JP4034041B2 - Manufacturing method of optical waveguide grating - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method of manufacturing an optical waveguide grating used for an optical filter or the like important for wavelength division multiplexing transmission using an optical transmission line such as an optical fiber. In particular, the present invention forms a grating collectively on a plurality of optical waveguides. The present invention relates to a method of manufacturing an optical waveguide grating having excellent wavelength selection characteristics.
[0002]
[Prior art]
With the recent IT revolution, the need for high-capacity and high-speed transmission systems has also increased, and wavelength division multiplexing transmission systems have been adopted to meet this demand.
In a maintenance monitoring system for optical subscriber line network operation, test light (eg, 1.65 μm) other than the communication wavelength (1.31 μm, 1.55 μm) is incident from the station side so that the test and monitoring can be performed even during communication. Although the light is reflected at the end of the optical cable, a dielectric multilayer filter or the like has been conventionally used for the termination cable used at the end. However, recently, switching to an optical waveguide grating has been studied because low insertion loss, mechanical stability, low cost, and excellent wavelength selectivity are expected.
[0003]
This optical waveguide grating is formed in the core of the optical waveguide so that high refractive index portions and low refractive index portions are alternately repeated over a certain region.
As a method for forming the optical waveguide grating as described above, the phase mask method is generally used. As shown in FIG. 7, GeO ₂ or the like is doped in the core of an optical waveguide such as the quartz optical fiber 30 and the irradiation light L ₀ having a predetermined wavelength such as ultraviolet light is passed through the phase mask 35. In the irradiation method, the light interference fringes 31 generated by the irradiation light L ₁ that passes through the phase mask 35 and is diffracted are used to change the refractive index according to the intensity of the light (interference fringes). Is a half of the grating period d of the phase mask 35). For example, the refractive index of a core of silica glass fiber doped with GeO ₂ increases when irradiated with ultraviolet light having a wavelength of around 240 nm. It is also known that sensitivity to ultraviolet rays can be greatly improved by performing high-pressure hydrogen treatment in advance.
[0004]
By the way, if the grating is formed by performing such irradiation for each of the optical fibers, the production efficiency is low and the demand for increasing as described above cannot be endured. Therefore, for example, in Japanese Patent Application Laid-Open No. 2000-66040, as shown in FIG. 6, optical fibers 51 to 54 for forming a grating are arranged in the parallel arrangement means 30, and the irradiation light L ₀ output from the light source 40 is used. A manufacturing apparatus and a manufacturing method are disclosed in which a plurality of optical fibers 51 to 54 are irradiated through a reflecting mirror 43 and 44 and a phase mask 45 to collectively form an optical fiber grating. According to this method, the stage mirror 42 is controlled to move the reflecting mirror 41 and the irradiation light is scanned in a direction (Y-axis direction) orthogonal to the optical axis of each of the plurality of optical waveguides. Can be manufactured together.
[0005]
However, when forming the optical waveguide grating, there are the following problems.
B) Due to a slight positional shift of the irradiated portion in the optical axis direction (X-axis direction) of the optical waveguide, a shift in the center wavelength of the pass band or the reflection band of the optical filter, a shift in the bandwidth, or the like occurs.
B) When the grating is uniform in the light propagation direction, the cumulative dose distribution becomes a mountain shape, as will be described later, and the refractive index distribution also corresponds to it. In-band attenuation and out-of-band attenuation The difference between the two is so small that unnecessary waves cannot be removed sufficiently.
[0006]
Therefore, there is a method (apodization) that improves the wavelength characteristics by irradiating with irradiation light from one end to the other end of the optical waveguide grating formation region so that the refractive index modulation is bell-shaped with a flat average value in the grating direction. It has been broken.
For example, in Japanese Patent Application Laid-Open No. 11-326664, as shown in FIG. 8, the laser irradiation light amount R is decreased from one end (movement distance d = 0) to the center (movement distance d = 2.5 mm). A method is disclosed in which it is moved and moved while increasing from the center to the other end (movement distance d = 5 mm).
[0007]
[Problems to be solved by the invention]
However, an expensive apodized phase mask is used to simultaneously perform apodization when scanning irradiation light in the Y-axis direction in a manufacturing method for collectively forming a grating as disclosed in JP-A-2000-66040. Is required. Further, in the method of adding the irradiation process shown in Japanese Patent Laid-Open No. 11-326664 after the grating forming process of scanning the irradiation light in the Y-axis direction, a subtle irradiation amount for each optical waveguide in the grating forming process is obtained. Differences in the difference and subtle irradiation position overlap with control deviations such as irradiation start position, irradiation end position, and irradiation amount change during the subsequent irradiation process. Required.
[0008]
The present invention is intended to solve the above-described problems, and is capable of forming grazing in a plurality of optical waveguides at the same time, and also capable of easily and accurately controlling apodization. It is an object of the present invention to provide a method for manufacturing a waveguide grating.
[0009]
[Means for Solving the Problems]
In order to solve the above-described problem, a method for manufacturing an optical waveguide grating of the present invention includes:
An optical waveguide grating comprising: an arrangement step of arranging a plurality of photosensitive optical waveguides substantially in parallel; and an irradiation step of irradiating irradiation light having a wavelength that causes a change in refractive index to the plurality of optical waveguides. In the manufacturing method,
In the irradiation step, the irradiation light having a substantially flat intensity distribution in the major axis direction of the beam cross section is made to substantially coincide with the direction (Y axis direction) perpendicular to the optical axis of the plurality of optical waveguides. A grating forming step of irradiating while scanning in the optical axis direction (X-axis direction) of each optical waveguide through a predetermined phase mask, and forming a grating all over the plurality of optical waveguides;
Irradiation step of irradiating the irradiation light having a major axis direction coincident with the Y-axis direction by positioning, fixing and irradiating near the both ends of the grating forming region in the X-axis direction of the plurality of optical waveguides without using a phase mask It is characterized by including.
[0010]
According to this method of manufacturing an optical waveguide grating, since the irradiation light has a substantially flat intensity in the major axis direction of the beam cross section, there is no need to scan in the Y axis direction, and the optical waveguide grating is uniformly distributed to each of the plurality of optical waveguides. Intense light can be irradiated.
Also, in the irradiation step, the irradiation light whose major axis direction coincides with the Y-axis direction is positioned and fixed near both ends of the grating forming region in the X-axis direction of the plurality of optical waveguides without using a phase mask. Therefore, positioning is easy, and appropriate apodization can be performed only by controlling the irradiation time.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described based on illustrated examples.
FIGS. 1 and 2 are explanatory views of a method of manufacturing an optical waveguide grating according to the present invention. FIGS. 1 (a) and 2 (a) are explanatory views of a grating forming step, and FIGS. 1 (b) and 2 are used. (b) is an explanatory view of an irradiation step for apodizing the formed optical waveguide grating. FIG. 3 is an explanatory diagram of a refractive index distribution obtained by the manufacturing method of the optical waveguide grating of the present invention, FIG. 4 is an example of a cutoff characteristic of the optical waveguide grating obtained by the manufacturing method of the present invention, and FIG. It is an example of the cutoff characteristic of the optical waveguide grating which has not performed the step.
[0012]
In FIG. 1 and FIG. 2, reference numerals 11, 12, 13, and 14 denote photosensitive optical fibers before the grating formation, and are arranged substantially in parallel by using a base 3 having a V groove. Reference numeral 1 denotes irradiation light having a wavelength that causes a change in refractive index, and has a substantially flat intensity distribution in the major axis direction of the beam cross section. Reference numeral 2 denotes a phase mask, which causes interference fringes of light on the optical fiber core as described with reference to FIGS. 6 and 7, and changes the refractive index according to the intensity of the light intensity associated therewith. It is.
The optical fibers 11 to 14 are, for example, quartz glass fibers doped with GeO ₂ in the core, and the coating is previously removed from the region where the grating is to be formed. The base 3 is a rectangular frame and is provided with a through portion 3a. And the V-groove which supports the optical fibers 11-14 is formed in the support parts 3b and 3c which are parallel frames at equal intervals.
[0013]
First, in the arranging step, the optical fibers 11 to 14 are placed in the V-grooves of the support portions 3b and 3c so that the grating formation region from which the coating has been removed is positioned on the penetrating portion 3b. Secure with.
The phase mask 2 is formed so as to generate interference fringes corresponding to a desired grating period, and is arranged so as to generate uniform gratings in each of the plurality of optical fibers 11 to 14.
[0014]
Next, the irradiation process will be described.
First, as the light source of the irradiation light 1, when the optical waveguide is a quartz glass fiber doped with GeO ₂ in the core, as described above, an excimer laser that emits ultraviolet light having a wavelength of about 240 nm is used. As shown in the figure, a lens or the like is required if an irradiation width W ₁ having a substantially flat saddle-shaped intensity distribution in the major axis direction of the beam cross section and wider than the optical fiber arrangement width W ₂ is used. Even if necessary, the light is condensed to increase the intensity. Further, even if the irradiation width W ₁ of the light source is narrower than the arrangement width W ₂ of the optical fiber, it may be converted to a wide parallel light from the arrangement width W ₂ using a lens or the like.
[0015]
Irradiation light 1 obtained from such a light source is aligned in the optical axis direction (X-axis direction) by making the long-axis direction 1 _L of the beam cross section substantially coincide with the direction orthogonal to the optical axis of the optical fiber (Y-axis direction). By irradiating while scanning S, as shown in FIG. 1 (b), four optical fibers 21 to 24 each having a uniform grating 25 are obtained (in FIG. The stripe patterns 21 to 24 schematically show the refractive index distribution generated in the core, and such a refractive index distribution is usually formed in the core, but in some cases, the clad together with the core is clad. May also form).
Since the irradiation light 1 has a substantially flat intensity in the major axis direction of the beam cross section, there is no need to scan in the Y axis direction, and it is possible to irradiate a plurality of optical waveguides collectively with uniform intensity light. it can.
[0016]
Next, the dose distribution in the grating forming step will be described with reference to FIG.
FIG. 2A shows the amount of light emitted when the irradiation light 1 irradiated in the Z-axis direction via the phase mask 2 on the optical fibers 11 to 14 arranged substantially parallel to the X-axis direction is scanned S in the X-axis direction. The solid line 1 a is the intensity distribution in the XZ plane of the irradiation light 1.
Now, when the irradiation light 1 is irradiated in the Z-axis direction while scanning S in the X-axis direction without passing through the phase mask, the distribution of the accumulated irradiation amount in the XZ plane becomes a mountain shape as indicated by the dotted line P ₀ . Therefore, when irradiated through the phase mask 2, it becomes a mountain-shaped pulsating wave inscribed in the envelope P ₀ as shown by the solid line P ₁ in FIG. 2B, and the average refractive index also corresponds to this.
Therefore, in the optical fibers 11 to 14 in this state, as described above, the shift of the center wavelength, the shift of the bandwidth, and the like occur, and the difference between the attenuation amount in the band and the attenuation amount outside the band is small, and unnecessary waves are sufficiently generated. Cannot be removed.
[0017]
Therefore, as shown in FIG. 1 (b), the phase mask 2 is removed and irradiation is performed.
That is, first, the position of the light source is positioned by using a moving stage so that the long axis 1 _L of the beam cross section is positioned on one end 25s of the grating forming region G, and the irradiation light 1s emitted from the fixed light source is used. Irradiate.
Next, the position of the light source is positioned by using a moving stage so that the long axis 1 _L of the beam cross section is positioned on the other end 25e of the grating forming region G, and the irradiation light 1e emitted from the fixed light source is irradiated. To do.
[0018]
FIG. 2 (b) shows the distribution of the accumulated dose in the XZ plane.
The dotted line Ps indicates the distribution of the cumulative irradiation amount of the irradiation light 1s emitted from the light source positioned and fixed so that the major axis 1 _L of the beam cross section is positioned on one end 25s of the grating formation region G, and the dotted line Pe is shows the cumulative dose distribution of the irradiation light 1e emitted from the fixed light source and positioning in such a manner that the long axis 1 _L of the beam cross section on the other end 25e of the grating formation region G. In either case, the distribution shape is similar to the solid line 1a in FIG. 2A, but as the irradiation time T becomes longer, the cumulative irradiation amount also increases.
[0019]
Therefore, when the irradiation time T is controlled so that the cumulative dose distributions Ps and Pe are substantially equal to the dose envelope P ₀ for the grating, the envelope P ₀ , the cumulative dose distribution Ps, and the cumulative dose distribution are set. The refractive index distribution of the regions As and Ae overlapping with Pe is increased to the dotted lines Ps and Pe, and the refractive index distribution of the grating region is as shown by a solid line n ₂ as shown in FIG. This refractive index distribution n ₂ has a waveform that pulsates above and below the average value n _A flat in the X-axis direction, and since there is no portion with a relatively low average refractive index such as the regions As and Ae, the cutoff characteristic is good. I can say.
[0020]
In this irradiation step, since the irradiation light whose major axis direction coincides with the Y-axis direction is only positioned and fixed near both ends of the grating formation region, positioning is easy and the irradiation time is controlled. Just a proper apodization can be done.
[0021]
In the above embodiment, the optical fiber is exemplified as the optical waveguide. However, it is needless to say that the optical waveguide can also be applied. Further, a quartz glass fiber doped with GeO ₂ in the core is exemplified as a photosensitive optical fiber, and ultraviolet light having a wavelength of about 240 mm is exemplified as irradiation light having a wavelength that causes a change in refractive index, but the present invention is not limited thereto. It is not a thing.
[0022]
【Example】
Examples of the present invention are shown below together with comparative examples.
<Example>
Four quartz glass optical fibers doped with GeO ₂ in the core were treated in high-pressure hydrogen of 150 kg / ≡ for one week.
Twenty silica glass optical fibers were arranged in parallel at intervals of 250 μm to form a grating.
Using an excimer laser device as a light source, the output is 130 mJ, the laser repetition frequency is 20 Hz, and the length of the long axis of the beam is about 20 mm. This beam was converted into parallel light having a width of 5 mm using a lens and scanned at a scanning speed of 0.12 mm / min for about 57 minutes.
Next, the grating forming region G of the 20 optical fibers after completing the grating forming step was set to 8 mm and positioned so as to be irradiated with irradiation light near both ends thereof, and irradiation was performed for 10 minutes for both ends.
The wavelength-reflection characteristics of the optical fiber glazing thus obtained were measured using a spectrum analyzer. An example of the result is shown in FIG. 4 (one scale on the vertical axis represents 5 dB).
The measurement results of the other samples were almost the same, and there was almost no variation.
[0023]
<Comparative example>
Twenty optical fibers that were treated with hydrogen in the same manner as in the above example were scanned for about 40 minutes using a similar light source and ultraviolet light at a scanning speed of 0.12 mm / min.
The thus obtained optical fiber grating without performing the irradiation step was measured for wavelength-reflection characteristics using a spectrum analyzer. An example of the result is shown in FIG. 5 (one scale on the vertical axis represents 5 dB).
In any case, gratings could be performed on 20 optical fibers at a time. As is clear from the comparison of the above results, the amount of reflection at a wavelength of 1.66 μm or more is large in the comparative example. Although the wavelength-reflection amount characteristic is poor, the embodiment in which apodization is performed by the irradiation step has a smaller out-of-band reflection amount and a better wavelength-reflection amount characteristic.
[0024]
【The invention's effect】
As described above, according to the first aspect of the present invention,
Since the irradiation light has a substantially flat intensity distribution in the major axis direction of the beam cross section, there is no need to scan in the Y axis direction, and a plurality of optical waveguides can be irradiated with uniform intensity light collectively, Also, in the irradiation step, the irradiation light whose major axis direction coincides with the Y-axis direction is positioned and fixed near both ends of the grating forming region in the X-axis direction of the plurality of optical waveguides without using a phase mask. Therefore, positioning is easy, and there is an effect that appropriate apodization can be performed only by controlling the irradiation time.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of a method for producing an optical waveguide grating of the present invention.
FIG. 2 is an explanatory diagram of a method for manufacturing an optical waveguide grating according to the present invention.
FIG. 3 is an explanatory diagram of a refractive index distribution obtained by the method of manufacturing an optical waveguide grating according to the present invention.
FIG. 4 is a diagram illustrating an example of wavelength-reflection amount characteristics of an optical waveguide grating obtained by the manufacturing method according to the embodiment of the present invention.
FIG. 5 is a diagram showing an example of wavelength-reflection amount characteristics of an optical waveguide grating obtained by the manufacturing method of the comparative example of the present invention.
FIG. 6 is an explanatory diagram of a conventional method for manufacturing an optical waveguide grating.
FIG. 7 is an explanatory diagram of a conventional method for manufacturing an optical waveguide grating.
FIG. 8 is an explanatory diagram of a conventional method for manufacturing an optical waveguide grating.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Irradiation light 1s, 1e Longitudinal direction 2 of the irradiation light 1 _L irradiation light located in the edge part of a grating formation area | region 3 Base 11, 11, 13, 14 Optical fiber 21, 22, 23, 24 Grating Formed optical fiber G Grating formation region

Claims (1)

An optical waveguide grating comprising: an arrangement step of arranging a plurality of photosensitive optical waveguides substantially in parallel; and an irradiation step of irradiating irradiation light having a wavelength that causes a change in refractive index to the plurality of optical waveguides. In the manufacturing method,
In the irradiation step, the irradiation light having a substantially flat intensity distribution in the major axis direction of the beam cross section is made to substantially coincide with the direction (Y axis direction) perpendicular to the optical axis of the plurality of optical waveguides. A grating forming step of irradiating while scanning in the optical axis direction (X-axis direction) of each of the optical waveguides through a predetermined phase mask, and forming a grating all over the plurality of optical waveguides;
Irradiation step of irradiating the irradiation light having a major axis direction coincident with the Y-axis direction by positioning, fixing and irradiating near the both ends of the grating forming region in the X-axis direction of the plurality of optical waveguides without using a phase mask The manufacturing method of the optical waveguide grating characterized by including these.

Images