfaces of the high refractive index portion 1 a in the length direction of the core 1 are substantially orthogonal to the central axis of the core 1. The period Λ of the high refractive index portion 1a shown in the drawing is called a grating period. The grating period of LPG is 200-300 μm
It is about. When light in a relatively wide wavelength range is incident on this long-period grating, light in a predetermined wavelength range is coupled to the forward cladding mode traveling in the same direction in the grating section 3, and light in this wavelength range is lost. Transmitted light is obtained. Therefore, the gain of the EDFA can be flattened by selectively losing the light in the wavelength region where the intensity is increased by the LPG by the amplification of the EDFA.

[0004] The LPG has an advantage that there is essentially no minute ripple which causes deterioration of a signal waveform. The minute ripple is a minute loss fluctuation in the spectrum of transmitted light with the wavelength on the horizontal axis and the transmittance on the vertical axis. Therefore, a smooth curve (smooth spectral characteristic) is obtained in the spectrum. On the other hand,
There are the following disadvantages. 1) The temperature dependence is large, for example, the shift (Δλ) of the loss wavelength due to a temperature change is as large as about 50 pm / ° C. 2) It is difficult to adjust the transmission characteristics, and it is difficult to obtain any transmission characteristics. 3) When trying to narrow the loss wavelength band, the grating length (length of the grating portion) becomes, for example, about 10 cm at the maximum.

FIG. 21 is a side sectional view showing an example of a general SPG. The difference from the LPG shown in FIG. 20 is the grating period Λ. The grating period of the SPG is as short as 0.1 to 1 μm, for example. LP for SPG
Unlike G, light in a predetermined wavelength range is reflected by the grating unit 3, and as a result, transmitted light in which light in this wavelength range is lost is obtained. In the SPG, in addition to the grating period and the amount of change in the refractive index of the high-refractive-index portion 1a, a chirped grating that changes the grating period 徐 々 に by gradually expanding or reducing it along the length direction of the grating portion 3 is used. Is applied, the wavelength range of the loss light can be widened, the intensity of the loss light can be adjusted, and an arbitrary transmission characteristic can be realized relatively freely. Further, SPG has an advantage that its temperature dependency is small (for example, Δλ is about 12 pm / ° C.).

[0006]

However, the SPG
In, the reflected light goes back through the core 1, so that in the grating section 3, for example, the light reflected at one high refractive index section 1 a is further reflected at the other high refractive index section 1 a in the same direction as the incident light. This causes multiple reflections that repeat such reflections. As a result, there is a problem that minute ripples occur in the transmitted light spectrum at a period of about 0.01 to 0.05 nm, and smooth spectral characteristics cannot be obtained. Therefore, recently, a slant-type SPG that is less likely to generate minute ripples has been developed by making use of the degree of freedom of design and the temperature stability of the SPG.

FIG. 22 is a side sectional view showing an example of a slant type SPG. The difference from the ordinary SPG shown in FIG. 21 is that both end surfaces of the high refractive index portion 1a in the length direction of the core 1 are different from each other. The point is that the core 1 is formed obliquely at a desired angle without being orthogonal to the central axis. High refractive index part 1a
The direction of the line orthogonal to the end face of the is referred to as the grating direction. The angle θ between the grating direction and the central axis of the core 1 indicates the degree of inclination of the high refractive index portion 1a. This angle is called a “slant angle”. That is,
In a normal SPG, the grating direction coincides with the central axis of the core 1 and the slant angle θ is zero. In the slant type SPG, the angle is 0.5 to 8 degrees, although not particularly limited. The degree is set to be oblique.

As a result, the light reflected by the high refractive index portion 1a is radiated to the cladding 2 and does not go back through the core 1, so that multiple reflection is less likely to occur. Then, the magnitude of the minute ripple obtained in the spectrum of the transmitted light can be reduced to, for example, about 0.1 to 0.2 dB, and a spectral characteristic that is smoother than general SPG can be obtained. However, conventionally, even with a slant-type SPG, the suppression of minute ripples is not sufficient, and there has been a demand for an SPG having smoother spectral characteristics.

The generation of minute ripples in the slant-type SPG is considered to be one of the causes, for example, that light emitted from the core to the cladding is coupled back to the core. Therefore, a method for reducing minute ripples by immersing a slant type SPG in matching oil is known.

FIG. 23 shows a slant type SPG in the case where the surroundings of the clad are air, FIG. 24 shows a case where the cladding is immersed in a matching oil having a lower refractive index than the clad (refractive index 1.4), and FIG. FIG. 26 shows the spectrum of transmitted light when immersed in a matching oil (refractive index 1.5) having a refractive index higher than that of the cladding, when immersed in a matching oil having a refractive index of 1.46. It is a thing. In this example, the radius of the core is 4 μm.
m, radius of clad (1/2 of outer diameter of clad) is 6
2.5 μm, grating period ５３ 531.4 to 54
6.8 nm, θ is 4.3 degrees, grating length is 45 m
m. The core is made of quartz glass to which germanium is added (refractive index: 1.466), and the clad is made of pure quartz glass (refractive index: 1.46).

From the transmitted light spectra shown in FIGS. 23 to 26, in order to effectively reduce the minute ripple,
The refractive index of the material around the cladding with which the cladding is in contact is important. Specifically, it is necessary to have a refractive index equal to or higher than that of the cladding. However, since the matching oil is liquid, long-term stability could not be ensured. Also, it is difficult to perfectly match the refractive index of the cladding with the refractive index of the matching oil, and in some cases, optimal conditions cannot be realized.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide an SPG which is less likely to generate minute ripples and has a smooth spectral characteristic. Still another object of the present invention is to provide an SPG that can maintain the effect of reducing minute ripples stably for a long period of time. It is another object of the present invention to provide an SPG that can easily set conditions under which a minute ripple can be sufficiently reduced.

[0013]

According to a first aspect of the present invention, there is provided an optical fiber comprising a core and a clad formed around the core, the optical fiber comprising one or both of the core and the clad. In the slant-type short-period grating in which the grating is formed at a predetermined period along the length direction of the optical fiber and at a predetermined slant angle at a predetermined period, the above-mentioned cladding is formed on the cladding where the grating is formed. A slant-type short-period grating provided with a first coating layer made of plastic having a refractive index. A second invention is the slanted short-period grating according to the first invention, wherein the thickness of the first coating layer is 50 μm or more. According to a third invention, in the slanted short-period grating according to the first invention or the second invention, the plastic forming the first coating layer has a Young's modulus of 100.
It is a slanted short-period grating characterized by being at most MPa. According to a fourth aspect, in the slanted short-period grating according to the first to third aspects, the second coating layer having higher water resistance or moisture resistance than the first coating layer around the first coating layer. Is a slanted short-period grating. A fifth invention is a slanted short-period grating according to any one of the first to fourth inventions, wherein the slanted short-period grating is housed in a reinforcing material. A sixth invention is the slanted short-period grating according to the fifth invention, wherein a space is provided between the inner wall of the reinforcing member and the first or second coating layer. This is a slant type short-period grating. A seventh aspect of the present invention is the slant-type short-period grating according to the fifth or sixth aspect, wherein the first coating layer is formed of plastic filled in a reinforcing material. Type short period grating. According to an eighth invention, in the slanted short-period grating according to any one of the fifth to seventh inventions, an optical fiber having a grating portion formed therein is housed inside the reinforcing material, and the optical fiber is used as the reinforcing material. A slant-type short-period grating, wherein the first covering layer is formed by filling the inside of the reinforcing material with plastic after fixing. A ninth invention is a slant-type short-period grating according to any one of the fifth to eighth inventions, wherein the linear expansion coefficient of the reinforcing material is substantially the same as that of the clad. It is. A tenth invention is characterized in that the reinforcing material is made of quartz glass.
A slanted short-period grating according to any one of the first to ninth inventions. An eleventh invention is directed to the slanted short-period grating according to any one of the fifth to tenth inventions, wherein the reinforcing member has a first member provided with a recess for accommodating an optical fiber, and a first member covering the opening of the recess. 2 is a slant-type short-period grating comprising:

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below in detail, following the history of the study of the present invention. The slant-type SPG according to the present invention is, for example, the slant-type SPG shown in FIG. 22, as shown in FIG. Is provided with a first coating layer 5 made of plastic having a refractive index not less than the value of the refractive index of -5% of the refractive index. The first coating layer 5 is preferably provided so as to cover the entire outer periphery of the cladding 2 at the portion where the grating portion 3 is formed. By providing the first coating layer 5 in this manner, the cladding 2
Light emitted from the first coating layer 5 can be prevented from returning to the core 1 again. As a result, minute ripples can be reduced. In the figure, reference symbol a denotes the radius of the cladding 2 and b denotes the thickness of the first coating layer 5. The first coating layer 5 made of plastic is stable for a long time. Further, since various refractive indexes can be obtained by changing the composition, it is easy to match the refractive index of the first coating layer 5 with the refractive index of the cladding 2. Therefore, it is possible to obtain much more excellent long-term stability and excellent spectral characteristics than when the above-described matching oil is used.

The lower limit of the refractive index of the plastic constituting the first coating layer 5 is about -5% of the refractive index of the cladding. Therefore, if the refractive index of the clad is 100%, any plastic having a refractive index equal to or higher than the refractive index corresponding to 95% can be used. Although the upper limit of the refractive index of the first coating layer 5 made of plastic is not particularly limited,
It is preferable that the refractive index is about 5% with respect to the refractive index of the cladding (about 105% when the refractive index of the cladding is 100%). This is because if the refractive index is too large, light emitted to the cladding tends to couple to the core again. Specifically, for example, when the cladding is made of pure quartz glass (refractive index: 1.46), it is preferable to use plastic having a refractive index of 1.38 or more, preferably about 1.46 to 1.55. Examples of the plastic for forming the first coating layer include an epoxy resin, an acrylic resin, and a silicone resin. Among them, an epoxy resin is preferable. Specifically, R1000 series manufactured by Desolite Co., Ltd. and the like are preferable.

FIGS. 2 to 5 show a slant type SPG in which a grating portion is formed on a core, a refractive index of 1.48 and a Young's modulus of 1.4 MP on a cladding having a refractive index of 1.46.
3A shows a spectrum of transmitted light when a first coating layer made of the epoxy resin of FIG. 3A is provided and its thickness is changed. 2 shows the case where the first coating layer is not provided (when the surroundings of the clad are air), FIG. 3 shows the case where the thickness b of the first coating layer is 62.5 μm, and FIG. Thickness b
5 is 150 μm, FIG. 5 shows that the thickness b of the first coating layer is 2
It is the case of 00 μm. Other specific conditions were the same as those in the above-described example using the matching oil. FIG.
It is clear from the graphs shown in FIGS. 5 to 5 that the provision of the first coating layer reduces the minute ripple.
It is preferable that the thickness of the first coating layer is 50 μm or more. If it is less than 50 μm, the effect of reducing minute ripples may be insufficient. In addition, the thickness b of the first coating layer is preferably as large as possible. In particular, by setting the thickness b to 200 μm or more, minute ripples can be almost completely eliminated. The upper limit of the thickness b of the first coating layer is not particularly limited, but is set to 500 μm, for example, in view of small space efficiency, effect saturation, and manufacturability.

Further, when the first coating layer 5 is provided, the transmission spectrum is deformed and the wavelength of the reflected light is shifted as compared with before the first coating layer 5 is provided. The optical characteristics of the slant type SPG may change. Further, after the first coating layer 5 is provided, a similar phenomenon may occur due to a change in environmental temperature, and the temperature characteristics of the slant-type SPG may be degraded. These are due to the effects of the linear expansion coefficient and the curing shrinkage of the plastic forming the first coating layer 5.

The material of the core 1 and the cladding 2 is generally made of pure quartz glass or quartz glass obtained by adding a dopant such as germanium or fluorine to pure quartz glass (hereinafter collectively referred to as quartz glass). The linear expansion coefficient of plastic is usually larger than that of quartz glass. Therefore, the first coating layer 5 expands and contracts more than the core 1 and the clad 2 due to a change in environmental temperature, so that stress is mainly applied to the grating portion 3 and the optical characteristics change.

When a plastic having a high curing shrinkage is used, the plastic before curing is applied onto the cladding 2 when the first coating layer 5 is formed, and the plastic shrinks in the process of curing. As a result, distortion occurs in the grating portion 3 and the like, and the above-described change in optical characteristics occurs. Therefore, when providing the first coating layer 5, it is necessary to select an optimum material in consideration of not only the refractive index but also these effects.

FIGS. 6 to 9 show the spectra of transmitted light when the first coating layers made of plastics having different Young's moduli are provided. FIG. 6 shows a Young's modulus of 0.1 MP.
This is the case of a. 7 shows a case where the Young's modulus is 20 MPa, FIG. 8 shows a case where the Young's modulus is 500 MPa, and FIG. 9 shows a case where the Young's modulus is 100 MPa. In the measurement of the results shown in FIG. 6, the core radius is 4 μm, the cladding radius is 62.5 μm, the grating period is 531.4 to 546.8 nm, the chirp pitch is 3 degrees, the grating length is 40 mm. did. The thickness of the coating layer was 200 μm. The chirp pitch is obtained by gradually changing the grating period in the length direction of the optical fiber. The core is made of quartz glass doped with germanium (refractive index 1.4).
66), the cladding is pure quartz glass (refractive index: 1.46)
It is formed from In the measurement of the results shown in FIGS. 7 to 9, the radius of the core, the radius of the clad, the grating period, θ, the grating length, the material of the core, and the material of the clad were measured as shown in FIGS. The same as above. The thickness of the coating layer was 200 μm. The plastic having a Young's modulus of 0.1 MPa is trade name: TB30
18 (manufactured by Three Bond) was used. The plastic having a Young's modulus of 20 MPa is trade name: 950Y2.
00F (manufactured by Desolite) and 100 MPa plastic used were AT9576 (manufactured by NTT Advantest Technology), and 500 MPa plastic used was 950Y100F (manufactured by Desolite). When plastic having a large Young's modulus is used, as shown in FIG. 8, distortion occurs near the peak of the loss peak.

From these results, it is preferable that the plastic constituting the first coating layer is soft, and the Young's modulus is 10%.
It is clear that the pressure is preferably 0 MPa or less. In addition, when these slant-type SPGs were observed at a change in the optical characteristics while changing the environmental temperature between -40 and 100 ° C., there was no significant change in those using plastics having a Young's modulus of 100 MPa or less. For those using 500MPa plastic,
The wavelength shift amount of the loss peak is large, and the temperature dependency is large. The lower limit of the Young's modulus is not particularly limited, and any plastic can be used without limitation as long as it does not become a gel or liquid but solidifies. In order to secure long-term stability, the lower limit of the Young's modulus is 0.1MP.
a, preferably 1 MPa.

The slant type SPG can be manufactured, for example, by utilizing the photorefractive effect. The photorefractive effect is a phenomenon in which the refractive index of a quartz-based glass changes when light of a specific wavelength is irradiated on the quartz-based glass to which a photosensitive dopant is added. Germanium is generally used as a light-sensitive dopant.
Irradiation with ultraviolet light near m increases the refractive index.
In the example shown in FIG. 22, a grating portion is formed on the core, but the refractive index of both the core and the clad or only the clad is set to a predetermined value along the length direction of the optical fiber. May be a slant-type SPG in which a grating portion is changed with a predetermined slant angle θ at a period of. When forming a grating portion in the core, the core is formed from quartz glass to which a photosensitive dopant is added, and when forming a grating portion to the cladding, the cladding is formed from quartz glass to which a photosensitive dopant is added. When grating portions are formed on both claddings, both of them are formed from quartz glass to which a photosensitive dopant is added.

It is to be noted that germanium, which is generally used as a photosensitive dopant, has the property of increasing the refractive index of quartz glass only by adding it. It is preferable to adjust the refractive index of the core and the cladding by adding aluminum or phosphorus having a property of increasing the refractive index, or fluorine or boron having a property of decreasing the refractive index, if necessary.
Also, when forming a grating part in the cladding,
The clad may be formed from two or more layers, and the grating portion may be formed only on the layer adjacent to the core of the clad.

Specifically, for example, a slant type SPG is manufactured by the following operation. That is, a bare optical fiber (optical fiber) in which a portion forming a grating portion is made of quartz glass to which a photosensitive dopant is added is provided with an optical fiber wire provided with a protective coating layer made of an ultraviolet curable plastic or the like. prepare. Note that an optical fiber core wire provided with a coating layer made of nylon or the like can also be used. Then, a part of the protective coating layer in the length direction is removed to expose the clad.
Then, when light of a specific wavelength is irradiated from an excimer laser or the like to a portion where the clad is exposed through a phase mask provided with a diffraction grating, the light is irradiated from the quartz glass to which a photosensitive dopant is added. The refractive index of the portion that has been increased increases, and a grating portion is formed.

It is preferable to use the optical device processed by exposing the clad in a state of being housed in a reinforcing material in order to secure mechanical strength. FIG. 10A to FIG.
0 (c) shows an example in which a general cylindrical tube is used as a reinforcing material such as an optical fiber grating. The cylindrical tube is divided into two parts in parallel in the longitudinal direction, and is constituted by two symmetrical semi-cylindrical tubes. FIG. 10 (a), FIG.
0 (b) is a plan view from the opening of the first semi-cylindrical tube (first member) for accommodating the slant type SPG, FIG. 10 (c).
FIG. 11 is a cross-sectional view taken along the line AA ′ shown in FIGS. 10 (a) and 10 (b).

An operation for accommodating a slanted short-period grating in a reinforcing material for the structure shown in FIG. 10A will be described below. In the figure, reference numeral 10 denotes an optical fiber, in which a part of the protective coating layer 11 in the length direction is peeled off and the clad 2 is exposed, and the slant short period is applied to the core 1 inside the exposed clad 2. A mold grating portion 3 is formed. Next, after the clad 2 is placed in the concave portion 12a of the first semi-cylindrical tube 12, plastic is filled into the concave portion 12a, and the outer surface of the clad 2 and the concave
The first coating layer 13 is formed between the first coating layer 13 and the inner wall of FIG. As described above, the first portion having the concave portion 12a for accommodating the grating portion 3 is provided.
The use of the member (first semi-cylindrical tube 12) makes it possible to easily form the soft first coating layer 13 and to easily put the delicate grating portion 3 in a reinforcing material, which is preferable. . Finally, the first semi-cylindrical tube 12
As shown in FIG. 11, another symmetrical second semi-cylindrical tube (second member) 14 is put on the opening 12b of
The first semi-cylindrical tube 12 and the second semi-cylindrical tube 14 are
Fix it with an adhesive and make a pipe. By using the second member (second semi-cylindrical tube 14) provided with a concave portion like the first member (first semi-cylindrical tube 12), a space 15 described later can be easily formed. Is preferred.

The outer diameter of the cladding 2 is generally 100
μm or more, substantially 120-130 μm (usually about 1 μm).
25 μm), and as described above, the thickness of the coating layer is most preferably 200 μm or more. Therefore, the inner diameter c of the first semi-cylindrical tube 12 is, for example, 500 μm
As described above, it is particularly preferable that a coating layer having a thickness of 200 μm or more can be formed all around the clad 2. If the difference in the linear expansion coefficient between the core 1 and the clad 2 is large, the first semi-cylindrical tube 12 deteriorates the temperature characteristics of the slanted short-period grating. Here, the same degree means that it is about ± 3% with respect to the linear expansion coefficient of the clad.
Specifically, the first semi-cylindrical tube 12 is preferably formed from quartz glass. In general, the second semi-cylindrical tube 1
4 is also made of the same material as the first semi-cylindrical tube 12 and has the same size. Also, the first semi-cylindrical tube 1
2. The length of the second semi-cylindrical tube 14 is not particularly limited, but is preferably about 10 to 30 mm longer than the length of the exposed clad 2.

As shown in FIG. 11, in this structure, the outer surface of the first coating layer 13 on the opening 12b side is
A space (gap) 15 is formed between the second semi-cylindrical tube 14 and the inner wall thereof. Thus, the outer surface of the first coating layer 13 and the reinforcing member (the first semi-cylindrical tube 12 and the second semi-cylindrical tube 14)
If the space 15 is formed between the inner wall and the inner wall, even if the plastic forming the first coating layer 13 expands and contracts due to factors such as a change in environmental temperature, the effect of the space 15 is reduced, It is more preferable because direct stress is hardly applied to the grating portion 3. Although the range of the space 15 is not particularly limited, in the cross-sectional view shown in FIG.
For example, the cross-sectional area of the space 15 is preferably about 1 to 3 times the cross-sectional area of the first coating layer 13. In the example shown in FIG. 11, these cross-sectional areas are substantially equal. If it is less than 1, the sufficient effect may not be obtained, or the workability when covering the second member (second semi-cylindrical tube 14) may be reduced depending on the form of the reinforcing member.
If it exceeds three times, the size of the reinforcing material may be unnecessarily large.

Further, in this structure, the optical fiber tends to be weak in pulling in the longitudinal direction. For example, when a portion of the optical fiber, which is located outside the reinforcing material, is pulled in the length direction of the optical fiber with a force of about 500 g, the cladding near the grating portion and the first coating layer around the cladding are pulled. May peel off.

Therefore, as shown in FIG. 10B, the exposed portion of the clad 2 is placed in the concave portion 12a of the first semi-cylindrical tube 12, and the vicinity of both ends of the grating portion 3 of the clad 2 is coated with an adhesive. After fixing to the inner wall of the concave portion 12a in advance by fixing means such as 16 and 16, it is preferable to form the first coating layer 13 by filling the concave portion 12a with plastic. As the adhesive 16, for example, an epoxy resin (trade name: World Rock (manufactured by Kyoritsu Chemical Co., Ltd.)) or the like can be used. Further, it is preferable that the fixing positions by the adhesives 16, 16 are both end portions of the grating portion 3, and are in a range that does not contact the grating portion 3. Specifically, the position is, for example, about 1 to 5 mm away from the end of the grating section 3.

Actually, as shown in FIG. 10A, the core radius is 4 μm and the cladding outer diameter is 125 μm (radius 62.5 mm).
μm), outer diameter of protective coating layer (outer diameter of optical fiber) 2
Using an optical fiber of 50 μm, the protective coating layer was peeled off over 50 mm to expose the cladding, and a slant type grating portion having a grating period of 531.4 to 546.8 mm, θ 4.3 degrees, and a grating length of 45 mm was formed. . The core was made of germanium-doped quartz glass, and the clad was made of pure quartz glass. As the semi-cylindrical tube, an inner diameter of 650 μm and a length of 60 mm made of quartz glass was used. The material of the first coating layer formed in the semi-cylindrical tube was an epoxy resin having a refractive index of 1.48 and a Young's modulus of 1.4 MPa. The thickness of this first coating layer is about 200
μm (Example 1).

When the temperature characteristics of the slanted short-period grating were measured while changing the ambient temperature between -40 and 100 ° C., the shift of the loss wavelength (Δλ) was measured.
Is 0.0090 nm / ° C. before being housed in a semi-cylindrical tube, and 0.0090 nm / ° C.
° C. Therefore, the optical characteristics were maintained before and after the formation of the coating layer. Also, as shown in FIG. 10 (b), a slant mold manufactured under the same conditions as in the example shown in FIG. 10 (a) except that a position 2 mm from the grating portion 3 is fixed with adhesives 16 and 16. Short period grating (Example 2)
When the optical fiber is pulled in the longitudinal direction with a force of about 2 kg, the optical characteristics are not changed as compared with the first embodiment, the optical fiber is broken, and the cladding 2 and the first coating layer 13 are not changed.
Did not occur.

As described above, the first coating layer is preferably formed of a plastic having a small Young's modulus.
Therefore, water resistance and moisture resistance may be poor. Therefore,
As shown in FIG. 12, at least on the outer surface where the first coating layer 5 comes into contact with air, a second coating layer made of a plastic having better water resistance or moisture resistance than the first coating layer 5. 6 is preferably provided. In this example, the second coating layer 6 is provided on the entire outer periphery of the first coating layer 5. The thickness d of the second coating layer 6 is, for example, 30 μm or more, preferably 50 to 500 μm. If it is less than 30 μm, no effect can be obtained, and if it exceeds 500 μm, the effect may be saturated. Examples of the plastic forming the second coating layer 6 include an epoxy resin, an acrylic resin, and a silicone resin. Among them, an epoxy resin is preferable. The term “higher water resistance” than the plastic forming the first coating layer 5 means that the Young's modulus is larger than that of the plastic suitable for the first coating layer 5 and 1
MPa or more, preferably 10 to 500 MPa. Specifically, the product name TB3052D (manufactured by Three Bond Co., Ltd.) is suitable.

As described above, the second coating layer only needs to be provided on at least the surface where the first coating layer comes into contact with air. In the structure contained in the reinforcing material shown in FIG.
First covering layer 13 that contacts space 15 on opening 12b side
Is in contact with air, and the rest is in contact with the inner wall of the recess 12a of the first semi-cylindrical tube 12. Therefore, as shown in FIG. 13, it is preferable that the second coating layer 17 is provided on the outer surface of the first coating layer 13 on the opening 12b side. In this case, as described above, after the grating portion 3 is housed in the concave portion 12a of the first semi-cylindrical tube 12,
After the recess 12a is filled with plastic and the first coating layer 13 is provided, the plastic forming the second coating layer 17 is further filled on the opening 12b side to provide the second coating layer 17. Can be.

FIG. 14 shows the slant type S of the first embodiment.
It is the graph which showed the result of having measured the transmission spectrum before and after immersing PG in water for 3 hours. The smooth curve above the graph is before immersion, and the rattled curve below is after immersion. As described above, if the first coating layer has low water resistance or low moisture resistance, the first coating layer, for example, peels off from the clad under high-temperature and high-humidity conditions or when immersed in water, thereby reducing the minute ripple. May not be maintained. FIG.
FIG. 13 is a graph showing the results of measuring the transmission spectrum before and after immersion in water for 200 hours when the second coating layer was provided as shown in FIG. The slant type SPG used here had the same configuration as that of Example 1 except that a second coating layer having a thickness of 70 μm was formed of an epoxy resin having a Young's modulus of 170 MPa. The upper curve is before immersion, and the lower curve is after immersion. All are smooth curves, and the effect of reducing minute ripples is maintained even after immersion.

The present invention can be applied without any particular limitation as long as it is a slanted short-period grating. The grating period Λ, θ, grating length, etc. of the slant type short-period grating to be applied are not particularly limited.
It can be set arbitrarily according to desired characteristics. For example, the grating period is 520 to 570 nm, the slant angle is 0.5 to 8 degrees, and the grating length is 20 to 50.
mm. Also, a chirped grating in which the grating period is changed in the length direction of the core can be applied. Further, the shape of the reinforcing material is not limited to the cylindrical tube type combining the semi-cylindrical tubes, and may have a rectangular parallelepiped outer shape.

[0037]

As described above, in the present invention,
By providing a first coating layer made of plastic and optimizing the first coating layer, a slant-type short-period grating that is less likely to generate minute ripples, has smooth spectral characteristics, and is excellent in long-term stability Can be provided.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of a slant type SPG of the present invention.

FIG. 2 is a graph showing a transmission spectrum when a first coating layer is not provided on a slant type SPG.

FIG. 3 shows a slant type SP provided with a first coating layer.
9 is a graph showing a transmission spectrum of G.

FIG. 4 shows a slant type SP provided with a first coating layer.
9 is a graph showing a transmission spectrum of G.

FIG. 5 shows a slant type SP provided with a first coating layer.
9 is a graph showing a transmission spectrum of G.

FIG. 6 is a graph showing a difference in transmission spectrum due to a difference in Young's modulus of the first coating layer.

FIG. 7 is a graph showing a difference in transmission spectrum due to a difference in Young's modulus of the first coating layer.

FIG. 8 is a graph showing a difference in transmission spectrum due to a difference in Young's modulus of the first coating layer.

FIG. 9 is a graph showing a difference in transmission spectrum due to a difference in Young's modulus of the first coating layer.

10 (a) and 10 (b) are plan views showing an operation example of placing a slant type SPG in a reinforcing material.
(C) shows the A- shown in FIGS. 10 (a) and 10 (b).
It is sectional drawing in A '.

FIG. 11 is a step view showing a state in which a first semi-cylindrical tube (first member) and a second semi-cylindrical tube (second member) are integrated.

FIG. 12 shows a slant type SP provided with a second coating layer.
It is sectional drawing which showed an example of G.

FIG. 13 shows a slant type SP provided with a second coating layer.
It is sectional drawing which showed another example of G.

FIG. 14 is a graph showing the results of a flood test of a slant-type SPG without a second coating layer.

FIG. 15 shows a slant type SP provided with a second coating layer.
9 is a graph showing the results of a water immersion test for G.

FIG. 16 is a schematic configuration diagram illustrating an example of an optical communication system.

FIG. 17 is a schematic configuration diagram showing an operation of an erbium-doped optical fiber amplifier.

FIG. 18 is a schematic configuration diagram showing a configuration of an amplifier in which an erbium-doped optical fiber amplifier and a gain equalizer are combined.

19 is a schematic configuration diagram showing a configuration example of a wavelength division multiplexing transmission system using the optical amplifier shown in FIG. 18, for example.

FIG. 20 is a side sectional view showing an example of a general LPG.

FIG. 21 is a side sectional view showing an example of a general SPG.

FIG. 22 is a side sectional view showing an example of a slant type SPG.

FIG. 23 is a graph showing a spectrum of transmitted light in a slant type SPG when the surroundings of the cladding are air.

FIG. 24 is a graph showing a spectrum of transmitted light in a slanted SPG when immersed in a matching oil having a refractive index lower than that of a clad.

FIG. 25 is a graph showing a spectrum of transmitted light in a slant type SPG when immersed in a matching oil having a refractive index similar to that of a clad.

FIG. 26 is a graph showing a spectrum of transmitted light in a slant type SPG when immersed in a matching oil having a higher refractive index than the cladding.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Core, 1a ... High refractive index part, 2 ... Clad, 3 ... Grating part, 5 ... First coating layer, 6 ... Second coating layer,
12: first member (semi-cylindrical tube), 14: second member (semi-cylindrical tube), 17: second coating layer, b: thickness of first coating layer, c: inner diameter of semi-cylindrical tube .

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Satoshi Okude 1440, Mukurosaki, Sakura City, Chiba Prefecture Inside Fujikura Sakura Office (72) Inventor Kenji Nishiide 1,440, Musaki, Sakura City, Chiba Prefecture Fujikura Sakura Business Co., Ltd. In-house (72) Inventor Akira Wada 1440 Mutsuzaki, Sakura City, Chiba Prefecture Fujikura Co., Ltd.Sakura Office F-term (reference) 2H050 AB05Z AC82 AC84 AD00 BA32 BB04S BB05Q BB05S BB07S BC03 BD00 BD05

Claims (11)

[Claims] 1. An optical fiber comprising a core and a clad formed around the core, a refractive index of one or both of the core and the clad is set at a predetermined cycle along a length direction of the optical fiber. In a slanted short-period grating in which a grating portion changed with a slant angle is formed, a refraction not less than a refractive index value of -5% of a refractive index of the cladding is provided on a cladding in a portion where the grating portion is formed. A slanted short-period grating comprising a first coating layer made of a plastic having a modulus. 2. The slanted short-period grating according to claim 1, wherein the thickness of the first coating layer is 50 μm or more. 3. The slanted short-period grating according to claim 1, wherein the plastic forming the first coating layer has a Young's modulus of 100 MPa or less. 4. The slanted short-period grating according to claim 1, wherein the first coating layer has a higher water resistance or moisture resistance around the first coating layer than the first coating layer. A slanted short-period grating comprising a second coating layer. 5. The slanted short-period grating according to claim 1, wherein the slanted short-period grating is housed in a reinforcing material. 6. The slanted short-period grating according to claim 5, wherein a space is provided between the inner wall of the reinforcing member and the outer surface of the first coating layer or the second coating layer. Slant type short period grating. 7. The slant-type short-period grating according to claim 5, wherein the first covering layer is formed of plastic filled in a reinforcing material. Grating. 8. The slanted short-period grating according to claim 5, wherein an optical fiber having a grating portion formed therein is accommodated in the reinforcing member, and the optical fiber is fixed to the reinforcing member. A slant-type short-period grating, wherein the first covering layer is formed by filling the inside of the reinforcing material with plastic. 9. The slanted short-period grating according to claim 5, wherein a linear expansion coefficient of the reinforcing material is substantially equal to that of the clad. . 10. The slanted short-period grating according to claim 5, wherein the reinforcing material is made of quartz glass. 11. The slant-type short-period grating according to claim 5, wherein the reinforcing member covers a first member having a recess for accommodating an optical fiber, and an opening of the recess. A slant-type short-period grating comprising a second member.