JP2022074424A - Optical fiber grating manufacturing device and optical fiber grating manufacturing method - Google Patents

Abstract

To provide an optical fiber grating manufacturing device and an optical fiber grating manufacturing method, capable of easily manufacturing a high-quality optical fiber grating.SOLUTION: An optical fiber grating manufacturing device 1 comprises: a phase mask 11 on which a grating pattern 11a is provided; an irradiation unit 13 irradiating an optical fiber FB via the phase mask with a laser beam LB; and a fiber guide 12 arranged between the phase mask and the optical fiber, having a flat surface on the phase mask side, and including a groove 12d for disposing the optical fiber on the optical fiber side. The groove is formed to be parallel to the flat surface, and includes an open end in an extension direction. The flat surface of the fiber guide is arranged to be parallel to the phase mask.SELECTED DRAWING: Figure 1

Description

The present invention relates to an optical fiber grating manufacturing apparatus and an optical fiber grating manufacturing method.

An optical fiber grating is formed by forming a periodic change in the refractive index (grating) in the core of an optical fiber, and is also called an FBG (Fiber Bragg Grating). The optical fiber grating is manufactured, for example, by irradiating the core of the optical fiber with the interference light of the laser beam in the ultraviolet region. When the light radiated to the optical fiber to form the glazing is collected by the cylindrical clad of the optical fiber and irradiated non-uniformly to the core, the quality of the optical fiber glazing deteriorates.

The following Non-Patent Document 1 discloses a method for producing a high-quality optical fiber grating by using a cylindrical capillary having a flat surface irradiated with light. In this method, the optical fiber is inserted into the capillary, and light is incident on the clad of the optical fiber through the capillary to alleviate the light being condensed by the clad. As a result, the energy density of the light applied to the core of the optical fiber is made uniform, so that a high-quality optical fiber grating can be manufactured.

Emma Lindley, Seong-Sik Min, Sergio Leon-Saval, Nick Cvetojevic, Jon Lawrence, Simon Ellis, and Joss Bland-Hawthorn, “Demonstration of uniform multicore fiber Bragg gratings”, 2014, Optics Express Vol. 22, Issue 25, p . 31575-31581

By the way, in the method disclosed in Non-Patent Document 1 described above, in order to arrange the cylindrical capillary at a desired position of the optical fiber (for example, a position where a grating should be formed), the optical fiber is inserted. So we need to move the grating along the fiber optics. Further, in the process of moving the capillary to a desired position, the capillary and the optical fiber may rub against each other, and the surface of the optical fiber may be scratched or soiled. As described above, the method disclosed in Non-Patent Document 1 described above can produce a high-quality optical fiber grating, but has a problem that the production is not easy.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an optical fiber grating manufacturing apparatus and an optical fiber grating manufacturing method capable of easily manufacturing a high-quality optical fiber grating.

In order to solve the above problems, the optical fiber grating manufacturing apparatus according to one aspect of the present invention has a phase mask (11) provided with a lattice pattern (11a) and a laser on the optical fiber (FB) via the phase mask. An optical fiber grating manufacturing apparatus (1 to 7) having an irradiation unit (13) for irradiating light (LB), which is arranged between the phase mask and the optical fiber, and the phase mask side is a flat surface. An optical correction member (12) having a groove (12d, 12f, 12j, 12m) for installing the optical fiber is provided on the optical fiber side, and the groove is formed so as to be parallel to the plane. The end portion in the stretching direction is an open end, and the optical correction member is arranged so that the plane is parallel to the phase mask.

In the optical fiber grating manufacturing apparatus according to one aspect of the present invention, an optical correction member having a flat surface on the phase mask side and a groove for installing the optical fiber on the optical fiber side is arranged between the phase mask and the optical fiber. .. Here, the groove of the optical correction member is formed so as to be parallel to the plane, and the end portion in the stretching direction is an open end, and the optical correction member has the plane with respect to the phase mask. Arranged so that they are parallel to each other. By incident the laser light emitted from the inner wall surface of the groove through the optical correction member onto the optical fiber, the energy density of the laser light emitted to the core of the optical fiber is made uniform, so that the quality of the grating is improved. improves. Further, unlike the conventional case, it is not necessary to insert the optical fiber into the optical capillary, and any part of the optical fiber can be easily arranged inside the groove only by bringing the optical fiber close to the optical correction member. As described above, the optical fiber grating manufacturing apparatus according to one aspect of the present invention can easily manufacture a high quality optical fiber grating.

Further, in the optical fiber grating manufacturing apparatus according to one aspect of the present invention, the optical correction member extends the groove in the extending direction (D1) so that the laser light irradiated to the optical fiber is not focused inside the optical fiber. Within the cross section orthogonal to D3), the optical path of at least a part of the laser beam irradiated to the optical fiber is corrected by the groove.

Further, in the optical fiber grating manufacturing apparatus according to one aspect of the present invention, the shape of the groove in the cross section orthogonal to the extending direction (D1) of the groove is an arc.

Here, in the optical fiber grating manufacturing apparatus according to one aspect of the present invention, all the optical fiber grating manufacturing apparatus is centered on the central axis (L) of the optical fiber in the cross section in which the refractive index of the optical correction member is orthogonal to the stretching direction of the groove. The value obtained by dividing the radius (a) of the circular region having the minimum radius including the core (C) by the radius (R) of the strands of the optical fiber is the value obtained by dividing the refractive index (n ₀ ) of air by the optical correction member. _The radius of curvature (r) of the arc is equal to or greater than the radius (R) of the strand of the optical fiber.

Alternatively, in the optical fiber grating manufacturing apparatus according to one aspect of the present invention, the shape of the groove in the cross section orthogonal to the stretching direction (D2) of the groove (12f) is the central axis of the optical fiber and the deepest portion of the groove. The first straight line portion (12 g) that is in contact with or closest to the peripheral surface of the optical fiber on one side with respect to the line connecting the optical fiber and the optical fiber on the other side with respect to the central axis of the optical fiber. It has a shape having a second straight line portion (12h) that is in contact with or closest to the peripheral surface, and a bottom arc portion (12i) that connects the end portion of the first straight line portion and the end portion of the second straight line portion. ing.

Here, in the optical fiber grating manufacturing apparatus according to one aspect of the present invention, all the optical fiber grating manufacturing apparatus is centered on the central axis (L) of the optical fiber in the cross section in which the refractive index of the optical correction member is orthogonal to the stretching direction of the groove. The value obtained by dividing the radius (a) of the circular region having the minimum radius including the core (C) by the radius (R) of the strands of the optical fiber is the value obtained by dividing the refractive index (n ₀ ) of air by the optical correction member. The radius of curvature ( _ra ) of the bottom arc portion is not less than or equal to the value obtained by dividing by the refractive index (n ₁ ) of the optical fiber.

Here, the optical fiber grating manufacturing apparatus according to one aspect of the present invention changes the ratio of the energy density of the laser light after being incident on the optical fiber to the energy density of the laser light before being incident on the optical fiber. Let (β) be the lower limit change rate (β), where the energy density of the laser light after being incident on the optical fiber is the allowable lower limit of the energy density required for the laser light incident on the optical fiber. When _min ) is set, the radius of curvature of the bottom arc portion is larger than the value obtained by multiplying the radius of the strand of the optical fiber by the lower limit change rate.

Here, in the optical fiber grating manufacturing apparatus according to one aspect of the present invention, the groove depth (h) is the square of a sine and cosine value of half the angle (θ) of the central angle of the bottom arc portion. It is larger than the value obtained by multiplying the radius of curvature of the bottom arc.

Alternatively, in the optical fiber grating manufacturing apparatus according to one aspect of the present invention, the shape of the groove in the cross section orthogonal to the stretching direction (D3) of the groove (12j) is connected by bending a plurality of straight portions (12k) to each other. It is said to have a rectangular shape.

Further, in the optical fiber grating manufacturing apparatus according to one aspect of the present invention, the optical correction member has a base portion (12a) having a flat surface on the phase mask side and a groove provided on the optical fiber side, and the base portion. A reinforcing portion (12b) provided so as to project from the base portion outside the region (R1) through which the laser beam is transmitted is provided.

Further, the optical fiber grating manufacturing apparatus according to one aspect of the present invention includes a protective foil (14) interposed between the optical correction member and the phase mask.

Further, the optical fiber grating manufacturing apparatus according to one aspect of the present invention includes an optical fluid (15) filled and arranged between the inner wall surface of the groove and the optical fiber.

Further, the optical fiber grating manufacturing apparatus according to one aspect of the present invention includes a delivery spool (16) that sends out one end side of the optical fiber and a take-up spool (17) that winds up the other end side of the optical fiber.

Further, the optical fiber grating manufacturing method according to one aspect of the present invention is an optical fiber grating manufacturing method in which (C) grating (G) is formed in a core of an optical fiber (FB), and one side thereof is a flat surface. A phase mask (11) is arranged on the plane side of the optical correction member (12) provided with grooves (12d, 12f, 12j, 12m) on the other side so as to be parallel to the plane. The optical fiber is irradiated with laser light (LB) via the arrangement step (S1), the optical fiber installation step (S2) for installing the optical fiber in the groove, and the phase mask and the optical correction member. It has a grating forming step (S3) for forming a grating, the groove is formed so as to be parallel to the plane, and an end portion in the stretching direction is an open end.

In the optical fiber grating manufacturing method according to one aspect of the present invention, the phase mask side is a flat surface and an optical correction member having a groove for installing the optical fiber is arranged between the phase mask and the optical fiber. .. Here, the groove of the optical correction member is formed so as to be parallel to the plane, and the end portion in the stretching direction is an open end, and the optical correction member has the plane with respect to the phase mask. Arranged so that they are parallel to each other. By incident the laser light emitted from the inner wall surface of the groove through the optical correction member onto the optical fiber, the energy density of the laser light emitted to the core of the optical fiber is made uniform, so that the quality of the grating is improved. improves. Further, unlike the conventional case, it is not necessary to insert the optical fiber into the optical capillary, and any part of the optical fiber can be easily arranged inside the groove only by bringing the optical fiber close to the optical correction member. As described above, the optical fiber grating manufacturing apparatus according to one aspect of the present invention can easily manufacture a high quality optical fiber grating.

According to the present invention, there is an effect that a high quality optical fiber grating can be easily manufactured.

It is a figure which shows the schematic structure of the optical fiber grating manufacturing apparatus by 1st Embodiment of this invention. FIG. 3 is a cross-sectional arrow view taken along the line AA in FIG. It is sectional drawing along the optical axis of the optical fiber used in 1st Embodiment of this invention. It is a three-view view of the fiber guide provided in the optical fiber grating manufacturing apparatus according to 1st Embodiment of this invention. It is a figure for demonstrating the shape of the groove of the fiber guide in 1st Embodiment of this invention. It is a figure which shows the state which installed the multi-core fiber in the groove of the fiber guide in 1st Embodiment of this invention. It is a flowchart which shows an example of the optical fiber grating manufacturing method by 1st Embodiment of this invention. It is sectional drawing which shows the schematic structure of the optical fiber grating manufacturing apparatus by 2nd Embodiment of this invention. It is a figure for demonstrating the shape of the groove of the fiber guide in 2nd Embodiment of this invention. It is a figure for demonstrating the radius lower limit value of the wire | wire of the optical fiber in 2nd Embodiment of this invention. It is a figure which shows the state which installed the multi-core fiber in the groove of the fiber guide in the 2nd Embodiment of this invention. It is a figure which shows the state of irradiating the multi-core fiber installed in the groove of the fiber guide in the 2nd Embodiment of this invention with a laser beam. It is sectional drawing which shows the schematic structure of the optical fiber grating manufacturing apparatus according to 3rd Embodiment of this invention. It is sectional drawing which shows the schematic structure of the optical fiber grating manufacturing apparatus according to 4th Embodiment of this invention. It is a figure which shows the schematic structure of the optical fiber grating manufacturing apparatus according to 5th Embodiment of this invention. It is sectional drawing along the line BB in FIG. It is sectional drawing which shows the schematic structure of the optical fiber grating manufacturing apparatus according to the 6th Embodiment of this invention. It is a figure which shows the schematic structure of the optical fiber grating manufacturing apparatus according to 7th Embodiment of this invention. It is sectional drawing which shows the other example of the groove of a fiber guide. It is a figure which shows the state which installed the large-diameter optical fiber in the groove shown in FIG.

Hereinafter, the optical fiber grating manufacturing apparatus and the optical fiber grating manufacturing method according to the embodiment of the present invention will be described in detail with reference to the drawings.

[First Embodiment]
<Optical fiber grating manufacturing equipment>
FIG. 1 is a diagram showing a schematic configuration of an optical fiber grating manufacturing apparatus according to the first embodiment of the present invention. FIG. 2 is a cross-sectional arrow view taken along the line AA in FIG. As shown in FIGS. 1 and 2, the optical fiber grating manufacturing apparatus 1 includes a phase mask 11, a fiber guide 12 (optical correction member), and an irradiation unit 13. In such an optical fiber grating manufacturing apparatus 1, the laser beam from the irradiation unit 13 is irradiated to the optical fiber FB via the phase mask 11 and the fiber guide 12, so that the core C of the optical fiber FB (see FIG. 3). It forms a grating G.

FIG. 3 is a cross-sectional view taken along the optical axis of the optical fiber used in the first embodiment of the present invention. As shown in FIG. 3, the optical fiber FB has a cylindrical core C and a wire composed of a cylindrical clad CL covering the outer surface of the core C, and a cylindrical coated CV covering the outer surface of the wire. It is a single core fiber. This optical fiber FB is, for example, an LMA (Large Mode Area) fiber.

The core C is formed of, for example, quartz glass containing germanium (Ge), and the clad CL is formed of quartz glass. The coated CV is formed of acrylic, ultraviolet light transmitting silicone, polyimide, or the like. As shown in FIG. 1, at the portion where the phase mask 11, the fiber guide 12 (optical correction member), and the irradiation unit 13 are arranged, the coating CV of the optical fiber FB is removed, and the surface of the clad CL is exposed. ing.

The phase mask 11 is arranged on the side of the optical fiber FB (above the optical fiber FB in the example shown in FIG. 1) at the portion where the clad CL of the optical fiber FB is exposed. The phase mask 11 is for forming a grating G on the core C of the optical fiber FB. The phase mask 11 is provided with a grid pattern 11a, and is irradiated with the laser beam LB in the ultraviolet region emitted from the irradiation unit 13. As a result, +1st-order diffracted light and -1st-order diffracted light are generated, and the interference light of these diffracted lights is applied to the core C of the optical fiber FB via the fiber guide 12, so that the grating G is applied to the core C of the optical fiber FB. It is formed.

The fiber guide 12 is arranged on the opposite side of the irradiation unit 13 with respect to the phase mask 11, and is interposed between the phase mask 11 and the optical fiber FB. It can also be said that the phase mask 11 is arranged between the fiber guide 12 and the irradiation unit 13. The fiber guide 12 guides the optical path of at least a part of the laser light LB irradiated on the optical fiber FB so that the laser light LB irradiated on the optical fiber FB is not focused inside the optical fiber FB. to correct. That is, the fiber guide 12 equalizes the energy density of the laser beam LB irradiated to the core C of the optical fiber FB. The details of the fiber guide 12 will be described later.

The irradiation unit 13 is arranged above the phase mask 11. The irradiation unit 13 emits the laser beam LB irradiated on the phase mask 11 under the control of a control device (not shown). As the laser beam LB emitted from the irradiation unit 13, for example, a laser beam having a wavelength of about 240 to 360 nm emitted from an excimer laser can be used. The light source device such as the excimer laser described above may be provided in the irradiation unit 13 or may be provided separately from the irradiation unit 13.

<Fiber guide>
FIG. 4 is a three-view view of a fiber guide provided in the optical fiber grating manufacturing apparatus according to the first embodiment of the present invention. In FIG. 4, (a) is a front view, (b) is a plan view, and (c) is a right side view. The fiber guide 12 is made of a material having the same or similar refractive index as the clad CL of the optical fiber FB, and is entirely made of quartz glass in this embodiment.

As shown in FIG. 4, the fiber guide 12 has a base portion 12a and a reinforcing portion 12b. Although the base portion 12a and the reinforcing portion 12b are integrated, in FIG. 4A, the boundary surface between the base portion 12a and the reinforcing portion 12b is shown by a virtual line.

In the base portion 12a, the surface on the phase mask 11 side (the upper surface in FIG. 2 in this embodiment) is the contact surface 12c with the phase mask 11. The contact surface 12c is a flat surface. The fiber guide 12 is arranged so that the contact surface 12c is parallel to the phase mask 11. On the optical fiber FB side of the base portion 12a, a groove 12d extended along the central axis L of the optical fiber FB is provided. An optical fiber FB is installed in this groove 12d. That is, in the present embodiment, the fiber guide 12 has a flat contact surface 12c on the phase mask 11 side, and a groove 12d on which the optical fiber FB is installed is provided on the optical fiber FB side.

The shape of the groove 12d in the cross section orthogonal to the stretching direction D1 of the groove 12d is not particularly limited, but in the present embodiment, it is an arc as shown in FIG. 4C. That is, the inner wall surface of the groove 12d is a smooth curved surface without a bent portion. As described above, since the shape of the groove 12d in the cross section orthogonal to the stretching direction D1 of the groove 12d is an arc, the groove 12d can be easily formed as compared with the case where the shape of the groove 12d is a polygonal shape. Is possible.

The thickness d1 of the base portion 12a at the deepest position P of the groove 12d is set to, for example, 100 to 200 μm. By setting the thickness d1 to 100 to 200 μm, the phase mask 11 can be brought close to the optical fiber FB, and the optical fiber FB can be irradiated with a laser beam LB having a sufficient intensity for forming the grating G.

Further, as shown in FIG. 4A, the groove 12d is linearly provided with a length extending from one end to the other end of the base portion 12a in the stretching direction D1. The groove 12d is formed so as to be parallel to the contact surface 12c (that is, the thickness d1 of the base portion 12a at the deepest position P is constant over the stretching direction D1). .. Both ends of the groove 12d are open ends 12e. As described above, since the groove 12d of the fiber guide 12 has an open end 12e in the stretching direction D1, the optical fiber FB can be arranged in the groove 12d without bending. This makes it possible to prevent the optical fiber FB from unintentionally moving inside the groove 12d due to the restoring force generated when the optical fiber FB is curved. The details of the shape of the groove 12d will be described later.

The reinforcing portion 12b is provided so as to project from the contact surface 12c to which the phase mask 11 of the base portion 12a abuts. Reinforcing portions 12b are provided at each of the two ends of the base portion 12a in the stretching direction D1 of the groove 12d. That is, in this embodiment, the reinforcing portions 12b are provided at two locations. These reinforcing portions 12b improve the strength of the fiber guide 12 by increasing the thickness of the end portion of the fiber guide 12. The laser beam LB emitted from the irradiation unit 13 passes through the central portion of the fiber guide 12 and does not transmit the end portion. That is, the reinforcing portion 12b is provided so as to project from the base portion 12a outside the region R1 through which the laser beam LB of the base portion 12a passes.

As described above, the fiber guide 12 is provided from the base portion 12a having the phase mask 11 side flat and the groove 12d provided on the optical fiber FB side, and from the base portion outside the region R1 through which the laser beam LB of the base portion 12a is transmitted. It has a reinforcing portion 12b provided so as to project. Therefore, the strength of the fiber guide 12 can be improved as compared with the case where the reinforcing portion 12b is not provided, and the fiber guide 12 can be easily handled.

FIG. 5 is a diagram for explaining the shape of the groove of the fiber guide according to the first embodiment of the present invention. As shown in FIG. 5, let a be the radius of the circle region having the minimum radius including the core C centered on the central axis L of the optical fiber FB (corresponding to the radius of the core C in this embodiment). Further, the radius of the wire of the optical fiber FB (the radius of the portion where the coated CV is removed) is defined as R. Further, the radius of curvature of the groove 12d is r. Further, the refractive index of air is n ₀ , and the refractive index of the fiber guide 12 is n ₁ .

Here, when the following equations (1) and (2) are satisfied, the degree of focusing of the laser beam LB emitted from the fiber guide 12 is suppressed. Therefore, the energy density of the laser beam LB incident on the core C of the optical fiber FB is made uniform as compared with the case where the fiber guide 12 is not installed.

Further, when the above equation (2) is satisfied, the optical fiber FB can be brought into contact with the inner wall surface of the groove 12d at the deepest position P of the groove 12d. In this case, there is no theoretical limitation on the radius of curvature r of the groove 12d in the cross section orthogonal to the stretching direction D1 of the groove 12d. However, as the radius of curvature r of the groove 12d becomes larger, the fiber guide 12 becomes unnecessarily large. Further, as the radius of curvature r of the groove 12d becomes larger, the circumference of the deepest position P of the groove 12d becomes flat and the optical fiber FB becomes easier to move in the horizontal direction (X direction in FIG. 5), and the stability of the optical fiber FB becomes stable. Decreases. Therefore, it is preferable that the radius of curvature r of the groove 12d is up to 1.5 times the radius R of the wire of the optical fiber FB.

FIG. 6 is a diagram showing a state in which the multi-core fiber is installed in the groove of the fiber guide in the first embodiment. As shown in FIG. 6, when the circular region having the minimum radius including all the cores C centered on the central axis L of the multi-core fiber FBM is set as the core region RC, the radius of the core region RC is a. Even when such a multi-core fiber FBM is installed in the groove 12d and the above-mentioned equations (1) and (2) are satisfied, the laser beam LB does not become parallel light in the core region RC, but the degree of light collection is high. It can be suppressed. Therefore, the energy density of the laser beam LB incident on the core C of the multi-core fiber FBM is made uniform as compared with the case where the fiber guide 12 is not installed. Therefore, it is possible to prevent the reflectance of the grating G from becoming non-uniform in the plurality of cores C.

As described above, in the optical fiber grating manufacturing apparatus 1 of the present embodiment, a circular region having a minimum radius including all cores C centered on the central axis L of the optical fiber FB in a cross section orthogonal to the stretching direction D1 of the groove 12d. The value obtained by dividing the radius a of the optical fiber FB by the radius R of the strands of the optical fiber FB is equal to or less than the value obtained by dividing the refractive index n ₀ of air by the refractive index n ₁ of the fiber guide 12. ing. Further, the radius of curvature r of the groove 12d provided in the fiber guide 12 is set to be equal to or larger than the radius R of the strands of the optical fiber FB. As a result, the energy density of the laser beam LB incident on the core C of the optical fiber FB (or the multi-core fiber FBM) is made uniform as compared with the case where the fiber guide 12 is not installed. Can be formed.

<Optical fiber grating manufacturing method>
FIG. 7 is a flowchart showing an example of an optical fiber grating manufacturing method according to the first embodiment of the present invention. When the production of the optical fiber grating is started, first, a step of arranging the phase mask 11 on the contact surface 12c of the fiber guide 12 is performed (step S1: phase mask arranging step). That is, a step of arranging the phase mask 11 on the flat surface (contact surface 12c) side of the fiber guide 12 having a flat surface on one side and a groove 12d on the other side is performed. As a result, the phase mask 11 is arranged so as to be parallel to the contact surface 12c of the fiber guide 12. In other words, the fiber guide 12 is arranged so that the contact surface 12c is parallel to the phase mask 11.

The phase mask 11 and the fiber guide 12 having the above arrangement are positioned below the irradiation unit 13 with the phase mask 11 facing the irradiation unit 13. In other words, the phase mask 11 and the fiber guide 12 are positioned in a state where the phase mask 11 is arranged between the fiber guide 12 and the irradiation unit 13. The phase mask 11 and the fiber guide 12 may be fixed by an adhesive or a fastening structure (not shown) while avoiding the region R1 through which the laser beam LB is transmitted.

Next, a step of installing the optical fiber FB in the groove 12d of the fiber guide 12 is performed (step S2: optical fiber installation step). Specifically, the optical fiber FB is brought close to the fiber guide 12 from the lower side, and at least a part of the portion where the wire (clad CL) of the optical fiber FB is exposed enters the inside of the groove 12d of the fiber guide 12. To do so. The optical fiber FB may be in contact with the inner wall surface of the groove 12d, or may be arranged with a slight gap from the inner wall surface of the groove 12d.

Here, as shown in FIG. 4C, the shape of the groove 12d of the fiber guide 12 is a shape that opens toward the side opposite to the side on which the phase mask 11 is arranged. Therefore, by bringing the optical fiber FB closer from the lower side of the fiber guide 12, any portion of the optical fiber FB can be easily arranged inside the groove 12d. Further, since the groove 12d is formed so as to be parallel to the contact surface 12c, if the optical fiber FB is arranged in the groove 12d, the optical fiber FB can be placed on the contact surface 12c and the phase mask 11. Can be arranged so as to be parallel to each other.

Next, a step of irradiating the optical fiber FB with the laser beam LB via the phase mask 11 and the fiber guide 12 to form the grating G is performed (step S3: grating forming step). When this step is started, laser light is emitted from the irradiation unit 13. The laser beam LB emitted from the irradiation unit 13 irradiates the upper surface of the phase mask 11.

When the upper surface of the phase mask 11 is irradiated with the laser beam LB, diffracted light is generated, and the diffracted light is emitted from the inner wall surface of the groove 12d via the fiber guide 12 and incident on the clad CL of the optical fiber FB. The diffracted light of the laser beam LB is optical path corrected by the fiber guide 12 so as not to be focused inside the wire of the optical fiber FB as compared with the case where the fiber guide 12 is not installed. Therefore, the energy density of the diffracted light inside the wire of the optical fiber FB is made uniform. By irradiating the core C of the optical fiber FB with the interference light of such diffracted light, a grating G is formed on the core C of the optical fiber FB.

Here, an example in which the phase mask 11 and the fiber guide 12 are arranged below the irradiation unit 13, the optical fiber FB is brought close to the fiber guide 12 from the lower side, and the laser beam LB is irradiated from the upper side of the phase mask 11. explained. However, the phase mask 11 and the fiber guide 12 may be arranged above the irradiation unit 13, the optical fiber FB may be brought close to the fiber guide 12 from above, and the laser beam LB may be irradiated from below the phase mask 11. .. Alternatively, the phase mask 11 and the fiber guide 12 are arranged on the side (for example, the right side) of the irradiation unit 13, the optical fiber FB is brought close to the side (for example, the right side) of the fiber guide 12, and the laser light LB is phased. Irradiation may be performed from the side surface (for example, the left side) of the mask 11.

As described above, in the present embodiment, the optical fiber FB is brought close to the fiber guide 12 arranged between the phase mask 11 and the optical fiber FB, and the wire of the optical fiber FB is installed in the groove 12d of the fiber guide 12. are doing. Then, the laser beam emitted from the irradiation unit 13 is irradiated to the strands of the optical fiber FB via the phase mask 11 and the fiber guide 12. As a result, the energy density of the laser beam LB irradiated to the core C of the optical fiber FB can be made uniform, so that a high-quality optical fiber grating can be easily manufactured.

[Second Embodiment]
<Optical fiber grating manufacturing equipment>
FIG. 8 is a cross-sectional view showing a schematic configuration of an optical fiber grating manufacturing apparatus according to a second embodiment of the present invention. In FIG. 8, the same reference numerals are given to the configurations similar to those shown in FIG. The optical fiber grating manufacturing apparatus 2 of the present embodiment is different from the optical fiber grating manufacturing apparatus 1 shown in FIG. 2 in the shape of the groove provided in the fiber guide 12. Since the optical fiber grating manufacturing method in the present embodiment is the same as that in the first embodiment, the description thereof will be omitted.

<Fiber guide>
The cross-sectional shape of the groove 12f provided in the fiber guide 12 is a shape having a first straight line portion 12g, a second straight line portion 12h, and a bottom arc portion 12i. The first straight line portion 12g is in contact with or closest to the peripheral surface of the optical fiber FB on one side (right side in FIG. 8) with respect to the line connecting the central axis L of the optical fiber FB and the deepest portion of the groove 12f. It is a linear part. The upper end of the first straight line portion 12g is connected to one end of the bottom arc portion 12i (right end in FIG. 8) without bending, and the first straight line portion 12g is horizontally separated from the second straight line portion 12h as it goes downward from the bottom arc portion 12i. Is tilted to.

The second straight line portion 12h is a linear portion that is in contact with or closest to the peripheral surface of the optical fiber FB on the other side (left side in FIG. 8) with respect to the central axis L of the optical fiber FB. The upper end of the second straight line portion 12h is connected to the other end of the bottom arc portion 12i (left end in FIG. 8) without bending, and is horizontally separated from the first straight portion 12g as it goes downward from the bottom arc portion 12i. It is tilted like this.

The bottom arc portion 12i forms the bottom portion of the groove 12f, and is an arc-shaped portion connecting the upper end of the first straight line portion 12g and the upper end of the second straight line portion 12h. The radius of curvature of the bottom arc portion 12i is constant. The first straight line portion 12g and the second straight line portion 12h are provided so as to overlap with the tangent line of the bottom arc portion 12i at the connection point with the bottom arc portion 12i.

FIG. 9 is a diagram for explaining the shape of the groove of the fiber guide in the second embodiment of the present invention. In FIG. 9, the same reference numerals are given to the configurations similar to those shown in FIG. As shown in FIG. 9, the radius of curvature of the bottom arc portion _12i of the groove 12f is ra. Further, the depth of the groove 12f is set to h.

According to Snell's law, the critical angle θ _c of total reflection of light traveling from the inside of the fiber guide 12 to the outside (air) of the fiber guide 12 is expressed by the following equation (3).

Therefore, assuming that the angle of half of the central angle of the bottom arc portion 12i is θ, it is expressed as the following equation (4).

Here, when the above-mentioned equation (1) holds, the radius of curvature _ra is limited to the range shown by the following equation (5).

In the above equation (5), R _min is a lower limit value (radius lower limit value) of the radius of the wire of the optical fiber FB. FIG. 10 is a diagram for explaining the lower limit radius of the wire of the optical fiber according to the second embodiment of the present invention. As shown in FIG. 10, when the laser beam LB reaches the inner wall surface of the groove 12f from the inside of the fiber guide 12, only the laser beam LB in the range shown by the width W1 narrower _than the diameter of the wire of the optical fiber FB is available. It is incident on the optical fiber FB.

The laser beam LB passing through the range of the width W ₁ is refracted on the inner wall surface of the groove 12f, and the range of the width W ₂ wider than the width W ₁ inside the wire of the optical fiber FB (the range including the core C). Irradiate. In other words, the laser light LB that irradiates the range of the width W ₂ including the core C is only the laser light LB that passes through the range of the width W ₁ narrower than the width W ₂ inside the fiber guide 12.

Since the laser light LB spreads inside the wire of the optical fiber FB in this way, the energy density of the laser light LB decreases inside the wire of the optical fiber FB. That is, the energy density (light receiving energy density) of the laser beam LB received by the optical fiber FB is smaller than the energy density (incident energy density) of the laser beam LB incident on the optical fiber FB.

The rate of change β of the energy density can be expressed by the following equation (6).

As shown in the above equation (6), the rate of change β changes depending on the radius R of the strands of the optical fiber FB. Here, consider a case where the output of the laser beam LB emitted from the irradiation unit 13 is constant. In this case, the lower limit of the rate of change (lower limit change rate β _min ) that can secure the minimum value of the energy density required to form the grating G, and the lower limit radius R _min of the wire of the optical fiber FB described above. The relationship of is expressed by the following equation (7).

That is, when the above equation (5) is satisfied, the radius of curvature ra of the bottom arc portion _12i becomes larger than the value obtained by multiplying the radius R of the optical fiber FB by the lower limit change rate β _min . Thereby, the energy density of the laser beam LB transmitted through the strands of the optical fiber FB can be made higher than the minimum energy density required for forming the grating G.

Returning to FIG. 9, the depth h of the groove 12f is the curvature of the bottom arc portion 12i with respect to the square of the sine and cosine value of the angle θ which is half the central angle of the bottom arc portion 12i, as shown in the following equation (8). Greater than the value obtained by multiplying the radius _ra . This makes it possible to reliably irradiate the entire core C with the laser beam LB.

When the following equation (9) is satisfied, it is preferable to arrange a refraction matching material that fills the space between the optical fiber FB and the fiber guide 12. The refraction matching material is a fluid or solid and is formed of a material whose refractive index is closer to the fiber guide 12 than air. As a result, the laser beam LB can be more reliably irradiated to the entire core C.

FIG. 11 is a diagram showing a state in which a multi-core fiber is installed in a groove of a fiber guide according to a second embodiment of the present invention. Further, FIG. 12 is a diagram showing a state in which the multi-core fiber installed in the groove of the fiber guide according to the second embodiment of the present invention is irradiated with the laser beam. As shown in FIGS. 11 and 12, when the circular region having the minimum radius including all the cores C centered on the central axis L of the multi-core fiber FBM is defined as the core region RC, the radius of the core region RC is a.

Even when such a multi-core fiber FBM is installed in the groove 12f and the above-mentioned equations (1) and (5) are satisfied, the laser beam LB transmitted through the optical fiber FB is used as parallel light and is irradiated to the core C. The energy density can be made more uniform. Further, the energy density of the laser beam LB irradiated to the core C can be set to the strength that the grating G can surely form.

[Third Embodiment]
<Optical fiber grating manufacturing equipment>
FIG. 13 is a cross-sectional view showing a schematic configuration of an optical fiber grating manufacturing apparatus according to a third embodiment of the present invention. In FIG. 13, the same reference numerals are given to the configurations similar to those shown in FIG. The optical fiber grating manufacturing apparatus 3 of the present embodiment is different from the optical fiber grating manufacturing apparatus 1 shown in FIG. 2 in the shape of the groove provided in the fiber guide 12. Since the optical fiber grating manufacturing method in this embodiment is the same as that in the first embodiment, the description thereof will be omitted.

<Fiber guide>
In the present embodiment, the cross-sectional shape of the groove 12j provided in the fiber guide 12 is an angular shape in which a plurality of straight portions 12k are bent and connected to each other. The length of each straight line portion 12k is the same, and the angle at which the straight line portions 12k are connected is also the same.

According to the groove 12j of the present embodiment as described above, the inner wall surface of the groove 12j and the optical fiber FB can be brought into contact with each other at many points. Therefore, when the optical fiber FB is abutted against the inner wall surface of the groove 12j, the optical fiber FB can be stably positioned inside the groove 12j.

[Fourth Embodiment]
<Optical fiber grating manufacturing equipment>
FIG. 14 is a cross-sectional view showing a schematic configuration of an optical fiber grating manufacturing apparatus according to a fourth embodiment of the present invention. In FIG. 14, the same reference numerals are given to the configurations similar to those shown in FIG. The optical fiber grating manufacturing apparatus 4 of the present embodiment is different from the optical fiber grating manufacturing apparatus 1 shown in FIG. 2 in that it includes a protective foil 14. Since the optical fiber grating manufacturing method in this embodiment is the same as that in the first embodiment, the description thereof will be omitted.

As shown in FIG. 14, the protective foil 14 is interposed between the phase mask 11 and the fiber guide 12. That is, in the present embodiment, the phase mask 11 is in contact with the contact surface 12c of the fiber guide 12 via the protective foil 14. The protective foil 14 is made of, for example, a material having a high transmittance of laser light LB and a refractive index comparable to that of the fiber guide 12. As the protective foil 14, for example, a fused silica glass plate having a thickness of about 10 to 20 μm can be used.

By inserting such a protective foil 14 between the phase mask 11 and the fiber guide 12, the phase mask 11 can be strongly pressed against the fiber guide 12. This makes it possible to bring the phase mask 11 and the fiber guide 12 close to each other while preventing the phase mask 11 and the fiber guide 12 from being damaged. Further, it is possible to prevent a gap from being generated between the phase mask 11 and the fiber guide 12, and to prevent the energy of the laser beam LB from being lost between the phase mask 11 and the fiber guide 12. ..

[Fifth Embodiment]
<Optical fiber grating manufacturing equipment>
FIG. 15 is a diagram showing a schematic configuration of an optical fiber grating manufacturing apparatus according to a fifth embodiment of the present invention. Further, FIG. 16 is a cross-sectional arrow view taken along the line BB in FIG. In FIGS. 15 and 16, the same reference numerals are given to the same configurations as those shown in FIG. 1.

The optical fiber grating manufacturing apparatus 5 of the present embodiment has substantially the same configuration as the optical fiber grating manufacturing apparatus 1 shown in FIGS. 1 and 2. However, the optical fiber grating manufacturing apparatus 5 of the present embodiment irradiates the multi-core fiber FBM having the entire coated CV with the laser beam LB to form the grating G, which is the light shown in FIGS. 1 and 2. It is different from the fiber grating manufacturing apparatus 1.

In the present embodiment, the coated CV is provided seamlessly in the entire length direction of the multi-core fiber FBM. That is, there is no portion in the middle of the multi-core fiber FBM where the coated CV is removed and the outer surface of the strand (clad CL) is exposed. The coated CV is made of a material capable of transmitting ultraviolet rays, such as acrylic, ultraviolet light transmitting silicone, and polyimide.

<Optical fiber grating manufacturing method>
The optical fiber grating manufacturing method according to the present embodiment is basically the same as the optical fiber grating manufacturing method according to the first embodiment, and the process shown in the flowchart shown in FIG. 7 is performed. However, in step S2, an arbitrary portion of the optical fiber FB (arbitrary portion provided with the coated CV) is arranged inside the groove 12d of the fiber guide 12, which is different from the first embodiment. Further, in step S3, the point that the laser beam LB via the phase mask 11 and the fiber guide 12 is transmitted through the coated CV and irradiated to the core wire of the optical fiber FB is different from the first embodiment.

In this embodiment, an example of irradiating a multi-core fiber FBM with a laser beam LB to form a grating G has been described. However, similarly, it is also possible to irradiate the single-core optical fiber FB with the laser beam LB to form the grating G.

[Sixth Embodiment]
<Optical fiber grating manufacturing equipment>
FIG. 17 is a cross-sectional view showing a schematic configuration of an optical fiber grating manufacturing apparatus according to a sixth embodiment of the present invention. In FIG. 17, the same reference numerals are given to the configurations similar to those shown in FIG.

The optical fiber grating manufacturing apparatus 6 of the present embodiment has substantially the same configuration as the optical fiber grating manufacturing apparatus 5 shown in FIG. However, the optical fiber grating manufacturing apparatus 6 of the present embodiment is different in that the matching oil 15 (optical fluid) is filled and arranged between the multi-core fiber FBM coated on the entire surface and the fiber guide 12. ..

The multi-core fiber FBM and the inner wall surface of the groove 12d of the fiber guide 12 are arranged so as to face each other with a slight gap. The size of this gap is set so that the matching oil 15 can be held between the multi-core fiber FBM and the fiber guide 12 due to the capillary phenomenon. By filling and arranging the matching oil 15 in such a small gap, it is not necessary to separately provide a mechanism for holding the matching oil 15 or a mechanism for immersing the fiber guide 12 in the matching oil 15. In addition, the amount of matching oil 15 used can be minimized. In addition, the possibility of particles entering the gap can be reduced.

The matching oil 15 is a liquid having a refractive index closer to that of the fiber guide 12 than air. By filling the matching oil 15 between the multi-core fiber FBM and the fiber guide 12, it is possible to suppress the transmission of the laser beam LB through the air and irradiate the core C with the laser beam LB more uniformly. It will be possible.

<Optical fiber grating manufacturing method>
The optical fiber grating manufacturing method according to the present embodiment is basically the same as the optical fiber grating manufacturing method according to the fifth embodiment. However, in step S2, the multi-core fiber FBM is arranged so as to face the inner wall surface of the groove 12d of the fiber guide 12 with a slight gap, which is different from the fifth embodiment.

Further, it is different from the fifth embodiment in that a step of filling the gap between the multi-core fiber FBM and the fiber guide 12 with the matching oil 15 is provided between steps S2 and S3. When the fiber guide 12 is arranged below the multi-core fiber FBM, the matching oil 15 may be arranged in the groove 12d before arranging the multi-core fiber FBM in the groove 12d.

In this embodiment, an example of irradiating a multi-core fiber FBM with a laser beam LB to form a grating G has been described. However, as in the fifth embodiment, it is also possible to irradiate the single-core optical fiber FB with the laser beam LB to form the grating G.

[7th Embodiment]
<Optical fiber grating manufacturing equipment>
FIG. 18 is a diagram showing a schematic configuration of an optical fiber grating manufacturing apparatus according to a seventh embodiment of the present invention. In FIG. 18, the same reference numerals are given to the configurations similar to those shown in FIG. The optical fiber grating manufacturing apparatus 7 of the present embodiment has a point that the optical fiber grating manufacturing apparatus 1 shown in FIGS. 1 and 2 includes a transmission spool 16 and a take-up spool 17, and is a multi-core fiber having a coated CV as a whole. The difference is that the FBM is irradiated with the laser beam LB to form the grating G.

In the present embodiment, the coated CV is provided seamlessly in the entire length direction of the multi-core fiber FBM. That is, as in the sixth embodiment, there is no portion in the middle of the multi-core fiber FBM where the coated CV is removed and the outer surface of the strand (clad CL) is exposed.

The delivery spool 16 is arranged on the upstream side of the phase mask 11, the fiber guide 12, and the irradiation unit 13 (upstream side in the transport direction D4 of the multi-core fiber FBM). The delivery spool 16 delivers the multi-core fiber FBM in which the grating G is not formed in the transport direction D4 under the control of a control device (not shown). For example, the delivery spool 16 rotates by a rotation amount instructed by a control device (not shown) to intermittently deliver the multi-core fiber FBM in which the grating G is not formed by a certain length.

Further, the delivery spool 16 adjusts the tension applied to the multi-core fiber FBM on the upstream side of the phase mask 11, the fiber guide 12, and the irradiation unit 13 under the control of a control device (not shown). The tension applied to the multi-core fiber FBM by the transmission spool 16 is adjusted in order to adjust the Bragg wavelength of the grating G formed on the multi-core fiber FBM.

The take-up spool 17 is arranged on the downstream side of the phase mask 11, the fiber guide 12, and the irradiation unit 13 (downstream side in the transport direction D4 of the multi-core fiber FBM). The take-up spool 17 winds the multi-core fiber FBM on which the grating G is formed under the control of a control device (not shown). For example, the take-up spool 17 rotates by a rotation amount instructed by a control device (not shown) to intermittently wind the multi-core fiber FBM on which the grating G is formed by a certain length. The take-up spool 17 operates in conjunction with the delivery spool 16.

Further, the take-up spool 17 adjusts the tension applied to the multi-core fiber FBM on the downstream side of the phase mask 11, the fiber guide 12, and the irradiation unit 13 under the control of a control device (not shown). The tension applied to the multi-core fiber FBM by the take-up spool 17 is adjusted in order to adjust the Bragg wavelength of the grating G formed on the multi-core fiber FBM, similarly to the delivery spool 16.

As described above, the optical fiber grating manufacturing apparatus 7 of the present embodiment has a delivery spool 16 that sends out one end side of the multi-core fiber FBM and a take-up spool 17 that winds up the other end side of the multi-core fiber FBM. Therefore, it is possible to adjust the tension acting on the multi-core fiber FBM.

Further, the transmission spool 16 and the take-up spool 17 are movable in a direction in which the multi-core fiber FBM is brought close to or separated from the fiber guide 12 (in the example shown in FIG. 18, the vertical direction of the multi-core fiber FBM). .. The delivery spool 16 and the take-up spool 17 bring the multi-core fiber FBM close to the fiber guide 12 when irradiating the multi-core fiber FBM with the laser beam LB under the control of a control device (not shown). Further, the delivery spool 16 and the take-up spool 17 separate the multi-core fiber FBM from the fiber guide 12 when the multi-core fiber FBM is sent out or taken up under the control of a control device (not shown).

Since the transmission spool 16 and the take-up spool 17 can move in the direction in which the multi-core fiber FBM is brought close to or separated from the fiber guide 12, the multi-core fiber FBM is prevented from sliding with respect to the fiber guide 12. can. Therefore, it is possible to prevent the surfaces of the multi-core fiber FBM and the fiber guide 12 from being damaged or soiled.

In the present embodiment, an example in which the transmission spool 16 and the take-up spool 17 move the multi-core fiber FBM in the direction of approaching or separating from the fiber guide 12 has been described. However, the sending spool 16 and the take-up spool 17 may move the fiber guide 12 and the phase mask 11 so that the fiber guide 12 is separated from the multi-core fiber FBM without moving the multi-core fiber FBM.

Further, in the present embodiment, an example in which the multi-core fiber FBM is irradiated with the laser beam LB to form the grating G has been described. However, as in the fifth and sixth embodiments, it is also possible to irradiate the single-core optical fiber FB with the laser beam LB to form the grating G.

Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment and can be freely changed within the scope of the present invention. For example, the optical fiber FB and the multi-core fiber FBM may be a single clad fiber or a double clad fiber. The single clad fiber is an optical fiber having one cylindrical clad covering the outer surface of the core, and the double clad fiber is a cylindrical clad (inner clad) covering the outer surface of the core and the outer side of the inner clad. It is an optical fiber having a cylindrical clad (outer clad) that covers the side surface.

Further, in the first embodiment, the cross-sectional shape of the groove 12d of the fiber guide 12 is an arc having a constant radius of curvature. However, as shown in FIG. 19, the groove of the fiber guide 12 may be a groove 12 m having a cross-sectional shape that is half of an elliptical shape. FIG. 19 is a cross-sectional view showing another example of the groove of the fiber guide. As shown in FIG. 20, a large-diameter optical fiber FB may be installed in the groove 12 m so that a gap is provided between the groove 12 m and the bottom of the groove 12 m. FIG. 20 is a diagram showing a state in which a large-diameter optical fiber is installed in the groove shown in FIG.

Further, in the present invention, the cross-sectional shape of the groove provided in the fiber guide 12 is not limited to the above-mentioned example, and a parabolic shape, a shape obtained by halving the race track shape, and two straight lines are bent and connected. It can be made into various shapes such as a shape. Further, the contact surface 12c of the fiber guide 12 is not limited to a flat surface as in the above example, and may be a curved surface. For example, it may be a curved surface having a convex shape in the vertical direction shown in FIG. 2, or a curved surface having a concave shape.

Further, in the above embodiment, a configuration is adopted in which the grating G is formed by irradiating the core C with the laser beam LB in the ultraviolet region. However, the present invention is not limited to this. For example, it does not exclude the formation of the grating G by irradiating the core C with light other than the laser beam in the ultraviolet region.

The present invention can be widely used in the sensing field, the processing field, the communication field, and various other fields.

1-7 ... Optical fiber grating manufacturing equipment, 11 ... Phase mask, 11a ... Grating pattern, 12 ... Fiber guide (optical correction member), 12a ... Base, 12b ... Reinforcing part, 12c ... Contact surface, 12d ... Groove, 12e ... Open end, 12f ... Groove, 12g ... First straight part, 12h ... Second straight part, 12i ... Bottom arc part, 12j ... Groove, 12k ... Straight part, 12m ... Groove, 13 ... Irradiation unit, 14 ... Protective foil , 15 ... Matching oil (optical fluid), 16 ... Delivery spool, 17 ... Take-up spool, C ... Core, CL ... Clad, CV ... Coating, FB ... Optical fiber, FBM ... Multi-core fiber, G ... Grating, L ... Center Axis, LB ... Laser light

Claims (11)

An optical fiber grating manufacturing apparatus comprising a phase mask provided with a grating pattern and an irradiation unit for irradiating an optical fiber with laser light through the phase mask.
An optical correction member is provided between the phase mask and the optical fiber, the phase mask side is a flat surface, and the optical fiber side has a groove for installing the optical fiber.
The groove is formed so as to be parallel to the plane, and the end portion in the stretching direction is an open end.
The optical correction member is arranged so that the plane is parallel to the phase mask.
Optical fiber grating manufacturing equipment. The optical correction member is a member of the optical correction member, so that the laser light emitted to the optical fiber is not focused inside the optical fiber, so that the laser light emitted to the optical fiber is provided in a cross section orthogonal to the extending direction of the groove. The optical fiber grating manufacturing apparatus according to claim 1, wherein at least a part of the optical path of the laser beam is corrected by the groove. The optical fiber grating manufacturing apparatus according to claim 2, wherein the shape of the groove in a cross section orthogonal to the extending direction of the groove is an arc. The refractive index of the optical correction member is the radius of the circle region of the minimum radius including all the cores centered on the central axis of the optical fiber in the cross section orthogonal to the stretching direction of the groove, and the radius of the strand of the optical fiber. The value obtained by dividing by is set to be equal to or less than the value obtained by dividing the refractive index of air by the refractive index of the optical correction member.
The radius of curvature of the arc is equal to or greater than the radius of the wire of the optical fiber.
The optical fiber grating manufacturing apparatus according to claim 3. The shape of the groove in a cross section orthogonal to the extending direction of the groove is in contact with the peripheral surface of the optical fiber on one side with respect to the line connecting the central axis of the optical fiber and the deepest portion of the groove. The closest first straight line portion, the second straight line portion that is in contact with or closest to the peripheral surface of the optical fiber on the other side of the central axis of the optical fiber, the end portion of the first straight line portion, and the above. The optical fiber grating manufacturing apparatus according to claim 2, which has a shape having a bottom arc portion connecting an end portion with a second straight line portion. The refractive index of the optical correction member is the radius of the circle region of the minimum radius including all the cores centered on the central axis of the optical fiber in the cross section orthogonal to the stretching direction of the groove, and the radius of the strand of the optical fiber. The value obtained by dividing by is set to be equal to or less than the value obtained by dividing the refractive index of air by the refractive index of the optical correction member.
The radius of curvature of the bottom arc portion is equal to or less than the radius of the wire of the optical fiber.
The optical fiber grating manufacturing apparatus according to claim 5. The ratio of the energy density of the laser light after being incident on the optical fiber to the energy density of the laser light before being incident on the optical fiber is defined as the rate of change.
When the rate of change in which the energy density of the laser light after being incident on the optical fiber is the allowable lower limit value of the energy density required for the laser light incident on the optical fiber is set as the lower limit change rate.
The radius of curvature of the bottom arc portion is larger than the value obtained by multiplying the radius of the wire of the optical fiber by the lower limit change rate.
The optical fiber grating manufacturing apparatus according to claim 6. The optical fiber according to claim 5, wherein the depth of the groove is larger than the value obtained by multiplying the square of the sine and cosine value at half the angle of the central angle of the bottom arc portion by the radius of curvature of the bottom arc portion. Grating manufacturing equipment. The optical fiber grating manufacturing apparatus according to claim 2, wherein the shape of the groove in a cross section orthogonal to the extending direction of the groove is an angular shape in which a plurality of straight portions are bent and connected to each other. The optical fiber grating manufacturing apparatus according to any one of claims 1 to 9, further comprising a delivery spool that feeds out one end side of the optical fiber and a take-up spool that winds up the other end side of the optical fiber. It is an optical fiber grating manufacturing method in which a grating is formed on the core of an optical fiber.
A phase mask arrangement step of arranging a phase mask so as to be parallel to the plane on the plane side of the optical correction member having a plane on one side and a groove on the other side.
An optical fiber installation step for installing an optical fiber in the groove,
A grating forming step of irradiating the optical fiber with a laser beam through the phase mask and the optical correction member to form the grating.
Have,
The groove is formed so as to be parallel to the plane, and the end portion in the stretching direction is an open end.
Optical fiber grating manufacturing method.

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