JP2000028835A - Mask for forming chirp grating and formation of chirp grating - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to easily form chirped fiber grating having an arbitrary wavelength characteristic by using the same phase mask. SOLUTION: N pieces of grating stripe 53-1 to 53-N constituting a phase grating 52 of the mask are arrayed in such a manner that the X-direction spacings in a Y-direction top end side position are constant at a small set value and that the X-direction spacings in a Y-direction bottom end side position are constant at a large set value. The optical fibers 1 which are the objects for formation of the chirp gratings are extended in the X-direction and are intersected with the respective grating stripes. The optical fibers are so arranged as to pass the first grating stripe portion 54-1 between the first grating stripe 53-1 and second grating stripe 53-2 at the left end. Only the first grating stripe portions are irradiated with a UV laser beam. Next, the optical fibers are moved in parallel in the Y-direction and are so positioned as to pass the second grating stripe portion 54-2 between the second grating stripe portion 53-2 and the third grating stripe 53-3. Only the second grating stripe portion is irradiated with the UV laser beam.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber in which a diffraction grating (grating) having a refractive index difference is written in the form of a stripe in a core of an optical fiber, and the grating pitch of the grating stripe in the fiber axis direction. The present invention relates to a chirp grating creation mask and a chirp grating creation method used for easily creating a chirped grating (Chirped Fiber Grating) in which the chirp gratings are sequentially changed.

[0002]

2. Description of the Related Art Hitherto, as a fiber grating, there has been known a method of forming a grating on a core of an optical fiber by a two-beam interference method or a phase mask method (for example, JP-A-6-235808, JP-A-7-235808). No. 140311 and Japanese Patent No. 2521708). The phase mask method uses a mask 500a on which a phase grating 520a having a uniform grating pitch (mask pitch) as shown in FIG. 10 is formed. Irradiates a light-induced refractive index change at a corresponding portion of the core of the optical fiber, thereby producing a periodic refractive index modulation fringe corresponding to the uniform pitch of the phase grating in the fiber axis direction with respect to the core. Is formed (written). Such a fiber grating is considered to be applied to applications such as a filter, a duplexer, a dispersion compensator, a fiber laser mirror, and a temperature sensor by changing a period and a modulation shape of a refractive index modulation fringe. .

As one type of the fiber grating, there is known a chirp grating in which the period of the refractive index modulation fringes is sequentially increased or decreased in the fiber axial direction so that the intervals between the refractive index modulation fringes are different in the fiber axial direction. (IEICE Transactions on Communications C-1, Vol.J8
0-c-1, No. 1, January 1997, pp. 32-40).
Such a chirp grating is created using a chirp type phase mask 500b as illustrated in FIG. This mask 500b is different from that of FIG. 10 in the mask pitch from the grid stripe 530 at the start end (left end in the figure) to the grid stripe 530 at the end (right end) in the X direction of the X direction and the Y direction orthogonal to each other. The phase grating 520b is formed so as to increase sequentially. Then, by irradiating the optical fiber with ultraviolet laser light through such a mask 500b, a refractive index modulation fringe having a period corresponding to the mask pitch, that is, a chirp grating is written. Note that the above figures are shown as an image diagram because the unit of the mask pitch is on the order of μm, and the figures shown in FIG.
The grid pattern 530 is representatively shown for every 10 grid patterns, for example. Therefore, FIG.
The grid stripes having different directions in the direction are shown as one grid stripe 530 with 10 equally spaced mask pitches as one unit, and the mask pitch in the X direction changes (increases) for each unit. . An example of such a mask is a quartz glass plate having a thickness of about 1 mm in which a large number of linear grooves of minute width are formed as lattice fringes at a mask pitch on the order of μm as described above.

[0004]

By the way, in the above-described chirped grating, when this chirped grating is considered as a reflection filter or a transmission filter, the wavelength of light reflected or transmitted by the period of the refractive index modulation fringe written. That is, the wavelength characteristics are determined. For this reason, in order to have a wavelength characteristic according to the application as a chirp grating or a wavelength characteristic according to the wavelength of the light to be reflected and transmitted even if the application is the same, a refractive index modulation fringe of a specific period is converted into an optical fiber. Need to write to the core. This writing requires a mask having a mask pitch corresponding to the specific period. Therefore, if the wavelength characteristics required for the chirp grating are different, a phase grating having a different mask pitch is required for each required wavelength characteristic.

In this case, a single chirp grating forming mask as shown in FIG. 11 is used to form a chirp grating having a certain wavelength characteristic on one side of the mask in the X direction (for example, the left side of the drawing). By using the other range in the Y direction of the mask (for example, the long wavelength range which is the right range in the drawing) of the mask in order to create a chirped grating having other wavelength characteristics using one short mask, It is also conceivable to deal with the creation of chirp gratings having different wavelength characteristics. However, the mask length (length in the X direction) of the above mask
Is limited, and the range in which an arbitrary mask pitch can be selected, that is, the range in which the wavelength characteristic can be changed, is extremely limited. As a result, in order to manufacture chirp gratings having different chirp degrees, there is a disadvantage that a mask having a required chirp degree must be manufactured each time.

The present invention has been made in view of such circumstances, and an object of the present invention is to facilitate the production of a chirp grating, thereby facilitating the production of a chirp grating having an arbitrary wavelength characteristic. To be able to be created. Specifically, while providing a chirp grating creation mask capable of creating a chirp grating having an arbitrary wavelength characteristic different from one another, creation of a chirp grating having an arbitrary wavelength characteristic using such a mask It is to provide a method.

[0007]

In order to achieve the above object, a first aspect of the present invention is to provide a phase grating in which a large number of lattice fringes constitute a phase grating. The phase grating is formed so as to extend from one end to the other end, and the phase grating is formed on the optical fiber in a state where the optical fiber to be chirped with respect to the phase grating is positioned so as to extend in a direction intersecting the lattice fringes. The present invention relates to a chirp grating creating mask for creating a chirp grating on the core of the optical fiber by irradiating ultraviolet rays through the optical fiber. In the first invention, each of the plurality of lattice fringes adjacent to each other in the X direction is used as the plurality of lattice fringes.
Basically, the arrangement is such that the direction interval is larger at the other end position than at the one end position in the Y direction. Here, the distance between the two grid stripes adjacent to each other in the X direction is relatively small at the one end in the Y direction and relatively large at the other end in the X direction between the one end and the other end in the Y direction. The intervals in the X direction need not always be constant. Further, each of the lattice fringes may extend from one end side to the other end side in the Y direction so as to pass through respective positions at predetermined intervals in the X direction on both sides. Therefore, each grid stripe may be curved and extend between the two Y-direction positions as long as it passes through such a position. However, from the viewpoint of facilitating grasp of the grid stripe interval (mask pitch) at an arbitrary position in the Y direction. It is preferable that the lattice fringes be extended linearly.

In the case of the chirp grating producing mask of the first invention, the interval in the X direction between the lattice fringes of the phase grating increases from one end in the Y direction to the other end. Therefore, the optical fiber for which the chirp grating is to be prepared is arranged so as to intersect each of the lattice fringes of the phase grating, preferably to extend in the X direction so as to intersect with each of the lattice fringes, and to move the optical fiber from this initial position to Y. When the optical fibers are sequentially moved in the direction, the intervals in the X direction of the respective lattice fringes at which the optical fibers intersect sequentially increase with each movement. Therefore, the optical fiber arranged at the initial position is irradiated with ultraviolet rays at a relatively narrow interval between the lattice stripes at one end in the X direction of the phase grating to thereby reduce the mask pitch of the lattice stripe having the narrow interval. A portion of the refractive index modulation fringe having a corresponding period is written on the optical fiber, and then the optical fiber is moved by a predetermined amount in the Y direction to move the refractive index modulation fringe to the portion of the optical fiber adjacent to the X direction in the X direction. X of the checkerboard part irradiated with ultraviolet rays
By irradiating ultraviolet rays through the lattice fringe portions adjacent in the direction, the refractive index modulation fringes having a wider cycle than the portion of the refractive index modulation fringes written at the above initial position are written. Then, by repeating the operation of moving the optical fiber by a predetermined amount and irradiating the optical fiber with ultraviolet rays through the lattice stripes adjacent to each other in the X direction, while using the same mask, the optical fiber differs in the fiber axial direction. It is possible to create a chirp grating having an arbitrary period, that is, an arbitrary chirp degree.

Here, each of the lattice fringes constituting the phase grating is:
It is preferable that the X-direction interval at the one end position in the Y direction is relatively small and the interval is relatively constant, while the X-direction interval at the other end position in the Y direction is relatively large and the interval is preferably constant. . That is, one end in the Y direction,
By adding a condition that the X-direction interval is constant at each position in addition to the magnitude relationship of the X-direction interval at each position with the other end side, the mask pitch at any position in the Y direction can be grasped. It becomes even easier, and it becomes even easier to create a chirp grating by the chirp grating creation method described below. Also,
From the viewpoint of facilitating the grasp of the mask pitch of each of the lattice stripes at which the optical fibers intersect after such a movement, it is preferable that the movement of the optical fiber be translated in the Y direction.

Further, the mask base material is formed in a rectangular flat plate shape formed by sides extending in the X direction and the Y direction, respectively. It is preferable to extend in the Y direction. As a result, the phase grating specified in the relationship between the X and Y directions orthogonal to each other and the mask substrate on which the phase grating is formed are related to each other based on both the X and Y directions. Thus, both the facilitation of the formation of the phase grating with respect to the mask base material and the positioning of the optical fiber with respect to the phase grating can be performed based on the mask base material, thereby facilitating the positioning of the optical fiber.

A second invention relates to a method for producing a chirp grating using the chirp grating producing mask according to the first invention. That is, the second invention irradiates an optical fiber to be formed with ultraviolet rays from a certain direction through a mask on which a phase grating is formed as described in claim 4, thereby chirping the core of the optical fiber. A method for producing a chirped grating for producing a grating, wherein, as the mask, a large number of lattice fringes constituting a phase grating are arranged in a Y direction in an X direction and a Y direction orthogonal to each other on a surface of a mask substrate.
The plurality of lattice stripes are formed so as to extend from one end side in the direction to the other end side, and the interval between two lattice stripes adjacent to each other in the X direction is larger at the other end position than at the one end position in the Y direction. Are arranged as described above. Then, in the second invention, after covering the optical fiber with the mask facing the surface on which the phase grating is formed, the following initial position setting step, initial irradiation step, moving step, The irradiation step is performed, and the above-described moving step and the selective irradiation step are alternately repeated until a refractive index modulation fringe at the terminal position of the chirp grating for forming the moving step and the selective irradiation step is formed. That is, in the initial position setting step, the optical fiber is selected as an initial position from the lattice stripes at one end in the Y direction and one end in the X direction of the phase grating with respect to the irradiation direction of the ultraviolet light with respect to the irradiation direction of the ultraviolet light. The position is set so as to intersect with the checkered part. Next, as an initial irradiation step, a refractive index modulation fringe is formed at the start position of the chirp grating by irradiating the optical fiber with the ultraviolet light so that the ultraviolet light passes only through the lattice fringe portion. Then, in the moving step, any one of the irradiated optical fiber and the mask is so moved that the irradiated optical fiber is moved in parallel by a set amount toward the other end in the Y direction of the phase grating. One is moved relative to the other in parallel with the Y direction to temporarily stop. After the temporary stop, as a selective irradiation step, the temporarily stopped optical fiber is selected at a position on the other end side in the X direction from the lattice stripe portion which is to intersect the irradiation direction of the ultraviolet ray and which is irradiated before the movement. By irradiating ultraviolet rays so as to pass through only the lattice fringe portion, a refractive index modulation fringe adjacent from the start end position to the end side of the chirp grating is selectively formed.

In the case of the second invention, in the initial position setting step, the optical fiber is positioned with respect to a lattice fringe portion corresponding to the refractive index modulation fringe on the start end side of the chirp grating to be written into the optical fiber, and the next initial irradiation is performed. The process forms the refractive index modulation fringe portion on the start end side. Next, the relative positional relationship between the optical fiber and the phase grating is changed by the moving step, and the optical fiber intersects with the lattice fringe having a wider mask pitch than the lattice fringe part irradiated in the initial irradiation step. For this reason, the refractive index modulation fringe portion having a wider cycle than the refractive index modulation fringe portion created by the initial irradiation process after being irradiated with ultraviolet rays by the subsequent selective irradiation process is formed next to the X direction. Become. By sequentially repeating such a moving step and a selective irradiation step, a chirp grating is created in a range up to the refractive index modulation fringe portion on the end side of the planned chirp grating. At this time, it is possible to change and set the mask pitch of the lattice fringe of the phase grating, at which the optical fibers intersect, depending on the magnitude of the parallel movement amount (set amount) in the moving step. Since the range of the lattice stripe portion in the X direction in which the ultraviolet ray is irradiated in the irradiation step can be arbitrarily selected and set, a chirp grating with an arbitrary chirp degree can be created by one mask.

In the second invention, the relative movement between the mask and the optical fiber in the moving step is performed by fixing the mask at a fixed position and moving the optical fiber parallel to the mask, or vice versa,
Either of fixing the optical fiber at a fixed position and moving the mask parallel to the optical fiber may be adopted. If the former mask is fixed at a fixed position, the irradiation system for irradiating ultraviolet rays must also be translated in parallel with the optical fiber. This is a preferable device.

In the above-mentioned irradiation step, after irradiating ultraviolet rays to the grid stripes on one side in the X direction of the phase grating where the optical fibers intersect, the range of the grid stripes to be irradiated at each temporary stop position is changed to the above-mentioned phase grating. It is preferable that ultraviolet rays are irradiated while sequentially moving to the range of the lattice fringes adjacent to the other side in the X direction. By sequentially moving to the lattice fringe range adjacent to the other side in the X direction, it is easy to grasp the mask pitch of the lattice fringe at the paused position, that is, to grasp by calculation or the like. The change setting of the cycle can be performed more reliably.

[0015] In the case of a short-period fiber grating, the chirped grating produced in this way can correct the difference in the propagation speed based on the difference in the wavelength of the light propagating in the optical fiber, for example, at the same time. In the case of long-period fiber gratings, for example, it can be applied to a gain equalizer to eliminate light of a certain wavelength from light propagating in an optical fiber. can do.

[0016]

Embodiments of the present invention will be described below with reference to the drawings.

<First Embodiment> FIG. 1 shows a chirp grating produced using a chirp grating producing mask according to a first embodiment of the present invention, and 1 denotes a light to be produced (written) for a chirp grating. An optical fiber core 2 having a predetermined length as a fiber is provided with refractive index modulation fringes 21, 21,... Constituting a chirp grating.
3 is a cladding of the optical fiber core wire 1, 4 is a coating layer coated on the outer surface of the cladding 3,
Reference numeral 5 denotes a mask for forming the refractive index modulation fringes 21. In each of the refractive index modulation fringes 21, the period (interval) of both refractive index modulation fringes 21 and 21 adjacent to each other sequentially increases from left to right in the figure in the fiber axis direction (X direction) and becomes longer wavelength side. It was written to migrate.

The mask 5 will be described. The mask 5 is a flat mask base material 51 made of, for example, quartz glass.
A phase grating 52 having a predetermined shape is formed on one side surface (the surface facing the optical fiber core wire 1). As shown in FIG. 2, the mask base material 51 has four sides 511, 512, 5 extending in the X direction and the Y direction orthogonal to each other in plan view.
13, 514, and a phase grating 52 is formed on one side surface of the mask base material 51 in a manner defined by the X direction and the Y direction.

The phase grating 52 is provided on the mask substrate 51.
(N) of lattice fringes 53, 53, 53, 53 extending in a straight line from one end to the other end in the Y direction.
(Hereinafter, an unspecified lattice fringe is represented by reference numeral 53). Each lattice 53
2 will be described with reference to the image diagram of FIG. 2. In the X direction of any two adjacent lattice fringes 53, 53 adjacent to each other at one end of the N lattice fringes 53, 53,. The interval becomes constant at a preset small set value M1 as a relatively small value, and the X-direction interval between the arbitrary two lattice fringes 53 at the other end (the lower end in the drawing) in the Y direction is relatively small. They are arranged so as to be constant at a large set value M2 preset as a large value. Then, the first lattice stripe 53 on the left end (start end) side of FIG.
-1 is arranged in parallel with the left side 512 extending in the Y direction, and the second grid pattern 5 adjacent to the right side of the first grid pattern 53-1 in the X direction.
3-2 is slightly inclined with respect to the first lattice stripe 53-1, and the third lattice stripe 53-3 adjacent to the right side of the second lattice stripe 53-2 is slightly inclined with respect to the second lattice stripe 53-2. The first grid pattern 53-1 on the start end side is arranged so as to be inclined.
From the end to the N-th grid stripe 53-N on the end (the right end in the same figure), the inclination in the Y direction is gradually reduced.

More specifically, each of the lattice fringes 53 in FIG. 2 has a plurality of (for example, 10) lattice fringes as one unit, and ten lattice fringes are represented by one lattice fringe 53. This is shown as an image diagram. That is, FIG. 3 shows the eighth grid pattern 5 shown in FIG.
As shown in an enlarged manner at the lower end portion in the vicinity of the 3-8 to the tenth lattice stripes 53-10, the lattice stripes 53-7 to 53-11 each have 10 lattice lattices.
And the X-direction interval between the ten grid stripes is also the X-direction interval M of each of the grid stripes 53-7 to 53-11.
They are arranged so as to have a constant value at m1 of 1/10 of 2. Although only the other end (lower end) in the Y direction is shown in FIG. 3, the X-direction interval at one end (upper end) in the Y direction of each of the ten grid stripes is also the same as each of the grid stripes 53-7 to 53-5.
They are arranged so as to have a constant value at m1 of 1/10 of the distance M1 in the X direction of 3-11. Each of the ten grid stripes is formed by engraving a linear groove on the surface of the mask substrate 51 as shown in FIG.

As an example of the distances m1 and m2 in the X direction, in the case of a chirp grating mask in a short-period fiber grating, m1 = 0.9 μm m2 = 1.15 μm is a typical example. If the dimension in the X direction on the upper end side of the lattice 52 is about 58 mm, the X on the lower end side
The dimension in the direction is about 74 mm, and the dimension in the Y direction is preferably about 60 mm. In the case of a chirp grating mask in a long-period fiber grating, m1 = 200 μm m2 = 250 μm is a typical example. In this case, if the dimension in the X direction on the upper end side of the phase grating 52 is set to about 40 mm, the lower end is reduced. X on the side
The dimension in the direction is about 50 mm, and the dimension in the Y direction is 5
It is preferable to set it to about 0 mm.

Next, an outline of an apparatus for producing a chirped grating using the above-described mask 5 will be described with reference to FIG. 5. First, an optical fiber whose fiber axis direction is matched with the X direction described above. Immediately before the core 1, the mask 5 is disposed so that the phase grating 52 faces the optical fiber core 1.
From the d-YAG laser light source 6, for example, four times the wavelength (4
ω) of 266 nm is emitted while being condensed by the cylindrical lens system 7. In the same figure, reference numeral 8 denotes a beam expander for expanding the ultraviolet laser beam into a parallel beam, 9 denotes a slit having a minute width for cutting out a portion where the power of the above-mentioned parallel laser beam is uniform and 10;
Is a movable reflection mirror.

While the mask 5 is fixed at the initial setting position, the Nd-YAG laser light source 6, the cylindrical lens system 7, the beam expander 8, the slit 9, the reflection laser 10, and the ultraviolet laser irradiation system 11, The optical fiber holding system that holds the fiber core 1 is held so as to be integrally movable and adjustable in the Y direction (a direction perpendicular to the plane of FIG. 5) by a moving mechanism (not shown). As an example of such a moving mechanism, the ultraviolet laser irradiation system 11 and the optical fiber holding system are connected by the ultraviolet laser light to the optical fiber core 1.
The XY table mechanism may be supported in a state where the two parts are coupled to each other in such a positional relationship as to irradiate the core 2 and are relatively immovable.

In addition, the reflection mirror 10 of the ultraviolet laser irradiation system is configured to be movable so as to be movable in the X direction (the same direction as the fiber axis direction). The movement of the moving mechanism in the Y direction and the movement of the reflecting mirror 10 in the X direction are controlled by control means (controller) using a microprocessor (not shown).
The irradiation position of the ultraviolet laser light on the mask 5 is controlled to be changed in each of the X direction and the Y direction.

Next, a method of forming a chirped grating by the above-described forming apparatus using the mask 5 will be described.

To create a chirp grating,
First, after performing the initial position setting step and the initial irradiation step at the start end position of the chirp grating to be created, the moving step and the selective irradiation step are performed to form a refractive index modulation fringe at the end position of the chirp grating. Alternately until

That is, as the initial position setting step,
The above optical fiber core wire 1 is connected to the optical fiber core wire 1 shown in FIG.
As shown by a solid line in FIG.
2 is set so as to extend in the same direction as the X direction at one end side in the Y direction. At this time, the optical fiber core 1
Is the optical fiber core 1 from the phase grating 52 with a grating fringe portion (for example, a grating fringe portion indicated by 54-1 in FIG. 7) having an X-direction interval corresponding to the period of the refractive index modulation fringe 21 at the start position of the chirp grating. Are set so as to pass (see the dashed line in FIG. 7). Next, as an initial irradiation step,
By irradiating only the lattice stripe portion 54-1 with the ultraviolet laser beam, the refractive index modulation stripe 21 on the starting end side is written on the core 2 of the optical fiber core 1.

Next, in the moving step, the moving mechanism is controlled by the control means to move the optical fiber holding system and the ultraviolet laser beam irradiation system 11 in parallel in the Y direction by a set amount. Pause. At this time, the set amount to be translated is a lattice fringe portion having an X-direction interval corresponding to the cycle from the refractive index modulation fringe 21 at the start end position to the next refractive index modulation fringe 21 (for example, 54-2 in FIG. 7). (The lattice fringe portion shown) is determined so that the optical fiber core wire 1 passes therethrough. In addition, the reflecting mirror 10 is slightly moved in the X direction by the control signal from the control means so that the ultraviolet laser light for irradiating the irradiation position of the ultraviolet laser light passes through the lattice stripe portion 54-2 in FIG. Let it. Then, as the selective irradiation step, an ultraviolet laser beam is applied only to the lattice stripe portion 54-2 to the optical fiber core wire 1 in the pause state, and the refractive index modulation stripe 21 on the start end side is adjacent to the X direction. The refractive index modulation fringe 21 is connected to the optical fiber core 1 as described above.
Is written to the core 2.

Thereafter, the lattice stripe portions to be irradiated with the ultraviolet laser beam (for example, the lattice stripe portions indicated by 54-3 and 54-4 in FIG. 7) are sequentially selected, and the above-described moving step and the selective irradiation step are alternately repeated. I should go. Thus, the refractive index modulation fringes 21 are provided on the core 2 of the optical fiber core 1 such that the period in the fiber axis direction increases sequentially in accordance with the X-direction interval of the lattice fringe portions 54-1, 54-2,. , 21,... Are written. FIG. 7 shows, by bold lines, examples of lattice fringe portions selected to form refractive index modulation fringes 21, 21,... Having a period corresponding to the wavelength characteristic expected to be possessed by the chirp grating to be produced. . That is, the first grid pattern 53-1 and the second grid pattern 53-2
The checkerboard portion 54-1 is selected, and the second checkerboard 53-2 and the third checkerboard 53-2 are selected.
The second lattice fringe portion 54-2 is selected between the third lattice fringe 53-3 and the fourth lattice fringe 53-4.
The interval in the X direction is sequentially increased so that the checkerboard portion 54-3 is selected to have a predetermined size.

That is, by changing the set amount of the parallel movement in the moving step, the interval in the X direction of the lattice fringe portion can be changed to an arbitrary value. It becomes possible to write the refractive index modulation fringes 21 having an arbitrary period corresponding to the changed interval in the X direction. Therefore, it is possible to create a chirp grating whose period is arbitrarily changed in the fiber axis direction using one mask 5.

FIG. 8 shows an example different from that of FIG. 7 in selecting the lattice fringe portion to be irradiated with the ultraviolet laser light. That is, as shown by a thick line in FIG. 8 as a grid stripe portion selected from the phase grating 52,
The first grid stripe portion 55-1 is selected between -1 and the third grid stripe 53-3, and the second grid stripe portion 55-2 is selected between the third grid stripe 53-3 and the fifth grid stripe 53-5. And the fifth plaid 53-5
The third lattice fringe portion 55-3 is selected between the third lattice fringe 53-7 and the seventh lattice fringe 53-7, and the lattice fringe portions at intervals in the X direction according to the wavelength characteristic expected for the chirp grating to be created are freely selected. be able to.

FIG. 9 shows a phase grating 52 'having a different arrangement from the phase grating 52 shown in FIG. That is, the phase grating 52 'shown in FIG. 9 has a small set value M1 as an X-direction interval at one end position in the Y direction, and a small set value M1 at the other end position in the Y direction.
As shown in FIG.
In this example, N grid stripes 53-1 to 53-N are arranged so as to form a mountain shape as a whole, although the intervals are set to be the same as the phase grating 52 of FIG. Even with such a phase grating 52 ', it is possible to create a chirped grating whose period is arbitrarily changed in the fiber axis direction, as in the case of the phase grating 52 of FIG. However, in this case, in the moving step, in addition to the movement of the ultraviolet irradiation system 11 and the optical fiber holding system in the Y direction, the lattice fringe portion to be irradiated with the previous ultraviolet laser beam and the current lattice fringe portion are not moved. It is necessary to perform position correction in the X direction between the two.

The phase gratings 52, shown in FIGS.
Regardless of which one of the optical fibers 52 'is used, if the optical fiber core 1 is arranged so as to extend in the X direction at an arbitrary Y direction position, the X of each of the lattice stripes 53 intersecting the optical fiber core 1 is determined.
Since the direction intervals are all constant values, by irradiating ultraviolet laser light over the entire length in the X direction of the phase grating at a position intersecting with the optical fiber core 1, the optical fiber core 1 is irradiated.
Gratings having the same period are written in the core 2 of the optical fiber in the axial direction of the optical fiber. Therefore, not only a chirp grating but also a normal fiber grating can be formed using the same mask 5.

In the method of producing a chirped grating described above, the optical fiber to be irradiated with the ultraviolet laser beam through the mask 5 is an optical fiber consisting of the core 2 and the clad 3 without the coating layer 4. , Coating layer 4
May be used, and any optical fiber can produce a chirped grating. When a chirped grating is formed by irradiating an ultraviolet laser beam from the outside of the coating layer 4, in order to steadily increase the photo-induced refractive index change of the core 2, in addition to the same concentration of Ge as that of the normal specification core, Ge is added. Sn or S
The core 2 is preferably formed by adding dopants of n and Al or Sn, Al and B. Or,
Similarly, in order to increase the photoinduced refractive index change, the core 2 may be filled with high-pressure hydrogen before irradiation with ultraviolet rays. Further, it is preferable that the coating layer 4 is formed of an ultraviolet transmitting resin having a property of transmitting ultraviolet light.

[0035]

As described above, according to the chirp grating forming mask according to the first aspect of the present invention, using one mask, the period in the fiber axis direction can be determined. It becomes possible to prepare a chirp grating of a refractive index modulation fringe having an arbitrary increasing or decreasing degree, that is, a chirp grating having a chirp degree exhibiting an arbitrary wavelength characteristic.

According to the chirp grating creating method of the second aspect of the present invention, the amount of parallel movement (set amount) in the moving step is set to be large or small, and ultraviolet rays are emitted in the selective irradiation step. By setting the range of the lattice fringe portion in the X direction to be irradiated, it is possible to easily and reliably create a chirp grating having a chirp degree exhibiting an arbitrary wavelength characteristic using the same mask.

[Brief description of the drawings]

FIG. 1 is an explanatory cross-sectional view showing a chirp grating to be produced according to the present invention.

FIG. 2 is an image diagram of a chirp grating producing mask according to an embodiment of the present invention as viewed from the front.

FIG. 3 is a partially enlarged view of the phase grating of FIG. 2;

FIG. 4 is an enlarged sectional view taken along line AA of FIG. 3;

FIG. 5 is a schematic diagram of an apparatus for producing a chirp grating.

FIG. 6 is a perspective view showing the principle of a method for producing a chirp grating.

FIG. 7 is an explanatory diagram showing an example of selection of a lattice fringe portion for irradiating an ultraviolet laser beam to a phase grating.

8 is a diagram corresponding to FIG. 7, showing a selection example different from that of FIG. 7;

FIG. 9 is a view showing a chirp grating creating mask according to an embodiment of the present invention having an arrangement different from that of FIG. 2;
FIG.

FIG. 10 is a front image diagram showing an example of a conventional phase mask used for producing a fiber grating.

FIG. 11 is a front image diagram showing an example of a conventional phase mask used for producing a chirp grating.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Optical fiber core wire (optical fiber) 2 Core 5 Mask (Chirp grating creation mask) 21 Refractive index modulation stripe 51 Mask base material 52, 52 'Phase grating 53 Lattice stripe 53-1 to 53-N Lattice stripe 54-1 ... Lattice stripe Part 55-1 ... Plaid part XX direction Y Y direction

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Yasuhide Sudo 4-3 Ikejiri, Itami-shi, Hyogo Mitsubishi Electric Cable Industry Co., Ltd. Itami Works F-term (reference) 2H049 AA04 AA14 AA59 2H050 AC03 AC82 AC84 AD00

Claims (7)

[Claims] 1. A large number of lattice fringes constituting a phase grating are formed on a surface of a mask base material so as to extend from one end side in the Y direction in the X direction and the Y direction orthogonal to each other, to the other end side.
The chirp grating is formed by irradiating the optical fiber with ultraviolet light through the phase grating in a state where the optical fiber to be chirped with respect to the phase grating is positioned so as to extend in a direction intersecting each of the lattice fringes. A chirp grating forming mask formed on the core of the optical fiber, wherein the plurality of lattice fringes is arranged such that an interval between two lattice fringes adjacent to each other in the X direction in the X direction is closer to the other end than the position in the Y direction. A chirp grating creation mask, which is arranged so as to be larger at a position. 2. The method according to claim 1, wherein each of the lattice fringes forming the phase grating has a relatively small interval in the X direction at one end position in the Y direction and a constant interval in the X direction at the other end position in the Y direction. A chirp grating producing mask, wherein the intervals are relatively large and are arranged so as to be constant. 3. The mask substrate according to claim 1, wherein the mask base material is formed in a rectangular flat plate shape formed by sides extending in the X direction and the Y direction, respectively, and one side in the X direction of a large number of grid stripes forming the phase grating. A chirp grating creating mask, wherein a lattice fringe at an end position extends in the Y direction. 4. A chirp grating producing method for producing a chirp grating on the core of the optical fiber by irradiating an optical fiber to be produced from a certain direction through a mask on which a phase grating is formed. In the mask, a large number of lattice fringes forming a phase grating are orthogonal to each other in the X direction and the Y direction on the surface of the mask substrate.
The plurality of lattice fringes are formed such that each interval between two lattice fringes adjacent to each other in the X direction is the other end than the position in the Y direction one end. After using the thing arranged so that it may become large in a side position, covering the above-mentioned optical fiber with the above-mentioned mask facing the side where the phase grating was formed, the above-mentioned optical fiber is covered with the above-mentioned ultraviolet rays An initial position setting step of setting a position on the one end side in the Y direction of the phase grating with respect to the irradiation direction and intersecting a lattice stripe portion selected as an initial position from the lattice stripes on the one end side in the X direction; An initial irradiation step of forming a refractive index modulation fringe at the starting end position of the chirp grating by irradiating the optical fiber with the ultraviolet light so as to pass only through the lattice fringe portion; One of the optical fiber after irradiation and the mask is moved relative to the other such that the optical fiber after irradiation is in a state of being translated by a set amount toward the other end in the Y direction of the phase grating. A moving step of making relative movement in parallel with the Y direction to temporarily stop, and a lattice stripe in which the optical fiber in the suspended state intersects with the irradiation direction of the ultraviolet ray, wherein the lattice stripe radiated before the movement is in the X direction and the like. A selective irradiation step of selectively forming adjacent refractive index modulation fringes from the start end position to the end side of the chirped grating by irradiating ultraviolet rays so as to pass through only the selected lattice fringe portion at the end side position is sequentially performed. The moving step and the selective irradiation step are alternately repeated until a refractive index modulation fringe at the end position of the chirp grating to be formed is formed. Chirped grating created wherein the. 5. The method according to claim 4, wherein the moving step is performed by fixing the mask at a fixed position and moving the optical fiber parallel to the mask. 6. The method according to claim 4, wherein the moving step is performed by fixing the optical fiber at a fixed position and moving the mask parallel to the optical fiber. 7. The method according to claim 4, wherein, as the irradiating step, after irradiating the ultraviolet rays to the grid stripes in the X direction on one side in the X direction of the phase grating where the optical fibers intersect, the grid stripes to be irradiated for each temporary stop position are changed. A method for producing a chirped grating, characterized in that the phase grating is successively moved to a range of a lattice fringe adjacent to the other side in the X direction of the phase grating and irradiated with ultraviolet rays.