JPH11160511A - Device and method for generating long-cycle fiber grating - Google Patents

Abstract

PROBLEM TO BE SOLVED: To generate the long-cycle fiber grating in an optical fiber in high- precision pattern stably in a short time. SOLUTION: The optical fiber 1 is irradiated cyclically with an ultraviolet light beam 2 along its length to form the long-cycle fiber grating 3. This device is equipped with a multi-slit mask 5 on which the ultraviolet light beam is made incident and a condenser lens 6 on which the ultraviolet light beam projected from the multi-slit mask is made incident to irradiate the optical fiber.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a long-period fiber grating generating apparatus and method, and more particularly to a long-period fiber grating generating apparatus and method for stably generating a high-precision long-period fiber grating on an optical fiber in a short time. .

[0002]

2. Description of the Related Art Heretofore, the following technology has been proposed as an apparatus or method for generating such a long-period fiber grating (LPFG). <Prior Art 1> A method of generating a grating (refractive index grating) by using a single slit mask, moving the single slit mask in the longitudinal direction of the optical fiber while shifting it at regular intervals, and exposing with an ultraviolet beam (US Patent No. 5,216,739).

[0003] This method of generating a long-period fiber grating has the following difficulties. Since a mechanical process such as movement of a single slit mask is included, processing accuracy is low. In order to generate gratings one by one in order,
The processing time is long and not suitable for mass production. Since the single slit mask absorbs ultraviolet light, irradiation with a high power density damages the single slit mask.

[0004] For this reason, irradiation at a low power density is forced, and the processing time is prolonged. <Prior art 2> Similar to prior art 1, but without using a single slit mask, move a narrow beam focused by a condenser lens at regular intervals in the longitudinal direction of the optical fiber, and intermittently irradiate to generate a grating. (“Temperature-independent long-period fiber grating”, Fujikura Technical Report No. 92 (April 1997, pp. 11-13)).

[0005] This method of producing a long-period fiber grating also has the disadvantages of prior art 1. <Prior art 3> A method of collectively generating a grating by irradiating an optical fiber with a KrF laser using a photomask (“Long-Period Fiber Grating as Band-Rejection Fi
lters ", JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 14,
No. 1, January 1996). As the photomask, a fused quartz substrate having a lattice pattern formed on its surface by plating with Cr or the like is used.

In this method of producing a long-period fiber grating, the metal plating has a strong ultraviolet absorption, and when irradiated with ultraviolet light at a light power density exceeding the mask limit intensity (mask damage limit), the mask is damaged due to heat generation or the like. There are difficulties. In addition, in this method, since the photomask is brought close to the optical fiber and the optical fiber and the photomask are exposed to ultraviolet light at the same power density, the power density of the ultraviolet light applied to the optical fiber is less than the mask damage limit. And there is a drawback that long-time exposure is required.

[0007]

As described above, in the conventional long-period fiber grating manufacturing technique, an ultraviolet laser (λ = 248) used for manufacturing a long-period fiber grating is used.
Most of the materials other than fused silica have strong electron absorption at a wavelength of (nm), and when irradiated with high-power light, they are destroyed by heat or the like. The photomask used to make LPFG is
A lattice pattern is formed by metal plating of Ni or the like, and the pattern is damaged when irradiated with ultraviolet light having a high power density.
Therefore, the photomask needs to be used at a low power density within the breakdown limit. Further, in the prior art, a photomask is brought close to the fiber, and the mask and the fiber are irradiated with light having the same power density. This forces the fiber to be exposed at low power densities that are within the mask breakdown limit, resulting in very long exposure times. Long-time exposure is not only unsuitable for mass production, it is also susceptible to vibrations during exposure, and the filter characteristics are degraded due to a decrease in the contrast of the exposure pattern.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned difficulties, and has an object to provide a space between a plurality of slit masks and an optical fiber,
By inserting a lens in the meantime and condensing the light on the optical fiber, it is possible to expose the optical fiber with a high power density, and to stably generate a high-precision long-period fiber grating on the optical fiber in a short time. An object of the present invention is to provide an apparatus and a method for generating a periodic fiber grating.

[0009]

In order to achieve this object, a long-period fiber grating generating apparatus according to the present invention provides a long-period fiber grating by periodically irradiating an optical fiber with an ultraviolet light beam along its longitudinal direction. A long-period fiber grating generating apparatus for generating a fiber grating, comprising: a plurality of slit masks into which an ultraviolet light beam is incident; and an ultraviolet light beam emitted from the plurality of slit masks, and irradiating the emitted ultraviolet light beam onto the optical fiber. And a condensing lens.

[0010] In the long-period fiber grating generator, an ultraviolet light beam is irradiated on the optical fiber orthogonally to the optical fiber along the longitudinal direction. In the long-period fiber grating generation apparatus, the multiple slit mask is formed by depositing a plurality of metal grating films on a glass substrate in parallel. The multi-slit mask is obtained by perforating a plurality of lattice openings in parallel in a light-shielding substrate.

The condenser lens collects light in a direction perpendicular to the longitudinal direction of the optical fiber. The condenser lens is a cylindrical lens. The center line of the spherical surface of the cylindrical lens and the longitudinal direction of the optical fiber are parallel. The method for generating a long-period fiber grating according to the present invention includes a method of generating a long-period fiber grating by periodically irradiating an optical fiber with an ultraviolet light beam along the longitudinal direction of the optical fiber, and generating a long-period fiber grating by applying a plurality of slit masks to the ultraviolet light beam And irradiating the optical fiber through a condensing lens.

In this method of generating a long-period fiber grating, the optical fiber is irradiated with an ultraviolet light beam along the longitudinal direction thereof at right angles to the optical fiber. The multiple slit mask is formed by depositing a plurality of metal grating films on a glass substrate in parallel. The multi-slit mask is obtained by perforating a plurality of lattice openings in parallel in a light-shielding substrate.

The condenser lens collects light in a direction perpendicular to the longitudinal direction of the optical fiber. The condenser lens is a cylindrical lens. The center line of the spherical surface of the cylindrical lens and the longitudinal direction of the optical fiber are parallel.

[0014]

In the apparatus and method for producing a long-period fiber grating, a long-period fiber grating is applied to the optical fiber by irradiating the optical fiber along the longitudinal direction thereof through a condensing lens through a plurality of slit masks. Can be generated stably in a short time in a highly accurate pattern.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of a long-period fiber grating generating apparatus and method according to the present invention will be described below with reference to the drawings. A long-period fiber grating generating apparatus periodically or quasi-periodically applies an ultraviolet light beam 2 to an optical fiber 1 comprising a core 1a and a clad 1b along the longitudinal direction thereof as shown in FIGS. Irradiation produces a long-period fiber grating (LPFG refractive index grating) 3.

The long-period fiber grating 3 is obtained by changing the core refractive index of the core 1a of the optical fiber 1 in the longitudinal direction at a period of several hundred μm, for example, at a period of 200 to 600 μm. The change in the core refractive index can be achieved by irradiation with an ultraviolet laser light beam 2 emitted from an ultraviolet light source 4 (for example, a KrF Excimer laser, λ = 248 nm). The long-period fiber grating generating apparatus collects the plurality of slit masks 5 on which the ultraviolet light beam 2 is incident and the ultraviolet light beam 2 emitted from the plurality of slit masks and irradiates the emitted ultraviolet light beam onto the optical fiber 1. And a lens 6.

In this long-period fiber grating generator, the optical fiber 1 is irradiated with an ultraviolet light beam 2 orthogonally to the optical fiber 1 along its longitudinal direction. In the long-period fiber grating generation apparatus, the plurality of slit masks 5 are formed by depositing a plurality of metal grating films 8 on a glass substrate 7 in parallel. The multiple slit mask 5 is formed as a photomask in which a pattern is formed on a fused quartz substrate by plating with Cr or Ni. This method is suitable for mass production, since long-period fiber gratings can be written collectively. If the mask accuracy is sufficiently high, a high-accuracy long-period fiber grating can be formed with good reproducibility.

Alternatively, a plurality of slit masks 5 are provided on a light-shielding substrate 9 made of an opaque medium such as a metal by forming a lattice opening 10.
May be perforated in parallel (FIG. 3). In the long-period fiber grating generation apparatus of the present invention, the interval between the optical fiber 1 and the plurality of slit masks 5 is widened within a range where a sufficiently clear pattern can be exposed (for example, 200 m).
m), a condenser lens 6 having an appropriate focal length is inserted between them, and the distance between the condenser lens 6 and the optical fiber 1 is, for example, 100 to 18;
The light is condensed near the optical fiber 1 at intervals of 0 mm, and the exposure power density of the optical fiber 1 is set to a sufficiently large value.

In the above example, the plurality of slit masks 5 are arranged in front of the condenser lens 6. However, if the optical power density is below the destruction limit of the plurality of slit masks 5, the plurality of slit masks 5 are placed on the condenser lens 6. May be arranged at the subsequent stage.
The condenser lens 6 condenses light in a direction orthogonal to the longitudinal direction of the optical fiber 1. For this reason, the condenser lens 6 is constituted by a cylindrical lens 6a, and the center line 12 of the spherical surface 11 of the cylindrical lens and the longitudinal direction of the optical fiber 1 are arranged in parallel.

The contrast of the pattern formed by the multiple slit mask 5 is a function of the distance from the multiple slit mask 5. When the distance from the plural slit masks 5 increases, the contrast deteriorates. A condensing lens having an appropriate focal length so that the distance between the optical fiber 1 and the plurality of slit masks 5 is within a range that maintains a sufficient pattern contrast and that the optical fiber 1 is exposed with a sufficient power density. 6 is used.

In the long-period fiber grating generating apparatus configured as described above, the core 1a of the optical fiber 1 is used.
The optical fiber 1 is periodically irradiated with the ultraviolet light beam 2 along its longitudinal direction to generate a long-period fiber grating. In this case, the ultraviolet light beam 2 is applied to the optical fiber 1 via the condenser lens 6 via the plural slit masks 5. In the generation of the long-period fiber grating, the optical fiber 1 is irradiated with the ultraviolet light beam 2 orthogonally to the optical fiber 1 along the longitudinal direction.

According to the manufacturing technique of the long-period fiber grating, the optical fiber 1 can be exposed to high-power-density ultraviolet light without damaging the plurality of slit masks 5, thereby greatly reducing the exposure time. Can be
The simplest, high-precision, long-period fiber grating can be manufactured in a short time. According to such a manufacturing technique, it is suitable for manufacturing a long-period fiber grating filter used for a gain flattener of an optical fiber amplifier as a related product, and a photomask is applied to a process such as a semiconductor, a thin film transistor, and a micromachine as an applied product. The present invention can be applied to all industrial products having an exposure process using the same.

[0023]

As is apparent from the above description, according to the manufacturing technique of the long-period fiber grating filter of the present invention, a high-precision pattern can be exposed at once by using a plurality of slit masks, so that mass production becomes easy. Since the low-power-density light is transmitted through the multiple-slit mask, the multiple-slit mask is not damaged. Since it can be shortened, mass production becomes easy, and since the exposure time is short, a decrease in the contrast of the written pattern due to vibration or the like can be suppressed.

[Brief description of the drawings]

FIG. 1 is a side view showing a long-period fiber grating generating apparatus according to the present invention.

FIG. 2 is a perspective view showing a long-period fiber grating generating apparatus according to the present invention.

FIG. 3 is a diagram showing an example of a multi-slit mask used in the long-period fiber grating generator of the present invention.

[Explanation of symbols]

 1 ··· Optical fiber 2 ···· Ultraviolet light beam 3 ···· Long-period fiber grating 5 ··· Multiple slit masks 6 ···· Condenser lens 7 ···・ Glass substrate 8 ・ ・ ・ ・ ・ ・ ・ Metal lattice film 9 ・ ・ ・ ・ ・ ・ ・ Light shielding substrate 10 ・ ・ ・ ・ ・ ・ ・ Grating opening 6a ・ ・ ・ ・ ・ ・ ・ ・ ・ Cylindrical lens 11 ・ ・ ・ ・ ・ ・ Spherical surface 12 ・ ・ ・ ・ ・ ・ Center line

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Kenichi Muta 2-1-1 Oda Sakae, Kawasaki-ku, Kawasaki City, Kanagawa Prefecture Inside Showa Electric Cable Co., Ltd. (72) Inventor Kazunari Sugi, Oda Ei Kawasaki-ku, Kawasaki City, Kanagawa Prefecture 2-1-1, Showa Electric Wire & Cable Co., Ltd.

Claims (14)

[Claims] 1. A long-period fiber grating generating apparatus for generating a long-period fiber grating by periodically irradiating an optical fiber with an ultraviolet light beam along a longitudinal direction of the optical fiber, wherein the ultraviolet light beam is A long-period fiber grating comprising: a plurality of slit masks to be incident; and a condenser lens to which an ultraviolet light beam emitted from the plurality of slit masks is incident and irradiates the emitted ultraviolet light beam to the optical fiber. Generator. 2. A long-period fiber grating generating apparatus according to claim 1, wherein an ultraviolet light beam is irradiated on said optical fiber at right angles to said optical fiber along its longitudinal direction. 3. A long-period fiber grating generating apparatus according to claim 1, wherein said plurality of slit masks are formed by depositing a plurality of metal grating films on a glass substrate in parallel. 4. A long-period fiber grating generating apparatus according to claim 1, wherein said plurality of slit masks are formed by perforating a plurality of lattice openings in a light-shielding substrate in parallel. 5. A long-period fiber grating generating apparatus according to claim 1, wherein said condenser lens focuses light in a direction orthogonal to a longitudinal direction of said optical fiber. 6. A long-period fiber grating generator according to claim 1, wherein said condenser lens is a cylindrical lens. 7. A long-period fiber grating generator according to claim 6, wherein a center line of a spherical surface of said cylindrical lens and a longitudinal direction of said optical fiber are parallel. 8. A condenser lens for periodically irradiating the optical fiber with an ultraviolet light beam along a longitudinal direction of the optical fiber to generate a long-period fiber grating. Irradiating the optical fiber via the optical fiber. 9. The method for producing a long-period fiber grating according to claim 8, wherein the optical fiber is irradiated with an ultraviolet light beam at right angles to the optical fiber along its longitudinal direction. 10. The method according to claim 8, wherein the plurality of slit masks are formed by depositing a plurality of metal grating films on a glass substrate in parallel. 11. A method for generating a long-period fiber grating according to claim 8, wherein said plurality of slit masks are formed by perforating a plurality of lattice openings in a light-shielding substrate in parallel. 12. The method according to claim 8, wherein said condenser lens focuses light in a direction orthogonal to a longitudinal direction of said optical fiber. 13. The method according to claim 8, wherein the condenser lens is a cylindrical lens. 14. The method according to claim 13, wherein a center line of a spherical surface of the cylindrical lens and a longitudinal direction of the optical fiber are parallel to each other.