JPH09288204A - Production of optical waveguide grating - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily change a design by making the change rate of the refractive index of the cores in the respective parts of grating parts uniform. SOLUTION: Production of the radiation mode coupling type optical waveguide gratings is executed in this process. In such a case, the process is provided with a stage for irradiating a quartz optical fiber 1 formed by adding germanium oxide to at least the core with UV light 2 via a mask 3 formed with slits 3a for allowing the transmission of light at prescribed intervals and moving the irradiation position of the UV light 2 in the longitudinal direction of the optical fiber 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical waveguide grating, and more particularly to a method of manufacturing a radiation mode coupling type optical waveguide grating.

[0002]

2. Description of the Related Art Optical waveguide gratings are obtained by forming a constant periodic change, for example, a periodic change in core refractive index, in the length direction of an optical fiber or a planar optical waveguide. Generally, there are a radiation mode coupling type and a reflection mode coupling type in a grating. The radiation mode coupling type grating couples a mode propagating in a core and a mode propagating in a cladding, thereby transmitting light of a specific wavelength outside the optical waveguide. To attenuate it by radiating it. The reflection mode coupling type grating reflects light of a specific wavelength by coupling a mode propagating in the core in a positive direction and a mode propagating the core in the opposite direction (negative direction). The characteristic is obtained.

For example, in the case of a grating realized in an optical fiber, a radiation type grating is obtained by setting the cycle of the change in the refractive index of the core (hereinafter sometimes referred to as the grating pitch) to several hundred μm,
The reflection type grating has a grating pitch of 1μ
It is obtained by setting it to about m.

In the radiation mode coupling type grating, for example, a wavelength-transmission loss characteristic (transmission spectrum) as shown in FIG. 3 is obtained, and the transmission loss of light in a specific wavelength band is selectively increased. . The width of the wavelength band in which the transmission loss increases is called the stop band width, the center wavelength is called the center wavelength of the stop band, and the magnitude of change in the transmission loss is called the stop ratio.
These grating characteristics change depending on each parameter of the grating, that is, the variation amount of the core refractive index, the grating pitch, the grating shape (profile of core refractive index change), the grating length in the optical fiber length direction, and the like. Table 1 below shows the effect of each parameter in the grating on the grating characteristics. In the table, × has no effect, ○
Indicates that there is an influence, and Δ indicates that the influence is small. Further, ↑ (↓) indicates that as the parameter value increases, the value of the grating characteristic increases (decreases) accordingly.

[0005]

[Table 1]

By the way, as a method for producing a grating by causing a periodical change of the core refractive index in an optical waveguide, quartz glass containing germanium is irradiated with strong ultraviolet light, and the refractive index is changed according to the irradiation amount. There is known a method of utilizing the phenomenon that the power rises. For example, a silica-based optical fiber to which germanium oxide has been added to the core is subjected to hydrogenation treatment in a hydrogen pressure vessel (100 atm), and then ultraviolet light is periodically applied to this along a length of the optical fiber using a photomask. A method of irradiating and a method of irradiating with ultraviolet light at equal intervals in the length direction of the optical fiber are known.

FIG. 4 shows an example of a conventional optical fiber grating manufacturing apparatus. Reference numeral 11 in the figure denotes an excimer laser device, which can generate ultraviolet light having a wavelength of 248 nm. Reference numeral 12 in the figure is an optical system, which is configured to expand the ultraviolet light emitted from the laser device 11 to a predetermined size with a spot width of several mm to several tens of mm. In the figure, reference numeral 13 is a metal mask, which has slits at regular intervals of several tens to several hundreds μm. In the figure, reference numeral 14 is a fixed base, to which the optical fiber 1 from which the coating layer 4 is partially removed is fixed. The ultraviolet light emitted from the laser device 11 is radiated to the portion of the optical fiber 1 from which the coating layer 4 has been removed through the mask 13 via the optical system 12.

In order to manufacture an optical fiber grating using the apparatus having such a structure, it is sufficient to emit ultraviolet light from the laser device 11 and irradiate the optical fiber 1 through the mask 13. As a result, the refractive index of the core increases only in the portion of the optical fiber 1 irradiated with the ultraviolet light, so that the grating portion 5 in which the core refractive index changes periodically is formed. However, in this method, since the spatial distribution of the laser light intensity is not uniform, that is, the laser light intensity in the spot of the laser light is non-uniform, the mask 13 cannot be uniformly irradiated with the ultraviolet light. It was Therefore, the amount of change in the core refractive index in each part of the grating part 5 is not uniform, and the transmission spectrum of the optical fiber grating is broad or asymmetrical, which causes deterioration of the grating characteristics.

FIG. 5 shows another example of a conventional optical fiber grating manufacturing apparatus. The same components as those in FIG. 4 are designated by the same reference numerals to simplify the description.
Reference numeral 22 in the drawing is an optical system, which is configured to collect the ultraviolet light emitted from the laser device 11 into a predetermined size with a spot width of several tens μm to several hundreds μm. Reference numeral 24 in the figure
Is a moving stage, to which the optical fiber 1 from which the coating layer 4 is partially removed is fixed. Moving stage 24
Are controlled so that they can be finely moved by a predetermined distance in the length direction of the optical fiber. The ultraviolet light emitted from the laser device 11 is radiated through the optical system 12 to the portion of the optical fiber 1 where the coating layer 4 has been removed.

In order to manufacture an optical fiber grating using the apparatus having such a configuration, first, the laser device 11 emits ultraviolet light and irradiates the optical fiber 1. After irradiation for a fixed time, the moving stage 24 is finely moved to move the optical fiber 1 in the length direction by a predetermined distance, and then the optical fiber 1 is irradiated again with ultraviolet light for a fixed time. The irradiation of ultraviolet light and the movement of the optical fiber 1 are repeated, and the work is terminated when the total moving distance of the optical fiber 1 reaches a predetermined distance. By doing so, the refractive index of the core changes only in the portion of the optical fiber 4 irradiated with the ultraviolet light, so that the grating portion 5 is formed.

According to this method, it is possible to make the amount of change in the core refractive index in the grating portion 5 uniform by repeating the irradiation of ultraviolet light under the same irradiation condition with good reproducibility. However, since the grating pitch is determined by the size of the spot of the laser light and the movement pitch of the optical fiber 1, if the grating pitch is to be changed, the spot size of the laser light and the movement pitch of the optical fiber 1 must be changed. I won't. As a method of controlling the spot size of laser light, there are a method of using a slit, a method of using a lens, a method of combining these, and the like, but it is difficult to finely control the spot size by any method. Therefore, when changing the grating characteristics, it is necessary to perform the complicated work of determining the irradiation conditions of the laser light,
There was a drawback that design changes were not easy.

[0012]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to make it possible to make uniform the amount of change in the core refractive index in each part of the grating part when manufacturing a radiation mode coupling type optical waveguide grating, and to design the same. The purpose is to make changes easily.

[0013]

In order to solve the above-mentioned problems, the invention according to claim 1 is a method of manufacturing a radiation mode coupling type optical waveguide grating, wherein the core has a refractive index changed by irradiation with ultraviolet light. In the optical waveguide made of material,
Manufacture of an optical waveguide grating characterized by having a step of irradiating ultraviolet light through a mask formed with slits that transmit light at predetermined intervals and moving the irradiation position of the ultraviolet light along the core. Is the way. The invention according to claim 2 is the method of manufacturing an optical waveguide grating according to claim 1, wherein substantially all of the ultraviolet light emitted from the light source is used for irradiation of the mask and the optical waveguide.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is described in detail below.
FIG. 1 is an explanatory view showing an embodiment of a method for manufacturing an optical waveguide grating of the present invention, and FIG. 2 is a graph showing an example of a core refractive index profile of a grating portion formed by the method of the present invention. Here, an example in which an optical fiber is used as an example of the optical waveguide and a radiation mode coupling type optical fiber grating is manufactured will be described. Reference numeral 1 in the figure
Is an optical fiber, 2 is ultraviolet light, and 3 is a mask.

The optical fiber 1 used in the present invention comprises a core and a clad having a refractive index lower than that of the core. The core of the optical fiber 1 is made of a material whose refractive index changes depending on the intensity of the ultraviolet ray and the irradiation time when the ultraviolet ray is irradiated, and is preferably made of quartz glass to which at least germanium oxide is added. . In addition to germanium oxide, aluminum, erbium, titanium or the like may be appropriately added to the core of the optical fiber 1. The clad of the optical fiber 1 is made of silica glass, and for example, pure silica glass or fluorine-doped silica glass is preferably used. The core and the clad of the optical fiber 1 are manufactured by various known methods so as to have a predetermined relative refractive index difference and refractive index profile.
In the case of the optical fiber 1 generally used for the optical fiber grating, germanium oxide is added to the core in an amount of about 3 to 40%, and the core-cladding relative refractive index difference is 0.3.
It is set to about 6%. As the optical fiber 1,
For example, a coating layer such as an optical fiber core wire may be removed as necessary, or an optical fiber manufactured by drawing and before the coating layer is formed may be used.

The mask 3 used in the present invention is an ultraviolet light 2
Made of a material that does not pass through and is not easily damaged by the ultraviolet light 2, and a metal such as stainless steel is preferably used. A plurality of slits 3a having a constant width are formed in parallel on the mask 3 at regular intervals. The width of the slits 3a in the mask 3 and the interval between the adjacent slits 3a change the grating pitch, and are accordingly set according to the grating characteristics to be obtained.
Further, the length L in the width direction of the slit 3a of the portion of the mask 3 where the slit 3a is formed is appropriately set according to the grating characteristic to be obtained because the grating length changes accordingly. In the present invention, the grating pitch is preferably set within the range of several tens to several hundreds of μm in order to obtain the characteristics of the radiation mode coupling type. The grating length is preferably set to about 5 to 20 mm. Further, in this embodiment, the slits 3a are not formed at both ends of the slit 3a in the width direction of the portion where the slits 3a are formed, and the light blocking portion 3b that completely blocks the ultraviolet light 2 is provided.
Are preferably provided. When it is desired to make the change amount of the core refractive index due to the irradiation of the ultraviolet light 2 uniform in the length direction of the optical fiber 1, the spot diameter of the ultraviolet light 2 at both ends of the mask 3 in the length direction of the optical fiber 1 is Large light shield 3
It is preferable to provide b, but it is also possible to adopt a configuration without this.

The wavelength of the ultraviolet light 2 used in the present invention is 20.
It is preferably about 0 to 300 nm, and as the light source, for example, a KrF laser (248 nm) is preferably used. In the present invention, the spatial distribution of the light intensity of the ultraviolet light 2 (the ultraviolet light intensity distribution within the spot) does not need to be uniform,
It can be uneven. Therefore, it is not necessary to use the optical system to magnify a part of the ultraviolet light emitted from the light source, and use the optical system to magnify or collect substantially all of the light emitted from the light source. Then, it is preferable to adjust the spot diameter to a predetermined size before irradiation. Here, irradiating substantially all of the ultraviolet light emitted from the light source means that the emitted ultraviolet light is directed toward the mask 3 without intentionally attenuating the emitted ultraviolet light in addition to the attenuation of the light which cannot be avoided due to the configuration of the device. It means irradiating. If the spot diameter of the ultraviolet light with which the mask 3 and the optical fiber 1 are irradiated is too large, the energy density becomes small and it is necessary to lengthen the irradiation time. Since the influence of the position change becomes large, it is preferably 2
It is set to about 20 mm, more preferably about 2 × 20 mm.

In order to manufacture an optical fiber grating by the manufacturing method of the present invention, first, the optical fiber 1 is prepared,
Preferably, the hydrogenation treatment is performed before the irradiation with the ultraviolet light 2. This hydrogenation treatment is performed in order to obtain a sufficient change in the refractive index of the germanium-doped silica glass (core) due to the irradiation of ultraviolet light.
It is achieved by holding in a hydrogen pressure container adjusted to about 50 ° C. for about 60 hours. Then, the optical fiber 1 is installed directly below the mask 3. At this time, it is installed so that the length direction of the optical fiber 1 and the width direction of the slit 3a of the mask 3 are exactly parallel to each other. The distance between the optical fiber 1 and the mask 3 is preferably set to about 0 to 1 mm.

Next, the ultraviolet light 2 is irradiated onto the mask 3 and the optical fiber 1 from above the mask 3, and the irradiation position of the ultraviolet light 2 is moved in the length direction of the optical fiber 1 by using an appropriate driving means. Let In order to move the irradiation position in this way, the mask 3 and the optical fiber 1 and the ultraviolet light 2 may be moved relatively to each other. The ultraviolet light 2 may be fixed and the mask 3 and the optical fiber 1 may be moved in the longitudinal direction of the optical fiber 1, or they may be performed simultaneously. Further, it is necessary to prevent the optical fiber 1 and the mask 3 from moving relatively while irradiating the ultraviolet light 2.

Here, since the amount of change in the core refractive index in the optical fiber 1 changes depending on the intensity and the irradiation time of the irradiated ultraviolet light, the core refractive index changes by appropriately adjusting the moving speed of the irradiation position. The amount and profile of the core refractive index change (grating shape) can be controlled. For example, even if the intensity of the irradiated ultraviolet light 2 is spatially non-uniform, by moving the irradiation position from one end of the mask 3 to the other end along the core at a constant speed, as shown in FIG. It is possible to obtain an optical fiber grating in which the core refractive index change amount is uniform in each part of the part. Further, the moving speed of the irradiation position of the ultraviolet light 2 can be arbitrarily changed, and by appropriately changing the moving speed in the length direction of the optical fiber 1, a profile (grating shape) of the core refractive index change of an arbitrary shape can be obtained. It is also possible to obtain.

According to the manufacturing method of the present invention, even if the ultraviolet light intensity distribution in the spot of the ultraviolet light 2 is not uniform,
It is possible to obtain a grating shape in which the amount of change in core refractive index is uniform in the length direction of the optical fiber 1, and it is also possible to control the grating shape to an arbitrary shape by controlling the moving speed of the irradiation position. Further, since the grating portion is formed by irradiating the optical fiber 1 with ultraviolet light through the mask 3, the design can be easily changed and the manufacturing efficiency is also high. Further, substantially all of the ultraviolet light emitted from the light source is masked by the mask 3 and the optical fiber 1.
Since it can be used for irradiating a laser beam, the energy efficiency is very good and the time required for producing the grating can be shortened.

The radiation mode coupling type optical fiber grating thus obtained is used in, for example, the field of optical communication, and particularly in an optical communication system using an erbium-doped optical fiber amplifier, a natural light from the erbium-doped optical fiber is used. It is preferably used for suppressing emitted light and reducing the wavelength dependence of the gain of an erbium-doped optical fiber amplifier.

In the above description, an example in which a radiation mode coupling type optical waveguide grating is constructed by using an optical fiber as the optical waveguide has been described, but the same manufacturing method can be applied even when a planar optical waveguide is used as the optical waveguide. Can be used.

[0024]

As described above, the method for manufacturing an optical waveguide grating of the present invention is a method for manufacturing a radiation mode coupling type optical waveguide grating, and the core is made of a material whose refractive index changes by irradiation with ultraviolet light. The optical waveguide has a step of irradiating ultraviolet light through a mask in which slits for transmitting light at predetermined intervals are formed, and moving the irradiation position of the ultraviolet light along the core. Is. Therefore, even if the intensity of the irradiated ultraviolet light is spatially non-uniform, it is possible to obtain a grating shape in which the core refractive index change amount is uniform in the optical fiber length direction. It is also possible to control the grating shape to an arbitrary shape by controlling the moving speed of the irradiation position. Further, by changing the shape of the mask, the grating pitch and the grating length can be changed, so that the design can be easily changed.

Further, in the present invention, since the intensity of the ultraviolet light to be irradiated may be spatially non-uniform, substantially all of the ultraviolet light emitted from the light source should be used for irradiation of the mask and the optical waveguide. You can By doing so, the energy efficiency can be made extremely high, and the time required for producing the grating can be shortened.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an embodiment of a method for manufacturing an optical waveguide grating of the present invention.

FIG. 2 is a graph showing an example of a core refractive index profile in an optical waveguide grating obtained by the manufacturing method of the present invention.

FIG. 3 is a graph showing an example of characteristics of a radiation mode coupling type optical waveguide grating.

FIG. 4 is a schematic configuration diagram showing an example of a conventional optical fiber grating manufacturing apparatus.

FIG. 5 is a schematic configuration diagram showing another example of a conventional optical fiber grating manufacturing apparatus.

[Explanation of symbols]

1 ... Optical fiber, 2 ... Ultraviolet light, 3 ... Mask, 3a ... Slit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Satoshi Okude 1440 Rokuzaki, Sakura City, Chiba Prefecture Fujikura Ltd. Sakura Factory (72) Masaaki Sudo 1440, Rokuzaki, Sakura City, Chiba Prefecture Fujikura Sakura Plant Ltd. (72) Inventor Tetsuya Sakai 1440 Rokuzaki, Sakura City, Chiba Prefecture Fujikura Co., Ltd.Sakura Factory (72) Inventor Akira Wada 1440 Rokuzaki, Sakura City, Chiba Prefecture Fujikura Sakura Co., Ltd. (72) Inventor Ryozo Yamauchi Chiba Fujikura Co., Ltd. Sakura Factory, 1440 Rokuzaki, Sakura City, Japan

Claims (2)

[Claims] 1. A method of manufacturing a radiation mode coupling type optical waveguide grating, wherein an optical waveguide whose core is made of a material whose refractive index changes by irradiation with ultraviolet light is provided with slits for transmitting light at predetermined intervals. And a step of moving the irradiation position of the ultraviolet light along the core while irradiating the ultraviolet light through the mask. 2. The method of manufacturing an optical waveguide grating according to claim 1, wherein substantially all of the ultraviolet light emitted from the light source is used for irradiation of the mask and the optical waveguide.