JP2000066041A - Manufacturing method of fiber grating and manufacturing device thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily manufacture a fiber grating permitting to suppress noise generation caused especially by ripples in a reflection characteristic. SOLUTION: An ultraviolet laser beam radiated from a laser source 6 of a front irradiating system 6 via a beam expander 8 and slit 9 is branched by a beam splitter 15, and is changed in the irradiating direction by a reflecting mirror 16 and a movable reflecting mirror 10 of a rear irradiating system 32, and a range P is irradiated from the other side (backward) via an optical system 14 which alters the beam irradiating quantity to a specified characteristic. While keeping both positions of the front irradiation and the rear irradiation at the same relative position, the reflecting mirrors 10 are synchronously controlled with a synchronous interlocking mechanism 41 to move from one end to the other in the direction of the fiber axis, and the forward irradiation and the backward irradiation are carried out at the same time. In such a manner, a flat refractive index profile is obtained by carrying out a simultaneous apodization to make an average refractive index constant in the direction of the fiber axis.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fiber grating capable of minimizing and suppressing the generation of noise such as ripples and side lobes which are problematic when a fiber grating is used as a filter for reflecting light of a specific wavelength. The present invention relates to a method and apparatus for producing a fiber grating used for producing a fiber grating.

[0002]

2. Description of the Related Art Conventionally, in the case where a fiber grating is used as a reflection filter, various methods for suppressing noise such as ripble and side lobes in order to improve the reflection characteristic (wavelength selectivity) with respect to the wavelength of the light to be reflected. Techniques have been attempted.

[0003] Of these methods, methods for suppressing the generation of ripples can be roughly classified into two methods: a method using a core material of an optical fiber to be written with a grating, and a method for manufacturing a grating. There are two types;

[0004] As a device using the above-mentioned core material to add a device, a device utilizing the thermal diffusion of a core dopant has been proposed (Satoshi Okude et al., "Chirped fiber utilizing thermal diffusion of a core dopant"). Grating ", IEICE Technical Report, OPE96-8, pp43-48, 1996, The Institute of Electronics, Information and Communication Engineers). This means that 100
When heated to a high temperature exceeding 0 ° C., in consideration of the fact that the core dopant contained in the core is thermally diffused and the refractive index profile of the effective refractive index changes, the optical fiber is heated by an oxyhydrogen flame before writing the grating. After the diffusion, the grating is written by irradiating ultraviolet light (ultraviolet laser light) to a half of the range of the fiber axis direction in which the refractive index profile has changed.

[0005] In addition, as a method of devising the above-described method of manufacturing the grating, the irradiation of ultraviolet light to the optical fiber is divided into two times and apodization (Apodizatio) is performed.
n) has been proposed (Tetsuro Komukai et al., "Application of Fiber Grating to Spectral Filtering", IEICE Transactions, C-1, Vol. J80-
C-1, No. 1, pp. 32-40, January 1997). This is because the first irradiation of the ultraviolet laser beam to the optical fiber is performed without a phase mask so that the change in the refractive index gradually decreases from the periphery to the center of the range in the fiber axis direction with respect to the portion to be written. Is controlled by a spatial filter, and in the second time, with the phase mask interposed, the beam irradiation amount is changed in such a manner that the refractive index change gradually increases toward the center of the fiber axial direction range. By controlling with a spatial filter, the average refractive index of the core in the fiber axial direction is made substantially constant.

[0006] The above-mentioned ripple causes a Gaussian profile in which a change in the refractive index in the fiber axis direction becomes convex at the center position in the fiber axis direction, and a ripple caused by Fabry-Perot resonance occurs. In order to prevent this, in the method using the thermal diffusion of the core dopant, half of the range of the refractive index profile changed by heating as described above in the fiber axial direction is used as the writing portion of the grating, and the apodization method is performed twice. The average refractive index after irradiation is made substantially constant in the fiber axis direction.

[0007]

However, in the above-mentioned method using a core material or in the method of performing apodization by dividing the irradiation into two times, the process of fabricating the fiber grating increases, which takes time and effort. There is a disadvantage that the manufacturing apparatus itself becomes large-scale. That is, in the above-described method of changing the refractive index profile by thermal diffusion of the core dopant, it is necessary to apply a non-uniform and specific pattern of heating in the fiber axis direction of the portion to be written, and to irradiate ultraviolet light. When writing a grating, it is necessary to suppress the occurrence of ripples by irradiating ultraviolet light to exactly half the fiber axial direction range around the peak position of the refractive index profile changed by the above thermal diffusion. After the above-mentioned heating, it is necessary to measure and grasp the refractive index profile to accurately determine the starting point of the irradiation position of the ultraviolet light, and these operations and operations require a great deal of labor.

Further, in the above-described method of performing apodization by dividing the irradiation into two times, it is necessary to exactly match the first irradiation range and the second irradiation range in the fiber axis direction, so that the second irradiation is performed. It is necessary to accurately position the start position and the end position in the fiber axial direction, and since the first irradiation and the second irradiation are performed with a time lag, the refractive index is increased by the first irradiation. It is necessary to cause the refractive index change due to the second irradiation to the refractive index profile after the change in the direction of the fiber axis by accurately corresponding to the above refractive index profile, which requires a great deal of work and operation. It will cost.

The present invention has been made in view of such circumstances, and an object of the present invention is to easily produce a fiber grating capable of suppressing noise generation in reflection characteristics, particularly due to ripple.

[0010]

In order to achieve the above object, the present invention provides apodization in which a lattice fringe is formed by causing a refractive index modulation at a predetermined grating pitch in the direction of the fiber axis which is the main body of the grating. Of ultraviolet light for irradiation and ultraviolet light irradiation for homogenizing the average refractive index in the fiber axial direction range where the lattice fringes are formed, one of the irradiations is orthogonal to the fiber axis direction of the grating writing portion. The above two types of irradiation are simultaneously performed by separately performing the irradiation from one side in the direction and the other irradiation from the other side in the orthogonal direction.

(First invention) Specifically, a first invention according to a fiber grating manufacturing method is directed to a method of manufacturing a fiber grating, wherein the fiber is provided on a portion of the optical fiber to be written where the grating is to be written. A first irradiation step of irradiating ultraviolet light from one side in a direction orthogonal to the axial direction to cause a refractive index modulation on the core of the optical fiber at every predetermined grating pitch in the fiber axis direction, and On the other hand, by irradiating ultraviolet light from the other side in the orthogonal direction simultaneously with the irradiation of the ultraviolet light in the first irradiation step, refraction having a change characteristic opposite to the change characteristic of the average refractive index of the core in the first irradiation step is performed. A second irradiation for causing a refractive index modulation in the core to make the average refractive index uniform in the fiber axis direction at the portion to be written; Is that a degree.

Here, in the "first irradiation step", one ultraviolet laser beam is split into two beams by a beam splitter, and the two beams are caused to interfere with each other to irradiate an optical fiber, thereby refracting the laser beam at a predetermined grating pitch. Two-beam interferometry that causes rate modulation, or by disposing a phase mask having diffraction grating fringes of a predetermined pitch formed immediately before the optical fiber and irradiating the optical fiber with ultraviolet laser light through this phase mask Conventionally known methods such as a phase mask method for producing a refractive index modulation of the grating pitch corresponding to the pitch of the diffraction grating fringes (for example, JP-A-6-235808, JP-A-7-144031, JP-A-2521708) Publication). By irradiating a germanium (Ge) -doped core glass with an ultraviolet laser beam, a light-induced refractive index change is caused at a corresponding location, so that a semi-permanent refractive index modulation fringe (grating) is generated (written). It has become.

[0013] In the "second irradiation step", when the first irradiation step is performed using the above-mentioned phase mask, the second irradiation step is performed without the above-mentioned phase mask. Ultraviolet light is radiated through an optical system (for example, a filter) having a transmission characteristic corresponding to a refractive index profile required for causing a refractive index modulation of an inverse change characteristic to make the average refractive index uniform. I just need.

Further, in particular, when the first irradiation step is performed using a phase mask, the first and second irradiation steps are performed by setting the irradiation position of the ultraviolet light to one end of the fiber axial range of the portion where the grating is to be written. It is preferable that the irradiation is performed while the irradiation position in the first irradiation step and the irradiation position in the second irradiation step are aligned with each other in the fiber axis direction. The irradiation position may be sequentially moved in the fiber axis direction. Further, in the first irradiation step, the average refractive index change of each refractive index modulation gradually increases from the one end side in the fiber axis direction toward the center position by generating the refractive index modulation for each predetermined grating pitch by the ultraviolet light irradiation. While performing a convex curve that gradually decreases from the center position toward the other end,
In the above-mentioned second irradiation step, the refractive index modulation of the core by the ultraviolet light irradiation is opposite to the above, and the change in the refractive index gradually decreases from one end side in the fiber axial direction toward the center position, and then from the center position toward the other end side. It is only necessary to draw a concave curve that gradually increases.

According to the first aspect of the present invention, a grating is written by generating a refractive index modulation at a predetermined grating pitch from one side in a direction orthogonal to the fiber axis direction with respect to a portion where an optical fiber is to be written. (First irradiation step) and ultraviolet light irradiation (second irradiation step) for setting the effective refractive index of the core to be written into a predetermined refractive index profile from the other side in the orthogonal direction. Will be done. Then, the average refractive index in the fiber axis direction of the grating formed in the first irradiation step is superimposed on the refractive index profile in the fiber axis direction formed in the second irradiation step, and the fiber axis in the portion where the grating is to be written is written. The average refractive index in the direction is uniform, that is, a flat shape. As a result, the generation of Fabry-Perot resonance is suppressed, the generation of ripples in the reflection characteristics is suppressed as much as possible, and the wavelength selectivity of the light to be reflected is improved.

In addition, since the first irradiation step and the second irradiation step are performed separately on one side and the other side in the direction perpendicular to the fiber axis direction with respect to the writing target of the optical fiber, the two irradiation steps are performed. The steps can be performed simultaneously. For this reason, when performing both irradiation steps, the positioning only needs to be performed relative to the portion of the optical fiber to be written, as viewed from the outside. Operations such as measuring the state of the refractive index profile can be omitted. Furthermore, by setting in advance the characteristics of the refractive index modulation by the irradiation of the ultraviolet light in the first irradiation step and the irradiation of the ultraviolet light in the second irradiation step, the average refractive index of the manufactured fiber grating can be reduced. The profile can be surely made flat in the fiber axis direction.

(Second Invention) A second invention according to a fiber grating manufacturing apparatus for carrying out the fiber grating manufacturing method according to the first invention,
In one aspect of the present invention, there is provided an optical fiber which is a target for fabricating a fiber grating. A first irradiation system for irradiating ultraviolet light from the side, and a refractive index modulation having a change characteristic opposite to a change characteristic of an average refractive index of the core generated by irradiation of the core at the portion to be written by the first irradiation system. A second irradiation system that irradiates ultraviolet light from the other side in the orthogonal direction so as to uniformize the average refractive index of the portion to be written with respect to the fiber axis direction, and both the first and second irradiation systems. A state in which both irradiation systems are set so that each ultraviolet light irradiation position with respect to the above-mentioned planned writing position is the same position in the optical fiber axial direction. In which and a synchronous interlocking mechanism for advancing simultaneously in synchronization toward the other end from one end of the optical fiber axis direction.

Here, the "first irradiation system" and the "second irradiation system"
For example, various configurations may be adopted as described below. For example, the first and second irradiation systems are mutually independent, each having an ultraviolet light radiation source and an optical system for guiding and irradiating the ultraviolet light from this radiation source to a predetermined position of an optical fiber. The irradiation system may be configured to be a modified irradiation system. In this case, as an “synchronous interlocking mechanism”, two independent irradiation systems may be moved in the fiber axis direction in synchronization with each other. In addition, both the first and second irradiation systems may be configured to share one radiation source, split the same ultraviolet light, and irradiate the portion of the optical fiber where the grating is to be written from each side. Good. When one radiation source is shared, a means (for example, a beam splitter) for splitting the same ultraviolet light emitted from the same ultraviolet light radiation source into two parts, What is necessary is just to comprise both said 1st and 2nd irradiation system by what provided with a pair of optical system which guide | induces to irradiate from a side. In this case, two ultraviolet rays branched from each other are radiated from both sides by sandwiching a portion where the fiber is to be written by using mirrors, respectively. What is necessary is just to comprise so that translation may be carried out in synchronization with each other. In the above case, if the writing of the grating by the first irradiation system is performed using a phase mask, the “first irradiation system” may be configured to include a phase mask in addition to the above. Good. Further, the “first irradiation system” is configured by a system including the ultraviolet light radiation source and an optical system for guiding and irradiating the ultraviolet light to a predetermined position of the optical fiber, while the “second irradiation system” includes the “second irradiation system”. As the “irradiation system”, the first irradiation system is configured to irradiate the optical fiber from the opposite side using ultraviolet light transmitted from one side of the orthogonal direction to the optical fiber using the ultraviolet light transmitted to the other side. Is also good. In this case, the reflected ultraviolet light is reflected by receiving the transmitted ultraviolet light, and the reflected ultraviolet light is radiated from the opposite side to the portion to be written of the optical fiber from the opposite side. What is necessary is just to comprise an irradiation system. In addition, in the case where the second irradiation system is configured in this way, and when the first irradiation system is configured with a phase mask, the optical system of the second irradiation system is made of an optical fiber as much as possible. It is preferable to dispose them at separate positions so as to reduce the influence of the phase mask as much as possible. The “synchronous interlocking mechanism” in such a case may be configured so that the first irradiation system and the reflecting optical system as the second irradiation system are synchronized with each other and moved in parallel in the fiber axis direction. .

In the case of the second invention, the first irradiation step in the first invention is performed by the first irradiation system, and the second irradiation step is performed by the second irradiation system. Both the first and second irradiation steps will be performed synchronously and simultaneously. For this reason, the first invention can be implemented easily and reliably.
It is possible to reliably obtain the operation according to the invention of (1).

[0020]

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

FIG. 1 shows a fiber grating manufactured using the method and apparatus for manufacturing a fiber grating according to the embodiment of the present invention, wherein 1 is a predetermined length (as an optical fiber to be manufactured). 2 is a core on which the grating 20 is written, 3 is a cladding of the optical fiber core 1,
Reference numeral 4 denotes a coating layer coated on the outer surface of the clad 3, and reference numeral 5 denotes a phase mask for writing the grating 20. As shown in FIG. 2, the optical fiber core 1 is obtained by coating a coating layer 4 on an optical fiber 1 'comprising a core 2 and a clad 3 manufactured by drawing from an optical fiber preform. . Grating 2 above
Irradiation of ultraviolet light (ultraviolet laser light) for writing 0
Usually, the coating is performed in a state where the coating layer 4 is removed from the above-mentioned optical fiber core 1. However, as described later, the core 2 and the coating layer 4 are modified so that the coating layer 4 can be removed without removing the coating layer 4. The above-mentioned irradiation may be performed from the outside.
When the irradiation is performed in a state where the coating layer 4 is removed, the “optical fiber” to be made of the fiber grating is the optical fiber 1 ′. When the irradiation is performed from outside the coating layer 4, the above “light” is used. The “fiber” becomes the optical fiber core 1. In the present embodiment, a case will be described in which ultraviolet laser light is irradiated from the outside of the coating layer 4 and writing of the grating 20 in the first irradiation step is performed by the phase mask method using the phase mask 5 described above. An ultraviolet laser beam is radiated from the outside of the coating layer 4 through the phase mask 5, so that the refractive index modulation fringes (grating 20) that are periodic in the fiber axis direction with respect to the core 2 of the optical fiber core 1. Is written to produce a fiber grating. The interval between these many refractive index modulation fringes is the grating pitch.

In order to effectively write the grating 20 by irradiating an ultraviolet laser beam from the outside of the coating layer 4, a special structure is adopted as the core 2 and the coating layer 4 as described below. Is preferred.

That is, as the core 2, a core obtained by adding a dopant of Sn, Sn and Al, or Sn, Al and B in addition to Ge having the same concentration as that of the core of the normal specification optical fiber is used. It is preferable to constantly increase the photo-induced refractive index change. Here, the normal specification optical fiber is an optical fiber core to be connected to the optical fiber core 1, and such an optical fiber core has a relative refractive index difference with respect to its core. It is manufactured by doping Ge with an amount of about 0.9%.
The core 2 of the optical fiber core 1 has the same amount (a relative refractive index difference of 0.9
%) And a concentration of 10,000 pp
m or more, preferably at a concentration of 10,000 to 15000 ppm
Of Sn or such a concentration of Sn and a concentration of 100
Al and the like at 0 ppm or less may be co-doped. The above dope may be carried out by various known methods, for example, when carried out by immersion, the compound of the above Ge and Sn (For Sn, for example, Sn Cl ₂ · 2H ₂ O) was mixed with methyl alcohol, What is necessary is just to immerse in the solution.

The coating layer 4 is formed so as to have a thickness of at least about 30 μm by a single coating after the step of drawing the optical fiber 1 ′. As a material for forming the coating layer 4, an ultraviolet transmitting resin having a property of transmitting ultraviolet light is used. As the UV-transmitting resin, a specific wavelength band (for example, 2
Any wavelength that transmits at least the wavelength of 40 nm to 270 nm) is preferable, and it is particularly preferable to transmit the ultraviolet light of the specific wavelength band with little absorption, and to transmit the ultraviolet light of a shorter wavelength or a longer wavelength than the specific wavelength band. What absorbs and causes a hardening reaction may be used. In other words, although the same resin, the ultraviolet absorption characteristics differ depending on the wavelength,
It is most preferable that the coating layer 4 is formed of a resin which is of an ultraviolet transmission type in the specific wavelength band and of an ultraviolet curing type in a wavelength range shorter or longer than the specific wavelength range. Examples of such a resin include a photoinitiator (photoinitiator) that initiates and accelerates a curing reaction by receiving ultraviolet light having a wavelength range shorter than 240 nm or a wavelength range longer than 270 nm with respect to urethane acrylate or epoxy acrylate. ) May be used.

Further, the core fiber 2 coated with the coating layer 4 is irradiated with ultraviolet light, especially before the core 2 is irradiated with ultraviolet light.
Is preferably filled with hydrogen in order to increase the photoinduced refractive index change. In the case of filling with hydrogen, the optical fiber core wire 1 may be placed in a sealed container filled with hydrogen and left at room temperature under a pressure of about 20 MPa for about 2 weeks.

Hereinafter, various embodiments of a fiber grating manufacturing apparatus and method will be specifically described.

<First Embodiment> A fiber grating manufacturing apparatus according to a first embodiment will be described with reference to FIG.

The above-mentioned fiber grating manufacturing apparatus comprises:
The writing of the grating 20 is performed by irradiating the grating writing portion of the optical fiber core 1 with ultraviolet laser light from one side (upper side in FIG. 3) in a direction orthogonal to the fiber axis direction X (see FIG. 1). The front irradiation system 21 as one irradiation system, and the average refraction of the core 2 at the portion to be written by irradiating an ultraviolet laser beam from the other side (lower side in FIG. 3) in the direction orthogonal to the portion to be written to the grating. Back irradiation system 3 as the second irradiation system for keeping the rate constant
1 and a synchronous interlocking mechanism 41 that synchronizes the irradiation positions of the ultraviolet laser beams by the irradiation systems 21 and 31 and sequentially moves the irradiation positions in the fiber axis direction. In FIG. 3, reference numeral 51 denotes a measurement system.

The front irradiation system 21 and the rear irradiation system 31 are configured independently of each other. The front irradiation system 21 includes a lattice-shaped phase mask 5 immediately before the side of the optical fiber core wire 1 where the grating is to be written.
The Nd-YAG laser source 6 as an ultraviolet light radiation source for the phase mask 5 has, for example, four times the wavelength (4
The 266 nm coherent ultraviolet laser beam, which is ω), is emitted while being condensed by the cylindrical lens system 7. As a result, the ultraviolet laser light passes through the phase mask 5 and the coating layer 4, and the refractive index of the core 2 at each grating pitch corresponding to the grating pitch of the phase mask 5 is increased, and the grating 20 is written. It is supposed to be. Further, the forward irradiation system 21 includes a beam expander 8 that expands the ultraviolet laser light from the Nd-YAG laser source 6 into a parallel beam, and a portion having a uniform power from the parallel laser light. A slit 9 of a minute width for cutting out
A movable reflection mirror 10 for changing an irradiation direction to guide the ultraviolet laser light passing through the slit 9 to the cylindrical lens system 7 and the phase mask 5 is provided. The reflection mirror 10 is supported so as to be able to move in parallel with the fiber axis direction X integrally with the cylindrical lens system,
The movement is controlled by the synchronous interlocking mechanism 41 in synchronization with the reflection mirror 10 of the rear irradiation system 31 described later.

The rear irradiation system 31 has substantially the same configuration as the front irradiation system 21 and has the same Nd as that described above.
A YAG laser source 6, a beam expander 8, a slit 9, and a reflection mirror 10; in addition,
The rear irradiation system 31 is interposed between the reflection mirror 10 and a portion to be written of the optical fiber 1 so that the refractive index profile of the portion to be written after the refractive index modulation with respect to the core 2 becomes a predetermined shape. A system 14 is also provided. The optical system 14 may be configured by a filter that adjusts the irradiation amount of the ultraviolet laser light to the portion to be written to have the refractive index profile. The optical system 14 is fixed at a predetermined relative position with respect to the portion of the optical fiber core 1 to be written, while only the reflection mirror 10 is reflected by the synchronization mirror 41 of the front irradiation system 21. At the same time, the movement is controlled so as to translate in the fiber axis direction X.

Further, the measuring system 51 includes an optical spectrum analyzer 11, an optical isolator 12, and an optical coupler 13, and is a device for inspecting the wavelength characteristics of the manufactured fiber grating.

In FIG. 3, reference numerals 1a and 1a denote the ends of the optical fiber core wires 1, respectively, which are reflection-suppressed ends.

Next, a method of manufacturing a fiber grating using the above-described fiber grating manufacturing apparatus will be described.

To make a fiber grating,
A front irradiation step as a first irradiation step of irradiating a portion to be written of the optical fiber core wire 1 with the ultraviolet laser light through the phase mask 5 by the front irradiation system 21 and an optical system 14 by the rear irradiation system 31. A rear irradiation step as a second irradiation step of irradiating the portion to be written with the ultraviolet laser light via the above-mentioned portion may be performed simultaneously while changing both irradiation positions by the synchronous interlocking mechanism 41.

That is, first, the phase mask 5 is disposed on one side of the portion of the optical fiber core 1 where the grating is to be written, while the optical system 14 is disposed on the other side of the portion where the writing is to be performed. The position of the phase mask 5 and the optical system 14 are both fixed. Next, the reflection mirror 10 and the cylindrical lens system 7 of the front irradiation system 21 are set in such a manner that the irradiation positions of the ultraviolet laser beams from the irradiation systems 21 and 31 are both located at one end of the range P in the fiber axis direction of the portion to be written. , The position of the reflection mirror 10 of the rear irradiation system 31 is set. Then, while irradiating the ultraviolet laser light from both irradiation systems 21 and 31, the reflection mirror 10 of the above-described front irradiation system 21 is used.
Then, the cylindrical lens system 7 and the reflection mirror 10 of the rear irradiation system 31 are sequentially moved by the synchronous interlocking mechanism 41 to the other end of the fiber axial direction range P.

It should be noted that the irradiation of the ultraviolet laser light from the rear irradiation system 31 to the optical fiber core 1 is not directly opposite to the irradiation of the ultraviolet laser light from the front irradiation system 21 to the optical fiber core 1. It is preferable to set the direction so that the irradiation direction is appropriate. This direction is set as shown in FIG. 4 by the ultraviolet laser beam UL3 from the rear irradiation system 31.
On a plane including the ultraviolet laser beam UL2 emitted from the front irradiation system 21 and orthogonal to the fiber axis X of the optical fiber core 1, the ultraviolet laser beam U from the front irradiation system 21 is provided.
The irradiation direction may be set so as to irradiate the optical fiber core 1 from a direction having a slight declination δ with the extension line ULe of L2.

By the above operation, the refractive index modulation is caused in the core 2 at the portion to be written, and the refractive index profile becomes as shown in FIG. That is, the irradiation of the ultraviolet laser light from the front irradiation system 21 causes the refractive index of the core 2 to increase periodically (per grating pitch) in the fiber axis direction from the original refractive index n1, as shown in the upper part of FIG. And the average refractive index gradually increases from one end of the fiber axial direction range P toward the center position and gradually decreases from the center position toward the other end. Will change. On the other hand, the irradiation of the ultraviolet laser light from the rear irradiation system 31 increases the refractive index of the core 2 from n1 to n2 at one end and the other end of the range P in the fiber axial direction as shown in the lower part of FIG. And a concave curve R2 in which the refractive index gradually decreases from n2 from one end of the range P toward the center position, gradually increases from the center position toward the other end, and returns to the above-described n2. This results in a changed refractive index profile. Then, the refractive index change of the convex carp R1 and the refractive index change of the concave carp R2 are combined, and as shown in the middle part of FIG. A constant refractive index profile is achieved. As a result, the occurrence of ripples in the reflection characteristics is suppressed as much as possible.

<Second Embodiment> In a second embodiment, as shown in FIG. 6, a front irradiation system 22 as a first irradiation system and a second irradiation system
Nd-YAG with back irradiation system 32 as irradiation system
The laser source 6 and the beam expander 8 are shared, and both forward irradiation and rear irradiation are performed by using the ultraviolet laser light from the same Nd-YAG laser source 6.

That is, similarly to the first embodiment, the forward irradiation system 22 includes the Nd-YAG laser source 6, the beam expander 8, the slit 9, the movable reflection mirror 10, and the cylindrical lens system 7, , And a phase mask 5. In addition, the rear irradiation system 32 includes the above-described Nd-
A YAG laser source 6 and a beam expander 8, a beam splitter 15 for splitting the ultraviolet laser beam into two, and an optical fiber core 1 split by the beam splitter 15
A reflection mirror 16 for changing the path of the ultraviolet laser light guided backward (downward in FIG. 6) parallel to the fiber axis, and the ultraviolet laser light whose path is changed by the reflection mirror 16 is to be written on the optical fiber 1. It includes a movable reflecting mirror 10 that changes the course so as to be directed to a part, and an optical system 14 similar to the first embodiment. The reflection mirror 10 and the cylindrical lens system 7 of the front irradiation system 22 and the reflection mirror 10 of the rear irradiation system 32 are synchronized with each other by the synchronous interlocking mechanism 41 and have one end in the fiber axial direction range P, as in the first embodiment. The movement is controlled from the side to the other end. Also, the optical fiber cable 1 from the rear irradiation system 32
Is also displaced by an angle δ (see FIG. 4) with respect to the irradiation direction from the front irradiation system 22.
This is the same as the embodiment. Note that components having the same contents as those in the first embodiment are denoted by the same reference numerals as those in the first embodiment, and detailed description thereof is omitted.

In order to manufacture a fiber grating using the fiber grating manufacturing apparatus of the second embodiment, writing is to be performed by the forward irradiation system 22 in the same manner as in the manufacturing method described in the first embodiment. A forward irradiation step as a first irradiation step of irradiating an ultraviolet laser beam through the phase mask 5 to the fiber axis direction range P of the part, and a rear irradiation system 32 to the part to be written via the optical system 14 by the rear irradiation system 32 The rear irradiation step as the second irradiation step of irradiating the ultraviolet laser beam may be performed simultaneously while changing both irradiation positions by the synchronous interlocking mechanism 41.

Thus, the same operation and effect as those described in the first embodiment can be obtained.

Further, in the case of the second embodiment, since one Nd-YAG laser source 6 is shared by the front irradiation system 22 and the rear irradiation system 32, the overall configuration of the manufacturing apparatus can be made compact. it can.

<Third Embodiment> In the third embodiment, as shown in FIG. 7, a rear irradiation system 33 as a second irradiation system is provided with a first irradiation system.
Optical fiber core wire 1 by forward irradiation system 23 as an irradiation system
The optical fiber core wire 1 is configured to receive and reflect the ultraviolet laser light emitted from the front, thereby irradiating the optical fiber core wire 1 from behind. That is, the rear irradiation is also performed using the transmitted light of the phase mask 5 by the front irradiation.

That is, similarly to the first embodiment, the forward irradiation system 23 includes an Nd-YAG laser source 6, a beam expander 8, a slit 9, and a movable reflection mirror 10
, A cylindrical lens system 7, and a phase mask 5. On the other hand, the rear irradiation system 33 irradiates the optical fiber core 1 from the front irradiation system 23 through the phase mask 5 from the front and transmits the ultraviolet laser transmitted through the phase mask 5 and the optical fiber 1. A reflection optical system 17 is provided for receiving light and reflecting the light so as to irradiate the portion to be written of the optical fiber 1 from the rear. The reflection optical system 17 may include, for example, a reflection mirror or the like, and uses the transmitted light of the phase mask 5. Therefore, the ultraviolet laser light that reaches the reflection optical system 17 is reflected by the phase mask 5. It is arranged at a distance from the phase mask 5 so that the influence of the diffraction grating fringes does not remain. Although not shown, the rear irradiation system 33 includes an optical system similar to the optical system 14 according to the first embodiment between the optical system 17 and the optical fiber core 1. In addition, the ultraviolet laser light reflected by the reflection optical system 17 is deflected δ with respect to the irradiation direction of the ultraviolet laser light from the front similarly to the first and second embodiments (see FIGS. 2 and 4). Optical fiber 1 from the direction shifted by
To be irradiated.

Then, the reflecting mirror 10 and the cylindrical lens system 7 of the front irradiation system 23 and the reflecting optical system 17 are synchronized by the synchronous interlocking mechanism 41 from one end to the other end of the fiber axial direction range P. The movement is controlled in synchronization with up to.

In the case of the fiber grating manufacturing apparatus of the third embodiment as well, to manufacture a fiber grating, the synchronous interlocking mechanism 41 irradiates ultraviolet laser light from the forward irradiation system 23 to produce the fiber axis range P. The front irradiation from the front irradiation system 23 and the rear irradiation from the rear irradiation system 33 may be simultaneously performed. Thereby, the same operation and effect as the operation and effect of the first embodiment can be obtained.

<Other Embodiments> The present invention relates to the first embodiment.
The present invention is not limited to the third embodiment, but includes various other embodiments. That is, the first
In the third to third embodiments, simultaneous apodization is performed by synchronously moving (scanning) forward irradiation and rear irradiation in the fiber axis direction with respect to the fiber axis direction range P of the portion where the grating is to be written. However, the present invention is not limited to this, and when the length of the fiber axial direction range P (the length of the grating forming range in the fiber axial direction) is relatively short, both the front and rear sides are fixed to the same fixed position in the fiber axial direction. May be simultaneously performed, and the control of sequentially moving the irradiation position in the fiber axis direction by the synchronous interlocking mechanism 41 as in the above-described first to third embodiments may not be performed.

[0048]

As described above, according to the fiber grating manufacturing method according to the first aspect of the present invention, the fiber axis of the optical fiber is adjusted with respect to the portion where the grating is to be written. Irradiation of ultraviolet light from one side in a direction perpendicular to the direction (first irradiation step);
By simultaneously irradiating the ultraviolet light from the other side (second irradiation step), it becomes possible to simultaneously perform apodization on the above-mentioned grating writing planned portion. For this reason, the positioning at the time of performing both irradiation steps only requires the relative positioning of the portion to be written on the optical fiber as viewed from the outside thereof, which is necessary when performing apodization in the conventional two times. The operation of measuring the state of the existing internal refractive index profile and the like can be omitted. Furthermore, by setting in advance the characteristics of the refractive index modulation by the irradiation of the ultraviolet light in the first irradiation step and the irradiation of the ultraviolet light in the second irradiation step, the average refractive index of the manufactured fiber grating can be reduced. The profile can surely be made flat in the fiber axis direction.

Then, the refractive index profile of the average refractive index in the fiber axis direction of the grating formed in the first irradiation step is superimposed on the refractive index profile in the fiber axis direction formed in the second irradiation step, The average refractive index in the fiber axis direction at the portion where the grating is to be written can be made uniform, that is, a flat shape, whereby the occurrence of Fabry-Perot resonance can be suppressed and the occurrence of ripples in the reflection characteristics can be minimized. And the wavelength selectivity of the light to be reflected can be improved.

Further, according to the fiber grating manufacturing apparatus according to the second aspect of the present invention, the first aspect can be easily and reliably implemented. Thus, the effect of the first invention can be reliably obtained.

[Brief description of the drawings]

FIG. 1 is an explanatory front view showing a fiber grating according to the present invention.

FIG. 2 is an enlarged cross-sectional view of FIG.

FIG. 3 is a schematic view showing a fiber grating manufacturing apparatus according to the first embodiment.

FIG. 4 is a partial perspective view showing an irradiation direction.

FIG. 5 is a diagram illustrating a relationship between a fiber axis direction and an average refractive index.

FIG. 6 is a schematic view showing a fiber grating manufacturing apparatus according to a second embodiment.

FIG. 7 is a schematic view showing a fiber grating manufacturing apparatus according to a third embodiment.

[Description of Signs] 1 Optical fiber core wire (optical fiber) 1 ′ Optical fiber strand (optical fiber) 2 Core 10 Movable reflective mirror 21, 22, 23 Forward illumination system (first illumination system) 31, 32, 33 Back irradiation system (second irradiation system) 41 Synchronous interlocking mechanism P Fiber axial direction range of writing planned part X Fiber axial direction

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Yasuhide Sudo 4-3 Ikejiri, Itami-shi, Hyogo Mitsubishi Electric Cable Industry Co., Ltd. Itami Works F-term (reference) 2H038 AA24 BA24 BA25 2H049 AA33 AA51 AA59 AA62 2H050 AA07 AC82 AC84 AD00

Claims (7)

[Claims] 1. An optical fiber from which a fiber grating is to be fabricated is irradiated with ultraviolet light from one side in a direction orthogonal to the fiber axis direction to a portion where the grating is to be written, and is refracted at a predetermined grating pitch in the fiber axis direction. A first irradiation step of causing a rate modulation to occur in the core of the optical fiber, and simultaneously irradiating ultraviolet light from the other side in the direction orthogonal to the portion to be written with the ultraviolet light in the first irradiation step. A second irradiation for causing a refractive index modulation of a change characteristic opposite to the change characteristic of the average refractive index of the core in the first irradiation step to be generated in the core so as to make the average refractive index in the fiber axis direction of the portion to be written uniform. And a method for producing a fiber grating. 2. The method according to claim 1, wherein the irradiation of the ultraviolet light in both of the first and second irradiation steps sequentially changes the irradiation position of the ultraviolet light with respect to a fiber axial direction range of a portion where a grating is to be written in a fiber axial direction. In the state where the irradiation positions in both irradiation steps are set so as to be identical to each other in the fiber axis direction, the irradiation positions are moved in synchronization with each other in the fiber axis direction. A method of manufacturing a fiber grating. 3. The average refractive index according to claim 1, wherein the first irradiation step is such that the average refractive index change gradually increases from one end side to the other end side in the fiber axis direction and then gradually decreases to become convex at the center position. While irradiating ultraviolet light so that a profile is formed, the second irradiation step gradually increases after the average refractive index change gradually decreases from one end side to the other end side in the fiber axis direction, and then gradually increases to become concave at the center position. A method for producing a fiber grating, comprising irradiating ultraviolet light so as to form an average refractive index profile. 4. An optical fiber from which a fiber grating is to be produced, from one side in a direction orthogonal to the fiber axis direction so that a refractive index modulation is generated at a predetermined grating pitch in the fiber axis direction with respect to a core of a portion where a grating is to be written. A first irradiation system for irradiating ultraviolet light, and a refractive index modulation having a change characteristic opposite to a change characteristic of an average refractive index of the core generated by irradiation of the core at the portion to be written by the first irradiation system. A second irradiation system that irradiates ultraviolet light from the other side in the orthogonal direction so as to equalize the average refractive index of the portion to be written with respect to the fiber axis direction, and both the first and second irradiation systems. The optical fiber is set in such a manner that the positions of the ultraviolet light irradiation with respect to the above-mentioned planned portions of the irradiation system are the same in the optical fiber axial direction. Fiber grating fabricating apparatus, characterized in that it includes a synchronization link mechanism for advancing simultaneously in synchronization toward the other end from one end of the driver shaft direction. 5. The first irradiation system and the second irradiation system according to claim 4, wherein the same ultraviolet light emitted from the same ultraviolet light radiation source is split into two and guided to each other. An apparatus for producing a fiber grating. 6. The optical system according to claim 4, wherein the second irradiation system is configured to reflect the ultraviolet light applied to the optical fiber by the first irradiation system and to irradiate the optical fiber. Fiber grating manufacturing apparatus. 7. The mirror according to claim 4, wherein the first and second irradiation systems each include a mirror for changing an irradiation direction of the ultraviolet light so as to irradiate the ultraviolet light from the ultraviolet light radiation source to a portion to be written of the optical fiber. The synchronous interlocking mechanism is configured to synchronize and simultaneously move the mirror of the first irradiation system and the mirror of the second irradiation system from one end to the other end in the optical fiber axial direction at the same time. A fiber grating manufacturing apparatus, comprising: