JP2008242326A - Method of manufacturing fiber bragg grating and apparatus for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of forming a fiber Bragg grating having high accuracy with which manufacturing cost is reduced and lead time is shortened by forming a fiber Bragg grating without giving a removing process to an optical fiber, and to provide an apparatus for manufacturing the fiber Bragg grating. <P>SOLUTION: The fiber Bragg grating is formed by irradiating an optical fiber with interfered solid laser light having wavelength of from 300 to 360 nm. Particularly, such elements as germanium, tin, aluminum, bismuth or the like having absorption effect to the solid laser light are added to the core of the optical fiber by 10 mol% or larger and the core is irradiated with the solid laser light with a power of 50 W/cm<SP>2</SP>or larger. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a fiber Bragg grating and an apparatus for manufacturing the same.

  In recent years, an optical component composed of an optical fiber in which a fiber Bragg grating (hereinafter simply referred to as “FBG”) is formed is used as a kind of strain sensor.

  The FBG is a diffraction grating (grating) formed by alternately arranging a portion having a high refractive index and a portion having a low refractive index at a certain interval in the longitudinal direction in a part of the core of the optical fiber, When light is incident on the optical fiber on which the FBG is formed, reflected light based on the diffraction conditions in the diffraction grating is generated.

Here, when the pitch of the high refractive index portion and the low refractive index portion of the FBG that are alternately continuous is Λ, and the effective refractive index of the FBG portion is n _eff , the FBG has λ _B = 2 × n _eff × Λ. When an optical component composed of an optical fiber having such an FBG is used as a strain sensor, a portion having a high refractive index is refracted by the strain generated in the FBG portion. The wavelength of the reflected light fluctuates due to the change in the pitch of the low rate part, and the amount of distortion is measured from the fluctuation amount of this wavelength.

  When an FBG is formed on an optical fiber, a phase mask is usually disposed along the optical fiber, and the optical fiber core is irradiated with ultraviolet laser light through the phase mask to thereby adjust the refractive index of the optical fiber core. Different regions are formed at predetermined intervals.

  The phase mask is a filter in which a plurality of slits are provided in the longitudinal direction of the optical fiber on the surface facing the optical fiber at a pitch twice the pitch Λ of the high refractive index portion and the low refractive index portion formed on the FBG. When an ultraviolet laser beam is incident, the ultraviolet laser beam is diffracted and applied to an optical fiber, and an interference fringe having a pitch Λ is generated in the optical fiber to form an FBG (for example, (See Patent Document 1).

When irradiating an optical fiber with ultraviolet laser light, deep ultraviolet laser light having a wavelength of 248 nm is generally used in many cases.
JP 2005-127744 A

  However, a light source that outputs a deep ultraviolet laser beam having a wavelength of 248 nm has poor output stability and requires frequent maintenance, so that it is difficult to improve productivity, and the light source is not stable. A large individual difference is likely to occur in the formed FBG due to a deviation of an irradiation position with respect to the optical fiber, a non-uniformity of a change in refractive index in the core, or the like.

  In particular, a sensing system using an FBG is generally configured by combining a plurality of FBGs. Therefore, when the individual difference for each FBG is large, the sensing system is high in spite of high accuracy. There was a problem that the accuracy of the system could not be improved.

  In addition, when forming FBGs using deep ultraviolet laser light having a wavelength of 248 nm, the coating material covering the core of the optical fiber absorbs deep ultraviolet laser light, so that a removal process is performed to remove the coating material once. The FBG can only be formed after the formation of the FBG. Further, after the FBG is formed, a recoating process for re-coating the exposed core is necessary, which increases the manufacturing cost and inhibits the shortening of the lead time. As a result, there is a problem that the production efficiency cannot be improved.

  In view of the present situation, the present inventors have made the present invention by conducting research and development of a manufacturing technique capable of efficiently forming FBG while suppressing individual differences of FBGs.

  That is, in the method for forming a fiber Bragg grating of the present invention, the fiber Bragg grating is formed by irradiating the optical fiber with solid laser light having a wavelength of 300 to 360 nm while interfering with the optical fiber.

Furthermore, the method for forming a fiber Bragg grating of the present invention is also characterized by the following points. That is,
(1) The optical fiber has a core doped with an element that causes an absorption effect on solid laser light.
(2) 10 mol% or more of the element is added to the core.
(3) The element is at least one of germanium, tin, aluminum, and bismuth.
(4) Irradiate the solid laser beam with a power of 50 W / cm ² or more.

  In the fiber bragg grating manufacturing apparatus of the present invention, in the fiber bragg grating manufacturing apparatus that forms the fiber Bragg grating by irradiating the optical fiber while interfering with the laser light irradiated from the light source, the light source has a wavelength of 300 to A light source for irradiating 360 nm solid laser light was used.

  In the present invention, a fiber Bragg grating is formed by irradiating an optical fiber with a solid laser beam having a wavelength of 300 to 360 nm, so that the light source that outputs the solid laser beam having a wavelength of 300 to 360 nm operates extremely stably. Therefore, it is possible to form a fiber Bragg grating with little variation.

  In addition, since the solid laser light having a wavelength of 300 to 360 nm is not easily absorbed by the coating material of the optical fiber, a fiber Bragg grating can be formed without performing a removal process, and the manufacturing efficiency can be improved. A fiber Bragg grating can also be formed by performing a removal process.

  In the FBG manufacturing method and the manufacturing apparatus according to the present invention, a fiber Bragg grating (hereinafter simply referred to as “FBG”) is formed by irradiating an optical fiber with solid laser light having a wavelength of 300 to 360 nm while interfering with the optical fiber. is there.

  Originally, the quartz that forms the core of the optical fiber does not absorb deep ultraviolet laser light having a wavelength of 240 to 250 nm, but in an optical fiber in which germanium or the like is added to the core, it is bonded between germanium and silicon. Since there should be no oxygen bonding, there is a GODC (Germanium Oxygen Deficient Center) defect in which germanium and silicon are directly bonded. Absorption of deep ultraviolet laser light having a wavelength of 240 to 250 nm occurs in this defect. As a result of the direct bond breakage between germanium and silicon, a refractive index change is caused for light having a wavelength of 1.5 μm.

  Since the GODC defect causes weak absorption even for light with a wavelength of 300 to 360 nm, in the present invention, the core is irradiated with a near ultraviolet laser beam with a wavelength of 300 to 360 nm to break the bond between germanium and silicon in the GODC defect. Thus, the FBG is formed by changing the refractive index.

  In particular, by using a solid-state laser as the light source of near-ultraviolet laser light with a wavelength of 300 to 360 nm, the output is extremely stable, so that an FBG with little variation can be formed, and the light source is maintenance-free and easy to maintain. It can be.

  In addition, solid laser light with a wavelength of 300 to 360 nm is hardly absorbed by the coating material covering the core of the optical fiber, so that FBG can be formed without removing the coating material by the removal process, and the removal process and the recoating process are unnecessary. As a result, the lead time can be shortened, the manufacturing cost can be reduced, and the manufacturing efficiency can be greatly improved.

  Specifically, FBG can be manufactured with the manufacturing apparatus shown with the schematic schematic diagram of FIG. Here, the optical fiber F is an optical fiber having a diameter of 150 μm in which germanium is added to the core.

  The manufacturing apparatus includes a first light source 11 (manufactured by MegaOpt Co., Ltd.) that emits solid laser light having a wavelength of 335.5 nm, a second light source 12 that emits blue-violet laser light, and the first light source 11 and the second light source 12. The laser beam emitted from the laser beam is divided into the first laser beam L1 and the second laser beam L2 by the beam splitter 21, and the adjusting unit 20 that adjusts the irradiation directions of the first laser beam L1 and the second laser beam L2, respectively. An irradiation unit 30 for irradiating the optical fiber F with the first laser beam L1 and the second laser beam L2 emitted from the irradiation unit 20 is provided.

  The solid-state laser light emitted from the first light source 11 is reflected by the first mirror M1 and the second mirror M2 provided on the optical path of the blue-violet laser light emitted from the second light source 12, and bluish-violet laser light. To follow the same optical path. In FIG. 1, A1 is a first aperture.

  The solid-state laser light and the blue-violet laser light pass through the mechanical shutter S and the second aperture A2, are reflected by the third mirror M3, and enter the adjustment unit 20. In FIG. 1, A3 is a third aperture.

  The adjusting unit 20 reflects the incident solid-state laser light and blue-violet laser light by the fourth mirror M4 and makes them incident on the beam splitter 21, and divides them into the first laser light L1 and the second laser light L2. In FIG. 1, A4 is the fourth aperture.

  The first laser beam L1 passes through the beam splitter 21, is sequentially reflected by the fifth mirror M5 and the sixth mirror M6, and enters the irradiation unit 30. On the other hand, the second laser beam L2 is reflected by the beam splitter 21, reflected by the seventh mirror M7, and incident on the irradiation unit 30.

  The angles of the fifth mirror M5, the sixth mirror M6, and the seventh mirror M7 are adjustable, and the irradiation directions of the first laser light L1 and the second laser light L2 are adjusted by adjusting the angles. ing. Further, the fifth mirror M5 is also translated.

  The first laser light L1 and the second laser light L2 incident from the adjustment unit 20 pass through the cylindrical lens 31 and irradiate the optical fiber F, and interfere with each other to generate interference light. An FBG is formed in the fiber F.

FIG. 2 shows the reflectance when an FBG is formed using the fourth harmonic of Nd: YVO ₄ emission at 1342 nm as the light source. With this FBG, a sharp reflection peak with a half-value width of about 120 pm centered around the wavelength of 1567.14 nm was obtained, and it was confirmed that FBG can be formed by irradiation with near ultraviolet light with a wavelength of 335 nm. The light source is not limited to the fourth harmonic of Nd: YVO ₄ emission at 1342 nm, but is the third harmonic of emission from 900 to 1080 nm of a solid material such as Nd: YAG, or 1200 to 1440 nm. The fourth harmonic of emission can be used.

  Further, as shown in FIG. 3, it was confirmed that the writing speed can be adjusted by adjusting the output of the light source used for writing.

That is, it is possible to increase the writing speed by the output of the light source used for writing and 50 W / cm ² or more power, the output of the light source used for writing, it is desirable that at least 50 W / cm ² or more.

  In addition, as shown in FIG. 4, when the amount of germanium added to the core of the optical fiber, which is usually about 3 mol%, is increased, the FBG writing speed can be improved. By doing so, it is possible to achieve a writing speed of about the same or higher without applying a hydrogen load in which hydrogen is added to the core of the optical fiber in advance in order to improve the writing speed. Therefore, it is not necessary to load hydrogen into the optical fiber and remove hydrogen after forming the FBG, and the lead time can be further shortened.

  The element added to the core of the optical fiber is not limited to germanium, and tin, aluminum, bismuth, etc. can be used, or a combination thereof can be used. Any element can be used as long as it can cause the core to absorb light with a wavelength of 300 to 360 nm by doping.

  In the manufacturing apparatus described above, the FBG is formed by using a so-called two-beam interference method, but the FBG may be formed on the optical fiber F by using the phase mask 40 as shown in the schematic schematic diagram of FIG. .

  In this manufacturing apparatus, a light source unit 50 that emits laser light, a phase mask 40 that causes interference with the laser light emitted from the light source unit 50, and light that is irradiated with interference light generated by the phase mask 40 And a feeding control unit 60 for controlling the feeding of the fiber F.

  The light source unit 50 includes a solid-state laser device (manufactured by MegaOpt Co., Ltd.) 51 that outputs a laser beam having a wavelength of 335.5 nm, an aperture 52, and an irradiation lens 53.

  The phase mask 40 is a glass plate in which a plurality of slits are provided along the longitudinal direction of the optical fiber F on the surface facing the optical fiber F. The pitch of the slits is the same as that in the FBG formed in the optical fiber F. The pitch Λ between the high refractive index portion and the low refractive index portion is set to twice.

  The feeding control unit 60 includes a reel 62 around which the optical fiber F is wound, a pair of feeding rollers 63 and 63 that feed the optical fiber 61 drawn from the reel 62, and the feeding rollers 63 and 63. A take-up reel 64 for taking up the fed optical fiber F is provided. A driving motor (not shown) is connected to either one of the feeding rollers 63, 63 and the take-up reel 64, and the driving roller 63 and the take-up reel 64 are driven to rotate by driving these drive motors. ing.

  In the present embodiment, the reel 62, the feeding rollers 63 and 33, and the take-up reel 64 are arranged at predetermined positions on the base 65 via appropriate supports. Two pairs of auxiliary rollers 66, 66 having the same shape as the feeding rollers 63, 63 are provided between the reel 62 and the feeding rollers 63, 63, and between the auxiliary rollers 66, 66 and the feeding rollers 63, 63. This region is an FBG formation region 67. In FIG. 5, 68 is a tension roller for applying a predetermined tension so that the optical fiber F in the FBG formation region 67 is not slackened, and 69 is an effective tension to the optical fiber F by the tension roller 68. These are two pairs of tension auxiliary rollers for applying the pressure. The tension roller 68 applies a predetermined tension to the optical fiber F while being moved up and down by a control device (not shown).

  The phase mask 40 is arranged at a predetermined position in the FBG formation region 67 so as to be separated from the optical fiber F by a predetermined distance.

  When manufacturing the FBG with the manufacturing apparatus configured as described above, the reel 62 around which the optical fiber F is wound is disposed at a predetermined position, and the optical fiber F is connected to the tension auxiliary roller 69 → the tension roller 68 → the auxiliary roller 66. → The feed roller 63 is drawn in the order of being hung, and one end of the optical fiber F is mounted on the take-up reel 64.

  In the manufacturing apparatus, the optical fiber F is fed out from the reel 62 by a predetermined amount by the feeding roller 63, and the optical fiber F is sufficiently tensioned by applying a predetermined tension to the optical fiber F by the tension roller 68. Irradiation of the laser beam is started.

  The solid-state laser device 51 forms an FBG at a predetermined position of the optical fiber F by irradiation with laser light for a predetermined time. At this time, the FBG keeps the core covered with the coating material, and by outputting laser light with a wavelength of 335.5 nm from the solid-state laser device 51, this laser light is effectively applied to the core to cause phase change. The FBG is formed by changing the refractive index of the core.

  Since the laser beam is output from the solid-state laser device 51, the output is stable, and an extremely uniform FBG can be formed.

  After the laser beam irradiation for a predetermined time, the solid-state laser device 51 stops the laser beam irradiation, the feeding roller 63 feeds the optical fiber 61 from the reel 62 by a predetermined amount, and the take-up reel 64 is the light on which the FBG is formed. The fiber F is wound up.

  By repeating this operation, the manufacturing apparatus can continuously form the FBG. In particular, by using the solid-state laser device 51 for laser light irradiation, laser light can be output with relatively little power, and the solid-state laser device 51 is maintenance-free, so maintenance work is reduced, but individual differences Can be produced stably.

It is a schematic diagram of the manufacturing apparatus of FBG concerning embodiment of this invention. Nd: the fourth harmonic of the emission of 1342nm of YVO ₄ with the light source is a graph of the reflectance in the case of forming the FBG. It is a graph which shows the dependence of the output of the light source used for writing. It is a graph which shows the dependence of the addition of germanium in the core of an optical fiber. It is a schematic diagram of the manufacturing apparatus of FBG concerning other embodiment.

Explanation of symbols

F optical fiber
11 First light source
12 Second light source
20 Adjustment section
21 Beam splitter
30 Irradiation part
31 Cylindrical lens S Mechanical shutter
L1 First laser beam
L2 Second laser beam
M1 first mirror
M2 second mirror
M3 3rd mirror
M4 4th mirror
M5 5th mirror
M6 6th mirror
M7 7th mirror
A1 1st aperture
A2 2nd aperture
A3 3rd aperture
A4 4th aperture

Claims (6)

  A method for forming a fiber Bragg grating, which forms a fiber Bragg grating by irradiating an optical fiber with solid laser light having a wavelength of 300 to 360 nm while interfering with the optical fiber.   2. The method of forming a fiber Bragg grating according to claim 1, wherein the optical fiber has a core doped with an element that causes an absorption action on the solid-state laser light. 3.   The method for forming a fiber Bragg grating according to claim 2, wherein 10 mol% or more of the element is added to the core.   The method for forming a fiber Bragg grating according to claim 2 or 3, wherein the element is at least one of germanium, tin, aluminum, and bismuth. The method for forming a fiber Bragg grating according to any one of claims 1 to 4, wherein the solid-state laser light is irradiated with a power of 50 W / cm ² or more. In a fiber Bragg grating manufacturing apparatus that forms an optical fiber Bragg grating by irradiating an optical fiber while interfering with laser light emitted from a light source,
An apparatus for manufacturing a fiber Bragg grating, wherein the light source is a light source that emits solid laser light having a wavelength of 300 to 360 nm.

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