JP3693494B2 - Chirped optical fiber filter manufacturing method and chirped optical fiber filter - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical filter manufacturing method and an optical filter, and more particularly to an optical filter manufacturing method and an optical filter using, for example, a fiber Bragg grating.
[0002]
[Prior art]
In the conventional optical communication field, fiber Bragg gratings (hereinafter referred to as FBGs) are frequently used as optical filters such as wavelength filters and dispersion compensators. This FBG is formed by periodically changing the refractive index of the core of the optical fiber. The periodic refractive index change (refractive index modulation) is formed by, for example, a phase mask method. An example of this phase mask method is “US Pat. No. 5,367,588” (Document 1).
[0003]
FIG. 7 is a conceptual diagram of FBG fabrication using the conventional phase mask method, and FIG. 8 is an external view of the phase mask.
[0004]
First, an outline of FBG fabrication will be described.
[0005]
The optical system includes a laser light source 1, an attenuator (output adjuster) 3, a mirror 4, and a cylindrical lens 5. Laser light 2 having a wavelength of 248 nm is output from a laser light source 1 (for example, KrF excimer laser manufactured by Lambda Physics). The laser light 2 passes through an attenuator 3 and is subjected to a 90 ° direction change by a mirror 4. The beam diameter is adjusted by the cylindrical lens 5 and the phase mask 6 is irradiated.
[0006]
The laser beam 7 is diffracted by the phase mask 6, and striped diffracted light 8 is generated below the phase mask 6 as shown in the enlarged portion of FIG. 7. Under this, a photosensitive optical fiber 10 (for example, Corning filled with hydrogen) with the clad 9 exposed is installed, so that the core portion 11 of the photosensitive fiber 10 has a high diffracted light intensity. A local refractive index change occurs. In the figure, reference numeral 12 denotes this refractive index changing portion (refractive index modulating portion).
[0007]
When the laser beam 13 is incident from the axial direction of the photosensitive fiber 10, the reflected light λb 14 having the wavelength shown in Expression (1) is emitted to the incident end 15 by Bragg reflection.
[0008]
λb = 2 · n eff · Λ (1)
Here, n eff is the effective refractive index of the core of the grating portion, and Λ is the period of change in the refractive index of the fiber.
[0009]
In the phase mask method, the optical fiber is irradiated with ultraviolet light through the phase mask. The phase mask is a plate-like body that can transmit ultraviolet light. A plurality of recesses are formed on the surface of the plate-like body, and each recess is linearly arranged with a predetermined interval. Ultraviolet light is diffracted by these recesses. The intensity of the diffracted light is increased or decreased at a position corresponding to the arrangement interval (pitch) of the recesses. On the other hand, the core of the optical fiber is made of a material whose refractive index changes with ultraviolet light. Such an optical fiber is called a photosensitive fiber.
[0010]
Since the above-described diffracted light is irradiated onto the optical fiber, periodic refractive index modulation, that is, a grating is formed in the core along the extending direction (longitudinal direction, light guiding direction) of the optical fiber.
[0011]
The above-described method for producing the phase mask is formed by a manufacturing method described in, for example, “PRODUCTION OF IN_FIBER GRATINGS USING A DIFFACTIVE ELEMENT ELEMENT” DZAnderson et.al., Electronic Letters 18th Mar 1993 Vol 29 No. 6 (reference 2). Is done.
[0012]
A method of manufacturing the phase mask 6 described in the above-mentioned document 2 will be described below without showing it. First, a Cr thin film is formed on a quartz glass plate by sputtering or vapor deposition. Next, the Cr thin film is patterned by electron beam lithography. At this time, the line (Cr) / space is set to an equal dimension (Λ / Λ). 2Λ is the period of the subsequent diffraction grating array. Thereafter, the underlying quartz is etched using reactive ion etching using the Cr pattern as a mask to form grooves. Thereafter, the Cr thin film is removed with an acid, whereby an uneven diffraction grating array 17 (FIG. 8) is produced on the quartz substrate.
[0013]
On the other hand, in the laser irradiation method, since the size of the laser beam 7 is about 25 × 10 mm, the mirror 4 or the phase mask 6 is directly applied when the refractive index changing portion 12 is sufficiently short (≦ 15 mm) or directly. And the photosensitive fiber 10 is scanned.
[0014]
When it is desired to widen the reflection band of the Bragg reflection wavelength λb14, the chirped grating structure described in, for example, “Fiber grating and its application”, Inoue et al., Applied Physics Vol. 66, No. 1, pp33-36 (reference 3). You can do it. The chirped grating structure described in Document 3 is such that Λ, which is called a chirped grating, changes from small to large continuously and stepwise (see FIG. 8).
[0015]
Next, the apodization method will be described.
[0016]
FIG. 9 is a diagram showing a flat refractive index distribution, and FIG. 10 is a diagram showing reflection characteristics of an FBG filter.
[0017]
When the laser is irradiated with a uniform intensity in the longitudinal direction of the fiber shown in FIG. 9, as shown in FIG. 10, the generation of the side mode 20, the reflection band, the ripple of the flat top portion, etc. are generated as the FBG filter characteristics.
[0018]
An apodization method has been proposed as one solution to these problems. The apodization method is described in, for example, “Apodised in-fibre Bragg grating refiectors photo imprinted using a phase mask” B. Malo et.al., Electronics Letters 2nd February 1995 Vol.31 No.3, pp.223-225 (reference 4). There is what is described.
[0019]
FIG. 11 is a diagram for explaining the apodization method, and FIG. 12 is a diagram showing the reflection characteristics of the FBG filter using the apodization method.
[0020]
The apodization method (apodization method) is a method in which the refractive index change is made as shown in FIG. 11, and the envelope of the refractive index change in the fiber length direction is made into a bell-like 33 like a Gaussian function and a COSIN function. A constant window function is used for the intensity distribution of the grating so that the intensity of the grating does not change discontinuously in the longitudinal direction. As can be seen by comparing FIG. 12 and FIG. 10, by using the apodization method, the generation of the side mode 20, the reflection band, and the ripple of the flat top portion are alleviated in the FBG filter characteristics.
[0021]
[Problems to be solved by the invention]
However, such a conventional method for manufacturing an optical filter has the following problems.
[0022]
That is, when a wideband filter using a chirped grating mask is manufactured using the apodization method, the long wavelength side and the short wavelength of the chirped grating mask are required to achieve flattening of the flat top and suppression of side lobes in the filter characteristics. Many areas on the side need to be apodized areas. For this reason, the band of the manufactured FBG becomes narrower than the band of the chirped grating mask.
[0023]
Further, as shown in FIG. 13, when the current apodization method is applied under normal conditions, the uniformity of the slope of the group delay time of the dispersion compensation characteristic is reduced as shown in FIG. 13 (a). To do. That is, when the apodized region is defined so that the slope of the group delay time of the dispersion compensation characteristic on the light incident side (long wavelength side in the case of a normal dispersion compensation element) is good, the opposite side (short wavelength side) A ripple 47 appears in the wavelength region as shown in FIG. This ripple 47 causes a problem that the chromatic dispersion compensation element becomes a filter having a very narrow compensation band. Here, for the convenience of the computer, the light incident side was simulated as the short wavelength side.
[0024]
It is an object of the present invention to provide an optical filter manufacturing method and an optical filter capable of widening a reflection band while flattening a flat top in filter characteristics, or shortening a phase mask and shortening a laser irradiation time. Objective.
[0025]
[Means for Solving the Problems]
According to the present invention Chirped optical fiber filter In the optical filter manufacturing method, a grating region is selectively formed by irradiating a selective region of the photosensitive fiber with ultraviolet light using an ultraviolet light and a phase mask. The apodized region in which the amount of change in the refractive index continuously changes in the longitudinal direction is asymmetric on the short wavelength side and the long wavelength side. The apodized area on the light incident side is 2 to 8 times longer than the apodized area on the opposite side. It is characterized by that.
[0027]
According to the present invention Chirped optical fiber filter In the manufacturing method, the apodized region which is asymmetric on the short wavelength side and the long wavelength side is moved in the optical path of the laser beam at the time of writing, and the moving speed is changed to change the moving speed of the fiber light receiving surface per unit area or unit time. By changing the intensity and changing the refractive index change continuously Form It may be a thing.
[0028]
According to the present invention Chirped optical fiber filter In the manufacturing method, the apodized region, which is asymmetrical between the short wavelength side and the long wavelength side, is moved by moving the stage equipped with the fiber at the time of writing, and the moving speed is changed to receive the fiber per unit area or per unit time. The surface intensity is changed and the refractive index change is continuously changed. Form It may be a thing.
[0029]
According to the present invention Chirped optical fiber filter In this manufacturing method, the apodization region that is asymmetrical between the short wavelength side and the long wavelength side is modulated with a difference in laser frequency, or the energy of the light source is made different by an attenuator that can automatically modulate the attenuation rate. To change the fiber receiving surface intensity per unit area or unit time and continuously change the amount of refractive index change. Form It may be a thing.
[0030]
The light incident side may be a long wavelength side in the case of a dispersion compensating fiber Bragg grating, and the refractive index change amount is the intensity of the grating, that is, the light intensity irradiated when forming the grating, or Change the irradiation time Brought about by It may be a thing.
[0031]
According to the present invention Chirped optical fiber filter In the optical filter in which the grating region is selectively formed by irradiating the selective region of the photosensitive fiber with ultraviolet light using ultraviolet light and a phase mask for the photosensitive fiber, the optical filter is a fiber The apodized region where the refractive index change continuously changes in the longitudinal direction is asymmetric between the short wavelength side and the long wavelength side The apodized area on the light incident side is 2 to 8 times longer than the apodized area on the opposite side. It is structured.
[0032]
DETAILED DESCRIPTION OF THE INVENTION
The method for manufacturing an optical filter according to the present invention can be applied to a method for manufacturing an FBG used as an optical filter such as a wavelength filter or a dispersion compensator.
[0033]
First embodiment
FIG. 1 is a diagram showing a configuration of an optical filter manufacturing method according to the first embodiment of the present invention, and shows a conceptual diagram of FBG fabrication using an apodization method.
[0034]
The present invention relates to a novel apodization method, and since it is the same as the conventional production method described in FIGS. 7 and 8 except for the apodization method, only the novel apodization method will be described in detail below.
[0035]
In FIG. 1, reference numeral 100 denotes an ultraviolet writing device for a fiber. The ultraviolet writing device 100 for a fiber basically includes a laser light source 121, a reflection mirror 122 for guiding the ultraviolet light from the laser light source 121 to the fiber, a phase mask 123, and a fiber. It is composed of a fiber stage 124 to be mounted and a fiber 125 to which ultraviolet rays are written. At this time, the reflection mirror 122 is allowed to move. When the reflection mirror 122 moves 126, the minute ultraviolet spot moves in the longitudinal direction of the fiber, and ultraviolet rays are written on the long fiber.
[0036]
Here, in order to continuously generate a refractive index change, as shown in FIG. 1, in the phase mask 123, a phase mask region (fiber longitudinal direction) is composed of an apodized region 127 on the long wavelength side and an apodized region 128 on the short wavelength side. Difference in the length). As shown in FIG. 1, the moving speed of the reflecting mirror 122 that guides the ultraviolet rays from the laser light source 121 while moving to the fiber corresponds to the apodized region 127 on the long wavelength side and the apodized region 128 on the short wavelength side. In the range, as shown in the lower side of FIG. 1, speed modulation 129, 130 is performed to give a difference in the optical path moving speed of the optical system.
[0037]
Thereby, in the apodized region 127 on the long wavelength side and the apodized region 128 on the short wavelength side, the fiber light receiving surface intensity per unit area and unit time can be continuously changed with a desired difference. .
[0038]
Furthermore, in FIG. 1, the apodized regions 127 of the long wavelength side region 127 and the short wavelength side apodized region 128 in the longitudinal direction of the fiber are allocated non-equally (asymmetrically). That is, speed modulation is performed so that the apodized region 127 on the long wavelength side is narrower than the apodized region 128 on the short wavelength side.
[0039]
Thus, in the apodization method according to the present embodiment, the ratio between the apodized region and the non-apodized region is set to a certain range in the longitudinal direction of the fiber, and the certain range of apodized regions is set to the short wavelength side and the long wavelength side. Allotted to the side in an unequal (asymmetric) manner. Hereinafter, this novel apodization method is referred to as an asymmetric apodization method.
[0040]
Here, the ratio of the unequal portions of the apodized regions on the long wavelength side and the short wavelength side will be described.
[0041]
As a basic idea of apodization, it is preferable that the apodization region is narrow as long as side lobe suppression and flat top flattening are achieved. In other words, the narrower one shortens the writing length necessary to obtain a desired bandwidth, so that the laser irradiation time and the phase mask can be shortened, and finally the production volume and cost can be reduced. .
[0042]
In the present asymmetric apodization method, for the same reason, the apodization region on the long wavelength side (grating writing start side) for the unequal division of the apodization region is substantially the same as the conventional apodization region. That is, in FIG. 8, it is arbitrarily set appropriately according to the period Λ of the diffraction grating, the step number S of the step chirp, the intensity of the laser light source, and the like. However, the present asymmetric apodization method is characterized in that the apodization region on the short wavelength side (the grating writing end side) is set to 1/8 to 1/2 of the apodization region on the long wavelength side.
[0043]
Although not shown, in order to use the FBG manufactured by the above-mentioned method as a device such as an optical filter and a dispersion compensation element, a connector is connected to the input end of the signal light of the fiber, and on the opposite side It is necessary to attach a terminator for preventing the transmitted light from being reflected.
[0044]
As described above, in the method for manufacturing the FBG filter according to the first embodiment, the apodized region in which the amount of change in refractive index continuously changes in the longitudinal direction of the fiber is made asymmetric on the short wavelength side and the long wavelength side. Therefore, in the phase mask 123, there is a difference in the phase mask region between the long wavelength side apodized region 127 and the short wavelength side apodized region 128, and the moving speed of the reflection mirror 122 is set to the long wavelength side apodized region 128. Since the velocity modulation 129, 130 is performed in a range corresponding to the apodization region 127 and the short wavelength side apodization region 128, the reflection band is widened or the phase mask is shortened while flattening the flat top in the filter characteristics. And the laser irradiation time can be shortened.
[0045]
Hereinafter, the effect of this embodiment will be described in detail.
[0046]
FIG. 2 is a diagram showing the chromatic dispersion characteristics of the FBG filter according to the present embodiment, and is a result of performing a simulation with a change in the apodized regions on the long wavelength side and the short wavelength side.
[0047]
FIG. 2 shows a simulation result in this asymmetric apodization method for comparison with the conventional symmetric apodization method shown in FIG. 13, and assumes a phase mask with a wavelength band of 1.0 nm and a dispersion compensation amount of 800 ps / nm. In this case, the phase mask length (exposure length) is about 8 cm. As a result of calculating the light input end on the short wavelength side under the above conditions, sufficient side lobe suppression and flat top flattening can be obtained when the light input side apodized region is 15% (12 mm) or more. found.
[0048]
In the conventional apodization method shown in FIG. 13, the flat reflection band 48 with a small dispersion ripple is 0.6 nm. However, according to the method using the asymmetric apodization method, as shown in FIG. In the case of 12 mm and long wave side apodization 4 mm (ratio: 3: 1), the flat reflection band 48 with a small dispersion ripple was 0.73 nm. This is because the ripple 47 seen in FIG. 13 is eliminated by this method.
[0049]
In other words, according to the present embodiment, there is a difference in the optical path movement of the optical system, for example, by giving a difference in the length of the phase mask in the area corresponding to the apodized area and by making a difference in the range in which the mirror moving speed is modulated. By providing it, an apodized region in which the intensity of the grating changes rapidly in the longitudinal direction of the fiber can be asymmetrical at a desired ratio (1/8 to 1/2) between the short wavelength side and the long wavelength side.
[0050]
FIG. 3 is a diagram for explaining the asymmetric apodization method, and FIG. 4 is a diagram showing the reflection characteristics of the FBG filter using the asymmetric apodization method, which corresponds to the conventional apodization method of FIGS.
[0051]
As apparent from the comparison with the conventional example of FIG. 11, the flat top region is greatly flattened 162 (FIG. 3), and the occurrence of the side mode 46 of the reflection spectrum shown in FIG. 12 is suppressed as shown in FIG. 160.
[0052]
Thus, under the condition that the side mode of the reflection spectrum is suppressed 160 and the flat top is also flattened 162, the reflection band can be widened as shown in FIG. 2, or the phase mask can be shortened. Laser irradiation time can be shortened. This makes it possible to reduce the product cost.
[0053]
If a stage moving speed control program or the like is prepared, various types of FBGs having arbitrarily improved filter characteristics and arbitrary lengths (0.1 to 4 meters) can be easily produced.
[0054]
Second embodiment
FIG. 5 is a diagram showing a configuration of an optical filter manufacturing method according to the second embodiment of the present invention, which is a modified example of the apodization method.
[0055]
In the first embodiment, the method of applying apodization by modulating the mirror moving speed has been described. However, this embodiment describes an apodization method using other means.
[0056]
FIG. 5 shows a method of apodization by moving the fiber stage 134, which fixes the fiber and the phase mask, with velocity modulation.
[0057]
In FIG. 5, an ultraviolet writing device for a fiber basically includes a laser light source 131, a reflection mirror 132 for guiding the ultraviolet light from the laser light source 131 to the fiber, a phase mask 133, a fiber stage 134 on which the fiber is placed, and a fiber 135 into which the ultraviolet light is written. Consists of At this time, the fiber stage 134 is allowed to move. As the fiber stage 134 moves 136, the minute ultraviolet spot moves along the longitudinal direction of the fiber, and ultraviolet rays are written on the long fiber.
[0058]
Here, in order to continuously generate the refractive index change, as shown in FIG. 5, in the phase mask 133, the difference in the mask length is caused between the apodized region 137 on the long wavelength side and the apodized region 138 on the short wavelength side. Give it. Further, as shown in the lower side of FIG. 5, the stage moving speed on which the fiber is mounted is set within a range corresponding to the mask length of the apodized region 137 on the long wavelength side and the apodized region 138 on the short wavelength side. By modulating 139 and 140, the stage moving speed is made different.
[0059]
Thereby, in the apodized region 137 on the long wavelength side and the apodized region 138 on the short wavelength side, the fiber light receiving surface intensity per unit area and unit time is continuously changed while giving a desired difference.
[0060]
Further, the ratio of the short wavelength side apodization region, the long wavelength side apodization region, and the flat top region is set in the same manner as in the first embodiment.
[0061]
As described above, in the method for manufacturing the FBG filter according to the second embodiment, the phase mask region has a difference between the apodized region 137 on the long wavelength side and the apodized region 138 on the short wavelength side, and the fiber The stage movement speed is adjusted within a range corresponding to the mask length of the apodized area 137 on the long wavelength side and the apodized area 138 on the short wavelength side area, so that there is a difference in the stage moving speed. As in the first embodiment, the reflection band can be widened or the phase mask can be shortened while flattening the flat top in the filter characteristics.
[0062]
In particular, in this embodiment, the difference in the amount of ultraviolet light is given by making a difference in the moving speed of the stage on which the fiber is mounted, so the optical path (distance until the light reaches the fiber) is fixed. Therefore, as a unique effect added to the effect of the first embodiment, since the optical path does not change, there is an advantage that there is no change in laser characteristics such as energy and polarization dependency, and ultraviolet rays can be stably written.
[0063]
Third embodiment
FIG. 6 is a diagram showing a configuration of an optical filter manufacturing method according to the third embodiment of the present invention, which is a modified example of the apodization method.
[0064]
FIG. 6 shows a method of applying apodization by applying intensity modulation to the laser light source itself using the attenuator modulator 150 while moving the mirror moving speed or the fiber stage moving speed at a constant speed.
[0065]
In FIG. 6, an ultraviolet writing device for a fiber basically includes a laser light source 141, an attenuator 142, a reflection mirror 143 for guiding the ultraviolet light from the laser light source 141 to the fiber, a phase mask 144, a fiber stage 145 for placing the fiber, and ultraviolet light writing. Fiber 146.
[0066]
At this time, the fiber stage 144 or the reflection mirror 143 is allowed to move. When the fiber stage 145 or the reflection mirror 143 moves 147 at a constant speed, the minute ultraviolet spot moves along the longitudinal direction of the fiber, and ultraviolet rays are written on a long fiber.
[0067]
Here, in order to continuously generate the refractive index change, as shown in FIG. 6, in the phase mask 144, the difference between the mask lengths of the long wavelength side apodized region 148 and the short wavelength side region apodized region 149 is obtained. Give it. As shown in the lower side of FIG. 6, the transmittance of the attenuator 142 is set to 0 to 100% within a range corresponding to the mask length of the apodized region 148 on the long wavelength side and the apodized region 149 on the short wavelength side region. Change arbitrarily within the range. In this way, the attenuation rate of the attenuator 142 is automatically modulated while being synchronized with the apodized region 148 on the long wavelength side and the apodized region 149 on the short wavelength side, thereby making a difference in ultraviolet energy. Modulate. In the figure, 150 indicates this modulation. As a result, the intensity of ultraviolet rays on the fiber light receiving surface changes.
[0068]
Instead of the above-described modulation 150, the laser frequency may be modulated with a difference. In the figure, reference numeral 151 denotes this modulation. That is, by changing the laser frequency, for example, in the range of high frequency (50 Hz) to low frequency (1 Hz), the ultraviolet energy changes about 50 times. This change changes the intensity of the ultraviolet light on the fiber light receiving surface.
[0069]
By the method as described above, in the apodized region 148 on the long wavelength side and the apodized region 149 on the short wavelength side region, the fiber light receiving surface intensity per unit area and unit time is continuously changed while giving a desired difference. Change.
[0070]
Further, the ratio of the short wavelength side apodization region, the long wavelength side apodization region, and the flat top region is set in the same manner as in the first embodiment.
[0071]
As described above, in the method of manufacturing the FBG filter according to the third embodiment, the length of the mask is different between the apodized region 148 on the long wavelength side and the apodized region 149 on the short wavelength side, and The transmittance of the attenuator 142 is arbitrarily changed within a range of 0 to 100% within the range corresponding to the mask length of the apodized region 148 on the long wavelength side and the apodized region 149 on the short wavelength side region, and the attenuation rate of the attenuator 142 is changed. Since the modulation is automatically performed in synchronization with the apodization region 148 on the long wavelength side and the apodization region 149 on the short wavelength side region, in addition to the effects of the first and second embodiments, the stage movement is fixed. In order to stabilize at high speed, the uniformity of grating writing characteristics can be improved. Further, since the light source intensity is modulated, the refractive index change can be substantially started from zero. That is, in the first and second embodiments, since it is practically impossible to increase the moving speed to infinity, the refractive index change Δn does not become 0 at the start and end of apodization, but in this embodiment, It becomes possible to start the refractive index change from zero.
[0072]
Therefore, if the manufacturing method of the optical filter having such excellent features is applied to, for example, the manufacturing method of the FBG by the phase mask method, the flat top is flattened in the filter characteristics, the reflection band is widened, and further the manufacturing time is reduced. It is possible to shorten the manufacturing cost.
[0073]
In addition, although the manufacturing method of the optical filter which concerns on each said embodiment can also be applied to FBG as mentioned above, of course, it is not limited to this, It selects using an ultraviolet light and a phase mask for a photosensitive fiber Needless to say, the method can be applied to all manufacturing methods and apparatuses as long as the optical filter manufacturing method forms a grating region.
[0074]
In addition, it goes without saying that the types, number, arrangement relationship, and materials and numerical values of the optical system, phase mask, fiber stage, etc. constituting the optical filter manufacturing method are not limited to the above-described embodiments. .
[0075]
【The invention's effect】
According to the present invention Chirped optical fiber filter Manufacturing method and Chirped optical fiber filter Then, since the apodized region in which the refractive index variation continuously changes in the longitudinal direction of the fiber is made asymmetric on the short wavelength side and the long wavelength side, the reflection band is widened while flattening the flat top in the filter characteristics, Alternatively, the phase mask can be shortened, and the laser irradiation time can be shortened.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of an optical filter manufacturing method according to a first embodiment to which the present invention is applied.
FIG. 2 is a diagram showing wavelength dispersion characteristics of an FBG filter in the method for manufacturing an optical filter.
FIG. 3 is a diagram for explaining an asymmetric apodization method of the manufacturing method of the optical filter.
FIG. 4 is a diagram showing the reflection characteristics of an FBG filter using the asymmetric apodization method of the optical filter manufacturing method.
FIG. 5 is a diagram showing a configuration of an optical filter manufacturing method according to a second embodiment to which the present invention is applied.
FIG. 6 is a diagram showing a configuration of an optical filter manufacturing method according to a third embodiment to which the present invention is applied.
FIG. 7 is a diagram showing a configuration of a conventional method for manufacturing an optical filter.
FIG. 8 is an external view of a phase mask of a conventional method for manufacturing an optical filter.
FIG. 9 is a diagram illustrating a flat refractive index distribution of a conventional optical filter.
FIG. 10 is a diagram showing reflection characteristics of a conventional FBG filter.
FIG. 11 is a diagram for explaining an apodization method of a conventional method for manufacturing an optical filter.
FIG. 12 is a diagram showing reflection characteristics of an FBG filter using an apodization method of a conventional optical filter manufacturing method.
FIG. 13 is a diagram showing chromatic dispersion characteristics of an FBG filter in a conventional method for manufacturing an optical filter.
[Explanation of symbols]
100 UV writing device to fiber, 121, 131, 141 laser light source, 122, 132, 143 reflection mirror, 123, 133, 144 phase mask, 124, 134, 145 fiber stage, 125, 135, 146 fiber, 126 reflection mirror Movement, 127, 137, 148 long wavelength side apodized region, 128, 138, 149 short wavelength side apodized region, 129, 130, 139, 140 velocity modulation, 136 fiber stage movement, 142 attenuator, 147 fiber stage or Reflection mirror movement, 150, 151 modulation

Claims (7)

In the optical filter manufacturing method for selectively forming the grating region by irradiating the selective region of the photosensitive fiber with ultraviolet light, using the ultraviolet light and the phase mask for the photosensitive fiber,
The apodized region where the refractive index variation continuously changes in the longitudinal direction of the fiber is asymmetrical between the short wavelength side and the long wavelength side, and the apodized region on the light incident side is 2 to 8 times longer than the apodized region on the opposite side A method of manufacturing a chirped optical fiber filter , The apodized region that is asymmetric on the short wavelength side and the long wavelength side is moved along the optical path of the laser beam at the time of writing, and the moving speed is changed to change the fiber light receiving surface intensity per unit area or unit time. claim 1 Symbol placement chirped optical fiber manufacturing method of the filter and forming by a refractive index change continuously varied. The apodized region that is asymmetrical between the short wavelength side and the long wavelength side is moved by moving the stage equipped with the fiber at the time of writing, and the moving speed is changed to change the fiber receiving surface intensity per unit area or unit time. the method of chirped optical fiber filter according to claim 1 Symbol mounting and forming by continuously changing the refractive index change. The apodized region that is asymmetrical between the short wavelength side and the long wavelength side is modulated with a difference in the laser frequency, or is modulated with a difference in the energy of the light source by an attenuator that can automatically modulate the attenuation rate. per area, or the unit to change the fiber receiving surface strength per time, chirped according to any one of claims 1, 2, or 3, characterized in that formed by a refractive index variation is continuously changed Manufacturing method of optical fiber filter . The light incident side, a manufacturing method of the chirped optical fiber filter according to claim 1, wherein the in the case of dispersion compensating fiber Bragg grating is a long-wavelength side. The refractive index change amount, any claim 1, 2, 3 or 4, wherein the light intensity is irradiated or by changing the irradiation time are those brought about by Rukoto when forming the grating A method for producing a chirped optical fiber filter according to claim 1. In the optical filter in which the grating region is selectively formed by irradiating the selective region of the photosensitive fiber with ultraviolet light using ultraviolet light and a phase mask for the photosensitive fiber,
In the optical filter, the apodized region in which the amount of change in refractive index continuously changes in the longitudinal direction of the fiber is asymmetric on the short wavelength side and the long wavelength side, and the apodized region on the light incident side is twice the apodized region on the opposite side. A chirped optical fiber filter characterized in that the length is 8 times longer than

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